Robust Transmit Beamforming for Frequency-Selective Fading Channels with Imperfect Channel Feedback

Abstract

Abstract-In this paper, robust transmit beamforming (BF) for transmission over frequency-selective fading channels, taking into account the availability of imperfect channel state information at the transmitter (CSIT), is considered. In a realistic scenario, the CSIT differs from the true channel. The CSIT may be outdated due to channel variations or could be erroneous due to quantization effects and/or transmission errors. Transmit BF with reliable CSIT can improve the system performance significantly. On the other hand, pure space-time coding outperforms transmit BF if the CSIT is unreliable. The optimization criterion of the proposed robust BF scheme takes the reliability of the available CSIT in an optimum way into account. We show that the performance of the proposed robust BF scheme is upper and lower bounded by that of transmit BF with perfect CSIT and generalized delay diversity coding without instantaneous CSIT, respectively.

Robust Cyclic Space-Frequency Filtering for BICM-OFDM with Outdated CSIT

“…[1]- [4]. Similarly, it has been shown in [5] that imperfect CSIT can lead to significant performance improvements in frequency-selective channels. In [5], uncoded single-carrier modulation was considered which requires complex equalizers at the receiver.…”

Combined Time-Reversal Space-Time Block coding and Transmit Beamforming for Frequency-Selective Fading Channels

“…5, BER versus ρ for TR-STBC and TR-STBC-rBF-DFE with L g = 7 for E b /N 0 ∈ {8 dB, 12 dB}, respectively, are depicted. Additionally, the performances of rBF-DFE [5] and ODD-DFE [4] are shown for L g = 7, respectively. Note, that ρ has no impact on the performances of TR-STBC and ODD-DFE, respectively, since here no channel feedback is utilized.…”

“…The integral in (7) is evaluated numerically by the Riemann sum approximation with 21 areas of rectangles, cf. [4].…”

“…also [4], where d min is the minimum Euclidean distance of the signal constellation and Q (x) = 1/ √ 2π…”

“…Robust transmit BF has been proposed in [5], taking into account the reliability of the CSIT, for frequency-selective channels and DFE at the receiver (rBF-DFE). It has been shown, that the performance of rBF-DFE is upper and lower bounded by that of BF-DFE [3] with perfect CSIT and generalized delay diversity [4], respectively.…”