Pulse or digital communications – Transmitters
Reexamination Certificate
2001-05-10
2003-03-04
Chin, Stephen (Department: 2634)
Pulse or digital communications
Transmitters
C375S240270, C714S755000, C714S748000
Reexamination Certificate
active
06529561
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of transmitting data in a radio system from a transmitter to a receiver, and to a radio system, a radio transmitter and a radio receiver using the method. The use of the method is described in EGPRS (Enhanced General Packet Radio Service).
BACKGROUND OF THE INVENTION
EGPRS (Enhanced General Packet Radio Service) is a system based on GSM (Global System for Mobile Communications) utilising packet- switched transmission. EGPRS employs EDGE (Enhanced Data Rates for GSM Evolution) technique in order to increase data transmission capacity. In addition to GMSK (Gaussian Minimum-Shift Keying) modulation normally used in the GSM, 8-PSK (8-Phase Shift Keying) modulation can be used for packet data channels. The purpose is mainly to implement non-realtime data transmission services, such as copying files and use of an Internet browser, but also real-time services as packet-switched services for transmitting speech and video, for example. In principle, data transmission capacity can vary from a few kbit/s up to 400 kbit/s.
Also other procedures are used in order to increase capacity, for example blind detection of modulation, link adaptation and incremental redundancy.
Blind detection of modulation means that it is not necessary to signal to a receiver which modulation method is being used but the receiver detects the modulation method when it receives a signal.
Link adaptation refers to changing the code rates of blocks to be transmitted on the basis of measurements carried out on the channel. The code rate can be changed between retransmissions of the same block. Another alternative is to change the code rate between successive blocks, provided, however, that all transmissions of a single block are coded by the same code rate. The purpose is to optimize the use of radio resources taking instantaneous variations in the conditions of the radio interface into account. The purpose is to optimize user data throughput and to minimize delay.
The code rate of a block refers to the ratio of the number of user data bits to the coded data bits of a channel. If, for example, 100 user data bits are coded into 200 data bits to be transmitted over the channel, the code rate obtained is 100/200=½.
FIG. 3A
shows examples of changing the code rate of a block. In
FIG. 3A
, a data block to be transmitted is shown above the X-axis, and blocks transmitted actually over the radio link are shown below the X-axis. The Y-axis denotes passage of time. Block sizes are scaled in accordance with each other, i.e. the larger the block, the more bits to be transmitted said block comprises.
A block A
300
is to be transmitted over the radio link. First transmission
302
fails, so the transmission is repeated
304
. Link adaptation was not carried out, since as can be seen from
FIG. 3A
, the blocks
302
,
304
are equal in size. The code rate in both transmissions
302
,
304
is
1
.
In comparison with the transmission of the block A
300
, link adaptation is carried out in the transmission of a block B
306
by changing the amount of user data. Compared with the block A
300
, it is detected that the size of the block B
306
is reduced by half. The code rate of a block
310
to be transmitted has been reduced to ½.
Another way to carry out link adaptation is to change the size of a data block to be transmitted over the radio link. Compared with the transmission of the block A
300
, in the transmission of a block C
312
link adaptation is carried out by changing the size of the data block to be transmitted. The code rate of a block
316
to be transmitted is ½since the size of the data block to be transmitted over the link has been doubled.
Under favourable conditions, for example, coding can be reduced, which means that more user payload can be transferred. Similarly, one modulation method can be better suited than the other to certain conditions on the radio interface. Different combinations of modulation and channel coding can be called modulation and coding schemes MCS.
If the coding conditions of a channel change extremely rapidly, it is impossible for the system to optimally select the code rate for the forthcoming transmission in advance. Incremental redundancy enables better adaptation to changing conditions. In incremental redundancy, a receiver is equipped with a memory to store the bits of radio blocks that have been received erroneously. Retransmitted radio blocks are then combined with the stored radio blocks, whereafter the receiver attempts to decode the block. Since there are more coded channel data bits to be used for decoding after the combining and the number of user data bits remains the same, the effective code rate of the block is decreased after retransmission, which makes decoding more feasible. An example of such a protocol is the hybrid FEC/ARQ (Forward Error Correction/Automatic Repeat Request), which uses error correction coding in order to decrease the number of retransmissions.
The effective code rate of the channel is adapted automatically since the channel conditions determine the number of necessary retransmissions, which in turn determines the code rate.
FIG. 3A
shows the simplest retransmission method for a data block D
318
to be transmitted. An original transmission
320
is carried out by a code rate
1
, and a first retransmission
322
also by a code rate
1
. After the first retransmission the code rate of the combined data block is ½. A second retransmission would yield a code rate ⅓, a third retransmission a code rate ¼, and this could be continued until it would be possible to decode the combined data block.
The problem with the retransmission method disclosed is that the effective code rates are quantized with relatively large steps: after one retransmission the code rate is only half of the original. This means that the capacity of the system is wasted since a smaller reduction in the code rate would often be sufficient. A solution that has been provided discloses a method wherein the data block to be transmitted is divided into sub-blocks, for example into two sub-blocks, the number of the sub-blocks being denoted by D, which is described in
FIG. 3A
by a block E
324
. The code rate used in the transmission of an original block
326
is
2
. After a first retransmission
328
the code rate is
1
, after a second retransmission
330
the code rate is ⅔, after a third retransmission the code rate would be ½, after a fourth retransmission the code rate would be ⅖. The drawback of this method is that even under ideal channel conditions transmission of at least D data block(s) is necessary before the data block can be decoded, i.e. the code rate must be 1 at most.
BRIEF DESCRIPTION OF THE INVENTION
An object of the invention is thus to provide a method and an apparatus implementing the method so as to enable efficient simultaneous utilization of link adaptation and incremental redundancy. This is achieved by the method disclosed below of transmitting data in a radio system from a transmitter to a receiver, the method comprising: channel coding a data block into a coded data block by using a selected channel coding; puncturing the coded data block by using a first puncturing pattern; transmitting the coded data block punctured by the first puncturing pattern to the receiver; detecting a need for retransmission of the received coded data block; transmitting a retransmission request of the coded data block to the transmitter. The method further comprises: increasing the code rate of the coded data block to be retransmitted by puncturing the coded data block coded by the channel coding of the original transmission by using a second puncturing pattern comprising fewer symbols to be transmitted than the first puncturing pattern; transmitting the coded data block punctured by the second puncturing pattern to the receiver; combining the received coded data block punctured by the first puncturing pattern and the received coded data block punctured
Chin Stephen
Kim Kevin
Nokia Networks Oy
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