Abstract: A bi-directional protection facility is provided in an optical communication system in which an optical communications node communicates with another optical communications node via first and second bi-directional communications paths respectively serving as a service path and protection path, and in which a filter at each node processes signals respectively received over the service and protection paths and generates an in-band signal and out-of-band signal for each of the paths. A control unit then generates a Loss of Signal indication for the service path if the level of the out-of-band signal is found to be greater than the level of the in-band signal and protection switching is effectuated as a function of the presence of the control signal. In addition, an outgoing signal to the other communications node is interrupted for a sufficient period of time to cause a LOS at that node and thus trigger protection switching thereat to complete the bi-directional switching process.

Abstract: The encoding/transmission of information in an OFDM system is enhanced by using complementary codes and different patterns of amplitude modulation representing respective data words. The complementary codes, more particularly, are converted into phase vectors and modulated by the selected pattern. The result is then used to modulate respective carrier signals. The modulated result is then transmitted to a receiver which decodes the received signals to recover the encoded information.