Cooperative Secondary Beam Selection for Cognitive Multiuser MIMO Transmission With Random Beamforming

This paper studies the performance of a random beamforming-based secondary MIMO system, which coexists with a primary system with single primary transmitter (PT) and single primary receiver (PR). To ensure the performance requirement of the primary system, i.e., the received signal-to-interference-plus-noise-ratio (SINR) at PR is larger than a predefined threshold, we assume that the usability of the beamforming vectors of the secondary MIMO system are determined with the cooperation from PR. Specifically, we propose cooperative beam selection strategies for the secondary MIMO system considering both single-user and multiuser transmission. For both cases, the PR only needs to feed back to the secondary base station (SBS) its received signal power from PT, based on which the SBS calculates the received SINR at PR corresponding to each beam, and decides those usable beams that satisfy the performance requirement of the primary system. The SBS then selects the best beam from all usable beams to serve its user. For the multiuser case, we propose and compare two cooperative beam selection strategies for the secondary MIMO system to select a maximal number of active beams for transmission, while ensuring the received SINR at PR is above the predefined SINR threshold. For both single user and multiuser case, we analyze the outage probability of the primary system and the throughput/sum-rate of the secondary system, based on which we investigate the performance tradeoff between primary and secondary systems.