Channel Capacity Between Antenna Arrays— Part II: Amplifier Noise Dominates

In this paper (Part II of two), we continue examining the use of space-time coding techniques to achieve very-high spectral efficiencies in highly scattering environments, using multiple transmit and receive antennas. The goal is to increase as much as possible the number of antenna elements, which is particularly difficult at the remote station, which usually has a more limited space allotted to the antenna array than at the base station. Under the assumption that sky noise was the dominant noise source, Part I addressed the channel-capacity effects of mutual impedance between antenna elements in the remote array, and the correlation between the signal and noise fields received by these elements. In Part II, we consider the same effects under the assumption that amplifier noise is the dominant noise source. The question of how closely the receiving array elements can be spaced depends on how precisely the channel can be estimated. This is related to the high-precision requirement experienced with supergain antenna arrays. The supergain connection is made explicit by showing that the optimum channel capacity for the case of a single transmitting element is achieved by using the supergain weights for the receiving array. To indicate the effect of noisy channel estimation, the loss in receiver antenna gain due to noise in weight estimates is computed with a simple simulation model of scattered propagation for the single-transmitting-antenna element case