Asymmetric Network Coding for Two-Way OFDM Relay System with Power Allocation

Asymmetric data transmission commonly exists in two-way orthogonal frequency division multiplexing (OFDM) relay system. In this paper, we propose a novel asymmetric network coding scheme for two-way OFDM relay system with power allocation to improve the throughput and bit error rate (BER) performance. In the multiple access channel (MAC) phase, the relay receives asymmetric data from two terminals, respectively. The Max-Min power allocation is used to improve the system BER performance during the MAC phase. In the broadcast (BC) phase, a novel asymmetric network coding scheme based on the thought of adaptive modulation (AM) is proposed. The stronger link can reliably transmit more data by using higher-order modulation. The weaker link can adaptively reduce the modulation order with the help of bit-inserting zero approach and well-designed signal constellation and bit labeling, hence, improve the transmission reliability. Simulation results validate that the proposed scheme outperforms the symbol-inserting zeros scheme in BER and throughput.