Performance analysis of DS-CDMA wireless and mobile communication system in a Nakagami-m frequency selective multi-path fading channel

Abstract

In the recent years, code division multiplc access (CDMA) draws considerable intcrests of the wireless communication engineers to be used as a multiple access technique because of its some invaluable advantages over time division multiple access (TDMA) and frequency division multiple access (FDMA). Proposed air interface standards for the third generation (3G) mobile communication arc cdma2000-1 xRTT; cdma2000-3xRTT; cdma2000-1xEV, DV, DO; W-CDMA; TD-SCDMA and EDGE. For multiple access communication, direct sequence CDMA (DS-CDMA) is the specified technology for all the above mentioned air-interfaces except for EDGE whose standard is TDMA. The reverse link performance of DS-CDMA wireless and mobile (cellular and non-cellular) communication systems over Nakagami-m distributed frequency selective multi-path fading channel has been investigated in this thesis. Both the conventional correlator type receiver and the RAKE receiver have been considered for the analysis. Noise is taken as additive white Gaussian noise (AWGN) with two sided power spectral density No/2. To model multiple access interference (MAl), standard Gaussian approximation (SGA) has been considered in this work. Three different conditions with perfect, imperfect and absence of power control have been analyzed in this work. The signal-to-interferencenoise- ratio (SINR) and the bit error rate (BER) expressions for the system have been derived and simulated by varying the number of user, the number of fading path, the processing gain, the fading parameter m, the SNR per bit E. / No, the number of interfering cell, cell radius, the number of RAKE receiver finger and the variation in the amplitude of the received signal. The performance of the system is evaluated considering the acceptable BER equal to or less than 10.3. The analysis shows that in all the three cases of perfect power control (PPC), imperfect power control (IPC) and absence of power control (APC) for both cellular and 11011- cellular DS-CDMA systems, as the number of simultaneous active user and the number of fading path increases, the BER of the system increases indicating the performance degradation. For all the above cases, as the value of the processing gain, the r<:tio E,,/ No and the fading parameter m increases, the 13ER of the system improves. In case of IPC both the cellular and the non-cellular (single cell) systems, as the variation of the received signal amplitude with respect to the mean value increases, the SINR decreases and the BER increases. It also reveals that the performance of the cellular system degrades with the increase of the number of the interfering cell. In case of APC, as the cell radius increase, the performance of the system degrades. For the fading parameter m $\, the system performance with a eorrelator type receiver is very poor and impracticable for implementation as the BER remains always greater than 10,3 It is observed that the performance is much bettcr if a RAKE receiver is used. With the increase of the number of RAKE receiver finger, the system performance improves. From the analysis, it can be concluded that the best performance is achieved in case of PPC and the worst in case of APC. For APC, the BER less than 10,J is aehicvable only for very few numbcr of active user and a large value of m, Hence, to gct a satisfactory performance for DS-CDMA wireless mobile communication systems, some form of power control must be implemented.