Millimeter Wave Beamforming for Wireless Backhaul and Access in Small Cell Networks

TL;DR

This paper explores millimeter wave beamforming for small cell network backhaul and access, proposing adaptive beam alignment techniques to address environmental challenges like wind sway, and demonstrating improved performance over existing methods.

Contribution

It introduces an efficient beam alignment method using hierarchical codebooks and adaptive sampling, accounting for wind sway effects on large array beamforming.

Findings

Significant reduction in beam alignment search time.

Effective handling of wind-induced beam misalignment.

Tradeoff identified between array size and environmental movement.

Abstract

Recently, there has been considerable interest in new tiered network cellular architectures, which would likely use many more cell sites than found today. Two major challenges will be i) providing backhaul to all of these cells and ii) finding efficient techniques to leverage higher frequency bands for mobile access and backhaul. This paper proposes the use of outdoor millimeter wave communications for backhaul networking between cells and mobile access within a cell. To overcome the outdoor impairments found in millimeter wave propagation, this paper studies beamforming using large arrays. However, such systems will require narrow beams, increasing sensitivity to movement caused by pole sway and other environmental concerns. To overcome this, we propose an efficient beam alignment technique using adaptive subspace sampling and hierarchical beam codebooks. A wind sway analysis is presented to establish a notion of beam coherence time. This highlights a previously unexplored tradeoff between array size and wind-induced movement. Generally, it is not possible to use larger arrays without risking a corresponding performance loss from wind-induced beam misalignment. The performance of the proposed alignment technique is analyzed and compared with other search and alignment methods. The results show significant performance improvement with reduced search time.