Virtual Antenna Arrays

The ubiquitous trend to “go wireless” is a symbol of our need for independence and flexibility. To allow for such an “all-wireless” world, large amounts of information with widely varying content have to be exchanged, utilising a limited wireless spectrum. Wireless capacity is thus the keyword and research concentrates on an efficient utilisation of the available frequency spectrum. Recently, it has been proven that the link capacity in the Shannon sense of a Multiple-InputMultiple-Output (MIMO) system can be substantially higher than that of a single link system. The promised limits, however, can only be reached if appropriate coding schemes are applied to spatially decorrelated propagation channels. Naturally, physical limitations within the mobile terminal will lead to mutual correlation among the antenna elements, jeopardising MIMO capacity bounds. In this thesis, a novel implementation of a MIMO wireless system is presented that allows the application of MIMO capacity enhancement techniques to mobile terminals with a limited number of antenna elements. Such a system can be realised by permitting adjacent mobile terminals to cooperate among each other and thus form a Virtual Antenna Array (VAA). The analysis presented here relates to a generalised deployment of VAAs, where an information source communicates with an information target via a given number of relaying VAAs. Each relaying VAA consists of distributed and possibly cooperating mobile terminals, thereby realising a distributed-MIMO multi-stage communication system. Such a system is shown in this thesis to yield a drastic increase in data throughput, where analysis is composed of three stages. First, novel information theoretical results are presented which characterise the capacity for ergodic channels and rate outage probability for non-ergodic channels at each relaying stage. For example, the capacity integral is introduced, and solved, which enables the derivation of closed form capacity expressions for Rayleigh flat fading MIMO channels, as well as space-time block encoded fading channels with arbitrary statistics and channel gains. Second, the previously derived capacity and rate outage probabilities are utilised to derive communication protocols which allocate resources in terms of power, bandwidth, and frame duration to each relaying stage such as to achieve maximum end-to-end data throughput from source to sink. The strategies are derived for general MIMO and space-time block encoded communication scenarios with transceivers of infinite complexity, where resources may or may not be reused among the relaying stages. The applicability of the protocols is assessed by means of numerous example scenarios. Third, fractional resource allocation strategies are derived which are near-optimum for finitecomplexity transceivers. The analysis is performed for space-time block encoded transceivers only, which is easily extended to any form of channel and space-time coding schemes if required. The exposure of the allocation strategies is preceded by the derivation of the error rates of distributed space-time block encoded communication systems. Again, numerous simulation results corroborate the applicability of the derived protocols.