This invention relates to a channel monitoring circuit, particularly to a channel monitoring circuit in a radio digital transmission system including repeater stations.
A parity check method is widely used for monitoring the channel quality of a radio digital transmission system. As is well known in the art, according to the parity check method, a digital signal made up of a pulse series including marks and spaces to be transmitted is divided into a plurality of data sections of a suitable number of time slots at the transmitting terminal station. The numbers of the marks or spaces of respective sections are counted and the results are inserted in predetermined time slots of each data section as parity check data. In the receiving terminal station, the number of received marks or spaces of a data section is counted for calculating the parity and the parity check data in the data section is extracted. Then, calculated parity data and the extracted parity check data are compared for confirming whether there is a bit error in the data section. All of the data sections are checked in same manner as described above. With this method of detecting the bit error by inserting the parity check data into the transmitted data at the transmitting station and then checking the parity check data at the receiving station, although a fault on the transmission line between the transmitting and receiving stations can be detected, where more than one repeater stations are interposed between the transmitting and receiving stations, a position of the fault on the transmission line can not be determined.