1. Transmitter (10) for broadcasting data in a broadcasting system, comprising: - a data input for receiving at least one transmitter input data stream (Il,I2, ..., In) segmented into input data words (D), - an encoder (14; 141, 142, 143) for error correction code encoding the input data words (D) into codewords (Zl, Z2,23,24), a codeword comprising a basic codeword portion (B) and an auxiliary codeword portion (A), wherein said encoder (14) is adapted for generating said basic codeword portion (B) from an input data word (D) according to a frrst code and for generating said auxiliary codeword portion (A) from an input data word (D) according to a second code, said basic codeword portion (B) being provided for regular decoding and said auxiliary codeword portion (A) being provided as incremental redundancy if regular decoding of the codeword by use of the basic codeword portion (B) is erroneous, - a data mapper (16) for mapping the codewords (Zl, 22, 23, 24) onto frames of a transmitter output data stream (O), and - a transmitter unit (1 8) for transmitting said transmitter output data stream (0).

2. Transmitter as claimed in claim 1, wherein said data mapper (16) is adapted for mapping the basic codeword portion (A) of a codeword onto a different portion of the transmitter output data stream (0), in particular onto a different frame, than the auxiliary codeword portion (A) of the same codeword.

3. Transmitter as claimed in any preceding claim, wherein said data mapper (16) is adapted for mapping the basic codeword portion (B) of a codeword onto a frame of a first type of the transmitter output data stream, in particular onto a T2 frame of a transmitter output data stream in accordance with a DVB broadcasting system, and for mapping the auxiliary codeword portion (A) of the respective codeword onto a frame of a second type, arranged between frames of the first type, of the transmitter output data stream, in particular onto an FEF frame of a transmitter output data stream in accordance with a DVB broadcasting system.

4. Transmitter as claimed in any preceding claim, 38 wherein said encoder (141, 144) comprises a fust encoding unit (20) for encoding, according to said first code, the input data word into a basic codeword (Zl) including said basic codeword portion (B) and a second encoding unit (30,30a) for encoding, according to said second code, the input data word (D) into an auxiliary codeword (Z2,Z4) including at least said auxiliary codeword portion (A), and wherein said data mapper (16) is adapted for mapping the basic codeword (Zl) onto a different portion of the transmitter output data stream (0), in particular onto a different fiame, than the auxiliary codeword (22).

5. Transmitter as claimed in claim 4, wherein said second encoding unit (30) is adapted for encoding, according to said second code, the input data word into an auxiliary codeword (22) including said basic codeword portion (B) and said auxiliary codeword portion (A).

6. Transmitter as claimed in claim 4, wherein said second encoding unit (30a) is adapted for encoding, according to said second code, the input data word into an auxiliary codeword (24) including only said auxiliary codeword portion (A).

7. Transmitter as claimed in anyone of claims 1 to 3, wherein said encoder (142) comprises a single encoding unit for encoding the input data word into a codeword (22) including said basic codeword portion (B) and said auxiliary codeword portion (A), and wherein said data mapper (16) is adapted for mapping the basic codeword portion (B) of said codeword onto a different portion of the transmitter output data stream (0), in particular onto a different frame, than the auxiliary codeword portion (A) of said codeword.

8. Transmitter as claimed in any preceding claim, wherein said encoder (143) is adapted for encoding the input data words into codewords (Z3), a codeword comprising a basic codeword portion (B) and an auxiliary codeword portion (A), said auxiliary codeword portion (A) including at least two auxiliary codeword sub-portions (Pal, Pa2, Pa3), said basic codeword portion (B) being provided for regular decoding and said at least two auxiliary codeword sub-portions (Pal, Pa2, Pa3) being provided as incremental redundancies if regular decoding of the codeword by use of the basic codeword portion and less redundancies is erroneous.

9. Transmitter as claimed in claim 8, wherein said data mapper (16) is adapted for mapping the at least two auxiliary codeword sub-portions (Pal, Pa2, Pa3) of a codeword onto said transmitter output data stream (0) such that the auxiliary codeword sub-portion (Pal) used as first incremental redundancy is received by a receiver (50) after reception of the respective basic codeword portion (B) but before further auxiliary codeword sub-portions (Pa2, Pa3).

10. Transmitter as claimed in any preceding claim, wherein said data input (12) is adapted for receiving at least two transmitter input data streams (11,12, ..., In) segmented into input data words, and wherein the encoder (14) is adapted for selectively encoding a transmitter input data stream only according to the first code, according to the second code or according to both codes. 1 1. Transmitter as claimed in any preceding claim, wherein said data mapper (16) is adapted for mapping the basic codeword portions (B) of the codewords onto a fust transmitter output data stream (01) and for mapping the auxiliary codeword portions (A) of the codewords onto a second transmitter output data stream (02), and wherein said transmitter unit (18) comprises a MlMO precoder (162) for MIMO preceding said fust and second output data streams (01, 02) and at least two antennas including a first antenna (19a) and a second antenna (19b) for transmitting said MIMO precoded first and second transmitter output data streams (01 *, 02*).

12. Transmitter as claimed in any preceding claim, further comprising a modulator (1 7) for modulating the auxiliary codeword portions (A) by an auxiliary modulation code that is orthogonal to a basic modulation code used for modulating the basic codeword portions (B).

13. Transmitter as claimed in any preceding claim, 40 further comprising a modulator (17) for modulating the basic codeword portion (B) of a codeword differently than the auxiliary codeword portion (A) of the same codeword after mapping the codewords onto the frames of the transmitter output data stream (0).

14. Transmitter as claimed in any preceding claim, wherein said encoder (14) is adapted for generating said auxiliary codeword portions (A) such that they comprise parts of or the complete corresponding basic codeword portion (B).

15. Transmitter as claimed in any preceding claim, wherein said encoder (14) is adapted for applying a systematic code for generating said codewords such that said basic codeword portion (B) comprises a data portion, in particular the input data word (D), and a basic parity portion (Pb), and said auxiliary codeword portions (A) comprises an auxiliary parity portion (Pa).

16. Transmitter as claimed in any preceding claim, wherein said data mapper (16) is adapted for mapping the basic codeword portions (B) and the auxiliary codeword portions (A) onto frames of a transmitter output data stream (0) such that the auxiliary codeword portion (A) of a codeword is received by a receiver before the corresponding basic codeword portion (B) is received.

17. Transmission method for broadcasting data in a broadcasting system, comprising the steps of: - receiving at least one transmitter input data stream (11, 12, ..., In) segmented into input data words (D), - for error correction code encoding the input data words (D) into codewords (Zl, 22, 23, Z4), a codeword comprising a basic codeword portion (B) and an auxiliary codeword portion (A), wherein said encoder (14) is adapted for generating said basic codeword portion (B) from an input data word @) according to a first code and for generating said auxiliary codeword portion (A) from an input data word (D) according to a second code, said basic codeword portion (B) being provided for regular decoding and said auxiliary codeword portion (A) being provided as incremental redundancy if regular decoding of the codeword by use of the basic codeword portion (B) is erroneous, - mapping the codewords (Zl, 22, 23, 24) onto frames of a transmitter output data stream (O), and - transmitting said transmitter output data stream (0).

18. Receiver (50) for receiving data in a broadcasting system, comprising: - a receiver unit (52) for receiving a receiver input data stream (0') segmented into frames, - a data demapper (54) for demapping codewords (Zl, 22,Z3,24) mapped onto the frames of the receiver input data stream (0'1, a codeword comprising a basic codeword portion (B) and an auxiliary codeword portion (A), wherein said basic codeword portion (B) is generated from an input data word (D) according to a first code and said auxiliary codeword portion (A) is generated from an input data word (D) according to a second code, - a decoder (56) for error correction code decoding said codewords into output data words (D') of at least one output data stream (Il', I2', ..., In') in a regular decoding step by use of the basic codeword portion (B') comprised in a codeword and, if said regular decoding of a codeword is erroneous, in an additional decoding step by additionally using the auxiliary codeword portion (A') as incremental redundancy, - a check unit (58) for checking if the regular decoding of a codeword is erroneous, and - a data output (60) for outputting said at least one receiver output data stream (Il', I2', ..., In') segmented into said decoded output data words (D').

19. Receiver as claimed in claim 18, wherein said data demapper (54) is adapted for demapping the basic codeword portion (B') of a codeword from a different portion of the receiver input data stream (O'), in particular from a different frame, than the auxiliary codeword portion (A') of the same codeword.

20. Receiver as claimed in anyone of claims 18 to 19, wherein said data demapper (54) is adapted for demapping the basic codeword portion (B') of a codeword from a frame of a first type of the receiver input data stream, in particular from a T2 frame of a receiver input data stream in accordance with a DVB broadcasting system, and for demapping the auxiliary codeword portion (A') of the respective codeword from a frame of a second type, arranged between frames of the first type, of the receiver input data stream, in particular from an FEF frame of a receiver input data stream in accordance with a DVB broadcasting system.

21. Receiver as claimed in anyone of claims 18 to 20, wherein said decoder (561) comprises a first decoding unit (70) for decoding, according to said first code, the input data word (D') from a basic codeword (21) including said basic codeword portion (B') and a second decoding (80) unit for decoding, according to said second code, the input data word (D') from an auxiliary codeword (22) including said basic codeword portion (B') and said auxiliary codeword portion (A'), and wherein said data demapper (54) is adapted for demapping the basic codeword (21) from a different portion of the receiver input data stream (O'), in particular from a different frame, than the auxiliary codeword portion (A') of said auxiliary codeword (22).

22. Receiver as claimed in anyone of claims 18 to 20, wherein said decoder (562) comprises a single decoding unit for decoding, according to said second code, the input data word (D') from a codeword (22) including said basic codeword portion (B') and said auxiliary codeword portion (A'), and wherein said data demapper (56) is adapted for demapping the basic codeword portion (B') of said codeword (22) from a different portion of the receiver input data stream (O'), in particular from a different frame, than the auxiliary codeword portion (A') of said codeword (22).

23. Receiver as claimed in anyone of claims 18 to 22, wherein said decoder (56) is adapted for decoding the input data words from codewords (23) which comprise a basic codeword portion (B') and an auxiliary codeword portion (A'), said auxiliary codeword portion (A) including at least two auxiliary codeword sub-portions (Pal, Pa2, pa3 1, wherein said decoder (56) is adapted for using said basic codeword portion (B') for said regular decoding and said at least two auxiliary codeword sub-portions (Pal, Pa2, Pa3) as incremental redundancies if regular decoding of the codeword by use of the basic codeword portion and less redundancies is erroneous.

24. Receiver as claimed in claim 23, wherein said data demapper (54) is adapted for demapping the at least two auxiliary codeword sub-portions (Pal, Pa2, Pa3) of a codeword from said receiver input data stream (0') such that the auxiliary codeword sub-portion (Pal) used as fust incremental redundancy is demapped after demapping of the respective data portion (D) of said codeword but before demapping of further auxiliary codeword sub-portions (Pa2, Pa3).

25. Receiver as claimed in anyone of claims 18 to 24, further comprising a feedback loop (62) from said check unit (58) to said data demapper (54) andlor said decoder (56) for signalling if the last decoding of a codeword has been erroneous and for initiating another try of decoding by additional use of parts of or the complete auxiliary codeword portion, if available.

26. Receiver as claimed in anyone of claims 18 to 25, wherein said receiver unit (52) comprises a first antenna (61a) for receiving a first receiver input data stream (01') and a second antenna (61b) for receiving a second receiver input data stream (02'), wherein said data demapper (54) is adapted for demapping the basic codeword portions (B') of the codewords fkom said fust receiver input data stream (01') and for demapping the auxiliary codeword portions (A') of the codewords from said second receiver input data stream (02') .

27. Receiver as claimed in anyone of claims 18 to 26, further comprising a demodulator (53) for demodulating the auxiliary codeword portions (A') by an auxiliary modulation code that is orthogonal to a basic modulation code used for demodulating the basic codeword portions (B').

28. Receiver as claimed in anyone of claims 18 to 27, further comprising a demodulator (53) for demodulating the basic codeword portion (B') of a codeword differently than the auxiliary codeword portion (A') of the same codeword before or after demapping the codewords onto the frames fiom the receiver input data stream (0').

29. Receiver as claimed in anyone of claims 18 to 28, wherein said decoder (56) is adapted for applying a systematic code for decoding said codewords such that said basic codeword portion (B') comprises a data portion, in particular the input data word (D'), and a basic parity portion (Pb'), and said auxiliary codeword portions (A') comprises an auxiliary parity portion (Pa').

30. Receiver as claimed in anyone of claims 18 to 29, further comprising a buffer (64) for buffering auxiliary codeword portion (A'), wherein said data demapper (16) is adapted for demapping the auxiliary codeword portion (A') of a codeword before the basic codeword portion (B') is demapped from the frames of a receiver input data stream (0'). 3 1. Receiving method for receiving data in a broadcasting system, comprising the steps of - receiving a receiver input data stream (0') segmented into frames, - demapping codewords (Zl, 22, 23, 24) mapped onto the frames of the receiver input data stream (0')a' codeword comprising a basic codeword portion (B) and an auxiliary codeword portion (A), wherein said basic codeword portion (B) is generated from an input data word (D) according to a first code and said auxiliary codeword portion (A) is generated from an input data word (D) according to a second code, - error correction code decoding said codewords into output data words (D') of at least one output data stream (11'' I2', ..., In') in a regular decoding step by use of the basic codeword portion (B') comprised in a codeword and, if said regular decoding of a codeword is erroneous, in an additional decoding step by additionally using the auxiliary codeword portion (A') as incremental redundancy, - checking if the regular decoding of a codeword is erroneous, and - outputting said at least one receiver output data stream (Il', I2', ..., In') segmented into said decoded output data words (D').

32. Broadcasting system for transmitting and receiving data including a transmitter (10) as claimed in any one of claims 1 to 16 for transmitting data and a receiver (50) as claimed in any one of claims 18 to 30 for receiving data.

33. Broadcasting method for transmitting and receiving data including a transmission method as claimed in claim 17 for transmitting data and a receiving method as claimed in claim 3 1 for receiving data.

34. Computer program comprising program code means for causing a computer to carry out the steps of encoding and mapping of the method as claimed in claim 17, 31 or 33, when said computer program is carried out on a computer.

35. Computer readable non-transitory medium having instructions stored thereon which, when carried out on a computer, cause the computer to perform the steps of the method as claimed in claim 17,31 or 33. Dated this 1~/06/2012 HRIS O'F REMFRY AGAR ATTORNEY FOR THE APPLICANT[S]

[0001] The present invention relates to a transmitter and a corresponding transmission
method for broadcasting data in a broadcasting system. Further, the present invention relates to a
receiver and a corresponding receiving method for receiving data in a broadcasting system. The
present invention relates further to a broadcasting system and a corresponding broadcasting method
for transmitting and receiving data. Still further, the present invention relates to a computer
program for implementing said transmission method, said receiving method and said broadcasting
method on a computer.
[0002] The present invention relates, for instance, to the field of Digital Video
Broadcasting (DVB) utilizing Orthogonal Frequency Division Multiplexing (OFDM). Further, the
present invention can be applied in other systems, such as DAB (Digital Audio Broadcasting),
DRM, MediaFlo, or ISDB system.
BACKGROUND OF THE INIENTION
[0003] The transmission parameters of known broadcasting systems, such as the
broadcasting systems in accordance with the DVB-T2 standard (second generation digital
terrestrial television broadcasting systems standard), are generally optimized for fixed reception
with stationary receivers, e.g. with roof-top antennas. In future broadcasting systems, such as the
upcoming DVB-NGH (DVB Next Generation Handheld; in the following also referred to as NGH)
standard, a mobile receiver (which is the main focus of this upcoming standard) shall be enabled to
receive data correctly also in bad reception situations, e.g. despite suffering fkom multipath
propagation, fading effects and Doppler shifts. Such broadcasting systems are particularly
characterized by the fact that there is generally no feedback channel and no signalling from
receivers to transmitters.
SUMMARY OF INVENTION
[0004] It is an object of the present invention to provide a transmitter and a
corresponding transmission method for broadcasting data in a broadcasting system by which the
probability of error-free reception/reconstruction of data by a mobile receiver is increased
compared to transmitters and transmission methods in known broadcasting systems, even under
bad reception conditions. It is a further object of the present invention to provide a computer
program for implementing said transmission method.
[0005] According to an aspect of the present invention there is provided a transmitter
for broadcasting data in a broadcasting system, comprising:
- a data input for receiving at least one transmitter input data stream segmented into
input data words,
- an encoder for error correction code encoding the input data words into codewords,
a codeword comprising a basic codeword portion and an auxiliary codeword portion, wherein said
encoder is adapted for generating said basic codeword portion from an input data word according
to a first code and for generating said auxiliary codeword portion from an input data word
according to a second code, said basic codeword portion being provided for regular decoding and
said auxiliary codeword portion being provided as incremental redundancy if regular decoding of
the codeword by use of the basic codeword portion is erroneous,
- a data mapper for mapping the codewords onto frames of a transmitter output data
stream, and
- a transmitter unit for transmitting said transmitter output data stream.
[0006] According to further aspects of the present invention there is provided a
corresponding transmission method and a computer program comprising program means for
causing a computer to carry out the steps of encoding and mapping of the transmission method as
defined above, when said computer program is carried out on a computer.
[0007] Preferred embodiments of the invention are defined in the dependent claims. It
shall be understood that the claimed apparatus, the claimed methods and the claimed computer
program have similar andlor identical preferred embodiments as the claimed transmitter and as
defined in the dependent claims.
[OOOS] The present invention is based on the idea to enable a mobile receiver, for
instance an in-car receiver or a handheld receiver (e.g. in a mobile phone or a PDA) in a
broadcasting system to decode broadcast data even under severe transmission channel conditions
by improving the provided error correction measures. In particular, it is proposed to provide a
sufficient amount of redundancy by the encoder to increase the robustness of the code. Said
additional redundancy is provided by the transmitter such that a receiver can, but does not
mandatorily, use it if reception or reconstruction (decoding) of received broadcast data is erroneous
or could only be made with insufficient quality. The broadcasting operator also has the ability to
choose from a variety of different coding and modulation schemes, thereby trading off throughput
versus robustness.
[0009] To ensure that a receiver (e.g. an existing legacy receiver), in particular its
decoder, can correctly decode received data without any additional redundancy provided according
to the present invention, a first code is applied by the error correction code encoder (generally
applying forward error correction) of the proposed transmitter to generate a basic codeword portion
for the data words of the data to be broadcast. This way of encoding can be the known standard
way of encoding input data words into codewords, for instance the forward enor correction (FEC)
encoding as applied in DVB-T2 transmitters (e-g. LDPC encoding), i.e. the basic codeword portion
may correspond to a ("normal" error correction code) codeword according to the DVB-T2 standard
(in the following also referred to as T2). In addition, however, it is proposed according to the
present invention to provide incremental redundancy for the decoder of the receiver by generating
an auxiliary codeword portion from the input data words according to a second code. The "total"
code, i.e. the code according to which the ''total" codeword (comprising the basic codeword portion
4
and the auxiliary codeword portion) is generated, thus has a lower code rate than the first code.
Hence, said "total" code, in particular said auxiliary codeword portion, provides a higher
robustness and enables (better) decoding than the first code even under bad reception conditions.
[0010] Hence, under normal reception conditions the decoder does generally not (need
to) use the auxiliary codeword portion at all, but only uses the basic codeword portion to decode
the received data. In situations where the decoder realizes that the decoding of received data is
erroneous or with insufficient quality it uses part of or the complete auxiliary codeword portion to
better decode the received data. Thus, the basic codeword portion can be used as it is by a receiver /
decoder for decoding, and the auxiliary codeword portion needs only to be used if really needed for
decoding.
[0011] Furthermore, the auxiliary codeword portion represents an additional measure
for improving the decoding abilities, particularly for mobile receivers in case of bad reception
conditions. Both the basic codeword portion as well the auxiliary codeword portion are mapped
into the transmitter output data stream by an appropriate data mapper of the transmitter, said
transmitter output data stream generally being segmented into frames. For instance, a framing
structure as applied according to the DVB-T2 system using T2 frames and FEF (Future Extension
Frames) fiames can be used for transporting the two codeword portions in an appropriate way.
(00121 Preferably, the encoder and the decoder apply a systematic code for generating
said codewords such that said basic codeword portion comprises a data portion, in particular the
input data word, and a basic parity portion, and said auxiliary codeword portions comprises an
auxiliary parity portion. For instance, the basic codeword portion may be a combination of
information symbols (e.g. information bits or information bytes) of an input data word and
generated basic parity symbols (e.g. basic parity bits or bytes), said combination representing a
basic codeword of a fwst code, which can be decoded by the decoder. In this example, the auxiliary
codeword portion may comprise auxiliary parity symbols (e.g. auxiliary parity bits or bytes), said
auxiliary codeword portion representing an auxiliary codeword of a second code, which can be
used, to improve the likelihood of decoding said first codeword.
[0013] According to a preferred embodiment the data mapper is adapted for mapping
the basic codeword portion of a codeword onto a different portion of the transmitter output data
stream, in particular onto a different frame, than the auxiliary codeword portion of the same
codeword. This provides the advantage that the auxiliary codeword portion might not be affected
by disturbances of the channel that affect the basic codeword portion, such as time selective fadings
or noise bursts. Generally, the amplitude and phase of different reception paths also depend on the
position of the receiver. Further, in case of a moving receiver, especially the phase of the signals of
different reception paths changes, which causes a time-selective channel. The changes in the time
direction can also have a very regular structure, the change rate of which over the time axis being
proportional to the relative velocity of the receiver to the transmitter and the transmission
frequency of a signal. Also other disturbances, such as impulsive noise, can have a regular
structure, e.g. caused by the line cycle frequency of the power grid or by bursts from other data
transmission systems, e.g. a GSM communications system. Mapping the basic codeword portion on
the one hand and the corresponding auxiliary codeword portion on the other hand onto different
portions of the transmitter output data stream may in such situations avoid that all data related to a
particular codeword are affected by such regular disturbances and may thus ensure correct
decoding of the codeword at the receiver. Further, as will be explained below in more detail, a
receiver can fall into sleeping mode during the transmission of the auxiliary data portion, if said
auxiliary data portion is not required for decoding.
[0014] According to another preferred embodiment said data mapper is adapted for
mapping the basic codeword portion of a codeword onto a frame of a first type of the transmitter
output data stream, in particular onto a T2 frame of a transmitter output data stream in accordance
with a DVB broadcasting system, and for mapping the auxiliary codeword portion of the respective
codeword onto a frame of a second type, arranged between frames of the first type, of the
transmitter output data stream, in particular onto an FEF frame of a transmitter output data stream
in accordance with a DVB broadcasting system. This provides the advantage that stationary
receivers only access the data transmitted in the frames of the first type, for instance that receivers
in accordance with the DVB-T2 standard only access the data transmitted in the T2 frames. Mobile
receivers generally also access the data transmitted in the frames of the fmt type which are also,
according to the present invention, sufficient for correctly decoding the received codewords and for
reproducing the encoded data words. However, if the decoder realizes that the decoding is
erroneous or that the decoded data have insufficient quality, it may then also access the data, i.e.
the auxiliary codeword portion, transmitted in the frames of a second type and use these additional
data as incremental redundancy, i.e. use the basic codeword portion and @art or all of) the auxiliary
codeword portion for decoding, which finally provides an increased probability that the data are
decoded correctly since the total code of a codeword, i.e. a combination of the basic codeword
portion and the auxiliary codeword portion, has lower code rate than the first code according to
which the first codeword is encoded.
[0015] This embodiment provides the additional advantage that the existing framing
structure as defined in the DVB-T2 standard may be used, for instance in such a way that stationary
receivers (in accordance with the DVB-T2 standard) only access the data transmitted in the T2
frames and that mobile receivers access the data transmitted in the T2 frames and, if needed, in
addition the auxiliary codeword portions transmitted in the FEF frames. Stationary receivers may,
of course, also make use of the auxiliary codeword portions transmitted in the FEF frames if
needed, but will generally ignore these data.
(00161 In a preferred embodiment the encoder comprises a first encoding unit for
encoding, according to said first code, the input data word into a basic codeword including said
basic codeword portion and a second encoding unit for encoding, according to said second code,
the input data word into an auxiliary codeword including said auxiliary codeword portion. Further,
the data mapper is adapted for mapping the basic codeword onto a different portion of the
transmitter output data stream, in particular onto a different frame, than the auxiliary codeword.
Hence, according to this embodiment, an already existing encoder, i.e. the first encoding unit, can
be used without any changes, and simply a second encoder, i.e. the second encoding unit, is added
which is also provided with the input data words fiom which the auxiliary codewords are generated
according to the second code, which itself may also have a lower code rate than the first code
applied by the first encoding unit, but which can also have the same or a higher code rate.
[0017] While it is generally possible to map both the basic codewords and the auxiliary
codewords completely onto the transmitter output data stream, it is in certain embodiments (in
particular if the auxiliary codewords do not only contain auxiliary parities but also parts of or the
complete input data word andlor basic parities of the basic codeword) sufficient for achieving the
desired object that only the auxiliary parity portion is mapped onto the transmitter output data
stream in addition to the basic codeword. The receiver then exploits, in case of need, the auxiliary
parity portion as redundancy for decoding a received basic codeword that could not be decoded
correctly.
[0018] The second encoding unit may further be adapted for encoding, according to
said second code, the input data word into an auxiliary codeword including said basic codeword
portion and said auxiliary codeword portion. Hence, the basic codeword portion is part of both the
basic codeword and the auxiliary codeword, but is not further used in the auxiliary codeword, from
which basically the auxiliary parity portion is embedded into the transmitter output data stream.
Such an embodiment has the advantage that the first encoding unit can be the (conventional)
encoder of a known receiver, e.g. a receiver in accordance with the DVB-T2 standard, which can
generally be used without changes, and to which the second encoding unit is added according to the
invention.
[0019] Alternatively, the second encoding unit may further be adapted for encoding,
according to said second code, the input data word into an auxiliary codeword including only said
auxiliary codeword portion. Such an encoding unit can be easily added to an existing encoder and
performs only the minimum required steps for implementing the present invention on the
transmitter side.
[0020] According to an alternative embodiment said encoder comprises a single
encoding unit for encoding the input data word into a codeword including said basic codeword
portion and said auxiliary codeword portion, and wherein said data mapper is adapted for mapping
the basic codeword portion of said codeword onto a different portion of the transmitter output data
stream, in particular onto a different frame, than the auxiliary codeword portion of said codeword.
This embodiment requires less processing capacity since only a single encoding process is carried
out for generating the codewords, which are thereafter split up into the basic codeword portion, on
the one hand, and the auxiliary codeword portion on the other hand.
[0021] According to a further embodiment said encoder is adapted for encoding the
input data words into codewords, a codeword comprising a basic codeword portion and an
auxiliary codeword portion, said auxiliary codeword portion including at least two auxiliary
codeword sub-portions, said basic codeword portion being provided for regular decoding and said
at least two auxiliary codeword sub-portions being provided as incremental redundancies if regular
decoding of the codeword by use of the basic codeword portion and less redundancies is erroneous.
This embodiment provides the advantage that a receiver may decide how many additional
incremental redundancies it requires for correct decoding if the regular decoding, i.e. the decoding
by use of only the basic codeword portion, is erroneous. This is enabled by encoding the input data
words such that two or more auxiliary codeword sub-portions (e.g. two or more groups of auxiliary
parity symbols) are generated which can stepwise be used as such incremental redundancies, i.e.
the auxiliary codeword sub-portions are generated such that not all sub-portions are required
completely to perform a correct decoding of a received codeword, but one or more sub-portions
thereof are also suff~cienfto r a correct decoding. If more sub-portions are used, however, the code
rate decreases and the probability of correct decoding increases.
[0022] Thus, each receiver may decide by itself (which decision may also change from
time to time) how many additional incremental redundancies, i.e. how many of those at least two
auxiliary codeword sub-portions shall be used for increasing the quality of decoding, if needed.
Hence, if only a small sub-portion is additionally required, the other auxiliary codeword subportions
may be ignored and may not even be received or at least demapped at all so that during
time when these other auxiliary codeword sub-portions are transmitted the receiver can be switched
into sleeping mode saving battery power and processing time.
[0023] This embodiment may be developed further such that the data mapper is
adapted for mapping the at least two auxiliary codeword sub-portions of a codeword onto said
transmitter output data stream such that the auxiliary codeword sub-portion used as furst
incremental redundancy is received by a receiver after reception of the respective basic codeword
portion, but before further auxiliary codeword sub-portions. Such an embodiment ensures that a
receiver can be switched into sleeping mode after having received sufficient auxiliary codeword
sub-portions for enabling a correct decoding if, as proposed, the "most helpful" auxiliary codeword
sub-portions (e.g. the largest auxiliary codeword sub-portions) are transmitted first. In another
embodiment, the auxiliary codeword sub-portions may be mapped on the transmitter output data
stream such that at first a small auxiliary codeword sub-portion is provided, and that thereafter
auxiliary codeword sub-portions are provided with increasing size.
[0024] The sequence of the auxiliary codeword sub-portions can preferably be derived
by the receiver from the sequence of the related basic codeword portions transmitted before so that
no additional signalling is required for signalling the sequence of the auxiliary codeword subportions,
e.g. the sequence of the auxiliary codeword sub-portions is identical to the then already
known sequence of the related basic codeword portions.
100251 Further, if in the fiames (e.g. T2 frames) preceding a frame (e-g. FEF h e )
containing auxiliary codeword sub-portions data from various transmitter input data streams (e.g.
PLPs) are contained, the auxiliary codeword sub-portions may be grouped together such that, for
instance, the largest or smallest sub-portions of all auxiliary codeword portions are transmitted
first, and that thereafter further groups of sub-portions are transmitted.
[0026] Generally, the basic codeword portions and the auxiliary codeword portions are
mapped onto the transmitter output data stream such that a basic codeword portion of a codeword is
received by a receiver before the corresponding auxiliary codeword portion is received.
Alternatively, however, the data mapper is adapted for mapping the basic codeword portions and
the auxiliary codeword portions onto frames of a transmitter output data stream such that the
auxiliary codeword portion of a codeword is received by a receiver before the corresponding basic
codeword portion is received. The auxiliary codeword portions are thus buffered in the receiver in a
respective buffer. If it is clear that the decoding of the corresponding codeword based on only the
basic codeword portion was correct, the corresponding auxiliary codeword portion (if any) can be
deleted from the buffer. Even if decoding based on the basic codeword portion is not correct, the
corresponding auxiliary codeword portion is already available in the buffer. This provides the
advantage that no or reduced waiting times (for waiting for the auxiliary parity portion, if the
decoding was erroneous based on the basic codeword portion) occur, which is particularly
important for reducing zapping times and for mobile receivers in case of sudden signal distortions.
Hence, this embodiment also provides the advantage that no interruption of the service occurs (due
to waiting for reception of auxiliary codeword portions) in case of (e.g. sudden) bad reception
conditions of the basic codeword portions.
[0027] According to another embodiment the data input is adapted for receiving at least
two transmitter input data streams segmented into input data words and the encoder is adapted for
selectively encoding a transmitter input data stream only according to the first code, according to
the second code or according to both codes. Hence, according to this embodiment the transmitter,
for instance under control of the system operator of the broadcasting system, has the freedom to
apply the idea of the present invention to provide incremental redundancies into the transmitter
output data stream only for selected transmitter input data streams but must not generally apply it to
all transmitter input data streams. For instance, a system operator may decide to apply the present
invention for data streams that are provided for reception by both a stationary receiver and a mobile
receiver, while other data streams that shall generally only be received by stationary receivers are
not processed according to the present invention, i.e. no auxiliary codeword portions are generated
and transmitted.
[0028] Generally, the transmitter output data stream can be transmitted by any kind of
transmitter, for instance having only a single antenna or multiple antennas such as, for instance,
used in MIMO (Multiple Input Multiple Output) systems. In a preferred embodiment, however, the
data mapper is adapted for mapping the basic codeword portions of the codewords onto a first
transmitter output data stream and for mapping the auxiliary codeword portions of the codewords
onto a second transmitter output data stream, and the transmitter unit comprises a MlMO precoder
for MIMO precoding said first and second output data streams, and at least two antennas including
a first antenna and a second antenna for transmitting said MIMO precoded first and second
transmitter output data streams. For instance, the MIMO precoder is adapted for spatial
multiplexing such that a first antenna transmits said fust transmitter output data stream and a
second antenna transmits said second transmitter output data stream. Generally, however, any other
embodiment of MIMO precoding (e.g. Alamouti precoding) can also be applied on the two
transmitter output data streams before outputting them by two or more antennas of a MlMO
system.
[0029] A receiver may also have only a single antenna or multiple antennas, wherein
generally each antenna of the receiver receives signals from all antennas of the transmitter. It may,
however, also be possible that generally the antennas of the receiver are tuned to receive the signals
from the first antenna only (i.e. for receiving the first transmitter output data stream) and that only
in case of decoding problems or errors the antennas are additionally tuned to receive the signals
from the second antenna (for receiving the second transmitter output data stream). According to a
further embodiment it may be possible that the receiver comprises one antenna that is tuned to the
first antenna of the transmitter and that the receiver comprises a second antenna that is tuned to
receive the signals fiom the second antenna of the transmitter, and that the signals received at the
second antenna are only evaluated in case of need.
[0030] In a further embodiment the transmitter comprises a modulator for modulating
the basic codeword portion of a codeword differently than the auxiliary codeword portion of the
same codeword before or after mapping the codewords onto the fiames of the transmitter output
data stream. In general, the auxiliary codeword portion can be transmitted in any dimension, which
is orthogonal to the basic codeword portion of a codeword, such as time, ftequency, space (MIMO)
or spreading code. The term "orthogonal" shall be understood as generally known in the art of
coding and modulation, i.e. to provide separable data streams (which might even overlap before
separation, such as OFDM subcaniers and their related partial spectra). This provides the
advantage that the auxiliary codeword portion is additionally protected against disturbances by
which the basic codeword portion may be disturbed. Another possibility is the application of a
hierarchical modulation. In this case, the basic codeword portion addresses the more reliable bits of
the modulation scheme, while the auxiliary codeword portion addresses the less reliable bits.
[0031] According to another embodiment the encoder is adapted for generating said
auxiliary codeword portions such that they comprise parts of or the complete basic codeword
portion. Hence, according to this embodiment the auxiliary codeword portion comprises some
repetitions of data included in the basic codeword portion (e.g. the input data word andlor basic
parity symbols), which can then be used as additional redundancy for decoding at the receiver. This
embodiment is generally simple to implement and provides the advantage that umeliably
transmitted data are repeated again as part of the auxiliary data portion.
(00321 According to another aspect of the present invention there is provided a receiver
for receiving data in a broadcasting system, comprising:
- a receiver unit for receiving a receiver input data stream segmented into frames,
- a data demapper for demapping codewords mapped onto the frames of the receiver
input data stream, a codeword comprising a basic codeword portion and an auxiliary codeword
portion, wherein said basic codeword portion is generated fiom an input data word according to a
first code and said auxiliary codeword portion is generated from an input data word according to a
second code,
- a decoder for error correction code decoding said codewords into output data
words of at least one output data stream in a regular decoding step by use of the basic codeword
portion comprised in a codeword and, if said regular decoding of a codeword is erroneous, in an
additional decoding step by additionally using the auxiliary codeword portion as incremental
redundancy,
- a check unit for checking if the regular decoding of a codeword is erroneous, and
- a data output for outputting said at least one receiver output data stream segmented
into said decoded output data words.
[0033] According to further aspects of the present invention there is provided a
corresponding receiving method, a broadcasting method and a broadcasting method.
BRIEF DESCRIPTION OF DRAWINGS
[0034] These and other aspects of the present invention will be apparent from and
explained in more detail below with reference to the embodiments described hereinafter. In the
following drawings
Fig. 1 shows a schematic block diagram of an embodiment of a transmitter in
accordance with the present invention,
Fig. 2 shows a schematic block diagram of a fmt embodiment of an encoder used in
the transmitter,
Fig. 3 shows the arrangement of a data portion, a basic parity portion and an auxiliary
parity portion according to the present invention,
Fig. 4 shows the format of a BBFrame according to the DVB-T2 standard,
Fig. 5 shows the format of an FEC codeword in accordance with a DVB-T2 standard,
Fig. 6 shows the format of a codeword in accordance with the present invention,
13
Fig. 7 shows a diagram illustrating the DVB-T2 framing structure,
Fig. 8 shows a diagram illustrating the arrangement of T2 frames and FEF frames
within a superframe in accordance with the DVB-T2 standard,
Fig. 9 shows a schematic block diagram of a second embodiment of an encoder,
Fig. 10 shows a schematic block diagram of a third embodiment of an encoder,
Fig. 11 illustrates the arrangement of auxiliary parity portions according to the present
invention,
Fig. 12 shows the mapping of data PLPs onto a T2 h e according to the DVB-T2
standard,
Fig. 13 shows the mapping of segmented auxiliary parity portions onto an FEF fiarne,
Fig. 14 shows a schematic block diagram of a fourth embodiment of an encoder,
Fig. 15 shows a schematic block diagram of a receiver,
Fig. 16 shows a schematic block diagram of a first embodiment of a decoder used in the
receiver,
Fig. 17 shows a schematic block diagram of a second embodiment of a decoder,
Fig. 18 shows a schematic block diagram of a broadcasting system in accordance with
the present invention,
Fig. 19 shows a diagram illustrating the generation of the bits of a codeword according
to the present invention,
Fig. 20 shows the structure of a transmission frame as used according to DAB, and
Fig. 21 shows a block diagram of another embodiment of a receiver.
Embodiments of the invention will now be described with reference to the accompanying
drawings, throughout which like parts are referred to by like refdrences, and in which:
[0035] Fig. 1 shows an example block diagram of a transmitter 10 in accordance with
the present invention. Such a transmitter 10 can, for instance, be a Coded OFDM (COFDM)
transmitter which may be used to transmit video, images and audio signals in accordance with the
DVB-T2 (or an upcoming DVB-NGH) standard and in which the invention can be used. Said data
to be transmitted by the transmitter 10 are generally provided as at least one transmitter input data
stream 11, I2, ..., In, which data streams are generally segmented into input data words. Said
transmitter input data streams 11, I2, ..., In may be one or more (e.g. MPEG-2) Transport Stream(s)
andfor one or more Generic Strearn(s), and the data may be carried therein in individual Physical
Layer Pipes PLPs.
[0036] From the data input 12, in which some input processing may be performed on
the transmitter input data streams I1,12, ..., In, such as CRC (Cyclic Redundancy Check) encoding,
BB (BaseBand) header insertion, padding insertion and BB scrambling, the input data are provided
to an encoder 14 in which the input data words of the transmitter input data streams 11, I2, ..., In are
encoded into codewords as will be explained in more detail below. From the encoder 14 the
encoded data are then provided to a data mapper 16 for mapping the generated codewords onto
frames of a transmitter output data stream 0, which is then outputted by a transmitter unit 18.
Generally (but not mandatorily), a modulator 17 is provided for modulating the data before output
and transmission.
[0037] Fig. 2 depicts a first embodiment 141 of an encoder 14 according to the present
invention. Said embodiment of the encoder 141 comprises two branches, i.e. two encoding units
20, 30 to which a transmitter input data stream 11, called Physical Layer Pipe (PLP) in context of
DVB, is fed. With the, exception of the time interleavers 27, 37, the processing is preferably
performed on a fvred fiame level. An input frame of the transmitter input data stream 11, which
shall be looked at in the following as an example, is denoted as a BBFrame in the context of Dm.
[0038] The first encoding unit 20, i.e. the upper branch, in this embodiment
corresponds to the Bit Interleaved Coding and Modulation (BICM) chain as described in the Dm-
T2 standard (ETSI EN 302 755 V1.l.l (2009 - 09) "Digital Video Broadcasting (DVB); Framing
structure Channel Coding and Modulation for a Second Generation Digital Terrestrial Television
Broadcasting System (DVB-T2)"). Hence, it comprises an FEC encoding block 21 for subsequent
LDPC encoding, a bit interleaver 22, a demultiplexer 23 for demultiplexing bits to cells, a
constellation mapper 24 for mapping cells to constellations according to Gray mapping, a unit 25
for constellation rotation and cyclic Q-delay, a cell interleaver 26 and a time interleaver 27. The
function and operation of these units 2 1 to 27 is generally known and, for instance, described in the
DVB-T2 standard, which is herein incorporated by reference, so that no further explanations are
provided here.
[0039] The second encoding unit 30, i.e. the lower branch, is also provided with the
transmitter input data stream I1 in this embodiment. The FEC encoding block 3 1 is generally not
identical to the FEC encoding block 21 of the first encoding unit 20. While said FEC encoding
block 21 appends to the input data words parity bits of an LDPC codeword, said LDPC parity bits
being generally referred to herein as basic parity portion of a first code, the FEC encoding block 3 1
generates additional redundancy to increase the robustness of the overall channel code, said overall
channel code referring to the redundancy from both FEC encoding blocks 21 and FEC encoding
blocks 3 1. In other words, the FEC encoding block 3 1 generates auxiliary parity bits that can, in
addition to the basic parity bits, be used by a receiver to decode a received codeword as will be
explained in more detail below.
[0040] The consecutive blocks 32 to 37 can generally be identical to the blocks 22 to
27 and can thus be adopted from the DVB-T2 standard, but can also be adjusted according to the
specific circumstances and needs of the second encoding unit 30. The application of a time
interleaver 37 is optional since applying time interleaving within just one frame of auxiliary parity
bits is already covered within the cell interleaver 36. However, applying time interleaving over
more than one auxiliary parity data fiame allows for more time diversity.
[0041] In this embodiment, the input of the two FEC encoding blocks 21, 31 is
identical, in particular an input data stream I1 *, which substantially corresponds to the transmitter
input data stream, but wherein to the input data words (BBFrames in the context of DVB) parity
bits of a BCH codeword have been added by a BCH encoder 40 (as is generally known in the art of
DVB). Hence, the input data stream I1 has already been encoded by a BCH code, before further
encoding is performed in the FEC encoders 21 and 3 1. It should, however, be noted that the
encoder 40 is generally not an essential element of the present invention. In certain application the
encoder 40 can be completely omitted, can be replaced by a different encoder or this initial
encoding can be part of the encoding performed in the encoders 21 and 3 1.
[0042] Further, it shall be noted that hereinafter it is generally referred to parity "bits"
and input data "bits". The same idea is, however, also applicable using parity L'bytes" and input
data "bytes" or, generally, parity "symbols" and input data "symbols".
[0043] The outputs of the first and second encoding units 20, 30 are fed forward to a
data mapper 16, generally including a frame builder, and, optionally, an OFDM generator. The data
mapper 16 and the OFDM generator may generally operate according to the DVB-T2 standard
which particularly shows embodiments of these blocks. For mapping the outputs of the first and
second encoding units 20, 30, however, various embodiments exist which will also be explained
below in more detail.
(00441 By way of Fig. 3 the encoding performed in the FEC encoding blocks 2 1 and 3 1
shall be explained in more detail. Fig. 3A shows a fust codeword Zl which is the output of the
FEC encoding block 21. Said fust codeword Z1 comprises a data portion D, which generally
corresponds to the input data word of the FEC encoding block 21 and which, according to this
embodiment, comprises k input data bits sl, s2, ..., sk, and a basic parity portion Pb comprising, in
this embodiment, m parity bits pl, p2, ..., pm. This fvst codeword Z1 generally corresponds, in the
context of DVB-T2, to the LDPC codeword belonging to a code C1 with code rate R1 = kl(k+m),
where k is the amount of the systematic bits (input data bits) s and m is the amount of the basic
parity bits p. By use of these codewords a receiver, in particular a stationary receiver andlor a
mobile receiver that is not affected by too many disturbances, is able to decode the input data
encoded therein.
[0045] The second codeword 22 shown in Fig. 3B belongs to a second code C2 of a
lower code rate R2 = k/(k+m+v) < R1. Said second codeword 22 comprises, in addition to the data
portion D and the basic parity portion Pb, an auxiliary parity portion Pa of v auxiliary parity bits il,
iZ, ..., iv. Said auxiliary parity portion Pa may be used by a receiver, for instance in case of
transmissions errors, decoding errors and/or an insufficient quality of the decoding, as incremental
redundancy in addition to the codeword Z1 for decoding. Hence, if the first codeword Z1 cannot be
decoded correctly at the receiver, some or all of the auxiliary parity bits il, i2, ..., iv may be used for
decoding, in addition to the fmt codeword Z1, to increase the probability of correct and error-free
(or at least an increased quality of) decoding. For this purpose at least the auxiliary parity portion
Pa will also be mapped onto the transmitter output data stream for eventual reception and use by
the receiver. Said mapping will be explained below in more detail.
[0046] Hence, the combination of the codeword Z1 and the auxiliary parity portion Pa
(of the second codeword 22) can also be regarded as a "total" codeword of a "total" code having a
lower code rate than the fmt code of the codeword Z1, i.e. the codeword Z1 can be regarded as a
basic codeword portion B of this "total" codeword and the auxiliary parity portion Pa can be
regarded as a auxiliary parity portion A of this "total" codeword. Here in this embodiment shown
in Fig. 3 this "total" codeword is identical to the codeword 22. This does, however, not hold for all
embodiments as will be shown below.
[0047] In the context of DVB-T2 the transmitter input data stream to the encoder 14 is
generally segmented into frames referred to as BBFrames comprising Kbch bits as exemplarily
depicted in Fig. 4. A first codeword Z1 (in this context) generated therefrom by the BCH encoder
40 and the first encoding block 21, i.e. in accordance with the encoding as performed according to
the DVB-T2 standard, is schematically depicted in Fig. 5. This codeword is a standard FEC
codeword comprising the (systematic) input data portion, which itself consists of Lh bits,
followed by Nbch - Kbch parity bits of the BCH encoder, followed by Nldpc - Kidpc parity bits of the
LDPC encoder. In total, this codeword comprises NldP bits. Hence, the basic LDPC code has a
code rate of R, = Kldpc/NldPR. eferring to the above explanations provided with reference to Figs. 3
and 4 Kldpc corresponds to k (i.e. the portions BBFRAME and BCHFEC are regarded as the input
data word D) and NldP corresponds to k+m (i-e. the portion LDPCFEC is regarded as the basic
parity portion Pb).
[0048] The second encoding block 31 computes auxiliary parity bits for use as
incremental redundancy, based on its input, which generally is the same as the input of the FEC
encoding block 2 1. In general, these are v auxiliary parity bits which can be partitioned into q subportions.
The k-th sub-portion is of length vCk)T. hus, it holds
[0049] If the bits from the first x sub-portions are then appended to the first basic
codeword (Zl) generated by the first encoding unit 20 and generally received and evaluated by a
receiver, an auxiliary codeword (Z3*) of the "total" code is generated which stems from an encoder
with the overall code rate &* of
which is smaller than &, which means that this overall code is more powerful.
[0050] Fig. 6 shows such an embodiment of a codeword 22 (in the context of DVT-T2)
generated by the second FEC encoding block 31 which, according to this embodiment, also
comprises BCH and LDPC encoding, but additionally generates v auxiliary parity bits for use as
incremental redundancy at the receiver in case of need.
[0051] The generation of additional LDPC parity bits, e.g. of a known LDPC code, and
their use as incremental redundancy is generally known, e.g. from Kim J. et al. ,,Design of Rate-
Compatible Irregular LDPC Codes for Incremental Redundancy Hybrid ARQ Systems", ISIT
2006, Seattle, USA, July 9-14, 2006. A diagram illustrating such an "extended" code and its
generation is shown in Fig. 19. Therein, it is shown how each of the bits of the basic codeword
portion B and of the auxiliary parity portion A are generated from other, in particular all "previous"
bits in the codeword by use of modulo-2 units 45. This way of generating the codeword ensures
that a decoder can decode a codeword by use of only the basic codeword portion B or by additional
use of one or more of the auxiliary parity bits of the auxiliary parity portion A.
[0052] Next, an embodiment of the data mapper 16 shall be explained. Generally, it is
sufficient if the first codeword (generally, the basic codeword portion B) generated by the first
encoding unit 20 and the auxiliary parity portion (generally, the auxiliary codeword portion A)
generated by the second encoding unit 30 for the same input data word are mapped in any way onto
the frames of the transmitter output data stream 0. In other words, using the terminology from Fig.
3, for each input data word the corresponding data portion D, the basic parity portion Pb and the
auxiliary parity portion Pa are mapped onto the transmitter output data stream 0 according to the
present invention. Preferably, however, the data mapper 16 is adapted such that the data portion D
and the basic parity portion Pb are mapped onto a different portion, for instance onto a different
frame, than the corresponding auxiliary parity portion Pa of the same codeword. This provides the
advantage that regular channel disturbances do generally not affect both the data portion D and the
basic parity portion Pb on the one hand and the auxiliary parity portion Pa on the other hand.
[0053] A particular embodiment for such a mapping structure shall be illustrated with
reference to Figs. 7 and 8. Fig. 7 illustrates the framing structure as applied according to the DVBT2
standard. In particular, according to DVB-T2, a superframe structure is applied where each
superhame is subdivided into a multitude of T2 frames. After each predetermined number of
consecutive T2 frames an FEF part (Future Extension Frame part) is inserted for future use. This is
also schematically illustrated in the data stream structure shown in Fig. 8. When applying such a
framing structure in the transmitter 10 according to the present invention, the data mapper 16 is
adapted in one embodiment such that the data portion and the basic parity portion of a codeword,
which can also be regarded as the basic codeword portion B and, in this embodiment, the basic
codeword Z1 (see Fig. 3A), are mapped onto the T2 hmes and that the auxiliary parity portion Pa
(generally the auxiliary codeword portion A) of the same codeword (taken from the auxiliary
codeword 22) is mapped onto the FEF part, preferably the FEF part following next to the T2
frame(s) into which the corresponding data portion D and basic parity portion Pb are mapped.
[0054] Such a mapping provides the advantage that a conventional receiver in
accordance with the DVB-T2 standard simply ignores the data transmitted in the FEF parts and
only evaluates the data transmitted in the T2 fiames as usual. Mobile receivers, however, for
20
instance in accordance with the upcoming DVB-NGH standard, whose decoding and reproduction
capability may often be affected by disturbances, may also access the T2 frames and decode, in a
first step, the codewords embedded therein. In addition, however, particularly in case of
disturbances and decoding errors resulting therefiom, such mobile receivers access the FEF parts
and use parts or all of the auxiliary parity data contained therein for decoding, in a second step, the
codeword received in the corresponding T2 fiame again, as will be explained in more detail below.
[0055] According to still another embodiment of the data mapper 16 all data required
for decoding by a mobile receiver are transmitted in the FEF parts, i.e. a complete codeword
comprising the data portion D, the basic parity portion Pb and the auxiliary parity portion Pa is
mapped onto the FEF part. Such mobile receivers thus ignore the data contained in the T2 frames
which are only accessed by stationary receivers, in particular receivers in accordance with the
DVB-T2 standard.
[0056] In such a situation, however, the auxiliary parity portion Pa is preferably
modulated in a different way than the data portion D and the basic parity portion Pb. Preferably, an
auxiliary modulation code is applied for modulating the auxiliary parity portions, said auxiliary
modulation code being orthogonal to a basic modulation code that is used for modulating the data
portions and the basic parity portions, generally after the data mapping. For instance, an orthogonal
time, frequency, space (MIMO) or a spreading code may be applied. Another possibility would be
the application of hierarchical modulation.
[0057] Of course, there may be further embodiments of the data mapper 16. The
framing structure applied by the transmitter 10 may also be completely different than the framing
structure used according to the DVB-T2 standard as shown in Figs. 7 and 8. Generally, any framing
structure, e.g. a newly created framing structure, may be applied as long as the receiver is able to
detect or know in advance where to find the data portions and the various parity portions. Further,
in embodiments of the invention BCH and LDPC encoding is not required, but other codes (e.g.
other FEC codes) can be applied.
[0058] A simplified block diagram of another embodiment of an encoder 142 and a
data mapper 16 is shown in Fig. 9. According to this embodiment the encoder 142 comprises a
single encoding unit by which the input data words are encoded, i.e. by which both the basic parity
portions Pb and the auxiliary parity portions Pa are generated. In other words, in said single
encoding unit of the encoder 142 the complete codeword 22 (see Fig. 3B) is generated. These
codewords 22 are provided to the data mapper 16 which splits off the auxiliary parity portion Pa
and maps it onto a different portion of the transmitter output data stream than the data portion D
and the basic parity portion Pb. For the data mapper 16 generally the same embodiments exist as
have been explained above.
[0059] As shown in Fig. 1 the data input 12 may be adapted for not only receiving a
single transmitter input data stream, but may generally receive a number n of transmitter input data
streams, for instance a number n of physical layer pipes. The encoder 14 may, in such a case,
however be adapted to select if a transmitter input data stream is encoded as usual, i.e. according to
the basic code and without the generation of any auxiliary parity data, or if another code having a
lower code rate shall be applied and auxiliary parity data for use as incremental redundancies by
the receiver shall be generated. It may also be possible that various codes with different (e.g.
decreasing) code rates may be available for application by the encoder so that even more than two
possibilities exist. Which code and which code rate to apply may be prescribed, e.g. by the operator
of the transmitter or the owner of the broadcast channel. But the choice of the code may also
depend on the kind of data to be transmitted. For instance, audio data may be encoded with a code
having a higher code rate than video data so that only for video data such auxiliary parity data are
generated or vice versa. As another example, any decoding errors may be acceptable when
watching news, but may not be acceptable when watching a movie for which auxiliary parity data
may thus be generated and transmitted.
[0060] A still further embodiment of an encoder 143 is illustrated in Fig. 10. Said
encoder 143 is adapted such that it generates two or more auxiliary parity sub-portions Pal, Pa2,
Pa3 in addition to the data portion D and the basic parity portion Pb thus forming a codeword 23.
Hence, comparing the codewords 22 and 23, the auxiliary parity sub-portions Pal, Pa2, Pa3 of the
codeword 23 can be seen as segments of the auxiliary parity portion Pa of the codeword 22, having
in total the identical content, although generally the auxiliary parity sub-portions Pa2 and Pa3 can
also be additional auxiliary parity portions in addition to the auxiliary parity portion Pal that
(alone) corresponds to the auxiliary parity portion Pa.
[0061] These auxiliary parity sub-portions Pal, Pa2, Pa3 are generated such that they
can be stepwise used by a decoder as incremental redundancies. In other words, generally it is
possible to decode the codeword by use of only the data portion D and the basic parity portion Pb
(i.e. the basic codeword portion). If such decoding fails, the fust auxiliary parity sub-portion Pal
(i.e. a part of the auxiliary codeword portion) may be used in addition for decoding. If this again
fails (or provides insufficient quality) the second auxiliary parity sub-portion Pa2 may be added
and so on.
(00621 All the auxiliary parity sub-portions Pal, Pa2, Pa3 may be grouped together and
mapped onto a single portion of the transmitter output data stream. However, it is also possible and
advantageous to distribute the various auxiliary parity sub-portions of a single codeword 23,
preferably such that the first auxiliary parity sub-portion Pal is received before the second auxiliary
parity sub-portion Pa2, which again is received before the third auxiliary parity sub-portion Pa3.
This provides the advantage that a receiver which, after using the first auxiliary parity sub-portion,
can decode the codeword with sufficient quality, can fall into sleeping mode for the time period
during which other auxiliary parity sub-portions are transmitted that are no longer needed and/or
from other data streams that shall currently not be decoded. This provides some power saving and
less calculation efforts at the receiver.
[0063] An embodiment of the arrangement of auxiliary parity sub-portions of various
input fiames (BBFrames, generally referred to as input data words) is shown in Fig. 11. The input
frames are enumerated in this embodiment by two indices (e, f), where the index e corresponds to
the PLP-ID (PLP number, also referred to here as the number of the transmitter input data stream),
and where f relates to the input frame (input data word). The index e is part of a set Sz, i-e., the set
of PLPs that are protected by additional incremental redundancy. Assuming that n different PLPs
are transmitted, i.e. e E S1 = (1, ..., n), S2 is a subset of S1 of PLPs that are protected by additional
incremental redundancy according to the present invention since, as mentioned above, not all PLPs
need necessarily use this idea.
[0064] Thus, the f-th input frame of the e-th PLP is denoted as Z,f. The index f E (1, ...,
F,), where F, is the number of input fiames of the e-th PLP, which precede the FEF, starting from
the end of the previous FEF. Hence, in one embodiment, the auxiliary parity sub-portions Pale,f up
to Payef may be mapped onto an FEF frame in the sequence as shown in Fig. 11 and may belong to
codewords mapped onto preceding T2 frames.
[0065] Fig. 12 illustrates more details of the arrangement of data within a T2 frame in
accordance with the DVB-T2 standard. The PLPs in a T2 frame underlie a certain order. After the
preambles PI, P2 and after common PLPs the PLPs of type 1 are transmitted without subslicing,
then PLPs of type 2 are transmitted with subslicing. Both type 1 and type 2 PLPs have a fixed order
which is signalled in the P2 preamble. This is also illustrated and explained in detail in the DVB-T2
standard, which explanation is herein incorporated by reference.
[0066] Fig. 13 shows a proposal for arranging the auxiliary parity sub-portions in an
FEF frame that is made similar to the arrangement of the PLPs in the T2 frame. In this embodiment
the FEF also starts with a P1 preamble, i.e. an OFDM symbol, which is made to be used for (time,
frequency) synchronization purposes, for channel estimation and for signalling the most important
transmission parameters. The subsequent (one or more) P2 preamble(s) contain(s) more detailed
information about the content of the FEF. Using the notation explained with reference to Fig. 11
and assuming that there are two PLPs of three input frames each, the arrangement of the auxiliary
parity sub-portions in the FEF in this embodiment is such that the order of the partitioned auxiliary
parity sub-portions is derived fiom the slicinglordering of the T2 frames, even if not all PLPs from
T2 frames have auxiliary parity sub-portions to be mapped onto the FEFs. Thus, the order of the
auxiliary parity sub-portions does not have to be signalled explicitly.
[0067] The auxiliary parity portions are sorted in the time domain, in particular such
that the first portion Palef, for instance the more robust portion, of all PLPs having auxiliary parity
portions is inserted at the beginning of the FEF, i.e. right after the preambles PI, P2. The second
portion Pa2 of all PLPs with auxiliary parity portions follows afterwards etc. As mentioned above,
if basic codewords are not decodable the related fmt portion Pal of the FEF is evaluated. If the
receiver can now correctly decode the overall codeword without error it falls into sleeping mode to
save power. Otherwise it will additionally include the second auxiliary parity portion Pa2 etc.
[0068] It shall be noted also that the FEFs may contain signalling information, e.g. in
the preamble or in a ModCod header, regarding the link of the auxiliary parity portions used in the
FEFs and the PLPs mapped onto the T2 h e s (which itself remain unchanged in this
embodiment). Further, other data may be contained in the FEFs as well, for instance low-bitrate
information for use by a mobile receiver.
[0069] Fig. 14 shows still another embodiment 144 of an encoder according to the
present invention. Similar to the embodiment shown in Fig. 2 the encoder 144 comprises a first
encoding unit 20 for encoding, according to said first code, the input data word into said basic
codeword Z1 as explained above. Further, a second encoding unit 30a is provided for encoding,
according to said second code, the input data word into an auxiliary codeword portion (which can
be regarded as an auxiliary codeword 24) comprising only said auxiliary parity portion Pa. Hence,
the second encoding unit 30a only generates the data ultimately necessary for improving decoding
at the decoder, if required, but does not generate other codeword portions that are already generated
by the first encoding unit 20.
[0070] Fig. 15 shows a schematic block diagram of a receiver 50 for use in a
broadcasting system comprising a transmitter 10 as illustrated above. The receiver 50 is particularly
adapted for making use of the auxiliary parity portion (generally, the auxiliary codeword portion)
as incremental redundancy in case of erroneous or low quality decoding.
[0071] The receiver 50 comprises a data input 52 for receiving a receiver input data
stream 0' which generally corresponds to a transmitter output data stream 0 that has been
transmitted over a broadcast channel of the broadcasting system by a transmitter and which may
thus be affected by disturbances that may appear in such a broadcasting system, particularly in case
of using mobile receivers which are the main application of the present invention on the receiver
side.
(00721 Optionally, a demodulator 53 is provided that is interrelated with the (optional)
modulator 17 of the transmitter 10 for demodulating the received receiver data input stream 0'. A
demapper 54 demaps the (optionally demodulated) receiver data input stream O', particularly at
least the data portions and the basic parity portions (i.e. the basic codeword portions) of the
codewords mapped into the receiver data input stream 0' as will be explained below in more detail.
A decoder 56 then decodes these codewords by use of the basic codeword portions according to the
same code as applied by the encoder 14 of the transmitter 10. As particularly in case of mobile
receivers severe disturbances, for instance due to the high velocity of the moving receiver, might
appear a check unit 58 is provided in the receiver 50 by which it is checked if decoding has been
made correctly and/or with sufficient quality ,and/or below a tolerable error level as will be
explained below. If the decoding is made without errors or with sufficient quality the decoded data
are provided to an output unit 60. The output thereof might be one or more receiver output data
streams 11' I2', ..., In' which should as much as possible correspond to the transmitter input data
streams Il,I2, ..., In.
[0073] If, however, the check by check unit 58 shows that a decoding is erroneous or
that the decoded data have an insufficient quality and would, for instance, result in a noisy receiver
output signal (e.g. insufficient picture quality of a movie), a feedback loop 62 is provided from the
check unit 58 to the demapper 54 and/or the decoder 56 in order to make use of the auxiliary parity
portion (generally, the auxiliary codeword portion) (completely or in part) for improving the
quality of decoding. Hence, in such a situation the demapper 54 then also demaps the auxiliary
parity portion (completely or in part) from the (optionally demodulated) receiver input data stream
0'. By use of this additional redundancy the decoder 56 will then again decode the received
codewords, but now applies a code having a lower eode rate which thus has a higher robustness
against the disturbances. Hence, there is a high likelihood that the decoding quality will be better
than before. In some embodiments, a feedback loop 62 is also provided from the check unit 58 to
the demodulator 53, e.g. if auxiliary parity portions are required by the decoder 56 from another
receiver input data stream, e.g. from data received at a different antenna in a MIMO receiver or
from another channel (e.g. using another frequency).
[0074] Thereafter, again a check can be made by the check unit 58 if the decoding has
now been made error-free or with sufficient quality, and, if not, a still further part of the auxiliary
parity portion can be used in another iteration of demapping and decoding. If, on the other hand,
the complete auxiliary parity portion of a codeword has already been completely used for decoding
the check can also be omitted and the decoded data can be outputted directly.
[0075] Similarly as for the encoder 14 of the transmitter 10 there exist various
embodiments of the decoder 56 of the receiver 50. A first embodiment 561 of the decoder 56 is
schematically depicted in Fig. 16. According to this embodiment the decoder 561 comprises a first
decoding unit 70 and a second decoding unit 80, similarly as the embodiment of the encoder 141
depicted in Fig. 2. Further, an additional decoder 90 (e.g. a BCH decoder) is provided for BCH
decoding the output of the decoder 56 1, if the corresponding transmitter used in the broadcasting
system applies a step of BCH encoding. The first decoding unit 70 generally corresponds to the
decoding unit as used in receivers in accordance with the DVB-T2 standard. It comprises a time
deinterleaver 71, a cell deinterleaver 72, a cyclic delay remover 73, a constellation demapper 74, a
bit deinterleaver 75 and a first LDPC decoding block 76. Such a decoder is, for instance, explained
in more detail in the DVB document A133, February 2009 "Implementation Guidelines for a
Second Generation Digital Terrestrial Television Broadcasting System (DVB-T2)" which is herein
incorporated by reference. This first decoding unit 70 thus is provided with the data portions D'
and the basic parity portions Pb' (generally the basic codeword portion B') as demapped by the
demapper 54 from a received receiver input data stream 0' and decodes, as usual, these codewords.
[0076] In addition, in this embodiment of the decoder 561 a second decoding unit 80 is
provided which basically comprises the same elements, in particular a time deinterleaver 81, a cell
deinterleaver 82, a cyclic delay remover 83, a constellation demapper 84, a bit deinterleaver 85 and
a second decoding block 86, whose function is identical to the function of the respective elements
of the first decoding unit 70. However, the parameters of those blocks may differ, if different
parameters are applied in the encoder, e.g. in the second encoding unit 30 (see Fig. 2). The second
decoding unit 80 is, however, provided, in addition to the data portions D' and the basic parity
portions Pb', with the additional auxiliary parity portion Pa' (generally the auxiliary codeword
portion A') (completely or in part) for decoding the codewords with high reliability using said
auxiliary parity portion Pa' as redundancy information. Hence, the second decoding unit 80 only
becomes active in case of need, i.e. if "instructed" by the check unit 58 through feedback loop 62.
Alternatively, the second decoding unit 80 is provided with only the auxiliary codeword portion A'.
[0077] An alternative embodiment 562 of a decoder is depicted in Fig. 17. According
to this embodiment the demapper 54 accesses the T2 frames of a received receiver data input
stream 0' to demap the data portions D' and the basic parity portions Pb' therefrom and accesses
FEF frames to demap the auxiliary parity portions Pa' therefrom, i.e. the demapper 54 is adapted to
interrelate with the mapper 16 as illustrated in Fig. 9. The decoder 562, however, only comprises a
single decoding unit which is both able to decode the codewords according to the first code (with a
higher code rate) based on only the data portion D' and the basic parity portion Pb' and according
to the second code (with a lower code rate) using as redundancy information (part of or all of) the
auxiliary parity portion Pa', if needed.
[0078] A standard LDPC decoder as, for instance, provided in a DVB-T2 receiver
accepts at its input a (channel disturbed) codeword, as well as signalling information about the code
rate and the length of the codewords (either 16200 or 64800 bits). Based on the signalling
information, it applies an appropriate decoding algorithm (typically so called iterative message
passing) based on that particular code realization and outputs an estimate of the data portion.
[0079] The same applies for an extended LDPC decoder included in the decoder 56, in
particular the extended LDPC decoder 76 and 86, which receive in addition auxiliary codeword
portion, in particular auxiliary parity bits. The number of auxiliary bits is generally signalled in
addition to the applied code rate and the length of the basic codeword portion to the decoder. Given
these parameters, the decoder 56 applies an appropriate decoding algorithm based on this extended
(or "total") code.
[OOSO] As mentioned above, in a preferred embodiment the demapper and the decoder
are preferably adapted to stepwise add more parts ("sub-portion") of an auxiliary parity portion to
improve the decoding. Preferably, once a sufficient decoding quality has been reached the
demapper and the decoder are adapted for going into a sleeping mode while other parts of the
(segmented; see for instance Fig. 13) auxiliary sub-portions are provided in a received receiver
input data stream, i.e. those additional segments of an auxiliary parity sub-portion are preferably
not demapped and used for decoding. This particularly saves power in the receiver which is
especially advantageous in case of mobile receivers using a battery as power source.
[OOSl] A generic LDPC decoder has as input a received codeword (with or without
additional parity bits) as well as signalling information about the code rate and the codeword
length. The latter is in addition implicitly updated by the feedback loop 62, which signals, if (and
how many) auxiliary parity bits are appended. In contrast to such a generic decoder, the LDPC
decoder in the decoder 56 according to the present invention outputs its estimates on each code bit
of the (received) codeword C', i-e. an estimate C" on the codeword C'. Preferably, the bitwise
estimates are expressed in terms of log likelihood ratios (LLRs), whose magnitude reflects the
reliability of the estimate.
[0082] If the check unit 58 decides that the estimate C" is probably the transmitted
codeword C, it outputs the (hard decided) estimates of the data portion D' and sets a flag S to 1,
which corresponds to a decoding success. Otherwise, S = 0, which is signalled within the feedback
loop 62 to initiate the suffvring of auxiliary parity bits (if still available). The indicator E from the
check unit 58 is optional and gives an estimate of how many additional auxiliary parity subportions
are still needed. In case of E > 1, the LDPC decoder 56 does not even have to try to
I
decode the next larger codeword, but has to wait for E additional auxiliary parity sub-portions to
restart decoding.
[0083] The criteria for decoding success (S=l) are:
a) Within a maximum number of allowed decoder processing steps (typically a maximum
number of iterations is imposed), a valid codeword C" (after hard decision) is found.
b) The estimate of the data portion D' (can be derived from the estimate C", or is even
included in C", in case of a systematic code (as in DVB-T2)) can be decoded by a BCH decoder.
Note that the BCH decoder has also some error detection capabilities.
c) Afler BCH decoding, the stream 11' should correspond to a BBFrame, whose header
(BBHeader) is protected by a CRC. If this check is successful, the likelihood that the whole
BBFrame is correct, is increased.
d) Preferably, the reliabilities of all LLRs (log-likelihood ratios) are checked by check unit
58. This could be done by averaging the magnitudes of all LLRs belonging to the codeword. If this
average is larger than a certain threshold (which depends on the code and has to be defined), a
decoding success is very likely.
[0084] If S=O, the last criterion (d) can also offer an estimate of how unreliable the
codeword (after decoding) is. Assuming that the following auxiliary code portions have a similar
quality than the previous codeword, an estimate E can be made about how many additional portions
are needed for successful decoding.
[0085] It should be noted that there a two ways of combining the previous codeword
(which the decoder wasn't able to decode correctly) with the auxiliary code word portions:
1) store the previous codeword, which entered the decoder, and append the auxiliary
codeword portion at its end or
2) store the final estimate C" of the LDPC decoder 56 (e.g. after the maximum number of
iterations has passed) and append the auxiliary codeword portion at its end.
[0086] In addition to the embodiments explained above the encoder of the transmitter
may also be adapted such that the auxiliary parity portion (generally, the auxiliary codeword
portion) may not (only) comprise "real" parity information, but that it may also comprise a
repetition of (part of or all) of the information of the "basic" codeword, i.e. (some or all) bits of the
data portion D and/or the basic parity portion Pb (i-e. of the basic codeword portion). Hence, in a
very simple embodiment, the auxiliary parity portion Pa simply comprises a copy of the data
portion D and/or the basic parity portion Pb. This will also improve decoding if the basic codeword
is disturbed but the auxiliary parity portion is not (or less) disturbed. Further, even if both the basic
codeword portion and the auxiliary codeword portion are disturbed, by use of both portions for
decoding the result of the decoding may be improved, e.g. by applying the principle of soft
combining, e.g. by improving the soft values obtained in a first decoding step using only the basic
codeword portion in a second decoding step using in addition the auxiliary codeword portion.
[0087] An embodiment of a broadcasting system in accordance with the present
invention is schematically depicted in Fig. 18. The broadcasting system generally comprises a
transmitter (Tx) 10 and one or more receivers (Rx) 50% 50b, 50c. While it is generally sufficient
that the transmitter 10 has a single antenna for transmitting the transmitter output data stream 0,
here in this embodiment the transmitter 10 is provided with two antennas 19% 19b.
[OOSS] In a first mode both antennas can be used for simultaneously transmitting the
identical transmitter output data stream 0 (or a modified stream thereof, e.g. in accordance with the
Alamouti scheme of the DVB-T2 standard), for instance to increase coverage.
[0089] In another mode, that is specifically depicted in Fig. 18, the data mapper 161
provided in this embodiment of the transmitter 10 is adapted for generating two transmitter output
data stream 01 and 02, wherein the data portions D and the basic parity portions Pb of codewords
(i.e. the basic codeword portions) are mapped onto the first transmitter output data stream 01 and
wherein the auxiliary parity portions Pa of codewords (i.e. the auxiliary codeword portions) are
mapped onto the second transmitter output data stream 02. In this embodiment the first antenna
19a can then be provided with the first transmitter output data stream 01 for transmission and the
second antenna 19b can be provided with the second transmitter output data stream 02 for
transmission. For instance, during the transmission of T2 frames only the fust transmitter output
data stream 01 is transmitted, while during the transmission of FEFs both transmitter output data
streams 0 1 and 02 are transmitted.
[0090] In still another mode, the first transmitter output data stream 01 may be
transmitted by a horizontally polarized antenna, whereas the second transmitter output data stream
02 my be transmitted by a vertically polarized antenna, or vice versa.
[0091] Optionally, a MIMO precoder 162 is provided to which said first and second
transmitter output data streams 01,02 are provided fiom the data mapper 161 for precoding them
according to any MIMO precoding scheme. For instance, the first and second transmitter output
data streams 01,02 can be spatially multiplexed onto the precoded transmitter output data streams
01 *, 02* which are then transmitted by the antennas 19% 19b, or Alamouti precoding can be
applied to the first and second transmitter output data streams 01, 02. The precoded transmitter
output data streams Ol*, 02* may then both contain a mix of data fiom the first and second
transmitter output data streams 0 1,02.
[0092] In this embodiment illustrated in Fig. 18 the transmitter 10 is provided with two
antennas 19% 19b. It should be noted, however, that the transmitter, in particular a MlMO
transmitter, comprises more than two antennas to which said precoded transmitter output data
streams 01 *, 02* are provided for transmission.
[0093] A fust receiver 50a having a single antenna 61 may be adapted for receiving
only the first transmitter output data stream 01 (as first receiver input data stream Ol'), but not the
second transmitter output data stream 02. Such a receiver 50a might be an existing, e.g. legacy or
stationary, receiver that is not adapted for using any auxiliary parity portions at all. For instance, if
the transmitter 10, particularly the second transmitter output data stream 02, is directed to
reception by mobile receivers in accordance with a new standard, e.g. the DVB-NGH standard, the
receiver 50a could be a stationary receiver in accordance with the DVB-T2 standard.
[0094] Another embodiment of the receiver 50b comprises two antennas 61% 61b. In
this embodiment the first antenna 61a is adapted for reception of the fust transmitter output data
stream 01 (as first receiver input data stream 01 '), and the second antenna 61b is adapted for
reception of the second transmitter output data stream 02 (as second receiver input data stream
02'). For instance, if the two antennas 19% 19b of the transmitter 10 make use of different
transmission channels, e.g. transmission frequencies, the two antennas 61% 61b of the receiver 50b
can be adapted for reception on the same respective transmission channel.
[0095] A third embodiment of a receiver 50c again has a single antenna 61, but is
adapted for reception of the signals from both antennas 19% 19b. The receiver 50c comprises
means for internally splitting up or decomposing the two received input data streams 01 ', 02'
accordingly.
[0096] The embodiment of the receiver 50b, having two separate antennas 6 la, 61 b for
receiving the different transmitter output data streams 01, 02 separately, provides the advantage
that the second antenna 61b and the subsequent processing means within the receiver 50b need
only be activated if any auxiliary parity portions are required as incremental redundancies for
improvement of the decoding. This holds also for an embodiment of a transmitter, where the
second transmitter output data stream 02 does not only carry the auxiliary parity portions, but also
the data portions and the basic parity portions of the codewords. In the latter case the transmission
can be even made more stable. For instance, if the transmission channel between the transmitter
antenna 19a and the receiver antenna 61a is disturbed, it can be switched to the other transmission
channel between transmitter antenna 19b and the receiver antenna 61b. The advantage of a more
stable transmission is also achieved with the receiver 50c which, in the latter case, can switch
between reception of the fust or second transmitter output data streams 01, 02 or which
continuously receives both transmitter output data streams 01, 02. Further, such an embodiment
generally also provides an increased spectral density.
[0097] In the above, particularly with respect to the transmitter 10, various
embodiments have been illustrated, particularly how the data portions, the parity portions and the
auxiliary parity portions are mapped onto the transmitter output data stream. Further, various
examples have been given regarding the framing structure of the transmitter output data stream. It
shall be understood that the data demapper 54 of the receiver 50 is, of course, adapted appropriately
for demapping the required data from the receiver data input stream, i.e. the demapper 54 is aware
of the particular framing structure andlor the locations at which the respective data are placed in the
receiver data input stream. Known measures for signalling this information to the receiver from the
transmitter andlor for prescribing this information, for instance in a standard, and for enabling the
transmitters and receivers accordingly are generally applied to ensure this.
[0098] The fiaming structure applied according to the present invention may generally
be adapted to be in consistence with the framing structure according to an existing standard, e.g.
the DVB-T2 standard, so that existing receivers in accordance with this standard may also receive
and process such data streams, even if they do not make use of the auxiliary parity information
contained therein as incremental redundancy. However, the framing structure may be freely
selected and newly created according to specific needs of the broadcasting system.
[0099] Generally, the present invention can be applied in all broadcasting systems, by
which data are transmitted over a channel. For instance, the invention can be applied in a DAB
system which shall be explained with reference to Fig. 20.
[00100] Fig. 20 shows the structure of a transmission frame as described in the DAB
standard (ETS 300 401 "Radio broadcasting systems; Digital Audio Broadcasting (DAB) to
mobile, portable and fmed receivers", May 1997, REIJPT-OODAB-4). The DAB transmission
system combines three channels, in particular a Synchronization Channel which is used internally
with the transmission system for basic demodulator functions (e.g. transmission frame
synchronization), a Fast Information Channel (FIC) which is used for rapid access of information
by a receiver, which is a non-time-interleaved data channel and which can be sub-divided into Fast
Information Blocks (FIBS), and a Main Service Channel (MSC) which is used to carry audio and
data service components and which is a time-interleaved data channel divided into a number of
sub-channels, which are individually convolutionally coded.
[00101] .The MSC can also be seen as being made up of Common Interleaved Frames
(CIFs), comprising Capacity Units (CU) as smallest addressable units. Each sub-channel of the
MSC occupies an integral number of consecutive CUs and is individually convolutionally encoded.
More details regarding the structure of the transmission frame and its content can be found in the
above cited DAB standards, which explanations are herein incorporated by reference.
[00102] According to the present invention one of the sub-channels, e.g. SubCh a could
comprise the basic codeword version, whereas one or more of the subsequent sub-channels, e.g.
SubCh b, comprises the auxiliary codeword portion. A receiver can now process SubCh a and, if
necessary, SubCh b for improving the decoding. As illustrated in an embodiment shown above the
auxiliary codeword portion can be further segmented into sub-portions all carried in the same subchannel
or carried in various sub-channels. This again has the advantage that the receiver can fall
into sleeping mode after successful decoding until the next basic codeword portion is transmitted.
[00103] If and for which sub-channels auxiliary parity bits are provided, could be
signaled in the Fast Information Channel (FIC). Since this channel is, however, fured and
predefined, the signalling should preferably be done in another sub-channel which comprises the
basic codeword portion, for instance in a newly defined header. Hence, receivers modified in
accordance with the present invention can make use of this additional information. In addition, the
FIC could signal, which sub-channel is adapted for reception by all DAB receivers (legacy
receivers and receivers according to the present invention) and which sub-channels are decoded for
reception by receivers according to the present invention (only).
[00104] The error correction code applied in DAB is a convolution code. Different code
rates are generally achieved according to DAB by puncturing of a mother code. This mother code
generally has a code rate of 114, and by puncturing of certain parity bits higher code rates are
obtained. These punctured parity bits could be used as auxiliary parity bits for providing
incremental redundancy in accordance with the present invention. Alternatively, a completely new
mother code is also applicable, from which all the DAB code rates can be obtained by puncturing
and where the punctured bits are used as auxiliary parity bits in accordance with the present
invention.
[00105] Fig. 21 shows a block diagram of another embodiment of a receiver 50d.
Generally, the basic codeword portions B and the auxiliary codeword portions A are mapped by the
transmitter onto the transmitter output data stream 0 such that a basic codeword portion of a
codeword is received by a receiver before the corresponding auxiliary codeword portion is
received. Alternatively, however, the data mapper can also be adapted for mapping the basic
codeword portions B and the auxiliary codeword portions A onto hmes of a transmitter output
data stream such that the auxiliary codeword portion of a codeword is received by a receiver before
the corresponding basic codeword portion is received. For the embodiment of the receiver 50d
shown in Fig. 21 it shall be assumed that the transmitter is adapted in this way.
[00106] In such a receiver 50d the data demapper 54d is thus adapted to demap the (first
received) auxiliary codeword portions A' from the receiver input data stream 0' and forward them
to a buffer 64. Thereafter (whenever received) the corresponding basic codeword portions B' are
demapped and forwarded to the decoder 56d for decoding them. If the check in the check unit 58d
shows that additional redundancies shall be used for improved decoding the buffer 64 is informed
via the feedback loop 62 to provide the buffered auxiliary codeword portion A' to the decoder 56d
and the decoder is informed to then decode the codeword (now by additional use of the (complete
or partial) auxiliary codeword portion again. If it is clear that the decoding of the corresponding
codeword is correct the buffered auxiliary codeword portion (if any) is deleted from the buffer.
[00107] This embodiment provides the advantage that no waiting times (for waiting for
the auxiliary parity portion, if the decoding was erroneous based on the basic codeword portion)
occur, which is particularly important for reducing zapping times or for mobile receivers. Hence,
this embodiment also provides the advantage that no interruption of the service occurs (due to
waiting for reception of auxiliary codeword portions) in case of (e.g. sudden) bad reception
conditions of the basic codeword portions.
[00108] The present invention thus provides an effective and easily implementable
measure for improving the reliability of decoding, particularly for mobile receivers in a
broadcasting system, without any feedback from a receiver to the transmitter. If the DVB-T2
framing structure is kept unchanged and the FEFs contain the additional redundancy, i.e. the
auxiliary codeword portion, there are basically two aspects that make a (mobile) receiver, or
generally any receiver exploiting the present invention, more robust for mobile reception: i) The
3 5
incremental redundancy as described and ii) the FEFs themselves with the embedded incremental
redundancy, which can (and typically will) select transmission (e.g. OFDM) parameters that have a
better behaviour in mobile channels. The most important ones are lower FFT sizes and higher pilot
pattern densities (being related to the FFT and guard interval sizes). Of course the incremental
redundancy data in the FEFs can additionally be protected by using lower modulation schemes,
other interleaving depths etc..
[00109] The time interleaver depth chosen in the FEFs could, for example, complement
the time interleaver depth of the T2 frames. If the T2 frame time interleaver fails (e.g. signal
interrupted for a dedicated time (e.g. due to a tunnel etc.)), the other settings in the FEF time
interleaver might be better suited and allow overall correct decoding. Different time interleaver
settings of the T2 frame and the FEF frame overall improve the system performance.
[00110] The receiver in accordance with the present invention benefits therefore from
the fact that in addition to the basic T2 reception the data in the FEFs (i.e. additional incremental
redundancy) is more robust in mobile channels. Another main advantage of preferred embodiments
of the present invention is that broadcasters do not have to transmit the data for mobile, (e.g. NGH)
receivers, but only incremental redundancy is transmitted to enable a more robust reception of T2
data even with a mobile receiver. Thus, transmission bandwidth is utilized most efficiently.
[00111] The invention has been illustrated and described in detail in the drawings and
foregoing description, but such illustration and description are to be considered illustrative or
exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other
variations to the disclosed embodiments can be understood and effected by those skilled in the art
in practicing the claimed invention, fiom a study of the drawings, the disclosure, and the appended
claims.
[00112] In the claims, the word "comprising" does not exclude other elements or steps,
and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit
may fulfill the functions of several items recited in the claims. The mere fact that certain measures
are recited in mutually different dependent claims does not indicate that a combination of these
measured cannot be used to advantage.
[00113] A computer program may be stored 1 distributed on a suitable medium, such as
an optical storage medium or a solid-state medium supplied together with or as part of other
hardware, but may also be distributed in other forms, such as via the Internet or other wired or
wireless telecommunication systems.
[00114] Any reference signs in the claims should not be construed as limiting the scope.
In so far as the embodiments of the invention described above are implemented, at least in
part, using software-controlled data processing apparatus, it will be appreciated that a
computer program providing such software control and a transmission, storage or other
medium by which such a computer program is provided are envisaged as aspects of the
present invention.

We claim:
1. Transmitter (10) for broadcasting data in a broadcasting system, comprising:
- a data input for receiving at least one transmitter input data stream (Il,I2, ..., In)
segmented into input data words (D),
- an encoder (14; 141, 142, 143) for error correction code encoding the input data
words (D) into codewords (Zl, Z2,23,24), a codeword comprising a basic codeword portion (B)
and an auxiliary codeword portion (A), wherein said encoder (14) is adapted for generating said
basic codeword portion (B) from an input data word (D) according to a frrst code and for
generating said auxiliary codeword portion (A) from an input data word (D) according to a second
code, said basic codeword portion (B) being provided for regular decoding and said auxiliary
codeword portion (A) being provided as incremental redundancy if regular decoding of the
codeword by use of the basic codeword portion (B) is erroneous,
- a data mapper (16) for mapping the codewords (Zl, 22, 23, 24) onto frames of a
transmitter output data stream (O), and
- a transmitter unit (1 8) for transmitting said transmitter output data stream (0).
2. Transmitter as claimed in claim 1,
wherein said data mapper (16) is adapted for mapping the basic codeword portion (A) of a
codeword onto a different portion of the transmitter output data stream (0), in particular onto a
different frame, than the auxiliary codeword portion (A) of the same codeword.
3. Transmitter as claimed in any preceding claim,
wherein said data mapper (16) is adapted for mapping the basic codeword portion (B) of a
codeword onto a frame of a first type of the transmitter output data stream, in particular onto a T2
frame of a transmitter output data stream in accordance with a DVB broadcasting system, and for
mapping the auxiliary codeword portion (A) of the respective codeword onto a frame of a second
type, arranged between frames of the first type, of the transmitter output data stream, in particular
onto an FEF frame of a transmitter output data stream in accordance with a DVB broadcasting
system.
4. Transmitter as claimed in any preceding claim,
38
wherein said encoder (141, 144) comprises a fust encoding unit (20) for encoding,
according to said first code, the input data word into a basic codeword (Zl) including said basic
codeword portion (B) and a second encoding unit (30,30a) for encoding, according to said second
code, the input data word (D) into an auxiliary codeword (Z2,Z4) including at least said auxiliary
codeword portion (A), and
wherein said data mapper (16) is adapted for mapping the basic codeword (Zl) onto a
different portion of the transmitter output data stream (0), in particular onto a different fiame, than
the auxiliary codeword (22).
5. Transmitter as claimed in claim 4,
wherein said second encoding unit (30) is adapted for encoding, according to said second
code, the input data word into an auxiliary codeword (22) including said basic codeword portion
(B) and said auxiliary codeword portion (A).
6. Transmitter as claimed in claim 4,
wherein said second encoding unit (30a) is adapted for encoding, according to said second
code, the input data word into an auxiliary codeword (24) including only said auxiliary codeword
portion (A).
7. Transmitter as claimed in anyone of claims 1 to 3,
wherein said encoder (142) comprises a single encoding unit for encoding the input data
word into a codeword (22) including said basic codeword portion (B) and said auxiliary codeword
portion (A), and
wherein said data mapper (16) is adapted for mapping the basic codeword portion (B) of
said codeword onto a different portion of the transmitter output data stream (0), in particular onto a
different frame, than the auxiliary codeword portion (A) of said codeword.
8. Transmitter as claimed in any preceding claim,
wherein said encoder (143) is adapted for encoding the input data words into codewords
(Z3), a codeword comprising a basic codeword portion (B) and an auxiliary codeword portion (A),
said auxiliary codeword portion (A) including at least two auxiliary codeword sub-portions (Pal,
Pa2, Pa3), said basic codeword portion (B) being provided for regular decoding and said at least
two auxiliary codeword sub-portions (Pal, Pa2, Pa3) being provided as incremental redundancies if
regular decoding of the codeword by use of the basic codeword portion and less redundancies is
erroneous.
9. Transmitter as claimed in claim 8,
wherein said data mapper (16) is adapted for mapping the at least two auxiliary codeword
sub-portions (Pal, Pa2, Pa3) of a codeword onto said transmitter output data stream (0) such that
the auxiliary codeword sub-portion (Pal) used as first incremental redundancy is received by a
receiver (50) after reception of the respective basic codeword portion (B) but before further
auxiliary codeword sub-portions (Pa2, Pa3).
10. Transmitter as claimed in any preceding claim,
wherein said data input (12) is adapted for receiving at least two transmitter input data
streams (11,12, ..., In) segmented into input data words, and
wherein the encoder (14) is adapted for selectively encoding a transmitter input data stream
only according to the first code, according to the second code or according to both codes.
1 1. Transmitter as claimed in any preceding claim,
wherein said data mapper (16) is adapted for mapping the basic codeword portions (B) of
the codewords onto a fust transmitter output data stream (01) and for mapping the auxiliary
codeword portions (A) of the codewords onto a second transmitter output data stream (02), and
wherein said transmitter unit (18) comprises a MlMO precoder (162) for MIMO preceding
said fust and second output data streams (01, 02) and at least two antennas including a first
antenna (19a) and a second antenna (19b) for transmitting said MIMO precoded first and second
transmitter output data streams (01 *, 02*).
12. Transmitter as claimed in any preceding claim,
further comprising a modulator (1 7) for modulating the auxiliary codeword portions (A) by
an auxiliary modulation code that is orthogonal to a basic modulation code used for modulating the
basic codeword portions (B).
13. Transmitter as claimed in any preceding claim,
40
further comprising a modulator (17) for modulating the basic codeword portion (B) of a
codeword differently than the auxiliary codeword portion (A) of the same codeword after mapping
the codewords onto the frames of the transmitter output data stream (0).
14. Transmitter as claimed in any preceding claim,
wherein said encoder (14) is adapted for generating said auxiliary codeword portions (A)
such that they comprise parts of or the complete corresponding basic codeword portion (B).
15. Transmitter as claimed in any preceding claim,
wherein said encoder (14) is adapted for applying a systematic code for generating said
codewords such that said basic codeword portion (B) comprises a data portion, in particular the
input data word (D), and a basic parity portion (Pb), and said auxiliary codeword portions (A)
comprises an auxiliary parity portion (Pa).
16. Transmitter as claimed in any preceding claim,
wherein said data mapper (16) is adapted for mapping the basic codeword portions (B) and
the auxiliary codeword portions (A) onto frames of a transmitter output data stream (0) such that
the auxiliary codeword portion (A) of a codeword is received by a receiver before the
corresponding basic codeword portion (B) is received.
17. Transmission method for broadcasting data in a broadcasting system, comprising the steps
of:
- receiving at least one transmitter input data stream (11, 12, ..., In) segmented into
input data words (D),
- for error correction code encoding the input data words (D) into codewords (Zl,
22, 23, Z4), a codeword comprising a basic codeword portion (B) and an auxiliary codeword
portion (A), wherein said encoder (14) is adapted for generating said basic codeword portion (B)
from an input data word @) according to a first code and for generating said auxiliary codeword
portion (A) from an input data word (D) according to a second code, said basic codeword portion
(B) being provided for regular decoding and said auxiliary codeword portion (A) being provided as
incremental redundancy if regular decoding of the codeword by use of the basic codeword portion
(B) is erroneous,
- mapping the codewords (Zl, 22, 23, 24) onto frames of a transmitter output data
stream (O), and
- transmitting said transmitter output data stream (0).
18. Receiver (50) for receiving data in a broadcasting system, comprising:
- a receiver unit (52) for receiving a receiver input data stream (0') segmented into
frames,
- a data demapper (54) for demapping codewords (Zl, 22,Z3,24) mapped onto the
frames of the receiver input data stream (0'1, a codeword comprising a basic codeword portion (B)
and an auxiliary codeword portion (A), wherein said basic codeword portion (B) is generated from
an input data word (D) according to a first code and said auxiliary codeword portion (A) is
generated from an input data word (D) according to a second code,
- a decoder (56) for error correction code decoding said codewords into output data
words (D') of at least one output data stream (Il', I2', ..., In') in a regular decoding step by use of
the basic codeword portion (B') comprised in a codeword and, if said regular decoding of a
codeword is erroneous, in an additional decoding step by additionally using the auxiliary codeword
portion (A') as incremental redundancy,
- a check unit (58) for checking if the regular decoding of a codeword is erroneous,
and
- a data output (60) for outputting said at least one receiver output data stream (Il',
I2', ..., In') segmented into said decoded output data words (D').
19. Receiver as claimed in claim 18,
wherein said data demapper (54) is adapted for demapping the basic codeword portion (B')
of a codeword from a different portion of the receiver input data stream (O'), in particular from a
different frame, than the auxiliary codeword portion (A') of the same codeword.
20. Receiver as claimed in anyone of claims 18 to 19,
wherein said data demapper (54) is adapted for demapping the basic codeword portion (B')
of a codeword from a frame of a first type of the receiver input data stream, in particular from a T2
frame of a receiver input data stream in accordance with a DVB broadcasting system, and for
demapping the auxiliary codeword portion (A') of the respective codeword from a frame of a
second type, arranged between frames of the first type, of the receiver input data stream, in
particular from an FEF frame of a receiver input data stream in accordance with a DVB
broadcasting system.
21. Receiver as claimed in anyone of claims 18 to 20,
wherein said decoder (561) comprises a first decoding unit (70) for decoding, according to
said first code, the input data word (D') from a basic codeword (21) including said basic codeword
portion (B') and a second decoding (80) unit for decoding, according to said second code, the input
data word (D') from an auxiliary codeword (22) including said basic codeword portion (B') and
said auxiliary codeword portion (A'), and
wherein said data demapper (54) is adapted for demapping the basic codeword (21) from a
different portion of the receiver input data stream (O'), in particular from a different frame, than the
auxiliary codeword portion (A') of said auxiliary codeword (22).
22. Receiver as claimed in anyone of claims 18 to 20,
wherein said decoder (562) comprises a single decoding unit for decoding, according to
said second code, the input data word (D') from a codeword (22) including said basic codeword
portion (B') and said auxiliary codeword portion (A'), and
wherein said data demapper (56) is adapted for demapping the basic codeword portion (B')
of said codeword (22) from a different portion of the receiver input data stream (O'), in particular
from a different frame, than the auxiliary codeword portion (A') of said codeword (22).
23. Receiver as claimed in anyone of claims 18 to 22,
wherein said decoder (56) is adapted for decoding the input data words from codewords
(23) which comprise a basic codeword portion (B') and an auxiliary codeword portion (A'), said
auxiliary codeword portion (A) including at least two auxiliary codeword sub-portions (Pal, Pa2,
pa3 1,
wherein said decoder (56) is adapted for using said basic codeword portion (B') for said
regular decoding and said at least two auxiliary codeword sub-portions (Pal, Pa2, Pa3) as
incremental redundancies if regular decoding of the codeword by use of the basic codeword portion
and less redundancies is erroneous.
24. Receiver as claimed in claim 23,
wherein said data demapper (54) is adapted for demapping the at least two auxiliary
codeword sub-portions (Pal, Pa2, Pa3) of a codeword from said receiver input data stream (0')
such that the auxiliary codeword sub-portion (Pal) used as fust incremental redundancy is
demapped after demapping of the respective data portion (D) of said codeword but before
demapping of further auxiliary codeword sub-portions (Pa2, Pa3).
25. Receiver as claimed in anyone of claims 18 to 24,
further comprising a feedback loop (62) from said check unit (58) to said data demapper
(54) andlor said decoder (56) for signalling if the last decoding of a codeword has been erroneous
and for initiating another try of decoding by additional use of parts of or the complete auxiliary
codeword portion, if available.
26. Receiver as claimed in anyone of claims 18 to 25,
wherein said receiver unit (52) comprises a first antenna (61a) for receiving a first receiver
input data stream (01') and a second antenna (61b) for receiving a second receiver input data
stream (02'),
wherein said data demapper (54) is adapted for demapping the basic codeword portions
(B') of the codewords fkom said fust receiver input data stream (01') and for demapping the
auxiliary codeword portions (A') of the codewords from said second receiver input data stream
(02') .
27. Receiver as claimed in anyone of claims 18 to 26,
further comprising a demodulator (53) for demodulating the auxiliary codeword portions
(A') by an auxiliary modulation code that is orthogonal to a basic modulation code used for
demodulating the basic codeword portions (B').
28. Receiver as claimed in anyone of claims 18 to 27,
further comprising a demodulator (53) for demodulating the basic codeword portion (B') of
a codeword differently than the auxiliary codeword portion (A') of the same codeword before or
after demapping the codewords onto the frames fiom the receiver input data stream (0').
29. Receiver as claimed in anyone of claims 18 to 28,
wherein said decoder (56) is adapted for applying a systematic code for decoding said
codewords such that said basic codeword portion (B') comprises a data portion, in particular the
input data word (D'), and a basic parity portion (Pb'), and said auxiliary codeword portions (A')
comprises an auxiliary parity portion (Pa').
30. Receiver as claimed in anyone of claims 18 to 29,
further comprising a buffer (64) for buffering auxiliary codeword portion (A'),
wherein said data demapper (16) is adapted for demapping the auxiliary codeword portion
(A') of a codeword before the basic codeword portion (B') is demapped from the frames of a
receiver input data stream (0').
3 1. Receiving method for receiving data in a broadcasting system, comprising the steps of
- receiving a receiver input data stream (0') segmented into frames,
- demapping codewords (Zl, 22, 23, 24) mapped onto the frames of the receiver
input data stream (0')a' codeword comprising a basic codeword portion (B) and an auxiliary
codeword portion (A), wherein said basic codeword portion (B) is generated from an input data
word (D) according to a first code and said auxiliary codeword portion (A) is generated from an
input data word (D) according to a second code,
- error correction code decoding said codewords into output data words (D') of at
least one output data stream (11'' I2', ..., In') in a regular decoding step by use of the basic
codeword portion (B') comprised in a codeword and, if said regular decoding of a codeword is
erroneous, in an additional decoding step by additionally using the auxiliary codeword portion (A')
as incremental redundancy,
- checking if the regular decoding of a codeword is erroneous, and
- outputting said at least one receiver output data stream (Il', I2', ..., In') segmented
into said decoded output data words (D').
32. Broadcasting system for transmitting and receiving data including a transmitter (10) as
claimed in any one of claims 1 to 16 for transmitting data and a receiver (50) as claimed in any one
of claims 18 to 30 for receiving data.
33. Broadcasting method for transmitting and receiving data including a transmission method
as claimed in claim 17 for transmitting data and a receiving method as claimed in claim 3 1 for
receiving data.
34. Computer program comprising program code means for causing a computer to carry out
the steps of encoding and mapping of the method as claimed in claim 17, 31 or 33, when said
computer program is carried out on a computer.
35. Computer readable non-transitory medium having instructions stored thereon which, when
carried out on a computer, cause the computer to perform the steps of the method as claimed in
claim 17,31 or 33.
Dated this 1~/06/2012
HRIS
O'F REMFRY AGAR
ATTORNEY FOR THE APPLICANT[S]