Capacity When Using Diversity at Transmit and Receive Sites and the Rayleigh-faded Matrix Channel is Unknown at the Transmitter
G.J. Foschini, Michael J. Gans · Kluwer Academic Publishers eBooks · 2005
We report on theoretical studies of higher bit-rates for burst mode communication in wireless LANs and wireless interbuilding links. We discuss an information theoretic investigation of the benefits of multi-element arrays (MEAs) when communicating in a narrowband Rayleigh fading environment. While the channel is unknown at the transmitter, it is assumed known (tracked) at the receiver. Say that the same number of antennas, n, is used at both sites and that beside bandwidth, total radiated power is fixed. We show that for large n capacity increases linearly with n. The signal components launched from distinct transmit elements interfere at the receiver but in the large n, large ñ, realm, capacity is the same as if there were no interference but SNR was reduced by 10·log10e ≈ 4.343 dB (e ≈ 2.7183...). The derivations hint at the existence of an architecture with extraordinary capacity that can be approached using one dimensional codecs as building blocks. We exhibit this means of communication, which is termed the layered space-time architecture because of the way signals are stratified along diagonals in space-time.