Trellis coded modulation and multiuser detection techniques for DS/CDMA mobile communication systems

Abstract

In these days, there has been an explosive increase in the number of mobile communication users. To accomodate the demand of mobile communications, more efficient modulation/demodulation techniques and signal processing techniques are required. While DS/CDMA has higher spectral efficiency than other systems, the interuser interference and near-far effect, which are the major drawbacks of CDMA, reduce the system capacity. Therefore, some additional techniques, such as channel coding, use of base station antenna array, and multiuser detection techniques, are required to satisfy the mobile communication users in the near future. First, we analyze the performance of the DS/CDMA systems, which use TCM and convolutional code, in the impulsive noise environment when Rician fading is present. We also investigate the effect of impulsive noise on the DS/CDMA systems employing symmetric TCM, optimum asymmetric TCM, and convolutional code, and compare them in various channel states. It is shown that the performance of the trellis coded DS/CDMA systems and convolutionally coded DS/CDMA systems degrades as the noise becomes more impulsive. It is also seen that we can get some coding gain over uncoded system except at low SNR and that we can get additional coding gain by using optimum asymmetric TCM. We can also see that the performance of the low rate convolutionally coded DS/CDMA system is better than that of the trellis coded DS/CDMA in the impulsive noise environment as in the Gaussian noise environment and that we can achieve similar performance by employing asymmetric TCM. Secondly, we investigate quasi-ML multiuser detectors of DS/CDMA systems with base station antenna arrays in mobile communication systems. We consider the case where the channel vector is time-invariant and extend it to the case where the channel vector is time-varying. Channel vector estimation algorithms are also proposed. It is shown that the performance of the proposed systems is better than tho...