Smartlink: Exploiting Channel Clustering Effects for Reliable Millimeter Wave Communications

Millimeter wave (mmW) communications have recently attracted considerable attention as a key element of next-generation (5G) wireless systems. Despite significant efforts in this domain, establishing and maintaining directional mmW links in a dynamic environment are still quite challenging, largely due to the search-time overhead of beam scanning, and the vulnerability of directional links to beam misalignment, blockage, and outages. In this paper, we propose SmartLink, a protocol that exploits the multi-cluster scattering phenomenon at mmW frequencies to establish a multi-directional link between a base station and a user. By exploiting multiple clusters, SmartLink enables fast initial access and link maintenance, along with sustained throughput. A search algorithm called multi-lobe beam search (MLBS) is used to discover multiple channel clusters by probing several directions simultaneously using carefully designed multilobe beam patterns. MLBS reduces the search time from linear to logarithmic with respect to the number of directions. We provide detailed analysis of the false alarm and misdetection probabilities for the designed beam patterns. Following cluster discovery, SmartLink divides antennas into sub-arrays to generate the optimal multi-lobe pattern with respect to cluster powers and blockage probabilities. Finally, extensive trace-driven simulations at 29 GHz frequency using phased-array antennas verify the efficiency of SmartLink.