Joint channel decoding and physical-layer network coding in two-way QPSK relay systems by a generalized Sum-Product Algorithm

Abstract

Abstract-A physical-layer network coded two-way relay system applying Low-Density Parity-Check (LDPC) codes for error correction is considered in this paper, where two sources A and B desire to exchange information with each other by the help of a relay R. The critical process in such a system is the calculation of the network-coded transmit word at the relay on basis of the superimposed channel-coded QPSK words of the two sources. For this joint channel-decoding and network-encoding task a generalized Sum-Product Algorithm (SPA) over F16 is developed. This novel iterative decoding approach outperforms other recently proposed schemes as demonstrated by simulations.

Generalized Sum-Product Algorithm for Joint Channel Decoding and Physical-Layer Network Coding in Two-Way Relay Systems

“…The most robust scheme with respect to the angle is our new approach based on the G-SPA. The G-JCNC approach has recently been extended for the transmission of QPSK signals leading to an G-SPA over F 16 [13]. Based on this framework, extensions for other modulation alphabets are straightforward.…”

Physical-Layer Network Coding in Coded OFDM Systems with Multiple-Antenna Relay

“…In this section the decoding schemes based on a-posterior probability (APP) detectors introduced in [4] with singleantenna relay are extended to a multiple-antenna scenario. The APP that s is transmitted conditioned on receiving y is represented as…”

“…It has been shown in [3] that the useful information provided by the two channel codes applied at the sources is not fully exploited by JCNC, which motivates a generalized sumproduct algorithm for LDPC codes, as proposed in [4]. In the G-JCNC scheme, the APPs defined in (3) are directly used and updated iteratively in the non-binary belief propagation decoder instead of the LLRs.…”

“…In order to handle such a MA problem, one possible solution is that the relay estimates the bitwise modulo-2 (XOR) of the two source messages, which is sent back to the sources in the broadcast (BC) phase. The concept of PLNC was jointly considered with channel coding for repeat accumulate (RA) codes in [3] and for low-density parity-check (LDPC) codes in [4] based on aposterior probability (APP) detection. Different APP-based decoding schemes to either first decode the individual messages from the sources explicitly or directly estimate the network coded packet from the receive signal were investigated in [5] based on mutual information.…”

“…The analysis from the APP-based decoding schemes in [4] is extended to the multiple-antenna relay scenario. Furthermore, the impact of employing multiple antennas at the relay on the MA phase comparing to the singl-antenna relay scenario is investigated for the different APP-based schemes and several common MIMO detection schemes with respect to mutual information (MI).…”