RESEARCH INTERESTS

It is concerned with shadowing due to diffraction by multiple knife-edge obstacles. The statistical properties of shadowing, characterized by the diffraction theory, are compared with the log-normal shadowing model, which is widely used in the communications theory. The mean and the standard deviation of the shadowing loss and the correlation distance is investigated in relation with the range, the number and the heights of diffracting edges and the transmit antenna height. The height of the transmit antenna is assumed to be above and below the mean edge height to simulate, respectively, macro- and micro-cellular propagation environments. The log-normal probability density function (pdf) was observed to simulate better the statistical behavior of the shadowing loss in micro-cellular environments, in the presence of sufficiently large number of diffracting edges. The correlation distance in macro-cellular environments was observed to be much shorter than that in the micro-cellular environments. Correlation distance was also observed to increase with increasing values of the range for a given number of diffracting edges.

This presents a performance analysis of a relay system, which consists of single antennas at the source and the destination, of a MIMO system at the relay with N antennas at both sides. The direct connection between the source and the destination is also considered. The relay matrix and the output signal-to-noise ratio (SNR) are obtained by minimizing the mean square error (MMSE) between the symbol transmitted by the source and the symbol received at the destination. The relay is assumed to multiply the incoming vector with a relay matrix and to forward the resulting signal vector to the destination. The optimal relay matrix performs maximal ratio combining (MRC) of the received signals and maximal ratio transmission of the signals forwarded to the destination. The analytical results and simulations show that the MIMO relay link is symmetrical with respect to the SNR’s of source-relay and relay-destination links. MIMO relaying was observed to improve the spectral efficiency, the array gain and the bit error probability (BEP) performance.