Performance enhancement for microwave and millimetre wave indoor communication systems by quasi-coherent combining of multiple antenna signals

The paper analyses the performance of quasi-coherent combining of signals from a small circular antenna array in a Rician fading indoor multipath channel at microwave or millimetre wave frequencies. Instead of maximum ratio combining, where the complex weighting of signals results in an optimum for a single frequency, the proposed concept is based on quasi-coherent combining of the dominant component of the multipath signal of each antenna. The resulting channel impulse response, shows less delay spread and a higher signal to noise ratio. A scheme for this combining technique is given for a coherent binary phase shift keying receiver and evaluated by simulation. Cumulative BER results for the Rician channel and normalised bit rates are presented for circular arrays of 1, 2 and 4 antennae with a diameter of one wavelength. It is shown that this combining technique results in a significant improvement of the BER or application of higher bit rates,