Fifth IEEE Workshop on Signal Processing Advances in Wireless Communications, Lisboa, Portugal, July 11-14, 2004

In this paper we investigate a chip rate implementation of the MMSE multiuser receiver in the case of uplink UMTS context where data are scrambled by long codes (Gold sequences). The main problem is the resolution of a high dimension linear system involving a band-diagonal auto-correlation matrix. Using a Cholesky (or LDU) decomposition and taking advantage of the multiuser correlation expression, we show that the complexity of this chip rate MMSE is similar to that of the more classical symbol rate MMSE receiver. Then, a theoretical equivalence between these two receivers is demonstrated. Finally, simulation results are presented which show the performance gains of the MMSE receiver when compared to the RAKE receiver

K-products a clustering criterion for signal processing

Cet article passe en revue plusieurs domaines d’applications du critère de classification « K-produits » introduit dans [10]. Ce critère est appliqué à l’estimation de mélange de lois, à l’extraction de lignes droites dans des images binaires et à l’estimation aveugle de canal en radiocommunications. Plusieurs algorithmes d’optimisation du critère sont présentés et des comparaisons avec d’autres approches sont conduites.This article presents several applications of the clustering criterion « K-products » introduced in [10]. This criterion is applied to the unsupervised mixture estimation, the straight lines extraction in binary images and the blind channel estimation in radiocommunications. Some optimization algorithms are proposed and comparisons with other known methods are presented

A Fast Algorithm for Joint Downlink Beamforming

Downlink Beamforming and Power Control are techniques used to improve the capacity or the quality of service in wireless systems. In this paper we propose a fast iterative algorithm for joint downlink beamforming and power control. The performance of this algorithm is compared with decoupled strategies through simulations. Results show that the fast algorithm outperforms the decoupled strategies and has a low computational complexity

Adding Diversity to Multi-User Downlink Beamforming by using BER Constraints

Abstract — In this work, we propose a novel structure and criterion for joint transmit diversity and multi-user downlink beamforming. The proposed structure can be seen as an extension of the purely spatial downlink beamforming and is a transformation that, for each user, transforms K real antennas into L virtual antennas, with L ≤ K. Classical transmit diversity is then applied to these virtual antennas. We propose a design criterion to optimize the precoders in order to find the best tradeoff between minimizing the interference generated towards the other users and maximizing the channel diversity for the desired user. This criterion is based on the minimization of the total transmit power subjected to a target BER constraint for each user. Applied to a multiple-antenna transmitter, the proposed technique outperforms the purely-spatial downlink beamformer by about 5 dB for a target BER of 10 −2 and by 9 dB for 10 −3 in a simple scenario