Interference alignment and bit allocation in heterogeneous networks with limited feedback

This paper focuses on downlink interference issues in the open subscriber group (OSG) mode of heterogeneous network (HetNet). In OSG mode, the inter macro-user interference is the main interference to macro user equipments (UEs), and the inter cell interference (ICI), containing the inter picocell interference and the cross-layer interference from macro base station (BS), is the main interference to pico UEs. An interference alignment (IA) scheme for such HetNet is proposed. The transceiver is designed as follows, 1) the precoding matrix for macro BS and the interference suppression matrices for macro UEs are used to eliminate the inter macro-user interference to macro UEs; 2) the precoding matrices of pico BSs are designed to align the inter picocell interference onto the space of the strongest cross-layer interference produced by macro BS; 3) the aligned interference is eliminated by the interference suppression matrices of pico UEs. In addition, the influence of imperfect channel state information at the transmitter (CSIT) on the proposed IA scheme is analyzed. By characterizing the rate loss as a function of the feedback bits number, a bit allocation scheme is given. The simulations show that the proposed scheme can reduce the requirement of the receive antennas number and improve the system throughput of HetNet.