A multitap transmit diversity scheme for the downlink is proposed where the transmit weight vectors are adjusted such that the SNR at each mobile is above a threshold. The proposed transmit diversity scheme can be applied to networks with multipath fading channels and in cases where the number

antennas. Theoretical performance bounds of the proposed transmit diversity scheme are derived. Simulation examples and theoretical analyses show that the proposed transmit diversity scheme outperforms not only the conventional open-loop transmit diversity techniques, but also some closed-loop transmit

Abstract — In this paper, we investigate different spatial transmit diversity concepts for orthogonal frequency division multiplexing (OFDM) systems. The idea is to artificially increase the frequency and time selectivity of the resulting channel transfer function at the receiver antenna

optimal diversitymultiplexing (DM) tradeoff curve. As a byproduct of our analysis, it follows that delay diversity and phase-rolling at the relay level are optimal with respect to the entire DM-tradeoff curve, provided the delays and the modulation frequencies, respectively, are chosen appropriately. I.

studies the performance of multiuser diversity introduced by a certain HSDPA scheduler together with different closed--loop transmit diversity schemes.

the optimal diversity-multiplexing (DM) tradeoff for all multiplexing gains. As a byprod-uct of our analysis, it follows that delay diversity and phase-rolling at the relay level are optimal with respect to the entire DM-tradeoff curve, provided the delays and the modulation frequencies are cho

-SIC as well as random spreading sequences, we find that the system's spectral efficiency is maximized if each user transmits different codewords spread by distinct signature sequences over its antennas. In contrast, for imperfect channel knowledge the optimum choice of spreading sequences as well

Abstract—Transmit diversity through multiple transmit antennas is generally regarded as beneficial to the link-level performance. In this paper, we shall investigate the role of transmit diversity with respect to the link level and the system-level performance. We focus on the reverse link analysis

compare incremental relaying to transmit diversity in terms of ǫ-outage capacity and signal-to-noise ratio gain. It is demonstrated that incremental relaying outperforms transmit diversity only in certain regions that determine the relay locations.

Adaptive space-time transmit diversity (ASTTD) is a scheme, which combines the ordinary STTD scheme (open loop transmit diversity) with information feedback from mobile terminals to adaptively adjust the transmit power at each transmit antenna. In comparison with the STTD system, the performance