Optimizing channel coding for orthogonal multiple access schemes with correlated sources

Abstract

Abstract-In this paper, we consider multiple access schemes with correlated sources. Distributed source coding is not used; rather, the correlation is exploited at the access point (AP). In particular, we assume that each source uses a channel code to transmit, through an additive white Gaussian noise (AWGN) channel, its information to the AP, where component decoders, associated with the sources, iteratively exchange soft information by taking into account the correlation. The key goal of this paper is to investigate whether there exist optimized channel codes for this scenario, i.e., channel codes which guarantee a desired performance level (in terms of average bit error rate, BER) at the lowest possible signal-to-noise ratio (SNR). A twodimensional extrinsic information transfer (EXIT) chart-inspired optimization approach is proposed. Our results suggest that by properly designing serially concatenated convolutional codes (SCCCs), the theoretical performance limits can be approached better than by using parallel concatenated convolutional codes (PCCCs) or low-density parity-check (LDPC) codes. It is also shown that irregular LDPC codes tend to perform better than regular LDPC codes, so that the design of appropriate LDPC codes remains an open issue.

Density evolution-based analysis and design of LDPC codes with a priori information

“…In [16], recursive nonsystematic convolutional encoders are proposed as constituent encoders for heavily biased sources, obtaining a performance between 0.74 dB and 1.17 dB from the Shannon limit. In [17], we show how turbolike codes allow to achieve a performance better than "simple" (either regular or irregular) LDPC codes in scenarios with correlated sources.…”

“…Density evolution, based on the assumption of Gaussian input distributions, has been widely used to analyze and design LDPC codes with good performance for classical point-to-point communication applications, e.g., communications over AWGN channels or binary erasure channels (BECs) [19], [20]. While in [17] simulations are considered for the LDPC-coded case, we now derive a density evolutionbased performance analysis framework, which significantly extends the results in [17]. In particular, we determine the exact two-dimensional signal-to-noise ratio (SNR) feasible region, where the proposed schemes guarantee error-free performance.…”

“…The convergence threshold is also computed for different classes of LDPC codes and proper design guidelines are derived. Although the degree distributions of both variable and check nodes can be optimized, we will show that the performance of LDPC-coded multiple access schemes is still far from that of previously optimized turbo-like coded multiple access schemes [17]. This paper is structured as follows.…”

Orthogonal multiple access and information fusion: How many observations are needed?

“…In this section, following the approaches introduced in [15], [16] (AWGN scenario) and in [17] (block fading), we try to gain insight on the impact of the number of correlated observations on the performance of JCD. This is expedient to understand the benefits (performance-wise) of the use of correlation in the decoding phase, before fusion.…”

“…This is expedient to understand the benefits (performance-wise) of the use of correlation in the decoding phase, before fusion. In order to derive theoretical performance limits, in the AWGN case we utilize the concept of feasible capacity region introduced in [15], [16], whereas in the block fading case we introduce the concept of outage feasible capacity region, which represents the feasible capacity region for a given (acceptable) outage probability.…”