Fujitsu Corporation

Takayuki Ozaki

Takanori Iwamatsu

Kenzo Kobayashi

Isamu Umino

Zenichi Ohsawa

Hideaki Itoh

Yasuhiro Yano

A distortion compensating device provided in a receiver for compensating distortion which is added to a signal in a transmission path. The signal is generated in a multi-level modulator of a transmitter in which a digital signal is mapped to one of a plurality of specified signal points in a signal space diagram. The device includes a signal-point-position averaging circuit for producing an average signal point for each of a plurality of distributions of received signal points in the signal space diagram. A discrimination circuit in the device discriminates the average signal point closest to a received signal point from other average signal points in the signal space diagram.

Distortion compensating device

A distortion compensating device provided in a receiver for compensating distortion which is added to a signal in a transmission path. The signal is generated in a multi-level modulator of a transmitter of which a digital signal is mapped to one of a plurality of specified signal points in a signal space diagram. The device includes discrimination circuits for discriminating a received signal according to threshold lines partitioning the signal space diagram into discrimination areas, the threshold lines being defined so that the discrimination areas on an outer side of the signal space diagram having each an area greater than an area of each of the discrimination areas on an inner side of the signal space diagram and a selection circuit for selecting one of a plurality of threshold line patterns based on a level of the received signal which is discriminated according to a selected threshold line pattern.

In an auxiliary signal transmission system used in a multiplex communication system, a first auxiliary signal which is necessary in a transmitting terminal and a receiving terminal is transmitted directly without processing in an intermediate repeater station, and a second auxiliary signal which is necessary in at least one intermediate repeater station is processed in the intermediate repeater station, and thereafter, is transmitted to the receiving terminal. Therefore, transmission discontinuity in the system caused by a fault in the intermediate repeater station can be prevented.

System for transmitting auxiliary signal in a multiplex communication

A digital radio receiving apparatus includes a transversal demodulator which is controlled under an internal control mode and an external control mode selectively by means of a control circuit. The control circuit operates under the external control mode every time an alarm signal is issued when the transversal modulator functions in an abnormal operation state due to fading. In the external control mode, the control circuit produces an optimum control signal for elimination of the alarm signal.

Digital radio receiving apparatus

A space-diversity receiving system for microwave band radio communication including two antennas and receivers, an endless phase shifter, a hybrid combiner, a hybrid distributor, a voltage controlled oscillator, a signal mixer, a low pass filter, a detector, and a control circuit. Microwaves received by the antennas are detected by the receivers. One received signal is directly applied to the hybrid combiner. The other received signal is applied to the hybrid combiner via the endless phase shifter. The hybrid combiner combines these signals and outputs to the hybrid distributor. The hybrid distributor distributes the amplified output to as an intermediate frequency output and a sub output. The voltage controlled oscillator generates a series of sequential frequencies based on the control of its input voltage. The signal mixer mixes the sub output with the each sequential frequency output. The detector detects the mixed signal and transmits the detected signal to the control circuit. The control circuit controls the endless phase shifter and the voltage controlled oscillator based on the deviation in the intermediate frequency band and the detection of the reception level so as to minimize the amplitude deviation of the combined IF output signal by using a microprocessor.

Space-diversity receiving system

A high frequency generator including a frequency generator and a multiplier, the multiplier including a diode, which multiplies the output frequency of the frequency generator, and shuts off or reduces an output by suspending or suppressing the multiplying operation through the control of a bias voltage applied to the diode used in the multiplier. The system for cutting off the output by controlling the multiplier is very effective for simplifying the circuit structure and reliably turning off the output.

Growing community of inventors

Kawasaki, Japan

Takayuki Ozaki