الملخص الإنجليزي
The influence of each mobile system parameter on the whole mobile system, and the benefits of adaptation to mitigate other users interference and channel fading were studied. The outcome of this study can be used in the design and operation of third generation mobile systems that can carry different services at different bit error rate. In addition, the optimization for code rate and optimum sets of modulation levels and codeword length was also covered. Code Division Multiplex Access (CDMA) was adopted as the multiple access scheme. For channel coding, BCH code was chosen as it is a powerful coding technique and easy to implement. Multilevel Phase Shift Keying (MPSK) and Multilevel Quadrature Amplitude Modulation (MQAM), which are bandwidth efficient modulation techniques were used. The effect of mobile parameters was investigated using the equation of the equivalent bit energy-to-noise density ratio at a fixed bit error rate. However, when obtaining the optimum code rate and the optimum set of M and n, the bit-error-rate equation of BCH code was used.
From the result of studying the effect of each mobile parameter on capacity, and bit rate, we can conclude that each parameter has a direct influence on the whole system capacity and bit rate. These effects can be exploited to mitigate channel fading and avoid increasing the transmitting power as it causes interference among the active users. Thus, the system can adapt and respond accordingly to unexpected different situations and fading channels. Therefore, it can accommodate the required capacities and bit rates at the specified service type performance. The optimization results at each channel type reveal that the optimum code rate for different modulation levels and codeword lengths is almost equal at a fixed bit error rate. The optimal signal alphabets are 4, 8, and 16 for Gaussian, Rician and Rayleigh channels, respectively. In general, the optimum parameters of the mobile system depend on the channel conditions of the whole system. Therefore, there is a range of optimal mobile parameters.
