The availability of low cost, low power, and miniature embedded processors, radios, and sensors, integrated on a single chip, is leading to the use of wireless communications and computing for interacting with the physical world in many civilian and military applications. The resulting systems, called Wireless Sensor Networks (WSN). The advances in the integration of complex wireless integrated products and the increase in performance and functionality of the design tools, the requirements and properties of a single device (sensor node) are well understood. Yet it is not simple and straightforward to implement WSN concepts into a functional prototype system or even a commercial product. This tutorial will address the key factors in WSN design. The capabilities of the current WSNs will be examined. The new security scenarios for WSN will be illustrated. Different localization techniques in WSN will be discussed and compared. Future trends in WSN research will be introduced

I.      Introduction

A wireless sensor network (WSN) consists of an array of sensors, of diverse types, interconnected by a wireless communication network. Sensor data is shared between these sensor nodes and used as input to a distributed estimation system whose function is to extract the relevant information from the available data. Fundamental design objectives of sensor networks include reliability, accuracy, flexibility, cost effectiveness and ease of deployment. Each node has one or more sensing unit, an embedded processor, and low-power radios. The nodes act as information sources, sensing and collecting data samples from their environment. They perform routing functions, creating multi-hop wireless networking fabric that conveys data samples to other sensor nodes. Nodes can also act as information sinks, receiving dynamic configuration information from other nodes or external entities. The rapid deployment, self-organization and fault tolerance characteristics for WSNs make them promising for a number of military and civilian applications [1].

Wide varieties of these applications have been enabled by the promise of inexpensive networks of wireless sensors. Dramatic advances in communication systems and micro- electro-mechanical systems (MEMS) IC design reduce the cost of the sensor nodes, which in turn enable the use of large scale WSNs for a variety of new monitoring and control applications. For these applications to be viable, the sensed/monitored data must be located. Traditional physical localization techniques are not well suited for these requirements. Including GPS on every device is cost and energy prohibitive for many applications. The solution is cooperative localization such that sensors work together in a peer-to-peer manner to make measurements and then form a map of the network forming local coordinate systems. Based on the local coordinates formed inside the WSNs, they can be transformed to global coordinates if at least two reference nodes in the WSNs have known coordinates or are equipped with GPS receivers [7].

II.      Cooperation in WSN

A Wireless Sensor Network (WSN) is a wireless network consisting of spatially distributed autonomous tiny devices (nodes) using several sensors to cooperatively monitor physical or environmental conditions, such as temperature, lighting, sound, vibration, pressure, motion or pollutants, at different locations. Localization is very important for self- configuring WSN and is essential to process the sensed data properly.

The cooperation between these autonomous tiny devices introduces a new domain of research, which is the distributed physical layer. The difference between embedded transmitters and locations of each node cooperatively transmitting to a desired node introduce new scenarios and challenging technical questions to be answered. As a fundamental design objective in WSN, transceivers embedded in each node must remain simple, low cost, and power consuming [3, 13].

Localization in WSN is an integral part in any application that requires monitoring, control and/or tracking functionality. In order to avoid such a higher cost and energy consumption by using GPS chip embedded in each node, different nodes can communicate in a peer-to-peer manner to establish cooperatively a location map for the entire nodes forming the WSN. The local coordinates formed inside the WSNs could be turned to the global coordinate system if at least two non- collinear nodes have known global coordinates [7, 9].

III.      Security challenges in WSN

As we deploy and rely on WSNs for monitoring, data gathering, collaborative communication and computing, these networks must be able to provide authentic information. While the wireless networks and their flexibility to form ad hoc networks with minimal or no prior infrastructure is desirable, the wireless medium is also vulnerable to unwanted eavesdropping, and other attacks such as wormholes. Such attacks have no counter part in wired/wireless networks. Moreover, due to new scenarios have emerged for WSN applications, solutions that have been developed for wired and wireless networks are often not applicable.

IV.      Draw backs in current WSN

There are a number of limitations in the current WSN products currently available in the market. Parts of these limitations are related to the software while others related to the hardware. This proposal will concentrate in the hardware parts related to the communication technologies. These limitations are the bit rates, power consumption, and multipath. Furthermore, current WSNs does not include any localization capabilities.

Localization in WSNs is an integral part in any application that requires monitoring, control and/or tracking functionality. Localization availability will open a new direction to find security solutions based on location aware. Previous studies have shown a superior improvement for location aware routing over the classical ones. Hence, localization is mandatory for practical WSNs. Traditional localization techniques are sometimes inadequate for some of these applications. For instance, using GPS (Global Positioning System) receiver on each device is energy prohibitive, and is limited to outdoor applications. Moreover, the cost becomes a major issue, especially if HSGPS (High Sensitivity Global Positioning System) is utilized.

V.      Summary

WSNs (Wireless Sensor Networks) represent a shift toward a new and exciting proactive computing model in which hundreds of tiny computers working together on the user's behalf. It is a model where people and businesses reap technology's benefits by getting more data that are useful when needed. There are many challenges in implementing WSN ranging from hardware, software, mechanical and even human-related. Keeping the power usage sufficiently low so that they operate for enough time involves careful power management and in some cases managing charging. Radio communication hardware has to be small enough while using a suitable network algorithm. These concerns illustrate the careful balance and compromises that are needed in WSN and designs.

This tutorial aims to introduce the potential market for WSN applications. A quick analysis for the design factors influencing the WSN from node and system level perspectives. We explore the new potential security threats arises in WSN. Investigation for the major localization techniques in WSN is addressed and compared. A complete view for the new era of distributed physical layer formed by WSN will be examined. Space time coding, virtual Multi- Input Multi-Output (MIMO) systems is addressed. As a matter of completeness, an overview for the current WSN available in the markets will be discussed. The draw backs in the current WSN will be summarized. Finally, hot areas for research in WSN will be discussed.

References

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