Predictive Transmit Antenna Selection with Maximal Ratio Combining

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 This outdated channel knowledge degrades system performance.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.