Non-orthogonal compute-and-forward with joint lattice decoding for the multiple-access relay channel

Abstract

Relay-aided multiuser communications are crucial for future 5G systems. In this paper, we consider the twouser multiple access relay channel (MARC), in which two users transmit messages to a common destination with the assistance of a half-duplex relay. The decode-and-forward (DF) based lattice coding was shown to be effective for the MARC in our previous work [1]. However when the links from the users to the relay are weak, DF protocol may fail to decode all users at the relay. Aiming to solve this problem, we propose a new lattice coding where the relay only needs to decode an integer-weightedsum of users' lattice codewords, re-maps it with a modulobased mapper and then forwards the corresponding codeword. Although the decoding at the relay is akin to the orthogonal compute-and-forward protocol, we relax the restriction imposed by previous works that the users have to be silent when the relay is transmitting to avoid interference. The key ingredient is the joint multi-user lattice decoding performed at the destination. This jointly decoding strategy not only complicates the corresponding code design but also the error analysis. To find the proper integerweighted-sum at the relay for the destination's joint decoder, we also solve a non-convex integer problem by carefully transforming and relaxing it to a convex one. Simulation results show that the proposed non-orthogonal lattice coding can outperform existing schemes in a variety of channel settings.

The Magic of Superposition: A Survey on Simultaneous Transmission Based Wireless Systems

“…The results reveal that CP&F shows better performance than lattice-based C&F. This work is later extended to a multi-user multi-relay cooperative scenario in [101]. Cooperative networks are also considered in [102]- [106]. The authors in [103], [104], [106] propose an CP&F method for the two transmitter single relay two receiver networks.…”

“…The authors in [103], [104], [106] propose an CP&F method for the two transmitter single relay two receiver networks. The CP&F is considered for the same scenario with single receiver in [102], [105].…”

The Magic of Superposition: A Survey on Simultaneous Transmission Based Wireless Systems

“…The results reveal that CP&F shows better performance than lattice-based C&F. This work is later extended to a multi-user multi-relay cooperative scenario in [62]. Cooperative networks are also considered in [63]- [67]. The authors in [64], [65], [67] propose an CP&F method for the two transmitter single relay two receiver networks.…”

“…The authors in [64], [65], [67] propose an CP&F method for the two transmitter single relay two receiver networks. The CP&F is considered for the same scenario with single receiver in [63], [66].…”