Fujitsu Corporation

Toshio Tamura

Kenzo Kobayashi

Hiroyuki Kiyanagi

Takanori Iwamatsu

Toshio Kawasaki

Takeshi Yagi

Takahiko Terakado

Yuitsu Ogata

Hisao Narita

The invention provides an automatic amplitude equalizer for compensating an amplitude characteristic of an input signal, wherein a control signal for equalizing an inclination amplitude distortion of an input signal is detected making use of a pair of digital demodulated signals to compensate for the amplitude characteristic of the input signal with a high degree of accuracy and which can be constructed with a reduced circuit scale and at a reduce cost. The automatic amplitude equalizer includes a first-order inclination amplitude equalization section for compensating for an amplitude characteristic of an input signal in accordance with a first-order inclination amplitude characteristic, and a control section for discriminating a direction of variation of a value of a first one of a pair of digital demodulated signals originating from the input signal, detecting error information from the other, second one of the digital demodulated signals which is orthogonal to the first signal, and outputting a control signal for the first-order inclination amplitude equalization section based on a correlation between the error information and the direction of variation of the value of the first signal.

Automatic amplitude equalizer

In the case where a received multi-level orthogonal amplitude signal is not synchronized with a local carrier frequency signal, a digital multiplexing radio receiver recognizes that an adaptively-equalized data exist in a specified area on the phase plane of Ich and Qch orthogonal coordinates. The receiver controls an operation of amplifying Ich and Qch demodulated signals to a fixed level, based on the data of which exist in the specified area. Similarly, the receiver controls a phase of the local carrier frequency signal based on the data of existing in the specified area, and controls tap coefficients of an adaptive transversal filter which equalizes the received multi-level orthogonal amplitude signal. In the specified area, a distance between signal points of multi-level orthogonal amplitude signal is large so that influence caused by a phase rotation is small. Accordingly, the digital multiplexing radio receiver can rapidly and stably return to a synchronous mode.

Radio receiver for use in the reception of digital multiplexing signals

A subsignal transmitting system had working lines for respectively transmitting multiplexed signals each including a main signal, and had at least one protection line for transmitting one of the multiplexed signals when it is detected that the transmitting conditions of one of the working lines along which the signals are being transmitted are deteriorated. To realize the switching of the subsignal transmitting through the protection line, the system comprises a switching signal transmission line for transmitting, in the direction opposite to the transmission of the multiplexed signals, a switching signal indicating which one of the working lines is too deteriorated for transmission of the corresponding multiplexed signal, a transmitting side subsignal switching unit for outputting one of the input subsignals to one of the working lines respectively and for outputting, in response to the switching signal, one of the input subsignals to the protection line; and a receiving side subsignal switching unit, operatively connected to the subsignal output terminals, for outputting the subsignal through the protection line to, in response to the switching signal, the corresponding one of the subsignal output terminals, the remaining subsignals through the working lines being output to the remaining output terminals, respectively.

Subsignal transmitting system

Growing community of inventors

Kawasaki, Japan

Toshio Tamura