Signal Alignment in MIMO Y Channels with Two-way Relaying and Unicast Traffic Patterns

摘要

In this paper, we study a network information flow problem for a multiple-input-multiple-output (MIMO) wireless network with three users where (i) two users equipped with the same number of antennas exchange independent messages via the relay and (ii) one user transmits and receives data from the relay. This is a specialized version of the MIMO Y channel where, in the multiple access phase, three users send all messages simultaneously to the relay, and, in the broadcast phase, the relay transmits messages to users also on a single MIMO channel access. Specifically, in the proposed signal alignment (SA) schemes, we design precoding and nulling vectors to improve the bit error rate (BER) performance. In addition to SA constraints, we introduce the orthogonality requirements between spatial signaling dimensions or utilize degrees of freedom in selecting precoding vectors to maximize distances between signaling points representing network coded messages and unicast data.