Impact of Transmit Antenna Array Geometry on Downlink Data Rates in MIMO Systems

For a cellular system with a fixed number of transmit antennas at each base station, we investigate how the data rate on the downlink varies as a function of the geometry of the transmit array and as a function of the linear precoding that precedes the transmit array. The maximum average data rate that can be reliably transmitted over the downlink channel (i.e. the ergodic capacity of the downlink channel) is used in this paper to compare various configurations of transmit antennas at the base stations. We show that the 3GPP Spatial Channel Model [7] can be used to semi-analytically evaluate the ergodic capacity for any configuration of transmit antennas. Based on the evaluation of ergodic capacity, we will compare several configurations of transmit antennas for a total of 2, 4, and 8 transmit antennas in a typical macro cellular environment.