The method and apparatus for mapping signals to subcarriers in Ml MO wireless network
Field of the Invention
The present invention relates to wireless network, and particularly to the method and apparatus for mapping signals lo subcarriers in M1MO wireless network.
Background of the Invention
Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) are promising multiple subcarriers high data rate transmission schemes, which are referred to as 'OFDM-like technology" uniformly hereinafter. The basic idea is to convert high speed serial data into branches of relatively low speed parallel data, and then modulate the orthogonal carriers. By using OFDM-like technology, the spectral utilization rate will be greatly enhanced, and the system becomes much stronger against Multipath Fading and narrowband interference. OFDM-like technology is considered as one of the core technologies of the fourth generation mobile communication, and is widely used in high speed wireless data telecommunication systems such as World Interoperability for Microwave Access (WiMAX).
Mulli-input Multi-output (MIMO) system is a telecommunication system whose receiver and transmitter are both configured with multiple antennas, so that it is possible to provide high speed wireless data transmission. In a flat fading channel with lower SNR but less influence to the Bit Error Rate, MIMO system can provide important data rale gain or diversity gain. In practice, there are ways to

implement MI MO, such as: Space-Time Coding (STC) based on Alamouti code and spatial multiplexing.
Obviously, the combination of OFDM and MI1MO can bring us better data transmission scheme with high speed.
See Fig. 1, Fig. 1 shows the schematic view of a typical sending means in a telecommunication network combining OFDM-like technology and MIMO.
Hereinafter, the signal processing flow in the sending means will be described, wherein, the MIMO system is applied with the Partial Usage of SubChannel (PUSC) mode; the modulation is QPSK; the rate of channel coding is 1/2; STBC is used.
1) Source bit stream bo b47 are channel coded, so that the channel
coded bit stream c0 c^ is generated.
2) Channel coded bit stream enters the interleave!- for interleaving (not
shown), and then will be mapped U» the constellation of the QPSK
modulator, so as to generate modulated symbol stream st> s-47, say
IS,,)(each modulated symbol comprising two channel coded bits). Hereunder, without specific statement, modulated symbols stand for the symbols generated after digital modulation in this step;
}) When using Space-Time coding, the MIMO coder will perform Space-lime coding on the input modulated symbol stream. Here, since (he aim of Space-lime coding is to realize MIMO, it is also called MIMO coding. The MIMO symbol stream generated can be in the form of:


1023 from low frequency to high frequency, as the physical address of suhcaniers. By eliminating the number zero subcarrier and the virtual suhcaniers therefrom, the remained siihcarriers are numbered again, as their first level logical address. Then, ihe siihcarriers with first level logical address are classified into clusters, so that each cluster will comprise physical suhcaniers as shown in Fig. 2. And the pilot suhcaniers shall be allocated according to the manner shown in Fig. 2.
5) Afte<" the allocation of pilot suhcaniers, other suhcaniers are called data suhcaniers. Then, a permutation will be done with respect to the data suhcaniers, and then they will be further numbered as I,J:,...JS4(h as the second level logical address of the data siihcarriers in correspondence with the discrete physical address.
6) Then, the subcarrier mapping module is responsible for mapping the MiMO symbol stream to the data suhcaniers with the second level logical address. It is easy to understand that, for a sending means using spatial multiplexing (no need of MIMO coding), the subcarrier mapping module will map the modulated symbol stream generated in the slep 21 10 the daia subcanieis.
In existing sending means using spatial multiplexing, after the aforesaid
steps, mapping the modulated symbol stream s0 s47 to data
siihcarriers is shown in Table. 1. Wherein, a sending means with 2 transmitting antennas is taken as an example. However, it should be understood that, the present invention is not limited to systems with 2 transmission antennas.



subcarrier, say their mapping objects have the same physical address. Then, the Inverse Fast Fourier Transform (IFFT) modules, corresponding to the two transmitting antennas respectively, will perform IFFT process on the signals in correspondence with the antennas, so that two OFDM symbols will he generated, realizing the conversion from frequency domain to time domain. Wherein, the modulated symbols mapped to the same data subcarrier will be located at
the same position in the two OFDM symbols. .sn s47 are the
modulated symbols generated by the digital modulator shown in Fig. I (using QPSK etc. modulation method) in the first time slot.

From Table I- it can be seen that, in prior an. the modulated symbols mapped to the same data subcarrier correspond io adjacent symbols in
v,, \4Tm Therefore, when ihe channel is in deep fading, the terminal has
moved into deep fading zones like a jungle, since the decoder at the receiver cannot decode successfully. sn and ,v/ will be deemed as wrong. Since .v„ and st are adjacent symbols in the modulated symbol sequence, and comprise adjacent coded bits such as c„. ci, c-and cmi in the coded bit streamr,,..(,„. hence, there is a burst error.
In a telecommunication system, burst errors are always undesired. Hence, a solution is needed to avoid burst errors in the aforesaid OFDM-like MIMO system.
For conciseness, Fig. 1 has not shown all means (modules) of the telecommunication system for implementing the combination of OFDM-like technology and MIMO technology. However, those skilled in this art can know well, with the aid of Fig. 1 and the description above, the technical problems existing in the prioi ait io be M.JIVC-U by the present invention. Also, those skilled in this art will have a good understanding of the solution provided by the present invention by reading the description below with reference to the drawings.
Summary of the Invention
The present invention is proposed to solve the problems of the prior art.
According to the first aspect of the invention, there is provided a method, in a sending means in MIMO-based wireless telecommunication network, for mapping signals to stibcarriers, characterized in that, controlling the mapping of the signals in an input signal sequence Io the subcarriers, so

that the signals sent by different antennas at the same time correspond to nonadjaeent signals in the input signal sequence. Particularly, the method comprises steps as follows; mapping consecutive signals in a signal sequence to M subcarriers, so that the signals mapped to the same subcarrier are nonadjaeent signals in the signal sequence; modulating the signals onto the corresponding subcarriers to which the signals have been mapped, so as to generate multiple modulated signal groups, wherein, every modulated signal group comprises M signals mapped to different suhcarriers; controlling to send said multiple modulated signal groups via different antennas.
According to the second aspect of the invention, there is provided a mapping controller, in a sending means in MIMO-based wireless telecommunication network, for mapping signals to subcarriers, characterized in that, controlling the mapping of the signals in an input signal sequence to the subcarriers, so that the signals sent by different antennas at the same time correspond to nonadjaeent signals in the input Mgnai sequence. Particularly, the control lev comprises: a mapping means, for mapping consecutive signals in a signal sequence to M subcarriers, so that the signals mapped to the same subcarrier are nonadjaeent signals in the signal sequence; a modulator, for modulating the signals onto the corresponding subcarriers to which the signals have been mapped, so as to generate multiple modulated signal groups, wherein, every modulated signal group comprises M signals mapped to different subcarriers; sending controller, for controlling to send said multiple modulated signal groups via different antennas.
As compared with the prior art, the solution provided hy the present invention has advantages as below;

1. when carrying out the first lime transmission using spatial
multiplexing, hurst error caused by deep laumg channel can be well
avoided;
2. the diversity gains have been enhanced.
Brief Description of the Drawings
Other features and advantages of the present invention will be obvious
by reading the following description of non-limiting exemplary
embodiments, with reference to the appended drawings.
Fig. I shows the schematic view of a sending means in
telecommunication system which has combined OFDM-like technology
and MIMO technology;
Fig. 2 shows the method for classifying subcarriers with first level
logical addresses into clusters, and allocating pilot subcarriers and data
subcarriers in each cluster;
Fig. 3 shows the flow chart of the method, in a sending means of a
MIMO-based wireless telecommunication network, for mapping the
signals to subcarrieis uuuuulirig an embodiment of the invention;
Fig. 4 shows the block diagram of the mapping controller, in a sending
means of a MIMO-based wireless telecommunication network, for
mapping signals to subcarriers according to an embodiment of the
invention.
Detailed description of embodiments
Detailed description of the invention is given below with reference to the appended drawings. It should be noted that, the illustrative steps for realizing the methods and the illustrative structures of the devices shall not be understood as limiting the protection scope of the present invention.

In order to describe the technical solution of the present invention clearer, some basic principles of OFDM-like systems arc explained as below:
In a lypical OFDM-like system, a modulated symbol stream |SL|] will be got alter the digital modulation with one of BPSK. QPSK, 16QAM, wherein, n=0,l,...,M-l. M modulated symbols thereof will be mapped onto M sub-channels (M data subcarriers). Each of the modulated symbols is used lo modulate one of the M data subcarriers. Then, the 1FFT module is used to perform IFFT process on them to generate an OFDM symbol. This flow is repeated to process the following M modulated symbols. Certainly, before being transmitted on the channel, an OFDM symbol will experience CP (Cyclic Prefix) adding. D/A (digital/analog) conversion, up frequency conversion etc. Since these processes are all well known and are not directly related to the present invention, they are not shown in Fig. I and there is no need to give unnecessary details.
The method of subcarrier mapping provided by the present invention will he described with reference to Fi^.3. Fig. 3 show:; the flow chart of the method, in a sending means in a MIMO-based wireless telecommunication network, for mapping the signals to subcarriers according an embodiment of the invention.
According to an embodiment of the invention, the method can be implemented in the subcarrier mapping module (mapping controller 1) shown in Fig.l, for achieving the technical object of the invention.
The innovation of the invention consist in that, controlling the mapping of the signals in an input signal sequence to the subcarriers , to be
specific, the data subcarrier, so that the signals sent by different

antennas at the same time correspond to nonadjacent signals in the input signal sequence. Wherein, according to one embodiment of the invention, the input signal sequence is a modulated symbol stream outputted by a digital modulator applying modulation method such as QPSK/I6QAM . And. said signals in the input signal sequence are the modulated symbols outputted by the digital modulator.
As mentioned above, in Table 1, sn and s, are signals sent on different antennas at the same time. But, contrary to the invention, s(l and S| correspond to adjacent signals in the input signals sequence{Sn},
The method shown in Fig.3 starts with the step SIO:
In step SIO, the mapping controller 1 maps the signals in the input signal sequence onto M data subcarriers, say M data subcarriers with different physical addresses, so that the symbols mapped onto the same data subcarriers are nonadjacent symbols in |S„} . Wherein, the aforesaid modulated symbol stream |Sn| is still taken as an example here, without iu.sN nf gcucicuity. For a better explanation of the invention, please «ee I able 2, wherein, one embodiment of the invention has been shown:



In this embodiment, M=24; modulated symbols S0...S47 correspond to the modulated symbols generated by the modulator in the first time slot and belong to a part of a packet. Said packet comprises % modulated symbols in total. When the decoding with respect to this packet at the receiver fails, the transmitter (said sending means) will resend the whole packet. The details about the resending will be described later.
Il should be understood that, the mapping method as shown in Table 2 is not the only one subcarrier mapping method provided by the present invention. On the premise that the signals sent by different antennas at the same time are nonadjacent signals in the original signal sequence, there are various ways to map So-..s47to the 24 data subcarriers. For conciseness, a slot comprising 10 modulated symbols So...st) is taken as an example. With the mapping process in step SIO, the symbobin-pair mapped to the same data subcarrier can be: (S(),SK), (s.i,s5), (S^ST), (S|,SM), (S1.S7). Il can be seen that, the symbols sent on the different antennas at the same time are nonadjacent symbols of said modulated symbol stream, so as to avoid burst error.

In order lo implement the signal transmission manner shown in Table 2, mapping symbols to the subeaniers only is not enough, the method further proceed to the step S I I.
In step SI 1, S0...S47, which are generated by the digital modulator in this lime slot (the first time slot) and mapped to the 24 data subeaniers in step SIO, will be used to modulate the data subeaniers to which they have been mapped, so as to generate two modulated signal groups, say s(|, S|...s^,and s^s^.-.s.^. It should be understood that, according to the different mapping methods used in SIO, the form of the modulated signal groups generated under the present invention are not limited to this. With the abovementioned example, it can be known that the modulated signal groups could be: {sn,s.i.sft,S|.S|} and {sn.s^s2,Sg,s7}. Then, the method enters SI2.
In step SI2, the mapping controller I controls to send the two modulated signal groups So,s, ...s^ and s2j,s»2s---^47 generated in SI1 via different antennas, [n particular, it determines the transmitting antenna for each modulated signal group. And then each modulated signal group will be allocated to the processing means such as PRBS (Pseudo Random Bit Sequence)module, IFFT (Inverse Fast Fourier Transform) module etc. which corresponds to the transmitting antenna determined for this modulated signal group, for the purpose of further processing. Similarly, the method for allocating modulated signal groups to transmitting antennas shown in Fig.2 is not the only one provided by the invention, that's to say, it is also doable to send s2->, S2.s--.S47 011 antenna 0 and send s,),s,...s2.i on antenna ), It should be understood that, in a multi-antenna sending device equipped with more than 2 antennas, the

process in S12 can have more choices.
Obviously, any one of the 24 pairs of symbols modulated to the 24 subcarriers consists of two nonadjacent symbols in{S„|, in particular, of
symbols corresponding to nonadjacent channel coded bits. Taking s<> and ST (in the first row of Table 2 as an example, wherein, the aforesaid channel coded bit stream rn...r,,. is also taken into account. And s()
corresponds to c(l and C\ ', s24 corresponds to c4ft and c47. Even the
channel encounters deep fading, s() , s24 go wrong due to the failed decoding, since Sn , s^4 correspond to nonadjacent channel coded bits (c„ , C| ; c4(-, , c47), the error brought by the failed decoding due to deep
lading will be random error, instead of burst error.
The mapping controller 1 provided by the present invention will be described with reference to Fig.4. Fig. 4 shows the block diagram of the mapping controller, in a sending means of a MIMO-based wireless telecommunication network, for mapping signals to subcarriers according to an embodiment of the invention.
According to an embodiment of the invention, the mapping controller 1 is an improved mapping controlling module as shown in Fig.I. That's to say, the subcarrier mapping module in Fig. 1 can be implemented by the mapping controller I provided by the present invention, so as to achieve the technical object(s) thereof.
The innovation of the invention consist in that, controlling the mapping of the signals in an input signal sequence to the subcarriers, , to be
specific, the data subcarrier, so that the signals sent by different antennas at the same time correspond to nonadjacent signals in the input

signal sequence. Wherein, according to one embodiment of the invention, the input signal sequence is a modulated symbol stream {Stl j
oulpulted by a digital modulator applying modulation method such as QPSK/I6QAM, And, said signals in the input signal sequence are the modulated symbols outputted by the digital modulator.
As mentioned above, in Table I. s() and S| are signals sent on different antennas at the same time, But. contrary to the invention. sn and s, correspond to adjacent signals in the input signals sequence.
The mapping controller I shown in Fig. 4 comprises; a mapping means 10. a modulator 1 I and a sending controller 12.
Said mapping means 10 maps the signals in the input signal sequence onto M data subcarriers, say M data subcarriers with different physical addresses, so that the symbols mapped onto the same data subcarriers are nonadjacent symbols in |SJ. Wherein, the aforesaid modulated symbol sue;iui {S„i is still taken as an example here, without loss of generality, and the symbols in {S1L| is also taken as an example. For a better explanation of the invention, please see Table 2.
In this embodiment, M=24; modulated symbols sn...s.|7 correspond to the modulated symbols generated by the digital modulator in the first time slot and belong to a part of a packet. Said packet comprises 96 modulated symbols So-.-s^in total. When the decoding with respect to this packet at the receiver fails, the transmitter (said sending means) will resend the whole packet. The details about the resending will be described later.

I( should be understood that, the mapping method as shown in Table 2 is not the only one mapping method provided by the present invention. On the premise that the signals sent by different antennas at the same time are nonadjacent signals in original signal sequence, there are various ways to map sn...s47to the 24 data subcarriers. For conciseness, a slot comprising 10 modulated symbols So-..s4 is taken as an example. With the mapping process in step SID, the symboMn-pair mapped to the same data subearrier can be: (s(,,Sxh (S;,sO. 4 go v\iung due to the failed decoding, since sn , s24 correspond to nonadjacent channel coded bits (Co , C| ; c4(l , C47), the error brought by the failed decoding due to deep
lading will be random error, instead of burst error.
By reading the description in connection with resending process hereinafter, the advantages of the present invention as compared with the prior art will be clearer.
In (he above paragraphs, for conciseness, when describing the background and one embodiment of the invention, only the modulated symbol stream outputted by the digital modulator in the first time slot

has been shown in Tables 1 and 2. The mapping schemes showing the whole packet is in Tables 3 and ! Similar to Table 2, Table 4 also stands for only one embodiment of the invention. The signal mapping scheme corresponding to the method and apparatus lor subcarrier mapping provided by the present invention shall not be understood to be limited by what in Table 4.



Wherein, the symbols on the same row are carried by the same data sLibearrier, say being mapped to and modulating the same data subcarrier. It can be seen that, the contents corresponding to Time slot I in Tables 3 and 4 are exactly the ones in Tables I and 2. As mentioned above, in this example, the packet comprises 96 symbols. When the decoding

with respect to said packet fails, because the channel is in deep fading or MHiiething like that, the sending means will need to resend this packet.
It should be understood that, in the prior art. and said embodiment of the invention, the initial transmission of signals uses the subcarrier mapping method shown in Table 3 or 4.

The Table 5 will be explained in conjunction with Table 3. Wherein, the subscript '2' at the left side of '=' (the equation) represents that the sending means is equipped with 2 transmitting antennas. For the initial transmission which can be considered as an even iiine of LutiiMii^Mon. please see the four symbols in the first row of Table 3. say s(J, s4H, S| and s,L|. Wherein, the symbols (.signals) sent on the two transmitting antennas in the first time slot are: suand S|. Then turn to Table 5, it is clear that the matrix for the initial transmission is S, =[s'|. Hence,
the matrix of an odd time of transmission should be S-, "!«$;'1,
wherein, since the initial transmission has been numbered with 0. all of the first time of resending, the third time of resending will be taken as an odd time of transmission. In an odd lime of transmission, the symbols (signals) sent on the two transmitting antennas in the first time slot are -s, and V,,. And the matrix of an even time of transmission, which

In an even time of transmission, (he symbols (signals) sent on the two transmitting antennas in the first time slot are: Lv„ and \, . For other
pairs of symbols (including the symbols corresponding to Time slot 2). the melhod shown in Table 5 is used to generate space-time coding incremental redundancy. Therefore, from Table 3, we can get:


can be seen from Table 5 that the subcarrier mapping scheme used in an even time of transmission is exactly the same as the one used in inilial transmission. Hence sec Table 3. obviously, by combining the incremental redundancy in Tables 3 and 6, spatial diversity can be achieved. Wherein, sending signals with multiple antennas or receiving signals with multiple signals can both achieve spatial diversity.
Nevertheless, the adjacent symbols in the input signal sequence (said modulated symbol stream), e.g. s()and si are more or less correlated with each oilier. Each pair of such adjacent or near symbols in Table 3 or Table 6, including the symbols in said modulated symbol stream and the redundancy generated via processing symbols in said modulated symbol stream with space-time coding like s„, are modulated onto the .same
subcarrier (corresponding to the same frequency) pair by pair, so that some frequency diversity has been lost.



The adjacent or near symbols in the input signal sequence (said modulated symbol stream), e.g. s(, and si are more or less correlated with each other. As in Table 4 or 7, each pair of such adjacent symbols, including the symbols in said modulated symbol stream and the redundancy generated via processing the symbols in said modulated symbol stream with space-time coding like s„, are modulated onto

different subcarriers (corresponding to the different frequency). Obviously, symbols modulated onto the same subcarriers, which means being sent/received with the same frequency, correspond to symbols much away from each other in said modulated symbol stream, so that the frequency diversity has been optimized.
Although the embodiments of the present invention have been described above, it is understandable by those skilled in the art that various modifications can be made without departing from the scope and spirit of the attached claims.

What is claimed is;
1. A method, in a sending means in MIMO-based wireless telecommunication network. Tor mapping signals to snbearriers. characterized in that, controlling the mapping of the signals in an input signal sequence to the subcarriers, so that the signals sent by different antennas at the same lime correspond to nonadjaccnt signals in the input signal sequence.
2. The method according to claim 1, characterized in that, said method comprising steps of:
a. mapping the consecutive signals in a signal sequence to M
subcarriers, so that the signals mapped to the same subcarrier are
nonadjacent signals in the signal sequence;
b. modulating the signals onto the corresponding subcarriers to
which the signals have been mapped, so as to generate multiple
modulated signal groups, wherein, every modulated signal group
comprises M signals modulated on different subcarriers;
c. controlling to send said multiple modulated signal groups via
different amentias.
3. The method according to claim 1 or 2, characterized in that, controlling the mapping of signals in the input signal sequence of the initial transmission to subcarriers, so that in each time of resending, the signals sent on different antennas at the same time correspond to nonadjacent signals in said input signal sequence of the initial transmission.
4. The method according to any of claims 1 to 3. characterized in that, every modulated signal group consists in the consecutive input signals of said input signal sequence.
5. The method according to any of claims I to 4, characterized in that, the initial transmission of signals in said MIMO-based wireless

telecommunication network uses spatial multiplexing as its transmission manner.
n. A mapping controller, in a sending means in MIMO-based wireless telecommunication network. Tor mapping signals to subcarriers, characterized in that, controlling the mapping of the signals in an input signal sequence to the subcarriers, so that the signals sent by different antennas at the same time correspond to nonadjacent signals in the input signal sequence.
7. The mapping controller according to claim 6, characterized in
that, comprising:
a mapping means, for mapping consecutive signals in a signal sequence to M subcarriers, so that the signals mapped to the same subearrier are nonadjacent signals in the signal sequence:
a modulator, for modulating the signals onto the corresponding subcarriers to which the signals have been mapped, so as to generate multiple modulated signal groups, wherein, every modulated signal group comprises M signals modulated on different subcarriers;
a sending controller, for controlling to send ^;iid multiple modulated signal groups via different antennas.
8. The mapping controller according to claim 6 or 7,
characterized in that, controlling the mapping of signals in the input
signal sequence of the initial transmission to subcarriers, so that in each
lime of resending, the signals sent on different antennas at the same time
correspond to nonadjacent signals in said input signal sequence of the
initial transmission.
9. The mapping controller according to any of claims 6-8,
characterized in that, every modulated signal group consists in the
consecutive input signals of said input signal sequence.
10. The mapping controller according to any of claims 6 to 9,

a
characterized in that, the initial transmission of signals in said MIMO-based wireless telecommunication network uses spatial multiplexing as its transmission manner.
II. A sending means in a MIMO-based wireless telecommunication network, characterized in that, comprising a mapping controller for mapping signals to subcarriers according to any of claims 6 to 10.