Measured performance of 4-QAM with 2-branch selection diversity in frequency-selective fading using only one receiver

The authors present the measured performance of a 500 kb/s 4-QAM (quadrature amplitude modulation) radio link with two-branch selection diversity using only one receiver subjected to hardware-simulated slow frequency-selective Rayleigh fading. The single coherent receiver input is switched between two uncorrelated Rayleigh-fading signals and the one with higher power is selected. The experimental radio link uses time-division multiplexing with a coherent receiver. Since the down-link transmitter is always on the received signal measurements and selection can be performed just before the reception of the user´s data burst. The measured performance compares favorably with computer simulation. The effect of delay between measurement/selection and the actual data burst demodulation is also presented. It is found from both experiment and computer simulation that selection diversity is effective in reducing the bit-error-rate floor caused by frequency-selective fading. As a result, a higher data rate can be supported by a multipath fading channel without using adaptive equalization. Thus, a low-complexity hardware design incorporating selection diversity is feasible for a portable radio communication system