E-systems, Inc.

Ncr Corporation

David E Sanders

Robert S Gordy

Ramon P Chambers

William H Mosley, Jr

Cameron E Morrison

Carl F Andren

Alfred T Anderson

Billy R Poston

George P Bortnyk

Michael S Masheff

Dennis A Sweeney

Richard E Roberson

A digitally-controlled quadrature signal generator is provided having a frequency synthesizer for receiving a digital input signal and in response thereto generating an output signal having a predetermined frequency. The output signal is split to produce an in-phase (I) signal and a quadrature-phase (Q) signal. A first table look-up memory is provided for generating a predetermined phase correction signal for use in cancelling any phase error in the quadrature-phase signal. A mixer receives the phase correction signal and the in-phase signal and in response thereto generates a phase error signal. The phase error signal is then added to the quadrature-phase signal to thereby cancel the undesirable phase error. Moreover, programmable attenuator circuits or limiter circuits are provided to limit the in-phase and quadrature-phase signals and thereby cancel any undesirable amplitude error components therein.

Quadrature signal generator having digitally-controlled phase and

A method and apparatus for baseband synchronizing of a local PN code sequence with a received PN code sequence incorporated in a received spread spectrum signal is provided. The received spread spectrum signal is translated to baseband to produce an I (in-phase) channel baseband signal and a Q (quadrature-phase) channel baseband signal. Data and error baseband correlators correlate the I channel and Q channel baseband signals with in-phase and quadrature-phase PN signals incorporating the local PN code sequence to produce despread on-time, advanced and delayed I channel and Q channel baseband signals. These despread baseband signals are processed and combined to produce an error signal proportional to a difference between the local PN code sequence and the received PN code sequence. A numerically-controlled oscillator circuit is responsive to the error signal to advance or delay the phase of a reference PN clock signal used to form a local PN clock signal. In operation, the rate of reading the local PN code sequence is accelerated or retarded to synchronize the local and the received PN code sequences.

Method and apparatus for baseband tracking of a PN code sequence in a

A method and apparatus for baseband generation of a spread spectrum reference signal for an LMS adaptive array processor is provided. An IF summed, weighted spread spectrum signal is output from the processor and translated to baseband to produce an I (in-phase) channel spread baseband signal and a Q channel (quadrature-phase) spread baseband signal. A baseband correlator receives the I channel and Q channel baseband signals and delayed versions of in-phase and quadrature-phase PN signals and produces despread I channel and Q channel baseband output signals. A baseband linear spreader receives the despread I channel and Q channel baseband output signals and the in-phase and quadrature-phase PN signals and produces respread I channel and Q channel baseband signals. A baseband modulator modulates the respread I channel and Q channel baseband signals with a phase-shifted local oscillator to produce the reference signal. The reference signal is subtracted from the spread spectrum signal to produce an error signal consisting essentially of the undesired signal components in the spread spectrum signal. The adaptive array processor minimizes the mean-square value of the error signal to minimize these undesired signal components. If desired, multi-channel capability can be provided by a summer for summing respread I channel and Q channel baseband signals from a plurality of channels in the spread spectrum communication system.

Method and apparatus for baseband generation of a spread spectrum

A method and apparatus for phase modulating a carrier signal to convey an information signal (12) such that the carrier signal has a constant amplitude envelope. A Hilbert transform signal (14) of the information signal (12) is produced. The signals (12, 14) are sampled to produce signals (16, 18), which represent cartesian coordinate values. The cartesian coordinate values are then converted into equivalent polar vectors (20-36) which have both an amplitude (R) and an angle (.theta.). The polar vector quantity (R, .theta.) is converted into two unity amplitude vectors (A, B). The unity amplitude vectors (A, B) are offset from the polar vector quantity by an angle the cosine of which is proportional to the amplitude of the polar vector (R). The carrier signal is sequentially phase modulated phase angles of the unity amplitude vectors (A, B) for each sample period of the information signal. This modulation procedure maintains a constant amplitude envelope for the carrier signal and makes possible simultaneous demodulation of a plurality of carrier signals in a single demodulation channel.

Method and apparatus for pulse angle modulation

A modulating circuit (10) receives a UHF carrier signal together with a digital input signal for data along with a data clock. A channelizer circuit (60) produces I and Q channel digital data signals derived from the digital input signal. The I and Q channel signals are utilized to trigger one shot circuits (70, 72, 74 and 76) to produce positive and negative pulses corresponding to the signal transitions of the input signals thereto. These pulse signals are provided to integrate and hold circuits (80, 82) which serve to have positive and negative integration, thereby producing ramp signal segments in place of the sudden transitions of the rectangular digital input signals. The resulting data signals from the integration process are passed through diode shaper circuits (82, 92) and low pass filters (88, 94) to produce spectrum shaped I and Q channel modulating signals which have a limited bandwidth. The modulating signals are input to mixers (36, 40) together with respective in-phase and quadrature phase carrier signals to provide amplitude and phase modulation of the carrier signals. The resulting amplitude and phase modulated carrier signals are combined in a summation circuit (44) to produce a resulting modulated, band limited carrier signal.

Method and apparatus for producing a shaped spectrum modulating signal

A method and apparatus for phase modulating a carrier signal to convey an information signal (12) such that the carrier signal has a constant amplitude envelope. A Hilbert transform signal (14) of the information signal (12) is produced. The signals (12, 14) are sampled to produce signals (16, 18), which represent cartesian coordinate values. The cartesian coordinate values are then converted into equivalent polar vectors (20-36) which have both an amplitude (R) and an angle (.theta.). The polar vector quantity (R,.theta.) is converted into two unity amplitude vectors (A, B). The unity amplitude vectors (A, B) are offset from the polar vector quantity by an angle the cosine of which is proportional to the amplitude of the polar vector (R). The carrier signal is sequentially phase modulated by each of the angles of the unity amplitude vectors (A, B) for each sample period of the information signal. This modulation procedure maintains a constant amplitude envelope for the carrier signal and makes possible simultaneous demodulation of a plurality of carrier signals in a single demodulation channel.

A baseband correlation circuit (10) receives an IF spread spectrum input signal which is phase compared with a local oscillator signal and a phase shifted local oscillator signal to produce I channel and Q channel spread baseband signals. Each of these signals is input to four sample and hold circuits (34-48). A local PN code signal is converted from two-phase to four-phase to produce I and Q channel local PN signals. These signals together with the logical inverses thereof are provided as the control inputs for the sample and hold circuits (34-48). For each pair of sample and hold circuits there is a respective summer (86-92). The pair of sample and hold circuits together with the corresponding summer comprises a double balanced multiplier. There are four double balanced multipliers for producing four respective product signals. The product signals are input as pairs into summers (106) and (108) to produce despread, narrowband baseband I and Q channel output signals at output lines (110, 112). The baseband correlator circuit (10) of the present invention serves to despread the spread spectrum IF signal at baseband, thereby eliminating the need for costly and bulky components which are required for despreading at RF frequencies.

Method and apparatus for despreading a spread spectrum signal at baseband

A fast slew rate automatic gain control circuit (10) includes a variable gain amplifier (14) which is responsive to a gain control signal and an amplitude detector (18) which produces an amplitude signal corresponding to the amplitude of the received signal transmitted through amplifier (14). The amplitude signal is provided to the input node of a loop filter (24) and to the inputs of threshold detectors (30, 32). Positive and negative slew threshold circuits (34, 38) provide threshold signals respectively for the threshold detector circuits (30, 32). When the amplitude signal is within the range of the threshold signals the loop filter produces the gain control as the function of the amplitude signal. When the amplitude signal is less than the positive slew threshold signal the threshold detector (32) produces a drive signal which is provided to the loop filter (24) and causes the generation of the gain control signal to have an accelerated positive slew rate which increases the gain. When the amplitude signal exceeds the negative slew threshold signal the threshold detector (30) produces a drive signal which is supplied to the loop filter (24). When the negative drive signal is supplied to the loop filter the gain control signal is generated with an accelerated negative slew rate which increases the gain. The slew rate of the gain control signal is thus a function of the amplitude of the received signal.

Fast AGC slew circuit

A peak detector circuit (10) is disclosed wherein an input signal is full-wave rectified by a circuit (14) and the rectified signal is provided simultaneously to peak detect, hold and dump circuits (18), (20). Each of the peak detect, hold and dump circuits is discharged at the start of periodic intervals with a phase offset between the intervals for the two circuits. The peak signals are discharged at essentially the start of the interval followed by rapid charging of the peak signal to the peak amplitude of the rectified input signal. The later portions of each of the intervals of the peak signals produced by the peak detect, hold and dump circuits (18) and (20) are transmitted alternately through a multiplexer circuit (24). The resulting output signal is transmitted through a high impedance buffer amplifier (30) to an output terminal (32) of peak detector circuit (10). The timing of the operation of multiplexer (24) serves to remove the discharge and charge transitions of the peak signals from the peak detected output signal.

Fast updating peak detector circuit

An anti-jam PN sequence spread spectrum conferencing communication system is disclosed for simultaneously transmitting and receiving in a plurality of communications channels secure voice communications. All received messages are modulated with the same pseudo noise sequence and arrive at any given channel at random time states, wherein the messages are separated, separately processed and finally conferenced, using a technique based upon the correlation of the PN sequence and dependent upon the randomness of the epoch state of a given PN sequence coded with a message in relation to the other coded messages.

Spread spectrum conferencing communication system

Improved acquisition of signals in a Gaussian noise environment is achieved by applying the output of a correlator (14) to a threshold detector (12). A correlation pulse output from the threshold detector (12) and the output of the correlator (14) are input to a false alarm processor (10) that includes multiple correlation checking channels (22). Each correlation checking channel (22) is assigned to sample an input at various points over a selected interval by an enable pulse generated at the output of select logic (30). Each correlation checking channel (22) includes correlation check enable logic (34), a blanking generator (36), and a confirmation logic (42). In the confirmation logic (42) samples of the analog input are taken at discrete times and integrated over a preselected number of intervals. If this integrated value exceeds a threshold level during the integration interval, the analog input signal is considered valid and a 'signal confirmed' pulse is generated and gated through a gate NAND (44) onto a signal confirm line 28.

False alarm processor

Acquisition of a carrier frequency lock and a symbol timing lock is efficiently achieved during the preamble of a data signal in a time division multiple access communication system by first operating the system in an acquisition mode and subsequently switching to a data recovery mode. In the acquisition mode, an input signal is passed through a transversal correlator and frequency multiplied by a factor of two. The multiplied signal is used to control a local oscillator for demodulating the carrier signal. Also in the acquisition mode, the output of the transversal correlator is envelope detected and applied to a symbol timing loop that produces a symbol timing signal. Upon the detection of a symbol timing lock, a lock detector switches the system to the data recovery mode. In the data recovery mode, the input signal is frequency multiplied by 4 and used to control the local oscillator for demodulating the input signal. The demodulated input signal is now applied to the symbol timing loop to maintain a symbol timing lock condition.

Apparatus for the acquisition of a carrier frequency and symbol timing

A radio receiver is disclosed which measures the statistics of an interfering narrow band noise signal and from these statistics generates a function which when mixed at baseband with a data signal combined with the narrow band noise reduces the interfering effect of the noise signal. The interference eliminating function is generated by processing signals representing an approximation of the data, the covariance of the narrow band noise interference, the noise figure for the receiver and the amplitude of the data signal. As the function is generated it is input to a mixer together with the combined narrow band noise and data signal. Iterated processing improves the estimation for the noise statistics thereby improving the approximation for the resulting data signal. This further enhances the solution for the noise elimination function thereby still further improving the desired data signal, thus creating a positive improving feedback loop.

Adaptive narrow band noise estimator/suppressor radio receiver

The carrier suppression circuit of the present invention is utilized to minimize electrical imbalances within double-balanced mixers. The circuit operates upon a modulating signal, having at least two states so as to adjust the dwell time that the signal stays in a particular state to counteract the effects of electrical imbalance within the mixer. Minimization of the electrical imbalance provides a greater suppression of the carrier signal which, in turn, improves the quality of the signal both at the transmitter and at the receiver.

Compensation circuit for an electrical signal mixer

A four phase to two phase correlator is incorporated within the demodulator section of a spread spectrum modem to process a received RF signal modulated by a transmitted PN code and a digital data signal. The correlator includes a first modulator for combining the channel 1 and channel 2 R code signals with the received RF input signal to generate a first channel 1 RF signal and a first channel 2 RF signal. The first channel 1 RF signal is modulated by the transmitted PN code signal, the channel 1 R code signal and the digital data signal. The first channel 2 RF signal is modulated by the transmitted PN code signal, the channel 2 R code signal and the digital data signal. A second modulator combines the channel 1 and channel 2 PN code signals and the channel 1 and channel 2 R code signals with a first unmodulated RF signal to generate a second channel 1 RF signal which is modulated by the channel 1 PN code signal and by the channel 1 R code signal, and a second channel 2 RF signal which is modulated by the channel 2 PN code signal by the channel 2 R code signal. A third modulator combines both channels of the first and second RF signals to generate a third RF signal which is modulated only by the digital data signal.

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St. Petersburg, FL, United States of America

David E Sanders