الفهرس 
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Abstract
This thesis is concerned with the performance evaluation of differential detection techniques for the Gaussian Minimum Shift Keying (GMSK) modulation technique in Land Mobile to Mobile (LMM) communication channel . The GMSK signal is a strong candidate for a modulation technique that satisfies the stringent out-of-band radiation power requirement of Mobile to Mobile Radio (MMR) application. Differential Detection (DD) is very suitable for MMR because the receiver structure is greatly simplified compared to other scheme. The thesis investigates the performance of several Differential Detection techniques such as 1- Conventional Differential Detection (CDD). 2- Center Sampling Differential Detection (CSDD) 3- Center Sampling Double Differential Detection (CSDDD) . To evaluate the performance of these differential detection techniques several factors should be taken into consideration such as : 1- The fading characteristics of a single path fast Rayleigh fadding LMM communication channel. 2- The frequency-selective nature of the channel due to the delay between the two paths. 3- The additive white Gaussian noise (AWGN). 4- The cochannel interference (CCI) due to geographical frequency reuse. 5- Multiple independent cochannel interferers. 6- ISI due to the Gaussian prefiltering of the data. 7- ISI due to the band limiting by Rx filter. 8- The Doppler spread in the carrier frequency due to the motion of the Tx and RX. 9- Random frequency shift due to the frequency instability in Tx. It has been found that the performance of CSDD scheme is better than CDD scheme , however, CSDD scheme is not attractive for detection of GMSK signals received over wide band channel, while it is substantially superior in severely restricted bandwidth channel, where CDD scheme becomes ineffective . The performance of CSDDD scheme is considerably degraded compared to CSDD scheme in the absence of frequency offset but , CSDDD scheme has the capability to remove completely the effect of frequency variation at the output of the receiver or to reduce the effect of frequency shifts and its performance is better than the CSDD scheme in presence of random frequency shifts.