Indonesian J our nal of Electrical Engineering and Computer Science V ol. 25, No. 3, March 2022, pp. 1518 1528 ISSN: 2502-4752, DOI: 10.11591/ijeecs.v25.i3.pp1518-1528 1518 An experimental e v aluation of localization methods used in wir eless sensor netw orks Mostapha Laaouafy , F atima Lakrami, Ouidad Labouidya, Najib Elkamoun Departement of Ph ysics, Laboratory of Sciences and T echnologies of Information and Communication, F aculty of Science, Chouaib Doukkali Uni v ersity , El Jadida, Morocco Article Inf o Article history: Recei v ed Apr 24, 2021 Re vised Dec 22, 2021 Accepted Jan 10, 2022 K eyw ords: Centroid Localization Localization accurac y MinMax Multilateration T rilateration WSN ABSTRA CT The problem of localization in wireless sens or netw orks has recei v ed considerable attention from researchers o v er the past decades. Se v eral methods and algorithms ha v e been proposed to solv e this problem. The ef fecti v eness of these algorithms depends on the accurac y of the estimated positions and t he information required to calculate the coordinates. In this paper , we propose to e v aluate four of the most commonly used localization methods in sensor netw orks. O ur study considers a mathematical description of the studied methods in order to e v aluate their comple xity , and then a practical implementation on the simulation tool Cooja . W e e v aluate the performance of the studied methods as a function of the number of deplo yed sensor nodes and their de gree of mobility in terms of se v eral performance metrics. The objecti v e is to r e v eal the most suitable localizati on method for a particular case of deplo yment. Impro v ement proposals are also pro vided to impro v e the most rele v ant localization method for the in v estig ated study . This is an open access article under the CC BY -SA license . Corresponding A uthor: Mostapha Laaouafy Departement of Ph ysics, Laboratory of Sciences and T echnologies of Information and Communication F aculty of Science, Chouaib Doukkali Uni v ersity Jabran Khalil Jabran A v enue, B.P 299-24000, El Jadida, Morocco Email: mostapha.laaouafy@gmail.com 1. INTR ODUCTION W ith the proliferation of smart objects, localization has become a critical component in deplo ying fu- ture IT servi ces and applications. These future applications will mainly in v olv e the e xchange of time-sensiti v e, fresh and re gular information for monitoring and control, as in the case of autonomous v ehicles [1]. Although man y localization met hods ha v e emer ged for ad hoc netw orks, fe w of them can adapt to all types of en viron- ments and support the multiple constraints of wireless communi cations, most notably wireless sensor netw orks. W ireless sensor netw ork (WSN) ha v e become increasingly popular in recent years a n d ha v e attracted a great deal of interest from researchers due to their wide range of applications. M an y applications rely on the kno wl- edge of the location of sensor nodes. An e v ent detected by a sensor is only useful in such applications if information about its geographical location is pro vided. This type of deplo yment requires calculating sensor positions in a x ed coordinate system, hence the need for localization algorithms. Indeed, the localization of nodes is an essential task in deplo ying a sensor netw ork to locate the v arious e v ents occurring in the monitored area and de v elop protocols for routing the collected information, and data aggre g ation. The performance of a localization method depends mainly on its accurac y b ut also on ener gy and po wer consumption. Sensor netw orks present particular ph ysical and transmission constraints [2], which com- J ournal homepage: http://ijeecs.iaescor e .com Evaluation Warning : The document was created with Spire.PDF for Python.
Indonesian J Elec Eng & Comp Sci ISSN: 2502-4752 1519 plicates the de v elopment of a generic localization method re g ardless of the deplo yed application. Locating mobile nodes in a sensor netw ork consists of determining these nodes’ positions autonomously and period- ically without using a x ed infrastructure. Some applications rely mainly on the detection and reporting of the e v ents, which require the kno wledge of the e xact coordinates of nodes detecting the e v ent. Localizat ion is also necessary for close-range applications that allo w dif ferent users who are ph ysically close to each other to share some of their information and locate a v ailable data. The importa nce of localization in sensor netw orks also re v eals itself in the management of certain functionalities specic to sensor netw orks, such as geographic routing. T o help netw ork designers in determining which techniques are appropriate for their applications, au- thors in [3] present a classication to compare dif ferent localization techni qu e s. This classicat ion is based on se v eral k e y features lik e the pres ence of anchor(s), implementation manner , range measurements, and in- frastructure type. Chelouah et al. [4] pro vides a detailed classication of man y algorithms of localization in mobile WSNs (MWSNs). Localization techniques, anchor -based/cooperati v e, netw ork mobility , and informa- tion state are all f actors that go into the classication. Shieh et al. [5] addresses the localization problem using heuristic optimization approaches, whil e Darak eha et al. [6] proposes a distrib uted Range-Free localization algorithm called distrib uted cooperati v e and range-free localization algorithm for WSNs (DCRL-WSN), which of fers high accurac y . F or both approaches, the authors propose distrib uted algorithms, which means that the sensor nodes are responsible for processing and e x ecuting these algorithms, this can increase the cost of com- putation and subsequently the po wer consumpti o n, leading to a rapid decrease in netw ork lifetime, especially in hostile re gions. Zhang et al. [7] propose a three-dimensional localization algorithm that combines recei v ed signal strength indicator (RSSI) and time of arri v al (T O A) ranging information, as well as a single mo v able anchor node to determine the precise dist ance between the unkno wn node and the anchor node. The maximum- lik elihood estimation method based on obtained ranging v alues is used to estimate the position of unkno wn nodes. Simulation results sho w that the proposed algorithm had lo wer localization ener gy consumption and higher localization accurac y , b ut it requires a lar ge computing capacity . Zhang and W u [8] de v elop a localization algorithm that allo ws estimat ing the positions of se v eral sources in a three-dimensional space using direction-of-arri v al (DO A); the results of the simulations sho w that the proposed method could reduce the computational cost without compromising the accurac y of the estimate. Ibrahim et al. [9] suggested a ne w range-based localization algorithm called triple mobile anchors for localiza- tion (TMAL). This technique is based on three mobile sensors that come together to create a mo ving triangle capable of locating unkno wn sensor nodes using recei v ed signal strength indicator (RSSI). The simulation re- sults sho w that this algorithm gi v es good accurac y . Ho we v er , authors did not c o ns ider ener gy consumption since the y assume that the batteries can be char ged to a v oid their depletion. In this paper , we propose a mathematical modeling of four localization methods for sens o r netw orks. W e also conduct a comparati v e study by simulation of the four in v estig ated methods using the Cooja simu- lator . Our objecti v e is to e v aluate the deplo yment limi ts of the e v aluated methods in the f ace of the increase in the number of nodes and the netw ork’ s mobility . Our w ork is intended as a perspecti v e for the impro v e- ment/de v elopment of a simple and reliable localization algorithm while considering sensor netw orks’ limits and constraints. The rest of the paper is or g anized as follo ws: Section 2 describes the research method. Section 3 presents the simulation and results, while section 4 concludes the paper . 2. RESEARCH METHOD Monitoring/controlling an area of interest is one of the principal purposes of wireless sensor netw orks (WSN) [10]. The anchors are particular nodes of wi tch positions are kno wn and allo w to b uild a complete netw ork mapping, which is required because a measurement reects the state of a specic point. Localization algorithm, measurement technologies and position calculation are the three parts that b uild a localization system [11]. When there is no kno wledge about the location of a wireless sensor netw ork’ s elements in the deplo yment en vironment, the collected data may become of limited usefulness. F or an y type of processing operation, it is necessary to estimate the location of these sensors at an y gi v en moment and with a high accurac y . This can be performed on the basis of the assumed kno wn position of anchors and an inter -sensor range measurements such as recei v ed signal strength indication (RSSI) [12]. The localization problem is still one of the important subjects of man y research in dif ferent elds. In the follo wing paragraphs, we present a description of four methods of localization most deplo yed by researchers in the eld, which are: T rilateration [13], Centroid [14], An e xperimental e valuation of localization methods used in wir eless sensor networks (Mostapha Laaouafy) Evaluation Warning : The document was created with Spire.PDF for Python.
1520 ISSN: 2502-4752 MinMax [15] and Multi lateration [16].These methods ha v e the adv antage of being independent of satel lites and GPS-based geolocation systems. The y are of reduced comple xity and of fer high accurac y . This mak es them highly recommended for embedded systems with limited battery capacity such as wireless sensor netw orks. 2.1. T rilateration This method is based on the kno wn distances between the tar get and se v eral anchors as well as its spatial coordinates. Consider a netw ork with three anchors B 1 ( x 1 , y 1 ) , B 2 ( x 2 , y 2 ) and B 3 ( x 3 , y 3 ) and a mobile node M(x,y) that needs to identied their coordinates [13]. T o be gin, the recei v ed signal strength indicator (RSSI) approach must be used to determine the distances between the mobile node and the three anchors. The signal strength depends on distance and transmitting Po wer v alue and then can be deplo yed to calculate the distance between tw o sensors. So, the RSSI [17] technique estimates the distance between a transmitter and a recei v er based on the the recei v ed signal po wer of a gi ving data/control pack et. In free space, the general formula for calculating RSSI is: P r = P r 0 20 log 10 ( d d 0 ) (1) with: - d : is the dif ference in distance between the transmitter and recei v er . - d 0 : is the user -specied distance. - P r 0 : is the signal strength estimated from the transmission rate at the start. The data transfers allo wed the mobile to kno w anchor positions and the triplet ( D 1 , D 2 , D 3) has been produced by e x ecuting the distance measurement protocol. The mobile node can estim ate its position by using (2) and (3) as a guide. ( X X 1 ) 2 + ( Y Y 1 ) 2 = D 1 2 (2) ( X X 2 ) 2 + ( Y Y 2 ) 2 = D 2 2 (3) As sho wn in Figure 1, the sought position is the point where the circles C 1( B 1; D 1) and C 2( B 2; D 2) cross. In the general scenario, C 1 and C 2 intersect at M and M . Thanks to the anchor node B 3 , the mobile node position is one of these tw o points. Figure 1. T rilateration principle [18] 2.2. Centr oid As sho wn in Figure 2, the centroid is the point at where the triangle’ s three medians cross. The trian- gle’ s gra vity center can be determined by taking the a v erage of the X and Y coordinates of all triangle v ertices. The centroid localization method relies on a thick layer of references, with each mobile node recei ving noti- cation from a fe w beacons [14]. By determining the center posit ion of all recei v ed anchor nodes depending on the assumption of round radio propag ation, e v ery mobile node can estimate its location. The centroid localiza- tion mechanism requires no cooperation between reference nodes and pro vides a decent le v el of localization accurac y . All anchors must communicate their coordinates to all mobile nodes within their transmission area to e x ecute the centroid algorithm, and all mobile nodes must compute their location M ( x, y ) using (4). M ( x, y ) = ( x 1 + x 2 + x 3 3 , y 1 + y 2 + y 3 3 ) (4) Indonesian J Elec Eng & Comp Sci, V ol. 25, No. 3, March 2022: 1518–1528 Evaluation Warning : The document was created with Spire.PDF for Python.
Indonesian J Elec Eng & Comp Sci ISSN: 2502-4752 1521 Figure 2. Centroid principle [18] 2.3. MinMax This method’ s principle consists of associating for each anchor a container area with the sensor node to be located, as sho wn in Figure 3. These areas are constructed as (5) [15]. ( X i dx i ; Y i dy i ) and ( X i + dx i ; Y i + dy i ) ; i = A, B , C (5) The intersection of these areas forms a ne w zone dened by (6). ( max ( X i dx i ); max ( Y i dy i )) and ( min ( X i + dx i ); min ( Y i + dy i )) ; i = A, B , C (6) The sensor node M to be located estimates its position as the center of gra vity of this area using (7). ( X ; Y ) = ( max ( X i dx i ) + min ( X i + dx i ) 2 ; max ( Y i dy i ) + min ( Y i + dy i ) 2 ) ; i = A, B , C (7) Figure 3. MinMax principle 2.4. Multilateration It is an e xtension of trilateration [14] that uses more than three anchors to locate sensor nodes. M ul- tilateration minimizes the error mar gin due to the high number of anchors. The multilateration scheme is illustrated in Figure 4. The estimation of the position of the sensor node S using multilateration results from the solution of (8). ( x x Ai ) 2 + ( y y Ai ) 2 = d 2 i (8) ( x Ai ; y Ai ) are the coordinates of the anchors A i whate v er i = 1 ..n ( n > 3) while ( x ; y ) are the coordinates of the sensor node S to be computed. An e xperimental e valuation of localization methods used in wir eless sensor networks (Mostapha Laaouafy) Evaluation Warning : The document was created with Spire.PDF for Python.
1522 ISSN: 2502-4752 Figure 4. Multilateration principle [19] 3. SIMULA TION AND RESUL TS There are fe w studies on modeling and simulating localization methods in wireless sensor netw orks. Authors focus generally on geolocalization methods, where at least one terminal is capable of being located using a satellite positioning system and a GPS recei v er . These methods are kno wn for their high precision error . This section pro vides a desc ription of some e xamples of related w orks. Sheltami et al. [20] proposed that three kno wn localization protocols (ngerprint, centroid, and D V -Hop) are e v aluated in terms of accurac y and po wer consumption; simulation results sho w that ngerprint is v ery accurate than centroid and D V -Hop, b ut the latest outperform in terms of po wer consumption and stability . Grigulo and Beck er [21] focused on v alidating e xperimentally the technique named ef cient geometry- based localization (EGL). This technique locates static sensor nodes in an e xperimental eld with an ef cient, distrib uted, and scalable manner . A unmanned aerial v ehicles (U A V) system with autonomous i g ht and a lo w- cost global na vig ation satellite system (GNSS) recei v er will carry the mobile sink node. The EGL technique w as v alidated by e xperimental re sults comparing localization with real time kinematic (R TK) and standalone GNSS technique. Priya and Ali [22] modeled and simulated the localization problem in WSN using an im- pro v ed D V -Distance algorithm combined with trilateration method to pre v ent increasing localization error . The results sho w that the estimated and the e xact coordinates are v ery close. In a pre vious w ork [18], we conducted a comparati v e study in terms of precision and ener gy con- sumption of the most well kno wn and free localization methods that are: trilateration and centroid methods. The current w ork presents an e xtension of the pre vious study by simulating 4 localization methods: trilatera- tion, centroid, MinMax and reduced MinMax (MinMax method with a minimal number of anchors). W e also pro vide some perspecti v es for the enhancement of the localization method that manifests the best results. 3.1. Simulation platf orm The COOJ A simulator stands for COntiki Os Ja v a simulator . It’ s a simulator for sensor netw orks. The Contiki OS is a portable operating system de v eloped for de vices with limited resources, such as sensor nodes [23], [24]. Thanks to this simulator , we can ef ciently test a code written in C language without using real ash sensors. W e can a llocate an y nu m ber of nodes o v er a gi v en area. W e then visualize in real-time (or accelerated) the e v olution of the netw ork topology . In a simulation, we ha v e se v eral windo ws lik e sho wn in Figure 5: - The netw ork windo w displays the netw ork’ s graphical representation and sho ws us all nodes in the sim- ulated netw ork. - The simulation control windo w is where the simulation is started, paused, stopped and wholly reloaded. - The notes windo w is where we can put notes for our simulation. - The mote output windo w is where the sensor outputs are printed. A te xt eld allo ws us to enter a lter to tar get a particular sensor or message type. - The timeline windo w displays all communication e v ents in the simulation o v er time and v ery con v enient to understand what is happening in the netw ork. The mobility model describes the mo v ement pattern of mobile nodes and ho w their loca lizations change in term of speed and frequenc y . This model denes also the trajectory of mobility . In this w ork, we use The random mobility model where mobile nodes that change their positions randomly and periodically . Indonesian J Elec Eng & Comp Sci, V ol. 25, No. 3, March 2022: 1518–1528 Evaluation Warning : The document was created with Spire.PDF for Python.
Indonesian J Elec Eng & Comp Sci ISSN: 2502-4752 1523 Figure 5. Cooja simulator graphical interf ace 3.2. Localization accuracy The localization accurac y [25] is e v aluated by analyzing the error in the deri v ed localization. A localization method is m ore accurate when its e rror is s maller . The estim ated error bet ween the mobi le node’ s e xact and estimated position is determined using (9). E r r or = p ( x exact x estim ) 2 + ( y exact y estim ) 2 (9) 3.3. T rilateration implementation The netw ork topology presenting the simulation scenario contains 14 s ensor nodes deplo yed in an area of 90 × 90 m 2 , including eight mobile de vices and six anchor de vices. 40 m is the wireless communication range, and the transmission rate is 40%. The mobile node starts e x ecuting the algorithm of the trilateration method by broadcasting a Hello message within its transmission range to all anchors. The mobile node mea- sures the RSSI v alue for each beacon when a neighbor node responds to the Hello message. The distance between mobile nodes and neighbor anchors is calculated using (1). By resolving the equation system created by (2) and (3), we obta in the mobile node position. The (10) and (11) are the equation system’ s solutions using Python programming language. Figure 6 represents the simulation results and the error between the e xact and estimated positions in the T rilateration localization method’ s. x = 1 2( x 1 x 2 ) × ( x 2 1 2 x 1 x 2 + x 2 2 + y 2 1 2 y 1 y 2 + y 2 2 ) ( y 1 y 2 ) × ( D 2 1 y 1 + D 2 1 y 2 + D 2 2 y 1 D 2 2 y 2 + x 2 1 y 1 + x 2 1 y 2 2 x 1 x 2 y 1 2 x 1 x 2 y 2 + x 2 2 y 1 + x 2 2 y 2 + y 3 1 y 2 1 y 2 y 1 y 2 2 + y 3 2 q ( D 2 1 + 2 D 1 D 2 D 2 2 + x 2 1 2 x 1 x 2 + x 2 2 + y 2 1 2 y 1 y 2 + y 2 2 ) × ( x 1 x 2 ) × q ( D 2 1 + 2 D 1 D 2 + D 2 2 x 2 1 + 2 x 1 x 2 x 2 2 y 2 1 + 2 y 1 y 2 y 2 2 ) + ( D 2 1 D 2 2 x 2 1 + x 2 2 y 2 1 + y 2 2 ) × ( x 2 1 2 x 1 x 2 + x 2 2 + y 2 1 2 y 1 y 2 + y 2 2 )) (10) y = 1 2( x 2 1 2 x 1 x 2 + x 2 2 + y 2 1 2 y 1 y 2 + y 2 2 ) × ( D 2 1 y 1 + D 2 1 y 2 + D 2 2 y 1 D 2 2 y 2 + x 2 1 y 1 + x 2 1 y 2 2 x 1 x 2 y 1 2 x 1 x 2 y 2 + x 2 2 y 1 + x 2 2 y 2 + y 3 1 y 2 1 y 2 y 1 y 2 2 + y 3 2 + q ( D 2 1 + 2 D 1 D 2 D 2 2 + x 2 1 2 x 1 x 2 + x 2 2 + y 2 1 2 y 1 y 2 + y 2 2 ) × ( x 1 + x 2 ) × q ( D 2 1 + 2 D 1 D 2 + D 2 2 x 2 1 + 2 x 1 x 2 x 2 2 y 2 1 + 2 y 1 y 2 y 2 2 )) (11) An e xperimental e valuation of localization methods used in wir eless sensor networks (Mostapha Laaouafy) Evaluation Warning : The document was created with Spire.PDF for Python.
1524 ISSN: 2502-4752 Figure 6. T rilateration localization method results 3.4. Centr oid implementation This method’ s e xper iments are carried out by deplo ying in an area of 90 × 90 m 2 in the Netw ork windo w of Cooja sim ulator 16 sensor nodes, six of which are anchor de vices and 10 of which are mobile de vices. The wireless communication range is 40 m, and the transmission rate is 40%. When we click on the b utton start in the simulation control windo w , the netw ork starts to communicate. The mobile node gets data from the rst three beacons and uses (4) to compute its o wn position. Figure 7 represents the results of simulations and the precision error relati v e to the centroid method. Figure 7. Centroid localization method results 3.5. MinMax implementation T o simulate this method, we rst congure a topology that contains 18 sensor nodes, e ight of which are anchor de vices and 10 of which are mobile de vices. The topology is represented in the Netw ork windo w of the Cooja simulator by a 90 × 90 m 2 area with a wireless communication range of 40 m and a transmission Indonesian J Elec Eng & Comp Sci, V ol. 25, No. 3, March 2022: 1518–1528 Evaluation Warning : The document was created with Spire.PDF for Python.
Indonesian J Elec Eng & Comp Sci ISSN: 2502-4752 1525 rate of 40%. When the start b utton is pressed, the mobile nodes be gin e xchanging data with their neighboring anchors. Figure 8 sho ws the simulation results and the precision error for the MinMax method. Figure 8. MinMax localization method results 3.6. Reduced MinMax implementation T o simulate this method, we adopt t he same sensor nodes topology used to e v aluate the MinMax method, b ut this time we congure only three anchor nodes whil e the other 15 nodes are set as mobile nodes dispatched in an area of 90 × 90 m 2 with a transmission rate of 40% and a communication range of 100 m. In this method, the same e v aluat ion principle of the original MinMax method is replicated b ut with a reduced number of anchor nodes and an increased transmission range. Figure 9 sho ws the simulati on results and the precision error obtained for this method. Figure 9. Reduced MinMax localization method results 3.7. Discussion of r esults T o compare the dif ferent simulated methods, we will refer to their accurac y in term of precision err o r s. In Figure 10 it is clear that the localization error of trilateration and centroid methods e xceeds four meters while it does not e xceeds one and a half meters for the MinMax method. Therefore we can deduce that the MinMax An e xperimental e valuation of localization methods used in wir eless sensor networks (Mostapha Laaouafy) Evaluation Warning : The document was created with Spire.PDF for Python.
1526 ISSN: 2502-4752 method is more precise than both trilateration and centroid methods, while the reduced MinMAx method allo ws locating man y mobile sensor nodes with better accurac y using a reduced number of anchors. Figure 10. Localization methods error comparison In terms of ener gy consumption the trilateration method is the most consuming because it uses the RSSI technique to estimate the distance between anchors and the mobile node before running i ts algorithm, and this is not the case for centroid and MinMax methods. T o locate e v ery mobile node using MinMax method it is necessary to associate for each anchor a pri v ate container area which increases the ener gy consumption unlik e the centroid method where the anchors broadcast their coordinates to e v ery mobile node in their transmission area. So we can conclude lik e sho wn in Figure 11 that the centroid method consumes less ener gy than the trilateration and MinMax methods. Figure 11. Localization methods po wer consumption 4. CONCLUSION W e presented in this paper a mathematical modeling and a comparati v e study throught si mulation of four basic localization methods: trilateration, centroid, MinMax and reduce d MinMax. Simulation results sho w that the MinMax method is more accurate thand other methods, while the centroid method is concluded to be the best in terms of ener gy consumption. F or the centroid and trilateration methods; it can be noticed that their performance deteriorates signicantly and rapidly as the number of mobile nodes increases. The reduced MinMax gi v es a v erage b ut acceptable results in terms of accurac y and ener gy consumption, its performance Indonesian J Elec Eng & Comp Sci, V ol. 25, No. 3, March 2022: 1518–1528 Evaluation Warning : The document was created with Spire.PDF for Python.
Indonesian J Elec Eng & Comp Sci ISSN: 2502-4752 1527 also de grades when increasing the number of nodes and their de gree of mobility , b ut not as signicantly as the other methods. W e are currently w orking on impro ving the reduced MinMax method to enable its scalability while inte grating a better netw ork management especially in the presence of a high number of mobile nodes or anchors. REFERENCES [1] M. A. Uthaib and M. S. Croock, “V ehicle plate localization and e xtraction based on hough transform and bilinear operations, Indonesian J ournal of Electrical Engineering and Computer Science (IJEECS) , v ol. 20, no. 2, pp. 1088–1097, 2020, doi: 10.11591/ijeecs.v20.i2.pp1088-1097. [2] J. Zhao, O. Y a ˘ gan and V . Gligor , “Connecti vity in secure wireless sensor netw orks under transmission constraints, 2014 52nd Annual Allerton Confer ence on Communication, Contr ol, and Computing (Allerton) , 2014, pp. 1294–1301, doi: 10.1109/ALLER- T ON.2014.7028605. [3] F . 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An e xperimental e valuation of localization methods used in wir eless sensor networks (Mostapha Laaouafy) Evaluation Warning : The document was created with Spire.PDF for Python.