Frank Burkert

On the equivalence between SOVA and max-log-MAP decodings

It is shown that after a proper simple modification, the soft-output Viterbi algorithm (SOVA) proposed by Hagenauer and Hoeher (1989) becomes equivalent to the max-log-maximum a posteriori (MAP) decoding algorithm. Consequently, this modified SOVA allows to implement the max-log-MAP decoding algorithm by simply adjusting the conventional Viterbi algorithm. Hence, it provides an attractive solution to achieve low-complexity near-optimum soft-input soft-output decoding.

Approaching Shannon's capacity limit by 0.2 dB using simple Hamming codes

The authors show that the Shannon capacity limit for the additive white Gaussian noise (AWGN) channel can be approached within 0.27 dB at a bit error rate (BER) of 10/sup -5/ by applying long but simple Hamming codes as component codes to an iterative turbo-decoding scheme. In general, the complexity of soft-in/soft-out decoding of binary block codes is rather high. However, the application of a neurocomputer in combination with a parallelization of the decoding rule facilitates an implementation of the decoding algorithm in the logarithmic domain which requires only matrix additions and multiplications. But the storage requirement might still be quite high depending on the interleavers used.

To compress or not to compress

For practical communications which transmit finite blocks of source data over noisy channels, we question the common practice to compress (C) the source and then to add redundancy for error control. Rather we exploit the redundancy of the non-compressed source (NC) at the channel decoder by source-controlled channel-decoding. For a simple binary Markov source and a Rayleigh fading channel we simulated in a fair comparison the 2 systems (C and NC) using an ARQ/FEC scheme with rate-compatible punctured convolutional (RCPC) codes, Lempel-Ziv compression and a modified Viterbi decoder. We indicate parameter regions where it is better not to compress.

Turbo decoding with unequal error protection applied to GSM speech coding

Two-dimensional, systematic and parallel concatenated convolutional codes are compatibly punctured in order to provide unequal error protection (UEP). They are iteratively decoded by the MAP algorithm and other soft-in/soft-out decoders. In a case study we replace the current GSM speech channel coding scheme by this new turbo scheme leaving all the interleaver interfaces and the total delays unchanged. It is shown that for independent and frequency-hopped Rayleigh channels and other standard GSM channels, the frame error rate and the residual BER of the class 1a bits drop by a factor of 1.4 and 2.0 respectively. Likewise the carrier to interference ratio (CIR) can be lowered by 0.8 dB at the same performance level. Contrary to the common belief that turbo codes gain only with large interleavers, we have shown that together with UEP they allow gains also with the modest interleaver sizes of the GSM scheme. All this offers a potential for a future evolutionary improvement of the GSM channel coding scheme.

Concatenated Reed-Muller codes for unequal error protection

We present a new coding scheme that combines the advantages of a product-like concatenation of Reed-Muller codes with so-called iterative turbo decoding and provides powerful unequal error protection abilities. It is shown that various levels of error protection can be realized using a sophisticated encoding scheme for Reed-Muller codes. A discussion of this code construction, the resulting distance profile between the different levels and the iterative decoding scheme is given. The results are very promising and impressively confirm the unequal error protection capabilities of the presented coding scheme.

Unequal error protection with product-like turbo codes

We present a new coding scheme that combines the advantages of a product-like concatenation of Reed-Muller codes with so-called iterative turbo decoding and provides powerful unequal error protection abilities. It is shown that various levels of error protection can be realized using a sophisticated encoding scheme for Reed-Muller codes. A discussion of this code construction, the resulting distance profile between the different levels as well as of the iterative decoding scheme is given.

Improving channel coding of the ETSI- and MPEG-satellite transmission standards

We propose the combination of two powerful decoding techniques in one concatenated coding scheme. Using turbo codes as inner codes and block codes as outer codes, and applying parallel and serial iterative decoding with feedback between the outer and the inner decoders, leads to a performance which clearly surpasses the one of common concatenated coding schemes used for deep space communications or digital TV transmissions via satellite as defined by ETSI and MPEG. At a BER of 10/sup -5/ and below, we achieve an additional decoding gain of 1.6 dB and more at the same rate and frame size as existing standards.