Maksymiv I. Increasing Noise Immunity of Demodulator in Cellular Communication Systems

The dissertation is dedicated to increasing the capacity of existing communication systems by reducing the threshold noise immunity of the receiver's detector preserving the dynamic properties of the device. In work carried out theoretical study of the original modified phase detector in modes with using complex phase shifted signals which take a place in modern cellular communication systems. The analytical expressions for the linear model of modified detector showed the possibility of reducing the signal error ratio without changing transmission speed rate. Using these mathematical models the simulation model of modified detector was implemented. The model was implemented using Matlab software. The adequacy of received imitational model was tested by plotting a diagram of depending of frequency distortion permissible values to SNR and by plotting a diagram of depending BER to SNR values, which correspond to existing values shown in modern literature. The adequate imitational models of CDMA cellular channel and TETRA radio channel were created and the noise immunity of OQPSK and 8PSK signals was investigated. During this work, it was determined the relationship between BER and SNR for classical phase detector and detector, modified by the system of narrowband proportional-integrated filters (PIF). The results of simulation of modified synchronous phase detector showed the possibility of an increase of noise immunity of receiving signals with phase shift keying and the ability of the modified detector to detect OQPSK and 8PSK signals even when signal strength is less than the capacity of obstacles. The detection quality of modified detector is higher than in classical detector. Modified phase detector has better noise immunity and in theory can improve existing wireless communications networks. First obtained the BER to SNR ratio for current communication systems using the modified detector. Received diagrams confirm the efficiency of modified phase detector. The recommendations on the parameters of filters used in the receiver were provided. This enabled during the design of such systems to rely on solid performance at high noise level or a greater number of users simultaneously present. Getting the simulation results, which showed a significant opportunity to increase the capacity of cellular communication systems by 20-35%.