CONTROL CHANNEL SIGNALING USING CODE POINTS
FOR INDICATING THE SCHEDULING MODE
FIELD OF THE INVENTION
The invention relates to a control channel signal for use in a mobile communication
system providing at least two different scheduling modes. Further, the invention relates
to a scheduling unit for generating the control channel signal and a base station
comprising the scheduling unit. The invention also relates to the operation of a mobile
station and a base station for implementing a scheduling mode using the control channel
signal proposed by the invention.
TECHNICAL BACKGROUND
Packet-Scheduling and Shared Channel Transmission
In wireless communication systems employing packet-scheduling, at least part of the
air-interface resources are assigned dynamically to different users (mobile stations - MS
or user equipments - UE). Those dynamically allocated resources are typically mapped
to at least one Physical Uplink or Downlink Shared CHannel (PUSCH or PDSCH). A
PUSCH or PDSCH may for example have one of the following configurations:
- One or multiple codes in a CDMA (Code Division Multiple Access) system are
dynamically shared between multiple MS.
- One or multiple subcarriers (subbands) in an OFDMA (Orthogonal Frequency Division
Multiple Access) system are dynamically shared between multiple MS.
- Combinations of the above in an OFCDMA (Orthogonal Frequency Code Division
Multiplex Access) or a MC-CDMA (Multi Carrier-Code Division Multiple Access)
system are dynamically shared between multiple MS.
Fig. 1 shows a packet-scheduling system on a shared channel for systems with a single
shared data channel. A sub-frame (also referred to as a time slot) reflects the smallest
interval at which the scheduler (e.g. the Physical Layer or MAC Layer Scheduler)
performs the dynamic resource allocation (DRA). In Fig. 1, a TTI (transmission time
interval) equal to one sub-frame is assumed. It should be born noted that generally a TTI
may also span over multiple sub-frames.
Further, the smallest unit of radio resources (also referred to as a resource block or
resource unit), which can be allocated in OFDM systems, is typically defined by one sub-
frame in time domain and by one subcarrier/subband in the frequency domain. Similarly,
in a CDMA system this smallest unit of radio resources is defined by a sub-frame in the
time domain and a code in the code domain.
In OFCDMA or MC-CDMA systems, this smallest unit is defined by one sub-frame in
time domain, by one subcarrier/subband in the frequency domain and one code in the
code domain. Note that dynamic resource allocation may be performed in time domain
and in code/frequency domain.
The main benefits of packet-scheduling are the multi-user diversity gain by time domain
scheduling (TDS) and dynamic user rate adaptation.
Assuming that the channel conditions of the users change over time due to fast (and
slow) fading, at a given time instant the scheduler can assign available resources (codes
in case of CDMA, subcarriers/subbands in case of OFDMA) to users having good
channel conditions in time domain scheduling.
Specifics of DRA and Shared Channel Transmission in OFDMA
Additionally to exploiting multi-user diversity in time domain by Time Domain Scheduling
Frequency Domain Scheduling (FDS). This is because the OFDM signal is in frequency
domain constructed out of multiple narrowband subcarriers (typically grouped into
subbands), which can be assigned dynamically to different users. By this, the frequency
selective channel properties due to multi-path propagation can be exploited to schedule
users on frequencies (subcarriers/subbands) on which they have a good channel quality
(multi-user diversity in frequency domain).
For practical reasons in an OFDMA system the bandwidth is divided into multiple
subbands, which consist out of multiple subcarriers. I.e. the smallest unit on which a user
may be allocated would have a bandwidth of one subband and a duration of one slot or
one sub-frame (which may correspond to one or multiple OFDM symbols), which is
denoted as a resource block (RB). Typically, a subband consists of consecutive

subcarriers. However, in some case it is desired to form a subband out of distributed
non-consecutive subcarriers. A scheduler may also allocate a user over multiple
consecutive or non-consecutive subbands and/or sub-frames.
For the 3GPP Long Term Evolution (3GPP TR 25.814: "Physical Layer Aspects for
Evolved UTRA", Release 7, v. 7.1.0, October 2006 - available at http://www.3gpp.org
and incorporated herein by reference), a 10 MHz system (normal cyclic prefix) may
consist out of 600 subcarriers with a subcarrier spacing of 15 kHz. The 600 subcarriers
may then be grouped into 50 subbands (a 12 adjacent subcarriers), each subband
occupying a bandwidth of 180 kHz. Assuming, that a slot has a duration of 0.5 ms, a
resource block (RB) spans over 180 kHz and 0.5 ms according to this example.
In order to exploit multi-user diversity and to achieve scheduling gain in frequency
domain, the data for a given user should be allocated on resource blocks on which the
users have a good channel condition. Typically, those resource blocks are close to each
other and therefore, this transmission mode is in also denoted as localized mode (LM).
An example for a localized mode channel structure is shown in Fig. 2. In this example
neighboring resource blocks are assigned to four mobile stations (MS1 to MS4) in the
time domain and frequency domain. Each resource block consists of a portion for
carrying Layer 1 and/or Layer 2 control signaling (L1/I2 control signaling) and a portion
carrying the user data for the mobile stations.
Alternatively, the users may be allocated in a distributed mode (DM) as shown in Fig. 3.
In this configuration, a user (mobile station) is allocated on multiple resource blocks,
which are distributed over a range of resource blocks. In distributed mode a number of
different implementation options are possible. In the example shown in Fig. 3, a pair of
users (MSs 1/2 and MSs 3/4) shares the same resource blocks. Several further possible
exemplary implementation options may be found in 3GPP RAN WG#1 Tdoc R1-062089,
"Comparison between RB-level and Sub-carrier-level Distributed Transmission for
Shared Data Channel in E-UTRA Downlink", August 2006 (available at
http://www.3gpp.org and incorporated herein by reference).
It should be noted, that multiplexing of localized mode and distributed mode within a
sub-frame is possible, where the amount of resources (RBs) allocated to localized mode
and distributed mode may be fixed, semi-static (constant for tens/hundreds of
sub-frames) or even dynamic (different from sub-frame to sub-frame).

In localized mode as well as in distributed mode in - a given sub-frame - one or multiple
data blocks (which are inter alia referred to as transport-blocks) may be allocated
separately to the same user (mobile station) on different resource blocks, which may or
may not belong to the same service or Automatic Repeat reQuest (ARQ) process.
Logically, this can be understood as allocating different users.
L1/L2 Control signaling
In order to provide sufficient side information to correctly receive or transmit data in
systems employing packet scheduling, so-called L1/L2 control signaling (Physical
Downiink Control CHannei - PDCCH) needs to be transmitted. Typicai operation
mechanisms for downlink and uplink data transmission are discussed below.
Downlink Data Transmission
Along with the downlink packet data transmission, in existing implementations using a
shared downlink channel, such as 3GPP-based High Speed Data Packet Access
(HSDPA), L1/L2 control signaling is typically transmitted on a separate physical (control)
channel.
This L1/L2 control signaling typically contains information on the physical resource(s) on
which the downlink data is transmitted (e.g. subcarriers or subcarrier blocks in case of
OFDM, codes in case of CDMA). This information allows the mobile station (receiver) to
identify the resources on which the data is transmitted. Another parameter in the control
signaling is the transport format used for the transmission of the downlink data.
Typically, there are several possibilities to indicate the transport format. For example, the
transport block size of the data (payload size, information bits size), the Modulation and
Coding Scheme (MCS) level, the Spectral Efficiency, the code rate, etc. may be signaled
to indicate the transport format (TF). This information (usually together with the resource
allocation) allows the mobile station (receiver) to identify the information bit size, the
modulation scheme and the code rate in order to start the demodulation, the
de-rate-matching and the decoding process. In some cases the modulation scheme
maybe signaled explicitly.
In addition, in systems employing Hybrid Automatic Repeat reQuest (HARQ), HARQ
information may also form part of the L1/L2 signaling. This HARQ information typically
indicates the HARQ process number, which allows the mobile station to identify the

Hybrid ARQ process on which the data is mapped, the sequence number or new data
indicator, allowing the mobile station to identify if the transmission is a new packet or a
retransmitted packet and a redundancy and/or constellation version. The redundancy
version and/or constellation version tells the mobile station, which Hybrid ARQ
redundancy version is used (required for de-rate-matching) and/or which modulation
constellation version is used (required for demodulation)
A further parameter in the HARQ information is typically the UE Identity (UE ID) for
identifying the mobile station to receive the L1/L2 control signaling. In typical
implementations this information is used to mask the CRC of the L1/L2 control signaling
in order to prevent other mobile stations to read this information.
The table below (Table 1) illustrates an example of a L1/L2 control channel signal
structure for downlink scheduling as known from 3GPP TR 25.814 (see section 7.1.1.2.3
- FFS = for further study):
Uplink Data Transmission
Similarly, also for uplink transmissions, L1/L2 signaling is provided on the downlink to the
transmitters in order to inform them on the parameters for the uplink transmission.
Essentially, the L1/L2 control channel signal is partly similar to the one for downlink
transmissions. It typically indicates the physical resource(s) on which the UE should
transmit the data (e.g. subcarriers or subcarrier blocks in case of OFDM, codes in case
of CDMA) and a transport format the mobile station should use for uplink transmission.
Further, the L1/L2 control information may also comprise Hybrid ARQ information,
indicating the HARQ process number, the sequence number or new data indicator, and
further the redundancy and/or constellation version. In addition, there may be a UE
Identity (UE ID) comprised in the control signaling.
Variants
There are several different flavors how to exactly transmit the information pieces
mentioned above. Moreover, the L1/L2 control information may also contain additional
information or may omit some of the information. For example, the HARQ process
number may not be needed in case of using no or a synchronous HARQ protocol.
Similarly, the redundancy and/or constellation version may not be needed, if for example
Chase Combining is used (i.e. always the same redundancy and/or constellation version
is transmitted) or if the sequence of redundancy and/or constellation versions is pre-
defined.
Another variant may be to additionally include power control information in the control
signaling or MIMO related control information, such as e.g. pre-coding information. In
case of multi-codeword MIMO transmission transport format and/or HARQ information
for multiple code words may be included.
In case of uplink data transmission, part or all of the information listed above may be
signaled on uplink, instead of on the downlink. For example, the base station may only
define the physical resource(s) on which a given mobile station shall transmit,.
Accordingly, the mobile station may select and signal the transport format, modulation
scheme and/or HARQ parameters on the uplink. Which parts of the L1/L2 control
information is signaled on the uplink and which proportion is signaled on the downlink is
typically a design issue and depends on the view how much control should be carried out
by the network and how much autonomy should be left to the mobile station.
Another, more recent suggestion of a L1/L2 control signaling structure for uplink and
downlink transmission may be found in 3GPP TSG-RAN WG1 #50 Tdoc. R1-073870,
"Notes from offline discussions on PDCCH contents", August 2007, available at
http://www.3gpp.org and incorporated herein by reference.
As indicated above, L1/L2 control signaling has been defied for systems that are already
deployed to in different countries, such as for example, 3GPP HSDPA. For details on
3GPP HSDPA it is therefore referred to 3GPP TS 25.308, "High Speed Downlink Packet
Access (HSDPA); Overall description; Stage 2", version 7.4.0, September 2007
(available at http://www.3gpp.org) and Harri Holma and Antti Toskala, "WCDMA for
UMTS, Radio Access For Third Generation Mobile Communications", Third Edition, John
Wiley & Sons, Ltd., 2004, chapters 11.1 to 11.5, for further reading.
L1/L2 control signaling reduction techniques
For scheduling (delay-sensitive) services with small data packets, such as e.g. VoIP
(Voice over IP) or gaming, the downlink L1/L2 control signalling can be quite significant if
each small data packet needs to be signalled. In a 5 MHz 3GPP LTE system, up to 400
VoIP users can be supported as has been shown in 3GPP TSG-RAN WG1 Meeting
#46 Tdoc. R1 -062179, "VoIP System Performance for E-UTRA Downlink - Additional
Results", (available at http://www.3gpp.org/ftp/tsg_ran/WG1_RL1/TSGR1_46/Docs/).
This results in roughly 10 VoIP packets on the uplink and 10 VoIP packet on the
downlink within a sub-frame, which requires 20 L1/L2 control channels (10 for uplink data
transmission and 10 for downlink data transmission). Assuming that the payload size of
an L1/L2 control channel carrying an uplink allocation is 35-45 bits and the payload size
of an L1/L2 control channel carrying an downlink allocation is approximately 35-50 bits,
this results in an downlink L1/L2 control channel overhead of roughly 25-34% (assuming
QPSK rate 1/3 transmission of the L1/L2 control channels). This overhead is significantly
larger than for other services (e.g. FTP, HTTP, audio/video streaming), where the data
can be transmitted in large packets (assumed downlink L1/L2 control channel overhead
in this case is approximately 8-12%). Therefore, within the 3GPP LTE standardization
the several reduction techniques for services with small data packets are investigated. In
the following two investigated schemes that are discussed by the 3GPP are briefly
explained:
One scheme discussed is based on a grouping of users (e.g. in similar radio conditions)
Examples of this scheme are described in the parallel European patent application no.
EP 06009854.8, "RESOURCE RESERVATION FOR USERS IN A MOBILE
COMMUNICATION SYSTEM" or in 3GPP TSG-RAN-WG2 Meeting #57 Tdoc.
R2-070758, "Scheduling for downlink" (available at http://www.3gpp.org/ftp/tsg_ran/
WG2_RL2/TSGR2_57/Documents/), both documents being incorporated herein by
reference. In this scheme, a single downlink L1/L2 control channel with a special "group
format" is used. This causes that less "group format" downlink L1/L2 control channels are
required to be transmitted than "normal" L1/L2 control channels. Although the payload
size of the "group format" L1/L2 control channels is larger than that of the "normal" L1/L2
control channel, a net saving in L1/L2 control signaling overhead is expected.
Another exemplary scheme is based on the use of a persistent allocation downlink
resources and using with blind detection. Examples of this scheme are described in the
parallel European patent application no. EP 06009854.8 mentioned above or in 3GPP
TSG-RAN WG2 Meeting #56bis R2-070272, "Signalling optimized DL scheduling for
LTE" (available at http://www.3gpp.org/ftp/tsg_ran/WG2_RL2/TSGR2_56bis/Documents/
and incorporated herein by reference). In this exemplary scheme, a certain set of
resource blocks and/or subframes (e.g. a certain time-frequency window) and possibly a
certain set of transport formats is pre-configured and the UE tries to blindly decode the
possibly transmitted packet on the pre-configured resources with the pre-configured set
of transport formats. For the initial transmission of a packet the downlink L1/L2 control
channel is omitted, whereas retransmissions are allocated by the downlink L1/L2 control
channel. Assuming that the packet error rate for the first transmission of a packet is
considerably low, L1/L2 control signaling overhead is reduced, e.g. for a 10% packet
error rate for the first transmission, the L1/L2 control signaling overhead can be roughly
reduced by 90%. Typically, in such a scheme, the L1/L2 control signaling transmitted
with the retransmission carries information about the initial transmission (e.g. information
about to a subframe at which the initial transmission took place, information about the
resource block(s) on which the initial transmission has been allocated and/or information
about the transport format).
It is therefore desirable to reduce of the mobile station (UE) complexity with respect to
decoding the downlink L1/L2 control channels. It is further desirable to achieve an
additional reduction of the downlink L1/L2 control signaling overhead and increase in
signaling efficiency. Additionally, it may be appreciated by those skilled in the art to
implement a simple and less complex downlink L1/L2 control channel structure.
SUMMARY OF THE INVENTION
One main aspect of the invention is the definition of at least one so-called code point in
the control channel signals, such as for example the L1/L2 control channels as described
previously herein. A code point may therefore be considered one specific value of a field
of the control channel signal which is indicating the scheduling mode for an associated
transmission of user data of a protocol data unit, and further the control channel format.
Alternatively, a code point may also be defined as a specific combination of values
represented by more than one control channel signal field. Likewise, different code points
may be defined for the control channel signal.
One benefit that can be achieved by using code points is the avoidance of flag fields
which indicate the scheduling mode or the format of the control channel. This reduces
the size of the control channel and, therefore, the signalling overhead.
According to another aspect of the invention, different scheduling modes may be used
for the transmission of the user data of a service, whereby a code point is used to identify

the use of a specific scheduling mode. The different scheduling modes may utilize
different formats of the control channel signal so that the code point further indicates a
specific format of the control channel.
Further, the use of different scheduling schemes also increases the flexibility in control
channel signalling so that the control channel overhead may be reduced. For example,
there may be two different scheduling modes defined, wherein one of the scheduling
modes only signals control channel information for retransmissions of a protocol data
packets (in contrast to providing a control channel signal for each protocol data unit
transmission - which could be the case for the other, second scheduling mode). This
exemplary scheduling mode may for example be advantageous for the transmission of
user data of delay-sensitive services, where the (average) user data size of a protocol
data unit is small in comparison to other service types.
According to one embodiment of the invention, a control channel signal is defined. This
control channel signal is suitable for the use in a mobile communication system providing
at least two different scheduling modes. The control channel signal comprises at least
one control information field consisting of a number of bits, where at least one of the
values that can be represented by the bits of the at least one control information field
defines a code point for indicating the scheduling mode for an associated transmission of
user data in for of a protocol data unit and the control channel format to the receiver. As
indicated above, alternatively, a code point may also be defined by a combination of
predetermined values of different control information fields in the control channel signal.
For example, at least the HARQ process field and the RV field may be used to define the
code point.
In one variation the number of bits of the control channel signal is equal for at least two
scheduling modes. This may be for example advantageous to simplify the rate matching
for the control channels or to reduce the number of different control channel sizes a
mobile station has to decode.
The at least one control channel field that is used to indicate a scheduling mode by
means of the code point may be located at a fixed position within the control channel
signal for all control channel formats. Accordingly, in case the control channel format size
is equal for the different scheduling modes and the control channel field(s) to indicate a
code point is/are located at fixed position(s), the detection of the code point in the control
channel signal is simplified for the receiver of the control channel signal.

Alternatively, in another embodiment of the invention, the control channel signal indicates
plural code points. These plural code points indicate the use of one scheduling mode but
different transport formats of the protocol data unit. Accordingly, not only one specific
values respresentable by the bits of a control channel field (or fields) may be defined as
a code point, but different values may be used to indicate different code points. Though
there may be plural code points defined, these different code points do not necessarily
indicate a corresponding number of different scheduling modes. For example, all code
points defined for a control channel field may indicate the same scheduling mode, but
different control channel information.
In one exemplary embodiment of the invention, the code point is specified as a specific
value of the HARQ process field contained in the control channel signal. For example,
one HARQ process may be reserved for a scheduling mode and the value represented
by the bits of the HARQ process field for indicating the reserved HARQ process defines
the code point. Accordingly, in this example, the code point indicates the scheduling
mode (dependent on which the remaining control channel signal may be interpreted) and
simultaneously specifies the HARQ process of the protocol data unit.
In another alternative embodiment of the invention the at least one control information
field for indicating the code point is a resource allocation field of the control channel
signal. The resource allocation field may optionally comprise a header and the code
point is could be defined by a specific bit combination of header bits of the resource
allocation field.
!n another embodiment, the control information field of the control channel signal defining
the codepoint is a transport format field of the control channel signal. For example, this
transport format field could indicate plural code points, wherein a subset of the plural
code points indicates the use of one scheduling mode.
According to a further embodiment of the invention, the control information field defining
the codepoint is used to indicate either a persistent scheduling mode or a dynamic
scheduling mode.
Another embodiment of the invention relates to a scheduling unit for use in a mobile
communication system providing at least two different scheduling modes. According to
this exemplary embodiment, the scheduling unit capable of generating and transmitting a
control channel signal as defined herein.

In a variation of this embodiment, the scheduling unit is further adapted to transmit a
control channel signal only for retransmissions of the protocol data unit, if a first
scheduling mode is used for the transmission of user data.
In an exemplary embodiment, the scheduling unit is adapted to utilize the first scheduling
mode for the transmission of protocol data units having a size below a threshold (e.g. for
protocol data units of a delay-critical service, such as VoIP). The second scheduling
mode may be used for the transmission of protocol data units having a size above or
equal to the threshold (i.e. for example for user data of delay-insensitive services).
In another exemplary embodiment, the scheduling unit is adapted to utilize the first
scheduling mode for the transmission of protocol data mapped onto a first set of priority
queues or logical channels (e.g. for protocol data units of a delay-critical service, such as
VoIP). The second scheduling mode may be used for the transmission of protocol data
units mapped onto a second set of priority queues or logical channels (i.e. for example
for user data of delay-insensitive services).
As indicated above, the control channel format may be different for the different
scheduling modes, so that the scheduling unit is capable of generating the different
control channel signal formats depending on the scheduling mode used for the
transmission of user data.
The scheduling unit according to another embodiment of the invention uses the HARQ
process field of the control signal as the at least one control information field for
indicating the code point. In an exemplary variation of this embodiment, one HARQ
process is reserved for one scheduling mode and the value represented by the bits of the
HARQ process field for indicating the reserved HARQ process defines the code point.
Alternatively, according to a further embodiment of the invention, the control information
field is a transport format field of the control channel signal. In this exemplary
embodiment, the transport format field may for example indicate plural code points, and
a subset of the plural code points could for example indicate the use of one scheduling
mode.
in another exemplary embodiment of the invention, the first scheduling mode is a
persistent scheduling mode and the second scheduling mode is a dynamic scheduling
mode.

Another embodiment of the invention is providing a base station comprising a scheduling
unit according to one of the different embodiments of the invention described herein.
In one embodiment of the invention, the base station further comprises a transmitter unit
for transmitting a control channel signal generated by the scheduling unit and protocol
data units comprising user data to a mobile terminal. The base station is further capable
of controlling the base station's transmitter unit to transmit the control channel signal only
for retransmissions of the protocol data unit, in case a first scheduling mode out of at
least two different scheduling modes is used for the transmission of the protocol data
unit.
The base station according to another embodiment further comprises a receiver unit for
receiving a feedback message from the mobile station. The feedback message indicates,
whether a protocol data unit previously transmitted by the base station has been
successfully decoded by the mobile station.
In some embodiments of the invention, the first scheduling mode is used for the
transmission of the user data to the mobile terminal, and a feedback message is
received by the receiver unit of the base station for an initial transmission of the protocol
data unit carrying the user data. It may be assumed that this feedback message is
indicating that the protocol data unit has not been decoded successfully by the mobile
station. Accordingly, the base station causes the scheduling unit to generate a control
channel signal for a retransmission of the protocol data unit. Moreover, the base station
may also cause its transmitter unit to retransmit the protocol data unit and the generated
control channel signal to the mobile station. This control channel signal at least indicates
the transport format and the downlink physical channel resources used for the
retransmission and the initial transmission of the protocol data unit.
A further embodiment of the invention relates to a mobile station for use in a mobile
communication system and for receiving user data on the downlink in form of protocol
data units. This mobile station comprises a receiver unit for receiving from a base station
a subframe of a downlink physical channel, and for performing a blind detection on the
received subframe to thereby decode an initial transmission of a protocol data unit
conveying user data within the received subframe. The mobile station further comprises
a transmitter unit for transmitting negative feedback to the base station indicating that the
protocol data unit has not been decoded successfully during blind detection. In response
to the negative feedback, the receiver unit will receive another subframe of the downlink

physical channel from the base station comprising a control channel signal indicating the
transport format and the downlink physical channel resources used for the
retransmission and initial transmission of the protocol data unit. Accordingly, the mobile
station's decoder is decoding the protocol data unit based on the control channel signal.
In a further embodiment of the invention, the mobile station comprises a (soft) buffer -
such as for example an HARQ buffer - for temporarily storing the unsuccessfully
decoded initial transmission of the protocol data unit. The decoder soft combines the
initial transmission and the retransmission of the protocol data unit prior to decoding.
Another embodiment of the invention provides a computer-readable medium storing
instructions that, when executed by a processor of a base station, cause the base station
to provide control channel signals in a mobile communication system. The base station is
caused to provide control channel signals in a mobile communication system by
generating a control channel signal according to one of the different embodiments
described herein, and transmitting the generated control channel signal in a subframe of
a physical channel.
A further embodiment of the invention relates to a computer-readable medium storing
instructions that, when executed by a processor of a mobile station, cause the mobile
station for receive user data on the downlink in form of protocol data units by receiving
from a base station a subframe of a downlink physical channel, and for performing a
blind detection on the received subframe to thereby decode an initial transmission of a
protocol data unit conveying user data within the received subframe, transmitting a
negative feedback to the base station indicating that the protocol data unit has not been
decoded successfully during blind detection, receiving, in response to the negative
feedback, another subframe of the downlink physical channel from the base station
comprising a control channel signal indicating the transport format and the downlink
physical channel resources used for the retransmission and initial transmission of the
protocol data unit, and decoding the protocol data unit based on the control channel
signal.
The computer-readable medium according embodiment of the invention is further storing
instructions that, when executed by the processor of the mobile station, cause the mobile
station to temporarily store the unsuccessfully decoded initial transmission of the protocol
data unit a buffer, and to soft combine the initial transmission and the retransmission of
the protocol data unit prior to decoding.

BRIEF DESCRIPTION OF THE FIGURES
In the following, the invention is described in more detail in reference to the attached
figures and drawings. Similar or corresponding details in the figures are marked with the
same reference numerals.
Fig. 1 shows an exemplary data transmission to users in an OFDMA system,
Fig. 2 shows an exemplary data transmission to users in an OFDMA system in localized
mode (LM) having a distributed mapping of L1/L2 control signaling,
Fig. 3 shows an exemplary data transmission to users in an OFDMA system in
distributed mode (DM) having a distributed mapping of L1/L2 control
signaling,
Fig. 4 shows two exemplary L1/L2 control channel signal formats for a specific
scheduling mode (scheduling mode 2), according to one embodiment of
the invention.
Fig. 5 shows an exemplary L1/L2 control channel signal according to one embodiment
of the invention in which a HARQ filed is used to indicate a scheduling
mode, and in which the use of the TF/RV/NDI field in the control channel
signal is depending on the scheduling mode,
Fig. 6 shows another exemplary L1/L2 control channel signal according to one
embodiment of the invention in which a HARQ filed is used to indicate a
scheduling mode, and in which the use of the resource assignment (RA)
field and the TF/RV/NDI field in the control channel signal is depending on
the scheduling mode,
Fig. 7 shows an exemplary message exchange between a base station and a mobile
station according to an embodiment of the invention for data transmission
using scheduling mode 1, and
Fig. 8 shows a mobile communication system according to one embodiment of the
invention, in which the message exchange of Fig. 7 may be implemented,
and

Fig. 9 shows a flow chart of an exemplary operation of a base station according to one
embodiment of the invention, and
Fig. 10 shows a flow chart of an exemplary operation of a mobile station according
to an exemplary embodiment of the invention using scheduling mode 1.
DETAILED DESCRIPTION OF THE INVENTION
The following paragraphs will describe various embodiments of the invention. For
exemplary purposes only, most of the embodiments are outlined in relation to an
(evolved) UMTS communication system according to the SAE/LTE discussed in the
Technical Background section above. It should be noted that the invention may be
advantageously used for example in connection with a mobile communication system
such as the SAE/LTE communication system previously described or in connection with
multi-carrier systems such as OFDM-based systems, but the invention is not limited to its
use in this particular exemplary communication network.
Before discussing the various embodiments of the invention in further detail below, the
following paragraphs will give a brief overview on the meaning of several terms
frequently used herein and their interrelation and dependencies. Generally, a protocol
data unit may be considered a data packet of a specific protocol layer that is used to
convey one or more transport blocks of user data. The user data are typically associated
to a service such as for example a VoIP service.
In some embodiments of the invention, the protocol data unit is a MAC Protocol Data
Unit (MAC PDU), i.e. a protocol data unit of the MAC (Medium Access Control) protocol
layer. The MAC PDU conveys data provided by the MAC layer to the PHY (Physical)
layer. Typically, for a single user allocation (one L1/L2 control channel - PDCCH - per
user), one MAC PDU is mapped onto one transport block (TB) on Layer 1. A transport
block defines the basic data unit exchanged between Layer 1 and MAC (Layer 2).
Typically, the when mapping a MAC PDU onto a transport block one or multiple CRCs
are added. The transport block size is defined as the size (number of bits) of a transport
block. Depending on the definition, the transport size may include or exclude the CRC
bits.
In general, the transport format defines the modulation and coding scheme (MCS) and/or
the transport block size, which is applied for the transmission of a transport block and is,
therefore, required for appropriate (de)modulation and (de)coding. In a 3GPP-based
system as for example discussed in 3GPP TR 25.814, the following relationship between
the modulation and coding scheme, the transport block size and the resource allocation
size is valid:

where NRE is the number of allocated resource elements (RE) - one RE being identical to
one modulation symbol -, CR is the code rate for encoding the transport block, and M is
the number of bits mapped onto one modulation symbol, e.g. M=4 for 16-QAM.
Due to this relationship described above, the L1/L2 control signaling may only need to
indicate either the transport block size or the modulation and coding scheme. In case the
modulation and coding scheme should be signaled, there are several options how to
implement this signaling. For example, separate fields for modulation and coding or a
joint field for signaling both, the modulation and coding parameters may be foreseen. In
case the transport block size should be signaled, the transport block size is typically not
explicitly signaled, but is rather signaled as a TBS index. The interpretation of the TBS
index to determine the actual transport block size may for example depend on the
resource allocation size.
In the following, the transport format field on the L1/L2 control signaling is assumed to be
indicating either the modulation and coding scheme or the transport block size. It should
be noted, that the transport block size for a given transport block does typically not
change during transmissions. However, even if the transport block size is not changed,
the modulation and coding scheme may change between transmissions, e.g. if the
resource allocation size is changed (as apparent for the described relationship above).
The main idea of the invention is the introduction of a so-called code point or code points
to the control channel signal. A code point is a specific value representable by a bit
combination of one field (out of plural fields) in the control channel signal format.
Alternatively, a code point may be defined as a specific combination of the values of
different control channel signal fields.
A code point (or code points) defined for the control channel signal is/are indicating the
use of a specific scheduling mode for the transmission of the associated user data (in
form of protocol data units). Depending on the code point, the receiver of the control
channel signal (e.g. the mobile station) recognizes the scheduling mode being utilized
and is capable of interpreting the control channel signal information (i.e. the values
17
indicated by the bits of the different fields in the control channel signal) based on the
code point, respectively the scheduling mode indicated by the code point.
In contrast to a (additional) flag (or bit) in the control channel signaling for indicating the
scheduling mode, a code point is corresponding to (at least) one predetermined value of
a (at least one) control channel signal field.
The use of code points avoids additional control signaling overhead (as for example
implied by an additional flag to indicate the scheduling mode). For example, an HARQ
field in the control channel signal indicating the HARQ process number used for
transmitting the associated protocol data unit conveying the user data may have 3 bits
which allows signaling 8 different values, while there may only be 6 HARQ processes
available. Hence, one of the "remaining" values (or both) may be defined as a code point
(or individual code points) to indicaie a different scheduling mode. Alternatively, there
may be 8 HARQ processes available (numbered 0 to 7), however, one (or more) of the
processes (e.g. process no. 7 = 1112) are configured for transporting VoIP service data.
Accordingly, this specific HARQ process number (e.g. process no. 7 = 1112) can be a
code point yielding a specific scheduling mode (and thus optionally a specific control
channel signal format). In both examples, no additional flag is needed for indicating a
second scheduling mode, which reduces the control signaling overhead.
In one embodiment of the invention, the format of the control channel information signal
(e.g. the configuration of the control channel in terms of its fields, the content of the
fields, the size of the fields, and/or the interpretation of the different field values) depends
on the respective scheduling mode. For example, it may be assumed that there are two
different scheduling modes available, whereas the scheduling modes each yield a
different control channel signal format. If the scheduler (e.g. located in a base station)
sends the control channel signal yielding the first of the two scheduling modes by means
of signaling a code point "value", the receiver of the control channel signal (for example a
mobile station) uses a first reference information to interpret the control channel
information, while the receiver uses a second reference information to interpret the
content of the control channel information, if the second scheduling mode is indicated.
Irrespective of the scheduling mode, the control channel signal size (in terms of the
number of bits spent for control channel) is identical. The scheduling mode is implicitly
indicated by the code point not being set (i.e. a value defining no code point is signaled).
In an advantageous embodiment of the invention, the different scheduling modes are
associated with different service types of the user services (user data). For example, a
first scheduling mode may be used for the transmission of user data of services that
typically produce only protocol data units for transmission that are relatively small in size
(e.g. below a certain threshold) and thus yield a high percentage of control signaling
overhead in conventional systems in comparison to the user data. One example for such
services are delay-sensitive services like VoIP, where only small data packets (or
protocol data units) are transmitted, so that the control channel signaling overhead may
be significant. The second scheduling mode may be for example a conventional
scheduling mode and the control channel signaling may be designed as described in the
Technical Background section.
The generation of small packet protocol data units may have another disadvantage in
terms of system throughput. Typically, the number of control channels is limited (e.g. the
control signaling may only indicate N different transmissions for a subframe of the
physical data channel). Accordingly, only M transmissions of protocol data units can be
signaled by the control channels per subframe. However, if there are mainly
transmissions of services generating small protocol data unit sizes, not all physical radio
resources (resource blocks) in a subframe of the physical data channel available for user
data transmission may be needed to transmit M protocol data units, so that system
resources are wasted. Accordingly, according to one embodiment of the invention, the
user services that are typically generating protocol data units small in size, like a VoIP
service, may be scheduled using one scheduling mode (scheduling mode 1), while other
services are scheduled using another scheduling mode (scheduling mode 2).
Whether a user service is typically generating protocol data units small in size may be for
example depend on the service class of the service, the type of the service, or may be
judged based on the (average) protocol data unit size provided by the service.
As the control channel signal size may be assumed constant in the communication
system (N bits / control channel) - for example to support simple rate matching - there
may be no direct improvement to the ratio of protocol data unit size to control channel
size. However, in this embodiment, there may be no control channel for initial
transmission of protocol data units of services generating protocol data units small in
size.
Instead, the receiver of the service (e.g. a mobile station) may receive a subframe from
the physical data channel and tries to decode the information thereof using blind
detection techniques to obtain the protocol data units. In order to avoid that the mobile
station has to try decoding the received subframe information using all possible transport
formats (i.e. all possible modulations and coding schemes available in the
communication system) there may be a pre-configuration of the transport formats that
may be used in connection with the scheduling mode so as to reduce the number of blind
detection attempts to a reasonable number. Alternatively, the transport formats the
mobile station should try for decoding when using blind detection and/or the subframes
which the mobile station should receive and try blind decoding (e.g. every kth subframe)
may also be configured (in advance) by control signaling (e.g. in a higher protocol layer).
If blind detection fails, i.e. no protocol data unit can be decoded successfully in a
received subframe, the mobile station may store the received physical channel
information of the subframe (e.g. the received soft-values of the received modulation
symbols or the log-likelihood ratios for the demapped modulation symbols) in a buffer
(e.g. the HARQ buffer) and sends a negative acknowledgment to the transmitter. The
transmitter may then respond by sending a retransmission for the protocol data unit
together with an associated control channel signal for this retransmission. Accordingly, in
this exemplary embodiment, no control channel signal is sent for the initial transmission
of a protocol data unit, but only for the retransmissions thereof. As the number of
retransmissions may be supposed to be significantly lower than the number of initial
transmissions, the control signaling overhead for the user data transmission may be
significantly reduced in this scheduling mode (scheduling mode 1) for user data of
services that yield small packet sizes, like VoIP services. The other services may be
scheduled using another scheduling mode (scheduling mode 2) which may be for
example a conventional scheduling mode where all transmissions of user data is
accompanied by a respective control channel signal.
It should be noted that the exact implementation of the blind detection procedure is out of
the scope of the invention and up to the system design and requirements. !n genera!,
blind detection is based on a concept similar to trial-and-error schemes, where the
receiving apparatus receives a physical channel resource (for example a subframe) and
tries to decode the received information by trying different resource allocations and
transport formats to demodulate and decode the information of the received physical
channel resource. In order to reduce the computational requirements of the receiving
apparatus, some implementations only predefine or configure only a given number of
different resource allocations and transport formats for transmissions that are received
using blind detection. Furthermore, the receiving apparatus may only try to receive
specific subframes of a physical channel (e.g. every kth subframe) or the subframes to
receive and to perform blind detection on may be configured (in advance) by control
signaling (e.g. in a higher protocol layer), as indicated above.
Next, the operation of the transmitter of the control channel signal according to one of the
various embodiments described herein and the receiver thereof will be described in
further detail, thereby exemplarily relating to the case of downlink data transmission via a
(shared) downlink physical channel. For exemplary purposes a 3GPP LTE network as
exemplified in Fig. 8 may be assumed. The mobile communication system of Fig. 8 is
considered having a "two node architecture" consisting of at least one Access and Core
Gateway (ACGW) and Node Bs. The ACGW may handle core network functions, such
as routing calls and data connections to external networks, and it may also implement
some RAN functions. Thus, the ACGW may be considered as to combine functions
performed by GGSN and SGSN in today's 3G networks and RAN functions as for
example radio resource control (RRC), header compression, ciphering/integrity
protection.
The base stations (also referred to as Node Bs or enhanced Node Bs = eNode Bs) may
handle functions as for example segmentation/concatenation of data, scheduling and
allocation of resources, multiplexing and physical layer functions, but also RRC
functions, such as outer ARQ. For exemplary purposes only, the eNodeBs are illustrated
to control only one radio cell. Obviously, using beam-forming antennas and/or other
techniques the eNodeBs may also control several radio cells or logical radio ceils.
In this exemplary network architecture, a shared data channel may be used for
communication of user data (in form or protocol data units) on uplink and/or downlink on
the air interface between mobile stations (UEs) and base stations (eNodeBs). This
shared channel may be for example a Physical Uplink or Downlink Shared CHannei
(PUSCH or PDSCH) as know in 3GPP LTE systems. It is also possible that the shared
data channel and the associated control channels are mapped to the physical layer
resources as shown in Fig. 2 or Fig. 3.
The control channel signals/information may be transmitted on separate (physical)
control channels that are mapped into the same subframe to which the associated user
data (protocol data units) are mapped or may be alternatively sent in a subframe
preceding the one containing the associated information. In one example, the mobile
communication system is a 3GPP LTE system, and the control channel signal is L1/L2
control channel information (e.g. information on the Physical Downlink Control CHannel -
PDCCH). Respective L1/L2 control channel information for the different users (or groups
of users) may be mapped into a specific part of the shared uplink or downlink channel, as
exemplariiy shown in Fig. 2 and 3, where the control channel information of the different
users is mapped to the first part of a downlink subframe ("control").
Fig. 7 shows an exemplary message exchange between a base station and a mobile
station according to an embodiment of the invention for data transmission using
scheduling mode 1. The message exchange may be performed in the mobile
communication network shown in Fig. 8. Accordingly, as the example in Fig. 7 is relating
to the downlink data transmission, the transmitter shown in Fig. 7 may be assumed to
correspond to base station/Node B NB1 in Fig. 8 and the receiver shown in Fig. 7 may
be assumed to correspond to mobile station/UE MS1 in Fig. 8. Generally, it may be
assumed in Fig. 7 that a retransmission protocol, such as Hybrid ARQ, is used between
the transmitter (here: base station NB1) and receiver (here: mobile station MS1) of the
data (protocol data unit) so as to ensure successful decoding of the data at the receiver.
In this exemplary 3GPP LTE system according to an embodiment of the invention a
mobile station may simultaneously run services, that are transmitted using large data
packets (e.g. FTP (File Transfer Protocol), HTTP (HyperText Transfer Protocol),
audio/video streaming) and services that are transmitted using small data packets (e.g.
VoIP (Voice over IP), gaming). As mentioned in the technical background section a
reduction in downlink L1/L2 control signaling is desirable for the services using smaii
data packets. In this exemplary embodiment a 1st scheduling mode (scheduling mode 1)
is used for the transmission of protocol data units (PDUs) of services typically having a
small packet size, while a "normal" 2nd scheduling mode (scheduling mode 2) is
employed for other services. Therefore, a mobile station may receive data transmitted
with a 1s' or 2nd scheduling mode as defined below.
Scheduling mode 1 allows to reduce the L1/L2 control signaling overhead by using a
persistent allocation of resources and utilizing blind detection for the reception,
demodulation and decoding of the downlink data. Hence, for the initial transmission of a
protocol data unit (packet) no L1/L2 control channel is transmitted, but only for first
retransmission of the protocol data unit (and optionally for all or selected ones of further
retransmissions).
Scheduling mode 2 may be considered a "norma!" or "dynamic" scheduling mode. In this
scheduling mode the initial transmission of a packet is signaled via a L1/L2 control
channel and retransmissions may or may not be signaled via a L1/L2 control channel
depending on the HARQ operation (e.g. asynchronous or synchronous or adaptive or
non-adaptive). This scheduling mode may be for example implemented according to the
scheduling proposed in the technical background section or as described in the parallel
EP patent application no. EP 07024829.9, entitled "Control Channel Signaling using a
Common Signaling Field for Transport Format and Redundancy Version" of the applicant
(filed December 20, 2007, representative's docket number: EP56004), which is
incorporated herein by reference.
Further, it may be assumed for exemplary purposes that for a given sub-frame and given
link (uplink or downlink), the mobile station MS1 is allocated either in scheduling mode 1
or in scheduling mode 2. Hence, there is no simultaneous allocation with both modes in a
given sub-frame. However, the scheduling mode can change from sub-frame to sub-
frame. Also, in a given sub-frame a mobile station may be scheduled.
Fig. 7 exemplifies the user data transmission using scheduling mode 1 described above,
where it is assumed that the initial transmission is not signaled by a L1/L2 control
signaling. In order to reduce the number of blind detection attempts, it may be assumed
that only a reduced number of resource assignment and transport format candidates are
allowed compared to scheduling mode 2, since the number of blind decodings and the
required soft buffer size are limited. For example, in a 10 MHz system with 50 resource
blocks (assuming 11 resource assignment bits) and 25 transport formats at least 1275 x
32 = 40800 candidates for scheduling mode 1 are possible (assuming only consecutive
allocations (50 x (50+1) / 2 possibilities) in the RB domain are possible and not
considering other factors like e.g. variable control region size). Due to UE complexity
constraints, the number of possible blind decodings per subframe is significantly less
than 40800.
Accordingly, the allowed resource assignment and transport format candidates may for
example be pre-configured or configured 701 by the access network using higher layer
protocols, such as for example a Radio Resource Control (RRC) Protocol or MAC control
signaling. Assuming for exemplary purposes 32 resource allocation and transport
formats combinations being (pre-)configured for scheduling mode 1, 32 blind decodings
per subframe are required. In addition, the mobile station may not know the subframe in
which the transmission of the initial transmission took place. I.e. the blind decoding may
need to be required in several subframes and several subframes may need to be
buffered.
In scheduling mode 1 it is assumed that the L1/L2 control channel of a retransmission
carries some information on the resource assignment and/or the transport format of the
initial transmission among possibly other information. In the above mentioned example,
this would require 5 bits (log2(32)) to exactly determine the resource allocation and
transport format, if the subframe number at which the initial transmission took place is
known (less bits could be used in order to reduce the candidates). If the subframe
number is not known to the mobile station additional information on the subframe number
may be included to the L1/L2 control channel signal sent with the retransmission.
It should be noted that the increase of subframe candidates for the initial transmission
does not impact the number of blind decoding complexity, since this is typically defined
by number of blind decodings per subframe. However, the required buffer size at the
receiver is increased since soft information (bits or modulation symbols) from additional
subframes of the (shared) downlink physical channel may need to be buffered to allow
for soft-combining prior to decoding. In case multiple subframe candidates for the initial
transmission are possible, the L1/L2 control channel of a retransmission may carry some
information of the subframe number being used for the initial transmission in order to
reduce the blind combining complexity.
Returning to Fig. 7, base station NB1 transmits 702 the initial transmission of a protocol
data unit to mobile station MS1 without control signaling, i.e. without explicitly indicating
the transmission on the L1/L2 control channel of the subframe for mobile station MS1.
For example due to a persistent allocation of resources on the (shared) downlink
physical channel, mobile station MS1 assumes a user transmission occurring in the
subframe and receives the subframe containing the initial transmission of the protocol
data unit and performs a blind detection 703 on the information received from the
physical channel by testing the resource allocations and transport formats candidates
that have been configures 701 previously.
In the example shown in Fig. 7, it is assumed that the blind detection 703 is not
successful, i.e. a successful decoding with the tested resource allocation and transport
format combinations was not possible (e.g. due to a transmission error in the received
information of the physical channel). Accordingly, mobile station MS1 transmits 704 a
negative acknowledgement to base station NB1 to indicate the unsuccessful decoding of

the initial transmission. Furthermore, in case the HARQ protocol supports soft-
combining, mobile station MS1 stores the received physical channel information (e.g. the
soft values of the individual modulation symbols or the log-likelihood ratios (LLRs) of the
channel bits) for soft-combining with the retransmissions.
Base station NB1 receives the negative acknowledgment (NACK) and generates 705 a
L1/L2 control channel signal for the retransmission of the protocol data unit. The content
of the L1/L2 control channel signal will be discussed in further detail below with respect
to Figs. 5 and 6. Subsequently, base station NB1 transmits 706, 708 the L1/L2 control
channel signal and the retransmission of the protocol data unit to mobile station MS1.
Mobile station MS1 receives the subframe comprising the L1/L2 control channel signal
and the retransmission of the protocol data unit and interprets the content of the control
channel signal depending on the scheduling mode indicated in the control channel
signal. Using the control channel information comprised in the control channel signal
from base station NB1, mobile station MS1 subsequently tries to decode 709 the protocol
data unit. Optionally, if soft-combining is provided by the HARQ protocol, the information
in the soft buffer of the respective HARQ process may are combined with the received
708 retransmission of the protocol data unit prior to decoding 709. If the decoding has
been successful, mobile station MS1 sends 710 a positive acknowledgement (ACK) to
base station NB1. If decoding of the protocol data unit is not successful, a NACK may be
sent and - if soft-combining is utilized - the received (shared) downlink physical channel
information of the retransmission may also be stored in the associated HARQ soft buffer
for later soft-combining with another retransmission.
The operation of mobile station MS1 and base station NB1 described above with respect
to Fig. 7 is exemplified in further detail in the flow charts shown in Figs. 9 and 10. Fig. 9
shows a flow chart of an exemplary operation of a base station according to one
embodiment of the invention, and Fig. 10 shows a flow chart of an exemplary operation
of a mobile station according to an exemplary embodiment of the invention using
scheduling mode 1.
In Fig. 9, upon receiving a new protocol data unit for transmission at the MAC protocol
entity of base station NB1 for transmission to mobile station MS1, the scheduling unit of
base station NB1 first determines 901 the scheduling mode that is to be used for the new
protocol data unit.

In case the protocol data unit is to be transmitted using scheduling mode 1, base station
NB1 transmits 902 the protocol data unit to mobile station MS1 (without control signaling)
in a similar fashion as described with respect to step 702 of Fig. 7 using a resource
allocation and transport format combination that has been for example pre-configured or
configured by a special L1/L2 control channel format or higher layer protocol (see step
701 in Fig. 7).
If the protocol data unit is to be transmitted using scheduling mode 2, base station NB1
selects the appropriate resource allocation and transport format for the transmission of
the protocol and generates 903 a L1/L2 control channel signal indicating the selected
resource allocation and transport format for the protocol data unit and not setting the
code point value in the field in order to indicate scheduling mode 2 to mobile station
MS1. Next, base station NB1 transmits 904 the generated control channel signal and the
protocol data unit to mobile station MS1.
In an exemplary embodiment of the invention, it is assumed that a L1/L2 control channel
in case of scheduling mode 2 contains at least the information depicted in Table 2 and
has one of the control channel formats shown in Fig. 4. The upper control channel format
in Fig. 4 is indicating the minimum content of the control channel signal according to the
exemplary definition in Table 2. The second control channel format at the bottom of Fig.
4 comprises the same control channel information as the upper control channel format
and optional additional information, such as e.g. power control for Physical Uplink
Control CHannel (PUCCH,) - e.g. for CQI (Channel Quality Indicator) or ACK/NACK -
precoding information, transport format information for 2nd codeword, HARQ information
for 2nd codeword may be also contained. This additional information may vary in size as
indicated by the question mark in Table 2.
Returning to Fig. 9, irrespective of the scheduling mode, base station NB1 may receive
905 a feedback for the initial transmission of the protocol data unit. Accordingly, base
station NB1 determines 906 based on the feedback from mobile station MS1, whether
the protocol data unit could be successfully decoded at mobile station MS1. If so, the
next protocol data unit may be sent.
If no successful decoding of the protocol data unit is indicated by the feedback message,
base station NB1 selects the appropriate resource allocation and transport format for the
transmission of the protocol data unit (typically the transport block size is constant for all
transmissions of a protocol data unit) and generates 907 a L1/L2 control channel signal
indicating the selected resource allocation and transport format for the protocol data unit
and setting an appropriate value in the field that is used to indicate the scheduling mode
io mobile station MSI. Here, the L1/L2 controi channel signal format may depend on the
utilized scheduling mode for the protocol data unit.
In case of utilizing scheduling mode 1, the generated L1/L2 control channel signal may
for example comprise the resource allocation for the already sent initial transmission (see
block 902) and the retransmission of the protocol data unit to be sent as well as the
transport format for the initial transmission and the retransmission of the protocol data
unit (which should however not change or could be calculated from each other in typical
cases). The indication of the resource allocation and transport format of the initial
transmission in the controi channel signai sent for the retransmission of the protocol data
unit may be used by mobile station MS1 to again try decoding the initial transmission
(stored in the HARQ buffer) using the control channel information, but is typically used to
properly combine the current retransmission with the correct content from the HARQ
buffer.
In case of utilizing scheduling mode 2 for the protocol data unit the control channel
information may have a similar content to those generated and sent in steps 903 and
904. Alternatively, the control channel signal may be formed for initial transmissions and
retransmissions of a protocol data unit as described in European patent application no.
EP 07024829.9 mentioned previously herein.
Upon having generated 907 the control channel signal associated to the retransmission
of the protocol data unit, the control channel signal and the retransmission of the protocol
data unit is transmitted 908 by base station NB1.
Fig. 10 shows a flow chart of an exemplary operation of a mobile station according to an
exemplary embodiment of the invention using scheduling mode 1. In a first step, mobile
station MS1 receives 1001 a subframe from the (shared) downlink physical channel. For
example due to a persistent allocation or reservation of resources on the (shared)
downlink physical channel, mobile station MS1 is aware of a potential user transmission
occurring in the subframe and performs a blind detection 1002 on the information
received from the physical channel by testing the resource allocations and transport
formats candidates that have for example been configured previously.
In case the blind detection is successful, i.e. the protocol data unit could be successfully
decoded by mobile station MS1, mobile station MS1 transmits 1004 a positive
acknowledgement (ACK) to base station NB1. If blind detection 1002 is not successful,
i.e. no matching resource allocation and transport format is found (e.g. due to a
transmission error in the received information of the physical channel), mobile station
MS1 transmits 1005 a negative acknowledgement to base station NB1 to indicate the
unsuccessful decoding of the initial transmission. Optionally, in case the HARQ protocol
supports soft-combining, mobile station MS1 stores 1006 the received physical channel
information (e.g. the soft values of the individual modulation symbols or the log-likelihood
ratios (LLRs) of the channel bits) for soft-combining with the retransmissions in the
HARQ buffer region associated to the protocol data unit's HARQ process.
After having sent a negative acknowledgement, mobile station MS1 further receives
another subframe 1007 of the (shared) downlink physical channel. This subframe
comprises a L1/L2 control channel signal that is indicating control channel information for
the initial transmission and the retransmission of the protocol data packets, as for
example described with respect to Figs. 5 and 6 below. Upon successfully obtaining
1008 the control channel signal, mobile station MS1 may perform 1009 a soft-combining
of the buffered physical channel information of the initial transmission and the physical
channel information of the retransmission contained in the subframe received in step
1007 prior to decoding the protocol data unit. If it is determined 1010 by mobile station
MS1 that the protocol data unit could be successfully decoded, mobile station MS1
transmits 1011 a positive acknowledgement to base station NB1. Otherwise it transmits
1012 a negative acknowledgement and stores the physical channel information of the
retransmission contained in the subframe received in step 1007 in the HARQ buffer
region of the process used for transmitting the protocol data unit.
As indicated previously herein, a code point may be defined in the HARQ process field of
the control channel signal. In this example, the control channel signal is assumed to have
a control channel field for signaling the HARQ process number of the protocol data unit.
Fig. 5 shows an exemplary L1/L2 control channel signal according to one embodiment of
the invention in which a HARQ filed is used to indicate a scheduling mode, and in which
the use of the TF/RV/NDI field in the control channel signal is depending on the
scheduling mode.
For scheduling mode 2, the TF/RV/NDI field is indicating the transport format (TF), the
redundancy version (RV) and the new data indicator (NDI). These parameters of the
control channel may be for example jointly encoded as exemplarily illustrated in Fig. 5
and as described in European patent application no. EP 07024829.9. Alternatively, these
parameters of the protocol data unit may also be encoded separately in individual fields,
or only the transport format and the redundancy version of the protocol data unit may be
jointly encoded as also described in European patent application no. EP 07024829.9.
In order to allow for a reasonable soft buffer management, for data transmitted with
scheduling mode 1 it may be beneficial to reserve a certain HARQ process out of the
existing processes, In this case, a preconfigured process ("code point"), e.g. 111, may be
used to indicate that the L1/L2 control channel has the format of scheduling mode 1.
In one exemplary embodiment, the resource assignment field is unchanged for
scheduling mode 1 and 2, since this allows for having full flexibility for the resource
allocation of the retransmission. Also the CRC/UE ID field (comprising the CRC
checksum masked with the identifier of the mobile station or group of mobile stations to
which the control channel information is destined) is not changed in the control channel
signal format for scheduling mode 1 and scheduling mode 2, since it may be required to
identify the targeted mobile station(s) and to prevent other mobile stations from reading
the content of the given control channel.
In the example shown in Fig. 5, the content/interpretation of the TF/RV/NDI field(s) is
(are) is depending on the scheduling mode. Using scheduling mode 1 for the
transmission of the protocol data unit, the control channel signal comprises a resource
assignment (RA) field indicating the resource block(s) of the subframe carrying the
protocol data unit (note that the resource assignment may have changed between initial
and retransmission). In this example, the resource allocation field has the same size as
in the control channel format for scheduling mode 2. As the transport block size of the
retransmission may be assumed identical to same for the initial transmission this
information may be encoded and obtained from the subsequent control channel field
providing information on the initial transmission.
Further, the control channel signal comprises the before mentioned field providing
information on the initial transmission (which is corresponding to the TF/RV/NDI field of
the format for scheduling mode 2 in its position in the control channel signal and the field
size). This field may for example be used to indicate the transport format (transport block
size) and redundancy version of the initial transmission. For scheduling mode 1 no NDI is
required, as the control channel signal is only sent for retransmissions. Therefore, in
comparison to the format for scheduling mode 2, the entire field can be used for control
information on the initial transmission. The control information on the transport format
and the redundancy version may be jointly encoded in the control channel field providing
information on the initial transmission. Alternatively, the control channel field providing
information on the initial transmission may be divided into separate sub-fields for the
transport format and the redundancy version. Alternatively, the control channel field
providing information on the initial transmission may only contain the transport format
and a redundancy version may not be required.
For scheduling mode 1, the code point "111" is set in the HARQ process field to indicate
on the one hand the HARQ process number of the protocol data unit and on the other
hand scheduling mode 1 being used for the transmission of the protocol data unit.
For scheduling mode 2, the HARQ process field indicates the appropriate HARQ process
number and thus implicitly indicates scheduling mode 2 being used for the transmission
of the protocol data unit and the corresponding control channel format.

In an alternative embodiment of the invention, the size and position of some fields
(except for the field(s) defining the code point(s)) in the control channel format may differ
for the different scheduling modes. This is exemplified in Fig. 6 showing another
exemplary L1/L2 control channel signal according to one embodiment of the invention in
which a HARQ filed is used to indicate a scheduling mode, and in which the use of the
resource assignment (RA) field and the TF/RV/NDI field in the control channel signal is
depending on the scheduling mode. Essentially, the formats of the control channel for
scheduling modes 1 and 2 in terms of the fields contained in the control channel signal
corresponds to the examples shown in Fig. 5. However, the size of the resource
assignment field is changed for scheduling mode 1 in comparison to the format of
scheduling mode 2. The same is true for size and use of the TF/RV/NDI field(s) in the
scheduling mode 2 control channel format.
In the example shown in Fig. 6, the resource assignment field for scheduling mode 1 is
smaller than the corresponding field for scheduling mode 2. This design is based on the
assumption that for scheduling mode 1 not all possible resource assignments (as for
scheduling mode 2) are needed to the retransmission of scheduling mode 1, since e.g.
only relatively small allocations are used for scheduling mode 1 or since a reduced
number of different allocations with the same allocation size are sufficient. Accordingly,
more control information bits may be assigned to the field indicating the control channel
information for the initial transmission of the protocol data unit.
In another embodiment, another field than the HARQ process field of the control channel
signal is used to define a code point. For example, the control channel signal may
comprise a separate field indicating the transport format of the protocol data unit (TF
field). According to this embodiment, a single value respresentable by the bits of the TF
field is reserved as a code point to indicate the use of scheduling mode 1 for the
transmission of the protocol data unit. Further, in a variation of this embodiment, the RV/
NDI field may be used in the control channel signal to jointly encode the redundancy
version and the new data indicator for the protocol data unit.
In another embodiment multiple TF "code points" may be reserved, as exemplarily shown
in Table 3 below. Assuming that the number of required transport formats (e.g. Transport
Block Sizes or MCS levels) for scheduling mode 1 is limited, this allows for determining
the TBS or MCS level from the (pre-)configured candidates with a relatively small loss of
TF values for scheduling mode 2. For example, if the TF field has 6 bits and 8 TBS
values are preconfigured for scheduling mode 2, only 8 out of 64 TF values are "lost" for
scheduling mode 1. In addition, the signaling of one of these "code points" could indicate
the change of usage of all or part of the remaining control channel fields as described
above.

Also in case the transport format is jointly encoded with the redundancy version of the
protocol data unit as described in European patent application no. EP 07024829.9 a
code point may be defines in the joint field as shown in Table 4. In a similar fashion as
exemplified in Table 4, also multiple code points could be defined.

As a further alternative embodiment of the invention, the resource assignment field of the
control channel signal could be used for defining one or more code points in a similar
fashion as described above. In a variation of this embodiment, the resource assignment
field has a header as specified in 3GPP RAN WG1 Meeting #51 Tdoc. R1-074582,
"Downlink Resource Allocation Mapping for E-UTRA", available at http://www.3gpp.org
and incorporated herein by reference, and a specific bit combination(s) of the header bits
in the resource allocation field may be defined as a code point(s).
Similarly, in a further embodiment the L1/L2 control channel signal comprises a seoerate
RV field for indicating the redundancy version and the RV field is used to define at least
one code point.
In a further alternative embodiment of the invention, the control channel (in scheduling
mode 2) may have a field carrying power control commands for the associated downlink
data transmission (on the PDSCH), for the PUCCH or for some other channel. To
indicate scheduling mode 1 a code point of this field may be used, since for scheduling
mode 1 this field is less important or not required.
In addition to the different approaches for defining code points in a single field of the
control channel signal, individual code points may be defined in respective fields could
be reserved to indicate scheduling mode 1. In an exemplary embodiment of the
invention, a combination of the values of the resource assignment field and the TF field
may define one or more code points. In this exemplary embodiment, the resource
assignment and transport format candidates of the blind detection (in the first
transmission) can be reduced, e.g. the "code points" in the in the TF field are used to
indicate the preconfigured TBSs as shown in Table 3 and a similar scheme for reducing
the resource allocation candidates can be used in the resource allocation field. In
addition, the signaling of these "code points" could indicate the change of the usage of
part of the remaining control channel fields as described above.
Examples of mobile communication systems in which the principles of the invention
outlined herein may be utilized are communication systems utilizing an OFDM scheme, a
MC-CDMA scheme or an OFDM scheme with pulse shaping (OFDM/OQAM).
Furthermore, it should also be noted that though most embodiments of the invention
have been described with respect to subframes of a (shared) downlink physical channel
which comprise the user data transmission and the associated control channel signal for
the user data transmission, also other designs are possible in which control channel
information of a user data transmission is sent in an earlier subframe of the (shared)
downlink physical channel than that containing the user data transmission, or where
there is a separate physical control channel for the signaling of the control channel
information.
Furthermore, the (shared) downlink physical channel mentioned herein may be for
example a Downlink Shared CHannel (PDSCH) of a 3GPP LTE system.
Another embodiment of the invention relates to the implementation of the above
described various embodiments using hardware and software. It is recognized that the
various embodiments of the invention may be implemented or performed using
computing devices (processors). A computing device or processor may for example be
general purpose processors, digital signal processors (DSP), application specific
integrated circuits (ASIC), field programmable gate arrays (FPGA) or other
programmable logic devices, etc. The various embodiments of the invention may also be
performed or embodied by a combination of these devices.
Further, the various embodiments of the invention may also be implemented by means of
software modules, which are executed by a processor or directly in hardware. Also a
combination of software modules and a hardware implementation may be possible. The
software modules may be stored on any kind of computer readable storage media, for
example RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROM, DVD,
etc.
Furthermore, it should be noted that the terms mobile terminal and mobile station are
used as synonyms herein. A user equipment may be considered one example for a
mobile station and refers to a mobile terminal for use in 3GPP-based networks, such as
LTE.
In the previous paragraphs various embodiments of the invention and variations thereof
have been described. It would be appreciated by a person skilled in the art that
numerous variations and/or modifications may be made to the present invention as
shown in the specific embodiments without departing from the spirit or scope of the
invention as broadly described.
It should be further noted that most of the embodiments have been outlined in relation to
a 3GPP-based communication system and the terminology used in the previous sections
mainly relates to the 3GPP terminology. However, the terminology and the description of
the various embodiments with respect to 3GPP-based architectures is not intended to
limit the principles and ideas of the inventions to such systems.
Also the detailed explanations given in the Technical Background section above are
intended to better understand the mostly 3GPP specific exemplary embodiments
described herein and should not be understood as limiting the invention to the described
specific implementations of processes and functions in the mobile communication
network. Nevertheless, the improvements proposed herein may be readily applied in the
architectures described in the Technical Background section. Furthermore, the concept
of the invention may be also readily used in the LTE RAN currently discussed by the
3GPP.
CLAIMS:
1. A control channel signal for use in a mobile communication system providing
at least two different scheduling modes, wherein the control channel signal
comprises control information fields consisting each of a respective number of
bits,
wherein a combination of predetermined values that can be represented by
the bits of different control information fields defines a code point used for
indicating the scheduling mode for an associated transmission of user data in
form of a protocol data unit, and the control channel format to the receiver.
2. The control channel signal according to claim 1, wherein the number of bits of
the control channel signal is equal for at least two scheduling modes.
3. The control channel signal according to claim 1 or 2, wherein at least the
HARQ process field and the RV field are used to define the code point.
4. The control channel signal according to one of claims 1 to 3, wherein the
control channel fields are located at a fixed position within the control channel
signal for all control channel formats.
5. The control channel signal according to one of claims 1 to 3, wherein the
control information fields for indicating the code point comprises a HARQ
process field of the control channel signal.
6. The control channel signal according to claim 5, wherein one HARQ process
is reserved for one scheduling mode and the value represented by the bits of
the HARQ process field for indicating the reserved HARQ process defines the
code point.
7. The control channel signal according to one of claim 1 to 3, wherein the
control information field is used to indicate either a persistent scheduling
mode or a dynamic scheduling mode.
8. A scheduling unit for use in a mobile communication system providing at least
two different scheduling modes, wherein the scheduling unit is adapted to
generate and transmit a control channel signal according to one of claims 1 to
7 to at least one receiver.
9. The scheduling unit according to claim 8, wherein the scheduling unit is
adapted to transmit a control channel signal only for retransmissions of the
protocol data unit, if a first scheduling mode is used for the transmission of
user data.
10. The scheduling unit according to claim 8 or 9, wherein the scheduling unit is
adapted to utilize the first scheduling for the transmission of protocol data
units having a size below a threshold, and to utilize the second scheduling
mode for the transmission of protocol data units having a size above or equal
to the threshold.
11. The scheduling unit according to one of claims 8 to 10, wherein the
scheduling unit is adapted to generate different control channel signal formats
depending on the scheduling mode used for the transmission of user data.
12. The scheduling unit according to one of claims 8 to 11, wherein the first
scheduling mode is a persistent scheduling mode and the second scheduling
mode is a dynamic scheduling mode.
13. A base station for use in a mobile communication system, wherein the base
station comprises a scheduling unit according to one of claims 8 to 12.
14. The base station according to claim 13, further comprising a transmitter unit
for transmitting a control channel signal generated by the scheduling unit and
protocol data units comprising user data to a mobile terminal,
wherein the base station is adapted to control the transmitter unit to transmit
the control channel signal only for retransmissions of the protocol data unit, in
case a first scheduling mode out of at least two different scheduling modes is
used for the transmission of the protocol data unit.
15. The base station according to claim 14, further comprising a receiver unit for
receiving a feedback message from the mobile station, wherein the feedback
message indicates, whether a protocol data unit previously transmitted by the
base station has been successfully decoded by the mobile station.
16. The base station according to claim 15, wherein the first scheduling mode is
used for the transmission of the user data to the mobile terminal, and wherein
a feedback message received by the receiver unit for an initial transmission of
the protocol data unit carrying the user data is indicating that the protocol data
unit has not been decoded successfully by the mobile station,
the base station being adapted to cause the scheduling unit to generate a
control channel signal for a retransmission of the protocol data unit and to
cause the transmitter unit to retransmit the protocol data unit and the
generated control channel signal to the mobile station, wherein the control
channel signal indicates the transport format and the downlink physical
channel resources used for the retransmission and initial transmission of the
protocol data unit.
17. A mobile station for use in a mobile communication system and for receiving
user data on the downlink in form of protocol data units, the mobile station
comprising:
a receiver unit for receiving from a base station a sub-frame of a downlink
physical channel, and for performing a blind detection on the received sub-
frame to thereby decode an initial transmission of a protocol data unit
conveying user data within the received sub-frame, and
a transmitter unit for transmitting a negative feedback to the base station
indicating that the protocol data unit has not been decoded successfully
during blind detection,
wherein, in response to the negative feedback, the receiver unit is further
adapted to receive another sub-frame of the downlink physical channel from
the base station comprising a control channel signal according to one of
claims 1 to 7 indicating the transport format and the downlink physical
channel resources used for the retransmission and initial transmission of the
protocol data unit, and
a decoder to decode the protocol data unit based on the control channel
signal.
18. The mobile station according to claim 17, further comprising a buffer for
temporarily storing the unsuccessfully decoded initial transmission of the
protocol data unit, and wherein the decoder is adapted to perform a soft
combining of the initial transmission and the retransmission of the protocol
data unit prior to decoding.
19. A method for providing control channel signals in a mobile communication
system, the method comprising the steps performed by a base station:
generating a control channel signal according to one of claims 1 to 7, and
transmitting the generated control channel signal in a sub-frame of a physical
channel.
20. The method according to claim 19, wherein the base station transmits the
control channel signal only for retransmissions of the protocol data unit, in
case a first scheduling mode out of at least two different scheduling modes is
used for the transmission of the protocol data unit.
21. The method according to claims 20, further comprising the steps of receiving
at the base station a feedback message from a mobile station, wherein the
feedback message indicates, whether a protocol data unit previously
transmitted by the base station has been successfully decoded by the mobile
station.
22. The method according to claims according to claim 21, wherein a first
scheduling mode is used for the transmission of the user data to the mobile
terminal, and wherein a feedback message received by the receiver unit for
an initial transmission of the protocol data unit carrying the user data is
indicating that the protocol data unit has not been decoded successfully by
the mobile station, the method further comprising the steps of:
generating a control channel signal for a retransmission of the protocol data
unit,
re-transmitiing the protocol data unit and the generated control channel signal
to the mobile station, wherein the control channel signal indicates the
transport format and the downlink physical channel resources used for the
retransmission and initial transmission of the protocol data unit.
23. A method for use in a mobile communication system and for receiving user
data on the downlink in form of protocol data units, wherein the method
comprises the following steps performed by a mobile station:
receiving from a base station a sub-frame of a downlink physical channel, and
for performing a blind detection on the received sub-frame to thereby decode
an initial transmission of a protocol data unit conveying user data within the
received sub-frame,
transmitting a negative feedback to the base station indicating that the
protocol data unit has not been decoded successfully during blind detection,
receiving, in response to the negative feedback, another sub-frame of the
downlink physical channel from the base station comprising a control channel
signal indicating the transport format and the downlink physical channel
resources used for the retransmission and initial transmission of the protocol
data unit, and
decoding the protocol data unit based on the control channel signal.
24. The method according to claim 23, further comprising the steps of temporarily
storing the unsuccessfully decoded initial transmission of the protocol data
unit a buffer, and
soft combining the initial transmission and the retransmission of the protocol
data unit prior to decoding.
25. A computer-readable medium storing instructions that, when executed by a
processor of a base station, cause the base station to provide control channel
signals in a mobile communication system by:
generating a control channel signal according to one of claims 1 to 7, and
transmitting the generated control channel signal in a sub-frame of a physical
channel.
26. The computer-readable medium according to claim 25, further storing
instructions that, when executed by the processor of the base station, cause
the base station to perform the steps of the method according to one of claims
22 to 24.
27. A computer-readable medium storing instructions that, when executed by a
processor of a mobile station, cause the mobile station for receive user data
on the downlink in form of protocol data units by:
receiving from a base station a sub-frame of a downlink physical channel, and
for performing a blind detection on the received sub-frame to thereby decode
an initial transmission of a protocol data unit conveying user data within the
received sub-frame,
transmitting a negative feedback to the base station indicating that the
protocol data unit has not been decoded successfully during blind detection,
receiving, in response to the negative feedback, another sub-frame of the
downlink physical channel from the base station comprising a control channel
signal indicating the transport format and the downlink physical channel
resources used for the retransmission and initial transmission of the protocol
data unit, and
decoding the protocol data unit based on the control channel signal.
28. The computer-readable medium according to claim 27, further storing
instructions that, when executed by the processor of the mobile station, cause
the mobile station to temporarily store the unsuccessfully decoded initial
transmission of the protocol data unit a buffer, and to soft combine the initial
transmission and the retransmission of the protocol data unit prior to
decoding.

The invention relates to a control channel signal for use in a mobile communication
system providing at least two different scheduling modes. Further the invention relates to
a scheduling unit for generating the control channel signal and a base station comprising
the scheduling unit. The invention also relates to the operation of a mobile station and a
base station for implementing a scheduling mode using the control channel signal
proposed by the invention. In order to facilitate the use of different scheduling schemes
for user data transmission while avoiding an additional flag for indicating the scheduling
mode in the control signaling, the invention proposes the use of code points in existing
control channel signal fields. Further, the invention proposes a specific scheduling mode
for use in combination with the proposed new control channel signal according to the
invention. According to this scheduling mode control channel information is only provided
for retransmissions, while initial transmissions are decoded using blind detection.