Sunday, March 13, 2011

Airfield Ground Lighting Automation Systems

Power line communications is using the existing power line infrastructure for communication purposes. While the recent contributions majority have discussed it for high data-rate applications like Internet access or multimedia communication serving a relatively small number of users, we are concerned about it as enabler for sensing, control, and automation in large systems comprising of tens or even hundreds of components spread over relatively wide areas.

Modern airfield ground lighting (AGL) automation system enable monitoring of sensors deployed and individual lamp control at airfields. Such functionalities are needed to meet the latest recommendations by national and international regulators to enhance safety of aircraft ground movement and to aid visual guidance systems. Devices such as microwave sensors and lamps are arranged in a ring structure of typically between 3 km to 15 km and connected to a constant-current supply via transformers.

PLC is an elegant solution and cost-effective to enable communication between the airport tower and the ground lighting system, particularly for existing airport infrastructures where build-up of new dedicated communication networks would be expensive. The communication network must bridge considerable distances and also connect across power-electric components, especially transformers, which are not designed for high-frequency communication signals. In terms of signal flow, we note that all data communication needs to go through a central node which is directly connected to the tower. Furthermore, the reaction time, i.e., the round-trip delay of a signal between the tower and a lamp, is critical. The PLC system needs to permanently monitor the communication quality to all network nodes to guarantee a certain maximal reaction time since the communication channels are time variant. The time variance of the channels is due to different current steps of the regulator, variable loads in the circuit, crosstalk from other rings which often run parallel over several kilometers, and even weather conditions. Hence, the PLC system needs to be sufficiently robust with respect to channel variations. In addition, a node failure must not affect communication to other nodes. Hence, redundant signal paths between the central and the other network nodes are mandatory for the PLC network.

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