Abstract: A method is presented herein whereby both transceivers of a full-duplex RF communications system can use the same spectrum at the same time. Self-interference is cancelled using a combination of antenna placement, analog RF suppression, and digital adaptive filtering. The details of this self-cancelling technique are presented.

Abstract: A structure and a method for transmitting digital data modulate the amplitude and the phase of a set of orthogonal band-limited finite duration waveforms. In one embodiment, a group of information symbols modulate in parallel a set of spectrally efficient orthogonal waveforms, known as prolate spheroidal wave functions. The modulated orthogonal waveforms are summed, and the resulting composite signal then modulates a carrier signal for transmission. The compressed spectrum modulated signal provides a robust data waveform which reduces the spectral bandwidth requirements compared to digital modulation formats employed in the prior art. The transmitter and the receiver for modulating and demodulating the orthogonal waveforms for transmission operate at slower speeds than corresponding equipment of existing modulation schemes of comparable symbol rate. Consequently, both simplicity of design and cost savings are realized in a compressed spectrum modulation scheme.

Abstract: An equalization and demodulation method for a structured digitally modulated signal provides a multiple filter equalizer, which comprises multiple, parallel, automatically adjustable processors. The multiple filter equalizer is applicable to a structured digitally modulated signal, such as a signal from time division multiplexing (TDM) of multiple data sources. The multiple filter equalizer exploits the repetitive structure of TDM signal data by employing multiple parallel processors each constructed according to the specific requirements at the position in the frame of a symbol to be demodulated. Each processor comprises one or more adaptive digital transversal filters, one or more nonlinear threshold operators, and a symbol decision operator. The transversal filters equalize the data, remove interfering signals, reduce intersymbol interference, and mitigate multipath and other propagation effects.

Abstract: Detection of a digitally modulated radio signal whose underlying data contain repetition structures is achieved by generating a binary spectrum from the frequency domain spectral amplitudes. The binary spectrum of the signal can be rastered at the signal's framing rate or other periodicity to create a two dimensional matrix with the set periodic bits falling along column of the matrix. Application of non-linear logical filtering operations removes speckle caused by aperiodic bits while maintaining the run of aligned periodic bits along the column of the matrix. To automate the line detection process, statistical values and measured line lengths in the binary matrix are used to adjust processing parameter values.

Abstract: A method and apparatus for ultrasonic frequency expansion is characterized by expanding audiometric frequencies before translation into the ultrasonic range. The audiometric signals are first expanded in time by a factor of 1/.beta. where .beta.<1 while generally maintaining the frequency content of the audiometric signals. Next the frequency of the signals is expanded by a factor 1/.beta. while compressing the time scale to that of the original signal. The frequency expanded signal is processed via a single-sideband upconverter to translate the frequency expanded signal into a single sideband signal in the ultrasonic range.

Abstract: A direction finding method and apparatus for a radio signal source, modulated by a digital information signal and existing in a heavy interference environment, is based on cyclic crosscorrelation. The direction finding technique exploits the second order periodicity of a transmitted signal having digital modulation, whereby the technique is immune to narrow-band interference. Radio frequency signals are received by two spaced antennas, and the signal of interest can be considered as a cyclostationary process. The signal time of arrival difference between the two antennas is determined using a cyclic crosscorrelation method. This is implemented by sending the electrical signals, developed by the antennas, through a variable delay device, then to a balanced mixer. The composite signal from the mixer is sent to a band-pass filter whose center frequency is equal to the baud rate of the signal of interest.

Abstract: An acoustical switch is actuated from a remote location by a sound generator such as an ultrasonic whistle. The switch includes a special tuned signal receiver coupled with an amplifier having a frequency selective feedback network. The output of the amplifier is an a.c. signal which is applied to a bistable circuit which, in one state, energizes a relay to turn on an appliance connected to the switch and, in its other state, turns the appliance off.