Abstract: A fast acquisition coherent code tracking loop for use in direct sequence spread spectrum systems is provided with an embedded frequency offset loop. The frequency offset loop in the code tracking loop is provided with a pair of multipliers, one of which is coupled to the carrier tracking loop through a scaling circuit and the second multiplier is coupled to the output of the highly stable VCO of the carrier tracking loop to provide extremely fast phase acquisition of the received PN code and very high frequency stability of the code tracking loop.

Abstract: A spread spectrum signal detector for sampling a modulated carrier employing a zero-crossing detection means having two independent control loops, a first loop for a zero-mean threshold control and a second loop for AGC control. An IF sampler quantizes the received spread spectrum signals at IF and provides high immunity to interference or jamming. The IF signal is sampled at a number of quarter cycle intervals to allow sampling in sequence of the in-phase (I) and quadrature-phase (Q) components. The output of the IF sampler is two bits, a sign bit and a magnitude bit. The zero-mean threshold control loop using only the sign bit of the I and Q samples sets a threshold level (T0) to detect the zero-crossings of a received waveform. Two magnitude threshold levels are set at fixed offsets from the T0 threshold level.

Abstract: A frequency diversity receiver system operating over a predetermined bandwidth comprising a first mixer receiving two identical information signals widely separated in frequency, a stepping oscillator with a predetermined number of steps controlling the output frequency of said mixer, two frequency channels at the output of said mixer, the first of said channels having a broad bandwidth filter and the second having a narrow bandwidth filter, a second mixer receiving simultaneously the output of said second filter and the output signal of a sweeping oscillator, said sweeping oscillator having a preselected sweep, means to synchronize said sweeping oscillator and said stepping oscillator, a multiplier simultaneously receiving the output signals from said first filter and said second mixer, a bank of parallel filters and associated detectors receiving the output signals from said multiplier, each of said filters of said bank having a predetermined bandwidth.

Abstract: A spread communication system comprising a receiver, a diffusion convertor for converting a signal from the receiver, a control signal generator for generating a control signal representing an output level of the diffusion convertor, another diffusion converter for converting data to be transmitted, a transmitter for transmitting data from the another diffusion convertor and a transmission controller for controlling a transmission level of the transmitter in accordance with the control signal from the control signal generator.

Abstract: A receiver utilizing a plurality of small paraboloid antennas in lieu of a single large antenna of equal area, each antenna connected to a separate phase coherent heterodyne receiver channel includes a main channel and branch channels, the channels being summed to provide a carrier phase locked loop local oscillator signal that is distributed to all channels producing phase coherent IF signals in all the channels. These are summed to enhance the carrier margin or dB from the sensitivity threshold, of the system combining the receiver channels, to a level greater than that of the single antenna of equivalent area with its single receiver. The tendency toward cycle slipping near threshold is further reduced by providing summed additional amplified uncorrelated predetection receiver noise in the IFs of the branch receiver coupled to the main receiver.

Abstract: A spread spectrum communication system has, in a transmission part, a first circuit for extracting a first carrier signal from a predetermined broadcase wave and generating a first clock signal by using the first carrier signal, a second circuit for generating a first pseudo-noise signal by using the first clock signal from the first circuit, and a third circuit for modulating an information signal and broadening a frequency band of the modulated information signal by using the first pseudo-noise signal from the second circuit. A reception part of the spread spectrum communication system uses a second clock signal, a frequency of which is identical to that of the first clock signal. Thereby the second clock signal becomes identical to the first clock signal in frequency.

Abstract: Two interference-proof techniques are shown for detecting binary radio sils transmitted by frequency hopping techniques. In the first, the decision as to which type of binary signal is being received is made by first comparing the energy on each mark and space channel with the energy contents of the same channels during a preceding baud which is blank except for jamming and interference, thus obtaining mark and space energy differences. The larger of these differences determines the type of signal received. In the other technique, the energy contents of both mark and space channels are compared with the energies received simultaneously on a nearby blank channel.

Abstract: For recombining a message transmitted by a frequency hopping transmitter at a fast changing transmitting frequency, there are used a digital FFT search receiver for cyclically evaluating the frequency band occupied by the frequency hopping transmitter, at least one interception receiver capable of being switched by the FFT search receiver to the respective instantaneously used transmitting frequency of the frequency hopping transmitter, and a digital storage in which the stream of digital output data from the output of the permanently operative analog-to-digital converter of the FFT search receiver is temporarily stored, the delayed stream of output data from the storage being supplied to the input of the interception receiver.

Abstract: There is disclosed a high frequency communication system of the type employing a high frequency terminal which terminal can transmit a processed signal in a transmitting mode or process a received signal in a receiving mode which terminal includes a first subsystem for voice processing, including a processor responsive to voice signals to provide a linear predictive coded voice signal at a given data rate which signal is coupled to a data modem subsystem that digitally encrypts said voice signal which data modem subsystem is coupled to a modem processor subsystem capable of processing said encrypted signal for providing frequency hopping, feedback equalization, intersymbol interference cancellation, error correction and interleaving to provide a transmitted signal which is relatively immune to jamming during said transmitting mode which includes a convolutional encoder means included in said modem processor subsystem responsive to said encrypted signal to provide a convoluted signal at a higher data rate than

Abstract: A receiver interface system for enabling an operator to access different types of services in a like manner, wherein the services contain different combinations of service components received by a receiver in different portions of one or more different frequency channels, such as television channels. The system includes a plurality of separate interface channels for carrying different types of services containing different combinations of the service components; switching means for selecting a said service, wherein the switching means is coupled to the interface channels for accessing the respective interface channels in a like manner; and a decoder coupled to the receiver and the interface channels for accessing the components of said selected service received by the receiver in different portions of one or more different frequency channels to provide said selected service on the interface channel carrying the selected service.

Abstract: A digital image exchange system comprises a data transmission line, at least one video RAM, at least one video signal generator for accessing data from the video RAM and for developing at least two video signals corresponding respectively to the accessed data, and at least one modulator for modulating the video signals to form transmitted signals in at least two different frequency bands to be transmitted on the data transmission line. At least one demodulator is coupled to the transmission line at a location remote from the modulator for demodulating the transmitted signals in each of the at least two frequency bands to form at least two corresponding video signals; and at least one video display device is operatively coupled with the demodulator for displaying visual images corresponding to the respective video signals.

Abstract: The present invention provides a novel burst erasing automatic gain control circuit which includes the basic elements of an automatic gain control circuit and further includes in the loop control circuit, slow response wideband filter means, and a hard limiter which limits the AGC'ed output from the amplifier so that the signal reaching the slow response wideband filter means never exceeds a predetermined value which would cause distortion in the feedback loop. The output of the novel automatic gain control circuit is coupled to a despreading circuit which removes substantially all of the remaining burst jamming signals.

Abstract: A trunked communications system that accommodates encrypted secure communications. The system uses both non-encrypted message detectors and encrypted message detectors to assure that the trunked central control unit receives the signals it must receive in order to properly allocate and maintain channel assignments.

Abstract: A frequency management scheme for a multistation H.F. communication network establishes communication channels among network stations over respective ones of K frequencies, so that network stations may communicate with one another. Any station desiring to communicate with another station, repeatedly transmits, on each of plural ones of the K communication frequencies in sequence, a probe message comprised of three successive symbols, each of which is defined in accordance with a prescribed pseudo random M-ary code, in the form of multi-chip sequence, that represents the address of the station to whom the communication is directed. The first symbol is effectively unmodulated to permit monitoring equipment of a receiving station of the network to settle out. The second symbol represents the address of the transmitting station. The third symbol identifies the number of times that the frequency which carries the probe message has been transmitted.

Abstract: System of orthogonal code generators, where a first code generator (1) generates a code sequence from a running counter reading (2) which sequence is different from the code generated by a second code generator (1') directed by the same counter reading. Each code generator comprises a number of individually arranged and counter-reading directed subcode generators (3.i), each generating a subcode (g.sub.i) together representing the code, where at least one subcode generator 3.i of the first code generator (1) generates a subcode (g.sub.i) which is different from the subcode g.sub.i ' of the similarly arranged subcode generator (3.i') of the second code generator (1').

Abstract: In a spread spectrum communication system, in which correlation output is obtained by giving a correlator a sender side output code and a receiver side output code, communication channels obtained by dividing the whole channel by using GOLD codes as the sender and receiver side output codes are used and the GOLD codes are constructed by adding preferred pairs of the two m sequences modulo 2.

Abstract: In a receiving station having an adaptive receiving antenna, a phasing system comprises a plurality of reception paths receiving telecommunications signals derived from the same useful signal combined in transmission with a disturbing signal having a frequency band outside the frequency band of the useful signal, via a plurality of primary sources of the receiving antenna. The phasing system includes a narrowband filtering circuit for filtering the overall telecommunications signal in one of the reception paths to derive a reference signal undisturbed by the disturbing signal and solely dependent on the useful signal. In phasing circuits respectively assigned to the reception paths, the useful signal alone is set to a phase as close as possible to the phase of the reference signal in order to obtain, after signal summing at outputs of the phasing circuits, a maximum power using signal mixed with an attenuated scrambling signal.

Abstract: A receiver for frequency hopped signal on which an information signal is modulated on one of a plurality of equally frequency spaced carrier signals. A mixer receives the frequency hopped signals on one input, and on a second input, a local oscillator signal have a comb spectrum. The local oscillator signal is generated by a short pseudo-random bit sequence generator providing the continuous comb spectrum with a frequency spacing equal to the spacing of the carrier frequency signals. A plurality of auxiliary signals are generated having a frequency spacing equal to the carrier frequency signal spacings. The auxiliary signals will have the same frequency and spacing from each other for all carrier frequency signals. The modulator means can be used to separate one of the frequency constant auxiliary signals which includes modulation produced from any one of the plurality of carrier signals.

Abstract: A method for jam-resistant transmission speech signals by radio which have been processed via vocoders, utilizing spread spectrum multiple access modulation (SSMA) or rapid frequency hopping (FH) provides, with respect to the danger of an inherent jamming brought about when a great number of stations simultaneously use the same frequency band for the same radio channel frequency group, activation and deactivation of the transmitter and receiver at the rate of the internal system frame clock pulse during a frame clock pulse period only when useful information is present. In this manner, in the case of simplexcommunication connections, on the average approximately 40% and, in the case of duplex operation, more than 60%, of the transmitting time can be saved, and hence, the inherent jamming of the system can be reduced in a corresponding fashion.

Abstract: A synchronous tracking device for a receiver in a direct-spread spectrum communication system in which a carrier frequency and a pseudo noise code for spreading it are coherent. A first circuit tracks the pseudo noise code in the received signal for a predetermined time after synchronous acquisition of the pseudo noise code. A second circuit tracks the pseudo noise code after the first tracking circuit stops tracking, while maintaining a locking condition achieved by the first tracking circuit.

Abstract: A system for data communication between ground stations using an orbiting satellite as a relay includes a technique for avoiding the loss of signals from the satellite during periods of heavy precipitation. Data is communicated from an orbiting satellite to a plurality of earth stations on a single transmission frequency. The data is communicated on two separate transmission channels on that one frequency by using orthogonal channels of a coherent phase quadrature transmission system. The overall data rate on one of the two transmission channels is much lower than the overall data rate on the other of the two channels. The data on the lower data rate channel is less likely to be affected by heavy precipitation occurring in the line of sight between the satellite and the ground station, and the lower data rate channel is thus used to communicate data to a ground station located in an area of heavy precipitation.

Abstract: A frequency hopping communication system whose transmitters and receivers after synchronization hop over a frequency series of a first type. To synchronize the transmitters and receivers, sync data from a transmitter are transmitted and received in portions spread over a frequency series of a second type in order to protect the transmission of sync data against jamming and eavesdropping.

Abstract: A frequency-hopping datalink and providing communication between a base station, relay unit and multiple remote units utilizes time-division multiplexing and transmits information signals containing information relevant to the next frequencies of transmission. Signals from the base station are transmitted on a first frequency to a relay unit which retransmits the signals on a second frequency to a group of remote units. The information signal from the base station contains information concerning the frequencies of the next transmission and the time slot allotted for the remote units to respond. The remote units respond back at the first frequency which is received by the relay unit and rebroadcast to the base station at the second frequency.

Abstract: PN sequence generators used in the scrambling and descrambling circuits at remote locations are periodically preset to the same value in order to maintain synchronism, with the preset value being also periodically changed. The preset value can be transmitted to the scrambling and descrambling circuits over a privacy channel once per frame and stored in storage registers associated with each of the scrambling and descrambling circuits. The stored starting state values can be loaded into the PN sequence generators as often is desired to maintain proper synchronization, with the stored values themselves being changed at a rate in accordance with the desired degree of security.

Abstract: Apparatus and a method of generating very very long pseudonoise (PN) spread spectrum codes is provided where the code is so long that it need never repeat itself during actual use. The transmitter is adapted to start to transmit one set of a plurality of component codes as a composite code having correlation properties with the component codes. When the first set of component codes are acquired at the receiver the composite code is then transmitted as a component of a different composite code which contains the previous composite code and a second new set of component codes which have correlation properties with the new set of component codes. When the second set of component codes are acquired by the receiver the composite code is then transmitted as a third new and different composite code which contains a third new set of component codes which have correlation properties with third new set of component codes.

Abstract: A scrambling method for TV pictures avoids deterioration of the reproduced picture by level compressing only selected horizontal flyback portions according to a randomly selected pattern to prevent synchronization at the receiver. Key signals are added repetitively to a plurality of horizontal synch signals in one frame so as to enable descrambling of the picture at the decoder, even if noise or data error interferes with one or more of the signals.

Abstract: In a data encrypting/decrypting system both the encoding and decoding stations are receptive of a common source of time varying digital signals. The digital signals in the encoding station are applied to one or both of circuits for encrypting data supplied to the encoding station and spreading the spectrum of a carrier which is modulated by the encrypted data. The digital signals in the decoding station are applied to one or both of circuits for despreading the carrier transmitted by the encoding station and decrypting the received encrypted data. In the decoding station and optionally in the encoding station delays are interposed between the circuits therein and the reception point of the digital signals of values such that the digital signals arrive at the decoding station circuit(s) in synchronism with when data encoded in accordance with a particular digital signal arrives at the decoding station.

Abstract: The present invention is concerned with an apparatus and a method of jumping a composite PN code from a current phase position to a desired predetermined phase position so as to enhance acquisition of a composite PN code. The apparatus includes a plurality of individual PN code generators which are connected to a code combiner to produce a composite PN code. Each of the individual PN code generators is driven by its own timing gate for supplying synchronized clock pulses to its own PN code generator. A master clock is connected to a timing gate before being connected to the individual PN code generators. An inhibit input at each of the individual timing gates is provided so that the individual PN generators may be inhibited a predetermined number of clock pulses which causes the PN code generated to be inhibited and has the effect of jumping the PN code a desired number of phase positions.

Abstract: A method for the transmission of digital data by means of phase modulation (PSK) and "frequency hopping", in which symbols are transmitted several times in different transmission sections as synchronization information for coherent demodulation, and wherein weighting factors taking into consideration the existence and influence of a disturbance source are calculated for each symbol. The symbol values are multiplied by these weighting factors before the values of corresponding symbols are linearly combined and utilized for evaluation.

Abstract: The spread spectrum communication system terminal comprises a first subsystem including a first arrangement to encode a locally generally digital data with an error correcting code, a second arrangement for spectrum spreading of the encoded locally generated digital data in at least one mode of operation of the communication system terminal, a third arrangement to receive remotely generated error correcting code encoded digitla data spectrum spread in the one mode of operation and a fourth arrangement to recover the remotely generated digital data. In addition, a second subsystem includes a fifth arrangement frequency hopping the encoded locally generated digital data prior to transmission to a remote location and a sixth arrangement frequency dehopping the encoded remotely generated digital data received from the remote location.

Abstract: In a pseudo-random communication system, a transmitter-generated encoded signal is to be correlated with a receiver-generated similarly encoded signal for recognizing synchronization of the transmitted and received signals in the presence of undesired received energy. The system comprises a spread-spectrum transmitter including at least two pseudo-noise generators for producing at least two pseudo-noise signals which are related in a predetermined fashion, a mixer for receiving and mixing the two pseudo-noise signals with respective carrier and information signals to produce an output signal, and apparatus for transmitting the output signal. The system also includes a spread-spectrum receiver comprising a correlator and a matched filter coupled in circuit to form a synchronization detector circuit for receiving and detecting the encoded output signal transmitted by the transmitter so as to recover the information therefrom.

Abstract: Windfinding apparatus is described in which receiver processing of the Global Positioning System (GPS) signals is without knowledge of the spread spectrum codes. The apparatus receiver ignores the bi-phase code and recovers the carrier frequency of all satellites in view of the receiving antenna. Two of these receivers are used in a windfinding system. One of the receivers is located on the ground at a known latitude and longitude. The other receiver is placed on a weather balloon sonde and launched into the atmosphere. A telemetry transmitter aboard the sonde transmits a signal that contains the GPS carrier frequency information to the ground-based telemetry receiver. The telemetry receiver output and the local codeless GPS receiver feed a set of tracking filters. The filtered signals are evaluated to obtain a measurement of the difference between the local GPS receiver carrier frequency and the sonde GPS receiver carrier frequency caused by the velocity of the sonde relative to the ground-based receiver (i.

Abstract: A method is provided for achieving initial synchronization of the transmission and reception of a frequency hopped communication signal, which comprises the steps of transmitting a preamble defined by a sequence of synchronizing pulses on a single channel and transmitting random dummy pulses over the remaining channels to hide the preamble. The received signal is filtered to obtain the preamble which is then convolved with a stored replica of the preamble to produce a synchronizing signal that is used to synchronize frequency hopping of the receiver and transmitter in preparation for the transmission of information. The received, constituent pulses of the preamble are delayed and accumulated by a baseband correlator (18) to form a composite pulse whose magnitude is detected by a threshold detector (20). The threshold detector produces the synchronizing signal (22) when the accumulated pulse reaches a prescribed value indicating that all of the bits of the preamble have been received.

Abstract: An hybrid array correlator is configured of a cascaded array of individually identical correlator cells, through which a preselectable reference symbol sequence, identifiable with a symbol to be acquired, is successively clocked, from cell to cell and then recirculated back to the beginning or first cell of the array. The physical span of the correlator covers one complete symbol time, with each cell imparting a one-half chip delay to the reference spreading sequence as it is clocked through the correlator. Yet, because of the recirculation of the reference spreading sequence from the last cell back to the first cell, the electrical span of the correlator is effectively infinite or time invariant. An incoming unknown symbol sequence capable of being acquired is applied in parallel to all the cells of the correlator array.

Abstract: In a signal transmission system for broadband signals wherein the transmitting transducer and/or the receiving transducer has a non-isotropic radiation characteristic, properties of the received broadband signal, for example waveform shape, spectrum, duration and probability density function, depend on the alignment orientation of the transducers. A discriminator circuit is provided in the receiver for identifying or estimating parameters related to one or more of such properties as a measure of alignment orientation of the transducers. The invention can be utilized, for example, in noise-suppressing radio frequency message transmission systems wherein band spreading modulation (spread-spectrum-system) results in transmission of a much greater bandwidth than a conventional transmission of the message baseband frequencies.

Abstract: A broadband signal broadcasting system comprising a circuit to encode video and audio signals forming a TV channel to be sent to a switching matrix, which is remotely operated by the subscriber; a circuit to multiplex two or more TV channel to be simultaneously transmitted on the subscriber's line, which can be a coaxial cable, a radio link or an optical fiber; and a circuit to receive the signals transmitted on the line, to separate two or more TV channels and to carry out channel decoding by supplying the subscriber's terminals with the corresponding video and audio signals. The system requires a single encoding and a single decoding of the nB.fwdarw.(n+m)B type on broadband signals, respectively at the output from signal sources and at the input of subscriber's terminals.

Abstract: A method and apparatus for detecting and identifying Doppler frequency and phase information contained within a signal of the direct sequence spread spectrum type. An incoming signal is split by a circuit and component parts mixed with first and second local oscillator signals, the frequency of the first local oscillator being less than that of the carrier and the second being greater than that of the carrier by the same amount, plus an amount equal to twice the maximum Doppler frequency shift. The heterodyned signals are then low pass filtered, mixed with each other to form a heterodyned output that is then low pass filtered. The resultant signal retains Doppler phase and frequency information and is independent of carrier frequency and modulating PN-code thereby providing an easily demodulated signal whose Doppler information may be readily identified.

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: A subsystem of a wave packet communication system uses the same sets of receivers and correlators to detect both the sync pulses and the messages carried by different wave packets. The system does this by taking the sync pulses from each packet and generating a corresponding preamble on the basis of a modular arithmetic algorithm based on prime numbers such that different messages from different transmitters can be received by the same subsystem simultaneously.

Abstract: A method and apparatus for generating a bent sequence code as a transform of an m-sequence code.

Abstract: In the disclosed digital circuit, a digital direct sequence modulation signal is converted to a suppressed clock pulse-duration modulation signal to thereby suppress the clock feature in the frequency spectra of a spread spectrum transmission system. The disclosed digital circuit includes a parallel output shift register for converting the direct sequence modulation signal to a corresponding series of four-bit digital words. The digital words supplied by the shift register are loaded into a four-bit synchronous binary counter circuit. The counter circuit counts upwardly from the value of the digital word and supplies a carry pulse to a logic circuit which, in turn, produces an output pulse, the duration of which is representative of value of the digital word supplied by the shift register.

Abstract: A two channel audio scrambling circuit for a television signal encoding system includes synchronized digital carrier switching means for deriving two suppressed carrier, switched audio signals that are 90 degrees apart, and combining them into a single output signal. A digital phase shifter, supplied with a carrier related to the horizontal line frequency develops properly phased outputs for controlling electronic switches to produce two phase displaced digital carrier switching signals. A plurality of scrambling modes are determined by logic means under control of a vertical interval signal, a video inversion signal and a tone signal input for controlling the digital phase shifter to change the carrier frequency. Complementary decoding circuitry for recovering the so-encoded audio signals is also described.

Abstract: A spread spectrum communication system having a correlation receiver for decoding an information signal transmitted on a pseudo-noise (PN) carrier. The receiver synchronizes to the transmitted signal by performing a continuous sequence of correlations until a correlation output exceeding a predetermined threshold level is detected. Thereafter, the receiver performs a plurality of correlations during a sampling interval which is timed to occur at approximately the time when high subsequent correlation output signals are likely to appear. After enhancement through adaptive filter processing, the correlation outputs generated during each sampling interval are accumulated (integrated and the summed output present at the end of the sampling interval is representative of the transmitted data message (a binary bit). The adaptive filter develops and stores weighting values representing the expected signal strength of the correlation outputs and the actual correlation outputs are multiplied by the weighting values.