1:00, SPCOM-P5.1
AREA-EFFICIENT HIGH SPEED DECODING SCHEMES FOR TURBO/MAP DECODERS
Z. WANG, Z. CHI, K. PARHI
Turbo decoders inherently have a large latency and low throughput due to iterative decoding. To increase the throughput and reduce the latency, high speed decoding schemes have to be employed. In this paper, following a discussion on basic parallel decoding architectures, two types of area-efficient parallel decoding schemes are proposed. Detailed comparison on storage requirement, number of computation units and the overall decoding latency is provided for various decoding schemes with different levels of parallelism. Hybrid parallel decoding schemes are proposed as an attractive solution for very high level parallelism implementations. Simulation results demonstrate that the proposed area-efficient parallel decoding schemes introduce no performance degradation in general. The application of the pipeline-interleaving technique to parallel Turbo decoding architectures is presented at the end.

1:00, SPCOM-P5.2
A STUDY ON THE PERFORMANCE, POWER CONSUMPTION TRADEOFFS OF SHORT FRAME TURBO DECODER DESIGN
Z. CHI, Z. WANG, K. PARHI
Protecting short frames using turbo coding is a challenging task because of the small interleave size and the need for transmission efficiency. In this paper, we explore possible trade-off between power consumption and performance of turbo decoders when short frame turbo codes are used. Three encoding/decoding schemes are proposed to improve performance of turbo decoder in terms of frame/bit error rate, and to increase the data transmission efficiency whether ARQ protocols are performed or not. Specifically, turbo decoding metrics aided short CRC codes are applied to terminated trellis codes, tail-biting encoded trellis codes and CRC embedded trellis codes with a two-fold purpose: to stop the iterative decoding processes and to detect decoding errors at the last iteration. We show that significant coding gains can be achieved by actually increasing the coding rate with negligible increase in power consumption. Performance improvement is demonstrated over both AWGN and Rayleigh flat fading channels.

1:00, SPCOM-P5.3
TURBO EQUALIZATION FOR GMSK SIGNALING OVER MULTIPATH CHANNELS
X. WANG, Z. YANG
A novel receiver is derived for Gaussian minimum shift keying (GMSK) signals through a multipath channel. A nonlinear signal model is derived which avoids the linear approximation in the conventional finite impulse response(FIR) system model. A Bayesian equalizer based on the Gibbs sampler, a Markov chain Monte Carlo (MCMC) procedure, is developed for joint channel estimation and symbol detection,and finally, a Turbo equalizer structure is proposed for a coded GMSK system, in which the Bayesian equalizer successively refines its processing based on the information from the decoding stage, and vice versa.

1:00, SPCOM-P5.4
TURBO-EQUALIZATION: CONVERGENCE ANALYSIS
A. ROUMY, A. GRANT, I. FIJALKOW, P. ALEXANDER, D. PIREZ
We investigate a sub-optimal iterative receiver for joint equalization and decoding called Turbo-equalizer. We view the evolution of the error variance of the trans- mitted symbols through the iterative processing, ob- taining convergence analysis. This allows us to predict the asymptotic performance (when the Turbo-equalizer has converged) but also the trigger point observed in its performance.

1:00, SPCOM-P5.5
ITERATIVE SOURCE AND CHANNEL DECODING FOR GSM
M. KAINDL, R. PERKERT, T. HINDELANG
When transmitting speech signals, residual redundancy is still left in the signal after source coding, due to limited complexity of the coding algorithms and delay constraints. This redundancy expresses in correlations inside one frame as well as in a time correlation of subsequent speech frames. The method of iterative channel and source decoding applied in this paper is based on exploiting this redundancy in terms of a priori knowledge of the source to improve decoding of the transmitted parameters. The used source a priori information is obtained and exploited directly on parameter level. In this paper we show the application of this theory to a real world mobile communication system. Here GSM speech transmission was chosen, but the presented method could also be applied to any other system which leaves a certain amount of redundancy in the speech coded signal.

1:00, SPCOM-P5.6
ITERATIVE SOURCE-CHANNEL DECODER USING EXTRINSIC INFORMATION FROM SOFTBIT-SOURCE DECODING
M. ADRAT, J. SPITTKA, P. VARY
In digital mobile communications efficient compression algorithms are needed to encode speech or audio signals. As the determined source parameters are highly sensitive to transmission errors, robust source and channel decoding schemes are required. This contribution deals with an iterative source-channel decoding approach where a simple channel decoder and a softbit-source decoder are concatenated. We will mainly focus on softbit-source decoding which can be considered as error concealment technique. This technique utilizes residual redundancy remaining after source coding. In this paper we derive a new formula that shows how the residual redundancy transforms into the extrinsic information utilizable for iterative decoding. The derived formula opens several starting points for optimizations, e.g. it helps to find a robust index assignment. Furthermore, it allows the conclusion that softbit-source decoding is the limiting factor if applied to iterative decoding processes. Therefore, no significant gain will be obtainable by more than two iterations.

1:00, SPCOM-P5.7
JOINT SOURCE-CHANNEL TURBO DECODING OF ENTROPY-CODED SOURCES
C. GUILLEMOT, E. FABRE, A. GUYADER
We analyse the dependencies between the variables involved in the source and channel coding chain. This chain is composed of 1) a Markov source of symbols, followed by 2) a variable length source coder, and by 3) a channel coder. The output process is analysed in the framework of Bayesian networks, which provide both an intuitive representation of the structure of dependencies, and a way of deriving joint (soft) decoding algorithms. Joint decoding relying on the hidden Markov model (HMM) of the global coding chain is untractable, except in trivial cases, due to the high dimensionality of the state space. We advocate instead an iterative procedure inspired from serial turbo codes, in which the global model is processed by parts: a joint decoding of 1/ + 2/ is done in alternance with a decoding of 3/. This idea of using separately each factor of a big product model inside an iterative procedure can be pushed further: one can also decompose the joint model of source + source coder. The Bayesian network representation shows that iterations are useless in this latter case: a sequential use of the two models is optimal. As a subproduct, we also derive a soft VLC decoder with good (and adjustable) synchronization properties.

1:00, SPCOM-P5.8
TURBO SPACE-TIME EQUALIZATION OF TCM FOR BROADBAND WIRELESS CHANNELS
M. KOCA, B. LEVY
This paper presents a turbo (iterative) equalization method for complex TCM signals over broadband wireless channels based on receiver antenna array measurements. The channel is highly dispersive at high data rates causing a severe intersymbol intereference (ISI) effect and making the direct application of any trellis based equalization algorithm infeasible. The problem of reducing this excess interference is solved by receiver diversity combining, i.e. using a linear antenna array and a broadband beamformer in the receiver. The beamformer output that contains less ISI is viewed as the output of a serial concatenated coding system and optimum symbol detection is achieved by a turbo equalization and decoding scheme. The proposed receiver structure is simulated for two dimensional TCM signals such as 8-16 PSK and 16-QAM and the results indicate an improved performance of the diversity receiver.