Multicell zero-forcing and user scheduling on the downlink of a linear cell-array

Coordinated base station (BS) transmission has attracted much interest for its potential to increase the capacity of wireless networks. Yet at the same time, the sum-rate with single-cell processing (SCP) is known to scale optimally with the number of users in a Rayleigh fading environment. One may therefore ask if the value of BS coordination is limited in the many user regime from a sum-rate perspective. With this in mind we consider multicell zero-forcing beamforming (ZFBF) on the downlink of a linear cell-array. We first identify the beamforming weights and the optimal scheduling policy under a perbase power constraint. We then compare the number of users m and n required per-cell to achieve the same mean SINR, after optimal scheduling, with SCP and ZFBF respectively. Specifically, we show that the ratio m/n grows logarithmically with n. Finally, we demonstrate that the difference in sum-rate between ZFBF and SCP is significant for all practical values of number of users.