An Efficient Beam Search Algorithm for mmWave Massive MIMO

Abstract

While Massive MIMO with millimeter-wave (mmWave) frequency band has enabled extremely high data rates, it suffers from severe path loss which can be compensated by highly directional beams using antenna arrays. For the establishment of a reliable communication link with User Equipment (UE), mmWave Base Station (BS) must determine the most suitable beam, based on UE location. These narrow beams have a lengthy search process, resulting in communication delays. Identifying the best beam with minimal discovery delay is a challenging problem since narrow beamwidth should capture the exact UE location to maintain the necessary signal-to-noise ratio (SNR) at mmWave frequency. In this paper, a novel two-stage search algorithm is proposed that allows faster discovery of a UE in the given angular space. A wide beam sequential search is performed by BS in the first stage, followed by an extremely narrow beam search in the second stage for two most likely angular spans identified within the best wide beam obtained. The search is performed on the SNR at UE to its main beam direction. Comparison with exhaustive and iterative search indicated a reduction in beam sweep time while maintaining the misdetection probability close to that of iterative search. By estimating the exact location of UE, a required SNR can be maintained resulting in low latency and reduced link failures. We will be investigating the improvement of misdetection probability as our future work.