Comparison of capacities of the transmit antenna diversity with the receive antenna diversity in the MIMO scheme

It is well known that spectral efficiency can be dramatically increased by employing multiple transmit and receive antennas. This multi-element technology processes the spatial dimension to improve wireless capacities. Since there are multiple antennas in both transmit and receive sides, a natural question is whether more antennas should be at the transmitter or the receiver in order to achieve greater capacity? A second question is how many antennas should be deployed in the transmitter and the receiver to make the channel capacities reach their saturation level? These two questions are important to the optimization of multiple input multiple output transmission schemes. To address these questions, we explore the important case of when the channel characteristic is known at the receiver. The analytical model assumes that the paths between antennas fade independently. Further, the channel is assumed to be fixed during a burst and to change randomly from burst to burst. To answer the first question, we use the outage capacity complementary cumulative distribution function to show that the capacity with more receive antennas and fewer transmit antennas is higher than the opposite configuration. To answer the second question, we use numerical simulation to explore the saturation points of the capacities for different signal-to-noise ratios. These simulations give results illustrating the relations among the saturation level capacity, antenna number and signal-to-noise ratio.