A space-time channel estimator and single-user receiver for code-reuse DS-CDMA systems

Published versio

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

Transmit diversity and linear and decision-feedback equalizations for frequency-selective fading channels

Abstract-Rapid growth and increasing demands for near-ubiquitous high-quality high-data-rate services present the most challenges for wireless system design. As an effective method to provide such services, space-time (ST) coding is gaining more and more attention. This paper extends ST coding, originally designed for known frequency-nonselective fading channels, to unknown frequency-selective channels. A novel scheme is presented to suppress intersymbol interference, coherently demodulate the information symbols with estimated channel state information in an ST transmit diversity wireless time-division multiple-access system that is equipped with multiple antennas at both transmit and receive sides. The proposed algorithm is powerful and computationally efficient. In addition to the discussion of system identifiability, both theoretical analysis and numerical simulation are presented to illustrate the performance of the proposed estimator and receiver in multipath fading channels

An adaptive correlator receiver for combined suppression of co-channel interference and narrow-band jammers in a slowly fading channel

This work deals with the adaptive correlation of a direct sequence spread spectrum signal in the presence of narrow-band, multipath and multiple user interference. The Least Mean Square and Recursive Least Square algorithms are employed for the adaptive convergence of the correlator receiver to minimize the mean squared error. The performance of the adaptive correlator is compared with the matched filter correlator receiver and the conventional prediction filter for the suppression of narrow-band interference by calculating the bit error probability rate. The adaptive correlator is also compared with the RAKE receiver for multipath suppression and compared to the decorelating detector for the suppression of multiple user interference. It is shown that the adaptive correlator is capable of suppressing interference when the spread spectrum signal is corrupted by a combination of disturbances, such as narrow-band jammers and multipath or multiple users on the same channel

A Variational Inference Framework for Soft-In-Soft-Out Detection in Multiple Access Channels

We propose a unified framework for deriving and studying soft-in-soft-out (SISO) detection in interference channels using the concept of variational inference. The proposed framework may be used in multiple-access interference (MAI), inter-symbol interference (ISI), and multiple-input multiple-outpu (MIMO) channels. Without loss of generality, we will focus our attention on turbo multiuser detection, to facilitate a more concrete discussion. It is shown that, with some loss of optimality, variational inference avoids the exponential complexity of a posteriori probability (APP) detection by optimizing a closely-related, but much more manageable, objective function called variational free energy. In addition to its systematic appeal, there are several other advantages to this viewpoint. First of all, it provides unified and rigorous justifications for numerous detectors that were proposed on radically different grounds, and facilitates convenient joint detection and decoding (utilizing the turbo principle) when error-control codes are incorporated. Secondly, efficient joint parameter estimation and data detection is possible via the variational expectation maximization (EM) algorithm, such that the detrimental effect of inaccurate channel knowledge at the receiver may be dealt with systematically. We are also able to extend BPSK-based SISO detection schemes to arbitrary square QAM constellations in a rigorous manner using a variational argument.Comment: Submitted to Transactions on Information Theor