Abstract-Antenna selection is a low-complexity method for pragmatically exploiting spatial diversity in wireless systems. It has potentially reduced hardware cost compared to space-time or MIMO (multiple-input and multiple-output) coding, due to the reduction in the amount of radio frequency (RF) hardware required. Whilst receive antenna selection is perhaps more common, transmit antenna selection also offers several advantages, particularly for hardware-costly transmit schemes such as those requiring linearisation. In use, transmit antenna selection (TAS) requires at least partial channel knowledge at the transmitter in order to perform selection. This knowledge usually comes in the form of an index to the best set of antenna/antennas fed back from the receiver; which implies a delay between the channel being sampled (at the receiver) and this knowledge being acted upon (at the transmitter). In this paper, performance degradation due to outdated channel knowledge is determined analytically, and related to channel characteristics. A predictive scheme is then developed to mitigate against delay-induced degradation. Several factors relating to TAS system performance under different channel scenarios both with and without mitigation are explored. Closed form expressions for performance metrics such as bit error rate (BER), outage probability, average signal-to-noise ratio (SNR) gain and higher order moments of output SNR are derived and verified by simulations. The impact of prediction is analyzed for different TAS setups and channel prediction scenarios, as are various system design parameters.

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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 This outdated channel knowledge degrades system performance.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.

Abstract-The performance of amplify-and-forward relaying in Rayleigh channels is explored for a dual-hop transmission system in which a transmission source selects one of several relays based upon instantaneous SNR (signal to noise ratio) to transmit a data packet to a destination receiver. Both source and receiver devices have multiple antennas, employing beamforming for transmission and MRC (maximal ratio combining) for reception. The chosen relay performs fixed gain forwarding. Closed form solutions for several performance measures are derived for this practical system, and the system is studied in terms of outage probability and symbol error rate which are verified through simulation. Several implementation alternatives are explored to note performance trade-offs, particularly between number of antennas and number of relays.Index Terms-Cooperative diversity, relay selection, amplifyand -forward, beamforming, symbol error rate, outage probability.

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