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

Due to the projected increase in demand for high data rate mobile services, interest has grown in new cellular network architectures such as tiered networks. These new architectures would likely use many-fold more cell sites than found today. These small cells will be mounted in ?cheap? deployments such as on existing poles. Two major challenges with this new architecture 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 wireless backhaul for backhaul communication between cells and access within the cell. To overcome the outdoor impairments found in millimeter wave wireless propagation (e.g., high path loss, oxygen absorption, weather, etc.), this paper studies the use of beamforming using a large array of antennas. However, the narrow beam required will make the system very sensitive to movement caused by pole sway and other environmental concerns. To overcome this obstacle, we propose an efficient beam alignment technique using an adaptive subspace sampling and hierarchical beam codebook. 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 a larger array 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. Simulation results of the proposed codebook and alignment search algorithms show significant performance improvement with reduced search time compared to other methods.