MAC Layer in Broadband PLC Networks - State of the Art, Solutions, and Modelling -

Broadband PLC systems, achieving data rates beyond 2 Mbps, which are applied to the low-voltage power supply networks to build up so-called PLC access networks, suppose to use a frequency spectrum up to 30MHz. However, the supply networks are not designed for communications and they act as antennas, producing electromagnetic radiation and causing disturbances to other telecommunications services which operate in this frequency range. Therefore, PLC networks have to operate with a limited signal power, which decreases data rates and makes PLC systems more sensitive to disturbances from the electrical power supply network, as well as from the network environment [1]. Well-known error handling mechanisms, such as Forward Error Correction (FEC), interleaving, and Automatic Repeat reQuest (ARQ) are applied to PLC systems to solve the problem of transmission errors [2]. However, application of these mechanisms consumes a part of the transmission capacity (due to coding overhead and data retransmissions) and further decreases the data rates. On the other hand, PLC networks have to provide a very good utilization of its shared transmission medium, keeping also a sufficient Quality of Service (QoS) for different telecommunications services. This is important because the broadband PLC access networks have to compete with other access technologies DSL and CATV. Both good network utilization and sufficient QoS can be achieved by using efficient methods for the network capacity sharing Medium Access Control (MAC) protocols. Nowadays, there are no existing standards or specifications considering physical and MAC layer for PLC access networks. The manufacturers of the PLC equipment developed proprietary solutions for the MAC layer incompatible to each other. In this paper, various implementation solutions for PLC MAC layer are considered; its general structure and specific requirements for PLC (Sec. 2), multiple access schemes (Sec. 3), an analysis of suitable MAC protocols for PLC (Sec. 4), a brief consideration of traffic control mechanisms including duplex mode, and presentation of a modeling approach for investigations of the PLC MAC layer and its protocols. 2. Structure of the MAC Layer