Conventional Single-user Receiver Research Articles

CDMA wireless system with blind multiuser detector

In this paper we present an approach capable of countering the presence of multiple access interference (MAI) in code division multiple access (CDMA) channels. We develop and implement a blind multiuser detector, based on an independent component analysis (ICA) to mitigate both MAI and noise. This algorithm has been utilized in blind source separation (BSS) of unknown sources from their linear mixtures. It can also be used for estimation of the basis vectors of BSS. The aim is to include an ICA algorithm within a wireless receiver in order to reduce the level of interference in CDMA systems. This blind multiuser detector requires less precise knowledge of the channel than does the conventional single-user receiver. The proposed blind multiuser detector is made robust with respect to imprecise knowledge of the received signature waveforms of the user of interest. Several experiments are performed in order to verify the validity of the proposed learning algorithm

Iterative multiuser turbo-code receiver for ds-cdma

A number of different iterative decoding methods are proposed for multiuser interference cancellation in a code-division multiple-access system where turbo-codes are utilized for forward error correction (FEC). The individual users are decoded separately with the operation of iterative interference cancellation being mixed with iterative decoding of the turbo-code. This results in a modest increase in the overall complexity as compared to a conventional single-user receiver utilizing turbo-code for FEC. Numerical results are presented showing that the proposed iterative decoders show an improvement in the bit error rate performance and/or a reduction in the computational complexity as compared to similar previously known methods reported by M.C. Reed et al. (see 8th IEEE Int. Symp. Personal, Indoor and Mobile Radio Commun. - PIMRC'97, vol.2, p.740-4, 1997; IEEE Trans. Commun., vol.46, p.1693-9, 1998).

A spatial-temporal decorrelating receiver for CDMA systems with base-station antenna arrays

We investigate multiuser signal detection with a base-station antenna array for a synchronous DS-CDMA uplink using nonorthogonal codes in Rayleigh fading channels. We have developed a new formulation for a spatial-temporal decorrelating detector using the maximum-likelihood criteria. The detector is shown to be near-far resistant. We propose to implement the spatial-temporal decorrelating receiver iteratively by applying the space-alternating generalized expectation-maximization (SAGE) algorithm. Simulation results show that the SAGE-based decorrelating receiver significantly outperforms the conventional single-user receiver and with performance close to that of a spatial-temporal decorrelating receiver with known channel parameters. We have observed that adding base-station antennas can actually improve convergence of the proposed iterative receiver.

Blind adaptive decorrelating detector for DS-CDMA systems: auxiliary-vector detector

A blind adaptive decorrelating detector is proposed which consists of two vectors: one is the pre-assigned spreading code of the desired user and the other is orthogonal to it. The orthogonal vector is adjusted adaptively to minimise the multiple access interference (MAI). This blind adaptive detector requires no more knowledge than does the conventional single-user receiver. Simulation results show that the obtained performance is close to that of the decorrelator.

Transmitter precoding in synchronous multiuser communications

A synchronous multiuser system operating in an additive white Gaussian noise channel, with or without multipath fading, is considered. It is shown that when either a conventional single user receiver or the RAKE receiver is employed, both multiple access and intersymbol interference can be eliminated by means of a suitable transmitter precoding scheme. Transmitter precoding represents a linear transformation of transmitted signals, such that the mean squared errors at all receivers are minimized. Precoding, with both conventional single user receiver and with the RAKE receiver, results in near-far resistant performance and outperforms considerably the respective schemes without precoding. The crucial assumption, in the multipath case, is that the transmitter knows the multipath characteristics of all channels and that channel dynamics are sufficiently slow so that multipath profiles remain essentially constant over the block of precoded bits.

Blind adaptive multiuser detection

The decorrelating detector and the linear minimum mean-square error (MMSE) detector are known to be effective strategies to counter the presence of multiuser interference in code-division multiple-access channels; in particular, those multiuser detectors provide optimum near-far resistance. When training data sequences are available, the MMSE multiuser detector can be implemented adaptively without knowledge of signature waveforms or received amplitudes. This paper introduces an adaptive multiuser detector which converges (for any initialization) to the MMSE detector without requiring training sequences. This blind multiuser detector requires no more knowledge than does the conventional single-user receiver: the desired user's signature waveform and its timing. The proposed blind multiuser detector is made robust with respect to imprecise knowledge of the received signature waveform of the user of interest.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>