Laurent Ros

SINR Estimation of OFDM-CDMA Systems with Constant Timing Offset: a Large System Analysis

This article presents the impact of a constant timing error on the performance of a downlink 2 dimensional spreading OFDM-CDMA system. This impact is measured by the signal to interference plus noise ratio (SINR) degradation after equalization and despreading. Using random matrix theory, an asymptotic evaluation of the SINR is obtained. It is independent of the value of users spreading code while taking into account their orthogonality. Simulation results are provided to evaluate and discuss the validity of this model

On the system level prediction of joint time frequency spreading systems with carrier phase noise

Phase noise is a topic of theoretical and practical interest in electronic circuits. Although progress has been made in the characterization of its description, there are still considerable gaps in its effects especially on multi-carrier spreading systems. In this paper, we investigate the impact of a local oscillator phase noise on the multi-carrier 2 dimensional (2D) spreading systems based on a combination of orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA) and known as OFDM-CDMA. The contribution of this paper is multifold. First, we use some properties of random matrix and free probability theory to give a simplified expression of signal to interference and noise ratio (SINR) obtained after equalization and despreading. This expression is independent of the actual value of the spreading codes and depends mainly on the complex amplitudes of estimated channel coefficients. Secondly, we use this expression to derive new weighting functions which are very interesting for the radio frequency (RF) engineers when they design the frequency synthesizer. Therefore, based on these asymptotic results, we adapt a new method to predict the bit error rate (BER) at the output of the channel decoder by using an effective SINR value. We show by simulations the validity of our models and that at a given BER, the required signal to noise ratio (SNR) may easily increase due to the carrier phase noise.

Sensitivity of Multi Carrier 2 Dimensional Spreading Systems to Carrier Phase Noise

Phase noise is a topic of theoretical and practical interest in electronic circuits. Although progress has been made in the characterization of its description, there is still considerable gaps in its effect especially on the multi carrier spreading systems. In this paper, we investigate the impact of a local oscillator phase noise on the multi carrier 2 dimensional spreading systems known as OFDM-CDMA. The contribution of this paper is twofold. First, we use some properties of random matrix and free probability theory to give a simplified expression of the signal to interference and noise ratio SINR obtained after equalization and despreading. The latter is independent of the actual value of the spreading codes of different users and depends principally on the complex amplitudes of the estimated channel coefficients. Second, we use this expression to derive new weighting functions which are very interesting for the RF engineers when they design the frequency synthesizer. Simulation results are provided to discuss and validate our model

INTERPRÉTATIONS ET PERFORMANCES DU RÉCEPTEUR LINÉAIRE SUR LIAISON DESCENDANTE TD-CDMA ET EXTENSION MULTI-CAPTEUR

This paper deals with a td-cdma multi-user system downlink through a radio-mobile multipath channel, such as TDD-UMTS. We propose interpretations and equivalent models specific to such a multiple access mode, mostly via a frequency approach. The expressions and performances of the classic linear multi-user detectors are then reformulated. Furthermore, performance computation is applied to indoor and vehicular channel environments, showing the benefit of joint detection and diversity reception with two or three sensors at the mobile.RésuméCet article s’intéresse à la liaison descendante ďun système radiocommunication avec les mobiles multiutilisateur td-cdma soumis à des trajets multiples, tel le mode TDD de ľumts. Il propose des interprétations et des modèles équivalents spécifiques è ce mode ďaccès multiple, avec une approche le plus souvent fréquentielle. Les expressions et performances des récepteurs linéaires classiques sont alors reformulées. A titre ďillustration, le calcul de performances est appliqué aux modèles ďenvironnement º Intérieur » et º Véhicule », montrant le bénéfice de la détection conjointe ainsi que ľapport ďune réception avec 2 ou 3 capteurs sur le mobile.Cet article s’interesse a la liaison descendante ďun systeme radiocommunication avec les mobiles multiutilisateur td-cdma soumis a des trajets multiples, tel le mode TDD de ľumts. Il propose des interpretations et des modeles equivalents specifiques e ce mode ďacces multiple, avec une approche le plus souvent frequentielle. Les expressions et performances des recepteurs lineaires classiques sont alors reformulees. A titre ďillustration, le calcul de performances est applique aux modeles ďenvironnement o Interieur » et o Vehicule », montrant le benefice de la detection conjointe ainsi que ľapport ďune reception avec 2 ou 3 capteurs sur le mobile.

Multi-sensor reception for TDD-UMTS mobile terminal in indoor and pedestrian environments

In the downlink TD/CDMA multiple access scheme through a multipath channel, the use of a short complex code enables a strategy of multi-user detection with great sensibility improvement compared to the traditional matched filter. Nevertheless, the performances are damaged compared to the situation with an ideal channel, more especially as the number of users increases. In this paper, we first use the cross-spectral matrix of the aliased coded channels to recall linear multi-user detector (ZF and MMSE) and express a degradation factor of interference and noise to signal ratio due to a non-ideal channel, with or without fading. The degradation and bit error probability are then computed in the concrete situation of indoor and pedestrian channel environments in order to show the great benefit of one or two supplementary sensors at the reception system.