Multiple Access Relay Network :: Technology, Network

We consider a multiple access relay network where each source transmit channel coded packets, relay decode the transmitted packet, generate network coded parity symbol, and retransmit it. We assume the relay has multiple antennas, so relay to destination link is MIMO channel. We consider two MIMO transmission mode at the relay, spatial multiplexing (SM) and beamforming as transmit diversity (TD), and assume that the relay use different network coding scheme depending on the MIMO transmission mode. In other words, we consider a network with three types of linear combination; channel coding at the source, network coding at the relay, and mixing over the air with MIMO channel. The main objective of the paper is to propose a transmission mode selection scheme at the relay which optimize these three linear combinations concurrently. There are numerous work that optimize either the network coding, MIMO transmission mode, or data rate over multiple access relay channel. Network coding techniques for single antenna relay network has been addressed in [1] - [4]. Authors in [1] investigated the cooperative diversity gain offered by the network coding. Authors in [2] proposed a network coding scheme based on low-density parity-check (LDPC) codes that accounts for the lossy nature of wireless networks and showed that a significant coding/diversity gain can be achieved. Author in [3] investigated the tradeoff between reliability and rate as a function of node density and SNR, and showed how the energy and node density can be traded in achieving a given reliability-rate pair in single antenna case. Authors in [4] analyzed an network coded cooperation which adaptively match networks-on-graphs to the well-known class of codeson- graphs such as LDPC codes. This approach enables realtime adaptation of network codes to variant link states and changing network topologies. Network coding for multiple antennas have been studied for special network geometry in [5], [6]. Authors in [5] proposed a cross-layer design employing multiple antenna techniques and network coding called MIMO two-way relay for one dimensional mesh network and authors in [6] investigated the performance of MIMO network coding in bi-directional relay network. Adaptive relay protocol has been proposed for a network with single antenna relays in [7] - [9] and for a network with multiple antennas using amplify and forward protocol in [10], [11]. Authors in [11] proposed an adaptive antenna selection scheme at both the relay and the source for half-duplex MIMO amplify and forward relay protocol. Rate optimization for relay network has been addressed in [12], [13]. Authors in [12] proposed throughput optimal control policy for a parallel relay network with decode and forward protocol. Authors in [13] analyzed the performance of variable-rate two phase collaborative diversity protocols and optimized the transmission rate based on the node location.