Average Transmit Power Gain of Adaptive ZF Large Scale Multi-user and Multi-antenna Systems

This paper investigates adaptive zero-forcing (ZF) uplink transmission for a large-scale multi-user multi-antenna (MUMA) system. It is assumed that power control can be done at these transmitters as channel condition changes, and the number of antennas at the base station (BS) is not less than the number of users with each having single antenna. Under the case where both individual user rates and maximum transmit powers are constrained, we adopt the optimal transmit strategy of minimizing the total average transmit power (ATP). We define a concept called average transmit power gain (ATPG) for each link in the MUMA system in order to get an insight into the power benefits provided by the MUMA system over a single-user and single-antenna (SUSA) system. In Rayleigh fading environments, then we derive several ATPG expressions with and without channel estimation error. These expressions imply the relationship among the individual ATP, the individual outage probability, the number of BS antennas, and the number of users.