Low complexity RF beam search algorithms for millimeter-wave systems

We consider a millimeter wave communication system with multiple RF beam-forming chains each capable of forming beams in different spatial directions. The optimal codebook-based RF beam search algorithm has an exponential complexity in both the number of RF chains at the transmitter and at the receiver, which is infeasible in practice. To enable implementations that scale with increasing number of RF chains, we propose a class of RF beam search algorithms with varying complexities that iteratively search for the capacity maximizing RF beams over subsets of RF chains. The performances of the two linear variations of the proposed algorithm, jointly linear and separately linear, are evaluated in a millimeter wave cellular setting that involves reference symbol transmission from the mobile station to the base station. We show that, for a 2 × 2 system, using the proposed algorithms achieves a computation savings of about 86% with minimal performance loss.