Localizacion por rssi

Is RSSI a Reliable Parameter in Sensor Localization Algorithms – An Experimental Study
Ambili Thottam Parameswaran, Mohammad Iftekhar Husain, Shambhu Upadhyaya Department of Computer Science and Engineering State University of New York at Buffalo 201 Bell Hall, Buffalo NY- 14260, USA {atp22, imhusain,shambhu}@cse.buffalo.edu

Abstract Wireless sensor networks are becoming ubiquitous and theirapplication areas are widening by the day. Localization algorithms play an important role in enhancing the utility of data collected by enabling sensors to determine the location from which each data packet is obtained. Localization can be done by implementing beacon based algorithms or signature based algorithms. Much of the research work in this area assumes received signal strength indicator(RSSI) as a parameter in their localization algorithms. Since RSSI is the key parameter, we conducted practical experiments to assess whether RSSI could indeed be used by localization algorithms to determine distances between sensors. In our experiments, we tried to calibrate and map RSSI to distance under various conditions and concluded that despite promising hypothetical advantages of RSSI, evenunder ideal conditions it cannot be used to determine inter nodal distances in wireless sensor networks. Keywords: Distance measurements, ESN, Localization Algorithms, LQI, Motes, RSSI, Wireless Sensor Networks 1. INTRODUCTION

emergency sensor networks (ESN) [2]. In most of the applications related to ESN the data collected will become useless unless the location information can be discernedfrom it. Thus localization algorithms [3, 6] play a significant role in the domain of wireless sensor networks. Mainly these algorithms are categorized into two – signature based and beacon based. RSSI (Received Signal Strength Indicator) [7] and LQI (Link Quality Indicator) [4] are considered as two parameters which play a pivotal role in the beacon based localization of sensor nodes. TypicallyRSSI is a measure of dBm, which is ten times the logarithm of the ratio of the power (P) at the receiving end and the reference power (Pref). Power at the receiving end is inversely proportional to the square of distance. Hence RSSI could potentially be used as an indicator of the distance at which the sending mote is located from the receiving mote. When data from many such neighboring motes arecombined, the location of the sending mote can be judged with reasonable accuracy. The literature study about RSSI shows that RSSI is not a good candidate for localization experiments [5]. Despite this, many papers assume the use of RSSI in distance measurements. Therefore, it is necessary to test whether this hypothesis is correct or not by creating a practical experimental setup on a more basiclevel than those used in previous studies. The organization of this paper is as follows: The next section presents the background information related to RSSI and localization.

Wireless Sensor Networks (WSN) are becoming more common in use and extensive research is currently underway to expand the application areas of WSN [1]. Some of the most important application areas of sensor networks includehurricane areas, volcano areas, forest fire areas, etc. and these networks are usually known as

Section 3 presents experimental setup for performing RSSI related measurements. Section 4 contains the results of our experiments. Section 5 discusses the implications and interprets the results we obtained. Finally, in Section 6, we conclude this paper with plans of future work. 2. BACKGROUNDTo put this mathematically, consider the standard graph given in Figure 1.

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RSSI and distance have a relationship which is derived as follows. As mentioned previously, RSSI is defined as ten times the logarithm of the ratio of power of the received signal and a reference power (e.g., 1mW). i.e., RSSI  10 log P/Pref. This would mean that RSSI  log P. It is known that power...