Intelligent antennas in personal communications

The use of antenna arrays in reciprocal channels is explored. A reciprocal channel for fading mobile or personal communications channels has identical short term characteristics in the uplink and downlink, which means that the channel characteristics may be known at the transmitter as well as at the receiver, making it possible to have joint transmit and receive diversity. Adaptive antenna arrays at both ends with M and N elements are applied and the channel is assumed to be random with uncorrelated antenna signals, like in an indoor environment. Fundamental limitations concerning the maximum gain and the diversity orders are given, indicating that the diversity order is MN, and the maximum gain is upper bounded by (√M+√N)². The capacity of the random channel is described through the eigenvalues of the correlation matrix, and it is indicated how the knowledge of the channel enhances the capacity, especially for M>N