Abstract: A method and apparatus for improved ghost cancellation for use in particular in television receivers. The sequence of coefficients derived from a received GCR signal, is further processed to effect a transfer of energy from minor echo coefficients to major echo coefficients thereby improving the overall performance of the ghost cancellation device.

Abstract: In a wireless alarm system an arrangement for increasing the reliability that messages will be received is provided. Each transmitter transmits an alarm message a plurality of times with delays between the messages. Successive delay times are of different duration to increase the likelihood that messages will not be lost if two transmitters transmit at the same time.

Abstract: An improved modem system for HF data transmission over a varying communication channel transmits data in packets formatted into successive frames, each having two identical training sequences following a sequence of data. Each training sequence has a time length longer than the expected time length of the multipath dispersion in the communication channel, in order to isolate one training sequence in each frame from multipath interference from the preceding data sequence. The "clean" training sequence allows the receiving modem system to derive very accurate channel estimates for each frame by autocorrelation to the known symbol sequence stored at the receiver. By interpolating across the channel estimates for the current and previous frames, the modem system can track the communication channel by interpolated estimates for any part or any point in time of the data sequence.

Abstract: A system for improved echo cancellation for use in particular in television receivers. The system features a superior ghost cancellation reference signal which exhibits improved performance in noisy environments and which exhibits the flat and wide bandwidth necessary for effective channel characterization while exhibiting a higher and more evenly distributed amplitude versus time characteristic than that provided by known, non-cyclic ghost cancellation signals.

Abstract: A method and apparatus for improved ghost cancellation for use in particular in television receivers. The sequence of coefficients derived from a received GCR (Ghost Cancellation Reference) signal, is further processed to effect a transfer of energy from minor echo coefficients to major echo coefficients thereby improving the overall performance of the ghost cancellation device.

Abstract: A communication system for relatively high data bit rate RF communication overcomes multipath interference by employing relatively narrow beam antenna sectors and by selecting the best communication path established between two terminals, at least one of which has narrow beam antenna sectors. The communication path selection process includes determining the signal integrity of data communicated between the terminals. One implementation includes the narrow beam antenna sectors at each terminal.

Abstract: A method and apparatus for associating received pulses with one of a plurality of emitters emitting pulses at periodic intervals. Periodic pulse trains are detected by computing the difference in arrival times between each received pulse and a fixed number of previously received pulses. In the simplest embodiment, a periodic pulse train is detected when one of the computed differences is one-half of another computed difference. In other embodiments, further processing is performed to detect staggered pulse trains or other periodic patterns.

Abstract: In accordance with the teachings of this invention, a multi-path distortion simulator is constructed having two paths, one path including a delay means, and both paths including phase shifters and attenuators. The phase shifters are closely matched, thereby compensating for drift and errors in the phase shifters. Similarly, the attenuators are closely matched, thereby compensating for drift and errors in the attenuators.

Abstract: A test signal is transmitted over a communication channel and the signal is received by a receiver. The temporal evolution of the test signal is represented in a matrix and the inverse of the test signal evolution matrix is stored in the receiver. Samples of the received signal and the test signal evolution matrix inverse are used to compute the channel impulse response, and the values of the channel impulse response set signal restoration filter coefficient values. The received signal is then restored by filtering.

Abstract: For generating an RF signal modulated by a message and distorted by a predetermined fading profile for testing RF receivers, a sequence of digital phase and amplitude values which corresponds to the message modulation is arithmetically processed by a predetermined fading profile and stored in memory, and an RF carrier is amplitude and phase modulated by the stored values to produce a testing signal for the RF receivers.

Abstract: A receiver comprising a multi-path detector which comprises a frequency noise peak detector, an AM-detector and a weighting circuit. When noise peaks and amplitude modulations occur in an antenna input signal selected by a diversity switch on account of a control signal of the weighting circuit one of a number of antennas is switched to. This switching is audible to an annoying degree. By inserting a threshold arrangement (31, 32) in the detector, by means of a low-pass filter and a rectifier circuit, an instantaneous threshold voltage is generated varying with the frequency swing of the modulating signal. With a large swing, corresponding with a large amplitude of the modulating signal, switching is audible to a less annoying degree. On the other hand, at moments when the modulating signal has a small amplitude, switching may take place more frequently and is less audible because of the small amplitude of the modulating signal.

Abstract: A method and means for reducing multipath interference distortion in a time-division multiple access (TDMA) communications system is disclosed. A transmitting station (100) formats one or more equalizer synchronization words with a first user's data word, time-multiplexes this formatted user message with at least one other user message, and transmits the combined signal. The receiving station (200) receives the transmitted TDMA signal, de-multiplexes the first user message from the other user messages, and equalizes the time delay spread characteristics of the data word portion of the first user message (or a stored version of such) in response to this de-multiplexing. Performing the adaptive equalization process more than once per user time slot provides an even higher data throughout for the system. Storing the first user message in a data buffer permits the adaptive equalization process to be performed in non-real time, thereby lowering the required signal processing data rate in any particular receiver.

Abstract: A receiver comprising a switching circuit responsive to an antenna switching signal for switching between two antennas to produce a received signal, a noise estimating circuit for estimating the quantity of noise from the received signal, and an integrating circuit for integrating the noise to produce a first control signal which serves as the antenna switching signal.

Abstract: The present invention provides a communication system which employs a signal whose carrier phase is shifted by a constant amount .DELTA..theta. per time slot in correspondence to each symbol (1 or 0) transmitted, and the phase shift is performed by .DELTA..theta./2 (or -.DELTA..theta./2) in the first 1/2 time slot and further by .DELTA..theta./2 (or -.DELTA..theta./2) in the second 1/2 time slot thereby to improve the bit error rate in multipath propagation.

Abstract: A high-cut and high-blend control voltage generating circuit for activating a noise reduction circuit of an FM stereo receiver is configured to be simply responsive to multipath noises and never to plug noises. A changing and discharging circuit in the control voltage circuit may have a relatively long charging time constant, and the voltage control circuit may be configured to be simply responsive to multipath noises above a predetermined level. Thus the circuit is much less liable to operate erroneously.

Abstract: The invention relates to a device for simulating multipath interference in order that the correction stages of a radio receiver can be tested. The device includes parallel paths, simulating the multipath environment, and a pilot tone generator for introducing pilot tone into the paths. A feedback loop continuously adjusts the phase and amplitude of segments in the paths so as to cancel pilot tone from the output whereby the loop maintains the adjustment need for maximum attenuation at the frequency of the pilot tone.

Abstract: A transmitter for digital radio communication creates a null by balanced encoding of data modulated on an RF carrier, and inserts a calibration tone within the null. By having the calibration tone coincide in phase and frequency with the transmitted radio frequency output for coherent demodulation of data at the receiver where the tone calibration signal is extracted and used for multipath fading compensation.

Abstract: For use in cancelling a distortion caused by multipath transmission to an original radio frequency pulse of an original pulse shape, a multipath canceller comprises a priliminary circuit for producing a distortionless pulse of the original pulse shape and a distortion cancelling circuit responsive to the distortionless pulse and each distorted pulse having the distortion for producing a distortion cancelled pulse at a correct pulse position which the original pulse would have if received through a direct path alone. The preliminary circuit may comprise a memory for the distortionless pulse.

Abstract: A communication system transmits information which may be in the form of frames or bursts of suppressed-carrier data over a dispersive transmission path which introduces multipath distortion. Each frame is stored as it is received and processed by iteratively simulating the multipath distortion, subtracting the distortion from the stored frame to form a corrected signal, and evaluating the quality of the resulting signal. The quality of the resulting signal is determined by frequency multiplying the corrected signal and evaluating the total power of components other than the frequency multiplied carriers. The iterative procedure adjusts the phase and, if deisred, the amplitude of signals tapped from a delay line.

Abstract: Frequency diversity is employed to counter selective fadings as a result of multi-path propagation for troposcatter and short-wave connections for digital useful signals employing frequency modulation. For this purpose, the digital useful signal is supported on a frequency arrangement comprising at least three radio frequencies in that the digital useful signal, together with at least one additional oscillation, and, in fact, an additional fundamental oscillation which determines the frequency of the spacing in radio-frequency frequency arrangement, is fed to the input of a frequency modulator. At the input end, the radio-frequency carriers of the frequency arrangement, which are each modulated with the useful signal, are all converted by coherent mixing into the same frequency level, from which, by way of a combiner, a sum signal is obtained which is the optimum in respect of signal-to-noise ratio.

Abstract: A transmitting-receiving station for transmitting information by frequency hopping comprises a code generator to define the use of a plurality of channels in accordance with a high-speed skip law for a transmitting-receiving station in the stand-by mode, the high-speed skip law consisting in the use of each of the channels during a period of time Tp, while the low-speed skip law governs the change of listening channels used during N.times.Tp, each corresponding to a center channel out of a sequence of N channels of the high-speed skip law. The center channel contains a synchronizing code. The station comprises a memory device to which a write circuit for progressively storing therein the codes produced by the generator and also to which a read circuit is connected to take the codes from the memory as a function of the positions of the transmitting-receiving station.

Abstract: A multipath distortion reducing circuit particularly adapted for use with stereophonic receiving circuits in which the amount of mixing between right and left channels is reduced. In accordance with the invention, the envelope of the received FM signal is AM detected, and the envelope detected circuit is multiplied by the FM detected signal differentiated to provide a distortion cancelling signal. The distortion cancelling signal is summed with the detected FM signal to provide an output having a reduced multipath distortion component.

Abstract: To utilize indirect-path signals in a receiver for fixed and mobile transmitter-receiver stations of a TDMA spread-spectrum digital radio system, coherent detection is employed. At the same time, the signal imaging the multipath profile is continuously regenerated by a regeneration circuit. The regeneration circuit provides a phase-coherent signal employed for demodulating the received signal.

Abstract: An FM diversity receiver system and method are disclosed which include two antennas and a switch for switching the receiver from one antenna to the other. A fade control signal is produced which is related to the received FM signal, in which fade control signal both multipath and non-multipath disturbances are manifested. Disturbances in the fade control signal are compared with a threshold voltage and, when the disturbance exceeds the threshold voltage, antenna switching is momentarily prevented to prevent antenna switching in response to electrical noise impulses, such as ignition noise, which are shorter than the period during which antenna switching is momentarily prevented. If the fade control signal disturbance continues to exceed the threshold voltage after the momentary period of disablement, the threshold voltage is reset to a level related to the maximum level of the fade control signal disturbance, after which antenna switching takes place.

Abstract: A multipath interference reduction system for mobile subscriber access systems, each occupying one of a plurality of time slot channels. Interference caused by multipath returns is eliminated in the receiver portion of digital signal communications apparatus by a plurality of cascaded signal subtraction units wherein the detected signal is successively delayed by increasing multiples of the pulsewidth of the main lobe, varied in amplitude and subtracted from itself until all the multipath amplitudes of significance are subtracted out of the composite received signal.

Abstract: Plural transmitters, which transmit signals to a common receiver, transmit their signals in a fixed time-staggered pattern. As a result, the individual signals which are transmitted by the respective transmitters do not interfere with one another or influence one another. Between the fixed time-staggered signals, which are sent out, for example, as standard signals to facilitate routinelike monitoring, signals of a higher priority, for example alarm signals, can be transmitted without any time delay. This is particularly suited for use in connection with a personal security and monitoring system, in which the function monitoring of the unit and the wireless connection between several transmitters and a receiving center must constantly be monitored, and signals of a higher priority, namely alarm signals, are transmitted without delay.

Abstract: This disclosure is concerned with a technique and apparatus for reducing CW and other inband interference in a broad bandwidth RF pulse navigation system to inobtrusive noise through the use of pulse-position random modulation, including, where desired, superimposed random phase modulation, with signal-random modulation code cross-correlation in reception.

Abstract: A method and apparatus are presented for detecting the presence of ghost signal contamination of a video signal by examining the picture information interval of the video signal. A baseband video signal is detected and examined to detect signal transitions. Transitions of the main video signal of a given polarity will be followed by corresponding transitions of a ghost signal. The time intervals between ones of the transitions are measured and stored. If a ghost signal is present, the time interval between corresponding ghost and signal transitions will occur more frequently than the relatively random time intervals between transitions of the main signal and the ghost signal considered separately. By correlating the time interval measurements, the recurring time interval between corresponding main and ghost signal transitions can be identified. This information may then be used to adjust the delay of a delay line in a ghost cancellation system.

Abstract: The fade character of a transmitted radio signal comprising an amplitude or phase modulated double-sideband signal is determined from the algebraic sign of the fade induced modulation and the location of the fade notch (.omega..sub.f) relative to the center (.omega..sub.c) of the double-sideband signal frequency spectrum. In the disclosed embodiment, the algebraic sign of the fade induced modulation is determined (e.g., 402, 403, 404, 405, 406, 409, 410, 411, 412, 413, 417) from the sign of the dc component of the product of the differentiated amplitude modulation and frequency modulation of the received signal. The relative location of the fade notch is determined by comparing the amplitudes (e.g., 402, 404, 405, 406, 415) of corresponding frequency components in each sideband of the received double-sideband signal.

Abstract: The fade character of a received double-sideband, phase coherent signal is determined from the location of the fade notch frequency, (.omega..sub.F) relative to the center (.omega..sub.c) of the received signal frequency spectrum and the phase between fundamental components of first (P.sub.1) and second (P.sub.2) product signals. These product signals are derived (401, 403, 411, 413, 419, 420, 421 or 801, 802, 803, 805, 811) using first (.omega..sub.1) and second (.omega..sub.2) spectral components that are symmetrically disposed about the center of the received signal frequency spectrum. The fundamental components of each product signal are at a common frequency.

Abstract: Apparatus is disclosed for reproducing transmitted information which is subject to multipath delay spread effects and doppler frequency-shift effects. The information is transmitted as a series of modulated information pulses of differing nominal frequencies. The nominal frequencies of successive pulses are repeatedly shifted through a predetermined sequence of frequencies. Arrivals of the transmitted pulses are detected at a receiver and are processed to determine the frequencies to which the transmitted pulses are doppler shifted and the multipath delays of each pulse. This frequency and delay information is then used to reproduce the transmitted information from the arrival pulses.

Abstract: The invention relates to the radio-electrical transmission of accurate timing-mark signals. A space-diversity electrical connection is formed between a station having one single antenna and a station having two antennae and one of the stations is equipped with a receiver device which combines into one composite timing-mark signal the different repetitive timing-marks decoded and rectified from high-frequency signals which have traversed several spatial propagation paths. A common automatic gain control circuit weights the decoded and rectified timing marks according to a weighting which diminishes with the level of high frequency reception. Preferably the rectification of the timing marks is carried out non-linearly.