The Bit Error Rate (BER) comparison of Adaptive Parallel Interference Cancellation (APIC) algorithms in asynchronous Multicarrier Direct Sequence Code Division Multiple Access (MC-DS-CDMA) system is introduced. The APIC is used to eliminate the Multiple Access Interference (MAI) in MC-DS-CDMA system. The Adaptive filtering algorithms considered are, Normalized Least Mean Squares (NLMS), Variable Step Size Normalized Least Mean Squares (VSS-NLMS), and Generalized Normalized Gradient Descent (GNGD) algorithms. These algorithms are used in coincidence with APIC system for updating cancellation weights. The performance comparison between these algorithms is performed via extensive computer simulations. Simulation results demonstrate that the VSS-NLMS algorithm outperforms all other algorithms, the NLMS is modular, while the worst performance is obtained by GNGD.

This paper characterizes the performance of direct sequence spread spectrum (DS-SS) signals from the detection probability point of view. The detection probability of DS-SS signals is estimated using wideband radiometer receiver over flat fading channel. Simulations are performed to evaluate detection probability of DS-SS signals over flat fading channel for various time bandwidth product values. The results are compared with the detection probability of DS-SS signals over AWGN channel. The results show that the fading parameter degrades the detection probability of DS-SS signals. The performance of DS will be discussed later in the presence of imperfect channel estimation errors.

Adaptive beamforming is used in many applications such as radar, sonar and wireless communications for separating desired signals from other unwanted signals. Beamforming is essentially applied to direct the pattern of the receiving antenna system towards the desired direction as well as to attenuate the received signals from unwanted directions. The process of adaptive beamforming is performed in two steps. The first step is assigned to estimate the direction of arrival of signals at the field of view of the receiving system. The second step is assigned to nullify the beam pattern in the directions of unwanted signals. To improve the performance of the adaptive beamforming, the number of array elements as well as the number of snapshots should be increased. However, this increase in both numbers of elements and snapshots leads to increase in the cost and the processing time. In this paper, a proposed iterative adaptive digital beamforming technique is presented to improve the array capability of interference cancellation while reducing the processing time. The proposed technique is based on the Jacobi theorem for iterative solution of a system of linear equation to determine the optimum weight vector at the array output. The proposed technique is compared with the optimal Minimum Variance Distortionless Response (MVDR) beamformer technique. Computer simulation is applied to verify the mathematical analysis that presented in the paper. The paper results show that the proposed technique can provide effective Co-Channel Interference (CCI) suppression better than MVDR, while increasing the strength of the desired signal.

Recently, the code division multiple access (CDMA) technique has become the most widely communication technique, because of its varity of applications. The well-known matched filter (MF) is considered as the optimum filter that recovers the CDMA signals. However; its performance recently becomes unsatisfying. This is due to increasing the multiple access interference (MAI), in addition to the other channel impairments such as the fading or the multi path interference (MPI). In this paper, an adaptive minimum mean square error-maximum likelihood (MMSE-ML) receiver is presented as an alternative solution to overcome the drawbacks of the MF receiver. This adaptive MMSE-ML receiver uses adaptive aided tentative coefficients in addition to the basic adaptive coefficients to increase the tracking ability of the channel impulse response variations. The performance of the adaptive MMSE-ML receiver is compared with the traditional adaptive MMSE receiver over a frequency selective fading channel. Moreover, the performances of both the presented and traditional adaptive receivers are compared with the performance of the MF under the same condition. It is found that the performance of the adaptive MMSE-ML receiver is much improved using the proposed technique.