Kokusai Denshin Denwa Co., Ltd.

Kokusai Denshin Denwa Kabushiki Kaisha

Communications Satellite Corporation

Yohtaro Yatsuzuka

Norio Seki

Haruo Sakaguchi

Hideki Honma

Henri G Suyderhoud

Takuro Muratani

Shigeru Iizuka

Takahiro Nomura

A phase lock loop for a digital input signal has a phase detector, a loop filter, a digital voltage controlled oscillator (VCO), an initial phase difference calculator, a center frequency difference calculator and an input buffer memory. In an initial training mode prepared in the PLL operation, an optimum initial phase and an optimum center frequency of the VCO to complete a lock-in state is searched for the input signal stored in the buffer memmory. By estimating the initial phase difference and the center frequency difference between the input signal and the VCO output with repetative kick-offs in calculators, optimum values mentioned above are obtained. In a normal operation mode as a second mode in which the PLL operates normally as a conventional PLL, a phase lock operation between the VCO outut as the reference signal and the input signal in the buffer memory is carried out after the PLL is kicked off with the optimum initial phase and the optimum center frequency determined in the initial training mode.

Adaptive phase lock loop system

An input speech signal is encoded by an adaptive quantizer device (16). The adaptive quantizer device quantizes the predicted residual signal produced by removing correlations from the digital input signal by predictors devices (6, 10). A coefficient or weighting factor, called a leakage, at the predictor device (6) is adaptively adjusted by a leakage selector device (47) depending upon a prediction gain. The prediction gain indicates the accuracy of the prediction. The value of leakage is in the range between 0 and 1, depending upon whether the speech signal is voiced sound or unvoiced sound.

Speech coding/decoding system with reduced quantization noise

A speech signal coding system comprises a prediction filter coupled with an output of a quantizer for prediction of a signal. A subtractor provides the difference between an input signal and an output of the prediction filter. A quantizer quantizes the residual signal, which is the difference provided by the subtractor. The quantizer is improved by adaptively adjusting step size for quantization. Thus, the coded outputs, according to the present invention, are the parameter information of the prediction filter, quantized output of the residual signal, and step information for quantization. The quantization step is determined according to the fundamental step size which provides the statistical variance, equal to one, to the quantized signal, and/or the power of the residual signal. Because of an efficient encoding with an adaptive control of the quantization step, the bandwidth for transmission of the coded signal in a communication system or transmission rate of coded speech signal is minimized. Excellent speech is reproduced through a narrow band channel, or low bit rate digital channel like 16 kbits/second digital channel.

Speech coding system

A system for transmitting a voice signal is disclosed, in which an input voice signal is predivided into low- and high- frequency residual signals. The low-frequency residual signal is transmitted in the form of waveform codes with higher possible fidelity and lower possible quality deterioration through utilization of the Adaptive Predicture Coding (APC) system or Multi Pulse Excited Coding (MPEC) system, while information on the short-time high-frequency spectrum is extracted from the high-frequency residual signal and is transmitted as information for use in the reproduction of the voice signal on the receiving side.

System for transmitting voice signal

A robust ADPCM encoder with a modified leaky quantizer and a pair of parallel predictors is provided. A large leakage is initially inserted into the quantization scale adaptation by utilizing a number of most recent multipliers in a modified leaky Jayant quantizer. Using a dual predictor feedback loop, inside predictor coefficients are updated by the step size having unit variance instead of by the quantized prediction error.

Adaptive quantizer with instantaneous error robustness

In an optical digital communication system having a plurality of optical repeaters inserted in an optical fiber cable, and a pair of terminal stations installed at the extreme ends of the optical fiber cable, the designation of the particular repeater from the terminal station is performed by the remote control signal which has the pulse pattern with the period designated to each repeater. Each repeater may have a plurality of switches for switching lasers for improving the operational reliability of the same by the redundant technique, and the control and/or the designation of the particular switch is also performed by said remote control signal by selecting the particular period and/or the repetition numbers of the period of the pulse pattern. Since the pulse pattern with the particular period and/or the repetition times of the period, and/or the repetition times and the sequence of the periods are utilized for designating the particular repeater and the switch in the designated repeater, the large number of objects (repeaters and switches) can be controlled, and the operational reliability of the control (designation) is very high.

Remote control system of an optical repeater

The operational reliability of a light source in an optical communication system has been increased by an improved redundant arrangement of light sources and the switching arrangement of the same. The present light source arrangement comprises a plurality of light sources each of which provides a different wavelength from one another, an electrical switch for actuating the selected one of the light sources, said electrical switch being arranged to replace the actuated light source when there is something wrong with the light source in operation, and an optical multiplexer the input of which is coupled to the outputs of the light sources, and the output of the optical multiplexer is connected to an optical fiber cable.

Light source arrangement in an optical communication system

A digital speech interpolation system is combined with an adaptive differential PCM (ADPCM), employing a speech detector for detecting speech signals and for discriminating voiced and unvoiced sounds. An adaptive quantization bit assignment to the speech is adopted to cope with any freeze-out condition. And further PCM speech signals with 8 KHz sampling are applied to ADPCM after shifted 250 Hz down and then converted into 6 KHz sampling frequency, thereby attaining a total gain of about 7 without degrading speech quality.

Digital speech interpolation system

An optical transmission repeater with high operational reliability comprises of a plurality of light sources for transmitting an optical energy into an optical fiber, an optical connector for introducing the optical energy from each of said light sources to an optical transmission line, and a switching circuit for selectively operating only one light source. When a light source in operation is deteriorated, the light source in operation is switched to another light source by said switch. Thus, high operational reliability of an optical repeater is obtained although each of light sources have a low operational reliability.

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Yokohama, Japan

Yohtaro Yatsuzuka