Résumé: In this paper, two efficient pilot-aided iterative space-time interference cancellation receivers are studied in order to increase the uplink capacity of the Universal Mobile Telecommunication System (UMTS) in frequency-division duplex (FDD) mode. Both iterative schemes use low-complexity beamforming and path combining techniques associated to soft-input soft-output decoding to mitigate the multiple-access interference in space and time. The difference of the proposed techniques relies on the way they deal with unknown channels: the addition of a space-time channel estimation in each iteration on one hand and iterative adaptive beamforming and path combining on the other hand. Thanks to the iterative structure, the observation signal used for estimation or adaptation contains less interference from one iteration to the following, and soft estimates of coded bits are available for data-aided estimation or adaptation. A detailed complexity analysis shows that renewing beamforming and path combining in each iteration without a-priori knowledge on the channel has no significant impact on the overall complexity of one iteration. Simulations of true UMTS-FDD uplink communications over a wide-band directional channel model reveal that near-single user performance can be obtained for very high system loads, whereas more conventional receivers, such as the interference canceller without beamforming and the two-dimensional Rake receiver, fail in recovering the transmitted information.

Langue: Anglais