Comparison of coherent and differential detection of BPSK and QPSK in a quasi-static fading channel

Abstract

The advantage of coherent detection over differential detection for both BPSK (binary phase-shift keying), and QPSK (quaternary phase-shift keying) in a multipath radio channel with either frequency-flat or frequency-selective fading is evaluated. The difference in receiver sensitivity is compared on the basis of three criteria: (1) bit-error rate (VER) averaged over fading samples, (2) BER distribution, and (3) distribution of block error rate. For a quasistatic fading channel, (2) and (3) provide a more meaningful comparison. Both analytical expressions and simulation are used in the comparison. The difference between differential detection of 2- and 4-level PSK is taken into consideration, as is the difference between pure coherent detection and coherent detection that uses differential encoding to resolve phase ambiguity. Both selection diversity and channel coding are considered as techniques for mitigating fading effects. It is found that coherent detection is superior to differential detection by at least 2.4 dB, which converts to about 30% improvement of spectral efficiency in a two-dimensional frequency reuse system with a fourth-power propagation exponent.