Uplink Throughput Enhancement by Employing Transmit-only AUX Antennas at Nomadic Terminals: A Capacity Analysis

Abstract

Employing transmit only AUX antennas is a rela-tively cheap way of enhancing the communication throughput of lightweight UAVs, nodes in unmanned field expeditions, racing circuits etc, where increased data-rate demands from the nomadic terminals to the base station (BS) may happen intermittently. Asymmetric load demands in the uplink often call for augmented infrastructure at the nomadic terminals or UEs. By omitting multiple receive chains onboard (along with the requirements of oversampling, synchronization and heterodyning), considerable savings in energy, ergonomics and cost is afforded by employing commercially available transmit only AUX antennas, along with the MAIN antenna subsystem possessing its own dedicated receive chain. The absence of AUX receive chains brings new design chal-lenges, for example, estimating the full channel becomes trouble-some at the UE, particularly when the BS has a large number of antennas. On the other hand, the MIMO capacity at high SNRs, effectively the full degrees of freedom, can be achieved even when the channel state information (CSI) is available only at the receiver, for many scattering environments. This motivates us to analyze the situation where the receiving BS has full CSI, however the UE transmitter only knows the CSI from its main antenna system. Channel statistics are assumed to be known at all the terminals. We investigate the uplink ergodic Shannon capacity of the resulting partial CSI MIMO system, and propose transmission schemes which are almost optimal, at all SNRs of interest. Our results show that even using a single additional AUX can provide 60 -70% capacity improvement for a receiver with more than two receive antennas, even at moderate SNRs.