1:00, SPCOM-P2.1
CONSISTENT ESTIMATION OF RAYLEIGH FADING CHANNEL SECOND ORDER STATISTICS IN THE CONTEXT OF THE WIDEBAND CDMA MODE OF THE UMTS
J. CHAUFRAY, P. LOUBATON, P. CHEVALIER
In this paper, we address the problem of second order statistics estimation of a selective Rayleigh channel in the context of the wideband CDMA mode of the UMTS. The data to be transmitted are sent over slots over which the channel is assumed to remain constant. Each slot contains a pilot symbol sequence from which the channel can be estimated. The covariance matrix of the channel is usually estimated by a denoised version of the empirical covariance matrix of the trained channel estimate. However, this estimate is not consistent in the UMTS context. In this paper, we propose a new consistent estimate of the channel covariance matrix, and evaluate the performances of two Wiener like channel estimation schemes based on the proposed estimate.

1:00, SPCOM-P2.2
ON ESTIMATING TEMPORAL AND SPATIAL CHANNEL PARAMETERS FOR DS-CDMA SYSTEM OVER MULTIPATH RAYLEIGH FADING CHANNELS
K. WANG, H. GE
In this paper, we develop an approximate maximum likelihood (ML) method for joint estimation of time delays and directions-of-arrivals (DOA's) for the direct-sequence code-division multiple-access (DS-CDMA) systems over the multipath Rayleigh fading channels. In developing the proposed estimation scheme, we model the known training sequence of the desired user as the desired signal and the multiple access interference (MAI)-plus-AWGN as unknown colored Gaussian noise uncorrelated with the desired signal. To reduce computational complexity, a fast algorithm realization is proposed taking advantage of the ridge structure of the objection function. Analytical and simulation results are presented to illustrate the performance in comparison with the Cramer-Rao bounds (CRBs). It is shown that the proposed algorithm is near-far resistant for both time delay and DOA estimations, with almost no performance loss compared with CRBs.

1:00, SPCOM-P2.3
BLIND MULTICHANNEL IDENTIFICATION AND PROJECTION RECEIVER DETERMINATION FOR MULTICODE AND MULTIRATE SITUATIONS IN DS-CDMA SYSTEMS
I. GHAURI, D. SLOCK
We consider multicode and multirate transmission scenarios in a DS-CDMA system operating in an asynchronous fashion in a multipath environment. Oversampling w.r.t. the chip rate is applied to the cyclostationary received signal and multisensor reception is considered, leading to a linear multichannel model. Channels for different users are considered to be finite-impulse response (FIR) and of possibly different lengths, depending upon their processing gains. We consider an individualized linear MMSE-ZF or projection receiver for a given user, exploiting its spreading sequence and timing information. In the multicode case, a certain user is considered to use several spreading codes in order to transmitat a higher rate. Considering different code sequences to be issuing from different virtual users, the propagation channel impulse responses of all these users are the same. However, the total channel impulse response which includes spreading sequences is different for all users. On the other hand, in the multirate case, a periodically varying set of periodic spreading codes spread successive symbols of a certain user. Symbols spread by different codes can therefore by considered to be issuing from different virtual users. The problem therefore boils down to classical multiuser detection with time-invariant interference canceling filters for each virtual user. A blind channel estimate is also obtainable through Capon's method (first used by Tsatsanis) as a by-product of the MMSE-ZF receiver algorithm.

1:00, SPCOM-P2.4
ASYMPTOTIC PERFORMANCE OF ML CHANNEL ESTIMATORS IN WCDMA SYSTEMS: RANDOMIZED CODES APPROACH
X. MESTRE, J. FONOLLOSA
This paper analyzes the asymptotic performance of Maximum Likelihood (ML) channel estimation algorithms in wideband code division multiple access (WCDMA) scenarios. We concentrate on systems with periodic spreading sequences (period larger than or equal to the symbol span) and high spreading factors, where the transmitted signal contains a code division multiplexed pilot for channel estimation purposes. Assuming randomized training and code sequences, we derive and compare the asymptotic covariances of the training-only (TO), semi-blind conditional ML (CML) and semi-blind Gaussian ML (GML) channel estimators.

1:00, SPCOM-P2.5
LOW-COMPLEXITY SYNCHRONIZATION IN A NAVIGATION RECEIVER UNDER MULTIPATH INTERFERENCE
J. SELVA
The time-of-arrival estimation error produced by multipath interference in a navigation receiver causes a strong degradation of the positioning accuracy. We present a synchronisation technique, operative in a navigation receiver under multipath interference, that takes into account its special conditions: low signal-to-noise ratio, DS-CDMA signals with long spreading codes, and very low data rates. The paper begins introducing the signal model of a deterministic antenna array. In this context, the system-specific features translate into the assumtion that all times of arrival must be inside a delay interval in which a truncated series approximation of the reference signal is valid. The introduction of this series in the signal model leads to an implementation based on a bank of correlators. Finally, the associated minimization problem is solved using three minimization algorithms: ESPRIT, IQML and a modification of Newton's Method. The latter calculates the maximum Likelihood estimator with a low computational burden.

1:00, SPCOM-P2.6
CODE TIMING ACQUISITION USING AN ANTENNA ARRAY FOR ASYNCHRONOUS DS-CDMA SYSTEMS IN A NEAR-FAR ENVIRONMENT
C. HU, I. REED, X. YU, P. THANYASRISUNG
An adaptive near-far resistant detector using a multiple antennas for acquiring synchronization of an asynchronous DS-CDMA system is presented. The only requirement is the prior knowledge of the desired user's spreading sequence. Also there is no need of a training sequence and period. Synchronization acquisition of asynchronous DS-CDMA signals is treated as a binary-hypothesis test. An adaptive generalized maximum likelihood ratio test (GLRT) is developed to acquire the multipath code timings of a single desired user in fading and near-far environment. The synchronization is obtained by sliding a search window in a sample-by-sample manner to perform the adaptive GLRT with the non-constrained maximum likelihood estimator (MLE) of Direction-Of-Arrival (DOA) during the symbol interval. The acquisition performance of the proposed detector is illustrated by computer simulations of an asynchronous BPSK DS-CDMA system and is shown to be potential to against multipath fading and near-far problems.

1:00, SPCOM-P2.7
BLIND TIME DELAY ESTIMATION IN ASYNCHRONOUS CDMA VIA SUBSPACE INTERSECTION AND ESPRIT
N. PETROCHILOS, A. VAN DER VEEN
The implementation of a RAKE receiver for a quasi-synchronous DS-CDMA (direct sequence code division multiple access) system requires the estimation of the dominant path delays for each user. Presented here is a blind method to estimate these parameters. The algorithm takes advantage of various signal space invariances in the frequency domain to isolate the subspace of interest for each user, then uses ESPRIT on these subspaces to estimate the delays. The method processes each user independently of the others, is near-far resistant, and allows several delays per user. Simulations indicate a fair accuracy.

1:00, SPCOM-P2.8
CRAMER-RAO BOUND FOR LOCATION ESTIMATION OF A MOBILE IN ASYNCHRONOUS DS-CDMA SYSTEMS
C. BOTTERON, A. HOST-MADSEN, M. FATTOUCHE
Commercial applications for the location of subscribers of wireless services continue to expand. Consequently, finding the Cramer-Rao bound (CRB), which serves as an optimality criterion for the location estimation problem, is of interest. In this article, we derive the CRB for the estimation of channel parameters and mobile position in an asynchronous direct sequence code division multiple access (DS-CDMA) system operating over fading channels. It is assumed that the location estimates are obtained from the bearings and/or propagation delays estimated at one or more cluster(s) of antenna array of arbitrary geometry. Among other applications, the CRB on the positioning accuracy may serve as a design tool to find an optimum antenna placement, or to evaluate the practicability of a legal demand for emergency location.

1:00, SPCOM-P2.9
AN ADAPTIVE CHANNEL ESTIMATOR FOR CDMA SYSTEMS IN MULTIPATH FADING CHANNELS
S. MO, V. MATHEWS
CDMA systems in multipath fading channels need to estimate channel parameters for coherent detection of the transmitted signals. In this paper we present a simple but effective channel estimation algorithm that can be incorporated into most types of multiuser receivers to obtain good detection performance. This technique uses a set of correlation filters to independently estimate each of the channel parameters. One advantage our method has over subspace-based algorithms for channel estimation is that it can estimate the channel parameters without phase or amplitude ambiguity. Simulation results demonstrating that our channel estimator is capable of tracking reasonably fast fading channels are also presented in the paper.