Initial Beam Association in Millimeter Wave Cellular Systems: Analysis and Design Insights

Wireless communication via millimeter wave (mmWave) frequencies is a key component of future cellular systems. mmWave deployments will use beamforming with large antenna arrays by both the base stations and mobile stations to ensure sufficient received signal power. Prior work on coverage and rate of mmWave cellular networks focused mainly on the case when base stations and mobile users beamfomring vectors are perfectly designed for maximum beamforming gains. Designing beamforming/combining vectors, though, requires training that may impact both the SINR coverage and rate of mmWave cellular systems. Therefore, it is important to evaluate the reliable performance of mmWave cellular systems with beam training and association overhead.

To provide an accurate evaluation of the performance of mmWave cellular systems, WNCG graduate student Ahmed Alkhateeb, Samsung Research America-Dallas researchers Dr. Young-Han Nam, Md. Saifur Rahman and Dr. Jianzhong (Charlie) Zhang, and WNCG Professor Robert W. Heath Jr. characterized the performance of mmWave cellular networks while accounting for the beam training/association overhead. First, a model for the initial beam association is developed based on beam sweeping and downlink control pilot reuse. To incorporate the impact of beam training into system performance, a new metric, called the effective reliable rate, is defined and adopted. Using stochastic geometry, the effective reliable rate of mmWave cellular networks is derived for two special cases: with near-orthogonal control pilots and with full pilot reuse. Analytical and simulation results provide insights into the answers of three important questions: (i) What is the impact of beam association on mmWave network performance? (ii) Should orthogonal or reused control pilots be employed in the initial beam association phase? (iii) Should exhaustive or hierarchical search be adopted for the beam training phase? The results show that unless the employed beams are very wide or the system coherence block length is very small, exhaustive search with full pilot reuse is nearly as good as perfect beam alignment.

Paper: Initial Beam Association in Millimeter Wave Cellular Systems: Analysis and Design Insights, available at: http://arxiv.org/abs/1602.06598

This work is supported in part by the National Science Foundation under Grant No. 1319556.