Performance improvement analysis of wireless MIMO channel in the presence of keyhole

Wireless communication systems always demand higher data rates and better quality of service (QoS). Transmission reliability in a wireless channel with high path loss, time-varying multipath fading and power and bandwidth limitations, is a testing issue. Multiple-input multiple-output (MIMO) systems can reduce the effect of these channel interferences and achieve reliable signal transmission at high data rate. Space-time block code (STBC) is a coding scheme for the use of multiple transmits antennas providing a simple transmit diversity scheme. In certain MIMO fading environments, the offered channel capacity can be very low, where despite rich local scattering and uncorrelated transmit and receive signals, the system has a single degree of freedom. This effect has been termed as keyhole or pinhole effect. This contribution analyzes the average symbol error rate (SER) performance of MIMO systems employing orthogonal STBC with M-PSK constellations over fading channels in the presence of the keyhole. The Nakagami-m distribution has been considered for MIMO channel modeling. We derive the probability density function (PDF) of instantaneous signal-to-noise ratio (SNR) and an integral equation to calculate the average SER after space-time block decoding in such channels. Numerical results show that the keyhole significantly degrades the SER performance of the STBC in MIMO channels. The performance of such channels is a function of fading figure, m and diversity.