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Recently, a novel MIMO transmitter architecture has been introduced that requires only a single radio-frequency (RF) chain and is built on parasitic antenna arrays. MIMO transmission in this case is achieved by shaping directly the radiation pattern with the aid of analog tunable loads attached to the parasitics. As it has been shown, such a single RF MIMO system can support all PSK modulation formats with purely imaginary loading values. This paper extends its capabilities and proposes a novel architecture for parasitic antennas that is able to provide complex loading values, even with a negative real part. Definitely, this will extend the flexibility of parasitic antennas to multiplex successfully over the air more complex signaling formats, for example, QAM signals. The bit error rate evaluation shows that the proposed architecture could be very promising in emerging devices and also illustrates its robustness under possible loading perturbations that might have been raised due to nonidealities in the design. [ABSTRACT FROM AUTHOR]

We take a capacity view of a number of different space-time coding (STC) schemes. While the Shannon capacity of multiple-input multiple-output (MIMO) channels has been known for a number of years now, the attainment of these capacities remains a challenging issue in many cases. The introduction of space-time coding schemes in the last 2-3 years has, however, begun paving the way towards the attainment of the promised capacities. In this work we attempt to describe what are the attainable information rates of certain STC schemes, by quantifying their inherent capacity penalties. The obtained results, which are validated for a number of typical cases, cast some interesting light on the merits and tradeoffs of different techniques. Further, they point to future work needed in bridging the gap between the theoretically expected capacities and the performance of practical systems. [ABSTRACT FROM AUTHOR]