168 PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 89 NR 4/2013 Alexandru LAVRIC, Valentin POPA, Ilie FINIS, Codrin MALES Stefan cel Mare University of Suceava Performance evaluation of Tree and Mesh ZigBee Network Topologies used in Street Lighting Control Systems Abstract. The design of a high performance street lighting control system is an important issue. This paper focuses on an assessment of the performance of the ZigBee mesh and tree network topologies which, can be implemented in different street lighting control network configurations. The paper also presents the performance evaluation of three configurations in order to select the best candidate that can be integrated within a street lighting control system. The data reveal that the tree topology is much more efficient than the mesh topology. Also, the impact of the acknowledgment (ACK) communication mechanism on the network throughput and on the end-to-end delay application parameter is analyzed. Streszczenie. W artykule przedstawiono wyniki analizy działania sieci w topologii siatki ZigBee oraz drzewa, w zastosowaniu do sterowania oświetleniem ulicznym. Ocenie poddane skuteczność doboru najlepszych kandydatów do integracji z systemem oświetlenia w odniesieniu do trzech konfiguracji. Stwierdzono znacznie większą skuteczność działania struktury drzewiastej w stosunku do struktury siatki. (Ocena działania sieci ZigBee i struktury drzewiastej w systemie sterowania oświetleniem ulicznych). Keywords: mesh – tree – performance evaluation – street lighting monitoring and control architecture – ZigBee. Słowa kluczowe: oczko, trzewo, ocena działania, architektura sterowania i monitorowania oświetlenia ulicznego, ZigBee. Introduction A problem that should not be neglected when implementing a street lighting monitoring and control system, is the careful selection of the communications protocol that must ensure a high level of performance. The systems presented in the scientific use the types of communication protocols presented in Tab. 1 for sending information. Table 1. Communication protocols used in street lighting control Long range communication Wi-Fi (802.11 standards) Ethernet (cable) GPRS (General Packet Radio Services) Wi-Max (802.16 standards) Short range communication ZigBee IEEE 802.15.4- based 6LoWPAN (IPv6 over Low power Wireless Personal Area Networks) Proprietary RF Solutions UWB (Ultra-Wide Band and Ultraband) PLC (Power Line Communication) The communication protocols used by street lighting control systems can be divided into two categories: local communication, using short range transmission (street lamp-to-street lamp) and long range communication such as the systems that link the command center to the sensor network [1]. The vast majority of the monitoring and control of street lighting systems proposes the use for local communication of a wireless protocol because it represents a cost effective solution. One such standard is ZigBee which is a low-cost and a LR-WPAN (Low Rate Wireless Personal Area Network) communication protocol. Fig. 1 presents the ZigBee communication protocol that defines the network (NWK) level and the APL application profiles over the MAC (Media Access Control) and physical level of the OSI model (Open Systems Interconnections) implemented by the IEEE 802.15.4 standard [2]. A ZigBee wireless sensor network can be implemented using three types of nodes: coordinator, routers and End Devices. The coordinator is an essential node in the network initialization which performs the following tasks: the selection of the radio channel on which communication is performed and the initialization of the network, allowing other nodes to join the network. In addition, the coordinator performs message routing, security management and many other services. Fig. 1. ZigBee Stack A router node can retransmit messages and allow other nodes to join the network. The main task of an End Device type device is sending and receiving messages, the latter has no routing capabilities if is of RFD (Reduced Function Devices) type, and is often powered by batteries. IEEE 802.15.4 standard defines two types of nodes: FFD (Full Function Devices) that can be coordinators or routers and RFD (Reduced Function Devices) nodes that can communicate only with FFD nodes and cannot act as coordinators. The RFD nodes are much cheaper because of the reduced RAM / ROM memory. Another issue that should not be overlooked is the selection of the best street lighting control system architecture that would ensure a high performance level at the lowest implementation cost as well. This entails choosing the optimum number of router nodes and End Device, as well as deciding on their position within the network. In a related paper [1] the software and hardware implementation of a street lighting control system are presented in detail. The ZigBee network topologies that can be implemented in street lighting control system may be of tree or mesh type. In the scientific literature there are several papers [3]-[8] that detail the performance evaluation of these network topologies but taking into account only the node mobility problem. None of these papers assess the performance of different network configurations that can be implemented within a street lighting control system. Street lighting control architecture The architecture of a street lighting control system has certain specific characteristics: it is of the long-thin type, it can incorporate more than a few hundred nodes spread over a wide geographical area and it has a central point