Abstract: A method of mitigating interference in a received wireless signal by adaptive digital filtering efficiently deploys computational resources by using at least one of a DDC, weight generator, and scrubber to perform calculations necessary to generate a plurality of output streams. Embodiments transition a weight generator and scrubber between receiver frequencies according to a known frequency hopping pattern of an FHSS transmission. Other embodiments dedicate scrubbers to receiver frequencies while transitioning a weigh generator between the frequencies to generate sets of weights that can be persistently used by the scrubbers. Embodiments generate sets of weights according to one received multipath signal copy, and then apply the generated weights to filter additional multipath copes received at the same frequency. Various embodiments dedicate a DDC to each receive frequency to form a bank of down-converted outputs, from among which each weigh generator can select primary and reference inputs.

Abstract: Techniques are disclosed for generating a featureless low-probability-of-intercept/low-probability-of-detection (LPI/LPD) waveform via a continuously variable symbol rate transmission. A continuous-phase-modulation (CPM) signal can be represented with a phase trellis. During each symbol duration, the trellis is traversed in either a positive or negative direction in a continuous fashion from the starting phase value to the end phase value. The rate at which the trellis is traversed is varied continuously as a time-varying function. The time-varying phase velocity function, or instantaneous symbol rate, is a type of spreading code or secret key shared between the transmitter and receiver. The disclosed techniques can be implemented with CPM compromising the constant-modulus property of CPM signals.

Abstract: A method of mitigating interference in a received wireless signal by adaptive digital filtering efficiently deploys computational resources by using at least one of a DDC, weight generator, and scrubber to perform calculations necessary to generate a plurality of output streams. Embodiments transition a weight generator and scrubber between receiver frequencies according to a known frequency hopping pattern of an FHSS transmission. Other embodiments dedicate scrubbers to receiver frequencies while transitioning a weigh generator between the frequencies to generate sets of weights that can be persistently used by the scrubbers. Embodiments generate sets of weights according to one received multipath signal copy, and then apply the generated weights to filter additional multipath copes received at the same frequency. Various embodiments dedicate a DDC to each receive frequency to form a bank of down-converted outputs, from among which each weigh generator can select primary and reference inputs.

Abstract: A method of mitigating interference in a wireless signal of interest (SOI) received on an active frequency channel due to a common template multi-channel jamming attack includes selecting at least one reference channel from among a plurality of monitored frequency channels in which correlated jamming patterns are present without the SOI. The method further includes generating a plurality of weights according to data obtained from the active and reference channels, and applying an adaptive digital filter to the active channel according to the generated weights. The monitored frequency channels can be centered about the active frequency channel. The selection of reference channels can be varied and optimized. The data from each reference channel can be used to create a single virtual antenna tap or a plurality thereof. Assignment of the active channel can be time-varied to match a hopping pattern of a frequency hopping SOI.

Abstract: Techniques are disclosed for generating a featureless low-probability-of-intercept/low-probability-of-detection (LPI/LPD) waveform via a continuously variable symbol rate transmission. A continuous-phase-modulation (CPM) signal can be represented with a phase trellis. During each symbol duration, the trellis is traversed in either a positive or negative direction in a continuous fashion from the starting phase value to the end phase value. The rate at which the trellis is traversed is varied continuously as a time-varying function. The time-varying phase velocity function, or instantaneous symbol rate, is a type of spreading code or secret key shared between the transmitter and receiver. The disclosed techniques can be implemented with CPM compromising the constant-modulus property of CPM signals.

Abstract: An electronic transmitter includes: a modulator to phase modulate a carrier signal with a baseband signal using a phase modulation sequence; and an emitter to emit the phase modulated signal. The phase modulated signal has poor autocorrelation, has a corresponding mismatched filter based on the phase modulation sequence, and is configured to demodulate into the baseband signal through poor cross-correlation with the mismatched filter. Sometimes, the transmitter is part of a sensing apparatus, where the emitter emits the phase modulated signal at a target and the emitted signal reflects off the target. The sensing apparatus includes a receiver that has a collector to collect the reflected signal, and a demodulator to demodulate the collected signal into the baseband signal through the poor cross-correlation with the mismatched filter. Sometimes, the transmitter is part of a communication system, where the emitter emits the phase modulated signal to an intended recipient.

Abstract: An electronic transmitter includes: a modulator to phase modulate a carrier signal with a baseband signal using a phase modulation sequence; and an emitter to emit the phase modulated signal. The phase modulated signal has poor autocorrelation, has a corresponding mismatched filter based on the phase modulation sequence, and is configured to demodulate into the baseband signal through poor cross-correlation with the mismatched filter. Sometimes, the transmitter is part of a sensing apparatus, where the emitter emits the phase modulated signal at a target and the emitted signal reflects off the target. The sensing apparatus includes a receiver that has a collector to collect the reflected signal, and a demodulator to demodulate the collected signal into the baseband signal through the poor cross-correlation with the mismatched filter. Sometimes, the transmitter is part of a communication system, where the emitter emits the phase modulated signal to an intended recipient.

Abstract: An electronic transmitter includes: a generator circuit to generate a baseband signal; a modulator circuit to modulate a carrier signal with the baseband signal; an emitter to emit the modulated signal at an intended recipient; and a distortion circuit to apply a final distortion to the baseband signal or the modulated signal. The final distortion is optimized to minimize the ability of unintended recipients to localize the emitter using correlation-based techniques, and to minimize any degradation to the data rate of the emitted signal at the intended recipient. In some cases, the transmitter is part of an electronic communication system that also includes a receiver at the intended recipient. The receiver is aware of the final distortion and includes a collector to collect the emitted signal, and a demodulator circuit to demodulate the collected signal using the final distortion to recover the baseband signal.

Abstract: A method of digital signal processing includes modeling a digitally-modulated radio frequency (RF) communication stream using a set of incoming samples of the stream collected from a single antenna. The stream includes a first signal, the first signal including a sequence of first digital symbols having a previous symbol and a current symbol. Each first digital symbol is chosen from a plurality of first possible values. The first signal is modulated by a first known RF communication protocol having unknown time-varying parameters, the parameters having estimated previous values from modeling the previous symbol using a previous interval of the samples corresponding to the previous symbol. The method further includes collecting a current interval of the samples, predicting current values of the parameters, deciding a value of the current symbol using maximum likelihood estimation, and estimating the current values of the parameters using maximum likelihood estimation.