ADAPTIVE SUBCARRIER USING MC CDMA

This paper deals with the estimation of rapidly time varying non isotropic Rayleigh fading channels in Space-Time (ST) coded direct sequence spread spectrum (DS-CDMA) systems. The effects of non isotropic scattering can be captured by using Von Mises distribution for the angle of arrival (AOA) of the scattered waves at the receiver. In order to benefit from the spatial diversity of ST coding, we need to have perfect channel information at the receiver. Kalman Filter (KF) with higher order autoregressive (AR) model is used for tracking and estimation of the non isotropic Rayleigh channel. The proposed algorithm outperforms the AR(1) based algorithms in tracking time varying channel especially under high Doppler spreads in directional scenarios. The effect of different Doppler rates and user loading on bit error rate (BER) performance of the proposed system are also studied.

A new wireless communication system denoted as Multi-Code Multi-Carrier CDMA (MC-MC CDMA), which is the combination of Multi-Code CDMA and Multi-Carrier CDMA, is analyzed in this paper. This system can satisfy multi-rate services using multi-code schemes and muti-carrier services used for high rate transmission. The system is evaluated using Traveling Wave Tube Amplifier (TWTA). This type of amplifiers continue to offer the best microwave high power amplifiers (HPA) performance in terms of power efficiency, size and cost, but lag behind Solid State Power Amplifiers (SSPA's) in linearity. This paper presents a technique for improving TWTA linearity. The use of pre-distorter (PD) linearization technique is described to provide TWTA performance comparable or superior to conventional SSPA's. The characteristics of the PD scheme is derived based on the extension of Saleh's model for HPA. Keywords Multi-Carrier CDMA, Multi-Code CDMA, MC-MC CDMA, TWTA, HPA, AM/AM, AM/PM, Saleh Model.

Abstract—In this paper, a comparative study between a blind
algorithm, based on higher order cumulants, and adaptive
algorithms, i.e. Recursive Least Squares (RLS) and Least
Mean Squares (LMS) forMultiCarrier Code DivisionMultiple
Access (MC-CDMA) systems equalization is presented. Two
practical frequency-selective fading channels, called Broad-
band Radio Access Network (BRAN A, BRAN B) normal-
ized for MC-CDMA systems are considered. In the part of
MC-CDMA equalization, the Zero Forcing (ZF) and the Min-
imum Mean Square Error (MMSE) equalizer techniques were
used. The simulation results in noisy environment and for
different signal to noise ratio (SNR) demonstrate that the
blind algorithm gives approximately the same results ob-
tained by adaptive algorithms. However, the proposed algo-
rithm presents the advantage to estimate the impulse re-
sponse of these channels blindly except that the input exci-
tation is non-Gaussian, with the low calculation cost, com-
pared with the adaptive algorithms exploiting the informa-
tion of input and output for the impulse response channel
estimation.
Keywords—blind identification and equalization, higher order
cumulants, RLS, LMS, MC-CDMA systems.