Mamoun Guenach

Downlink performance analysis of a BPSK-based WCDMA using conventional RAKE receivers with channel estimation

We consider the downlink of a Universal Mobile Telecommunication System terrestrial radio access-wideband code division multiple access (UTRA-WCDMA) system and we investigate the performance of the conventional RAKE receiver. A multipath slowly Rayleigh fading channel is assumed. For the purpose of channel tap weight estimation, a common control physical channel, that is either serial or parallel multiplexed with the dedicated physical channels, is used. The receiver sensitivity to imperfect knowledge of the path delays, to the number of pilot symbols, and to the power ratio of pilot to data channels is also investigated. The system performance is evaluated by means of bit-error rates (BERs) derived using quadratic forms and characteristic functions for a BPSK modulation. The mean-squared estimation error (MSEE) of the channel tap weights is also computed and compared to the classical Cramer-Rao lower bound (CRLB). The mutual interference between pilot and data symbols is taken into account.

Turbo Estimation and Equalization for Asynchronous Uplink MC-CDMA

In this contribution, we propose a new code-aided synchronization and channel estimation algorithm for uplink MC-CDMA. The space alternating generalized expectation- maximization (SAGE) algorithm is used to estimate the channel impulse responses, propagation delays and carrier frequency offsets of the different users. The estimator, multi-user detector, equalizer, demapper and channel decoder exchange soft information in an iterative way. The performance of the proposed algorithm is evaluated through Monte Carlo simulations. Impressive performance gains are visible as compared to a conventional data-aided estimation scheme.

Tracking performance of DA and DD multiuser timing synchronizers for short code DS-CDMA systems

We consider a direct-sequence code-division multiple-access system operating over frequency-selective multipath and slowly Rayleigh fading channels. In order to implement RAKE reception, the delays of the different paths have to be estimated and the estimates have to be updated. We extend interference mitigation to this estimation problem and design timing recovery schemes accounting for the intersymbol interference and the multiple-access interference present in the signal. Starting from the maximum likelihood approach, we derive data-aided and decision-directed early-late synchronizers and study their tracking performance. The advantage of the interference mitigating synchronizer is illustrated. The sensitivity of the synchronizer to imperfect knowledge of path gains and to near-far situations is also investigated.

Performance analysis of joint EM/SAGE estimation and multistage detection in UTRA-WCDMA uplink

This paper deals with the performance evaluation of an asynchronous UTRA-WCDMA uplink using a sequential algorithm for channel estimation and multiuser detection. A multipath slowly Rayleigh fading channel is considered. Both perfect and non-perfect channel estimations are studied with the pilot-to-data amplitude ratio as a parameter, when pilot symbols are transmitted in parallel with data. For channel estimation we use expectation maximization (EM) and spaced alternating generalized expectation maximization (SAGE) algorithms; for symbol detection we use interference cancellation. Bit Error Probabilities (BER) are derived using Monte Carlo simulations for binary phase shift keying (BPSK). The users may have different bit rates. In addition the mean squared estimation error (MSEE) of channel gains is computed and compared to the classical Cramer-Rao lower bound (CRLB).

Design and performance analysis of DA multiuser path trackers for long code DS-CDMA systems

We investigate timing recovery structures for a DS-CDMA multiuser uplink using codes with a period of several symbols named long codes and operating over frequency selective multipath and slowly Rayleigh fading channels. In order to implement RAKE reception the delays of the different paths have to be estimated and the estimates have to be updated. We extend interference mitigation to this estimation problem and design timing recovery schemes accounting for the intersymbol interference (ISI) and the multiple access interference (MAI) present in the signal. We first propose a multirate description of the long code DS-CDMA uplink. Then based on this formalism we revisit the optimum data-aided (DA) maximum likelihood (ML) delay estimation structure and the suboptimum early-late implementation. The sensitivity of the synchronizers to imperfect knowledge of path gains to the period of the long codes and to near-far situations is also investigated.

Performance analysis of DA and DD multiuser tap weight estimators for short code DS-CDMA systems

We investigate the performance of three multiuser tap weight estimators for multipath channels in data aided (DA) and decision directed (DD) modes for a BPSK DS-CDMA reverse link. The tap weights are estimated using different algorithms working separately or jointly in order to obtain good estimates as required for coherent detection or synchronization purposes. The performance of these algorithms and their sensitivity to the observation window, to the delay estimation error and to the difference between successive delays are investigated. A comparison between Hadamard and Gold codes is also included. The mean squared estimation error (MSEE) is computed and compared to the Cramer-Rao lower bound (CRLB).

Multiuser DD-ML estimation of multipath channel delays for a DS-CDMA uplink

We consider a direct sequence code division multiple access (DS-CDMA) system operating over frequency selective multipath and slowly Rayleigh fading channels. In order to implement RAKE reception the delays of the different paths have to be estimated and the estimates have to be updated. We extend interference mitigation to this estimation problem and design timing recovery schemes accounting for the intersymbol interference (ISI) and the multiple access interference (MAI) present in the signal. Starting from the maximum likelihood (ML) approach we derive a decision-directed (DD) early-late synchronizer and its tracking performance is studied. The advantage of the interference mitigating synchronizer is illustrated. The sensitivity of the synchronizer to near-far situations is also investigated.

Multiuser DA-ML estimation of multipath channel delays for a DS-CDMA uplink

This paper deals with the synthesis and the performance analysis of multiuser delay estimators of multipath channels according to the maximum likelihood (ML) criterion in data aided (DA) mode for a BPSK DS-CDMA uplink. We suppose the channel tap weights are known perfectly, and we are interested in the estimation of the path delays. We perform open-loop (S-curve) and closed loop mean squared estimated error (MSEE) analysis in tracking mode and we compare the results to the classical Cramer-Rao lower bound (CRLB).