Nippon Telegraph and Telephone Corporation

Kazuji Watanabe

Kozo Morita

Osamu Kagami

Shuta Uwano

In order to carry out high-precision control of distortion compensation, a received signal is split into two signals. One of the resulting signals ('the first signal') is provided to a distortion generator with similar characteristics to the distortion produced at the signal transmitting side, and the phase and amplitude of the other of the resulting signals ('the second signal') are controlled. By adding these two signals, the desired signal is suppressed and only the distortion component is extracted. This process is controlled by correlation detection of the desired signal. Next, the distortion component contained in the second signal is removed by controlling the phase and amplitude of this extracted distortion component and adding the result to the second signal. This process is controlled by detecting the correlation between the extracted distortion component and the error component contained in the signal after the addition. This enables compensation for distortion produced at the transmitting side to be performed at the receiving side, so that the size of transmitting equipment can be reduced.

Distortion compensator

A digital radio-relay system has a transmitting terminal station, at least one repeater station a receiving terminal station, a non-regenerative repeater station which does not regenerate a digital signal in order to simplify and reduce cost of the system, while keeping excellent signal quality in transmission. Each repeater station has a plurality of sub-units relating to respective sub-system signals each having a plurality of carriers so that the frequency spectrum of each sub-system signal is allocated on a frequency axis based upon a frequency division multiplex system. A repeater station having a first frequency converter to convert a received radio frequency to IF frequency, bandpass filters for deriving one of the carriers in each sub-system signal, amplifiers to amplify the derived carrier on IF band stage, and a second frequency converter to convert the IF frequency to radio frequency, has a common reference oscillator which generates a reference frequency which is a common divisor of all the local frequencies for all the radio frequencies of all the sub-system signals. Only one of an upper and lower heterodyne signals is taken in all the frequency conversions, so that distortion in each relay section is added in-phase. Leaked noise caused by the bandpass filters is added to original carrier in-phase. All the distortion thus added in the relay sections can be compensated by a transversal equalizer in the receiving terminal station. Therefore, excellent signal quality is obtained although a simple non-regenerative repeater station is used.

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Kanagawa, Japan

Kazuji Watanabe