Clarion Co

Masahiro Hamatsu

Masaharu Mori

Takao Kurihara

Shigeo Akazawa

Yoshitaka Uchida

Mamoru Endo

Shoichi Minagawa

Masaaki Harada

Noriyuki Hamao

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. In one embodiment for initial tracking, the three channels are displaced one chip from each other and, after failure to attain correlation in any of the channels, the three channels are displaced three chips to again seek synchronization. Initial Tracking, following initial synchronization, detects changes in correlation in the three channels, and adjust the frequency and/or the phase of the three reference PN codes to return the reference PN codes into a desired relationship with the transmitted PN code. In one embodiment of tracking, clockwise and counterclockwise cyclic permutation of the three reference PN codes is used to maintain alignment between the three reference PN codes and the transmitted PN code. In other embodiments, the condition of correlation, or lack thereof, in each channel is stored in a register and shifting of the reference PN codes is performed in response to the status of the register.

Sliding correlator

A spread spectrum receiver includes, for example, a correlator consisting of two convolvers whose correlation outputs are applied to a demodulator respectively via two variable gain amplifiers whose gains are controlled in response to a demodulation output from the demodulator.

Automatic gain control system

In a digital matched filter used as a correlator in a receiver in an SSC system, different bits of a received signal converted into a multi-bit signal are inputted into different correlators. After having weighted different correlation outputs, the different weighted correlation outputs are added together and weighting factors are varied, depending on a synthesized correlation output obtained by addition. When such a matched filter is used in an SSC system, it is possible to obtain precisely a desired signal without controlling transmission electric power.

Digital matched filter

On the transmitter side, data to be transmitted are converted into a plurality of parallel data sets by a serial-parallel converter 101 and spread spectrum modulation is effected by means of PN code generators 105 and selectors 102. Each of the modulated outputs is delayed by a delaying circuit 103 with reference to a sounder channel and the phase thereof. The output thus delayed and the output of the sounder channel are added by an adder 104 to be multiplexed and transmitted. On the receiver side, correlation between a received signal and a reference signal is formed by a correlator 201 to obtain a correlation pulse from the correlation output thus obtained. Data demodulation is effected by means of a sounder detecting circuit 209, a sampling pulse generating circuit 210 and an information detecting circuit 211, starting from this correlation pulse. According to the structure described above, in SS communication, data demodulation can be effected with a high efficiency by using a single correlator.

Spread spectrum communication device

On the transmitter side of a spread spectrum communication device according to the present invention, transmission date are converted into a plurality of parallel data sets by a serial-parallel convertor and spread-spectrum-modulation is effected by means of PN code generators and selectors. Different modulated outputs are delayed by delay devices, using a sounder channel and the phase thereof as a reference. The delayed outputs and the output of the sounder channel are added by an adder, multiplexed and transmitted. On the receiver side correlation of a received signal with a reference signal is formed by a correlator and a correlation pulse is obtained from the correlation output. Data are reproduced by means of a sounder detecting circuit, a sampling pulse generating circuit and an information detecting circuit. In this way data reproduction can be effected with a high efficiency by means of a single correlator.

A spread spectrum receiver using a correlator includes a pattern matching circuit for deciding presence or absence of a pulse output which is obtained upon coincidence between the pattern of a correlator output and a predetermined pattern, so as to switch a PN code inside the receiver or the center frequency of a received signal when absence of the pulse output is acknowledged.

Spread spectrum receiver

A signal processing circuit utilizes a convolver correlating a reference carrier signal with a received signal. The correlator output is detected and then demodulated to output the signal information originally present on the carrier. For a conventional AM signal the reference carrier signal is applied at a frequency offset from the AM center frequency. When the carrier is an FM signal, the reference signal is applied at a frequency equal to the center frequency of the FM signal. Similar procedures are followed for a spread-modulated AM signal, and the reference signal is modulated with a suitably timed-reverse replica of the pseudo-noise code. A similar procedure is used to process spread-spectrum frequency shift keyed FM signals.

Communication device

An SSC device according to the SSC method using a correlator is disclosed, in which a plurality of stages of shift register is connected in series, the outputs of the stages of the shift register being given selectively to the correlator and the initial value of the shift register in the pseudo noise code generator on the receiving side are set in a mirror image relation with respect to the initial value of the transmitted signals of the pseudo noise code generator at the code synchronization.

An SSC receiver, in which desired information is restored by means of a correlator, which forms the correlation between a received PN code included in a received signal and a reference PN code included in a reference signal, is disclosed, wherein it is so constructed that the output of the correlator stated above is inputted in pattern judging means, that in the case where no accordance with a predetermined judgment pattern is obtained, when a certain period of time has elapsed, judgment patterns, which are analogous to the predetermined judgment pattern stated above, are switched over one after another, every time a predetermined period of time has elapsed, and that the position, where the two codes are in accordance with each other, is set correctly by controlling the phase of the reference PN code by using the output, when the output of the correlator described above is in accordance with either one of the judgment patterns.

Spread spectrum communication receiver

The present invention is a spread spectrum communications system where the plural pseudonoise codes are switched such that one pseudonoise code represents binary '1' and another pseudonoise code represents binary '0' of the binary data to be transmitted. Further, in the receiver, a reference pseudonoise code is generated which is asynchronous with respect to the carrier and with respect to the pseudonoise codes of the transmitter. The reference pseudonoise code is used in a convolver to reproduce the transmitted information signal.

A correlation pulse generator used in a receiver of a spread spectrum communication system comprises peak hold circuit for holding peak values of positive and negative correlation spikes, threshold setting circuits for generating thresholds based on the peak values, and a comparing circuit for comparing the threshold with a correlation spike to generate a correlation pulse, so that when a level difference exists between positive and negative correlation spike levels of a correlation output, their peaks can be held independently, and thresholds based on the peaks can be generated independently.

Spread-spectrum receiver

A spread spectrum communication receiver is disclosed, which is provided with a correlator for correlating a received PN code contained in a received signal with a reference PN code contained in a reference signal generated on the receiver side, the output of which is given to pattern judgment means such as a matched filter, etc., and an operation of the initial synchronization of the two PN codes in the correlator is effected by using a judgment output obtained when the pattern of the output of the correlator is in accordance with a predetermined judgment pattern.

A phase shifter is disclosed which performs a desired phase shift by distributing an input signal to two signals whose phases are different by 90.degree. from each other which signals are added to each other after having been weighted with a sine and a cosine function signal, the sine and the cosine function signal being able to be set in a digital manner.

Spread spectrum receiver having phase shifter for effecting phase

A receiver for spread spectrum communication is disclosed, which is provided with two convolvers and in which a first and a second reference signal, each of which consists of a 4-phase-modulated signal formed on the basis of a first PN code, a second PN code and a first CW signal, are supplied to a second input of each of the convolvers, respectively, while a received signal is supplied to a first input of each of the convolvers so that the correlation output of each of the convolvers is decoded so as to obtain an information signal.

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Tokyo, Japan

Masahiro Hamatsu