COMM-4.1

Fixed Point Algorithm for Bit Rate Optimal Equalization in Multicarrier Systems
Mile Milisavljevic, Erik I Verriest (Georgia Institute of Technology)

In this paper we present a fixed point algorithm for bit rate optimal time domain equalization in multicarrier systems. The algorithm outperforms standard MMSE equalizers in capacity measure. Moreover, it adaptively estimates the optimal signal delay which was an exhaustive search problem in MMSE equalizers. We briefly discuss the convergence properties and demonstrate the performance of the algorithm on a twisted pair copper wire loop with additive non-white noise.

COMM-4.2

A Blind Projection Receiver for Coded CDMA Systems
Shan Mo, Christian Schlegel, V. John Mathews (University of Utah)

This paper presents a blind adaptive CDMA receiver that requires no knowledge of the spreading codes, the delays, and the energy of the received signals associated with the interfering users. Our receiver is based on linear interference cancellation and adaptive interference signal subspace tracking. It has error control coding embedded in the detector structure and employs ``branch processing'' to detect the bit stream. Simulation results demonstrating that the receiver suffers negligible performance loss over systems with complete knowledge of the interfering users are presented in the paper.

COMM-4.3

Rank Order Diversity Detectors for Wireless Communications
Alexander Flaig, Gonzalo R Arce (University of Delwaware)

A novel class of robust detectors, the rank order diversity (ROD) detectors, is proposed. The ROD detectors exploit the diversity inherent in any repetition code by sorting the sampled channel output, weighting each of the sorted samples according to their rank, and summing the weighted order statistics to form the test statistic. The ROD detectors subsume the globally optimal detectors for the short-tailed uniform and the normal distributions, as well as the locally optimal detector for the heavy-tailed double-exponential distribution, suggesting a high efficiency of the ROD detectors over a vast range of possible noises statistics. It is shown that for large sample sizes and under mild conditions on the noise statistics, the ROD detector achieves a probability of error less or equal than that of the linear detector with equality only for the normal distribution. The performance of the ROD detectors is illustrated in a DS-CDMA network.

COMM-4.4

Least-Squares CMA with Decorrelation for Fast Blind Multiuser Signal Separation
Francisco R.P. Cavalcanti, Joao M.T. Romano, Andre L. Brandao (Communications Department, Campinas State University)

A blind algorithm with implicit signal selectivity capability is proposed. The algorithm is an evolution of the original multiuser constant modulus algorithm. The new algorithm features a least-squares type updating rule for fast convergence rate and an adaptive control of the weight of the decorrelation term which improves the steady-state error variance. The expected improvements of the proposed algorithm are verified through simulations with smart antennas in a spatial-division multiple access system.

COMM-4.5

Blind Channel Estimation for Multiuser CDMA Systems with Long Spreading Codes
Zhengyuan (Daniel) Xu, Michail K Tsatsanis (Stevens Institute of Technology)

In this paper, correlation-matching techniques are employed to estimate multipath channel parameters for a multiuser CDMA system with long spreading codes. For given code sequences, the output correlation matrix (parametrized by the unknown channel coefficients) is compared with its instantaneous approximation. By minimizing the Frobenious norm of the resulting error matrix the channel parameters can be estimated up to a scalar ambiguity. Under the assumption of i.i.d. code sequences, identifiability for each channel is guaranteed and the asymptotic convergence of the proposed algorithm is established. Simulation results confirm our claims. Comparisons with other methods are also provided.

COMM-4.6

Channel Estimation for DS-CDMA with Aperiodic Spreading Codes
Kemin Li (Department of EE, University of Virginia, Charlottesville VA 22903), Hui Liu (Department of EE, university of Washington, Seattle WA 98195)

For high performance CDMA communications, multiuser detection is often required to suppress the multiple access interference (MAI). Most multiuser detectors rely on accurate channel information to recover the multiuser digital signals. This paper studies the blind channel estimation problem for DS-CDMA systems using aperiodic codes. The Maximum Likelihood estimator is formulated for channel estimation. We first convert the multiuser parameter estimation problem into a set of single user optimization problems via alternating optimization, and then determine the channel parameters for each user using an iterative algorithm derived. It is shown by computer simulation that this iterative algorithm can reach global maxima almost always under medium SNR values.

COMM-4.7

Decision Feedback Blind Symbol Estimation by Adaptive Least Squares smoothing
Qing Zhao, Lang Tong (Cornell University)

A decision feedback blind symbol estimation algorithm based on the least squares smoothing approach is proposed for single-input multiple-output finite impulse response systems. With the finite alphabet property, the input signal is estimated based on the past detected symbols and the least squares smoothing error of the observation. Implemented both time and order recursively, the proposed algorithm is adaptive to channel variation and has low complexity both in computation and in VLSI implementation. Based on a deterministic model, this algorithm has the finite sample convergence property, i.e., the input signal can be perfectly detected with a small set of data samples in the absence of noise.

COMM-4.8

Application of blind second order statistics MIMO identification methods to the blind CDMA forward link channel estimation
Loubaton Philippe (Laboratoire Systeme de Communication, Universite de Marne la Vallee, 5 Bd Descartes, Champs sur Marne, 77454 Marne la Vallee Cedex, France), Moulines Eric (ENST, Dept. Signal, 46 rue Barrault, 75634 Paris Cedex 13, France)

Blind channel estimation for periodic sequence DS-CDMA systems can be cast into the framework of "structured" blind estimation of multi-input / multi-output (MIMO) FIR systems, where the structure is imoosed by the user's signature. A possible approach to tackle this problem consists in looking for a structured solution to oneof the so-called blind MIMO-FIR system identification techniques proposed recently. This is the approach undertaken among others by Wang and Poor, who proposed to use the subspace method. In this contribution, we follow this approach to consider the particular blind forward link channel estimation problem, and improve quite significantly the results of Wang and Poor.

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Last Update: February 4, 1999 Ingo Höntsch