ERROR PERFORMANCE ANALYSIS FOR PI/M-DMPSK IN FAST FREQUENCY-SELECTIVE RICIAN FADING CHANNEL WITH DIVERSITY RECEPTION

Abstract

The Japanese Personal Handy Phone System (PHS) and the North American IS-54 mobile system have both adopted ?/4-DQPSK as the modulation scheme to be used in their modems. This modulation scheme has many advantages such as lower signal envelope fluctuation than QPSK [34], better spectrum efficiency than GMSK [35], and can be non coherently detected by differential detection or FM discriminator detection. In this thesis, we examined the upper bound on the symbol error rate of ?/M-DMPSK in a fast frequency-selective Rician fading channel with diversity reception. The ?/M-DMPSK signal is to be detected by differential detection. Our closed form SER (Symbol Error Rate) equations incorporated the effects of non-zero fading bandwidth, fixed line-of-sight (LOS) Doppler shift, mean delay between the LOS and the multipath components, and root-mean-square (rms) delay spread of a typical mobile channel. The analysis is more comprehensive than results published earlier. For example, Adachi[26] only considered frequency selective fading channel with no Doppler shift of the LOS component. Feher[17] uses the two-ray model to analyse ?/4-DQPSK in frequency selective fading channel but Doppler shift experiences by the LOS component is not considered. Chow[25] only analysed the error rate bound of MDPSK in Rician fading non-frequency selective channel. Other researchers have published results on Rayleigh fading frequency selective channels. Following on Chow's work[25], we introduced frequency selectivity into our analysis through Bello 's system functions for wide-sense stationary uncorrelated scattering (WSSUS) channel. Our result is then derived by using published expressions on the probability of complex vectors that can be expressed in quadratic form with complex-valued Gaussian random variables. In our analysis, three different delay profiles, namely double-spike, one-sided exponential and Gaussian are used. We have also derived from first principle the autocorrelation function of the input delay spread function of the fading channel. This autocorrelation function is needed in our analysis to obtain the SER. It is well known that Doppler spreading places a lower limit on the symbol rate while frequency selectivity of the channel restricts the maximum data rate attainable for a mobile communications system operating in a fading channel. Our channel model assumes these two fading phenomena exist in tandem to degrade the transmission. The work and observations contained in this thesis will therefore have practical usage for wireless mobile communications engineers designing a mobile communications system. The SER of ?/M-DMPSK in fast Rician fading channel is derived in Chapter 4 while Chapter 5 covers its performance in a fast frequency selective Rician fading channel. In brief, we found that the Doppler shift of the LOS component can introduce severe distortion to the received symbol in a fast fading non-selective channel. In a frequency selective channel, besides the rms delay spread, the mean delay of the multipath delay profile can also degrade the channel significantly.