Abstract: This invention relates generally to signal processing techniques for removing or reducing the effects of instabilities in pulsed signal sources, as in phase echo systems using a pulsed signal transmitter source, and, more particularly, to a technique for compensating for the varying amplitude, frequency and/or phase characteristics of the signal source pulses during operation.

Abstract: A signal processing system for measuring the amplitude and time delay responses of a network over the bandwidth allocated to the network wherein a plurality of subburst signals each in the form of a suppressed-carrier, amplitude-modulated signal, is applied to the network. The signals received from the network are provided in complex form having in-phase and quadrature components. Matched filters respond to such components and the matched filter outputs are processed so as to determine the estimated amplitude and time delay responses of the network at the carrier frequency of the subburst signals over the operating bandwidth of the network.

Abstract: A signal processing system in a transmitter/receiver system for reducing undesired amplitude, frequency and/or phase distortions arising due to variations from transmitter pulse to transmitter pulse. A plurality of sequential samples of transmitted pulses are averaged and a plurality of filter coefficients are determined therefrom. The coefficients are used in a plurality of filters which respond to a plurality of sequential samples of received pulses, the filters providing output signals in which such distortions are reduced.

Abstract: A channel propagation simulator simulates a multi-diversity branch signal channel, which simulator uses in a preferred embodiment appropriate filter means, such as a plurality of tapped delay lines 11, 14, each capable of representing the impulse response of a diversity branch by means of correlated tap multipliers 12, 12A, 15, 15A . . . 15N, i.e., multipliers using correlated weighting signals 12', 12'A, 15', 15'A . . . 15'N as supplied from a matrix weighting correlator 19. The correlated weighted signals are combined for each diversity branch by suitable summation circuits 13, 16 to provide the diversity branch simulated outputs. By using correlated weighting signals, the simulator can more accurately reproduces the statistical behavior of a given communications link and verify that a given modem will satisfy the communication link specifications.

Abstract: An adaptive filter (11) for use in a diversity receiver system (10) which includes circuitry (23, 24, 25, 26, 34) for determining the strongest received diversity signal or group of signals at each of a plurality of time delays or group of time delays and circuitry (27, 28, 29, 30, 31, 34) for calculating a weighting signal and for weighting only the strongest received diversity signal or group of signals at each of the time delays or group of time delays, the other received diversity signals at each time delay thereby being in effect weighted by zero. The weighted signals are then combined in a delay line (32, 33) having a plurality of taps at such time delays to produce an output receiver signal. In a particular embodiment, for example, the received signals are complex signals and the weights used for the strongest received diversity signal at each time delay are quantized weights selected from the group .+-.1.+-.j.

Abstract: A modem in which the transmitter uses spectrum spreading techniques applied to sequentially supplied input bits, a first group thereof having one spread spectrum sequence characteristic and a second group thereof having a different spread spectrum sequence characteristic, the spread spectrum bits being modulated and transmitted. The receiver generates complex samples of the received modulated signal at a baseband frequency and uses a detector for providing signal samples of the complex samples which are time delayed relative to each other. A selected number of the time delayed samples are de-spread and demodulated and the de-spread and demodulated samples are then combined to form a demodulated receiver output signal.

Abstract: An adaptive power equalizer circuit for use in a spread spectrum receiver system which includes an antenna system 12, 13 and a receiver 11, the circuit comprising adaptive power inversion circuitry 15 for producing a first signal having a minimized power level and a second signal having a substantially higher power level than that of the first signal. Such signals are supplied to a power equalizer circuitry 16 which equalizes the power levels thereof, such equalized power level signals then being combined in a suitable combiner circuit 30 for producing an output receiver output signal for the receiver 11.

Abstract: A method for processing a voiced speech waveform when the periods and amplitudes thereof may be non-uniform so that the intelligibility thereof is adversely affected. In accordance with such method successive portions of the speech waveform are processed so that each portion has a substantially uniform period and the intelligibility thereof is enhanced. In some instances the processing may be such as to provide in addition substantially uniform peak amplitudes in each processed portion. The voiced speech waveform enhancement technique may further be used in conjunction with methods for processing unvoiced speech waveforms so as to enhance the intelligibility thereof.

Abstract: In a communications system, consonant high frequency sounds are enhanced: the greater the high frequency content relative to the low, the more such high frequency content is boosted.

Abstract: Signal processing circuitry, preferably for use in multiplying two input signals, one at RF frequency and one at baseband frequency, which includes at least a basic four branch bridge circuit having a diode connected in each branch in a generally symmetrical four branch circuit configuration using a single bias supply and including a trimming resistor in at least one branch for controlling the current through the diodes in such branch so that the characteristics of the diodes in all branches can be matched over substantially the complete range of control current values therefor.

Abstract: Signal processing circuitry, preferably for use in multiplying two input signals, one at RF frequency and one at base-band frequency, which includes a pair of PIN diodes connected in a generally symmetrical circuit configuration using a single bias supply and including a trimming resistor for controlling the current through a selected one of the diodes so that the characteristics of both diodes can be matched over substantially the complete range of control current values therefor. Further, the circuit configuration permits the use of an easy and effective technique for compensating for temperature changes of the circuit during operation.

Abstract: A receiver system for processing diversity channel signals to substantially eliminate future and past intersymbol interference (ISI) in received signals which have been transmitted through a time-varying frequency selective transmission medium. The system includes lattice filter means which provide forward error residual signals which are used for generating uncorrelated adaptive weighting signals which eliminate future ISI and decision feedback circuitry which provide uncorrelated adaptive weighting signals which eliminate past ISI.

Abstract: An improved high speed digital communications diversity receiver using a forward adaptive transversal filter equalizer, having a plurality of weighting sections in each diversity channel to provide a combined weighting signal, wherein the required complex multiplications and correlations needed for weighting purposes are performed at IF frequencies, while the time-delayed combining operations for providing the desired combined weighted output signal are performed at baseband frequencies. Such an arrangement reduces the number of tapped delay lines normally needed for such transversal filter equalizer operation and further reduces the signal losses incurred in operating delay line devices at intermediate frequencies so that fewer large gain-bandwidth product amplifiers are required in the system than the number required in previously available systems using such forward transversal filter equalizers.

Abstract: A dual channel receiver system for receiving polarized signals, which system reduces cross-interference between the signal channels by utilizing adaptive filter equalization means responsive to the input received signals and to error control signals for providing a plurality of weighting signals which are used to combine selectively with the input received signals to reduce the errors, including particularly cross-polarization and noise errors therein. The channels each include decision-directed error signal generating means for providing such error control signals. The system also includes means for preventing system failures wherein both received signals fade simultaneously under which conditions data reversal in the channels could occur and wherein one received signal fades under which condition the same data is produced in both channels.

Abstract: An apparatus for simulating the characteristics of a signal channel which uses two or more cascaded delay lines each of which in one embodiment has a single input and a plurality of tapped outputs. The tapped output signals from each delay line are each multiplied by randomly characterized signals and the multiplied signals are combined to supply an input signal to the next succeeding delay line. The input signal to the first of the cascaded delay lines is the channel input signal and the output of the last of the cascaded delay lines is the simulated channel output signal. The randomly characterized signals associated with all but one of the delay lines may be signals having random polarities or having random phases while the randomly characterized signals associated with the remaining one of the delay lines has Gaussian characteristics.

Abstract: A signal multiplier for multiplying first and second input signals each having time-varying amplitudes and relatively wide bandwidths in which a first input signal is added to at least one sinusoidal reference signal having an amplitude larger than that of the first input signal. The amplitude of the signal so produced is limited and the limited amplitude signal is multiplied by the second input signal to produce an unfiltered signal. The signal components thereof having undesired frequency spectra are then filtered to produce a signal proportional to the product of the first and second input signals.