Abstract: A passive optical network communication system includes a number of subscribers' units connected to a central line termination unit through a passive optical coupler. The line termination unit includes a first section that transmits and receives a code division multiplex (CDM) signal, a second section that transmits and receives a time division multiplex (TDM) signal, and a wavelength multiplexing filter that combines the transmitted CDM and TDM signals into a single downstream optical signal, and separates the CDM and TDM components of an upstream signal received from the subscribers' units through the passive optical coupler. The CDM signal provides channels for digital video transmission to CDM-capable subscribers' units.

Abstract: A parallel decoder for decoding a code division multiplexed (CDM) signal. The parallel decoder has two matched filters, both operating at a frequency equal to half the chip rate of the CDM signal. One matched filter correlates odd-numbered chips of the CDM signal with odd-numbered chips of the spreading code. The other matched filter correlates even-numbered chips of the CDM signal with even-numbered chips of the spreading code. The two resulting correlated signals are combined, and the decoded signal is obtained from the combined signal. This arrangement doubles the maximum possible chip rate of the CDM signal.

Abstract: A passive optical network communication system transmits an optical time-division multiplexed signal from a central office through a passive optical coupler to a number of subscribers, and transmits optical encoded signals from the subscribers through the passive optical coupler to the central office. Optical encoded signals from different subscribers are separated by a decoding process performed at the central office. All operations can be synchronized with a clock signal which is generated at the central office and recovered from the optical time-division multiplexed signal by the subscribers' equipment. The communication range can be extended inexpensively by using a single high-power light source at the central office while using relatively low-power light sources at the subscribers' equipment.

Abstract: An optical access network system capable of transmitting and receiving high-speed signals and which allows the number of subscribers to be increased without increasing the number of wavelengths used is provided. An optical line terminal and an optical network unit are joined via an optical fiber transmitting line, a star coupler, and a plurality of branching optical fiber transmitting lines. The optical line terminal and optical network unit are constituted comprising an optical processing section and an electrical processing section. The optical processing section comprises a light-emitting element and a light-receiving element.

Abstract: A communication network which can use communication bandwidth effectively. Spreading codes of a first and a second code length are assigned for every communication terminal interfaces connected to the same communication network. The spreading codes of the first code length are used for data communications. The spreading codes of the second code length are used for the control communications between the interfaces and the server. The interfaces and the server receives mixed signals of the data and the control signals. When the received signals are decoded using the spreading code of the first code length, control signal components became equal to or lower than the noise level. When the received signals are decoded using the spreading code of the second code length, data components became equal to or lower than the noise level. Therefore, the interfaces and the server can extract one of these signal components.

Abstract: In a communication network which performs transmission from a plurality of first communication devices to a single second communication device using a synchronous code division multiplexing technique, the phases of signals transmitted from the first communication devices are synchronized easily. The first communication devices control the transmission phase of spread modulated signals using phase control information received from the second communication device. A repeater generates a code division multiplexed signal by superposing the spread modulated signals transmitted respectively from the first transmission devices. The second transmission device demultiplexes the code division multiplexed signal received from the repeater, determines the optimum phase of the demultiplexed signals, and transmits the determined optimum phase to the first transmission devices as the phase control information.

Abstract: The present invention provides an optical access network system that allows the transmission of packets irrespective of the packet length and which is also capable of adapting to cases where another user temporarily requires a large capacity bandwidth. This system performs two-way optical communications using a code division multiplexing system via an optical fiber channel and a star coupler between an optical line terminal and first and second optical network units. The optical line terminal comprises a bandwidth control section and a bandwidth allocation section and the bandwidth control section has signal converter pairs installed therein in a number equal to the number of optical network units. Further, the optical network units each comprise first and second bandwidth control sections and first and second bandwidth allocation sections. The bandwidth control sections each have one set of signal converter pairs installed therein.

Abstract: In 1 to N communication based on code division multiplexing, ranging is performed by following the first to ninth steps. First step: all the optical network units are set to standby status. Second step: first and second optical network units are set to transmission enable status. Third step: the phase shift amount is set for the variable phase shifters of the first and second optical network units. Fourth step: reception of a fixed signal is attempted in the optical line terminal. Fifth step: if the fixed signal is not received, processing returns to the second step, and if received, the phase amount of the variable phase shifter is defined and fixed. In the sixth to ninth steps, an operation the same as the first to fifth steps is performed for the third to N-th optical network units.

Abstract: A communication network which can use communication bandwidth effectively. Spreading codes of a first and a second code length are assigned for every communication terminal interfaces connected to the same communication network. The spreading codes of the first code length are used for data communications. The spreading codes of the second code length are used for the control communications between the interfaces and the sever. The interfaces and the server receives mixed signals of the data and the control signals. When the received signals are decoded using the spreading code of the first code length, control signal components became equal to or lower than the noise level. When the received signals are decoded using the spreading code of the second code length, data components became equal to or lower than the noise level. Therefore, the interfaces and the server can extract one of these signal components.

Abstract: A passive optical network communication system transmits an optical time-division multiplexed signal from a central office through a passive optical coupler to a number of subscribers, and transmits optical encoded signals from the subscribers through the passive optical coupler to the central office. Optical encoded signals from different subscribers are separated by a decoding process performed at the central office. All operations can be synchronized with a clock signal which is generated at the central office and recovered from the optical time-division multiplexed signal by the subscribers' equipment. The communication range can be extended inexpensively by using a single high-power light source at the central office while using relatively low-power light sources at the subscribers' equipment.

Abstract: A passive optical network communication system includes a number of subscribers' units connected to a central line termination unit through a passive optical coupler. The line termination unit includes a first section that transmits and receives a code division multiplex (CDM) signal, a second section that transmits and receives a time division multiplex (TDM) signal, and a wavelength multiplexing filter that combines the transmitted CDM and TDM signals into a single downstream optical signal, and separates the CDM and TDM components of an upstream signal received from the subscribers' units through the passive optical coupler. The CDM signal provides channels for digital video transmission to CDM-capable subscribers' units.

Abstract: A clock regeneration circuit includes a half-bit delay device that outputs a half-bit delayed signal B of a multi-level input signal A, a one-bit delay device that outputs a one-bit delayed signal C of the signal A, an adder, an attenuator that forms an threshold signal, an XOR circuit, and a BPF that outputs a clock signal with a frequency corresponding to a bit rate of the XOR signal. The XOR signal is calculated as an XOR of a two-level input signal F, which is a logical zero when a level of the signal A is no more than a level of the threshold signal and otherwise is a logical one, and a two-level input signal G, which is a logical zero when a level of the signal B is no more than the level of the threshold signal and otherwise is a logical one.

Abstract: A communication network which can use communication bandwidth effectively. Spreading codes of a first and a second code length are assigned for every communication terminal interfaces connected to the same communication network. The spreading codes of the first code length are used for data communications. The spreading codes of the second code length are used for the control communications between the interfaces and the sever. The interfaces and the server receives mixed signals of the data and the control signals. When the received signals are decoded using the spreading code of the first code length, control signal components became equal to or lower than the noise level. When the received signals are decoded using the spreading code of the second code length, data components became equal to or lower than the noise level. Therefore, the interfaces and the server can extract one of these signal components.

Abstract: A code division multiplexing communication system which transmits a single signal array in use of band for two channels. A first data generator generates a channel signal array. A data distributor branches the channel signal array into two. A first spread modulator converts one of the branch signal array to a signal array having values VL and VH by performing spread modulation in use of a predetermined spread code. A second spread modulator converts the other branch signal array to a signal array having signal values VL, VH and high impedance and then performs spread modulation in use of the same spread code as the first spread modulator. The outputs of the first and the second spread modulator are superimposed by an adder. Accordingly, a quaternary signal array using band for two channels can be generated.

Abstract: A parallel decoder for decoding a code division multiplexed (CDM) signal. The parallel decoder has two matched filters, both operating at a frequency equal to half the chip rate of the CDM signal. One matched filter correlates odd-numbered chips of the CDM signal with odd-numbered chips of the spreading code. The other matched filter correlates even-numbered chips of the CDM signal with even-numbered chips of the spreading code. The two resulting correlated signals are combined, and the decoded signal is obtained from the combined signal. This arrangement doubles the maximum possible chip rate of the CDM signal.

Abstract: A clock regeneration circuit includes a half-bit delay device that outputs a half-bit delayed signal B of a multi-level input signal A, a one-bit delay device that outputs a one-bit delayed signal C of the signal A, an adder, an attenuator that forms an threshold signal, an XOR circuit, and a BPF that outputs a clock signal with a frequency corresponding to a bit rate of the XOR signal. The XOR signal is calculated as an XOR of a two-level input signal F, which is a logical zero when a level of the signal A is no more than a level of the threshold signal and otherwise is a logical one, and a two-level input signal G, which is a logical zero when a level of the signal B is no more than the level of the threshold signal and otherwise is a logical one.

Abstract: The present invention provides an optical access network system that allows the transmission of packets irrespective of the packet length and which is also capable of adapting to cases where another user temporarily requires a large capacity bandwidth. This system performs two-way optical communications using a code division multiplexing system via an optical fiber channel and a star coupler between an optical line terminal and first and second optical network units. The optical line terminal comprises a bandwidth control section and a bandwidth allocation section and the bandwidth control section has signal converter pairs installed therein in a number equal to the number of optical network units. Further, the optical network units each comprise first and second bandwidth control sections and first and second bandwidth allocation sections. The bandwidth control sections each have one set of signal converter pairs installed therein.

Abstract: According to a CDMA communication system for the present invention, the transmission side for each channel increases the amplitude of a time slot period for self-channel synchronization until greater than the amplitude for another period, and outputs the resultant signal as a modulation signal. The reception side obtains a correlation between a multiplex signal obtained by superimposing modulation signals for multiple channels, and a spreading code allocated for the self-channel. Since the amplitude of the time slot period for the self-channel synchronization is increased by the transmission side, the large value portion indicating the synchronization timing is included in the correlation signal, and by detecting this value, the reception side can easily obtain the synchronization timing.

Abstract: The present invention is a high-speed and low-cost optical communication network. A preferred embodiment of this optical communication network comprises an accommodation device, optical couplers that are connected to corresponding ports of this accommodation device, and communication terminals that are connected to corresponding optical couplers. Further, data transmitted by the communication terminals to the accommodation device is code-division multiplexed. Because data collision is prevented by means of code division multiplexing, control of the timing with which the communication terminals transmit data is not required. Meanwhile, data transmitted by the accommodation device to the communication terminals is time-division multiplexed because there is no risk of collision.

Abstract: In 1 to N communication based on code division multiplexing, ranging is performed by following the first to ninth steps. First step: all the optical network units are set to standby status. Second step: first and second optical network units are set to transmission enable status. Third step: the phase shift amount is set for the variable phase shifters of the first and second optical network units. Fourth step: reception of a fixed signal is attempted in the optical line terminal. Fifth step: if the fixed signal is not received, processing returns to the second step, and if received, the phase amount of the variable phase shifter is defined and fixed. In the sixth to ninth steps, an operation the same as the first to fifth steps is performed for the third to N-th optical network units.