Abstract: A vehicle infotainment system that adds background sounds to an outgoing call on a mobile device. The infotainment system comprises: i) a database of selectable augmenting audio signals; and ii) audio processing circuitry configured to receive at a first input an uplink signal from the infotainment system and receive at a second input a selected augmenting audio signal. The audio processing circuitry adapts a spectrum of the first selected augmenting audio signal to prevent the selected augmenting audio signal from masking the uplink signal and combines the adapted selected augmenting audio signal and the uplink signal to produce an augmented uplink signal at an output.

Abstract: Methods and circuits for reducing power dissipation in wireless transceivers and other electronic circuits and systems. Embodiments of the present invention use bias current reduction, impedance scaling, and gain changes either separately or in combination to reduce power dissipation. For example, bias currents are reduced in response to a need for reduced signal handling capability, impedances are scaled thus reducing required drive and other bias currents in response to a strong received signal, or gain is increased and impedances are scaled in response to a low received signal in the presence of no or weak interfering signals.

Abstract: A processor-implemented neural network method includes: determining a respective probability density function (PDF) of normalizing a statistical distribution of parameter values, for each channel of each of a plurality of feature maps of a pre-trained neural network; determining, for each channel, a corresponding first quantization range for performing quantization of corresponding parameter values, based on a quantization error and a quantization noise of the respective determined PDF; determining, for each channel, a corresponding second quantization range, based on a signal-to-quantization noise ratio (SQNR) of the respective determined PDF; correcting, for each channel, the corresponding first quantization range based on the corresponding second quantization range; and generating a quantized neural network, based on the corrected first quantization range corresponding for each channel.

Abstract: A system for cancellation of a reciprocal-mixing noise may comprise a down-converter mixer that may be configured to down convert a radio-frequency (RF) signal and to generate a baseband signal. The RF signal may include a desired signal and a blocker signal. A first signal path may be configured to receive the baseband signal and to generate a first signal. A second signal path may be configured to receive the baseband signal and to generate a second signal. A subtraction module may be configured to subtract the second signal from the first signal and to generate an output signal. The second signal may comprise the reciprocal-mixing noise, and the output signal may comprise the desired signal substantially free from the reciprocal-mixing noise.

Abstract: An input signal to a filter device is allowed to be written into one of a plurality of sequentially connected cells if the input signal is not the zero-valued sample. Each cell receives the input signal and multiplies the input signal by one of a plurality of weight coefficients. The input signal is stopped to be written into any of the cells if the input signal is the zero-valued sample. A result of a filtering operation is output from the last cell.

Abstract: A noise suppression apparatus comprising: a complex signal generation unit configured to convert an intermediate frequency signal into a complex signal having a real part and an imaginary part, the intermediate frequency signal being obtained by frequency-converting a reception signal; a noise detection unit configured to detect whether or not variation in level of the complex signal is greater than a predetermined threshold value, to detect generation of noise; and a noise suppressing unit configured to suppress level of the complex signal if the variation in level is greater than the predetermined threshold value.

Abstract: An agile RF tuner circuit capable of converting a wide portion of RF signal into an IF signal suitable for analog-to-digital conversion. The circuit up converts a received RF signal to a high IF signal and then down converts the high IF signal to a low IF signal. Embodiments of the RF circuit incorporate harmonic reject mixers to suppress harmonics and intermodulations typically associated with the frequency conversion process.

Abstract: An amplitude control system including one or more multi-element array power amplifiers (MEA-PA), each MEA-PA including multiple amplifiers, multiple capacitors, and multiple enable circuits. Each amplifier has an input coupled to a common input node and an output coupled to a corresponding one of multiple intermediate nodes. Each capacitor has a first end coupled to an output node and a second end coupled to a corresponding intermediate node. The enable circuits are collectively controlled by an amplitude control value, and each is operative to enable or disable a corresponding amplifier. The enable circuits may be dynamically controlled to modulate amplitude. A coupling circuit may be provided to couple an intermediate node to a reference node when a corresponding amplifier is disabled to adjust a coupling ratio. Each amplifier, when enabled, may receive one of multiple supply reference voltages. The capacitors may have equal capacitance or may be binary-weighted.

Abstract: An agile RF tuner circuit capable of converting a wide portion of RF signal into an IF signal suitable for analog-to-digital conversion. The circuit up converts a received RF signal to a high IF signal and then down converts the high IF signal to a low IF signal. Embodiments of the RF circuit incorporate harmonic reject mixers to suppress harmonics and intermodulations typically associated with the frequency conversion process.

Abstract: A method and apparatus taught herein reduce the peak-to-average ratio (PAR) of a complex-valued signal based on detecting peaks in the signal that are above a peak threshold, characterizing the detected peaks in Cartesian coordinates, generating cancellation pulses in Cartesian coordinates based on the detected peak characterizations. PAR reduction processing continues with canceling the detected peaks by combining the cancellation pulses with a correspondingly delayed version of the signal. Advantageously, peak detection may be performed in polar form using a computationally efficient peak detection algorithm that avoids calculation of the I and Q peak waveforms unless a signal peak beyond a defined threshold is present. In one or more embodiments, the generation and use of asymmetric and/or shaped cancellation pulses offers further performance advantages.

Abstract: An agile RF tuner circuit capable of converting a wide portion of RF signal into an IF signal suitable for analog-to-digital conversion. The circuit up converts a received RF signal to a high IF signal and then down converts the high IF signal to a low IF signal. Embodiments of the RF circuit incorporate harmonic reject mixers to suppress harmonies and intermodulations typically associated with the frequency conversion process.

Abstract: A monitor provides a wireless signal with respective pulses, based on a heartbeat, repetitive physical movement, or other repetitive bodily action of a user. The pulses include longer duration pulses whose duration identifies the monitor, and distinguishes it from other monitors which may provide crosstalk interference. The longer duration pulses are interspersed among short duration pulses to reduce power consumption. A receiver unit processes the signal to determine a rate of the bodily action and provide a corresponding output. The receiver unit can operate in a baseline mode when crosstalk is not detected, where each pulse is used to determine the rate, or in a crosstalk mode when crosstalk is detected, where only the longer duration pulses are used to determine the rate. The receiver unit can synchronize with two or more consecutive longer duration pulses. The pulse duration can be fixed or determined dynamically, e.g., non-deterministically.

Abstract: A wideband receiver comprises a comb limiter combiner wherein the limiting is conducted by digitization and frequency excision in the frequency domain. The received signal is divided up into sub-bands by a bank of bandpass filters having contiguous pass bands spanning the entire receiver range. In each sub-band the band limited signal is digitized and subjected to digital signal processing. A threshold is set such that any frequency with a magnitude that exceeds the threshold is excised in the frequency domain. When converted back to the time domain, the high-power interference frequencies will no longer be present, thereby leaving only the low-power noise and the desired signal.

Abstract: A method and apparatus taught herein reduce the peak-to-average ratio (PAR) of a complex-valued signal based on detecting peaks in the signal that are above a peak threshold, characterizing the detected peaks in Cartesian coordinates, generating cancellation pulses in Cartesian coordinates based on the detected peak characterizations. PAR reduction processing continues with canceling the detected peaks by combining the cancellation pulses with a correspondingly delayed version of the signal. Advantageously, peak detection may be performed in polar form using a computationally efficient peak detection algorithm that avoids calculation of the I and Q peak waveforms unless a signal peak beyond a defined threshold is present. In one or more embodiments, the generation and use of asymmetric and/or shaped cancellation pulses offers further performance advantages.

Abstract: A peak suppressing and restoring method includes suppressing a peak of a signal, starting suppression when a suppression start value is lower than a suppression target value, using a function of a gain characteristic such that a peak amplitude value attains the suppression target value, and restoring the suppressed peak of the signal using an inverse function of the function of the gain characteristic.

Abstract: A transmitter includes a first limiter for performing a first clipping in which an amplitude part at a level higher than an amplitude level based on a first clipping level is cut out from an input signal to be subjected to power amplification, a second limiter for performing a second clipping in which an amplitude part at a level lower than the amplitude level based on a second clipping level is cut out from a first signal that has undergone the first clipping, a separation section for separating a second signal that has undergone the second clipping into an amplitude modulated part and a constant amplitude part, a first amplifier for amplifying the amplitude modulated part, a second amplifier for amplifying the constant amplitude part, and a combiner for outputting a third signal obtained by combining the amplitude part amplified by the first amplifier and the constant amplitude part amplified by the second amplifier.

Abstract: In an image suppression receiver which is employed in such as a heterodyne receiver, the inter-signal errors between the I signal and the Q signal becomes the noise of the image signal frequency components, and thereby the communication quality is deteriorated. In such a wireless communication device, a high performance image suppression circuit is realized. There are provided two image suppression circuits 6-1, 6-2, and in the one hand image suppression circuit 6-1, the I signal and the Q signal are replaced and the desired wave signal is recognized as an image signal and is suppressed, and on the other image suppression receiver 6-2, it is recognized as a desired wave signal and is made pass through without occurring losses, and the phases and the amplitudes of the I signal and the Q signal are adjusted by the IQ signal adjustment circuit so that the ratio between the outputs of the respective image suppression circuits 6-1, 6-2 become the maximum.

Abstract: A noise cancellation method includes: inputting an interference wave signal detected near a receiver, and changing the phase and the amplitude of the input signal to generate a cancellation signal that cancels the input signal; adding the cancellation signal to a received signal received by the receiver, amplifying the resulting signal by a given amplification factor, and converting the amplified signal into a digital signal; controlling the amplification factor based on a frequency ratio of each signal value of the digital signal; and controlling amounts by which the phase and the amplitude of the input signal are changed, based on the amplification factor.

Abstract: The present invention provides for a digital receiver arrangement and related method, in which a digital receiver arrangement comprises a tuner/demodulator circuit, an analogue-to-digital converting means, and further includes means for storing an impulse wavelet representation, means for determining if an interference impulse is present in a received signal, and means for introducing the stored representation of the impulse wavelet to a detected received impulse so as to counteract the effect thereof within the received signal.

Abstract: A hearing enhancement system that enhances a user's hearing based on a directional speaker is disclosed. In one embodiment, the system can include an interface unit that has a directional speaker and a microphone. The microphone captures input audio signals that are transformed into ultrasonic signals. The speaker transmits the ultrasonic signals, which are transformed into output audio signals by interaction with air. At least a portion of the output audio signals are modified to enhance the hearing of the user. Based on the system, the user's ear remains free from any inserted objects and thus is free from annoying occlusion effects. Compared to existing hearing aids, the system is relatively inexpensive. In another embodiment, the system can also be used as a phone. In yet another embodiment, the system can also access audio signals from other portable or non-portable instruments, wired or wirelessly, such as from home entertainment units, phones, microphones at a conference or speakers at a movie theater.

Abstract: A transmitting/receiving module includes a first amplifier for amplifying a transmission signal, a second amplifier for amplifying a receiving signal, and a low reflection limiter provided on an input side of said second amplifier. There may be further provided a radiator from which the transmitting signal is to be radiated into an air and to which the receiving signal is to be received, and a circulator having a first terminal, a second terminal and a third terminal, in which the transmitting signal is inputted to the first terminal, the receiving signal is received by the radiator connected to the second terminal, the third terminal is connected to the second amplifier, and the low reflection limiter is provided between the circulator and the second amplifier.

Abstract: A polyphase receiver comprises an RF front end (10 to 28) for receiving a wanted data signal modulated on a carrier signal and for producing quadrature related low IF signals, an image rejection filter formed by a polyphase filter (30) for filtering the quadrature related low IF signals, soft limiting means (36,38) for compressing the dynamic range of the filtered quadrature related IF signals and a signal demodulator (41) for recovering the data signal. The soft limiting means (36,38) has a characteristic which is substantially linear at signal levels 10 dB below a predetermined minimum wanted signal level, moves into compression for higher signal levels and hard limits at substantially 10 dB above the desired receiver sensitivity which avoids degrading the sensitivity of the receiver.

Abstract: A signal waveform detection circuit includes an amplifier circuit and a comparing circuit. The amplifier circuit has differential amplifiers connected in series. Each of the differential amplifiers has a common connection point. The comparing circuit is connected to the common connection points of the amplifier circuit. The comparing circuit includes comparing units connected to one of the differential amplifiers. Each of the comparing units has a threshold voltage generating circuit for generating signals. Each signal has a threshold voltage that is set between a maximum threshold voltage of a signal output from the corresponding differential amplifier during a maximum amplitude output and a minimum threshold voltage of a signal output from the corresponding differential amplifier during a minimum amplitude output. The comparing unit further has a comparator comparing a voltage at the common connection point with the threshold voltage.

Abstract: A phase interpolation receiver for receiving angle modulated radio frequency signals. The receiver comprises mixers for down-converting the received angle modulated signal to lower frequency signals, limiters, interpolation filters, and a demodulator. The mixers down-convert the received RF signal to a low IF intermediate frequency signal. The low IF intermediate frequency signal is limited. After further down-conversion to zero IF, using quadrature mixers, the limited signal is phase interpolated. The intermediate frequency is chosen such that the limited signal comprises an unwanted signal at twice the intermediate frequency that acts as a noise spreading signal for spectrally spreading of quantization noise generated by the limiters, and the cut-off frequency of the interpolation filters is chosen such that the unwanted signal and the spread quantization noise are suppressed.

Abstract: A multipath noise reducer extracts a high-frequency signal from a demodulated signal obtained from a frequency-modulated signal, and generates a noise reduction coefficient from the extracted high-frequency signal. The demodulated signal is also separated into high-frequency and low-frequency components, the high-frequency component is multiplied by the noise reduction coefficient, and the resulting product is added to the low-frequency component. An output signal is thereby obtained in which the spike noise that characterizes multipath reception of a frequency-modulated signal is reduced with relatively little distortion of other parts of the signal, including the parts between noise spikes. The distortion can be further reduced by replacing the demodulated signal with an interpolated signal during noise spikes before the low-frequency component is separated.

Abstract: A configurable adaptive filter that is used for echo cancellation is disclosed, which includes a method of detecting a voice or no-voice signal. The presence of a voice or no-voice signal is determined by calculating a histogram of signal amplitude value over a period of time. If this histogram has more than a predefined number of samples that are above a threshold then the signal is classified as no-voice or periodic otherwise the signal is classified as a voice signal. A variable maximum amplitude limit and lower amplitude thresholds are disclosed to detect a voice or no-voice from the histogram signal faster than traditional methods utilized in echo cancelers. A configurable hysteresis time is used to ensure the signal register primarily contains voice signal when the filter coefficients of the echo canceler are allowed to adapt.

Abstract: A direct conversion receiver including a filtering system for improving signal reception in the receiver is disclosed. In one embodiment, the direct conversion receiver comprises a first filter adapted to receive a plurality of receive signals comprising a receive band. The first filter is configured to attenuate a frequency range of the receive band to de-emphasize signals within of the frequency range. The direct conversion receiver also comprises a second filter coupled to a signal processing logic output and is configured to amplify the signals in the frequency range of the receive band, the signal processing logic being coupled to the output of the first filter and configured to substantially attenuate a plurality of unwanted signals in the receive band.

Abstract: The disclosed impulse noise rejection circuit and satellite communications terminal using the same are small in circuitry and small in the number of components. The limiter amplifier disposed before a narrow band pass filter controls a desired reception signal and an impulse noise to the same amplitude. The suppression of the amplitude of the impulse noise eliminates the effect of extension of fall time of the impulse noise, which is caused by a time constant of the narrow band pass filter, on the desired reception signal. Thus it realizes the impulse noise rejection circuit small in circuitry and small in the number of parts, and the satellite communications terminal using the same.

Abstract: A Radio Frequency (RF) receiver includes a low noise amplifier (LNA) and a mixer coupled to the output of the LNA. The gain of the LNA is adjusted to maximize signal-to-noise ratio of the mixer and to force the mixer to operate well within its linear region when an intermodulation interference component is present. The RF receiver includes a first received signal strength indicator (RSSI_A) coupled to the output of the mixer that measures the strength of the wideband signal at that point. A second received signal strength indicator (RSSI_B) couples after the BPF and measures the strength of the narrowband signal. The LNA gain is set based upon these signal strengths. By altering the gain of the LNA by one step and measuring the difference between a prior RSSI_B reading and a subsequent RSSI_B′ reading will indicate whether intermodulation interference is present.

Abstract: A simplified interference elimination system is provided for eliminating from a first radio signal transmitted from a first radio terminal to a first radio base station, the effect of interference due to a second radio signal transmitted from a second radio terminal to a second radio base station. The second radio base station has an extractor for extracting the second radio signal from radio signals received in the second radio base station, and a transmitter for transmitting the extracted second radio signal to the first radio base station. The first radio base station has an interference eliminator for eliminating the second radio signal transmitted from the second radio base station from radio signals received in the first radio base station.

Abstract: A radio communication device (100) such as a mobile telephone comprises signal converters (110, 130, 140), a band-pass filter unit (120) and an oscillator (150). In the receiving mode (I) a first converter (110) converts an HF signal into an intermediate ZF signal (20) which, upon filtering by the band-pass filter unit (120), is converted into an NF signal by means of a second converter (130). In the transmission mode (II), the device (100) employs the first converter (110) and the filter (120) for compression of the dynamic range of a microphone signal (40). The first converter (110) converts the microphone signal (40) into a further intermediate ZF signal (50) which is subjected to amplitude limitation by means of a limiter circuit (121) in the filter unit (120) and filtered by means of a filter (122). The third converter (140) converts the filtered and limited signal (51, 52) again into a low-frequency signal (60).

Abstract: A compressive receiver including a dispersive delay line (10) and a frequency translator (16, 18) is preceded by signal compressors (22a-d) that record the incoming signals at one speed and play them back at a higher speed. This increases the frequency spread and provides greater frequency resolution at the output of the receiver.

Abstract: A frequency mixing system that provides an expanded dynamic range when compared to the dynamic range(s) of an individual mixer(s) that makes up the frequency mixing system. The frequency mixing system adjusts the amplitude of an input signal to be frequency mixed to produce a frequency converted signal with an acceptable and/or lower (when compared to the amplitude of intermodulation distortion produced by mixing the input signal without amplitude adjustment) amplitude of intermodulation distortion. If the input signal were frequency mixed without the amplitude adjustment, an unacceptable and/or higher level of intermodulation distortion would result (when compared to the corresponding intermodulation distortion if the amplitude-adjusted signal were mixed by an individual mixer). Adjusting the amplitude of the input signal creates an adjusted signal with signal distortion on the first path.

Abstract: A multipath noise reducer detects and removes the individual noise spikes occurring in an interval of multipath noise, thereby reducing the multipath noise with relatively little distortion of the output signal. The threshold signal used to detect multipath noise is varied depending on reception conditions. The gate pulses indicating the presence of multipath noise spikes are preferably expanded by variable amounts, depending on both reception conditions and the signal level. Multipath noise spikes are preferably replaced by a smoothed signal. These provisions further reduce perceived distortion of the audio output signal.

Abstract: Device (200; 500) for minimizing the quantization noise in conversion between analogue and digital form of a multi-carrier signal comprising an AC component (VAC) with a particular RMS value (VRMS). The device comprises means (230; 530) for converting between analogue and digital form with a limited number (b) of bits within a quantization range (±VQR), means (215,235,245,255; 520) for minimizing the noise by creating an ideal ratio (VQR/VRMS) between the quantization range and the RMS value of the AC component, and means for reducing unwanted DC components in the signal and centering the signal by the wanted DC components being placed in the centre of the quantization range.

Abstract: An improved receiver architecture utilizing active filters for frequency conversion, wherein the final IF stage operates at a frequency higher than the previous IF stage, is disclosed to facilitate the processing by a baseband system operating at higher IF of signals from receivers operating at lower IFs and to enable the continued use of existing post-IF devices with multiple-conversion receivers. A low IF signal output is digitally mixed with a divided local oscillator signal to achieve a higher IF which is suited for processing by post-IF components such as a detector. The mixed signal is then filtered by a low dynamic range active filter and limited.

Abstract: A communication system having a radio master and a radio slave for communicating a communication signal and a control signal via a common channel is constructed by a receiver to receive a communication signal, a transmitter to transmit a control signal, and a limiter to limit an output of the signal received by the receiver for a period of time corresponding to a transmission of the control signal and a reception of a predetermined signal by the receiver. The limiter has a key to request the transmission of the control signal and limits the output of the reception signal in accordance with the key operation. The generation of an uncomfortable sound which is caused by a communication of the control signal can be prevented.

Abstract: Each complex signal sample a(k)+jb(k) of a frequency modulated signal is limited in order to reduce co-channel interference. The limiting is performed efficiently in a digital signal processor by determining a ratio r with a magnitude less than one, equal to b(k)/a(k) in a first case and a(k)/b(k) in a second case, determining from a look-up table a variable p with a magnitude equal to 1/.sqroot.(1+r.sup.2), and determining a number equal to sgn(a(k))p(1+jr) in the first case and sgn(b(k))p(r+j) in the second case as the limited output signal sample.

Abstract: A radio receiver is disclosed. An arbitrary receive signal received through an antenna is amplified by an input amplifier. The signal amplified by the input amplifier is converted into a predetermined frequency by a mixer. The signal frequency-converted by the mixer is shaped in waveform by a band-limiting filter. The signal thus shaped in waveform is amplified and amplitude-limited by a limiting amplifier. The signal limited in amplitude is demodulated by a demodulator. In order to prevent the mixer circuit from generating a distortion due to an excessive input, another amplitude-limiting circuit operated at a level not saturating the mixer circuit is arranged in a stage before the mixer circuit.

Abstract: In accordance with the present invention, a receiver of the type receiving both a signal subjected to FM (Frequency Modulation) and a signal subjected to orthogonal modulation is capable dealing with the two different kinds of signal by use of a single demodulator. This successfully scales down the circuitry of the receiver.

Abstract: A pager includes a radio frequency (RF) attenuator which is initially rendered inoperative and which initiates attenuation of an incoming RF signal in response to a control signal. An amplifier is coupled to amplify the output of the attenuator. A signal level monitor (24, 26), coupled to the amplifier, determines if the output of the amplifier exceeds a predetermined level. A demodulator (16) is coupled to reproduce a base band signal from the output of the amplifier. A controller, following the demodulator, attempts to establish bit sync during each of a plurality of conventional and intermittently executed preamble searches. If bit sync is not established in a given preamble search and if the level monitor indicates that the output of the amplifier exceeds the predetermined level, the controller applies the control signal to the attenuator for activating the attenuator.

Abstract: An IF receiver system includes an IF signal path formed by an IF amplifier section, a bandpass filter, and a limiter section. An RSSI (Receive Signal Strength Indicator) circuit is coupled to the IF amplifier section and the limiter section and generates an RSSI output signal which varies linearly with logrithmic changes in input power. A storage unit is coupled to the RSSI circuit and is configured to store a value which controls current limiting associated with the RSSI circuit. In one specific implementation, the limiter section includes a plurality of serially coupled limiter stages. The RSSI circuit includes a plurality of rectifying stages, wherein a separate rectifying stage is coupled to an input of a corresponding limiter stage. An additional rectifying stage is coupled to an output of a last of the limiting stages. The value within the storage unit controls the extent of current limiting associated with the additional rectifying stage.

Abstract: An apparatus and method are provided for a data communications device, such as a modem (100, 101) or facsimile machine, to detect and discriminate various amplitude modulated signals, such as an ANS signal of the ITU V.25 protocol and an ANSam signal of the ITU V.8 protocol, which may be subject to impulse distortions (FIG. 5B). The apparatus and method embodiments band pass filter (204) an incoming signal at a first frequency, and dynamically limit (208) any impulse distortions of the incoming signal to a limit threshold (211). The limit thresholds may be dynamically determined by rectifying (209) and low pass filtering (210) the band pass filtered signal to determine a low frequency average magnitude level of the incoming signal, with the limit thresholds set as a predetermined variance from this low frequency average magnitude level.

Abstract: A noise blanker (400) suitable for use with a radio receiver (500) having a track and hold unit (509) includes an impulse noise detector (401), a low pass filter (404) that is coupled to the impulse noise detector, and a first amplitude threshold detector (406) that is coupled to the output of the low pass filter and to the input of the track and hold unit. In one embodiment, this noise blanker is configured in conjunction with a radio receiver to yield a radio receiver that substantially minimizes the impact of noise impulses on resulting processed audio. In one embodiment, a second amplitude threshold detector (512) and a repetition rate threshold detector (513) are additionally utilized to allow gating of the internal signal processing paths of the radio receiver in conjunction with operation of the track and hold unit.

Abstract: Co-channel interference of a frequency modulated signal represented by complex signal samples is reduced by amplitude limiting each sample and non-linearly filtering the limited samples. The non-linear filter low pass filters the limited samples, multiplies the filtered samples by their complex conjugates, and high pass filters the products to produce resultant signal samples. It also squares the filtered samples, low pass filters the squared samples, multiplies the filtered squared signals by the complex conjugates of the filtered samples, combines the result with said resultant signal samples and the filtered samples, and low pass filters the combined signal to produce samples having reduced co-channel interference. The limiter and non-linear filter can be constituted by a digital signal processor.

Abstract: An enhanced nonlinear processor for RFI suppression uses a biased inverting limiter circuit. There are two parallel paths in the device; the first one is used to estimate the intensity of the RFI signal, the second one is used to process the signal. The first signal path employs an envelope detector and filter (to estimate RFI intensity) followed by a comparator circuit to avoid use of the processing if the RFI is too small; the second path has a biased inverting limiter whose characteristic is controlled by the output of the first path. When the estimate of the RFI intensity is close to being correct, the biased inverting limiter traps the large RFI signal, converting it into a higher order harmonic which is filtered out. The wanted signal is not trapped, but instead sees an "effective" positive gain which allows it to pass through unaffected except for a gain factor. The net result is a reduction in the ratio of unwanted signal to wanted signal.

Abstract: Each complex signal sample a(k)+jb(k) of a frequency modulated signal is limited in order to reduce co-channel interference. The limiting is performed efficiently in a digital signal processor by determining a ratio r with a magnitude less than one, equal to b(k)/a(k) in a first case and a(k)/b(k) in a second case, determining from a look-up table a variable p with a magnitude equal to 1/.sqroot.1+r.sup.2 , and determining a number equal to sgn(a(k))p(1+jr) in the first case and sgn(b(k))p(r+j) in the second case as the limited output signal sample.

Abstract: A detector circuit (100) for detecting signaling information transmitted with a radio frequency (RF) signal for interpretation by a radio receiver includes a first low pass filter (105) for filtering demodulated audio signals that are directly coupled thereto and for providing a first filtered signal. A second low pass filter (109) is directly coupled with the first low pass filter (105) for filtering the first filtered signal and providing a second filtered signal. A signaling detector (111) is then directly coupled with the second low pass filter (109) for determining the frequency and/or bit code of signaling information included in the second filtered signal.

Abstract: The present receiver includes a radiofrequency part (RF) coupled to a limiting amplifier (SL) which is in turn coupled to a demodulation means (DM) which recovers a digital signal from a received signal obtained by modulating a carrier signal with this digital signal. The limiting amplifier (SL) has an input-output characteristic which is substantially linear for smaller input signals and which strives with a decreasing gain towards a limit value for larger input signals. Due to this input-output characteristic smaller received signals are treated linearly up to the demodulation means (DM). The latter can therefore for these signals compensate for a specific spectrum shaping of the digital signal performed before the actual modulation. In this way the receiver will perform in a nearly optimal way resulting in low bit error rates. For larger received signals the limiting amplifier (SL) is non-linear and such compensation is consequently without effect resulting for these signals in a performance degradation.

Abstract: A circuit which limits to a fixed value the amplitude of a pilot signal received along with a modulated signal, mixes the amplitude-limited pilot signal with the modulated signal, and uses the random FM noise contained in the pilot signal to cancel the random FM noise contained in the modulated signal. The desired signal to be received is selected from the input signal at the high frequency band; this output is converted to a low frequency band signal by means of a frequency converter. The extraction of the pilot signal and the cancellation of the random FM noise is performed in the low frequency band, whereby the characteristics required for the high frequency band-pass filter are relaxed.