Effective Subcarrier Pairing for Hybrid Delivery in Relay Networks

The emerging 5G adopts OFDM modulation and deploys small-cell amplify and forward (AF) relays for in-cell capacity enhancement and energy efficiency. However, hybrid delivery services for multiple users where broadcast and unicast coexist are inefficient and unfair due to their different QoS requirements. Most existing work considering hybrid broadcast and unicast traffic focuses on different scheduling schemes in onehop scenarios. For dual-hop relay networks, subcarrier mapping or pairing has been studied, but none considers hybrid traffic with both broadcast and unicast. In this paper, we propose an effective subcarrier pairing (ESP) protocol, which exploits the performance diversity in subcarrier pairing at relays to improve the overall performance of hybrid broadcast and unicast traffic. ESP exquisitely pairs subcarriers of two hops into two kinds of subcarrier pairs separately. ESP then allocates subcarrier pairs with low outage probability for broadcast and subcarrier pairs with high capacity for unicast. In ESP design, we study several important metrics such as end-to-end outage probability, capacity, and bit-error-rate (BER) in AF assisted OFDM-CDMA relay networks. We conduct Monte Carlo simulations to verify the effectiveness and fairness of our approach in hybrid transmission. Results show that ESP is efficient in hybrid delivery for relay networks and improves the performance of broadcast services significantly without sacrificing unicast services.