Blind Adaptive Antenna Arrays for Increased Capacity in Cellular Communications

In this paper we describe a new cellular communication scheme, based on blind adaptive spatial filtering, for increasing spectral efficiency relative to existing and proposed systems. Depending on propagation conditions and the number of antennas in the array, between 2 and 64 times as many users can be accommodated as in existing and proposed systems. In this scheme, an antenna array at the base station is very rapidly adapted to separate spectrally overlapping (but individually bandwidth-efficient) signals received from multiple users. The adapted array is also used to transmit signals to the users. Transmission and reception are time-division multiplexed with each other, and are synchronized among all users; thus, antenna arrays are not required on the mobile units for co-channel interference suppression. Conventional adaptive array schemes require training signals and thus are limited in the allowable number of antenna elements by the tradeoff between training-signal length and message capacity that must arise in the rapidly varying propagation environment typical in land mobile cellular radio. In the new scheme, the Spectral Coherence Restoral (SCORE) algorithm, which adapts the antenna array to separate the signals of different users on the basis of their different cyclostationarity properties, does not require any training signals or calibration data. It is shown that the bandwidth efficiency of the scheme can be substantially higher than that of other schemes, primarily because a large number of antennas can be used in the array at the base station, and thus a large number of users can occupy the same frequency band. The performance of the new method is evaluated in computer simulations as a function of the number of antenna elements, the number of active spectrally overlapping users, and the spatio-temporal properties of the multipath.

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