Turbo space-time processing to improve wireless channel capacity

By deriving a generalized Shannon capacity formula for multiple-input, mult iple-output Rayleigh fading channels, and by suggesting a layered space-tim e architecture concept that attains a tight lower bound on the capacity ach ievable, Foschini has shown a potential enormous increase In the informatio n capacity of a wireless system employing multiple-element antenna arrays a t both the transmitter acid receiver. The layered space-time architecture a llows signal processing complexity to grow linearly, rather than exponentia lly, with the promised capacity increase. This paper includes two important contributions: First, we show that Foschini's lower bound is, in fact, the Shannon bound when the output signal-to-noise ratio (SNR) of the space-tim e processing in each layer is represented by the corresponding "matched fil ter" bound, This proves the optimality of the layered space-time concept. S econd, we present an embodiment of this concept for a coded system operatin g at a low average SNR and in the presence of possible intersymbol interfer ence, This embodiment utilizes the already advanced space-time filtering, c oding and turbo processing techniques to provide yet a practical solution t o the processing needed. Performance results are provided for quasi-static Rayleigh fading channels with no channel estimation errors. We see for the first time that the Shannon capacity for wireless communications can he bot h increased by N times (where N is the number of the antenna elements at th e transmitter and receiver) and achieved within about 3 dB in average SNR, about 2 dB of which is a loss due to the practical coding scheme we assume- the layered spare-time processing itself is nearly information-lossless!.