extreme learning machine for user location prediction in mobile environment

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Extreme learning machine for user location prediction in mobile environment Teddy Mantoro Department of Computer Science, KICT, International Islamic University Malaysia, Kuala Lumpur, Malaysia Akeem Olowolayemo Department of Information Systems, KICT, International Islamic University Malaysia, Kuala Lumpur, Malaysia Sunday O. Olatunji Department of Computer Science, FICT, Universiti Teknologi Malaysia (UTM), Johor Bahru, Malaysia, and Media A. Ayu and Abu Osman Md. Tap Department of Information Systems, KICT, International Islamic University Malaysia, Kuala Lumpur, Malaysia Abstract Purpose – Prediction accuracies are usually affected by the techniques and devices used as well as the algorithms applied. This work aims to attempt to further devise a better positioning accuracy based on location fingerprinting taking advantage of two important mobile fingerprints, namely signal strength (SS) and signal quality (SQ) and subsequently building a model based on extreme learning machine (ELM), a new learning algorithm for single-hidden-layer neural networks. Design/methodology/approach – Prediction approach to location determination based on historical data has attracted a lot of attention in recent studies, the reason being that it offers the convenience of using previously accumulated location data to subsequently determine locations using predictive algorithms. There have been various approaches to location positioning to further improve mobile user location determination accuracy. This work examines the location determination techniques by attempting to determine the location of mobile users by taking advantage of SS and SQ history data and modeling the locations using the ELM algorithm. The empirical results show that the proposed model based on the ELM algorithm noticeably outperforms k-Nearest Neighbor approaches. Findings – WiFi’s SS contributes more in accuracy to the prediction of user location than WiFi’s SQ. Moreover, the new framework based on ELM has been compared with the k-Nearest Neighbor and the results have shown that the proposed model based on the extreme learning algorithm outperforms the k-Nearest Neighbor approach. Originality/value – A new computational intelligence modeling scheme, based on the ELM has been investigated, developed and implemented, as an efficient and more accurate predictive solution for determining position of mobile users based on location fingerprint data (SS and SQ). Keywords Location awareness, Artificial neural network, Extreme learning machines, Mobile technology, Learning Paper type Research paper The current issue and full text archive of this journal is available at www.emeraldinsight.com/1742-7371.htm IJPCC 7,2 162 Received 14 December 2010 Revised 6 January 2011 Accepted 16 March 2011 International Journal of Pervasive Computing and Communications Vol. 7 No. 2, 2011 pp. 162-180 q Emerald Group Publishing Limited 1742-7371 DOI 10.1108/17427371111146446

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Extreme learning machinefor user location prediction

in mobile environmentTeddy Mantoro

Department of Computer Science, KICT,International Islamic University Malaysia,

Kuala Lumpur, Malaysia

Akeem OlowolayemoDepartment of Information Systems, KICT,

International Islamic University Malaysia, Kuala Lumpur, Malaysia

Sunday O. OlatunjiDepartment of Computer Science, FICT, Universiti Teknologi Malaysia (UTM),

Johor Bahru, Malaysia, and

Media A. Ayu and Abu Osman Md. TapDepartment of Information Systems, KICT,International Islamic University Malaysia,

Kuala Lumpur, Malaysia

Abstract

Purpose – Prediction accuracies are usually affected by the techniques and devices used as wellas the algorithms applied. This work aims to attempt to further devise a better positioning accuracybased on location fingerprinting taking advantage of two important mobile fingerprints, namely signalstrength (SS) and signal quality (SQ) and subsequently building a model based on extreme learningmachine (ELM), a new learning algorithm for single-hidden-layer neural networks.

Design/methodology/approach – Prediction approach to location determination based onhistorical data has attracted a lot of attention in recent studies, the reason being that it offers theconvenience of using previously accumulated location data to subsequently determine locations usingpredictive algorithms. There have been various approaches to location positioning to further improvemobile user location determination accuracy. This work examines the location determinationtechniques by attempting to determine the location of mobile users by taking advantage of SS andSQ history data and modeling the locations using the ELM algorithm. The empirical results show thatthe proposed model based on the ELM algorithm noticeably outperforms k-Nearest Neighborapproaches.

Findings – WiFi’s SS contributes more in accuracy to the prediction of user location than WiFi’s SQ.Moreover, the new framework based on ELM has been compared with the k-Nearest Neighbor and theresults have shown that the proposed model based on the extreme learning algorithm outperforms thek-Nearest Neighbor approach.

Originality/value – A new computational intelligence modeling scheme, based on the ELM has beeninvestigated, developed and implemented, as an efficient and more accurate predictive solution fordetermining position of mobile users based on location fingerprint data (SS and SQ).

Keywords Location awareness, Artificial neural network, Extreme learning machines,Mobile technology, Learning

Paper type Research paper

The current issue and full text archive of this journal is available at

www.emeraldinsight.com/1742-7371.htm

IJPCC7,2

162

Received 14 December 2010Revised 6 January 2011Accepted 16 March 2011

International Journal of PervasiveComputing and CommunicationsVol. 7 No. 2, 2011pp. 162-180q Emerald Group Publishing Limited1742-7371DOI 10.1108/17427371111146446

1. IntroductionThe prime goal of pervasive computing is the idea of information technology (IT)services every time and everywhere (Weiser, 1991; Stanton, 2001). This makesIT-enabled services available and responsive to user’s needs in mobile environmenttaking advantages of their location and context information. This implies that there isno gain saying about the importance of location and context aware computing owningto its pivotal role in context-based services management.

There have been wide areas of applications of context computing and locationawareness with a rapidly growing demand and research for its applications in variousnew areas. Some of the application areas include resources optimization (e.g. power,bandwidth, etc.), fleet tracking and shipping applications, underground as well asunderwater navigations, security – tracking criminals by law enforcement officials,automotive applications, advertisement and marketing, aged and disabled supportsystems, robot and machine control and a host of all others (Deitel, 2001; Mautz, 2008).

Obviously, there is an urgent need for better approaches that will improve theapplications of mobile positioning techniques, with adequate and up-to-date devices aswell as appropriateness of algorithms in ways that will carefully analyze the existingtechniques and methods to be able to develop sound strategies to further enhancecontext aware applications.

Through context computing, IT infrastructures and services can now be madeavailable and better utilized by adapting to users’ needs and thus facilitating enhancedresources management.

Prediction accuracies are usually affected by the techniques and devices used aswell as the algorithms applied (Mantoro and Olowolayemo, 2009). The appropriatemanagement of these components of context determination is more often than not oneof the major problem areas in location positioning systems.

The methodology adopted in this paper is to review existing positioning systemsand approaches, location referencing types, technologies, as well as differentpositioning algorithms. Subsequently, our approach at further improving our initialresults by modeling with extreme learning machine (ELM) algorithm is reported.

The work discusses previous approaches to location recognition based onfingerprinting of signal attributes peculiar to each position in the experimentallocation using wireless local area network (WLAN) signals. This work is an attempt atimproving previous positioning accuracy based on location fingerprinting takenadvantage of another important mobile fingerprints, namely signal quality (SQ) inaddition to signal strength (SS) that has been used extensively in previous works, suchas in (Kaemarungsi, 2006; Rohrig and Kunemund, 2007; Kumar et al., 2006) andsubsequently building a discovery model based on ELM, a new learning algorithm forsingle-hidden-layer neural networks (SLFNs) described in Huang et al. (2004). In thesubsequent section each of the components of positioning systems are furtherelaborated.

The remaining part of this paper is organized as follows. The next section gives areview of related work on key concepts in location and context awareness, locationfingerprinting and neural networks (NN) with special focus on ELM. Section 3discusses the system’s design techniques and the last section; conclusion, evaluates theresults of the study as well as the challenges encountered and also proposes our futuredirections.

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2. Related workLocation determination is the most important component of context awareness (Mantoroand Olowolayemo, 2009). There have been tremendous attempts previously to betterapproximate location of mobile users. These are due largely to the ever-growing needfor better positioning for improved location-based services’ management. Differentapproaches have been used and proposed in literatures. One such approach that hasgained more recognition recently is location fingerprinting. Location fingerprinting is toposition users based on differential signal attributes at different locations rather thancomputing the distance between the signal transmitting points, usually the access point,and mobile device terminal peculiar to other network-based approaches (Reyero andDelisle, 2008). The received SS is then compared to location history data previously storedin a radio map. Efforts at using location fingerprinting to determine mobile user locationshave been explored in several previous works such as in Tsai et al. (2009), Mantoro andOlowolayemo (2009), Mantoro et al. (2009), Kaemarungsi and Krishnamurthy (2004)and Kaemarungsi (2006). Specifically, in Tsai et al. (2009), a comparison of NN modelsusing SS was explored. The NN models were based on the simulated-annealingback-propagation and feedforward neural network (FFNN) with back-propagation(BPN), showing better performance results of the latter over that of the former models.

2.1. Positioning levels of orientationsPositioning systems accuracies can be tailored to three levels of orientation. Theseorientations are point-, line- and area-orientation (Brimicombe and Li, 2009). Locationpositioning systems’ accuracies is an issue of great concern especially, when thepositioning has to do with point-orientation, such as those services meant for disabledand aged citizens who require assistance. In such cases, the accuracy must be tailoredto the “exact” position of the person-concerned. However, in this and other orientationssuch as line or area-orientations, there is still need for improvement to give betterconfidence and better management of resources. A good example is the case of wrongpositioning of fleet management (Brimicombe and Li, 2009).

2.2. Positioning approachesPositioning approaches can be classified into three; network-based, device-based andhybrid methods, comprising both first two approaches (Brimicombe and Li, 2009).

Network-based positioning often regarded as integrated approach since the network isused for communication and data transmission to other networks as well as determinationof user location. In network-based positioning, user locations are determined byestimating the signal travelling to and from a set of transmitter base stations, such as,WLAN access points (APs) or global system for mobile communications (GSM) basestations. The position is, thereby measured through computation of the length anddirection of the radio path of a mobile device from these base stations (Brimicombe andLi, 2009). Network-based positioning methods do not require extra software or hardwareto be installed in the mobile device since the network is used for the computation. Power isalso relatively more conserved unlike in device-based methods that require high-power forcomputation. Network-based approaches are known to be more accurate since, they haveaccess to fine grained data which include transmission power, antenna location, and tilt;which are not available in device-based systems (Reyero and Delisle, 2008). There aremany network-based positioning techniques that are used in indoor users’ location

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techniques for measuring signals at a particular location to an Access Point. Theseinclude cell of origin (the earliest method of locating a wireless user by determining thetransmitting range where the call is made), angle of arrival (AOA) – locating a user’sposition by the overlapping of two cell where the cell phone receive signal, enhancedobserved time difference – determining user’s position by measuring the time travelbetween the phone and multiple towers, time of arrival (TOA), time difference of arrival(TDOA) – locating a user by determining the time, it takes the signal from the cell-phone toreach the transmitting tower. The other issue in device-based positioning is that there is anadded overhead of computation power as a result of processing of location information onthe device while at the same time being used for network (Brimicombe and Li, 2009;Mantoro and Olowolayemo, 2009).

However, for outdoor users’ location determination global positioning system (GPS)is used. It is the de facto standard for outdoor positioning. GPS uses satellites to track auser’s latitude, longitude and altitude, it can be used virtually everywhere in the world,including on airplanes and ship (Brimicombe and Li, 2009). The main drawback of GPSis that it is not effective for indoor location determination. Recently, assisted-GPS, thatis, a combination of GPS with one or more of network-based positioning approaches,such as Cell-ID, TDOA, AOA, has been used as hybrid approaches to work around thisshortcoming of GPS (Brimicombe and Li, 2009).

2.3. Location fingerprintingRecently, location fingerprinting, that is, recalling patterns (such as multipath) whichmobile phone signals are known to exhibit at different locations in each cell, has beenproposed and adjudged as better suited for indoor positioning. However, in locationfingerprinting positioning, the appropriate selection of location determination algorithmsand models for context enabled services has been very crucial for accuracy andenhancement of positioning systems and applications, which is one of the keys to futuremobile infrastructures and services management and security. Various indoor approachessuch as those used in location fingerprinting give some advantages over device-basedmethod that uses GPS. This is due to two important reasons. One, GPS performsinadequately in indoor environment due to obstruction to signal and non-line of sight,which lead to attenuation and poor SQ while location fingerprinting on the other hand isnot affected by non-line of sight. Out of these methods, location fingerprinting has beenconsidered a more appropriate choice. This is because other techniques are affected bynon-line of sight and multi-path in indoors space (Mantoro and Olowolayemo, 2009). Thisleads to errors and inaccuracies in the training datasets captured.

2.4. SensorsPositioning sensors are classified based on the level of precision to which they candetermine a mobile location. Broadly, there are Precise, Proximate and Predictedapproaches to level of precision positioning.

Precise sensors. Location estimation techniques that are based on sensors that candetermine a mobile user location to ,1 m accuracy. Examples in this category includeradio frequency identification, etc.

Proximate sensors. Location estimation techniques based on sensors that candetermine a mobile user location up to a meter accuracy. Examples of sensors that fallin this category include WiFi, GSM, WiMedia, ZigBee, active/passive badge, voicerecognition, face recognition, smart floor (Mantoro and Johnson, 2003).

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Predicted approaches. In this approach, historical data of mobile user location iscollected, stored in a repository which can then be used to estimate mobile user locationby pattern matching, using different types of models that are broadly classified asdeterministic, based on Euclidean or Manhattan norm, such as the k-Nearest Neighborand probabilistic, such as maximum-a-posterior or maximum-likelihood frameworks(Honkavirta et al., 2009).

2.5. PrinciplesThe principles for location determination can be broadly classified under proximity,trilateration or triangulation, multilateration and centroids. The fundamental principleas decribed in Reyero and Delisle (2008) is discussed below.

Proximity, the most primitive of the principles, rely on the transmitting tower’srange when a call is made from a cell phone. It is the least accurate since the user can beanywhere within a specific area or cell (Deitel, 2001; Figure 1).

Trilateration and triangulation use the overlap of towers cells to compute thelocation of a user. If a couple of towers receive signals from a phone their cells can beused to calculate the location of the phone. Trilateration, the basic principle underlyingcommon positioning technologies (Huang et al., 2010), uses distance or a measure ofdistance, inferred from other attributes such as SS, TOA, etc. to determine userlocation. The determination of mobile user location is computed from the intersectionof cells or signals from at least three sources. Solving the system of equations belowdescribed in Reyero and Delisle (2008) gives the location coordinates (Figure 2).

Triangulation uses signal AOA from at least two reference points, then determinesthe location as intersection of lines (Reyero and Delisle, 2008). The solution to thelocation coordinate is given by the system of equations below (Figure 3).

Multilateration, the technique finds the location of mobile users by preciselycomputing the TDOA of a signal emitted from the device to at least three receivers. It isoften referred to as hyperbolic positioning.

In centroid, a user location is calculated as an aggregated weighted mean of thedetected reference points’ location, where the weight could be calculated from the receivedSS, the reference point coverage, or the reliability of the reference points (Figure 4).

The linear centroid can be generally expressed as:

x ¼i

Xwixi; y ¼

i

Xwiyi

Figure 1.Cell of origin,the most primitivelocation principle

Cell-phone user canbe anywhere withinthe tower's range.

Source: Deitel (2001)

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The accuracy of these techniques improves as the number of reference points increases,the distance of the points decreases and with increase in the number of other factorsincluded (Reyero and Delisle, 2008).

2.6. AlgorithmsFurthermore, there are different algorithms that could be used to determine the userlocation. The major component of context awareness system that determines the accuracyof the predictions is the appropriateness and adequacy of the algorithm used. There are anumber of major algorithms that have been adopted or presented in context awarenesstexts. These include Markov models, Hidden Markov models (Wallbaum and Spaniol,2006; Nuno-Barrau and Paez-Borrallo, 2005), Bayesian networks (Fox et al., 2003),

Figure 2.Trilateration

y

x

(k,1)

(i,j)

(0,0)

Note: {r12 = x2 + y2, r2

2 = (x – i)2 + (y – j)2,[(r13)]r2 = [(x – k)]r2 + [((y – l))]r2}Source: Reyero and Delisle (2008)

r2

r1r3

Figure 3.Triangulation

(k,1)

(i,j)

(0,0) x

y

α

β

Note: y = (x–i)sin(a) + j, y = (x–k)sin(b) + lSource: Reyero and Delisle (2008)

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NN (Tsai et al., 2009) or time-series. In several previous works, location hasbeen estimated using a number of algorithms and techniques. The algorithms forlocation estimations can be classified as deterministic and probabilistic (Honkavirta et al.,2009). Under deterministic approach, which is based on the traditional Euclideandistance approximation method, approaches with different norms were considered.The probabilistic approach is generally based on the conditional probability distributionfunction using Bayes’ rule.

2.7. Proposed methodologyThe technique proposed in this work is to estimate users’ location based on locationfingerprinting specifically collecting mobile devices location data, namely, the SS and SQ, asfirst proposed in Mantoro et al. (2009), based on proximity to a number of APs.Subsequently, a model based on ELM modeling is used to estimate the location of the mobileuser, a process regarded as place detection in some literatures (Reyero and Delisle, 2008).

2.8. Artificial neural networkThe prediction technique used is discussed in this section. This involve the developmentand application of ELM, a new artificial neural network (ANN) framework which isderived from SLFNs (Huang et al., 2000), to the determination of location of mobile usersbased on the SS and SQ peculiar to the particular location. Our discussion opens with ANNto gain full understanding of the underlying principles of SLFNs and ELM.

ANN is a mathematical model that tries to stimulate the functions of the brain(Tan et al., 2006). Similar to the human brain, the neural network is composed ofan interconnected assembly of nodes and directed links. It is known that the humanbrain learns by changing the strength of the synaptic connection between neuronsupon repeated stimulation by the same impulse (Bernacki and Wlodarczyk, 2005).A generic structure of the traditional ANN is shown in Figure 5.

The aim is to compute the value of the computed output y close enough to the targetoutput f(x).

The ANN is defined, thus.Given a finite input nodes x ¼ xi; . . . ; xk with corresponding weight vector,

w ¼ wi; . . . ;wk the network’s response, y is given by:

Figure 4.Centroid

x(0,0)

(x1,y1)

(x3,y3)

w3 w4

w2w1

(x4,y4)

(x2,y2)

yIJPCC7,2

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y ¼ gX

kwk · xk

� �[ ð0; 1Þ

adjusting the weights sufficiently to estimate y, after a finite number of steps, suchthat:

y < f ðxÞ

by minimizing the difference between the network’s response, y and the desiredoutput, f(x). The termination condition is achieved after a specified number ofiterations, usually referred to as epoch is reached. The performance of ANN isoften specified in form of root mean square error (RMSE). The network is known tousually converge, however, optimal convergence is not guaranteed.

In order to accelerate convergence in multilayered feedforward neural network(MFN), BPN is often used. The goal is to learn the weights, thereby minimizing themean squared error. This implies that we first compute:

okj ¼ gjX

iwji · okj

� �

for each hidden and output unit.Subsequently, for each node uj, the accumulated error dkj:

dkj ¼ ðtkj 2 okjÞg0j

Xiwji · oki

� �

is computed. The computed d becomes the input of the reversed network, to adjust theweights vector, w. This is essentially the BPN. Thus, we compute for each node uj:

dkj ¼ f 0j

Xiwji · oki

� �t

Xdktw

k21tj

and the weight update is then computed for each wkji [ w:

wkji ¼ wk21

tj þ mdkjoki

The MFN with BPN is known to be far slower and a new learning algorithm based onthe SLFNs, the ELM has been proposed and found to outperform the traditional NN,

Figure 5.A generic model

of neural network

x2

w1

w2

yf(e)

x1

x2

w1Summingjunction

Source: Rumelhart et al. (1986)

e = x1w1+x2w2 y = f(e)Non-linearelement

f(e)w2

x1

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and when compared with k-Nearest Neighbour previously used on the same dataset ofSS and SQ (Mantoro et al., 2009), it also presents a better performance. A briefdescription of ELM is given in the subsequent section.

3. Extreme learning machinesThe ELM modeling scheme, a new framework based on the traditional FFNN proposedrecently (Huang et al., 2004), is composed of a single-hidden-layer. It randomly choosesthe input weights and analytically determines the output weights of the SLFNs (Han andHuang, 2006). Previous attempts have compared its performance with other variants ofthe traditional NN as well as other algorithms such as support vector machine, fuzzyneural network, fuzzy regression, multiple linear regression, generalized regressionneural network and other in different domains (Kwak and Kwon, 2008; Wessels andWang, 2010; Huang et al., 2004; Olatunji et al., 2010).

Previous study of the learning rate of FFNN have shown that it is time-consumingwhich hinders FFNN scalability, thereby necessitating the need for new frameworks toformulate faster and better performing networks (Huang et al., 2006a, b). There are twomain reasons behind this behavior (Huang et al., 2009), one is the slow gradient-basedlearning algorithms used to train NN and the other is the iterative tuning of theparameters of the networks by these learning algorithms.

To overcome these problems, Huang et al. (2004) proposed a learning algorithmcalled ELM for SLFNs which randomly selected the input weights and analyticallydetermines the output weights of SLFNs. In Huang et al. (2006a, b), it is stated that“In theory, this algorithm tends to provide the best generalization performance atextremely fast learning speed”. This is a breakthrough since, previously there existed astiff virtual speed barrier which classic learning algorithms could not overcome and,therefore, implementation of FFNN training itself requires longer time, irrespective ofthe application type, whether simple or complex.

The ELM has several interesting and significant features different from traditionalpopular gradient-based learning algorithms for FFNN. These features are enumeratedas follows:

. The learning speed of ELM is extremely fast. In simulations reported previously(Huang et al., 2006a, b, Olatunji et al., 2010), the learning phase of ELM can becompleted in seconds or less than seconds for many applications.

. The ELM has better generalization performance than the gradient-basedlearning such as back propagation in most cases.

. The traditional classic gradient-based learning algorithms and some otherlearning algorithms may face several issues like local minima, improper learningrate, over fitting, etc. In order to avoid these issues, some methods such as weightdecay and early stopping methods may need to be used often in these classicallearning algorithms. The ELM tends to reach the solutions directly without suchtrivial issues. The ELM learning algorithm looks much simpler than mostlearning algorithms for FFNN.

Unlike the traditional classic gradient-based learning algorithms which only work fordifferentiable activation functions, the ELM learning algorithm could be used to trainSLFNs with many non-differentiable activation functions (Huang et al., 2006a, b;Mao et al., 2006).

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3.1 How extreme learning machine algorithm worksTo appreciate ELM, a description of the standard SLFNs is necessary. A generalframework of extreme learning algorithm is presented here.

Given an N samples (xi, ti), where xi ¼ [xi1, xi2, . . . , xin]T [ Rn andti¼ [ti1, ti2, . . . ,tim]T [ Rn,

The standard SLFNs with ~N hidden neurons and activation function g(x) is defined as:

X~N

i¼1

bigðwi · xj þ biÞ ¼ oj; j ¼ 1; . . . ;N ;

wherewi ¼ [wi1,wi2, . . . ,win]T gives the weight vector that connects the ith hidden neuron

and the input neurons, bi ¼ [bi1,bi2, . . . ,bim]T is the weight vector that connects the ithneuron and the output neurons, and bi is the threshold of the ith hidden neuron. The “· ”in wi · xj indicates the inner product of wi and xj.

In SLFNs, just like the traditional FFNN with BPN, the aim is to minimize thedifference between, network response, oj and the target output, tj. That is:

X~N

i¼1

bigðwi · xj þ biÞ ¼ tj; j ¼ 1; . . . ;N

Or, more compactly, as:

Hb ¼ T

where H can be represented as:

H ðw1; . . . ;w ~N; b1; . . . ; b ~N; x1; . . . ; xN Þ ¼

gðw1 · x1 þ b1Þ · · · gðw ~N · x ~N þ b ~NÞ

..

.· · · ..

.

gðw1 · xN þ b1Þ · · · gðw ~N · xN þ b ~NÞ

26664

37775N¼ ~N

;

b ¼

bT1

..

.

bT~N

266664

377775

~N£m

; and T ¼

TT1

..

.

TT~N

266664

377775N£m

H is referred to as the neural network output matrix (Huang and Haroon, 1998).The processes of the ELM algorithm can be described as follows (Huang et al., 2004):Given a training set:

N ¼ ðxi; tiÞjxi [ R n; ti [ Rm; i ¼ 1; . . . ;Nf g;

activation function g(x), and hidden neuron number ¼ ~N, do the following:. Assign random value to the input weight wi and the bias bi, i ¼ 1, . . . , ~N.. Find the hidden layer output matrix H.. Find the output weight b as follows:

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b ¼ H þT

where b, H and T are defined in the same way they were defined in the SLFNsspecification above.

4. Experiment4.1 Experimental dataThe experimental location, Levels 4 and 5 of Kulliyyah of Information andCommunication Technology (KICT) Buildings, International Islamic UniversityMalaysia (IIUM) has wireless infrastructure available through installations ofwireless APs. The locations chosen for the study have a total of 179 room locations,numbered L4001-L4090 and L5001-L5080. The levels have measurable reception ofWi-Fi signals from 8 APs, where each access point produces four service set identifierand media access control addresses on signal reception.

The Wi-Fi SS and SQ were measured and collected from locations, at a distance of1 m in each of the room locations on the chosen levels of the building. In order tofacilitate instance-based learning, the Wi-Fi’s signal data collection was presented in amultivariate signal data.

The data were collected using multi-observers method by collecting the data in aparticular location, a number of times, specifically eight times for all experimentallocations. The calibration was such that the distance between subsequentmeasurements is 1 m.

We collected values of multiple-observed SS and quality in a database, such thatthe ELM algorithm can then estimate the SS and SQ as a data instance from a singlepoint/location which is then compared to the training dataset stored in our database,thereby able to determine the distance value between training data and data sample.The location positioning model is as shown in Figure 6.

Subsequently, the ELM algorithm deduces the closest member based on thetraining dataset by classifying the closest member based on the specified algorithmnumber of closeness. This results in the most user location that belongs to the member(Figure 7).

4.2 Collecting datasetMeasuring and collecting the training dataset are made at Levels 4 and 5 KICTbuilding’s corridor. Tape meters are used to calibrate the floors to measure signal dataat every 1 m. For Level 4, the measurement extends up to 105 m, while Level 5 was upto 88 m.

The data collection was in four folds:First, 8M multi-observer with SS and SQ measurements, by collecting eight data

readings at every single point along the corridor of 90 m at Level 4 and 88 m at Level 5.This results in 1,424 training dataset.

The second stage was collection of 8M multi-observer with SS measurements only,collecting eight data readings at every single point, along the corridor of 90 m at Level4 and 88 m at Level 5, which resulted in 1,424 training dataset.

Next, collection of 1 m multi-observer with SS and SQ measurements. That is,collecting one data reading (SS þ SQ) for both Levels 4 and 5 (Table I).

Finally, 1M multi-observer with SS measurements collecting one data reading (SS)for both Levels 4 and 5.

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The data were then prepared and stored in a common data repository for the models(Plate 1).

The ELM algorithm was built in the following stages:

(1) The multi-observers training data were partitioned into training and testingdata.

(2) Data preparation was carried out so that the data are well formatted andstructured to conform to the requirements of the network.

Figure 6.The location positioning

architecture

Location

Knowledgebase

Signal converter

Data partitioning

ELM traning

ELM testing

Signal capture

Signal attributes

Figure 7.Experimental locationlayout – user’s within

different location wouldget different signal

strength, quality and noisefrom the wireless access

point

AP1

AP1:–35

AP2:–57

AP3:–78

AP1:–80

AP2:–64

AP3:–39

User1User2

AP2 AP3

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(3) The network was trained with different parameters, 80 per cent training datawith 20 per cent test data and 85 per cent training data and 15 per cent test datato compare the performances of each model and, thereby able to select the bettermodel after validation.

An experimental procedure based on test set cross validation was employed in ourstudy. We used the stratified sampling approach to divide the dataset into bothtraining and testing data, such that the size of the training set is 80 per cent of theavailable data and the testing is the rest in the first case, and 85 per cent training datain the second case.

4.3 Simulation settingIn this work, we carried out three separate forms of classification on the same dataset:

(1) classification using the first eight predictor variables (tagged SS1-SS8);

(2) classification using the last eight predictor variables (tagged SQ1-SQ8); and

(3) classification using all the 16 predictor variables (tagged SS1-SS8 andSQ1-SQ8).

For each of the three different cases, the dataset were divided into both training andtesting set using the stratifying approach so that the data were randomly divided foreffective representation. In all, six experiments were recorded as adequaterepresentation among the different models.

4.4 Performance indicatorPercentage of correctly classified samples is the chosen performance indicator for thiswork. These criteria actually provide an easy, clear and more accurate evaluation of theclassifiers. To select the most efficient network based on RMSE and network simplicity,requiring less computation and memory, in the experiment, we differentiated based ononly SS comparing with the results of only SQ and later compare the results obtained basedon these models with the one that used both predictors, SS and SQ combined as dataset.

Plate 1.Capturing the WiFi data

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SS

SQ

Loc

atio

ns

SS

1S

S2

SS

3S

S4

SS

5S

S6

SS

7S

S8

SQ

1S

Q2

SQ

3S

Q4

SQ

5S

Q6

SQ

7S

Q8

L

272

251

279

299

299

299

299

299

5983

490

00

00

L40

012

692

522

802

992

992

992

992

9963

8248

00

00

0L

4002

264

299

277

299

299

299

299

299

690

520

00

00

L40

032

702

612

762

992

992

992

992

9962

7354

00

00

0L

4004

271

255

299

299

299

299

299

299

6179

00

00

00

L40

052

762

592

762

992

992

992

992

9954

7554

00

00

0L

4006

276

259

299

299

299

299

299

299

5475

00

00

00

L40

072

762

992

992

992

992

992

992

9954

00

00

00

0L

4008

277

252

275

299

299

299

299

299

5282

550

00

00

L40

092

792

492

732

992

992

992

992

9949

8458

00

00

0L

4010

274

251

277

299

299

299

299

299

5783

520

00

00

L40

11

Table I.Sample location data

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5. Results and discussionWe present here the results of the classification using 85 per cent for training and15 per cent for testing, then followed by the classification using 80 per cent for trainingand 20 per cent for testing. From the results in Tables II and III, it was shown that theproposed model outperforms the model based on k-Nearest Neighbor obtainedpreviously in Mantoro et al. (2009). The best result from all the parameter variationswas 93.26 per cent in the k-Nearest Neighbor model using 80 per cent training and20 per cent test datasets.

In this model, using all predictors, both SS and SQ, the model gives above 94 per centfor training in both parameter variations of 80-20 per cent training and test data,respectively, and 85-15 per cent variation. Using the latter variation of 85 per centtraining data to 15 per cent for test data was shown to have given the best result,overall, a little above 95 per cent. Generally for the training data, 80 per cent trainingdata for SS alone, without the SQ (SS1-SS8) gives the best performance of slightlyabove 95 per cent. This further confirms that the SS attribute is more relevant in theprediction of location than SQ. This can also be seen in the 85-15 per cent, where the SSalso outperforms the results from SQ. However, the effect of combining both the SQand SS as predictor variables is obvious as we can see that the highest performanceaccuracy was achieved for both training and testing set; specifically, it achievedperformance of above 94 per cent for training set and above 95 per cent for testing set.It can be said also that the average performance for both training and test data isaround 94 per cent using all predictors. This is a more remarkable performance thanthe previous work (Mantoro et al., 2009; Figure 8).

6. ConclusionIn this study, the following conclusions and recommendations could be drawn basedon previous analysis, discussions, deep investigation, experiments and comparativestudies in the work. A new computational intelligence modeling scheme, based on theELM has been investigated, developed and implemented, as an efficient and moreaccurate predictive solution for determining position of mobile users based on locationfingerprinting data – SS and SQ. The new framework based on ELM has beencompared with the k-Nearest Neighbor presented earlier in Mantoro et al. (2009).

SS1-SS8 predictors SQ1-SQ8 predictorsAll predictors

variableTr Ts Tr Ts Tr Ts

ELM 94.72 92.49 93.89 92.96 94.22 95.31

Table II.Results of using85 per cent for trainingand 15 per cent for testing

SS1-SS8 predictors SQ1-SQ8 predictorsAll predictors

variableTr Ts Tr Ts Tr Ts

ELM 95.09 91.55 93.95 93.31 94.47 93.66

Table III.Results of using80 per cent for trainingand 20 per cent for testing

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The empirical results have shown that the proposed model based on the extremelearning algorithm outperforms k-Nearest Neighbor approaches (Tables II and III).

It is noteworthy to mention based on this work that.While error could lead k-Nearest Neighbor to converge to a wrong prediction, or to

results to multiple or conflicting locations determination on the corridors, because ofdifficulty in conveniently differentiating patterns for each meter, the ELM model wasspecifically invented to overcome lower minima convergence problem, however,a 100 per cent prediction accuracy is still not achieved.

The ELM model outperforms k-Nearest Neighbor (94.22 and 93.26 per cent,respectively) with some noticeable margin.

WiFi’s SS is more relevant to the prediction of location than WiFi’s SQ.Further work is underway to compare the proposed model with other variants of

NN such as BPN, functional networks, simulated, annealing based and further improvethe accuracy with heavy statistics such as Bayesian, Kalman and Particle filters. Wehope to standardize the work to produce reliable campus radio map using a robustlight-weight user location algorithm for mobile devices.

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Figure 8.Interface for user location

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Further reading

Laurendeau, C. and Barbeau, M. (2010), “Centroid localization of uncooperative nodes in wirelessnetworks using a relative span weighting method”, EURASIP Journal on WirelessCommunications and Networking, Vol. 2010, pp. 1-10 (Article ID 567040).

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Yun, S., Lee, J., Chung, W. and Kim, E. (2008), “Centroid localization method in wireless sensornetworks using TSK fuzzy modeling”, Proceedings of the International Symposium OnAdvanced Intelligent Systems, Nagoya, Japan, 17-21 September, pp. 971-4.

Yun, S., Lee, J., Chung, W., Kim, E. and Kim, S. (2009), “A soft computing approach to localizationin wireless sensor networks”, Elsevier Journal of Expert Systems with Applications, Vol. 36,pp. 7552-61.

Zeimpekis, V., Giaglis, G.M. and Lekakos, G. (2003), “A taxonomy of indoor and outdoorpositioning techniques for mobile location services”, ACM SIGecom Exchanges – MobileCommerce, Vol. 3 No. 4, pp. 19-27.

About the authorsTeddy Mantoro (PhD) is currently the Head of Intelligent Environment Research Group (INTEG)and a Senior Lecturer at the Department of Computer Science, KICT, IIUM, Kuala Lumpur.He holds a PhD, an MSc and a BSc, all in Computer Science. He was awarded a PhD fromDepartment of Computer Science, the Australian National University (ANU), Canberra, Australiain 2006. He has authored several research papers, a book on Intelligent Environment, severalchapters in a couple of books and has three patents pending to his credit in the area of pervasivecomputing. Teddy Mantoro is the corresponding author and can be contacted at:[email protected]

Akeem Olowolayemo is a Research Assistant at the INTEG, KICT, IIUM. He holds aBSc (Hons) Degree in Computer Science, from Obafemi Awolowo University Ile-Ife,Nigeria (2000), a Masters (MIT) Degree in Information Systems, from IIUM and is currentlypursuing his PhD (IT) at the same university. His research interests include Location Awareness,Machine Learning and Intelligent Environment.

Sunday O. Olatunji received the BSc (Hons) Degree in Computer Science, Ondo StateUniversity Ado Ekiti, Nigeria (1999), MSc Computer Science, University of Ibadan, Nigeria(2003), MS Degree in Information and Computer Science, King Fahd University of Petroleum andMinerals (KFUPM), Saudi Arabia (2008). He is currently pursuing his PhD in Computer Science.He is a member of ACM and IEEE. He has several years of experience as a lecturer of computerscience, and authored several research papers.

Media A. Ayu is currently a Researcher in the INTEG and a Senior Lecturer at theDeptartment of Information Systems, KICT, IIUM, Kuala Lumpur. He was awarded a PhD fromDepartment of Engineering, College of Engineering and Computer Science, the ANU, Canberra,Australia. She has authored several research papers, several book chapters and has three patentspending to her credit in the area of pervasive computing.

Abu Osman Md. Tab is currently a Researcher in the INTEG and a Professor in Mathematicsat the Department of Information Systems, KICT, IIUM, Kuala Lumpur. He was awarded a PhDfrom University of Birmingham, UK and MSc from Iowa State University, Ames, Iowa, USA.He has authored several research papers, several book and book chapters in the area of fuzzylogic and mathematics.

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