A comparison of multipath effect of digital modulations for mobile channels

Binary phase-shift keying (BPSK), quaternary phase-shift-keying (QPSK), and minimum-shift-keying (MSK) are compared for transmission over multipath radio channels. The channel is modeled as a two-ray channel, with the reflected ray attenuated in amplitude, phase-shifted, and time-delayed with respect to the direct ray. Computer simulation is used to obtain the bit-error-rate for various fade parameters, transmission speeds and bit energy to noise spectral density ratios. It is shown that coherent PSK outperforms QPSK and MSK if compared at the same symbol rate. If a bit rate is kept unchanged, then QPSK slightly outperforms BPSK. MSK is more resistant to intersymbol interference caused by high transmission rate than BPSK. However, irreducible errors occur more often in MSK