Performance of differentially detected GMSK in a mobile radio channel

As the demand for current cellular voice-oriented networks to include other services such as data and video applications is increasing rapidly, the reliability of information transmission over the mobile radio environment is important. Performance evaluation in terms of the bit error rate (BER) and block (packet) error rate (BKER) of modulation schemes in such an environment is of considerable research interest. In this thesis, we study the BER as well as the BKER performance of Gaussian-filtered Minimum Shift Keying (GMSK) modulation, currently used in the Global System for Mobile Communication (GSM) standard, in additive white Gaussian noise (AWGN) as well as flat and frequency selective Rayleigh fading. 1-bit and 2-bit differential detectors are used for demodulation. A detailed analysis is carried out to examine the IF filtering effect on the BER performance over the fading channels. The BKER performance is mainly studied through simulations. Since the premodulation Gaussian filter at the GMSK transmitter introduces significant Intersymbol Interference (ISI), we also examine the performance of a decision feedback (DF) scheme which partially removes the ISI, over such channels. The BER results in both flat and frequency selective (FS) Rayleigh fading show that 2-bit conventional (with no decision feedback) GMSK performs slightly better than 1-bit conventional GMSK when Eb/NQ < 25 dB. Above this value, the latter performs better and has a lower irreducible error. Results also show that 2-bit conventional GMSK is more sensitive to the IF filtering distortion than 1-bit conventional GMSK in Rayleigh fading. The percentage improvement in BKER of 1-bit DF GMSK over 1-bit conventional GMSK is almost equal to that of the corresponding BERs. In the case of 2-bit DF GMSK, the BKER performance shows an increased improvement over 2-bit conventional GMSK when compared to the corresponding BER performance, owing to increased error propagation. Since fading gives rise to bursty bit errors, the actual BKER is lower than the predicted assuming independent bit errors. In all fading cases, 1-bit conventional GMSK has a better BKER performance over 2-bit conventional GMSK when Eb/NQ >25 dB. In the case of decision feedback, similar performance trends are observed.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat