Abstract: An enhanced P-code channel (60) for use in a GPS receiver (10) to simultaneously track L1 and L2 comprises a P-code clock generator (62) for generating two code clocks. The first code clock associates with L1 and the second associates with L2. The code clocks have the same frequency but different phases from one another. Circuitry (64) and (66) generate and store a plurality of P-code chips. A first circuit (68, 70) selects and updates P-code chips from the stored P-code chips that are in phase with the L1 code clock. A second circuit (72 and 74) selects and updates P-code chips from the P-code chips and phased with the L2 code clock.

Abstract: An interleaver processes information in a pseudorandom order to provide pseudorandom interleaved data for communication to a deinterleaver. The pseudorandom interleaved data is processed at the deinterleaver in a pseudorandom order corresponding to that used at the interleaver means, to recover the original information. The pseudorandom processing at the deinterleaver is synchronized with the pseudorandom processing at the interleaver on a trial and error basis. In one embodiment, full synchronization occurs when a Viterbi decoder receiving data from the deinterleaver has a renormalization rate within a designated threshold and when enough synchronization words are detected in data output from the deinterleaver to meet a predetermined criterion. In another embodiment, a timer is used to initiate a new starting address for the pseudorandom processing at the deinterleaver during successive time intervals.

Abstract: A spread spectrum communication system for direct sequence transmission of digital information having a modulation format which is particularly suitable for indoor communication within residential, office and industrial structures. The modulation format combines BPSK or MSK spreading with FM carrier modulation by data bits and a carrier frequency shift whose magnitude is related to both a chip rate and a spreading sequence length. The carrier, chip clock and data clock are all synchronous and the sequence length is an integral submultiple of the bit length. The system reduces the frequency error between the transmitter chip clock and the receiver chip clock to permit the elimination of a code phase tracking loop in the receiver to reduce the receiver complexity. The receiver has an extended dynamic range which makes possible the reception of very strong signal without an automatic gain control loop (AGC) as well as reducing the time needed for code phase acquisition.

Abstract: A cellular radio telephone system employs discontinuous transmission and reception of speech signals to conserve receiver processing resources. A frame structure is imposed on digitized speech data to divide the data into units of fixed transmission time. When no active speech is present for the entire duration of a frame, transmission of that frame of data is inhibited. At the receiver, decoding of received bits is performed to determine correlation with a defined set of code words. If no correlation is found after the first few received bits of a frame, due to the absence of active speech data, decoding is discontinued for the remainder of the frame's duration. This approach frees up the receiver's resources for other tasks, such as decoding of other received signals. Frames of data from different sources are transmitted with a defined time alignment to enable the receiver to remain synchronized in the absence of transmitted data.

Abstract: A modified RAKE receiver, referred to as a WRAKE receiver, is used in CDMA communications. It is particularly adaptable to a subtractive CDMA system. The receiver includes a radio receiver for receiving and demodulating a composite signal of overlapping transmitted signals (spread signals), a sampler to sample the received signals, a selector for selecting different groups of samples, a correlator for correlating the samples with known despreading codes and a comparator to determine the symbol transmitted. The receiver also includes a combiner which combines either different groups of samples together or combines different correlation values together. The sample groups selected are channel independent and combine data received from different time shifts. Likewise, the sample groups for each channel and the correlation values are time-of-arrival independent.

Abstract: A pseudo-noise (PN) correlation and demodulation method and apparatus, in which received signals are correlated with locally generated PN codes and correlation measurements are maintained for multiple time bins corresponding to signals received over possible multiple paths. Instead of selecting one or a small number of significant correlation measurements to control data demodulation, the method of the invention performs data demodulation over the multiple time bins, and then selects data values corresponding to significant correlation measurements and combines the selected data values, weighting them in accordance with their relative strengths a determined during correlation. Use of the invention provides improved performance in terms of signal quality and continuity in the presence of multipath conditions. Careful selection of design parameters allows the improved performance to be obtained in a compact and easily portable implementation including transmitter and receiver modules.

Abstract: A method and apparatus is provided for transmitting spread spectrum signals. The transmitter receives data symbols. Subsequently, the transmitter splits each particular set of two received data symbols into a first and second array of data symbols according to either of two algorithms. The first algorithm including providing both data symbols of the particular set to the first and second array of data symbols and the second algorithm including providing one of the data symbols of the particular set to the first array of data symbols and the other of the data symbols of the particular set to the second array of data symbols. Subsequently, the transmitter determines particular channels to transmit the first and second array of data symbols by spreading the first and second array of data symbols with a predetermined length Walsh code.

Abstract: A spread-spectrum noise canceller (390) is provided for cancelling user code noise from a spread-spectrum communication channel. The spread-spectrum noise canceller (390) includes a receiver for receiving a spread-spectrum signal (302) including a first and at least a second signal as well as a noise canceller (390) operatively coupled to the receiver for reducing spread-spectrum noise in the first received signal by substantially processing the at least second received signal out of the received spread-spectrum signal (302).In addition, a method is provided which cancels user code noise from a spread-spectrum communication channel. The method includes receiving a spread-spectrum signal (302) including a first and at least a second signal and subsequently reducing spread-spectrum noise in the first received signal by substantially processing the at least second received signal out of the received spread-spectrum signal (302).

Abstract: A method for establishing and communicating synchronous, code division multiple access communications between a base station and a plurality of remote units. A plurality of remote-communications signals which have spread-spectrum modulation are transmitted from the plurality of remote units and arrive simultaneously at the base station. The method includes transmitting repetitively from the base station a access signal having spread-spectrum modulation and receiving the access signal at an accessing-remote unit. The accessing-remote unit transmits an echo signal which has spread-spectrum modulation. The echo signal is received at the base station and a time delay is measured between the access signal and the received echo signal. A protocol signal which has spread-spectrum modulation is transmitted to the accessing-remote unit, with the protocol signal communicating a chip codeword and the time delay measured at the base station.

Abstract: A bidirectional data transmission system using the technique known as spectrum spreading by direct sequence comprises a first transmitter-receiver assembly consisting of a first transmitter section which generates a coded first data signal for transmission by modulation of a radioelectrical carrier by a spreading code of which the delay is modulated under the control of the first data, and a first receiver section which receives a coded second data signal and restores the second data therefrom, and a second transmitter-receiver assembly consisting of a second transmitter section which generates the coded second data signal for transmission by modulation of a transmission carrier by a spreading code, the carrier itself being modulated by the second data, and a second receiver section which receives the coded first data signal and restores the first data therefrom by demodulation of the delay in the spreading code contained in the coded first data signal, the restored first data being used to control the delay

Abstract: A repeater diversity spread spectrum communication system provides substantially fade free communications between a transmitter (1) and a receiver (7). A transmitted signal is relayed through a plurality of linear communications repeaters (3-6) that produce copies of the transmitted signal, the copies each arriving through an independently fading signal path. The transmitter and/or the receiver may be mounted upon a mobile platform, and the plurality of repeaters may be terrestrial, or may be provided in satellites in low earth orbit or in geosynchronous earth orbit. The receiver processes the received signal copies to equalize them to one another in delay, frequency, and phase, and then combines the multiple received and equalized signal copies to produce a composite signal having a greatly reduced fading depth.

Abstract: A spread spectrum communications system for use over a communications channel, including a transmitter-generic-chip-code generator, a transmitter-message-chip-code generator, an EXCLUSIVE-OR gate, a combiner, a transmitter, a receiver-generic-chip-code generator, a receiver-generic mixer, a generic-bandpass filter, a receiver-message-chip-code generator, a receiver-message mixer, a message-bandpass filter, and a synchronous detector. The transmitter-generic-chip-code generator generates a generic-chip-code signal and the transmitter-message-chip-code generator generates a message-chip-code signal. The EXCLUSIVE-OR gate spread-spectrum processes message data with the message-chip-code signal to generate a spread-spectrum signal. The combiner combines the generic-chip-code signal with the spread-spectrum-processed signal. The transmitter transmits the combined generic-chip-code signal and spread-spectrum signal, on a carrier signal over the communications channel as a spread-spectrum-communications signal.

Abstract: A multi-carrier communication system wherein a sender side apparatus and a receiver side apparatus are connected through a transmission line. The sender side apparatus contains a multi-carrier modulator for modulating data, where preset numbers of bits of the data are respectively modulated with a plurality of carriers in each cycle. The sender side apparatus transmits a training signal which is modulated by the multi-carrier modulating unit where the numbers are set equal to a predetermined maximum of the numbers, to the receiver side apparatus. The receiver side apparatus evaluates the quality of components of the training signal where the components are modulated with the respective carriers to determine the above numbers to be preset, ciphers information on the numbers, and transmits the ciphered information to the sender side apparatus. The sender side apparatus deciphers the information to obtain the determined numbers, and presets the numbers in a multi-carrier demodulator which is provided therein.

Abstract: A method and apparatus is offered of exchanging a communicated signal at a base site with a communication unit on an indexed frequency of a frequency hopping communication system. The method includes the steps of transceiving, through a first base site transceiver, a first communicated signal within a first frame on a first frequency of the indexed frequency; and, while transceiving within the first frame, tuning a second, extra base site transceiver to an indexed frequency of a second frame. The second transceiver may then be used to transceive a signal within the second frame while the first transceiver is tuned to the next indexed frequency. Additional communication units may be added by adding one base site transceiver per communication unit while maintaining a single extra transceiver per frame.

Abstract: A spectrum spread communication system capable of ensuring positive synchronization and improving error rate characteristics of data. At least one frequency is subject to hopping at an interval equal to one cycle of a DS signal during one cycle of frequency hopping and a cycle of changing-over of hopping is controlled depending upon an output signal of a correlation device, resulting in accomplishing synchronization.

Abstract: The transmitter for a direct-sequence spread-spectrum communication system encodes its code rate into the phase difference between a pair of identically modulated, sum and difference frequency carries which it transmits to the receiver. The receiver, in turn, mixes the two carriers with each other to recover a signal having a frequency representing their phase difference, thereby enabling the receiver to derive a synchronous code rate from the phase difference signal, directly or by means of a resettable oscillator which is driven by the phase difference signal. If desired, the sum and difference frequency carrier may have overlapping sidebands in the frequency domain.

Abstract: A remote-control system with position control includes a spread-spectrum where at least three independent spread-spectrum signals are transmitted. At the receiving end, these signals are separated into their individual components by means of at least three correlators and form the diode signals. Synchronizing means at the receiving end, including further correlators, synchronize the received spread-spectrum signals with associated reference signals with the aid of a phase-locked loop and a control unit.

Abstract: A spread spectrum processing system that employs wide bandwidth spread spectrum radio transmissions overlaid over the existing cellular voice signals to simultaneously provide additional cellular services without causing objectionable interference to current users of the cellular voice channel. The spread spectrum radio transmissions also support a large number of low rate digital messages. Both vehicle location and messaging functions are obtained without sacrificing any of the existing voice channel capacity. The cell site processor is designed to share the existing cellular frequencies, real estate, antenna towers, antennas, and low noise amplifiers used in the cell site radio frequency receiver chain. The only additional cell site equipment is the spread spectrum signal processor. The processing system provides a means for achieving vehicle location accuracies that are improved by greater than two orders of magnitude over that which is possible by the current transmissions in that band.

Abstract: Method and apparatus for changing the bit rate of a digitized analog signal stream from a first bit rate to a second bit rate. A first sequence generator provides a digital predictor sequence clocked at the first bit rate. A combiner has an output providing a combined digital stream at the first bit rate, combining the digital predictor sequence at the first bit rate and the digital analog signal stream at the first bit rate. An adaptive processor has its input coupled to at the output of the signal combiner. The adaptive processor has variable weights which are responsive to an error signal, an output providing a processed combined digital stream having a bit rate responsive to the weights, and an error signal input port. A second sequence generator provides the same digital predictor sequence, but clocked at the second bit rate.

Abstract: A spread spectrum communications system in which one of a transmitter or a receiver uses a PN code sequence while another side uses a code sequence to which is used constant pattern signals comprising an arbitrary combination of three values of positive, negative and zero for each code of a same PN code sequence. A correlator performs cross correlation process of a code sequence to which the PN code sequence and the pattern signal have been used.

Abstract: The receiver contains a correlator (TIC) for the correlation of the received signal with a reference code (R(k)) and a digital signal processor for evaluating the results of the correlation. The correlator is constructed as digital, time-integrating, multistage correlator (TIC), the individual stages (Kl to KN) of which are connected on the one hand to a digital delay line (17) fed with the reference code (R(k)) and to which on the other hand a digital signal (S(k)) recovered from the received signal is applied, to length (D) of the delay line (17) being adapted to the maximum expected impulse response to the transmission channel.

Abstract: An approximate figures measuring system includes a signal transmission device and a signal receiving device. The signal transmission device is arranged in each of any objects to be measured and emits a signal from which a peak can be generated at a receiving device in a predetermined period. The signal receiving device receives the signal transmitted from the signal transmission device and includes a peak detection circuit and a calculation circuit for obtaining an output corresponding to the number of the peaks of the signals from the objects.

Abstract: In a phase demodulator is received a signal of which the carrier is phase-modulated by a digital pseudorandom sequence itself phase-modulated by a data signal. A frequency close to that of the carrier is locally modulated by a sequence identical to the received sequence. The received and local signals are mixed into a filtered signal with an intermediary frequency band. A repetitive double integration step of the signal filtered into an integrated signal is used and is compared with a threshold in order to quantify the correlation between the received and local signals. Firstly, the local frequency varies according to a few discrete values spread over the uncertainty range of the carrier corresponding to intermediary frequencies in the vicinity of the filtering band. At each discrete frequency value, integration steps are carried out for half-bit local frequency shifts. Synchronization of the sequences is acquired in response to an integrated signal exceeding said threshold at the end of an integration step.

Abstract: A satellite communication system for providing maximum power output in a spread spectrum signal transmission is disclosed. Spectral shaping is provided at a satellite transmitter to shape a spread spectrum so that over a bandwidth of interest, the spectrum has a maximally flat characteristic. By maximizing the spectrum amplitude flatness, the required power density for a bandwidth limitation imposed to prevent interference with other communication facilities is maintained. In each earth station receiving the transmission from the satellite, a filtering is provided of the demodulated baseband satellite signal such that the spectrum is restored to its original shape. The filters on the receive side may be analog, having the same amplitude function as the transmit spectrum shaping filter, but having an inverse phase response. This insures a matched filter condition at transmitter and receiver, maximizing signal transfer. A programmable demodulator is provided to select a demodulation mode.

Abstract: A system and method for developing and assigning address codes in a radiotelephone communication system using spread spectrum modulation techniques based upon an analysis of signal strength and without reference to a geographic pattern.

Abstract: A system for decoding an IF signal modulated with 4-ary words generated at a known spreading rate (PN code) comprises a receiver in which four known 4-ary words are generated at the same rate. The system then compares the incoming signals modulated with unknown 4-ary words with each of four known 4-ary words. Only one of the known words will be in phase with a received unknown word. The disclosure describes a system which determines which of the four words is in phase, this being the determinant of the identity of the unknown word.

Abstract: A plurality of data carriers are prepared and possessed by, for example, persons who enter a building. The data carrier spread spectrum modulates a carrier signal of a predetermined frequency by an assigned Gold series corresponding to an ID code and transmits the modulated signal. Leaky cables each having a predetermined length are two-dimensionally distributed and arranged in the building. A frequency converter is connected to one end of each of the leaky cables and frequency converts the spread spectrum signal from the data carrier which has propagated the leaky cable into a frequency unique to the cable and sends the converted frequency signal to a central receiving unit through a transmission cable. The receiving unit individually demodulates the signal series from the reception signals and sequentially executes correlation calculations between the signal series and the Gold series assigned to the data carriers.

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 convertor 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 spread spectrum receiver is disclosed, in which influences of narrow band disturbing waves are reduced by converting the output of a correlator into base band information and removing frequency components from DC to about 1/.tau. from the conversion output thus obtained, .tau. being the gate delay time of the correlator.

Abstract: A method and apparatus is provided for improving detection of data bits in data samples (120) of a hop of a slow frequency hopping spread spectrum signal (112). In the detecting process, the carrier to interference (C/l) power ratio of the hop is estimated (124) by using the data samples (120) of the hop. Subsequently, a data bit (130) is detected by using the estimated C/l power ratio (126). The detection process (128) may include utilizing maximum likelihood decoding techniques to derive a data bit (130) from decision metrics and the estimated C/l power ratio (126). The decision metrics correspond to a measurement of the distance of data samples (120) from constellation points within a constellation space representing data samples (120) previously used to generate decision metrics. The detection process (128) also may include utilizing the estimated C/l power ratio (126) in combining data samples (120) of the hop as received from two or more diversity receiver branches.

Abstract: A conference call feature is offered for use with spread spectrum cordless communication systems. The conference call feature is achieved through the alternate use of redundant communication resources by units on the conference call. The redundant communication resources in spread spectrum communication systems transmit duplicate copies of messages in high noise environments. In residential environments, noise tends to be less of a problem and can, hence, be used to support a conference call feature.

Abstract: A demodulator for a spread spectrum communication system, including a piezoelectric substrate for causing elastic surface waves, an input electrode provided on the surface of the piezoelectric substrate, an intermediate electrode provided on the piezoelectric substrate surface a predetermined distance away from the input electrode, so as to form a matched filter together with the input electrode, and an output electrode provided on the piezoelectric substrate surface at a predetermined distance away from the intermediate electrode, so as to form a delay path together with the intermediate electrode.

Abstract: A spread spectrum CDMA communications system for communicating data and/or digitized voice between a plurality of users to a plurality of PCN units. The spread spectrum communications system is located within a same geographical region as occupied by an existing microwave system. The spread spectrum can operate without causing undue interference to the microwave system and the microwave system can operate without causing significant interference, less than 1% total users affected, to the PCN system. The spread spectrum CDMA communications system includes a plurality of PCN-base stations and a plurality of PCN units. A PCN-base station has a device for converting the format of the data into a form suitable for communicating over radio waves, a spread spectrum modulator for spread spectrum processing the data, a notch filter, and a transmitter for transmitting the spread spectrum processed converted data from the PCN-base station to a PCN unit.

Abstract: A privacy communication device uses a control channel (5) in addition to a voice channel (4) in communicating with other privacy communication device. Each privacy communication device employs a ring modulator (8) and a ring democulator (14). A specific modulator carrier frequency to be given to the ring modulator (8) is selected by function of a control signal transmitted on the control channel (5) out of a plurality of modulator carrier frequencies prepared in advance. Likewise, a specific demodulator carrier frequency to be given to the ring democulator (14) is selected by function of a control signal transmitted on the control channel (5) out of a plurality of demodulator carrier frequencies prepared in advance.Hence, when the specific modulator carrier frequency and the specific demodulator carrier frequency are updated at arbitrary intervals, a third person cannot easily identify the varied modulator carrier frequency and demodulator carrier frequency.

Abstract: A threshold level generator for generating threshold levels to detect zero-crossings of a spread spectrum received waveform. An IF sampler quantizes the received spread spectrum signals at IF. 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 outputs of the IF sampler are two bits, a sign bit and a magnitude bit. The threshold level generator 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 (D1 and D2) from the T0 threshold level.

Abstract: Spread spectrum communication system comprising a transmitter for transmitting data in bit form from one location to a remote location. An encoder is provided for encoding the data with a chip sequence at a predetermined clock rate to provide encoded data which is transmitted to the remote location. A receiver is provided at the remote location for receiving the encoded data. The receiver includes a correlator having a shift register for storing a chip sequence on the encoded data in bit form at least three sequential times. A decoder is provided for polling the shift register during the three sequential times of the stored chip sequence in bit form at a clock rate of at least three times that of the clock rate of the chip sequence to ascertain whether a majority of the corresponding chips of the chip sequence stored in the shift register at the at least three sequential times are the same to provide an output.

Abstract: A spread PN code signal receiver having a delay locked loop (DLL) circuit in an IF or RF stage characterized in that correlation outputs to be used for the DLL circuit control are (1) a correlation output between (a) a PN code advanced in phase with respect to the received signal and (b) the received signal and (2) a correlation output between (a) a PN code delayed in phase with respect to the received signal and (b) the received signal. The correlation outputs are used to detect the lock/unlock signal in the DLL circuit. In particular, AND logic for these two correlation outputs is employed to generate the lock/unlock signal only when the DLL circuit is perfectly synchronized in phase with the received signal. With this feature, a lock state can not de detected unitl a stable lock state is obtained.

Abstract: A data entry and retrieval system utilizing a plurality of remote units in radio communication with a plurality of base units in electronic communication with a central processing computer. The base units establish links with transmitting remote units by the remote units choosing the base units with the best signal. The linked remote unit and base unit transmit using frequency hopping spread spectrum modulation, using a predetermined frequency hopping sequence and at a point in the sequence unique to the particular base unit. The system may be configured with a plurality of NODES, each of which has a unique predetermined frequency hopping sequence and assigned base units and remote units.

Abstract: A unique method and system is disclosed for generating digital clock timing in a receiver for use in direct-sequence spread-spectrum digital communication systems wherein spread data is delivered from a transmitter to a receiver. The present invention provides at the transmitter frames of digital communication data with each frame having a plurality of time slots and with each time slot having a plurality of digital bits. The transmitter utilizes direct-sequence spreading codes for spreading the digital bits in the time frame. The direct sequence spreading codes each have the same fixed sequence length of M chips and, furthermore, the number of chips per bit CB to spread each digital bit is constant and fully aligned with each digital bit. The ration of M:CB is an integer and the ratio of time of each time slot to the time of the M chips also equals an integer. The spread frames of digital information are despread at the receiver with receiver provided identical direct-sequence codes.

Abstract: A system and method of driect-sequence spread-spectrum TDMA (or TDD) digital communication, wherein acquisition and tracking occurs for a plurality of frames having a predetermined number of time slots. One of the predetermined number of time slots in each frame is assigned for acquisition purposes and carries acquisition and sync digital information. The remaining time slots in each frame have assigned header bytes for tracking purposes. The assigned acquisition time slot is spread with an acquisition direct-sequence spreading code. The remaining time slots are spread with a communication direct-sequence spreading code. During acquisition, the signal strength in each successive time slot for each spread frame is measured for a given number of time frames. The peak is located within the given number of time frames through a major acquistion sweep and a refinement sweep. The major acquisition sweep and refinement acquisition sweep locate the frame and time slot boundaries of the transmitted signal.

Abstract: A digital signal receiver comprises receiver and demodulator means producing from the received signal a succession of complex elements. It produces sequences of successive complex elements consisting of conjugate elements of homologous elements used at the transmitting end. The sequences so used at the receiving end are synchronized to the homologous sequences used at the transmitting end. The complex elements obtained at the output of the demodulator are multiplied by a corresponding sequence of successive complex elements so produced and synchronized. The resultant complex elements appearing during the duration of an information symbol are summed over said duration to produce an estimate of the original information symbols used at the transmitting end. The complex elements obtained at the output of the demodulator are analyzed to identify a marking introduced at the transmitting end.

Abstract: In radio operation in tactical use, an increased jamming resistance with respect to intentional jamming is required. For protection against intentional jamming, frequency hopping techniques have proven very advantageous in which the signals are transmitted in the form of successive error-protected signal blocks where each signal block is transmitted on a different radio carrier frequency which changes in a pseudo-random manner. With this technique, phase shifts can occur which are greater than half a bit and therefore make analysis of the signal blocks difficult or impossible. It is proposed herein that each received signal block be checked after regeneration in a regenerative repeater, controlled by a bit clock pulse, as to its correct block phase and therefore, respectively, newly establish the block clock pulse phase required for further accurate processing of a signal block.

Abstract: A spread spectrum receiver with filters matched to transmitter chip codes are implemented in digital circuits along with a digital circuit for acquisition and tracking of the arrival times of the chip codes. The digital circuit implementations are used for the noncoherent demodulation of pulse position spread spectrum modulation signals where the pulse is a carrier modulator by a chip code and for the noncoherent demodulation of multiple chip code modulation signals where each information symbol is represented by one of several chip codes modulating a carrier.

Abstract: A spread spectrum CDMA communications system for communicating data and/or digitized voice between a plurality of users to a plurality of PCN units. The spread spectrum communications system is located within a same geographical region as occupied by a plurality of microwave users. The spread spectrum system can operate without causing undue interference to the microwave system and the microwave system can operate without causing significant interference (less than 1% total users affected) to PCN system. The spread spectrum CDMA communications system includes a plurality of PCN-base stations and a plurality of PCN units. A PCN-base station has a device for converting the format of the data into a form suitable for communicating over radio waves, a spread spectrum modulator for spread spectrum processing the data, and a transmitter for transmitting the spread spectrum processed converted data from the PCN-base station to a PCN unit.

Abstract: Apparatus for synthesizing complex composite RF signals comprising a source of unmodulated RF carrier signal, means for splitting the RF carrier signal output of the source into equal components, separate modulating means to which respective carrier signal components are applied, signal combining means to which the outputs of the modulating means are applied, and separate computerized in-phase and quadrature baseband control signal generating means the outputs of which are applied to respective modulating means to effect modulation of the respective carrier signal components.

Abstract: A spread spectrum receiver with filters matched to transmitter chip codes are implemented in digital circuits along with a digital circuit for acquisition and tracking of the arrival times of the chip codes. The digital circuit implementations are used for the noncoherent demodulation of pulse position spread spectrum modulation signals where the pulse is a carrier modulator by a chip code and for the noncoherent demodulation of multiple chip code modulation signals where each information symbol is represented by one of several chip codes modulating a carrier.

Abstract: A communications system which decreases noise errors and increases informon rate without sacrificing bandwidth is formed by a transmitter and a receiver designed to handle long pulse compression wavforms. An encoder connected to the transmitter converts a voice message into digitized voice words, encodes the digitized voice words into the time shifted code sequences, and phase modulates the long pulse compression waveform, producing a M-ary coded signal at the output of the transmitter. The receiver is connected to a decoder which includes at least one convolver for computing the correlation of received digitally coded words with independently generated time shifted code sequences, and a controller for generating a plurality of data values according to the largest correlation values, and a transducer responsive to the data values.

Abstract: A communication system for providing secured communication over a communication channel. The system includes a DES encryption device and a DES decryption device retrofittable into or within a conventional radio unit. The encryption device receives analog input at the transmitter end of the radio and converts the analog signal to digital signal, then encrypts this digital data, modulates the encrypted digital data using modified frequency modulation (MFM) which is then sent over the communication path. During decryption, the apparatus receives MFM data from the communication path, demodulates this digital data, decrypts the data and then outputs this decrypted digital data to the interface unit. The interface unit contains both a transmitter and a receiver which is capable of half duplex operation. The interface unit also contains a voice coder and a voice decoder which are of the sub-band type.

Abstract: A method for using coherent modulation and coding to improve the error-rate of non-coherent frequency-hopping data transmission systems includes aiding phase estimation by sending, in each hop, one or more reference bits, which are known to the receiver, and using the reference bits along with the data bits received in that same hop to estimate the channel phase. The data bits are then demodulated using the estimaated phase. The method also uses weighting of the demodulator output during each hop by a factor expressing the confidence level for the correctness of the phase estimated for that hop. Apparatus for implementing my novel methodology is also provided.

Abstract: An improved correlator for use in a spread spectrum communications system which operates with a predetermined chip sequence includes an N-stage correlation register, wherein each stage corresponds to a signal chip in the sequence, an a means for autocorrelating each of the N stages with the corresponding chips in the sequence. The correlator further includes a means for modifying the sequence to accomodate multiple communication channels.