Tradeoff between BER and Bandwidth Efficiency in MIMO Systems with ZF Equalization

Multiple-input multiple-output (MIMO) wireless systems offer multiplexing gain and diversity gain. While it is known that the diversity order of MIMO transmissions with N_t transmit and N _r receive antennas over i.i.d. Rayleigh fading channels is N _r - N_t + 1 at high signal-to-noise ratio (SNR), the same conclusion cannot in general be drawn for bit-error rate (BER) gain for all SNR and other channels. We show a BER performance ordering for different transmit antenna sizes in MIMO wireless systems with practical zero-forcing (ZF) equalization, which hold for all SNR. We prove that when the number of receive antennas is fixed, the average BER improves with a decrease in the number of transmit antennas, which shows the tradeoff between BER and bandwidth efficiency in MIMO with ZF equalization