Fujitsu Corporation

Susumu Sasaki

Hiroshi Nakamura

Eisuke Fukuda

Sadao Takenaka

Yukio Takeda

Yoshimasa Daido

In a transmitter, a modulator switchably operates on one of two modes of operations, that is, in a first mode of the operation, such as an offset QPSK, FSK or .pi./4 shift QPSK, an amplitude of an output signal of the modulator does not become zero at any instant, and in a second mode of the operation, such as two-phase FSK or four-phase PSK, the output signal of the modulator is 100% amplitude-modulated or 180 phase-modulated. Second mode operation. The operation mode is switched by changing the mode of the parallel input signals to the modulator, where the parallel signals have been converted from a serial input data signal to be transmitted. After the first mode operation is switched to the second mode operation the output signal is interrupted preferably on a first moment that the amplitude of the output signal becomes zero, as well as, before the second mode operation is switched to the first mode operation the output signal is resumed preferably on a second moment that the amplitude of the output signal is to become zero. The interruption of the modulated output signal may be done by cutting the local frequency or modulated signal, or by the parallel input signals. Thus, spurious wave is not generated on the transition of interrupting or resuming the modulated transmittal wave, and the period of the interrupting can be short enough.

System for interrupting a transmitter output wave

The present invention is a channel changing system in a mobile unit communication system comprising a plurality of radio base stations for communicating with movable stations through radio channels and a center station for accommodating such base stations and connecting these base stations with the public telephone network. The center station is configurated comprising a private branch exchanger for accommodating the public telephone network and the lines extending from a plurality of base stations and a controller for controlling changing of communication channels by supervising the signal receiving levels between a movable station and a plurality of base stations. The controller is configurated so that it issues a channel changing command by detecting, based on the signal receiving levels, that a movable station has transferred to the radio zone of an adjacent base station from the radio zone of a certain base station. The private branch exchanger conducts the line changing depending on the channel changing command through an extension transfer to the base station line of adjacent base station from the base station line of the relevant base station.

Channel changing system

The radio transmitter-receiver system for increasing or decreasing communication channels comprises radio transmitter-receivers each including a separated intermediate frequency portion for modulation and demodulation and a separated microwave portion, and having a multiplexer and a divider therebetween. Local oscillators in the intermediate frequency portion have a variable frequency function and the operating frequency of the intermediate frequency portion can be easily changed. The intermediate frequency portions are connected to the microwave portions through the multiplexer or the divider and the frequency of the microwave to be communicated is easily changed. Thus, an increase or decrease of the communication channels is possible at a low cost.

Radio transmitter-receiver system for increasing or decreasing

A digital radio communication system in the form of a multi-direction time division multiplex network including a central station having one working transmitter and receiver and one standby transmitter and receiver. Both the working and standby transmitters and receivers have a radio line terminating equipment, and each transmitter and receiver have a first phase shifting circuit for adjusting a phase of a transmission signal and a second phase shifting circuit for adjusting a phase of a sampling clock signal. A signal propagation delay time of the working transmitter and receiver is adjusted by the first phase shifting circuit to become equal to that of the standby transmitter and receiver, then, the phase of a sampling clock signal is adjusted between both second phase shifting circuits to be at a central position of bit width of a reception signal, and a plurality of substations are included, each operatively connected to the central station by time-divided digital radio signal, and each at least having a clock phase shifting circuit for adjusting a phase of a transmission signal transmitted from itself.

Digital radio communication system

A radio communication system using a QAM system. In the transmission system, the data of each channel to be transmitted is divided into data groups having frame slots. When the polarity of the mean value of a data summed in a present data group is the same as the polarity of the mean value of the deviation of all data group coming before, all data in the present data group is inverted, a direct current component and a lower frequency component near the direct current component are suppressed, and carrier waves are injected after encoding. In the receiving system, a decoder decodes a received signal to obtain the original data before the encoding by the transmission system.

Radio communication system

Time division communication system

A radio relay system for a fully-digitalized transmission network is disclosed. In the system, a received auxiliary signal can be by-passed from receiver to transmitter via a switching circuit provided in the auxiliary unit when an additional auxiliary signal is not input to the equipment. When a local auxiliary signal, for example, order wire signal from telephone equipment, is input, the switching circuit operatively disconnects the switching circuit and switches to supply the additional auxiliary signal to the transmitter. The auxiliary unit is thus by-passed upon the occurrence of a failure of the built-in circuit or power supply of the auxiliary unit.

Digital radio relay system

A radio communication system includes a transmitter unit, a radio transmission line and a receiver unit. The transmitter unit contains an insertion circuit for inserting one or two signals for carrier recovery into a modulated wave signal. Each signal for carrier recovery has a frequency (f.sub.O +f.sub.CL), where 0&lt;.vertline.k.vertline.&lt;1. The receiver unit receives, via the radio transmission line, the modulated wave signal, provided with the signals for carrier recovery therein. The receiver unit recovers, from the received signal, the frequency components f.sub.O and f.sub.CL and thereby reproduces the original data signal supplied to the transmitter unit with the use of the thus recovered frequency components f.sub.O and f.sub.CL.

A radio communication system includes a transmitter unit, a transmission line, and a receiver unit. The transmitter unit modulates an in-phase-channel (I-ch) data signal and quadrature-channel (Q-ch) data signal with two carriers having a .pi./2 phase difference with each other. A DC offset is added to either one of the I-ch and Q-ch data signals before they are modulated. In the receiver unit, a demodulation operation is performed, for the received transmission signal, by a synchronous detection with the use of a leakage carrier created due to the DC offset and included in the transmission signal.

QAM with DC bias in one channel

A data transmitting-receiving system includes a transmitter unit, a transmission line, and a receiver unit. The transmitter unit includes a first memory circuit receiving first digital input data to be transmitted, a first digital/analog (D/A) converter, a second memory circuit receiving second digital input data to be transmitted, and a second D/A converter. The first and second memory circuits can provide a first digital correction output and a second digital correction output, respectively. The first and second digital correction outputs are composed of both an own-side correction output connected to an own-side channel route and an other-side correction output connected to an other-side channel route.

Data transmitting-receiving system for suppressing data error

A multistage amplifier with a low noise figure linearly amplifies an input signal having a level which varies over a wide range. The first stage of the amplifier provides a low noise figure and sufficient power gain to ensure overall low noise performance. An interstage amplifier is protected from saturation by first and second variable attenuators, which are controlled by a level detector. The level detector detects the level of the input or output signal of the interstage amplifier and controls the forward bias current of a diode in each of the variable attenuators. The first variable attenuator functions as a level compressor for signals input to the interstage amplifier having a level higher than a preset level. The second variable attenuator functions as a level expander of the output signal from the interstage amplifier to equalize the signal level compressed by the first variable attenuator. By combining the two variable attenuators, it is possible to provide a multistage amplifier with an extended range of linear operation and which has low noise characteristics.

Multistage linear amplifier for a wide range of input signal levels

A carrier recovery circuit for use in a demodulator for a 2.sup.n -phase PSK modulated signal which comprises a phase-locked loop including a voltage-controlled oscillator (7) and an automatic frequency control (AFC) loop for avoiding the false lock phenomenon. The AFC loop is comprised of two differentiating circuits (21, 25), two mixer circuits (22, 26), and a difference circuit (27), and forms a symmetrical structure so as to exclude undesired noise, thereby carrying out a stable AFC operation.

Growing community of inventors

Fujisawa, Japan

Susumu Sasaki