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  • 1. Ashish Dahatonde, Amutha Jaykumar, Pritish Bhutmanghe /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1876-1881 Vertical Handover Decision (VHD) Algorithms Analysis and Efficient Approach for VHD Ashish Dahatonde*, Amutha Jaykumar**, Pritish Bhutmanghe*** (Department of Electrical Engineering, VJTI(Matunga), Mumbai.)ABSTRACT In the fourth generation wireless handoff as heterogeneous networks have differentnetwork, the main objective is to facilitate characteristics and their performance cannot beseamless mobility of users between simply compared using the signal strength of twoheterogeneous networks while satisfying QoS cells. Other new metrics such as service type,requirements Vertical handover decision (VHD) system performance, network conditions, mobilealgorithms are essential components of the node conditions, user preferences etc . must bearchitecture of the fourth Generation (4G) considered. Another challenge is that the verticalheterogeneous wireless networks. These handoff may not only take place at the cellalgorithms need to be designed to provide the edge. It could occur at any time depending onrequired Quality of Service (QoS) to a wide range the network condition and user preference such asof applications while allowing seamless in a situation of network congestion. The decisionroaming among a large number of access to trigger a vertical handoff according to thenetwork technologies. In this study paper we are system performance and QoS parameters becomespresenting analysis of existing VHD algorithms the main part of vertical handoff processand presenting new prediction based approach [3].Therefore, an effective and efficient verticalfor vertical handoff decision. The prediction hand off decision algorithm is needed to improve thebased vertical handoff decision algorithm has system performance.been proposed based on mobility. For the There are many VHD algorithms are presented byproposed algorithm HMM (Hidden Markov various researchers, however those all algorithmsModel) predictor is applied which has been have not considered the mobility prediction method sutilized in this algorithm that can accurately to take proactive measures.estimate the next location to be visited by a In this paper we are presenting the theoretical studymobile user, given current and historical over the Handover mechanism VHD mechanisms andmovement information. This paper we discuss proposed the efficient HMM based VHD algorithm.the theoretical In below section 2 we will present the literature review o ver the various aspects related to theanalysis of this approach. handover mechanism in various networks as well as VHD. Section 3 present the related work doneKeywords - Horizontal Handover, HMM, Vertical on VHD. In section 4 we will present theHandover, WLAN, WIMAX, UMTS. proposed prediction based approach for VHD and its mathematical model further. I. Introduction The future wireless networks current II. Literature reviewtrend is to provide accessibility for connecting to 2.1 Introduction to Integrated Systemsany network anywhere and anytime [1]. In such The existing demand to somehow providesystem, user will be roaming among different higher data rate and seamless connectivity has ledwireless access a technology which is known as to the integration of two major communicationVertical Handoff/Handoff [2]. Several issues such as networks. The complementary characteristicshandoff metrics, handoff decision algorithms and present in Wireless local area network and cellularhandoff technologies are individually considered network, the integration becomes a promisingthey have management are to be studied in order trend for the future generation wireless networks.to achieve seamless handoff. In horizontal handoff 802.1 1n, 3G are the latest types of technologies inwhich occurs between similar accesses WLAN and Mobile networks respectively, that aretechnologies, the handoff decision is mainly based widely used. When these technologies areon Received Signal Strength (RSS) in the border individually considered they have advantages asregion of two cells. However, in vertical handoff, the well as disadvantages. By collective usage of thesituation is more The users in "hot-spot" areas will advantages of these two technologies, i.e. 3Gbe provided with high complex, compared to the supports wide coverage area and WLAN supportshorizontal handoff, the signal strength is high data transfer, quality of service can be improved.sometimes not sufficient to trigger the vertical 1876 | P a g e
  • 2. Ashish Dahatonde, Amutha Jaykumar, Pritish Bhutmanghe /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1876-1881The users in "hot-spot" areas will be provided a horizontal handover. For example, if a mobilewith high Cellular networks and when the user is user moves from one base station to base station ofoutside a hot spot coverage area, one can use the other area, then the mobile user of GSM networkcellular network. However, this is not a simple makes a horizontal handover. A horizontal handoverprocess to implement. is a traditional handover. In other words, theIn the study of [Modelling and Analysis of difference between vertical and horizontalHybrid Cellular/WLAN System with Integrated handover is that the vertical handover changes theService-Based Vertical Handoff Schemes], a access technology and the latter does not change [3].CDMA cellular system is considered along with In comparison with micro and macro mobility,IEEE 802.11 network. Bandwidths of cellular they are differentiated into subclasses such asnetwork and WLAN are Cc and Cw respectively. vertical and horizontal micro mobility, vertical andThe total system resources are shared by both data horizontal macro mobility. Vertical micro mobilityand voice calls in integrated system. Particular is the handover within the same domain usingchannels are assigned to voice calls and hence have different wireless technologies. Horizontal micromore priority over the data calls, in accessing the mobility is the handover among the same domainsystem resources. The unused b and width by current using the same wireless technology. Vertical macrovoice calls is shared by the ongoing data calls. mobility is handover among different domainsVertical and Horizontal handoffs are also given using different wireless technologies and horizontalpriority, accordingly as voice and data calls. To macro mobility is handovers within variousprioritize the handovers, the channel reservation domains, using same wireless technology.approach is used in the cellular network. Vertical The handoff process can be characterized as hardhandover voice calls are given the highest priority handoff or soft handoff. Before making a handoff ifamong both the handover calls by limiting the there is a break in the communication, it is referrednumber of accepted horizontal handover calls, as a hard handoff (brake before make) andwhen voice calls are greater than or equal to the whereas in soft handoff, there is a connection tothreshold. [2] both of the base stations for some time before making the handoff (make before break).2.2 Horizontal and Vertical Handovers in To enhance the capacity and QoS of cellularIntegrated Systems systems, efficient hand off algorithms are cost An essential element of cellular effective ways. In a horizontal handover, the maincommunications is Handoff. This chapter of the concern is to maintain the ongoing service even ifthesis gives a summary of handover and mobility the IP address changes because of the movement ofamong heterogeneous networks. When a mobile the mobile node. The ongoing service is donestation moves from one wireless cell to another either by dynamically updating the changed IPwireless cell, it is a Handoff (or handover). It is address or by hiding the change of IP address.classified as horizontal (intra-system) and vertical Vertical handover takes place when the mobile(inter- system). Vertical refers to the overlapping of node moves over heterogeneous access networks.wireless networks. With the help of a simple tale, the The used access technology is also changed alongproblem of vertical mobility can be illustrated. with the IP address in the vertical handover, asConsider a relay team of mouse and a rabbit. To carry the mobile nodes moves across different networksa carrot as fast as they can is the task. A mouse can which use different access technology. In suchgo far, but it cannot carry heavy loads. The cases, the main issue is to maintain the ongoingrabbit, in this example is restricted in the fence. In service even when there is a change not only in IPthe fence, it can carry a heavy load of carrots, but it address but also in network interfaces, QoShas to give the carrots to the mouse at the fence. The characteristics etc. [4]rabbit represents a WLAN, and the mouse a cellularnetwork. The event where the exchange of carrot The main capabilities of Vertical handovers overloads between rabbit and mouse is called hand off, Horizontal handovers are:more precisely vertical handoff. This process refers 1. Vertical handovers use different accessto transition from WLAN to cellular network and technology.vice versa. The carrot represents the payload, which 2. Vertical handovers use multiple networkis carried by mouse (cellular network) and the interfaces.rabbit (WLAN). Payload means data in terms of bits 3. Multiple IP addresses are used in Verticalor bytes, which is a part of bigger files. To make the handovers.communication seamless, the problem is to make best 4. QoS parameters can be changed in Verticalof mouse and rabbit carrying the carrot together. handovers and multiple parameters are used.The access technology changes in vertical handover. 5. Multiple network connections are used inA mobile node moves with the single technology Vertical handovers.network from one access point to the other one in 1877 | P a g e
  • 3. Ashish Dahatonde, Amutha Jaykumar, Pritish Bhutmanghe /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1876-18812.3 Integrated Serviced based Handoff (ISH) and when the queue Qw is full on the arrival of manyISHQ Handoff Schemes: requests, the requests are blocked. Service dependent handoff schemes areintroduced in the integrated system of 2.4 Vertical Handovercellular/WLAN. On the basis of whether the vertical Vertical handover is happened when ahandoff request can be queued or not, the service mobile node moves across heterogeneous accessschemes are of two types. Integrated service networks. Differently from horizontal handover, thebased handoff and integrated service based handoff used access technology is also changed as well aswith queuing capabilities [2]. These two schemes are IP address, because the mobile nodes movesexplained in detail in the section below. different access network which uses differenta. Integrated Serviced based Handoff (ISH) Scheme: access technology. In this case, the main concernIn this proposed ISH scheme, the only calls that of vertical handover is to maintain on-goingcan request admission to the cellular network are service although not only the change of IPoriginating voice calls from area A and a handoff addresses but also the change of networkvoice calls from its neighboring cells. If < , the interfaces, QoS characteristics, and etc. Inoriginating call from area A is accepted and if == , horizontal handover, which occur between similarthe call is rejected. Also if < , the handoff voice networks, the handover decision is mainly basedcall from the neighbouring cell is accepted and when on received signal strength (RSS) in the border== , it is rejected. From area B, a voice call will try to region of two cells. However, in vertical handover,access the cellular network, and if < , it is accepted. the situation is more complex, compared to theThe call will now go to WLAN when = = , and horizontal handover, the signal strength isin WLAN if < , it accepts the call and rejects if sometime not sufficient to trigger the verticalotherwise. For calls moving into B area, no handoff handover because of heterogeneous networks haveis executed fo r ongoing voice calls. A vertical different system characteristics and their performancehandoff would take place, when a voice call cannot be simply compared using the signal strengthwhich was accepted by the WLAN moves out of of two cells. Other new metrics such has serviceB area. In a cellular network, if < , the vertical type, system performance, network conditions, andhandoff voice calls can be accepted. mobile no de network. Therefore, the user can choose If < , the data call originating from area B will be the best access point with maximum bandwidth forallowed to access WLAN and if otherwise is rejected. connecting to the internet.Similarly, if < , the data call moving into area B is A handover process can be split into three stages:handed to the WLAN, and it remains in the cellular handover information gathering, handover decisionnetwork otherwise. And if < , the data call and handover execution [2].originating from area A and data vertical handover Handover Information Gathering: used to collectrequests to cellular network is accepted and all the information required to identify the needrejected otherwise. for handover and can subsequently initiate it. Itb. Integrated Serviced based Handoff With Queue can be called also handover initiation phase or(ISHQ) Scheme : system disco very.Voice calls are handled the same way in both the Handover Decision: used to determine whether andproposed schemes ISHQ and ISH. In ISHQ handover how to perform the handover by selecting thescheme, there are two queues Qc and Qw with and most suitable access network (taking into accountas their respective capacities. The queue Qc is for some criteria such as user preferences) and byhandling vertical handover requests of data to giving instructions to the execution phase. It is alsocellular networks and the queue Qw is for vertical called network or system selection.handoff requests and originating data calls that Handover Execution: used to change channelsare entering into the WLAN from area B. There conforming to the details resolved during the decisionmay happen three different probabilities depending phase.upon the arrivals to the queue. If < , the verticalhandoff requests to the cellular network is accepted. 2.5 VHD CriteriaIf = , the request will be queued in Qc , and if the Handover criteria are the qualities thatqueue Qc is full on the arrival of requests, the are measured to give an indication of whether orrequests will b e dropped . These requests in the no t a handover is needed. We can regroup differentqueue Qc will be served on the basis of first-in, first- criteria as follows:out (FIFO) basis once the channel becomes • Received signal strength (RSS) is the mostavailable. This data call request is then deleted from widely used criterion because it is easy toQc once it is handed over to the WLAN. Also if < , measure and is directly related to the servicedata vertical handoff requests to WLAN or data quality. There is a close relationshipcalls originating from area B are processed by the between the RSS readings and the distanceWLAN. If = these requests are queued in Qw and from the mo bile terminal to its point of 1878 | P a g e
  • 4. Ashish Dahatonde, Amutha Jaykumar, Pritish Bhutmanghe /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1876-1881 attachment. Majority of existing horizontal plus dwelling timer method [5 , 6]. Relative RSS handover algorithms use RSS as the main is not applicable for VHD, since RSS from decision criterion, and RSS is an important different types of networks cannot be compared criterion for VHD algorithms as well. directly due to the disparity of the technologies • Available b and width is a measure of involved . In RSS with hysteresis method, handoff available data communication resources is performed whenever the RSS of new Base station expressed in bit/s. It is a good indicator of (BS) is higher than the RSS of old BS by a predefined traffic conditions in the access network value. In RSS with hysteresis plus dwelling timer and is especially important for delay-sensitive method, whenever the RSS of new BS is higher applications. than the RSS of old BS by a predefined hysteresis, • Network connection time refers to the a timer is set. When it reaches a certain specified duration that a mobile terminal remains value, handoff is processed. This minimizes Ping connected to a point of attachment pong handoffs. But other criteria have not been determining the network connection time is considered. very important for choosing the right In bandwidth based algorithms, the available moment to trigger a handover so that the bandwidth for a mobile terminal is the main service quality could be maintained at a criteria. In [7], a bandwidth based VHD method is satisfactory level. presented between WLANs and a WCDMA For example, a handover done too early fro network using Signal to Interference and Noise m a WLAN to a cellular network would ratio (SINR). It provides higher throughput than waste network resources while being too late RSS based handoffs since the available bandwidth would result in a handover failure. is directly dependent on the SINR. But it may • Cost: For different networks, there would introduce excessive handoffs with the variation of be different charging policies, therefore, in the SINR. These excessive handoffs are reduced some situations the cost of a network service by a VHD heuristic based on the Wrong Decision should be taken into consideration in making Probability (WDP) prediction [8]. The WDP is handover decisions. calculated by combining the probability of • Power consumption becomes a critical issue unnecessary and missing handoffs. This algorithm is especially if a mobile terminal’s battery is able to reduce the WDP and balance the traffic load. low. In such situations, it would be preferable But in both the papers, RSS is not considered. to handover to a point of attachment A hand off to a target network with high which would help extending valuable battery bandwidth but weak received signal is not life. desirable as it may result in breakdown of • Security: For some applications, connection. In user mobility based algorithms, confidentiality or integrity of the velocity information is a critical one for handoff transmitted data can be critical. For this decision. In the overlay systems, to increase the reason, a network with higher security level system capacity, micro/pico cells are assigned for may be chosen over another one which slow moving users and macro cells are assigned would provide lower level of data security. for fast moving users by using velocity information • User preferences: A user’s personal [9]. It decreases the number of dropped calls. An preference towards an access network could improved handoff algorithm [10] has been lead to the selection of one type of network presented to reduce the number of unnecessary over the other candidates. handoffs by using location and velocity information estimated from GSM measurement data of different III. Related Work on VHD signal strengths at MS received from base stations. Research on design and implementation From these papers, it is seen that velocity and locationof Vertical Handoff Decision (VHD) algorithms has information are also having great effectbeen carried out by many scholars using various on handoff management. Therefore they should betechniques. Based on the handoff decision criteria, taken into account in order to provide seamlessVHD algorithms are categorized as RSS based handoff between heterogeneous wireless networks.algorithms, Bandwidth based algorithms, User Cost function based algorithms combine metricsMobility based algorithms and Cost function such as monetary cost, security, powerbased algorithms. consumption and bandwidth in a cost function.In RSS based algorithms RSS is used as the main The handoff decision is made by comparing thecriteria for decision in this group . Various result of this function for the candidate networksschemes have been developed to compare RSS of the [11, 12, and 13]. Different weights are assigned tocurrent p oint of attachment with that of the different input metrics depending on the networkcandidate point of attachments. They are: Relative conditions and user preferences.RSS, RSS with hysteresis, and RSS with hysteresis 1879 | P a g e
  • 5. Ashish Dahatonde, Amutha Jaykumar, Pritish Bhutmanghe /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1876-1881A dynamic decision model (DDM) [14] has been We are using the HMM model for selection ofproposed to decide the best network at best moment optimal BS. In its discrete form, a hidden Markovfor handoff. The decision model makes the right process can be visualized as a generalization ofvertical handoff decisions by determining the best the Urn problem: For example, in a room whichnetwork among available networks based on, the not at all visible to an observer there is a genie.factors such as RSS of network and velocity of mobile The room contains urns X1, X2, X3 ... each of whichstation along with static factors like Usage contains a known mix of balls, every ball is labeledExpense, Link capacity (offered bandwidth) and with y1 , y2, y3 ... The genie selected an urn in thatpower consumption. This model not only meets the room as well as randomly draws a ball from thatindividual user needs b ut also improve the whole urn. Afterwards it puts that ball into conveyor beltsystem performance by reducing the unnecessary in which the observer can senses the sequence ofhandoffs. A trajectory-aware handoff algorithm [15] the balls however not the sequence of urns frommakes the decision based on position, velocity, which they were drawn. There is some process for thesignaling delay, and RSS of mobile station. In this genie in order to choose urns; the urn choice for the n-algorithm, velocity of MS is divided into two parts th ball basically depends only upon a randomas radial velocity and tangential velocity. For number and the choice of the urn for the (n - 1)-more precise handoff initiation, tangential velocity th ball. The urn selection doesn’t depends directlyof MS is neglected, and only radial velocity of over urns this single previous urn; and hence, this isMT is considered in handoff decision making. called as Markov process. This process isMoreover, before handoff decision, least square line presented in below figure 1.method is applied to RSS of MS to avoid unnecessaryback-and-forth handoffs (ping-pong handoffs)between different services. All the abovealgorithms have not considered the mobilityprediction methods to take proactive measures. IV. HMM Based VHD: Proposed Approach Thus according to problem stated in abovesection, in this project we are presenting the newalgorithm based on mobility prediction. A methodof mobility prediction, i.e., predicting a mobile Figure 1: Probabilistic parameters of a hiddennode’s next location based on Hidden predicting a Markov model ( example)mobile node’s next location based on Hidden x — statesMarkov Model (HMM) has been proposed. HMM y — possible observationspredictor can accurately estimate the next location a — state transition probabilitiesto be visited by a mobile no de, when the current b — output probabilitiesand historical movement information is available.In this prediction method, it has been assumedthat the MN is moving and able to regularly send V. Performance Metricsits physical position to the serving BS. Once the For the evaluation of Vertical handoverMN position has been determined , if a MN is likely decision approaches we have to majorly focusto perform a handover, the serving BS triggers the over the use of following performance metrics.Handoff decision control process. This case always • Handover delay: It refers to the periodhappens in the heterogeneous networks like between the initiation and completion of theUMTS, WiMAX, WI-FI, WLAN. handover method. Hand over delay isA proactive handoff technique has been developed expounded to the complexness of the VHDin which the Handoff Decision Controller (HDC) method, and reduction o f the handover delay iscollects the following factors from the particularly necessary for delay-sensitive voiceneighbouring attachment points (AP or BS): Current or multimedia system sessions.Network Load, Strong RSS and Power • Range of handovers: Reducing the amount ofconsumption of using the network access device. A handovers is typically most well-liked ascombined weight value has been calculated . Based frequent handovers would cause wastage ofon these values the priorities are assigned to network resources.networks and MS can handoff to a higher priority • Handover failure probability: A handovernetwork. failure occurs once the happens is initiatedFinding the optimal BS from the network for however the target network doesnt haveVertical handover is NP-complete problem: comfortable resources to complete it, or once the mobile terminal moves out of the 1880 | P a g e
  • 6. Ashish Dahatonde, Amutha Jaykumar, Pritish Bhutmanghe /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1876-1881 coverage of the target network before the Networks and Ap plicatio ns 11 (4) (20 method is finalized. Within the former case, 06)625–640. the handover failure chance is expounded to the [5] S. Mohanty, I.F. Akyildiz, A cross -layer channel availableness of the target network, (layer 2 + 3) handoff management protocol whereas within the latter case its associated for next-generation wireless systems, IEEE with the mobility o f the user [3]. Transactions on Mobile Computing 5 (10) • Throughput: The throughput refers to the (2006) 1347–1360. info rate delivered to the mobile terminals on [6] K. Yang, I. Gondal, B. Qiu, L.S. Dooley, the network. Handover to a network Combined SINR based vertical handoff candidate with higher throughput is algorithm for next generation heterogeneous typically fascinating. wireless networks, in: Proceedings o f the 2007 IEEE Global Telecommunications VI. Conclusion and Further Work Conference (GLOBECOM’07), Washington, In this literature paper, we have studied DC, USA, November 2007, pp. 4483–4487.the problems associated the vertical handovers. We [7] C. Chi, X. Cai, R. Hao, F. Liu. Modeling andhave presented the literature survey over the analysis of handover algorithms, in:handover concepts in details. Further we presented Proceedings of the 2007 IEEE Globalthe related works done over the VHD approach. Telecommunications ConferenceThe new solution is presented to overcome the (GLOBECOM’07), Washington, DC,USA,issues associated with existing methods of VHD. November 2007, pp. 4473–4477.This approach is based on use of HMM [8] Xiao.C, K.D.Mann and J.C.Olivier,2001,prediction model. A HMM predictor has been used Mobile speed estimation for TDMA-basedwhich accurately estimates the next location visited hierarchical cellular systems, Proc.Trans.by a mobile user, given current the received Veh.Techno l,50, 981-991.signal strength values of the MNs. The home AP [9] Juang.R.T, H.P.Lin and D.B.Lin,2005, Anthus predicts the list of possible APs in the improved location-based handover algorithm formovement direction of a mobile node and send s GSM systems, Proc of wirelessa request to the predicted APs. The current communications and networking conference,Network Load, Strong RSS and Power consumption Mar.13-17 , pp-1371-1376.are estimated in each AP. These APs after [10] F. Zhu, J. McNair, Optimizations for verticalcalculating combined weight value, sends it back to handoff decision algorithms, in: Proceedingsthe home AP. The home AP then selects an optimum of the 2004 IEEE Wireless CommunicationsAP for the MN to perform handover, based on the and Networking Conference (WCNC’04),sorted weight values. The information about the Atlanta, Georgia, USA, March 2004, pp.selected APs, are sent to the 867– 872.mobile user so that the user can move to that [11] F. Zhu, J. McNair, Multiservice verticalparticular AP. For the future work we will work handoff decision algorithms, EURASIPon practical impacts and simulation studies of this Journal on Wireless Communications andapproach and presents its comparative study in Networking 2006 (2) (2006) 52.terms of above defined performance metrics. [12] N. Nasser, A. Hasswa, H. Hassanein, Handoffs in fourth generation heterogeneousReferences and Bibliography networks, IEEE Communications Magazine 44[1] Q.-T. Nguyen-Vuong, N. Agoulmine, Y. (10) (2006) 96– 103. Ghamri- Doudane, Terminal controlled [13] N. Nasser, S. Guizani, E. Al-Masri, mobility management in heterogeneous Middleware vertical handoff manager: a wireless networks, IEEE Communications neural network-based solution, in: Proceedings Magazine 45 (4) (2007) 122–129. of the 2007 IEEE International Conference[2] W. Wang, Mobility management in next- on Communications (ICC’07), Glasgow, generation wireless systems, Proceedings of the Scotland, June 2007, pp. 56 71– 5676. IEEE 87 (8) (1999) 1347– 1384. [14] Thazin Ei and Furong Wang, A trajectory –[3] F. Barcelo, Performance analysis of handoff aware handoff algorithm based on GPS resource allocation strategies through the information , SpringerLink 2009 state-dependent rejection scheme, IEEE [15] B.Amutha and M. Ponnavaikko Energy Transactions on Wireless Communications fficient Hidden Markov Mo del Based Target 3(3) (2004) 900– 909. Tracking Mechanism in Wireless Senso r[4] A.H. Zahran, B. Liang, A. Saleh, Signal Networks Journal of Computer Science threshold adaptation for vertical handoff in 5(12): 1085-1093, 2009 ISSN 1549 -3636, heterogeneous wireless networks, Mobile 2009 Science Publication 1881 | P a g e