George Hallak, Gerd Bumiller

• Recently, standardization bodies such as IEEE and ITU addressed, independently, standards for the medium access control (MAC) and physical layer specification of PLCs. MAC designers develop coexistence mechanisms irrespectively of the physical layer. Power line channel behavior changes every time a modem sends/receives on the channel. Changing the channel behavior influences the communication between nodes. As a consequence, the MAC coexistence mechanisms are affected. Power line impedance is a very important parameter on the design of PLC architecture. The changed channel behavior is a result of changing the impedance values between sending and receiving states. Transmitter and receiver nodes behave simultaneously on the power line. Transmitter nodes transmit although other nodes receive at the same time. Changing states from the MAC layer simultaneously between send and receive for the different nodes influence the channel behavior, as a consequence, influence the physical layer and the coexistence between the different nodes even when the systems are separated in frequency. In this paper, we discuss the coexistence of the NB-PLC applications considering the communication requirements. We then investigate the impedance problem of the power line by providing a typical transmission scenario and simulation results on the CENELEC frequency bands. Finally, we introduce a transmission model which overcomes the impedance problem and optimizes the communications between the non-interoperable nodes.