Power Threshold Based Interference Alignment in Hybrid D2D & Cellular Uplink Transmissions

Abstract

In this paper, we consider a scenario of hybrid device-to-device (D2D) & cellular uplink transmissions, where K pairs of D2D user equipments (UEs) are considered. In each D2D pair, one UE intends to communicate with the other UE and access to the base station (BS) at the same time. To deal with the complicated interferences among D2D and cellular uplink transmissions, the power threshold based interference alignment (PTbIA) scheme will be proposed, where different power thresholds for received interference signal are considered in different UEs. In particular, only the interference with the power higher than the threshold will be aligned into the orthogonal space at each receiver. Otherwise, it will be treated as noise. In this context, more degrees of freedom can be achieved for UEs. The PTbIA scheme can also compute the precoding vectors and decoding matrices for each UE with low complexity. Moreover, the lower bound of the antenna number for each BS will be derived so as to guarantee that both D2D & cellular uplink transmissions achieve the required degrees of freedom. The outage probability of both D2D and cellular uplink transmissions will further be derived in closed-form formulas. Simulation results will illustrate the performance gain of the proposed algorithm and verify the theoretical derivations.