Cross-Tier Interference Alignment With Interfering Pair Selection in Uplink Heterogeneous Networks With Multiple Macrocells

In this paper, we have considered the uplink cross-tier interference in multi-macrocell heterogeneous networksystem, where each macrocell consists of a number of small cells. Cross-tier interference between macrocell user equipments (MUEs) and small cells base stations (SBSs) exists in both intra-macrocell and inter-macrocell due to high transmit power of MUEs. The MUE-to-SBS interference from both local and adjacent macrocells is dealt with interference alignment (IA) with the aid of a central processing node, and co-tier interference caused by small cell user equipments (SUEs) and MUEs is dealt with minimum mean square error method. To reduce the channel state information (CSI) bits transmitted through inter-cell backhaul with limited capacity required by IA, the idea of MUE-to-SBS interfering pair selection (IPS) is employed before IA. The effects of different IPS schemes on the performance of the system have been investigated. Results show that the proposed multi-macrocell IA algorithm improves the performance of SUEs while maintaining that of MUEs compared with others’ previous work in single-macrocell scenario. In addition, numerical results show that it is wise not to align all cross-tier interference. We can achieve better performance while decreasing the load for transmitting precise MUE-to-SBS CSI on inter-cell backhaul by selecting an appropriate number of participants in our proposed IA algorithm.