Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-12-07
2001-05-15
Baker, Stephen M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S794000
Reexamination Certificate
active
06233709
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to decoding of a coded information signal in a telecommunications system and, more particularly, to a method and apparatus for iterative decoding of a coded information signal that allows quality of service parameters to be dynamically balanced in a telecommunications system.
BACKGROUND OF THE INVENTION
Multidimensional coding, or turbo coding, and associated iterative decoding methods have increasingly important application as data transmission services grow in sophistication. For example, next generation wireless communications systems currently under development are expected to support internet-based services, such as e-mail and web browsing. It has been proposed for at least some of these wireless communications systems to utilize turbo coding for the higher speed data transmission of the system.
A turbo decoder decodes an encoded signal by recursively processing frames of the encoded signal using more than one iteration through the decoder, as described, for example, by Berrou in “New Shannon Limit Error-correcting and Decoding: Turbo-codes (1)” Proceedings ICC 1993, pp. 1064-1070, and by Berrou and Glavieux in “Turbo-codes: General Principles and Applications,”
Audio and Video Digital Radio Broadcasting Systems and Techniques,
1993, pp. 215-226.
Several schemes have been presented in the literature for improving the performance of iterative decoders. U.S. Pat. No. 5,761,248, “Method and Arrangement for Determining an Adaptive Abort Criterion in Iterative Decoding of Multi-Dimensionally Coded Information,” Hagenover, et al., discloses a method and apparatus for comparing a weighted decision on a soft output of a substep of iterative decoding to a weighted decision on a soft output and a combination of previous subsets of iterating and aborting the iterative decoding dependent on the comparison result. The publication,
Variable Latency Turbo Codes for Wireless Multimedia Applications
,” by C. Valenti and D. Woerner, Proceedings of International Symposium on Turbo Codes and Related Topics, Brest, France, September 1997, pp. 216-219, disclosed the use of interleavers of variable sizes to achieve different quality of service, QoS, requirements.
Each of the above methods has its drawbacks. Using the first approach, there is no adaptive QoS consideration. With the second approach, using different interleavers for QoS may be difficult due to incompatibility with specifications of transmission frames per data rate. It also requires both the transmitter and receiver to change interleavers frequently, which is undesirable.
SUMMARY OF THE INVENTION
The present invention provides an iterative decoder that allows quality of service, QoS, parameters to be dynamically balanced. By dynamically adjusting the number of iterations, N, within an appropriate range, a coded information signal may be iteratively decoded so that at least one quality of service parameter remains within an acceptable performance range.
In an embodiment of the invention, the invention is implemented in an iterative decoder that performs iterative decoding on a coded information signal based on minimum, N
min
, and maximum, N
max
, values for the number of decoding iterations, N, to be performed for a particular data transmission, with N
min
and N
max
determined according to QoS requirements. QoS requirements for a particular data service may be expressed in terms of a maximum delay, Tdelay, and a maximum bit error rate (BER). The BER and maximum Tdelay may then be used to determine N
min
and N
max
for decoding the coded information signal. The determination of N
min
and N
max
may be made based on data tables stored in memory that include data on BER versus N and Tdelay versus N for a particular decoder configuration to be used in the iterative decoder.
In the embodiment, the iterative decoder receives the coded information signal in the form of data frames over a data transmission channel. For each data frame, N
min
iterations of decoding are performed. After N
min
iterations are performed, a convolutional redundancy code (CRC) check is performed on the decoded results of N
min
iterations. If the CRC check indicates that the data frame has been correctly decoded, the iterative decoder outputs the result and processes the next frame. If the CRC check indicates that the data frame has not been correctly decoded, the iterative decoder performs at least one other decoding iteration and CRC check. The decoding iterations are repeated until the CRC check indicates that the data frame has been correctly decoded or until the number of iterations is equal to N
max
. If the number of iterations becomes equal to N
max
, the data frame is considered in error and discarded and the decoding is begun on the next data frame. The iterative decoder may be configured to initiate transmission of a frame retransmit request to the transmitter if the data frame is discarded.
REFERENCES:
patent: 5563897 (1996-10-01), Pyndiah et al.
patent: 5673291 (1997-09-01), Dent
patent: 5729560 (1998-03-01), Hagenauer et al.
patent: 5734962 (1998-03-01), Hladik et al.
patent: 5761248 (1998-06-01), Hagenauer et al.
Hong et al., “VLSI Design and Implementation of Low-Complexity Adaptive Turbo-Code Encoder and Decoder for Wireless Mobile Communication Applications”, SIPS '98, Oct. 1998, pp. 233-242.*
Hong et al., “VLSI Circuit Complexity and Decoding Performance Analysis for Low-Power RSC Turbo-Code and Iterative Block Decoders Design”, MILCOM 98, Oct. 1998, pp. 708-712.*
Mathew C. Valenti and Brian D. Woerner, “Variable Latency Turbo Codes for Wireless Multimedia Applications”.
Claude Berrou, Alain Glavieux and Punya Thitimajshima, “Near Shannon Limit Error-Correcting Coding and Decoding: Turbo-Codes,” (2/93).
Hsu Liangchi
Zhang Vicki Ping
Baker Stephen M.
Nokia Mobile Phones Ltd.
Rivers Brian T.
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