Abstract: A method of communicating between two or more radios each capable of transmitting and receiving signals between one another on two or more radio channels wherein the radios hop from channel to channel in a pseudo-random sequence. The method comprises establishing hop synchronization between the radios utilizing a first cycle and operating the radios in a communication mode utilizing a second cycle. The first cycle is shorter than the second cycle so as to facilitate rapid synchronization while preserving the benefits and security obtained through the use of longer cycle length during communication mode.

Abstract: A sliding correlator for initial synchronization and tracking of a SS (Spread Spectrum)-modulated signal containing a transmitted pseudo noise (PN) code, digitizes the received signal, and attempts to correlate the PN code in the received signal with a locally generated reference PN code. Initial synchronization employs correlation with three reference PN codes, an early, center and late channel. When correlation is found between the transmitted PN code and one of the reference PN codes, the three reference PN codes are shifted to align the center channel with the correlated channel and to displace the early and late channel reference PN codes to one side and the other of the center channel. In one embodiment, the displacement is one-third chip, and in another embodiment, the displacement is one-half chip.

Abstract: A system which receives a pseudonoise sequence signal, quantizes the signal during a fixed increment of time, and passes the quantized signal to a single "split" correlator channel. The system utilizes sub-correlation products from that single "split" channel to calculate correlation outputs of other desired correlation channels. Specifically, the "split" correlator channel includes a pair of shift register strings, with the corresponding stages of each string being of equal length, and with a phase rotator being provided between consecutive stages of the shift register strings. In-phase and quadrature components of the received signal are each provided as inputs to a respective one of the shift register strings, and each shift register string stage is correlated with the pseudonoise sequence.

Abstract: A method for RF communication between transceivers in a radio frequency identification system that improves range, decreases multipath errors and reduces the effect of outside RF source interference by employing spread spectrum techniques. By pulse amplitude modulating a spread spectrum carrier before transmission, the receiver can be designed for simple AM detection, suppressing the spread spectrum carrier and recovering the original data pulse code waveform. The data pulse code waveform has been further encrypted by a direct sequence pseudo-random pulse code. This additional conditioning prevents the original carrier frequency components from appearing in the broadcast power spectra and provides the basis for the clock and transmit carrier of the transceiver aboard an RFID tag. Other advantages include high resolution ranging, hiding transmissions from eavesdroppers, and selective addressing.

Abstract: A threshold detector for digital signal transmission systems using a transmission channel, in particular for transmission to mobiles, calculates a set of coefficients f.sub.n belonging to the group comprising a set of coefficients c.sub.n of the correlation between a first series of digital samples x.sub.n received by the receiver and a second series of reference digital samples p.sub.n known to the receiver, in order to acquire synchronization of the system, and a set of coefficients h.sub.n of an estimate of the impulse response of the transmission channel, when the system is already synchronized. It also calculates a decision variable A such that: ##EQU1## where L and N are predetermined integers. The device has many applications in mobile radio systems, for example for acquisition of synchronization in DS-CDMA systems or for optimizing the transmission channel estimate.

Abstract: A testing device is provided to test performance of transmission systems such as communication devices and transmission lines by transmitting and receiving specific patterns called pseudo-random patterns (i.e., PN patterns). A receiver unit of the testing device provides a synchronization detecting circuit. The synchronization detecting circuit comprises a pseudo-random-pattern creating circuit, a first coincidence detecting block, a second coincidence detecting block and an OR circuit. The first coincidence detecting block detects coincidence between a receiving-data input, a first detected-pattern input and a pseudo-random pattern created by the pseudo-random-pattern creating circuit so as to produce a first coincidence detecting signal. The second coincidence detecting block detects coincidence between the receiving-data input, a second detected-pattern input and the pseudo-random pattern so as to produce a second coincidence detecting signal.

Abstract: A synchronous pseudo-noise (PN) code sequence generating circuit generates a plurality of PN code sequences which should be synchronized with each other. A feedback-type PN code generator generates a master PN code sequence. Each of N code converters, which are provided for each of N channels, converts the master PN code sequence to a PN code sequence of the corresponding channel in accordance with a mask pattern unique to the corresponding channel. The mask patterns for each channel are stored in the corresponding mask memory.

Abstract: The present invention is for fast, reliable recognition of coded signals where the signal includes a predetermined code sequence in a lead portion thereof. This has particular application in spread spectrum transmission and receptions. The code sequence is a long sequence of bits known to the receiver which breaks the long sequence into a series of bit segments which are more easily analysed. Each series of bits is analysed for a direct match and a decision whether a code segment has been received is based on the number of direct matches. For example, if there are 8 bit segments, each 16 bits in length, high reliability has been achieved if two direct matches are received within a time period corresponding t the transmission time of the code sequence. This system can also be used for assessing signal strength where many matches indicate good signal strength, approximately 50% indicates moderate signal strength, and less indicating poor signal strength.

Abstract: A method of mobile station synchronization to a system time, wherein the time alignment is attained while the mobile station operates in analog mode. The mobile stations transmits a periodic signal, each period of which has a leading edge. The base station detects the leading edge of the periodic signal and compares it to an indication of system time. The base station generates an error message for the mobile station indicating an update to the phase of the periodic signal. When the mobile station and the base station are time aligned, the base station may send a message indicating the absolute time at some future leading edge of the periodic signal thereby eliminating ambiguities of time due to the finite time required to receive the message.

Abstract: Apparatus and a method for increasing the speed of acquisition of PN coded signals includes a novel PN code clock extraction circuit which is coupled in parallel to a code tracking loop and acquisition loop of a PN receiver of the type having a replica PN code generator which is slip controlled to synchronize with the received PN coded signals. The novel PN code clock extraction circuit detects the clock transition of the received PN coded signals and synchronized the replica PN code generator clock transition signals so that there is no misalignment during acquisition. A switch control in the acquisition loop circuit senses the synchronization of the replica PN code generator transition and the received PN code transition and disconnects the PN code clock extraction circuit after synchronization of clock transition and before acquisition of the PN code so that the acquisition loop detects the PN code synchronization with a full strength signal.

Abstract: Apparatus for rapidly acquiring a high performance gain long PN code having a preamble header in real time includes appratus for rapid acquiring and tracking a short PN code in said preamble header and further includes apparatus for demodulating and tracking a long PN code which follows said preamble header. After acquiring the short PN code, the short PN replica code is applied to the long code demodulation and tracking apparatus. The short PN code is employed to synchronize the long code demodulation and tracking apparatus by detecting the time of occurrence of a sync word in said preamble header and is employed to generate a switch point signal and switch from a short PN replica code to a long PN replica code at the input to the long code demodulation and tracking device in real time.

Abstract: In a spread spectrum communication apparatus, frame synchronization is established by inserting data for frame synchronization as a part of a synchronization word of a transmission frame on a sending side and detecting the data for frame synchronization from reproduction data of a reception frame on a receiving side. A frame synchronization pseudo-noise train generator section generates a pseudo-noise train for frame synchronization used as the frame synchronization data. A frame synchronization correlator section receives the pseudo noise train for frame synchronization and reproduction data to output a signal when the value of correlation of the pseudo noise train for frame synchronization and the reproduction data is not smaller than a reference value. A reception frame timing generator section outputs a reception synchronization word timing signal with the output signal of the frame synchronization correlator section being taken as a reference.

Abstract: Methods for synchronizing to a reference signal the timing of a received composite, code phase SATPS signal, which consists of a preferred, interference-free signal distorted by at least one interfering signal, to determine an undistorted timing point of the preferred signal. An idealized correlation function A.sub.I (t), formed from the product of a digital reference signal with a time-shifted reference signal, and a measured correlation signal A.sub.M (t), formed from the product of a received signal and a time-shifted reference signal, are computed. Peak amplitudes A.sub.M (p.sub.M) and A.sub.I (p.sub.I) are found for the respective measurable and idealized punctual code phase shifts p.sub.M and p.sub.I. In a first embodiment of the invention, the correlation measurements formed on the early side (or on the late side) of the peak for the correlation function A(t) are combined to form an estimate of the time delay associated with a multipath signal.

Abstract: A cascaded synchronized system includes a nonlinear transmitter, a nonlinear cascaded receiver, a phase-detector/controller coupled to the receiver, and a signal generator also coupled to the receiver. The transmitter is responsive to an externally generated transmitter forcing signal for producing and transmitting a chaotic communications signal containing phase information. The cascaded receiver is responsive to a receiver forcing signal and to the chaotic communications signal for producing a chaotic receiver output signal containing phase information. The phase-detector/controller is responsive to the chaotic communications signal and to the receiver output signal for producing a correction signal. The signal generator is responsive to the correction signal for producing the receiver forcing signal in phase with and having the same frequency as the transmitter forcing signal.

Abstract: Signals representing navigation messages from four GPS artificial satellites are received by a GPS receiver and supplied to receiving processors of respective channels, which spectrally reverse-spread and demodulate the signals by way of PSK to produce the navigation messages. The navigation messages are then supplied to a CPU that determines the position of the GPS receiver using satellite time and orbit data contained in the navigation messages. The CPU determines whether each channel is synchronized or not based on the level of a spectrally reverse-spread output (correlated output) signal. If a channel is out of synchronism, the CPU effects a synchronization process. After the synchronization process, the CPU obtains time base data equal to or higher than a bit number. To obtain such time base data in a channel after the synchronization process, the CPU uses time base data equal to or higher than a bit number of another channel that has already been synchronized.

Abstract: A synchronizing circuit comprises a controllable timer (9) and a PN-code generator (10) controllable thereby with at least three outputs (11.1, 11.2, 11.3), for the production of at least three PN-code signals phase-shifted with respect to one another. The PN-code signals phase-shifted with respect to one another are correlated, in parallel correlation paths, with the received signal. Upon the presence of a time drift, the phase position of the trailing PN-code signal, for example, is changed so that this signal is now leading. Thereby, the control range is shifted. At the same time, reassignment is effected between the correlation path and the demodulating output in such a way that in all cases the correlation path that is in the middle with respect to time and that has the maximum correlation power is utilized for demodulation.

Abstract: A self synchronizing automatic correlator, comprising apparatus for receiving an input data signal; apparatus for receiving a free running clock signal; a clock recovery circuit for comparing the input data signal and the free running clock signal and generating a phase error signal responsive thereto, and for frequency adjusting the clock signal by an amount equal to the phase error signal and in response generating a recovered clock signal synchronized to the input data signal; a shift register for receiving and storing the input data signal under control of the recovered clock signal; apparatus for storing a user data signal; and apparatus connected to the shift register and the apparatus for storing for comparing the input data signal and the user data signal and in the event of a match therebetween generating an output signal for indicating valid detection of the input data signal.