Abstract: A signal compression system for efficient transmission of an input binary digital signal, in the form of a binary pulse signal, in which bit polarity reversal is checked after sampling for a predetermined number of bits of the sampled binary pulse signal. In a case of detection of any bit polarity reversal, the sampled binary pulse signal is sent out into a converted output pulse signal for the predetermined number of bits. In a case of non-detection of any polarity reversal, the number of bits or the number of bit blocks having no polarity reversal is coded as a coded pulse signal and sent out into the converted output pulse signal. A coded pulse signal is distinguished, the the converted output pulse signal, from the binary pulse signal by at least one flag bit.

Abstract: A signal combining system employed for transmitting a plurality of pulse signals, in which if binary information of the same polarity is continuously transmitted for a period of time, in comparison with the last bit of the preceding period of time, in a main input communication circuit such as a facsimile circuit, signal combining is effected to insert therein other prestored binary information from another communication circuit. The above signal combining is performed for information blocks, each of which includes at least one sign bit for distinguishing pulse signals of the main communication circuit and another communication circuit from one another.

Abstract: A signal identification system, in which a signal of a specified frequency included in an analog signal indicated by an input pulse train converted from the analog signal is detected from the pulse train. The input pulse train is multiplied by two reference wave pulse trains having peak valves following the signal of the specified frequency but displaced by .pi./2 in phase from each other, respectively. The results of the multiplications are separately accumulated. The signal of the specified frequency is identified by utilizing a fact that the absolute value of at least one of the accumulated values exceeds a predetermined threshold value in the range of a permissible frequency deviation of the signal of the specified frequency and in the range of its permissible level fluctuation.

Abstract: A system for coding two-dimensional information of M lines and N columns, in which two-dimensional information of M lines and U columns is predetermined as a basic block. If any column information in the basic block has an information change with respect to column information immediately preceding it, information in the basic block is coded. If each column information in the basic block has no information change with respect to the column information immediately preceding it, information corresponding to the number of columns of the basic block and the number of subsequent columns having no information change is coded. Two-dimensional information obtained after the computation operation of a correlation function between an instant bit of information and an immediately preceding bit of information in at least either of the line direction and the column direction may be applied as the input of this system.