Survey on Vertical Handoff Decision

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1 urvey on Vertcal Handoff Decson.wedaa 1, I.Veronca Judth Joyce 2, J.Jayakumar 3 P.G. tudent, Department of Electroncs and Communcaton Engneerng, t.joseph's College of Engneerng, Chenna, Inda 1,2,3 ABTRACT: A Vertcal Handoff (VHO) or nter-system handoff s the process that occurs between attachment ponts supportng the dfferent network technologes. Vertcal handoff decson plays very mportant role n selecton of best network. Ths paper provdes a lterature revew on varous vertcal Handoff Algorthms such as R based algorthm, Cost functon Based Algorthm, Bandw Based Algorthm, MADM algorthm etc. KEYWORD: Vertcal Handoff; R; MADM; Bandw. I. INTRODUCTION The wreless technologes durng a heterogeneous wreless network are typcally completely dfferent from each other, from a technologcal purpose of read. Most of them typcally dsagree n terms of, however not restrcted to, ther offered bandws, operatonal frequences, costs, coverage areas, and latences. Currently, no sngle wreless technology provdes effcent servces, hgh bandws and low latences to any or all moble users durng a massve coverage space. ths can be wherever the requrement for well-organzed Vertcal Handoffs (VHO) between heterogeneous wreless technologes becomes necessary. A. Vertcal Handoff Process The vertcal handoff process [1] can be dvded nto three man steps, namely handoff ntaton, handoff decson, and handoff executon )Handoff Intaton Phase - so as to trgger the handoff occason, data to be gathered about the system from varous layers lkes Lnk Layer, Transport Layer and Applcaton Layer. These layers gve the data, for example, R, transmsson capacty, jon speed, throughput, jtter, cost, power, clent nclnatons and system membershp and so forth. In vew of ths data handoff wll be started n a fttng tme. )Handoff Decson Phase - The cell phone chooses whether the assocaton wth be proceeded wth current system or to be changed over to another. The choce mght rely on upon dfferent parameters whch have been gathered amd handoff start stage. )Handoff Executon Phase - Exstng afflatons ought to be re-guded to the new framework consstently. Ths stage also jons the acceptance and endorsement, and the tradng of customer's assocaton nformaton. B. Vertcal Handoff crera and Metrcs In heterogeneous systems, Vertcal handoffs can be started for comfort as opposed to network reasons. The decson may depend on varous groups of parameters such as, () Network- Related Parameters - Bandw, Latency, Recever sgnal strength (R), Cost, ecurty etc. () Termnal Related Parameters - Velocty, Battery, power, Locaton Informaton etc. () User-Related Parameters - user profle and preferences, (v) ervce Related Parameters - servce capactes, Qo etc. C. Classfcaton of Vertcal Handoff () R based algorthms - R s used as the man handover decson crteron n ths group. Varous strateges have been developed to compare the R of the current pont of attachment wth that of the canddate pont of attachment. Copyrght to IJIRET DOI: /IJIRET

2 () Bandw based algorthms - Avalable bandw for a moble termnal s the man crteron. In some algorthms, both bandw and R nformaton are used n the decson process. Dependng on whether R or bandw s the man crteron consdered, an algorthm s classfed ether as R based or bandw based. () Cost functon based algorthms - Ths class of algorthms combne metrcs such as monetary cost, securty, bandw and power consumpton n a cost functon, and the handover decson s made by comparng the result of ths functon for the canddate networks. (v) Combnaton algorthms - These VHD algorthms attempt to use a rcher set of nputs than the others for makng handover decsons. When a large number of nputs are used, t s usually very dffcult or mpossble to develop analytcal formulatons of handover decson processes. Due to ths reason, researchers apply machne learnng technques to formulate the processes. (v) Multple Attrbutes Decson Makng Based Algorthms - The multple attrbutes decson makng based algorthm (MADMA) calculates the quanttatve value of each normalzed attrbute and evaluates the target systems through the weghted functon of the quanttatve values, the fnal decson can then be made. Ths report s organzed as follows: ecton II descrbes varous Vertcal Handoff Algorthm by dfferent authors and fnally concluson s presented n secton III. II. VERTICAL HANDOFF ALGORITHM A. R Based Algorthms R s used as the man decson crteron n ths group. A large number of studes have been conducted n ths area. ome R based VHO algorthms are dscussed below: () An Adaptve Lfe Tme Based Handoff Heurstc Zahran et al (2006) [6] proposed an algorthm for handoff between 3G networks and WLANs by combnng the R measurements ether wth an estmated lfetme (expected duraton after whch the moble staton wll not be able to mantan ts connecton wth the WLAN) or the avalable bandw of the WLAN canddate. In the frst scenaro, when the M moves away from the coverage area of a WLAN nto a 3G cell, a handoff to the 3G network s ntated. The handoff s trggered under the condtons that (a) R average of the WLAN connecton falls below a predefned threshold, and (b) the estmated lfetme s less than or equal to the handoff delay. The M contnuously calculates the average R usng the movng average method W av 1 av 0 R ( k) 1/ W R( k ) (2.1) R (k) s the calculated average of R at tme nstant k. W av s the wndow sze of a slope estmator, a varable that changes wth the velocty of the M. In the second scenaro, when the M moves towards a WLAN cell, the handoff to the WLAN s ntated f (a) the average R measurements of the WLAN s larger than a threshold and (b) the avalable bandw of the WLAN meets the bandw requrements of the applcaton. nce the lfetme metrc and bandw are consdered, the algorthm adapts to the applcaton requrements and the user moblty and also the number of unnecessary handoffs s reduced. There s an mprovement n throughput for the user, because of the M s ablty to reman connected to the WLAN as long as possble. However, Packet delays can be ncreased wth an ncrease n the lfe tme, due to the deteroraton of the channel condton, as the M moves towards the boundary of the WLAN. Ths ssue can be crtcal for delay senstve applcatons and degrade ther performance. Copyrght to IJIRET DOI: /IJIRET

3 () An R Threshold Based Dynamc Heurstc Mohanty & Akyldz (2006) [5] proposed a handoff decson method from WLAN to 3G based on comparson of the current R and a dynamc R threshold ( connected to WLAN access pont. Where Rmn (n dbm) s calculated as ) when the M s d R mn 10 log (2.2) d LBA s the mnmum R requred for the M to communcate wth an access pont, s the path loss L coeffcent, d s the sde length of WLAN n meters, BA s the shortest dstance between the pont at whch handoff s ntated and WLAN boundary and s the zero-mean random varable wth a standard devaton representng statstcal varaton n R caused by shadowng. The dstance BA depends on desred handoff falure probablty, velocty of the moble staton and WLAN to 3G handoff delay. The use of a dynamc R threshold helps to reduce the false handoff ntaton and handoff falures. But ths algorthm s not effcent when the M s travelng tme nsde a WLAN s less than handoff delay. In such cases a handoff results n wastage of network resources. B. Bandw Based VHD Algorthms Avalable bandw for a moble staton s the man crteron n ths group. In some algorthms, both bandw and R nformaton are used n the decson process. The algorthms are dscussed below: () Bandw And Applcaton Type Based Heurstc Lee et al (2005) [8] dscussed an algorthm whch takes resdual bandw and applcaton requrements nto account n decdng whether to handoff from WLAN to WWAN and vce versa. When the M s connected to a WLAN, the handoff s ntated f the measured R s less than R threshold. The handoff decson s based on the user applcaton type. For delay senstve applcatons, a handoff occurs only f the current servng WLAN s not able to provde necessary bandw. For delay nsenstve applcatons, a handoff takes place f WWAN provdes hgher bandw than WLAN. By consderng the avalable bandw as the man VHD crteron, ths algorthm s able to acheve hgh system throughput and by takng applcaton types nto account, lower handoff delay for delay senstve applcatons s acheved. However, acqurng the avalable bandw nformaton n a cellular network for handoff decson s dffcult. () A gnal-to-interference and Nose Rato (INR) Based Heurstc Yang et al (2007) [7] presented an algorthm whch nvolves handoff between WLAN and Wdeband Code Dvson Multple Access (WCDMA) network usng gnal to Interference and Nose rato. If INR target > INR current, then handoff s ntated. Based on bandw avalable, the handoff takes place. INR based handoffs provde hgher throughput than R based handoff snce the throughput drectly depends on INR. Ths algorthm provdes balanced load between WLAN and WCDMA networks. Ths algorthm ntroduces excessve handoffs wth the varaton of INR causng the M to handoff back and forth between two networks. () A Wrong Decson Probablty (WDP) Predcton Based Heurstc In the work presented by Ch et al (2007), [8] the WDP s calculated by combnng the probablty of unnecessary and mssng handoffs. Assume that there are two networks and j wth overlappng coverage, and b and bj are ther avalable bandws. An unnecessary handoff occurs when the M s n network and decdes to handoff to j, but bj s less than b after ths decson. A mssng handoff occurs when the M decdes to stay connected to network, but b s less than bj after ths decson. L Copyrght to IJIRET DOI: /IJIRET

4 WDP algorthm avods ths knd of problem. A handoff from network to network j s ntated f p l 0 or b b L, where p s unnecessary handoff probablty, s traffc load of the network, l0 j =0.001 and L s a bandw threshold. Therefore, ths algorthm reduces wrong decson probablty and balances the traffc load. But R s not consdered n ths algorthm. A handoff to a target network wth hgh bandw but weak receved sgnal s not desrable as t results n connecton breakdown. C. Mult Attrbute Based Decson Algorthms Multple Attrbute Decson Makng algorthms are used for network rankng. They nclude mple Addtve Weghtng (AW), Technque for Order Preference by mlarty to Ideal oluton (TOPI), Analytc Herarchy Process and Grey Relatonal Analyss (AHP and GRA), Multplcatve Exponent Weghtng (MEW) and Elmnaton and Choce Translatng Prorty (ELECTRE) as gven n Zhang [6] (2004). () AW and TOPI In AW, the overall score functon of a canddate network s determned by the weghted sum of all the parameter values. The score functon of each canddate network s obtaned by addng the normalzed contrbutons from each parameter r j multpled by the mportance weght assgned w j of parameter j. The selected network A AW s: N A AW arg max wjrj (2.6) M j 1 Where N s the number of parameters and M denotes the number of canddate networks. In TOPI, the selected canddate network s the one whch s the closest to the deal soluton. The deal soluton s obtaned by usng the best values for each parameter. Let C denote the relatve closeness of the canddate network to the deal soluton. The selected network A TOP arg maxc M A TOP s: (2.7) () GRA The network selecton s decded based on Analytc Herarchy Process and Grey Relatonal Analyss. AHP decomposes the network selecton problem nto several problems and assgns a weght value for each sub-problem. GRA s then used to rank the canddate networks and selects the one wth the hghest rankng. The rankng of GRA s performed by buldng grey relatonshps wth a postve deal network. A normalzaton process to deal wth beneft and cost parameters s requred and the Grey Relatonal Coeffcent (GRC) of each network s calculated. The GRC s the score used to descrbe the smlarty between each canddate network and the deal network. The selected network s the one whch has the hghest smlarty to the deal network. The selected network A s: GRA Where A arg max 0, GRA M 0, s the GRC of network. D. Combned Algorthm Combnaton algorthms are based on artfcal neural networks or fuzzy logc, and combne varous parameters n the handoff decson such as the ones used n the cost functon algorthms. Many combnaton algorthms are proposed. (2.8) Copyrght to IJIRET DOI: /IJIRET

5 () A Fuzzy Logc Based Heurstc A Fuzzy MADM based numercal soluton for vertcal handoff decsons was frst ntroduced by Zhang [6] (2004), where mprecse, or fuzzy data n terms of Lngustc Varables s used to specfy network parameters and user preferences n the form of weghts. These Lngustc Varables are frst converted nto crsp numbers usng a fuzzy number converson scale and then classcal MADM methods lke AW and TOPI are appled to voce and Background traffc. The results ndcate that TOPI s more senstve to user-preferences and network-parameter values, and that AW gves relatve conservatve rankng results. () A Fuzzy Multple Objectve Decson Makng Algorthm In the paper publshed by Chan et al (2002), the authors demonstrate the use of fuzzy logc together wth AHP. Fuzzy Logc s used to calculate the membershp values of each parameter measured from dfferent networks whle AHP s used to determne the weghts assocated wth these parameters (data rate, usage cost, battery, latency, etc.). These weghts are used to evaluate the mportance of each network parameter based on the network-provder s and the endusers preferences. The objectve of ths scheme s to select a wreless network for a partcular servce that can satsfy end-users preferences such as low cost, good R, optmum bandw, low network latency, hgh relablty, and long battery lfe. III. CONCLUION In ths paper,varous Vertcal Handoff algorthm has been revewed from the most recent publshed research work. IV. ACKNOWLEDGEMENT we would lke to express our grattude to Head of the Department Mrs.B.Vctora Jancee M.E.,(Ph.D) who has been provdng us encouragement for the successful completon of ths project. we also very grateful to our Internal Gude Dr..Aghalya M.E., Ph.D.who has been provdng us valuable gudance, deas and encouragement for successful completon of ths project. REFERENCE [1] Heterogeneous Wreless Networks:" Heterogeneous-Wreless-NetworksNetworkng"-Protocol/dp/ [2] W. Qadeer, T. munc, J.Ankcorn, V. Krshnan and G. De Mchel, Heterogeneous wreless network management, prngerlnk [3] We hen and Qng-An Zeng, A Novel Decson trategy of Vertcal Handoff n Overlay Wreless Networks, Ffth IEEE Internatonal ymposum on Network Computng and Applcatons, [4] Enrque tevens-navarro, Vncent W.. Wong and Yuxa Ln, A Vertcal Handoff Decson Algorthm for Heterogeneous Wreless Networks, In Proc. of IEEE Wreless Communcatons and Networkng Conference (WCNC'07), Hong Kong, Chna, March [5]. Mohanty, I.F. Akyldz, "A cross-layer (layer 2 + 3) handoff management protocol for next-generaton wreless systems", IEEE Transactons on Moble Computng 5 (10) (2006) [6] A.H. Zahran, B. Lang, A. aleh, "gnal threshold adaptaton for vertcal handoff n heterogeneous wreless networks", Moble Networks and Applcatons 11 (4) (2006) [7] K. Yang, I. Gondal, B. Qu, L.. Dooley, "Combned INR based vertcal handoff algorthm for next generaton heterogeneous wreless networks", n: Proceedngs of the 2007 IEEE Global Telecommuncatons Conference (GLOBECOM 07), Washngton, DC, UA, November 2007, pp [8] C. Ch, X. Ca, R. Hao, F. Lee. "Modelng and analyss of handover algorthms", n: Proceedngs of the 2007 IEEE Global Telecommuncatons Conference (GLOBECOM 07), Washngton, DC,UA, November 2007, pp [9] Xao.C, K.D.Mann and J.C.Olver,2001, "Moble speed estmaton for TDMA-based herarchcal cellular systems", Proc.Trans. Veh.Technol,50, [10] Juang.R.T, H.P.Ln and D.B.Ln,2005, "An mproved locaton-based handover algorthm for GM systems", Proc of wreless communcatons and networkng conference, Mar.13-17, pp [11] Hasswa, N. Nasser, H. Hassanen, Tramcar: a context-"aware crosslayer archtecture for next generaton heterogeneous wreless networks", n: Proceedngs of the 2006 IEEE Internatonal Conference on Communcatons (ICC 06), Istanbul, Turkey, June 2006, pp [12] R. Tawl, G. Pujolle, O. alazar, "A vertcal handoff decson scheme n heterogeneous wreless systems", n: Proceedngs of the 67th Vehcular Technology Conference (VTC 08 prng), Marna Bay, ngapore, Aprl 2008, pp X. Yan et al. / Computer Network. Copyrght to IJIRET DOI: /IJIRET