Several senders are synchronized with a common clock. Each of the senders emits data signal which is expanded by given common bipolar pseud-random codes with different code sequence displacement. A receiver synchronized with the clock can distinguish emission signal of a given sender from the others. At first, the first pseud-random code is produced, which code is the duplication of the common bipolar pseud-random code and has the similar code seguence displacement to the prepared code sequence displacement of the sender. Then the second bipolar pseud-random code is produced, which code is the duplication of the comon bipolar pseud-random code and has a undefined code sequence displacement. The difference between the first and the second code sequence is a three state code sequence, which is correlated with input signals. |