Predictive Transmit Antenna Selection with Maximal Ratio Combining

Abstract

Abstract-Antenna selection has long been a pragmatic method for exploiting spatial diversity in wireless systems with lower complexity than space-time or MIMO coding, and potentially having reduced hardware cost due to the reduction in the number of RF chains required. Whilst receive antenna selection is perhaps more common, transmit antenna selection also has several advantages, particularly for hardware-costly transmit schemes such as those requiring linearisation. However transmit antenna selection (TAS) requires either channel knowledge, or receiver knowledge at the transmitter, typically achieved using data transmission in the reverse direction, and this implies a delay between the channel being sampled and being acted upon. This outdated channel knowledge degrades system performance. In this paper, the degradation is determined, and related to the channel characteristics. A prediction scheme is then applied to mitigate against this degradation for the case of a (2,1;2) TAS system, where one of two transmit antenna is selected to communicate with two receive antennae employing maximal ratio combining.

Effects of Channel Prediction for Transmit Antenna Selection With Maximal-Ratio Combining in Rayleigh Fading

“…Moving beyond this, a spatial diversity analysis of an ideal TAS/MRC scheme was published by Chen et al [4], where performance metrics such as BER for binary phase shift keying (BPSK), outage probability and gains of the TAS/MRC scheme for flat Rayleigh fading channels were derived. Finally, the authors recently introduced a similar TAS scheme limited to a two transmit, two receive configuration [17]. With only partial analysis, this did not consider outage probability, average SNR gains, amount of fading, antenna placement trade-offs, or the equal-performance threshold between predictive and nonpredictive TAS.…”

“…This predictor is designed for TAS in future transmission blocks based upon current and historical channel information [17]. The benefits of using long range prediction (LRP) of channel values for TASP decisions are evaluated and compared with a non-predictive (TASD) scheme acting on outdated channel information, for a range of system configurations.…”

“…Using (11)(12)(13) and (16)(17), the value of ρ p can now be determined. The power correlation coefficient can be shown to equal the square of the channel correlation coefficient so that ρ p = ρ 2 hĥ (note that this is because the coefficient vector w opt is also the underlying factor used in the channel power prediction calculation).…”

Analysis of adaptive modulation with antenna selection under channel prediction errors

“…In [15], we derive the PDF: f γT ASP (γ), which is equivalent to the the PDF of the true maximum SNR, γ max obtained by averaging out the conditional PDF f (γ|γ) a bivariate Gamma function [15], with PDF of fγ max (γ) . This is given as:…”

“…Large delays render the feedback information useless, effectively creating an openloop system. In [15], channel prediction was applied to a nonadaptive TASP/MRC (predicted TAS/MRC) system, where the effects due to delay is mitigated by predicting the antenna index at the receiver, several coherence intervals ahead. In this paper we consider an adaptively modulated TASP/MRC system, optimised for instantaneous BER (I-BER) constraint under constant power.…”