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.
