Rca Inc.

General Electric Company

Leonard N Schiff

Henry G Lewis, Jr

Jack S Fuhrer

Dipankar Raychaudhuri

Smith Freeman

Visvaldis Mangulis

A television system for generating video signals for reception by a receiver having adaptive processing circuitry susceptible of errors includes circuitry for emulating portions of the receiver and detecting the occurrences of such errors. A signal representing the occurrences of the errors is generated and combined with the transmitted video signal. At the receiver the error signal is separated from the video signal and utilized by the adaptive processing circuitry to ameliorate the effects of such errors.

Enhanced TV system using transmitted error signals

A transmitted signal includes a pilot signal, a plurality of information signals and a carrier signal modulated by a modulating signal related in frequency to the pilot signal frequency. At a receiving station, the carrier signal is demodulated and the demodulated signal is used to generate a reference signal to translate the frequencies of the recovered pilot signal and the plurality of information signals by an amount sufficient to correct for undesirable frequency shifts which have occurred in the transmitted signal.

Communications system utilizing a pilot signal and a modulated signal

A digital television transmitter has a buffer that receives a low resolution low pass filtered signal. A high resolution high pass filtered signal is applied to the buffer only when the buffer can accept it without overflowing. A digital television receiver receives a digital television picture signal and preferably a transmitter buffer occupancy state signal. A low resolution low pass filtered signal is applied to an adder. A high resolution high pass filtered signal is applied to the adder when the buffer state is low and also when it is intermediate and no substantial motion is present. The transmitter and receiver are useful in video teleconferencing.

Two resolution level DPCM system

A transmitter and receiver for direct sequence spread-spectrum (SS) communications is described. The audio or other analog information to be communicated controls the clock rate of a pseudorandom sequence (PRS) to produce clock rate encoded direct sequence spread spectrum signals. The signals are decoded by a feedback loop including a voltage controlled oscillator which clocks a local PRS generator. A phase detector responds to the clock rate encoded received PRS signal and to the local PRS signal to produce a control signal. The control signal is filtered and applied to the VCO to control the local PRS clock rate. The decoder loop forces the VCO rate to track the clock rate of the encoded signal, and the decoder loop VCO control signal reproduces the analog information. A demodulator for a clock rate encoded SS signal upconverted by a carrier includes a pair of mixers, a first of which receives the signal to be demodulated and the local PRS sequence from the decoder. When the local and received sequence are phase coincident, the first mixer produces the carrier. The second mixer receives the signal to be demodulated and the carrier from the first mixer and generates therefrom demodulated baseband clock rate encoded SS signals for application to the decoder.

Clock rate spread spectrum

An arrangement for generating an electrical audio signal in response to a sound signal applied to a microphone in a reverberating room removes the reverberations with an adaptive filter. The filter learns or adapts so as to cancel the room echoes by receiving both the audio signal affected by reverberation and a clean audio signal from a highly directional local-acting microphone placed near the source of the sound. The signal to be filtered is applied to a transversal filter including a tapped delay line having variable taps or multipliers to produce incrementally delayed multiplied samples. The multiplied samples are summed, and the sum signal is subtracted from the clean signal to produce a difference signal. A .mu.P is programmed to iteratively calculate the effects of changes to the tap values and to select tap values which tend to reduce the magnitude of the difference signal. When the filter is converged, the difference signal is near zero. At this time, the filtered signal and the clean signal are similar, and therefore the filter characteristic removes the effect of reverberation. The tap values are then fixed, and the signal with room reverberations can be made clean by the adapted filter.

Speakerphone with adaptive cancellation of room echoes

A high frequency code division multiple access spread spectrum (CDMA SS) communications system includes multiple transmitters and their associated receivers, and a pilot carrier source. In order to reduce errors in the receiver IF frequency due to unavoidable differences between the desired transmitted carrier and receiver local oscillator (LO), the transmitted carrier ferquency is related to the pilot frequency. The receiver phase-locks the pilot carrier to the local oscillator, thereby providing an IF data signal with reduced frequency error. The IF data signal is multiplied by sine and cosine demodulating signals related to the local oscillator frequency to produce inphase (I) and quadrature (Q) components of the received data signal. The I and Q signals are applied to code matched filters, which produce filtered or decoded signals the amplitudes of which are related to the phase error between the demodulating signals and the IF carrier. A logic arrangement responds to the decoded signals to generate a control signal which step-corrects the demodulating signal to the correct phase. Correction can occur within one or a few bit intervals, thereby allowing burst mode communications while maintaining high throughput for the multiple users of the communication system.

Fast acquisition burst mode spread spectrum communications system with

A communication system comprising a satellite, a master earth station (MES), and a plurality of small earth stations (SESs) provides signal transmissions addressed and transmittable to a selectable other SES via the satellite, the MES, and then the satellite again. The signal transmissions consist of bit representing pseudo random sequence (PRS) signals PRS.sub.SES which in turn consist of chips arranged in predetermined and identifiable patterns and with the bit and chip occurrence rates C.sub.SES and B.sub.SES of each SES being synchronized with each other as they arrive at the MES. The satellite responds to the signal transmissions from the SESs to retransmit the signal transmissions to the MES, which in turn responds to the signal transmissions from the satellite to amplify and retransmit such signal transmissions back to the satellite again. The satellite again responds to the signal transmissions from the MES to retransmit them to the SESs. The MES and SESs further include apparatus to maintain synchronism between the chip and bit rates of the PRS.sub.SES signals as they arrive at the MES.

Synchronizing system for spread spectrum transmissions between small

A system for determining the bit error rate in a communication system comprising logic for generating a stream of data bits, bit extracting logic for periodically extracting N consecutive bits after the occurrence of every Mth bit, where the N consecutive bits are divided into a group of A bits and a group of C bits, where A and C are equal integers, and a single B bit is positioned between the group of A and C bits, where M&gt;&gt;A, where the N bits can be any combination of binary 1's and 0's. Logic extracts and stores a finely quantized sample of the B bit of each group of N bits. An adder adds an auxiliary group of X bits to the N bits to form a memory address consisting of A, B, C, and X bits. A plurality of memories each has storage locations for a single finely quantized B bit sample. Each memory further is selectable by a unique combination of the binary bits A+B+C with any given storage location in each memory being accessible by various combinations of the X bits. Appropriate logic by a predetermined algorithm calculates the current probability of bit rate error.

Logic for calculating bit error rate in a data communication system

A system is described in which the audio subcarrier components are attenuated relative to the other components of composite television signals by an inexpensive IF filter. This filter incidentally produces quadrature distortion between the two color difference signal components of the composite television signals. The disclosed invention includes a differentiator, responsive to at least one of the color difference signals, that derives signals proportional to the quadrature distortion components present in the other color difference signal. These distortion components are then subtracted from the other color difference signal to produce a signal that is substantially free of quadrature distortion. The differentiator and subtracter are advantageously realized in the form of a simple FIR filter.

Sampled color difference signal processing system having a quadrature

Output weighted FIR filters usually consist of a tapped delay line, weighting circuits coupled to the taps for weighting delayed samples and adder circuitry for combining the weighted samples. In designing such circuitry, tradeoffs are made between device complexity and the desired filter transfer function. FIR filters employing shift-and-add weighting circuits may have the resolution of their weighting circuits significantly enhanced with slight added circuit complexity by providing a parallel tapped delay line to which scaled input samples are applied. The scaled and non-scaled signal samples from the parallel tapped delay lines are both made available to the weighting circuits. The availability of both such samples for shifting and adding, nominally increases the number of possible weighting coefficients realizable from the weighting circuits more than two fold and thus, improves the design flexibility of the filter significantly.

Digital FIR filters with enhanced tap weight resolution

Apparatus is disclosed for demodulating sampled data chrominance signals that include a first component that modulates a carrier to produce asymmetrical sidebands, and a second component modulated in quadrature to produce double sidebands. Samples representing the second component are derived and subtracted from the chrominance samples. The samples produced represent the asymmetrical sideband component. These samples are passed through a Nyquist filter to produce samples representing the first component signal but having the frequency spectrum of a vestigial sideband modulated signal. Demodulation of these samples by conventional means produces samples of the first component signal having a uniform range of amplitude values over the frequency band of the first signal.

Demodulator for sampled chrominance signals including a Nyquist filter

A low-power, spread spectrum synchronized communication system employing a satellite which continuously and iteratively re-transmits a PRS signal PRS.sub.m from a master earth station having a chip rate C.sub.m and a bit rate B.sub.m and comprising a plurality of ground stations each including a transmitter for transmitting a first PRS signal (PRS.sub.G) unique thereto and having a first chip rate C.sub.G and a first bit rate B.sub.G and a receiver for receiving and identifying PRS.sub.G after being returned by the satellite as PRS.sub.Gr with a chip rate C.sub.Gr and a bit rate B.sub.Gr. Also provided is a phase difference detector responsive to C.sub.m and C.sub.Gr to periodically produce a signal representative of the change of phase difference thereof and a frequency changing circuit responsive to such signal to change the chip rate C.sub.Gr by an amount which will cause the phase of C.sub.Gr to approach the phase of C.sub.m at a given rate.

Apparatus for synchronizing spread spectrum transmissions from small

A satellite communications system has a number of earth stations sharing an uplink carrier in a time division multiple access mode. One of the earth stations is designated as the master station for the carrier. The uplink transmissions from each station are synchronized by computing the time interval between the arrival at the satellite of the signal from the master station and the signal arrival from each of the other stations. The actual time intervals are compared to the optimum intervals for a properly synchronized transmission from each station. If the comparison indicates that a given earth station is not properly synchronized, that station's time of transmission is adjusted until the actual interval substantially matches the optimum interval.

Synchronization system for a regenerative subtransponder satellite

A transmitted signal includes a pilot signal at a given frequency and an information signal occupying a different band of frequencies. A noise reduction system for a signal receiver detects modulation on the pilot signal and generates a signal having a frequency that varies in response to the detected modulation. The system includes an apparatus for combining the received signal with the generated signal to produce a signal at another frequency with reduced frequency noise.

Noise reduction system for a single sideband multiplex signal

An improved companded transmission system uses a transmitter having a first compressor for compressing a signal m(t) of bandwidth B.sub.1 to form a signal C[m(t)]. The transmission system has a bandwidth B.sub.2 where B.sub.1 .ltoreq.B.sub.2. A receiver having an expander to expand the received signal r(t) is provided to produce a signal m.sub.E (t). The improvement consists of a circuit for recovering the frequency components f.sub.L lost during transmission of C[m(t)] and includes a second compressor for compressing m.sub.E (t) in the same manner as m(t) was compressed to produce a signal C[m.sub.E (t)] which contains frequency components f.sub.c lying above B.sub.2. A filter which is responsive to C[m.sub.E (t)] generates (C[m.sub.E (t)]-f.sub.c), and, a subtractor subtracts (C[m.sub.E (t)]-f.sub.c) from C[m.sub.E (t)]. An adder adds f.sub.c to r(t), and, an expander expands the summed signal f.sub.c +r(t) to produce a signal m.sub.1 (t) which is a first order corrected approximation of m(t). Similar structure can iteratively process m.sub.1 (t) to further refine or correct the received signal.

Growing community of inventors

Lawrenceville, NJ, United States of America

Leonard N Schiff