Abstract: A method of synchronizing a baseband demodulator in a radio receiver, which may be stationary or mobile. The demodulator is a phase-shift demodulator and detects a baseband signal incoming from a sampling A/D-converter in the receiver. The baseband signal is transmitted from a radio transmitter in the form of bursts, in time slots in accordance with the TDMA-principle. One time slot, in addition to the data word, also includes in a known manner a synchronization part which has a given, fixed bit pattern. Prior to demodulation in the baseband demodulator, differential correlation of the received baseband signal is effected with the known synchronization pattern, wherein a time-dependent correlation function is obtained. The absolute magnitude of the maximum value is calculated and the corresponding time position for this maximum value is detected, which denotes the time position of the synchronization part of the received baseband signal.

Abstract: An RS-232C line receiver IC includes a reference voltage generating circuit, a switching circuit, a switch control circuit and a hysteresis output circuit. The reference voltage generating circuit produces a first low reference voltage at a node and a second low reference voltage at a node. The switching circuit has a first and a second switching device connected respectively to the nodes of the reference voltage generating circuit. The switch control circuit selectively makes conductive the first or the second switching device. The hysteresis output circuit to which an input is applied is connected to the first and second switching devices and receives the first or second low reference voltage applied through the first or the second switching device as low input threshold voltages.

Abstract: A multistage decoder for decoding received symbols formed by symbols which have been subjected to multilevel coding in several successive partitioning levels from a constellation into several subsets. A symbol of the constellation is coded into several bits, and each stage of the multistage decoder determines a sequence of bits relative to a partitioning level for a sequence of estimated symbols which are selected from among the symbols of the constellation or of the subset as being each individually closest to the received symbols. The invention is characterized in that for at least one stage at least one detector generates an erasure bit for the estimated symbols whenever a received symbol lies in a predetermined erasure zone, whereupon the stage decoder then corrects the erasure bits. The decoder may operate in the adaptive or non-adaptive mode. The erasure zones may be angular sectors or bands of constant width. The widths of the zones are stored in preprogrammed memories.

Abstract: In a digital mobile system, to avoid distortions and fadings due to multiple propagation and the doppler shift, adaptive gain of the amplifier of a demodulator must be controlled with information derived from the signal at a high frequency. This is accomplished without the use of intermediate frequency selection filters by first demodulating the signal to base band, filtering out the desired signal and remodulating the desired signal to a higher frequency. From this remodulated signal the adjustable gain is controlled.

Abstract: An automatic equalizer includes an adaptive matched filter connected in front of a decision feedback equalizer of a conventional design. The adaptive matched filter has an A/D converter for sampling and quantizing an analog baseband signal into a digital signal, which is applied to a transversal filter. The transversal filter is supplied with tap coefficients adaptively controlled by a control signal generator which makes automatic adjustments to symmetrize the impulse response of a transmission path depending on the status of fading. The automatic equalizer can sufficiently equalize the fading in the range .rho.>1 in which the reflected wave is stronger than the direct wave, which fading cannot be adequately equalized only by the conventional decision feedback equalizer.

Abstract: A plural-differential phase shift keying (PDPSK) communication system has a transmitter (22) for encoding digital data as plural differentials of phase between successive pairs of channel symbols of a carrier, and a receiver (24) with a plurality of phase differential detectors (32, 48) connected in cascade for determining the plural differentials of phase of the incoming signals to achieve a bit error rate independent of frequency offsets and thereby an improved rate of signal acquisition.

Abstract: A transmission method and a transmitter and receiver Structure is disclosed which provides for transmission of modulated waves using long pulses with a plurality of frequencies. The method involves two consecutive frequencies being separated by 1/T, where T is the period of the useful transmission intervals. The method and the apparatus are particularly suited to broadcasting and reception of television and radio signals as well as telephone communications between exchanges and between radio telephones and communication stations including terrestrial stations and satellites and local computer networks. Most particularly the method is applicable to high fidelity radio transmissions as well as to high definition television (HDTV).

Abstract: An ISDN interface circuit is provided which is coupled to a terminal device via a transmission line and a reception line, the transmission line being formed of a pair of first and second wires, and the reception line being formed of a pair of third and fourth wires. The ISDN interface circuit includes a first resistor and a second resistor connected in series at a first node and between the first and second wires of the transmission line, and a third resistor and a fourth resistor connected in series at a second node and between the third and fourth wires of the reception line. The ISDN interface circuit also includes a D.C. power source connected to one of the first node, at which the first resistor and the second resistor are mutually connected in series and the second node, at which the third resistor and the fourth resistor are mutually connected in series. One of the first node and the second node, other than the above-mentioned one of the first node and the second node connected to the D.C.

Abstract: Briefly, according to the invention, a receiver (100) for receiving a carrier signal MSK (minimum shift keying) modulated with a bit stream of a digital information signal (302) is disclosed. The receiver (100) comprises a quadrature demodulator (128) for providing baseband quadrature demodulated signals (306 and 308). The quadrature demodulated (128) is coupled to an EXOR (126) for providing a decoded bit stream of the digital information signal (312) thereby avoiding complex decoder circuits. The quadrature demodulator (128) includes a pair of mixers (106 and 108) for quadrature mixing the received carrier signal and a pair of filters (114 and 118) for filtering the outputs of the mixers (106 and 108). The filters (114 and 118) are coupled to a pair of limiters (116 and 120) for limiting the filtered signals.

Abstract: A Ku band frequency signal transmitter using a minimum of Ku band signal processing components is shown. Inexpensive generation of Ku band signals is provided by frequency multiplying high power, lower frequency signals to a final Ku band signal frequency. The transmitter generates an intermediate frequency signal from a baseband modulated signal and a high frequency local oscillator signal. The baseband signal is FSK modulated and has a constant envelope. A dividing stage reduces the baseband frequency signal to improve the spectral purity of the final Ku band output signal.

Abstract: A system and method for optimal maximum a posteriori (MAP) demodulation. The present invention incorporates neural network technology, i.e., a Hopfield network, (1) to replace the function of the traditional, suboptimal phase-locked loop in an FM receiver and/or (2) to optimally estimate a discrete phase value using an expected value (obtained from the mean of the prior probability distribution of the phase) and statistical dependence between different phase values in a block of samples (described by the covariance matrix of the prior phase distribution). The definition of the Hopfield network includes particular bias currents, feedback weights and a sigmoid function for solving the nonlinear integral equation associated with optimal demodulation. The present invention also includes a signal classifier having a plurality of angled modulators for modeling different phase modulation processes.

Abstract: Disclosed is a hardware arrangement for equalizing waveform distortion caused by multipath fading in a digital radio communications system, which hardware arrangement uses a recursive least-squares algorithm into which a forgetting factor is introduced. An incoming signal (PSK signal for example) is applied to an automatic gain controller which generates a first signal whose value varies with a signal-to-noise ratio of the incoming signal. A forgetting factor controller is coupled to the automatic gain controller to receive the first signal and generates the forgetting factor the value of which varies with the value of the first signal. An adaptive equalizer receives the incoming signal and the forgetting factor. The adaptive equalizer equalizes the waveform distortion using the forgetting factor according to the recursive least-squares algorithm.

Abstract: Generation of a high power rf pulse is achieved in a simple transmitting device that uses permanent magnet material(s) to store energy. Such energy is released through the thermal quenching of the magnetic material(s). Thermal quenching is accomplished, e.g., through an explosion. Such thermal quenching is facilitated in one embodiment by using a magnetic composite material comprising both magnetic particles and explosive particles. The rf pulse thus generated may be used for any desired purpose, e.g., tracking or research. The transmitting device includes a permanent magnet for establishing a constant magnetic flux for so long as the magnet retains its normal magnetic properties. The magnetic flux passes through a coil. Upon the thermal quenching of the magnetic material(s), the magnetic properties rapidly change, causing the magnetic flux to also rapidly change, thus inducing a high power electrical pulse in the coil.

Abstract: Loop circuits lacking byte alignment are tested by test equipment signals at 9.6 kbps transmitted over a DS.phi. format 19.2 kbps communication network. Upon indication of loss of 19.2 kbps framing, return signals from the loop are reformatted into a 9.6 kbps format by selecting proper return bytes using a logic system stored in an office channel unit (OCU).

Abstract: A digital data transmission system includes a transmitter connected to a receiver by a twisted pair. A digital transversal filter, included in the transmitter, supplies output signals to a resistor bank. The output signals are weighted by the resistors of the resistor bank, summed, and used to generate the transmitted pulse. The values of the resistors are chosen to predistort the transmitted pulse so that, after distortion by the transmission medium, the transmitted pulse more nearly corresponds to the ideal pulse shape for which the receiver is designed.

Abstract: In a radio mobile system in which the radio signals are received by at least two antenna, the signals are filtered, weighted and then combined before being sent to an equalizer. The weighting coefficients are calculated as a function of signals corresponding to the power level received by each antenna and signals which is represent the quality of reception of each antenna. Furthermore, an equalizer control signal is generated from the combination of signals, weighted by the weighting coefficients, corresponding to the time response of the transmission channel to a single impulse.

Abstract: The correct sampling timing phase is obtained by a digital data receiver by averaging samples of the preamble of a received data burst and using the computed averages as addresses to a memory which stores correction values for the timing phase. The output of the memory is sent to a phase correction circuit for correcting the phase of the presently received data burst.

Abstract: A digital audio interface protocol carries multiple channels of digital audio information serially between a transmitting digital audio tape recorder and a plurality of receiving recording units. Using a three stage process, the circuitry of the present invention allows the receiving VCO's to "lock on" to the sampling rate of the serial digital data stream without any explicit sampling information. In a first stage, the VCO frequency is adjusted until a sync pattern is properly received. In a second stage, the VCO frequency is adjusted to oscillate a preselected number of times between sync pattern occurrences. In a third stage, the VCO phase is adjusted to match the phase of the serial data stream.

Abstract: A differential transimpedance amplifier used in amplifying optical signals transmitted with a balanced code has a level restore circuit which integrates the digital output of the amplifier and feeds back the result to one of the differential inputs of the amplifier. The feedback signal removes imbalances from the amplifier output. The balanced amplifier output can then be processed by a clock reconstruction circuit to accurately sample the received optical signal with a low bit error rate.

Abstract: A transmitter is provided with a distribution preserving Tomlinson coder which predistorts shaped data signals such that the power of each data signal exiting the coder is substantially similar to the power of the data signal entering the coder and such that upon transmission of the predistorted data signal over a channel, the effect of ISI of the channel is substantially removed. The transmitter is primarily intended for coded modulation systems utilizing a "coset" code, and the predistortion is preferably accomplished according to a linear function ##EQU1## where r.sub.k is a data signal entering the coder, a and.sub.i b.sub.i are the coefficients of polynomials relating to the channel impulse response, x.sub.k is the predistorted data signal exiting the coder, and s.sub.k is chosen to cause the signal power of x.sub.k on average to approximately equal the signal power of r.sub.k on average. Different methods for so choosing s.sub.k are disclosed.