Performance Improvement of a WCDMA system using pulse shaping filter and compensation for errors in the presence of interference channels

Abstract

Most mobile operators have rolled out 3G networks, which have more benefits compared to the second and first generation networks. This is because they can support voice, data and multimedia applications. The signal transmitted over these mobile systems suffers from interference due to thermal noise, propagation loss in space and distortion of bit sequence for higher bit rate applications. The current work focussed on performance improvement in a Wideband Code Division Multiple Access (WCDMA) system using pulse shaping filter and compensation for errors technique (channel coding) over the Additive White Gaussian Noise (AWGN) channel. The system model was simulated for a data rate of 2Mbps with and without convolutional coding scheme and using QPSK, 16-PSK, 16-QAM and 64-QAM modulation techniques to modulate the signal at the transmitter. The WCDMA system model was developed and simulated using computer simulation tool MATLAB 7.8 for different digital modulation techniques applied in turns and variation of filter roll off factor from 0.1 to 0.9. For the case of variation of roll off factor, the roll off factor with the minimum error rate in each case was noted. These results show that QPSK modulation format had better performance, with and without convolutional coding, when comparison was made with other modulation schemes making it an efficient modulation scheme at 2Mbps data rate. Therefore, it can be applied only for a system with poor channel conditions and other modulation schemes applied in systems with better channel conditions. The application of convolution coding reduced the BERs encountered in the system at 2Mbps which increased capacity due to lower error rate. The convolutional coding scheme also improved the power efficiency of the system, which meant that the power required to transmit a signal reduced for this high bit rate application. The variation of the pulse shaping filter roll off factor showed that the performance of a wireless communication system employing this type of filter depends on the value of its roll off factor. The filter roll off factor, α, of 0.3 was found to give a lower error rate in many levels of the bit energy to noise power spectral density ratio, which made it an most favourable value at 2Mbps data rate to achieve a better power efficiency and BER level without increasing the complexity of the filter.