Abstract: Disclosed herein are a remote monitoring transmitter, a remote monitoring receiver and a remote monitoring system. A remote monitoring transmitter includes a video input terminal; video compressing means for compressing at a variable compression ratio video data input through the video input terminal; a communication interface for conducting communications over a network; and controlling means for causing the video compressing means to control the compression ratio based upon receipt by the communication interface of control data for controlling the compression ratio for the video data; in which video data compressed by the video compressing means are transmitted through the communication interface.

Abstract: In a transmitting unit, an input signal is converted into an I data sequence of an in-phase (I) symbol and a Q data sequence of a quadrature (Q) symbol, a differential encoding is performed for the I and Q data sequences according to a differential binary phase shift keying (DBPSK) modulation to produce an I code sequence and a Q code sequence, a spectrum of the I code sequence is spread by a first spreading code signal to produce an I spread spectrum signal, a spectrum of the Q code sequence is spread by a second spreading code signal to produce a Q spread spectrum signal, the I and Q spread spectrum signals are quadrature-modulated to a synthesized signal, and the synthesized signal is transmitted to a receiving unit.

Abstract: A clock signal generator produces a basic clock signal. A variable delay device is operative for delaying the basic clock signal by an adjustable interval and thereby converting the basic clock signal into a delay-resultant clock signal. A pseudo-noise code is generated at a timing depending on the delay-resultant clock signal. A spread-spectrum information signal is despread into a non-spread information signal in response to the pseudo-noise code. A correlator detects a correlation between the spread-spectrum information signal and the pseudo-noise code. The adjustable interval provided by the variable delay device is controlled in response to the detected correlation to provide synchronization between the spread-spectrum information signal and the pseudo-noise code.

Abstract: A digital correlator used in a receiving component of a spread spectrum communication system of a direct sequence modulation type is disclosed. A polarity of an input baseband signal is controlled by being inverted or not inverted according to a polarity of a spreading code signal by an amplifier, and the input baseband signal controlled is converted by an analog-to-digital converter into a digital signal. The digital signal is integrated for a prescribed period in an integrator, and a square of an integrated digital signal is calculated in a squaring device to obtain a squared value indicating a degree of a correlation between the input baseband signal and the spreading code signal. In cases where the input baseband signal and the spreading code signal correlate with each other, the squared value gradually increases with the passage of time. In contrast, in cases where the input baseband signal and the spreading code signal do not correlate with each other, the squared value is maintained to a low value.

Abstract: A wireless data communication system comprises: base stations located to have cells arranged equidistantly therebetween; mobile units, each being located within either of the cells, each of the base stations communicating with mobile units within its cell through plural channels provided by FDM. In the system, each of the base station may comprise a detector for monitoring the channels and detecting a free channel, and a transmission portion for continuously transmitting a signal including data indicative of the detected free channel. In the system, the plurality of channels used in one of cells have given frequency bands respectively which are the same as given frequency bands in other cells. In the system, each of the mobile stations may comprise a chip synchronizing circuit for effecting chip synchronizing between the each of the mobile stations and its base station.

Abstract: A signal processing circuit provided with a frequency conversion circuit for converting a spread quadrature modulation signal of a carrier band into a baseband signal, a first correlator, a second correlator, a third correlator, a fourth correlator spreading code, a decoding circuit for decoding data from outputs of the first to fourth correlators, a first multiplier for calculating the square of the output of the first correlator, a second multiplier for calculating the square of the output of the second correlator, a first adder for adding up outputs of the first and second multipliers, a judgment circuit for performing a synchronization acquisition judgement, a second adder for adding up the outputs of the first and second correlators, or those of the first and fourth correlators, a subtracter for performing a subtraction between the outputs of the second and third correlators and a correction circuit for obtaining a frequency offset according to an output of the second adder and/or that of the subtracter

Abstract: Each of groups each has a plurality of communication channels. There are generated signals to be transmitted via the respective communication channels in the groups. The transmitted signals are time-division-multiplexed into a data sequence for each of the groups. The data sequences are spectrum-spread in response to different spread code patterns respectively. A reserve time slot may be provided. In cases where a reduction of a received signal quality related to one of the communication channels is detected, the reserve time slot is used in transmitting the signal of said one of the communication channels.

Abstract: In a first direct-sequence spread spectrum communication system having a transmission circuit where a data signal to be transmitted is coded by a first chip code signal and a receiving circuit for decoding the transmitted data signal with a second chip code signal, the synchronization between the said first and second chip code signals is performed when an asynchronous condition of said first and second chip code signals is detected over a predetermined interval. In a second direct-sequence spread spectrum communication system having a transmission circuit where a data signal having a variable data rate V to be transmitted is coded by a first chip signal having a data rate C and coded by a reference code signal having a data rate R, C>V, R>V. A receiving circuit receives the data signal from the above-mentioned transmission circuit decoded by a second chip signal and a second reference code signal.