Abstract: A discrete multitone stacked-carrier spread spectrum communication method is based on frequency domain spreading including multiplication of a baseband signal by a set of superimposed, or stacked, complex sinusoid carrier waves. In a preferred embodiment, the spreading involves energizing the bins of a large Fast Fourier transform (FFT). This provides a considerable savings in computational complexity for moderate output FFT sizes. Point-to-multipoint and multipoint-to-multipoint (nodeless) network topologies are possible. A code-nulling method is included for interference cancellation and enhanced signal separation by exploiting the spectral diversity of the various sources. The basic method may be extended to include multielement antenna array nulling methods for interference cancellation and enhanced signal separation using spatial separation. Such methods permit directive and retrodirective rev transmission systems that adapt or can be adapted to the radio environment.

Abstract: A method is disclosed for using feedback to reduce crosstalk between mobile receivers in a wireless communications system comprising an adaptive transmitting antenna array. Feedback signals from the receivers are time-averaged and used to calculate a set of weight vectors that minimize crosstalk and maximize desired signal without requiring burdensome feedback rates. Beamforming diversity is combined with feedback through the use of diversity vectors. The preferred embodiment includes a method for obtaining the required feedback by exploiting the SAT circuitry present in the AMPS system currently in use. Consequently, the method may be implemented without modification to existing cellular phone handsets.

Abstract: A method is disclosed for using feedback signals (32) to optimize the directional properties of information signals (19) with respect to their intended receivers (16), where information signals (19) are applied to the transmitting elements (14) of a transmitting antenna array (12). Feedback signals (32) generated at receivers (16) by probing signals (17) are monitored, and the weight matrix with which signals (17) are distributed among array elements (14) is adjusted according to feedback signals (32) to minimize cross-talk. Information signals (18) transmitted according to an optimized weight matrix will also have reduced cross-talk. A weight matrix may be optimized by perturbing an initial weight matrix, calculating an error function from the feedback signals (32) produced by each perturbed weight matrix, estimating the direction of an extremum from the error functions, and adjusting the initial weight matrix in that direction.