Single and multi scale direct sequence-code division multiple access for wireless communication networks

In this research, our goal is to increase the capacity of DS-CDMA based systems for future wireless communication networks. In order to achieve this goal, we have dealt with two new wavelet based DS-CDMA systems, single-scale DS-CDMA and multi-scale DS-CDMA. The innovative approach of this work is the use of wavelet waveforms as chip pulse shaping waveforms of DS-CDMA signals. We first use a single scale of wavelets in a single-scale DS-CDMA system, then multiple scales of wavelets in a multi-scale DS-CDMA system. In order to increase the capacity, we utilize the properties of wavelets such as time shift, scale and Hilbert Transform (HT) orthogonality, and the relationships between wavelets and FIR filter bank coefficients.; We have derived the Power Spectral Densities (PSD) for both systems. These PSDs are used in bandwidth comparisons. In order to investigate the probability of errors (P_e), we have analyzed both single and multi-scale DS-CDMA systems over a synchronous AWGN channel, then, over a Quasi-Synchronous (QS) AWGN channel. We initially compare Daubechies wavelets with conventional waveforms such as rectangular, half sine and raised cosine as chip waveforms in terms of the bandwidth and probability of error. Daubechies wavelets produce comparable results to the results of the conventional waveforms. To achieve better performance, we optimize the wavelet waveforms using their relation to the FIR filter coefficients. Optimum wavelets result in lower P_e than that of the conventional waveforms.; We also utilize a decorrelating detector that is a sub-optimum multi-user detector for improving the interference cancellation. Wavelets are optimized again for both systems using the decorrelating detector over a QS/AWGN channel. For this case, the P_e becomes much smaller than that of the previous cases. Finally, we utilize the Hilbert Transform of wavelets as second chip waveforms of single-scale DS-CDMA signals over a synchronous AWGN channel. The HT based design doubles the data rate without increasing the bandwidth or degrading the performance.