Dedicated LSAS for Metro-Cell Wireless Backhaul - Part II: Uplink

This is a continuation of the TM [Dedicated LSAS for Metro-Cell Wireless Backhaul - Part I: Downlink, Dec. 31, 2012], where now we treat the reverse-link backhaul problem. The scenario is the same as before: a service-provider has a network of hexagonal macro-cells, and wishes to add up to eighteen metro-cells in each macro-cell. Each macro-cell is provided with an LSAS array, operating in the unlicensed 750 MHz band, whose sole task is to provide backhaul service for the eighteen metro-cells. The required up-link backhaul rate is 10 Mb/s per metro-cell in contrast to the 30 Mb/s rate per metro-cell for down-link backhaul. Up-link LSAS differs qualitatively from down-link LSAS. To that end we derive entirely new expressions for up-link SINR for both matched-filtering (the up-link counterpart to conjugate beam-forming) and zero-forcing. In the Dec. 31, 2012 TM we designed LSAS systems that achieve the required down-link throughput with the minimum possible number of service-antennas. The radiated up-link power per metro-cell (used only to transmit up-link pilots) was assumed to be 50 mW. In our present analysis we start with the same LSAS systems that were designed for down-link backhaul, and the same realizations of the slow-fading coefficients. As before we use 50 mW for up-link pilot transmission, but we use power-control (e.g. less than 50 mW per metro-cell) for up-link data transmission. The principle question that we address is whether the 50 mW per metro-cell up-link power is sufficient to deliver the required throughput. We find, indeed, that 50mW per metro-cell is sufficient radiated power to deliver the required throughput. If the most troublesome 5% of the metro-cells are dropped from service, up-link backhaul data transmission requires no more than 7mW if matched-filter processing is employed, while zero-forcing requires no more than 16mW.