Power And Rate Control In CDMA Cellular Mobile Communication Systems

A feature of wide-band CDMA system is the ability to handle multiple-rate users, including voice, video, and data. In order to support multi-rate transmission in DS-CDMA, many CDMA techniques such as multi-code (MC) scheme, orthogonal variable spreading factor (OVSF) and variable modulation have been used. The structure and theory bit error rate of these schemes are introduced in this thesis.Variable Spreading Gain CDMA system is a candidate system that accommodates mixed traffic types, and supports variable data rate service. We proposed an integrated power and rate control scheme based on SIR balancing in this kind of CDMA systems. In this scheme, power control is primary to the rate control. When the fading channel changes slowly, the transmit data rate will be kept on an appropriate level, and only the power control works to keep up with the channel fading and balance the SIR. But when the channel quality is poor, the data rate will be switched down without sacrificing the BER; otherwise, high data rate was selected. The simulation results of the uplink show that our scheme achieves a good system performance and the number of slots involved should be selected according to the variation speed of the fading channel.Based on in-depth study on the MC-CDMA system structure, we proposed a combined power and rate control scheme for WCDMA over fading channels. In this scheme, power control is primary to rate control. The simulation results of WCDMA uplink is presented and analyzed. It shows that the combined power and rate control scheme achieve good spectrum efficiency and keep the data rate constant over long time periods. Our scheme decreases l-2dB required Eb/I0 relative to variable-power fixed rate transmission. We also show that this combined scheme avoid large errors occur. This allows the interleaving depth to be reduced.At last, the basic theory of fractal and its application in modeling multi-path fading channel are introduced. By studying its fractal parameters, the channel is reconstructed based on wavelet theory. Finally, we preset the possibility of applying this model to power and rate control in CDMA.