Polar-coded Sparse Code Multiple Access Research Articles

Sparse Neural Network for Detection and Decoding of Non-Binary Polar-Coded SCMA

Sparse code multiple access (SCMA) and polar codes have demonstrated superiority in supporting massive connections and short-packets, which are essential in the uplink transmission of the internet of things. This paper proposes a sparse neural network (SNN) for the detection and decoding of the non-binary polar-coded SCMA. The network consists of the message passing algorithms (MPA) and the sparse belief propagation (SBP) modules, which are immigrated from the MPA and BP algorithms, respectively. The nodes of the bipartite BP factor graph that do not contribute to the belief propagation are pruned to form the SBP module. A structure factor α defined by the ratio of the number of layers in the MPA modules and that of the SBP modules is analyzed to find a balance between the decoding performance and the complexity. The weights are set on the neurons of the layers and trained by the stochastic gradient descent. Finally, the simulation results show substantial improvements in bit error rate with low complexity over the traditional receiver. Specifically, the SNN receiver outperforms the traditional receiver by 2.56 dB in the AWGN channel when the code length is 16, the code rate is 1/2, and the user overloading factor is 150%.

An Ultra-Reliable Low-Latency Non-Binary Polar Coded SCMA Scheme

The joint transmission scheme of polar codes and sparse code multiple access (SCMA) has been regarded as a promising technology for future wireless communication systems. However, most of the existing polar-coded SCMA (PC-SCMA) systems suffer from high latency caused by the feedback iteration and list decoding. In addition, the error performance of PC-SCMA systems is unsatisfactory for ultra-reliable transmission. Inspired by the compelling benefits of non-binary polar codes, in this paper, we design a non-binary polar-coded SCMA (NB-PC-SCMA) system with a free order matching strategy to address the issues of delay and reliability. Specifically, we first formulate a joint factor graph for NB-PC-SCMA and propose a non-binary successive cancellation list (NB-SCL) and damping based joint iterative detection and decoding (NSD-JIDD) multiuser receiver to improve the BER and latency performance. Then, a lazy-search based NB-SCL (L-NB-SCL) decoding is proposed to reduce the computational complexity by simplifying the path search pattern of the list decoder. After that, we modify the update of user nodes for SCMA detection to improve the convergence error and finally propose the improved NSD-JIDD (ISD-JIDD) algorithm, which can avoid redundant operations by exploiting L-NB-SCL decoding. Simulation results show that the proposed NB-PC-SCMA system achieves better bit error rate (BER) performance and considerable latency gain when compared to its counterparts. In particular, the proposed ISD-JIDD can achieve similar BER performance of NSD-JIDD with less complexity.

Iterative Receiver Design for Polar-Coded SCMA Systems

An edge-cancellation-aided iterative detection and decoding (EC-IDD) algorithm is proposed for polar-coded sparse code multiple access (SCMA), which jointly performs Gaussian-approximated message passing (GA-MP) detection of SCMA supported by the soft list decoding (SLD) of polar codes. A reduced-edge factor graph is formulated in each consecutive iteration with the aid of the cyclic redundancy check (CRC) and EC. Based on the simplified factor graph, the EC-IDD gradually reduces its complexity in each subsequent iteration, while improving the bit error rate (BER) performance, compared to the state-of-the-art joint detection and decoding (JDD) of polar-coded SCMA. Furthermore, an embedded decision-directed channel estimator (DD-CE) is proposed for our polar-coded SCMA system under realistic imperfect channel state information (CSI). Our simulation results demonstrate that the proposed EC-IDD achieves better BER performance than the state-of-the-art JDD under both perfect and imperfect CSI, despite achieving a complexity reduction of 92%. Finally, the BER of the proposed joint DD-CE and EC-IDD algorithm under imperfect CSI converges to that of EC-IDD operating under perfect CSI.

Improving Polar-Coded SCMA System by Information Coupling and Parity Check.

In this paper, the uplink information-coupled polar-coded sparse code multiple access (PC-SCMA) system is proposed. For this system, we first design the encoding method of systematic joint parity check and CRC-aided (PCCA) polar code. Using the systematic PCCA-polar code as base code, the partially information-coupled (PIC) polar code is constructed. Then, a joint iterative detection and successive cancellation list (SCL)-decoding receiver is proposed for the PC-SCMA system. For the receiver, the coupled polar decoder’s extrinsic messages are calculated by the Bayes rule and soft cancellation (SCAN) algorithm. Based on the extrinsic information transfer (EXIT) idea, the PIC PCCA-polar code is optimized. Simulation results demonstrate that the PIC PCCA-PC-SCMA system outperforms the other polar (or LDPC) coded SCMA systems at various code rates and channel configurations. Additionally, compared with an uncoupled PC-SCMA system with SCL decoder, the complexity of PIC PCCA-PC-SCMA is reduced at a high

The optimization scheme for joint iterative detection and decoding of polar coded SCMA system

Abstract Polar coding and sparse code multiple access (SCMA) technique are excellent candidates for 5G, and have a promising prospect in optical communication, the joint design of polar coded sparse code multiple access (PC-SCMA) system is important to enhance the overall system performance. In this paper, a serial joint iterative detection and decoding scheme is proposed by passing message between serial max-log message passing algorithm and soft cancellation (SCAN) algorithm, the strategy can accelerate the algorithm convergence speed by reducing the number of required iterations, decrease the computational complexity and achieve ideal bit error rate (BER) performance. In order to further improve the BER performance, a cyclic redundancy check (CRC) is added in the joint iterative process as an early stopping criterion to avoid decoding divergence caused by a low signal to noise ratio (SNR). Simulation results demonstrate that the addition of a termination mechanism can obtain an excellent performance gain compares with the conventional JIDD algorithm.

Joint Channel Estimation and Decoding for Polar Coded SCMA System Over Fading Channels

Sparse code multiple access (SCMA) and polar codes are key techniques for 5G systems. Towards to the realization of massive machine type communications (mMTC) in Internet of Things (IoT), we propose a joint channel estimation and decoding (JCD) scheme to enhance the performance of polar coded SCMA system. There are three parts in our JCD scheme. First, a sparse Bayesian learning (SBL) algorithm is proposed to measure the initial channel state information (CSI) for the JCD scheme. Then, the JCD receiver performs an iterative channel estimation and detection and decoding (ICED) scheme between the SCMA detector and the polar decoder, where the log-likelihood ratio (LLR) from SCMA detector and polar decoder can iteratively update, and the channel gain is also adjusted by the frozen bit error rate (FBER) from the polar decoder in each ICED iteration. In addition, we propose a soft successive cancellation list (soft-SCL) decoding algorithm by calculating the path metric from an LLR based logarithm method, then the soft-SCL decoder outputs the LLR information and the SCMA detector can update the symbol probability in this ICED scheme. Simulation results demonstrate the superior performance of our JCD scheme over fading channels.

Polar coded iterative multiuser detection for sparse code multiple access system

Polar coded sparse code multiple access (SCMA) system is conceived in this paper. A simple but new iterative multiuser detection framework is proposed, which consists of a message passing algorithm (MPA) based multiuser detector and a soft-input soft-output (SISO) successive cancellation (SC) polar decoder. In particular, the SISO polar decoding process is realized by a specifically designed soft re-encoder, which is concatenated to the original SC decoder. This soft re-encoder is capable of reconstructing the soft information of the entire polar codeword based on previously detected log-likelihood ratios (LLRs) of information bits. Benefiting from the soft re-encoding algorithm, the resultant iterative detection strategy is able to obtain a salient coding gain. Our simulation results demonstrate that significant improvement in error performance is achieved by the proposed polar-coded SCMA in additive white Gaussian noise (AWGN) channels, where the performance of the conventional SISO belief propagation (BP) polar decoder aided SCMA, the turbo coded SCMA and the low-density parity-check (LDPC) coded SCMA are employed as benchmarks.

Design and Optimization of Joint Iterative Detection and Decoding Receiver for Uplink Polar Coded SCMA System

SCMA and polar coding are possible candidates for 5G systems. In this paper, we firstly propose the joint iterative detection and decoding (JIDD) receiver for the uplink polar coded sparse code multiple access (PC-SCMA) system. Then, the EXIT chart is used to investigate the performance of the JIDD receiver. Additionally, we optimize the system design and polar code construction based on the EXIT chart analysis. The proposed receiver integrates the factor graph of SCMA detector and polar soft-output decoder into a joint factor graph, which enables the exchange of messages between SCMA detector and polar decoder iteratively. Simulation results demonstrate that the JIDD receiver has better BER performance and lower complexity than the separate scheme. Specifically, when polar code length $N=256$ and code rate $R = 1/2$ , JIDD outperforms the separate scheme 4.8 and 6 dB over AWGN channel and Rayleigh fading channel, respectively. It also shows that, under 150% system loading, the JIDD receiver only has 0.3 dB performance loss compared to the single user uplink PC-SCMA over AWGN channel and 0.6 dB performance loss over Rayleigh fading channel.