On the Feasibility of Hybrid Interference Alignment in 60 GHz Millimeter-Wave Dense Networks

To address the challenge of poor link budget and co-channel interference (CCI) mitigation in 60 GHz millimeter-wave (mmWave) dense networks, we investigate the feasibility of employing hybrid interference alignment (IA) method to approach the capacity, where the analog precoder/combiner is utilized to harvest the largest array gain for improving the received signal strength on each communicating link, subsequently a low-dimensional digital IA processing is further performed to eliminate the CCI. This paper establishes a feasible condition on the required minimum number of RF chains to achieve hybrid IA, i.e., the number of RF chains at the transmitter (TX) and receiver (RX) only needs to be twice the number of data streams. In addition, a joint max-SINR and min-MSE iterative algorithm based on channel reciprocity is proposed. Furthermore, a detailed analysis of the proposed algorithm on the large scale system is also provided. The simulation shows that hybrid IA design outperforms the conventional digital and hybrid schemes under the conditions of different SNR and different numbers of users or antennas in 60 GHz mmWave system.