Adaptive space-time signal processing and coding

This paper considers the capacities available in multi-antenna or MIMO systems through the use of techniques such as space-time coding. In particular we compare the conventional space-time coding systems so far developed which do not make use of knowledge of the channel at the transmitter, with the optimum adaptive system which adapts the transmission to the channel characteristics. We show by a simple example that the capacity of the adaptive system may be significantly greater, especially at low signal to noise ratio. We also consider the directional characteristics of the transmitted signal, and show that while the non-adaptive systems transmit equally in all directions, the adaptive system transmits primarily in the wanted directions, and thus reduces interference in other directions very substantially.