Topologies of WSN

TOPOLOGIES OF WIRELESS SENSOR NETWORKS Zlatan Ganev Abstract – In this article a short description of topologies of The listed features of WSN lead to certain requirements: wireless sensor networks is made. It regards topology star, mesh low energy consumption (due to the use of restricted and cluster. More attention is paid to the third topology, as some autonomous power supply); small sensor sizes; security and of its advantages over the other two are listed. protection of the transmitted information and so on. Keywords –network, node, sensor, topologies, wireless, ICEST 2013. II.WSN TOPOLOGIES I. INTRODUCTION Most often nodes are randomly scattered, as the location and Wireless sensor networks (WSN) appear to be a subdivision the connections between them determine the network of wireless networks without infrastructure, where there are topology. higher requirements to the size of the sensor nodes and the Tree main types of topologies have been established in optimization of the activity time of each of them aiming at practice: energy saving. WSN are networks with decentralized structure in which the  star information is wirelessly transmitted, mainly through radio or  mesh optical connection and there are higher requirements to the  cluster/tree size and the duration of the nodes. The nodes main tasks in WSN are detection and reporting of Nodes in these main topologies could be divided into two different parameters as temperature, illumination, humidity, main classes: Full Function Devices-FFD (Router node) and radiation etc. The collection of the wanted information from a Reduced Function Devices-RFD (End node). certain district could take months and years. For this task FFD support full set of functions and could play the role of a fulfillment nodes functionality is divided into three groups [3], coordinator of network CN (Gateway) or of a common each of them is subject to optimization: device. At the same time RFD can be used as common devices. They have got smaller memory, computational  environment connection resource and smaller energy consumption [1].  computing and processing  communication 1. STAR TOPOLOGY Environment connection includes the environment factors and their values detection, as well as discovering neighboring nodes and their coordinates determination. This functionality is fulfilled in two modes – normal and that of reduced consumption. Computing and processing in the nodes are connected with analyzing, calculating and summarizing of the information. For this purpose different kinds of microcontrollers are used. For communications between nodes there are routing algorithms and protocols, which depend on the architecture of the network. They could be classified into two main groups according to their logical structure: data-centric, hierarchical and location-based. Wireless sensor networks are preferred when the infrastructure building is difficult, unprofitable; the network is of a temporary use etc. Fig.1 Star topology Zlatan Ganev is with the Faculty of KTT at Technical University of Varna, Bulgaria, E-mail: [email protected] In star topology devices could be FFD or RFD. They function as terminal devices and communicate directly with CN [5].  This is the simplest topology. Its name is connected with the receiver of the receiving node. It reacts quickly, accepts the spatial location of the end nodes around the coordinator node. data and switches off instantly. CN is a specialized device for quick date exchange, but it can With the appearance of a damaged node (Router node) or also be a personal or pocket computer (PDA).Its purpose is to large distortions through the rout, another one is automatically manage the work of the end devices, to exchange data with found, and for this reason these are Self-Healing Networks. them and to relay the collected date to other networks. With switching on and off of the devices to the network and Star topologies are Single-Hope Systems, which means that presence of moving nodes in it (as it is with GSM networks) it data from the transmitter is transferred to the receiver with also changes routs, which makes it Self-Configuring Network one hop. Their structure is point-to-multipoint type. too. Self-Configuring allows the network to recognize The main advantage of these networks is that they have the automatically and involve in action each new node. lowest energy consumption. The perimeter covered by the Network structure is called Point-to-Point-to-Point, Peer-to- network is equal only to the range of the end nodes, which is a Peer. Unlike WSN star topology, where all the management is disadvantage. concentrated in the CN node, here it is distributed between all Besides their reliability is not big – the disruption of the nodes and therefore this network type is with Distributed connection between the sensor nodes and the network Control. coordinator, due to malfunction for instance, could not be Apart from the much better communications in mesh compensated. It is recommended that these networks should topology there is a possibility for covering a significantly have up to 30 nodes and cover an area with a radius of 100 larger area compared to star topology. meters [2]. Another advantage is the facilitated check of nodes functionality and network as a whole by means of specialized diagnostic device or a computer. The fast and easy 2. MESH TOPOLOGY installation and starting of such a WSN should be noted as well. 3. CLUSTER TOPOLOGY Fig.2 Mesh topology In Mesh topology (fig.2) all the devices should be FFD, as an exception is made only for the most distant ones. In this case communication with CN could also be implemented with Fig.3 Cluster topology transition of the packages across multiple nodes, which indicates that these types of networks are Multi-Hop Systems In cluster topology (fig.3) groups of nodes that [4]. communicate only with one FFD, called cluster-head, are Furthermore several routs are possible between any two differentiated. nodes, as the network software chooses the shortest one of The head has more energy, memory and computational them. This means reduction of the energy being consumed, resource. There is also a possibility for collecting due to the well known fact that the necessary radiated power (aggregating) more information with buffering the packets in is proportional to the square of the distance. Furthermore for the memory and calculating the collected data. After that it consumption restriction the work algorithm of WSN ensures a transmits in multi-steps (via the other heads) only the precise synchronization of data exchange – the transmitting information that is approximated and updated without node sends a control package for the switching on of the surpluses to the base station.  In this network types each cluster could work at different Firstly it should be noted that Wireless sensor networks frequencies compared to the neighboring cluster and in this quickly find their application in different areas of surrounding way collisions could be avoided and network communication life. Rational methods for increasing of their energy quality can be improved. efficiency, duration, safety and so on are looked for. Each cluster can use different keys for data encryption and In building wireless sensor networks with cluster topology in this way network becomes more protected. energy efficiency is significantly improved because In cluster approach scalability as well as network transmitted data to the final user is reduced many times. In productivity could be improved. this way of connecting network has high communication There is self-organizing here as well, i.e. nodes find their quality and high safety degree that makes it hardly vulnerable neighbors by their own and are individuated in groups to external attacks. (clusters) with a central node (head). This happens without All this prolongs network’s life and makes it attractive for participation of centralized management of BS. For clusters construction and utilization life prolonging and consequently of network as a whole, protocols are used in which change of the heads in the group is laid. Schedules awake-asleep are used for receiving and transmitting the information, i.e. switching on and off of the transmitter and the receiver. Transmission is accomplished REFERENCES only when there is a change of parameters of the reported by [1] Engeneering review journal, Sept. 2007, no. 6 (In Bulgarian) the sensor information [2] Engeneering review journal, March 2012, no.2 (In Bulgarian) [3] Karakehayov Z., Sensor Networks, Technical University of III. CONCLUSION Sofia (In Bulgarian) [4] http://en.wikipedia.org/wiki/Mesh_network [5] Ganev Z.,Dimova R., Wireless Sensor Networks, Annual of From what has been written up to now several important Technical University of Varna, 2011 (In Bulgarian) conclusions could be made.