A PLNC Approach for K-pair-user Exchanging in Two-Tier HetNets with mmWave Wireless Backhaul

Although there have been many researches and corresponding degrees of freedom (DoF) analysis on multiple pairwise users exchanging data by one-hop relaying through one or more relays, the two-hop relay system still needs further exploring. In this paper, we design a communication scheme for multiple pairs of users in the two-tier heterogeneous networks (HetNets) with wireless backhaul link, which includes four phases: two multiple access (MAC) phases and two broadcast (BC) phases. Firstly, a new transmission and coding-decoding scheme combining generalized signal alignment (GSA), zero forcing (ZF) and physical layer network coding (PLNC) is proposed, which jointly takes account of users, small base-stations (SBSs) and macro BS (MBS). Furthermore, we analyze the sum rate for users relayed by SBS or also helped by MBS, the influence of the number of antenna configurations on the DoF, and the constraints that antenna should meet. Besides, compared with the traditional SSA scheme, the superiority of this scheme is highlighted. Meanwhile, simulation results illustrate that the proposed scheme can achieve much higher system sum rate than ZF scheme.