Blind Interference Alignment for a Class of K-user Line-of-Sight Interference Channels

We consider a class of K-user line-of-sight interference channels without channel state information at transmitters (CSIT). All transmitters are fixed while receiver i has high mobility if i∈{1,2,⋯,K₁} and has low mobility otherwise, where K-1≤ K₁≤ K, and the channel coherence times for high- and low-mobility receivers are given by one and T, respectively. In addition, we assume that both transmitter i and receiver i use M≥ T antennas if i∈{1,2,⋯K₁} and use only one antenna otherwise. In this paper, we propose an interference alignment (IA) scheme for these channels. The key idea is to group receivers with different mobility to have different coherence time. The results show that IA can improve the degrees of freedom even in the absence of CSIT under certain conditions.