Abstract: In a communication system for carrying out satellite communication through a satellite among users, a satellite communication center is located in a terrestrial network, such as an internet, and has a program table accessible through the terrestrial network and representative of a time schedule of each program to be broadcast through the satellite. The program table can be reserved to broadcast contents by a sender through the internet when an empty time zone is left on the program table. When the reservation is accepted, the contents are sent from the sender through the internet to the satellite communication center and are broadcast at a reserved time through the satellite to other users in accordance with the program table. The contents may be stored in advance in an information storage of the satellite communication center once before they are broadcast or be directly broadcast to the satellite at the reserved time.

Abstract: Connected to a satellite earth station for transmitting a broadcast signal to a communication satellite, a data (distribution) center publishes contents of stored information on a home page (HP) of the Internet to submit retrieval of users. When each user determines date to be gotten by retrieving on HP, the user transmits a request signal to the date center via a ground Internet or the communication satellite. Responsive to the request signal, the date center returns a reservation signal including a group address and a distribution scheduled time instant to a request source via the communication satellite. A user's terminal receives date with the group address at a reserved time instant, deciphers the date using a key given from the date center separately, and stores deciphered date in a memory thereof.

Abstract: A spreading code setting circuit generates N vectors, as spreading codes, which are +1 or ?1 polarity and are unique to users. A multiplier multiplies the nth data and the nth spreading code corresponding thereto for the spread modulation. An FDM combining circuit modulates N pieces of data according to the FDM method. A FDM separating circuit demodulates received signals according to the FDM method. An inverse spreading code setting circuit generates N vectors, as inverse spreading codes, which are +1 or ?1 polarity and are unique to users at the transmission side. A multiplier multiplies the nth data and the nth inverse spreading code corresponding thereto for inverse spread modulation.

Abstract: A satellite value added communication system includes an information distribution center which connects to a satellite ground station and controls transmission/receiving of information to/from a satellite communication terminal. The information distribution center connects to the Internet based on a request from the terminal, and distributes predetermined contents to the terminal. The information distribution center connects to a variety of networks, and based on requests of users through the networks, distributes a large amount of information (contents) directly to user's terminals through a communication satellite. In this system, the information distribution center can control a conference or a seminar among the terminals.

Abstract: In a communication system for carrying out satellite communication through a satellite among users, a satellite communication center is located in a terrestrial network, such as an internet, and has a program table accessible through the terrestrial network and representative of a time schedule of each program to be broadcast through the satellite. The program table can be reserved to broadcast contents by a sender through the internet when an empty time zone is left on the program table. When the reservation is accepted, the contents are sent from the sender through the internet to the satellite communication center and are broadcast at a reserved time through the satellite to other users in accordance with the program table. The contents may be stored in advance in an information storage of the satellite communication center once before they are broadcast or be directly broadcast to the satellite at the reserved time.

Abstract: An education system using satellite communications, including a satellite communication correspondence school for providing an education service, which is connected to subscriber terminals operated by subscribers for receiving lectures via a satellite communication earth station and a communication satellite, and also via a communication network on the ground including the Internet so as to distribute lectures and associated educational materials to subscriber terminals for receiving signals from the communication satellite and to communicate questions and answers of subscribers in a broadcasting manner. The satellite communication correspondence school is also connected to lecturer terminals via the satellite communication earth station and the communication satellite and via communication network on the ground.

Abstract: A content of a comment of a speaker participating in a conference is broadcasted, via a communication satellite, to a participant having a satellite communication terminal including a receiving unit for receiving a signal from the communication satellites. A conference center which is connected to a satellite earth station for satellite communication with the communication satellite includes a back-way communicating unit for accepting a voice request signal of the participant in the conference and a comment signal of the participant to whom a voice is granted, and ground communicates data via a ground communication network for the participant having a satellite communication terminal without a transmitting unit to the communication satellite.

Abstract: A spreading code setting circuit generates N vectors, as spreading codes, which are +1 or −1 polarity and are unique to users. A multiplier multiplies the nth data and the nth spreading code corresponding thereto for the spread modulation. An FDM combining circuit modulates N pieces of data according to the FDM method. A FDM separating circuit demodulates received signals according to the FDM method. An inverse spreading code setting circuit generates N vectors, as inverse spreading codes, which are +1 or −1 polarity and are unique to users at the transmission side. A multiplier multiplies the nth data and the nth inverse spreading code corresponding thereto for inverse spread modulation.

Abstract: A computer communication network, wherein a computer is specified by an address defined in a telephone network. In the computer communication network, the address defined in the telephone network may be used in place of an Internet protocol address. In the computer communication network, the address may be a telephone number. In the computer communication network, the address may be a number in the Integrated Service Digital Network. The computer communication network may comprise: an address server for correlatively storing the address defined in the telephone network and a name corresponding to the address, wherein the computer on a originating side comprises: means for inquiring of the address server about the address corresponding to a name of a computer on a terminating side; and means for calling the address received from the address server.

Abstract: Connected to a satellite earth station for transmitting a broadcast signal to a communication satellite, a data (distribution) center publishes contents of stored information on a home page (HP) of the Internet to submit retrieval of users. When each user determines date to be gotten by retrieving on HP, the user transmits a request signal to the date center via a ground Internet or the communication satellite. Responsive to the request signal, the date center returns a reservation signal including a group address and a distribution scheduled time instant to a request source via the communication satellite. A user's terminal receives date with the group address at a reserved time instant, deciphers the date using a key given from the date center separately, and stores deciphered date in a memory thereof.

Abstract: A variable-bandwidth frequency-division multiplex communication system which needs no interpolation circuits, but uses switch element of simple structure. The system includes a signal combining circuit which has N A/D converters associated respectively with independent information signals to be transmitted, a complex local oscillator for generating complex signals each having a frequency k.DELTA.f (1.ltoreq.k.ltoreq.N-1), .DELTA.f being the channel frequency interval, N complex multipliers for multiplying the outputs of the A/D converters by the respective complex signals, and producing N output signals, a circuit for effecting an inverse Fourier transform of N points, an N.times.

Abstract: A radio communication device includes a transmission carrier generating circuit, a reception intermediate-frequency local signal generating circuit), a transmission radio-frequency local signal generating circuit and a reception radio-frequency local signal generating circuit, each of which is in the form of a frequency synthesizer. The radio communication device further includes a channel connection signal control circuit which cooperatively controls the transmission carrier generating circuit and the transmission radio-frequency local signal generating circuit and cooperatively controls the reception intermediate-frequency local signal generating circuit and the reception radio-frequency local signal generating circuit.

Abstract: A TDMA timing control method and apparatus for use in a TDMA satellite communication network synchronizes land earth stations in a global beam system and even in a multi beam system having generally no return channel. A land earth station of the satellite network generates a transmission timing thereof on the basis of its own time base and detects a receiving time of a signal from another land earth station. Times of the land earth stations are synchronized by exchanging the information of their own transmission timing and the receiving times of the signals with other land earth stations through control bursts, calculating time errors of their own time bases by solving simultaneous equations including time errors of the time bases of the other land earth station and propagation times to the satellite as unknown quantities and correcting the times of the time bases on the basis of the time errors.

Abstract: A radio communication system comprises a plurality of personal terminals and a base station, the personal terminal being equipped with a non-directional antenna or a directional antenna directed to the base station, which transmits and receives a signal at an identical frequency, the base station, which establishes a communication path between the personal terminals by relaying of the signals, comprising a non-directional transmitting antenna and a receiving antenna located in such a positional relationship as to minimize the amounts of the signals coupled at the respective antennas, and feeds the received signal received by the receiving antenna to the transmitting antenna while cancelling a leakage signal from the transmitting antenna which is contained in the received signal, by using a reference signal set on a given frequency channel which may be modulated with a broadcast signal.

Abstract: In a high-power transmitter, an input complex signal is multiplied in a complex multiplier by control signals. The output complex signal from the multiplier is converted to a high frequency signal and amplified by a power amplifier for transmission. The amplitude of the input complex signal is detected to access a memory where amplitude and phase correction values are stored. During a read mode of the memory, a set of amplitude and phase correction values is specified by the detected amplitude and supplied to the complex amplifier as the control signals. During a write mode of the memory, a set of amplitude and phase correction values is specified by a delayed version of the detected amplitude and rewritten with a set of new amplitude and phase correction values. The amplified high frequency signal is down-converted to a low frequency complex signal.

Abstract: To establish radio channels according to a DAMA scheme, FDM radio channels are divided into channel groups, each containing a predetermined number of neighboring channels. The base station includes group modems for FDM modem processing, on a basis of each channel group, into uplink baseband signals uplink radio signals received from source stations in uplink channel groups and downlink baseband signals into downlink radio signals sent to destination stations in downlink channel groups and a switching unit for switching the baseband signals from the uplink channel groups into the downlink channel groups according to the destination stations.

Abstract: A first clock signal of fl in frequency is converted into a second clock signal having a frequency of f2=(n/m) f1. The first clock signal is converted by a tank circuit (12) and a converter (13) into an R-bit first phase signal (.theta.1) indicating the phase of the first clock signal. The first phase signal is multiplied by n (mod 2.sup.R) by a multiplier to provide a second phase signal (.theta.3). The second phase signal is supplied to a digital phase-locked loop (PLL) (3) comprising a subtractor (15), a low-pass filter (LPF) (16), a numerically controlled oscillator (NCO) (17) and a multiplier (18). The multiplier in the digital PLL (3) multiplies a third phase signal by m (mod 2.sup.R), indicating the phase of a second clock signal which is the output of the NCO (17), to generate a fourth phase signal. The subtractor (15) generates a signal representing the phase error between the second and fourth phase signals.

Abstract: A frequency synthesizer is composed of a reference oscillator, the first and the second integrators, a binary adder, a low pass filter and VCO forming a Phase Locked Loop (PLL). The first integrator, driven by the timing of a reference oscillator, integrates an externally supplied value K and generates the input signal. The second integrator, driven by the output signal of the VCO of the PLL, integrates an externally supplied value L. The binary adder detects the difference between the outputs of the first and the second integrators functioning as a phase comparator. The output of the phase comparator is converted into an analog voltage which is filtered to control the VCO to achieve frequency synthesis by the phase lock function of the loop.

Abstract: In a phase divider, a complex signal containing a sequence of samples of real and imaginary values is limited to a unit amplitude and multiplied by a first complex multiplier with a first feedback complex signal, the output the multiplier being fed through a loop filter to a second complex multiplier where the signal is multiplied with a second feedback complex signal. The output of the second multiplier is limited to a unit amplitude, delayed by a sample interval and applied to the second complex multiplier as the second feedback complex signal. The first feedback complex signal is derived by a circuit that raises the frequency the delayed signal by a desired factor.

Abstract: In a phase-locked circuit which is operable in response to an input complex signal to produce an output complex signal, a first complex multiplication is carried out between the input and the output complex signals to obtain a phase difference therebetween which appears as a complex phase difference. The complex phase difference is composed of a real part and an imaginary part which are individually allowed to pass through a low pass filter and to be supplied to a numerically controlled oscillator as a control signal. The control signal includes a frequency component even when the phase-locked circuit is put into an asynchronous state. The low pass filter may be replaced by a digital circuit comprising phase dividers.