Abstract: A system and method for maintaining privacy in transmission of a high bandwidth analog signal. A preferred system and method breaks an input signal into bands and then uses Walsh codes to overlay many signals on top of each other with a set of phase modulators to establish scrambling of the input signal. The scrambled signal is then transmitted. The received scrambled signal has the phase modulation removed and an inverse Walsh transform recovers the original bands. The recovered bands are added together to recover the original signal. The system and method use techniques that establish synchronization and phase coherency complete the process.

Abstract: A passband transversal equalizer that uses a novel partitioning of circuits to improve the dynamic range and minimize unwanted signal interactions. The passband transversal equalizer uses a novel interconnection matrix and may be implemented using GaAs monolithic microwave integrated circuit (MMIC) devices for improved performance. The passband transversal equalizer comprises a divider that splits an input signal along a predetermined number of signal paths. Coaxial delay lines delay the signals propagating along the respective signal paths by a first set of nominal relative delays. A plurality of active divider having push-pull outputs are respectively coupled to the coaxial delay lines. An interconnection matrix respectively couples outputs of the active divider to one of a plurality of complex weighting and combiner circuits. A second plurality of coaxial delay lines delay the signals output by the complex weighting and combiner circuits by a second set of nominal relative delays.

Abstract: A system and method for maintaining privacy in transmission of a high bandwidth analog signal. A preferred system and method breaks an input signal into bands and then uses Walsh codes to overlay many signals on top of each other with a set of phase modulators to establish scrambling of the input signal. The scrambled signal is then transmitted. The received scrambled signal has the phase modulation removed and an inverse Walsh transform recovers the original bands. The recovered bands are added together to recover the original signal. The system and method use techniques that establish synchronization and phase coherency complete the process.

Abstract: Systems and methods employing higher order modulation techniques to transmit information on passbands of a dispersion-limited fiber optic communication link. The present invention transmits data on previously unused passbands of the dispersion-limited optic link, thus increasing the total capacity of the link. Higher order modulated carrier frequencies (M-ary ASK, PSK, QAM, etc.) centered within the higher passbands are transmitted using the present invention. Thus, the present invention combines a multiplicity of encoded carriers into a composite microwave spectrum that is tailored to the passbands of the optical link.

Abstract: A transversal filter equalizer comprising a programmable transmitter baseband equalizer for use in high rate digital transmitters. The programmable transmitter baseband equalizer processes digital data using a 1/2-symbol spaced transversal filter to produce I and Q baseband signals. The 1/2-symbol spaced transversal filter comprises I and Q n-bit wide shift register stages having alternate pairs of I and Q shift register stages driven by opposite phases of an input data clock, multiplying digital-to-analog converters driven by two direct tap weights and two cross tap weights, and I and Q combiners for generating I and Q baseband signals. The I and Q baseband signals are fed to a quadrature modulator that produces the desired constellation.

Abstract: A digital communication system having a paired power amplifier circuit with two closely matched parallel paths including paired power amplifiers, and drift compensation feedback control loops that control the phase and amplitude characteristics of the paired parallel paths. The phase and amplitude characteristics of the paired parallel paths are monitored and matched to each other in real time. Outputs of the paired power amplifiers are summed together in a power combiner having difference and the sum ports. A transmit conditioner includes a lookup table receives a digital input and generates phase angles for each of the parallel paths. The drift compensation feedback control loops correlate signals derived from the difference and the sum ports of the power combiner to control the phase and the amplitude of carriers in the two parallel paths. Statistical and dynamic compensation may be employed to implement the phase compensation.

Abstract: An intermediate frequency adaptive cross polarization interference canceler for processing an interfering cross polarization signal distorted by dispersion. The canceler has right and left inputs for respectively receiving right and left polarized IF input signals. A plurality of serially coupled complex multiplier and control stages respectively process the right and left polarized signals to provide controlled amounts of coupling between them to cancel cross polarization interference therebetween. A plurality of delay lines add predetermined time shifts to the right and left polarized signals between stages, and which forms a transversal filter having a predetermined number of taps. The canceler outputs right polarized IF output signal and a left polarized IF output signal having substantially no cross polarization interference therebetween. A preferred embodiment of the adaptive cross polarization interference canceler uses a compensating five-tap transversal filter disposed in the cancellation path.

Abstract: A circuit that samples a through signal, while minimizing attenuation, distortion, or other perturbation to the through signal and sampled signal. The present invention provides for an active distributed signal sampler that includes two transmission lines. An input port is coupled to the first transmission line for receiving the through signal, and a through output port is coupled to an output end of the first transmission line for outputting the through signal. The second transmission line is terminated at one end and has a sampled output port at an output end of the second transmission line for outputting the sampled signal. A plurality of high impedance amplifiers bridge between the transmission lines, and a plurality of inductors are coupled between each of the high impedance amplifiers. A plurality of transmission lines may be optionally employed in the second transmission line.

Abstract: A circuit that injects an auxiliary signal into an existing signal path, thereby adding it to an existing main signal, while minimizing attenuation, distortion, or other perturbation to the main signal. The present invention provides for a active distributed signal injector that includes two transmission lines. An input port is coupled to the first transmission line for receiving the main signal, and a main output port is coupled to an output end of the first transmission line for outputting the main signal. The second transmission line is terminated at an output end and has an injected signal input port at an input end of the second transmission line. A plurality of high impedance amplifiers bridge between the transmission lines, and a plurality of inductors are coupled between each of the high impedance amplifiers. A plurality of transmission lines may be optionally employed in the second transmission line.

Abstract: A transversal filter allrate equalizer for use at intermediate frequency. The equalizer includes a signal divider coupled to receive the intermediate frequency input signal and a transversal filter comprising a plurality of analog delay lines and a plurality of multiplying circuits. The plurality of analog delay lines are coupled to the signal divider for producing a time-shifted replica of an intermediate frequency input signal. The plurality of multiplying circuits are respectively coupled to the delay lines for weighting the time-shifted replicas of the input signal by complex numbers, W.sub.i. A signal combiner is coupled to the plurality of multiplying circuits for recombining the time-shifted and weighted replicas of the input signal to produce an equalized output signal. The delay lines operate at an intermediate frequency, and produce a time delay for the modulation and a phase shift for the carrier. The phase shift may be compensated for by adjusting the phases of the tap weights, W.sub.i.

Abstract: This on-line circuit estimates the bit error rate (BER) of a binary data signal stream in the presence of noise uncorrelated with the signal. For a binary data signal having two states, e.g., plus V and minus V biased around a specified reference level (REF), the circuit counts the number of instances in which the received signal deviates more than 2V from the reference level. This accumulated count gives an accurate estimate of the BER over several orders of magnitude variation of the BER. One embodiment counts just the deviations in a positive direction. This circuit functions independently of any bit pattern and can be used for on-line monitoring without decreasing the information carrying capability of the link. The time required to accumulate a statistically significant sample is the same as for a direct comparison between sent and received bits.

Abstract: An adaptive equalizer for improving the quality of digital data contained in an electrical input signal supplied to the equalizer. The equalizer compensates for amplitude and delay distortion affecting the quality of the digital data contained in the electrical input signal. The equalizer includes a delay line having a plurality of discrete time delay elements and in a plurality of taps coupled to the delay elements. A clock circuit provides a plurality of clock signals of identical frequency but different phase, thereby, dividing a pre-selected time interval into a plurality of time-slots. A sequential switch controlled by the clock signals sequentially connects the delay line taps to a quality detector which also has as an input the equalizer output signal. The quality detector generates a signal, during each of the time slots, that represents the quality of the equalizer output signal.