Transient behavior of an adaptive synchronous CDMA receiver

A steepest descent algorithm is used to update the adaptive weights of a two-stage synchronous Code-Division Multiple-Access (CDMA) receiver that was proposed recently. An issue of the adaptive CDMA system - the convergence and stability property of the receiver is investigated in this thesis. This adaptive synchronous CDMA receiver uses a decorrelator at the first stage and adopts a neural network which acts as an interference canceler at the second stage. It can achieve near-optimum performance. Furthermore, its computational complexity is just a square function of the number of users. The only requirement is the knowledge of the users\u27 signature sequences. The analysis shows that the algorithm for the adaptive weights is convergent and straightforward in implementation. The guaranteed fast convergence of the receiver weights and the tractable theoretical analysis on it, as revealed in this thesis, make this adaptive receiver a promising approach for wireless communications

Adaptive interference suppression for DS-CDMA systems based on interpolated FIR filters with adaptive interpolators in multipath channels

In this work we propose an adaptive linear receiver structure based on interpolated finite impulse response (FIR) filters with adaptive interpolators for direct sequence code division multiple access (DS-CDMA) systems in multipath channels. The interpolated minimum mean-squared error (MMSE) and the interpolated constrained minimum variance (CMV) solutions are described for a novel scheme where the interpolator is rendered time-varying in order to mitigate multiple access interference (MAI) and multiple-path propagation effects. Based upon the interpolated MMSE and CMV solutions we present computationally efficient stochastic gradient (SG) and exponentially weighted recursive least squares type (RLS) algorithms for both receiver and interpolator filters in the supervised and blind modes of operation. A convergence analysis of the algorithms and a discussion of the convergence properties of the method are carried out for both modes of operation. Simulation experiments for a downlink scenario show that the proposed structures achieve a superior BER convergence and steady-state performance to previously reported reduced-rank receivers at lower complexity

Blind adaptive constrained reduced-rank parameter estimation based on constant modulus design for CDMA interference suppression

This paper proposes a multistage decomposition for blind adaptive parameter estimation in the Krylov subspace with the code-constrained constant modulus (CCM) design criterion. Based on constrained optimization of the constant modulus cost function and utilizing the Lanczos algorithm and Arnoldi-like iterations, a multistage decomposition is developed for blind parameter estimation. A family of computationally efficient blind adaptive reduced-rank stochastic gradient (SG) and recursive least squares (RLS) type algorithms along with an automatic rank selection procedure are also devised and evaluated against existing methods. An analysis of the convergence properties of the method is carried out and convergence conditions for the reduced-rank adaptive algorithms are established. Simulation results consider the application of the proposed techniques to the suppression of multiaccess and intersymbol interference in DS-CDMA systems

An adaptive asynchronous CDMA receiver and its convergence analysis

An adaptive CDMA receiver scheme assuming perfect synchronization has been generalized in this thesis to the asynchronous channel, a much more practical assumption of the real system. Similar formulas are derived and as its synchronous version, it is still near-far resistant and requires no knowldge [sic] of received signal amplitudes and training sequences. Thus, sophisticated high-precision power control and user power estimation are not necessary and the receiver is particularly useful in mobile communications since it can adjust itself adaptively to changes in the power of the users. Tile convergence and transient behavior of the receiver are also investigated and found to have similar results to its synchronous counterpart. A new way to analyze the error performance of the decorrelator is also proposed and the error probability of the one-shot decorrelator is formulated for the general case in an alternative way using the new idea, which is much simpler. Furthermore, the singularity problem associated with the one-shot decorrelator is addressed and its effect on the performance of the receiver is discussed