Vol 06, Article January 2015 International Research Journal of Mobile and Wireless Communications - IRJMWC ISSN:

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1 146 Improvised Handover Mobility Management using Multi-Criteria Metrics in Heterogeneous Wireless Network Platform SALAVADI ANANDA KUMAR 1, K.E.SREENIVASA MURTHY 2 1 Research Scholar Jawaharlal Nehru Technological University, Hyderabad, India 2 Professor Department of ECE, Adishankara College of Engineering & Technology, Nellore, India 1 anand.80.kumar@gmail.com, 2 kesmurthy@rediffmail.com ABSTRACT Vertical handover is essential to ensure service continuity in a heterogeneous network. Conventionally, a mobile user may roam and accomplish the vertical handover using single criteria, such as received signal strength (RSS). Single criteria vertical handover decision, however, has several drawbacks. It may cause inefficient handoff, unbalanced network load and service interruption. This paper proposed an improved vertical handover decision using multi-criteria metrics in the environment of heterogeneous network consists of three network interfaces: (i) Wireless Local Area Network (WLAN), (ii) Wideband Code Division Multiple Access (WCDMA) and (iii) Worldwide Interoperability for Microwave Access (WiMAX). In the vertical handover decision, four metrics are considered: (i) RSS, (ii) mobile speed, (iii) traffic class and (iv) network occupancy. Compared to conventional method, multi-criteria vertical handover decision algorithm provides higher performance in terms of number of handoff, balance index and average blocking probability.. Keywords: vertical handover, vertical handover algorithm, heterogeneous network, multi-criteria 1. INTRODUCTION Wireless networks allow a more adaptable communication than the progressive wire line networks because the user is not restricted to fixed position. The growing demand for high speed, bandwidth, low latency and data access at anytime, anywhere and any service are decisive for suggesting the next generation wireless access networks. In the near future, some urban areas will be served by a mix of overlapping signals reaching different distances (signals, for example, from IEEE a/b/g/n (Wi-Fi), IEEE (WiMAX), High-speed Downlink Packet Access (HSDPA), Long Term Evolution (LTE) can interoperate in order to always offer the best services, everywhere and at any time according to the always-best connected paradigm. Fig. 1 presents an illustration of heterogeneous network architecture. Certain network has unique characteristics, and heterogeneous network combines the advantages of each network to provide better service in terms of coverage, capacity and link performance. Figure 1: Heterogeneous Network Table.1 for four heterogeneous technologies Technology(standar ds) Data rate(bandwidth) Frequency Bandwidth Transmission carrier frequency Transmission carrier frequency WiMAX Up to 46Mbps in down link and 7Mbps in uplink 5MHz,8.75MHz,10M Hz and 20MHz 2.3GHz,2.5GHz and 3.5GHz 3-10 Km for outdoor,50 Km with fixed WiMAX 2.4GHz, 5GHz 30 mts indoor and 300 mts outdoor Wi- Fi(WLAN) Up to 100 Mbps in down link and 20 Mbps in uplink 20MHz 3G- WCDMA Up to 4.Mbps in downlink and 1.8 Mbps in Uplink 1.25 MHz 800, ,1900MH z 1-4 km Mobility Middle-High Low High The main benefit of heterogeneous networks is the effective utilization of available bandwidth to meet demands for high performance applications such as multimedia, video, video-conferencing, global mobility and service portability. Users with multi-mode mobile terminal can select the specific network from the different Radio Access Networks (RAN). For the heterogeneous networks handover scenario, we consider the MS roams over

2 147 WLAN, WiMAX and 3G hybrid networks. The table below shows the comparison table for 4 networks with their standards and technologies. A technique based on optimized adaptive handover triggering mechanism has been proposed in [1]. The proposed scheme efficiently minimized the network load to avoid link failure. Moreover, the proposed scheme maximizes the resource utilization and hence an MN can use the network with full potential. The schemes in [2] use the concept of adapt-or-handover for balancing the multimedia traffic during a handover process. The proposed scheme saves energy which is consumed due to the insignificant degradation in quality. The scheme obtains the information of available networks and on the basis of these networks the MN selects one of the appropriate networks for current multimedia streaming. A. Problem statement There are issues to be addressed in vertical handover decision: 1. First, the algorithm should have the reliability as inaccurate vertical handover decision may cause the excessive usage of network resource. 2. Second, the algorithm should have the function as a network balancer. The vertical handover decision algorithm should provide accuracy to balance the traffic load for all involved network. 3. Third, the algorithm should be accurate that it may reduce the network blocking probability. Multi-criteria decision making is an appropriate method for vertical handover decision because there are more than one target network as the decision alternatives. Furthermore, multi -criteria decision making provides flexibility to consider several criteria to decide the best networks. 2. RELATED WORK Various approaches have been developed and proposed in order to facilitate and to improve the vertical handover decision. Generally, it may be classified into five categories: (i) RSS-based, (ii) multi-criteria, (iii) context-aware, (iv) cost function and (v) fuzzy logic. RSS-based method is a conventional handover decision algorithm which uses RSS as the handover trigger [3] and as the main criteria to decide handover [4]. In [5] Taehoon Kim et al. proposed an algorithm that was based on service history. They proposed vertical handover decision algorithm reduces the handoff dropping probability, number of handoffs, and reduces the cost. Y. Wu et al. [6] proposes a traffic/load aware handoff algorithm for multi network wireless environment. Their algorithm provides users a seamless mobility between cellular network & ad hoc network as compared to received signal strength based traditional algorithms. Their simulation result shows a lesser call drop rate as compared to traditional signal strength based handoff during the handoff procedure. In [7] Racha Ben Ali et al. proposed a vertical handover decision algorithm which considers multi region mobility model. The proposed region prevents degradation in quality of service for voice traffic during handoff. In [8] Manoj Sharma, R.K. Khola proposed a vertical handover algorithm in which they consider quality of service, bandwidth and cost as input parameters for handover decision. They use TOPSIS method to rank the available networks and based upon rank the optimal networks was selected. In most cases, RSS-based method has the lowest complexity compared to other methods, even though the accuracy of RSS-based method may be the least. On the contrary, high complexity methods such as fuzzy logic and cost function provide higher accuracy and network efficiency. There are extensive works on multi-criteria vertical handover decision algorithm. Multi-criteria method has an ability to make quantitative calculation on decision using several criteria between several candidates [9]. The methods of Multiplicative Exponent Weighting (MEW), Simple Additive Weighting (SAW), Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and Grey Relational Analysis (GRA) [10] are compared and their performance (in terms of handover delay) is evaluated [11]. In multi-criteria vertical handover decision, the chosen criteria have to be appropriate to ensure the accuracy of the decision. 3. PROPOSED METHODOLOGY In this study, heterogeneous network consists of WLAN, WCDMA and WiMAX, as illustrated in Figure 2. The cell radius of WLAN is 700 m, WCDMA 2.3 km and WiMAX 5 km. WLAN covers 78.54% of the simulation area, meanwhile WCDMA covers 66.48% and WiMAX covers 75.43%. There are different propagation models for each type of network (WLAN, WCDMA and WiMAX. For WiMAX network, Empirical WiMAX propagation model is used to calculate the coverage dimensioning. Ao is db measured at do = 200 m. Path loss exponent, is Lower value of path loss exponent represents the more Line of Sight (LoS) propagation. In WCDMA network, the network propagation model follows COST 231 The COST 231 Model is the most sophisticated empirical model. All walls intersecting the direct ray between transmitter and receiver are

3 148 considered and for each wall individual material properties are taken into account. Walfish-Ikegami model as it is a standard model for 3G IMT 2000/UMTS. Figure 2: Network Topology Path loss arises when an electromagnetic wave propagates through space from transmitter to receiver. The power of signal is reduced due to path distance, reflection, diffraction, scattering, free-space loss and absorption by the objects of environment. It is also influenced by the different environment (i.e. urban, suburban and rural). Variations of transmitter and receiver antenna heights also produce losses. General classification includes three forms of modeling to analyze these losses. where d is distance from base station to mobile user in km, and is operating frequency in MHz The One Slope Model is very fast, because it depends only on the distance r between transmitter and receiver. The only parameter which is considered is therefore the path loss exponent. Empirical one-slope model is used as the propagation model for WLAN with formula as follow: Lo is reference loss value for the distance of 1 m. is pathloss exponent, and d is distance in meters. For operating frequency 2.45 GHz, Lo is 40 db and is 3.5. The timetrequired by MN to remain connected to an AP/BS with a speed V is shown by following equation as (4) Where is the diameter of a serving cell. Diameter is equal to the double of the radius; hence (4) becomes t=2. (5) The radius of the coverage area of AP/BS is not exactly circular and thus the propagation of signals at one direction is different from another direction. Thus to avoid changes of RSS in one direction from another we use an index γ as shown in t = (6) The total handover time must be less than the time required by MN to remain connected to an AP/BS. Therefore, the handover triggering point must be set as a distance equal to (1 γ). According to RSS at the border of the serving cell is equal to.. (7) where and are the antenna gain and path loss factor, respectively. We put a threshold of RSS level on the boundary of coverage area of a PoA of a network. In our scheme, to avoid false handover indications, the threshold δis computed by removing the path loss factor and the velocity effect on the RSS from current AP/BS. Thus the final RSS (δ) for handover triggering can be defined as follows:

4 149 When RSS from current AP/BS drops belowδ, the MN initiates network selection stage by using a specific interface based on the speed of MN. The proposed triggering scheme integrates the velocity and handover delay for identifying the appropriate RSS for handover. Table.2 Base Station Parameter Base stations parameter is presented in Table 2. The proposed model operates in two stages where in stage one a handover triggering mechanism is developed to reduce false handover indications and in stage two network selection schemes is used to provide an MN with appropriate network and PoA. A handover triggering mechanism facilitates MN to initiate handover process when it is required. The proposed model adopts threshold based mechanism for handover initiation session. In other words, handover is initiated if RSS from the current network drops below a predefined threshold. The advantages of the threshold based triggering mechanism are reducing the number of false handover indications and hence reducing total number of handover failures to a network with overloaded APs/BSs. A. Network Selection. When MN is moving at a high speed in a coverage area of WIFI network, it requires frequent switching from one AP to another since the radio coverage of WIFI AP is small. This frequent switching leads to much energy consumption, high packet loss, and breaking of connection. To deal with such situation, an optimized network selection scheme is proposed for handover based on the speed of MN. We assume that MN moving in heterogeneous networks has three different interfaces: WIFI, WiMAX, and 3G. o When the RSS from the current AP/BS drops below a particular threshold, it will initiate handover by selecting a network on the basis of its speed. o If the speed is slow, the MN will scan the available networks through WIFI interface and the rest of the interfaces will be in standby mode. o Similarly, if where ω represents the RSS level at current location of MN. We use two thresholds for network selection based on the value ofα:α1 and α2. o If the value of α is less than α1, then the MN turns on its WIFI interface and the rest of the interfaces is turned off. o If the value of αis between α1 and α2, it only turns on its cellular interface, and o If the value ofα1 is greater than α2, it only turns on its WiMAX interface and the rest of the interfaces are switched to standby state. The optimal network selection is a key issue in the vertical handoff decision phase. This multi-criteria nature of the algorithm allows simultaneous consideration of several significant aspects of the vertical handoff process in order to enhance the system performance in accordance with the defined heterogeneous network goals. Therefore, the multi-critical vertical handoff algorithm is essential in heterogeneous wireless networks, which can provide better performance than a single criteria vertical handoff algorithm due to the additional of evaluation parameters and the great potential for achieving the desired balance among different system characteristics [3]. IF RSSI is weak, network coverage area is bad, data rate is low, QoS is undesirable, THEN handoff factor is higher IF RSSI is medium, network coverage area is medium, data rate is medium, QoS is acceptable, THEN hand off factor is average and pre-connection is done IF RSSI is strong, data rate is high, network coverage area is good, QoS is desirable, THEN handoff factor is lower B. Mobility It is crucial in deciding handover on heterogeneous environment. In our study, we include speed as a criterion in handover decision. a) Movement of a mobile user may effect on choosing the suitable network as a point of attachment. b) Heterogeneous network combine several networks with different strength. c) Each network is suitable for certain type of velocity. WiFi, for example, is suitable for the users with low velocity or stationary because of its small coverage.

5 150 d) On the other hand, WiMAX network is preferable for users with high velocity (i.e. vehicular speed) because of its big coverage. Accordingly, in our study we classified mobile users into 4 (four) speed class:1) Stationary mobile users, 2) Mobile users with a velocity of 1.3 m/s which are considered as pedestrians. 3) Mobile users with a velocity of 3 m/s, where it is the average speed of a public bus in urban condition at peak hours,4) Mobile users with velocity of 4.7 m/s, the average speed of a public bus during off peak hours. START Mobile station parameters: RSS (WLAN, WCDMA, WIMAX) Traffic Class, Mobile Speed, Base station parameter Base station Parameter: Channel Occupancy (WLAN, WCDMA, WIMAX) Set priority weightage Number of handoff is a total vertical handover occurrence during active call. Number of handoff is an essential performance parameter in the mobile network because it is correlated with the signalling load and delivered QoS. Handover execution requires certain amount of network resources thus unnecessary handover may cause inefficiency. Multi-criteria decision making TOPSIS Criteria: RSSI, Traffic class, Mobile Speed, Network Occupancy Alternatives: (WLAN, WCDMA, WIMAX) Sort Target network (descend) Result: Network no. 1(target no 1) Network no.2 Network no 3(target no. 3) Channel Availability Network no. 1 1? N Channel Availability Network no. 2 1? N Channel Availability Network no 3 1? Y Y Y Handover to Network no.1 END Handover to Network no.2 END Handover to Network no.3 Load balance is also essential as unbalanced load may cause congestion in one network while excess network resources in other network are unused. By creating a balanced network, more mobile users may be served and the network will have a higher throughput and lower packet delay. The value of balance index represents the network balance, where the imbalance of the network is greater with the higher balance index value. Blocking probability model in this study follows Erlang B model, with M/M/c queuing model with multi-server. The call arrival model follows Poisson process, with limited server number c. Erlang B blocking probability complies with Lost Call Cleared model (Erlang Loss model) where blocked calls are immediately abandoned. Average blocking probability represents the blocking probability for the heterogeneous network which consists of three type of network, WLAN, WCDMA and WiMAX. N Drop call END END Figure 3.Flowchart of model

6 151 We propose traffic class that may accommodate different networks involved in this heterogeneous network. We classify the traffic into 3 (three) classes: Conventional service, streaming service and Best effort service. a) The conventional service includes voice calls, where the traffic has low tolerance for delay but high tolerance for bit error. b) Best effort service may have a relatively high delay, but it is strictly needed to be accurate in term of low bit error rate. c) Streaming service compromises those two extremes and provides service with average delay and bit error. WiFi network is a priority network for best effort services such as and web browsing. Voice calls are preferred to be handled by WCDMA network as streaming traffic is preferred to be served by WiMAX network. C. TOPSIS multi-criteria decision making Compared to other multi-criteria method, The Technique for Order Preferences by Similarity to an Ideal Solution (TOPSIS) has several advantages. It has conceptual simplicity, good computational efficiency and it has the ability to measure relative performance for each alternative. TOPSIS only requires one subjective input, the weightage, to calculate the decision. In simulation, TOPSIS provides higher throughput and lower packet loss compared to other multi-criteria decision making methods Multi Criteria Vertical Handover Decision Algorithm There are 4 (four) criteria involved in the handover decision algorithm. Those are RSSI, traffic class, speed and network occupancy. Input parameters of the algorithm are base stations parameters (network topology and radio parameters) and mobile stations parameters (speed class and traffic type). The flowchart of is presented in Figure 3.There are three performance parameters: a) Number of handoff, b) balance index and c) Average blocking probability. 4. RESULTS AND DISCUSSIONS Performance parameters of this simulation are number of handoff, load balance index and blocking probability. These parameters are calculated for both conventional and proposed algorithm.conventional method use RSSI as a single criteria meanwhile multicriteria method considers traffic class, speed and network occupancy. Figure 4 presents the distribution function of number of handoff after the implementation of proposed multi criteria where it reduced number of handoff by 90.41%. Number of handoff mean by using conventional method is 63, and the implementation proposed multi criteria has successfully dropped the number to 6. Conventional method vertical handover decision creates more number of handoff, and this may lead to additional signalling load on the network. Our proposed multi-criteria method has the best performance in decreasing the number of handoff, also weightage of multi criteria has a large proportion on mobile speed and traffic class. The emphasis of traffic class and mobile speed has successfully diminished unnecessary handovers. The implementation of proposed multi criteria slightly improved the performance of balance index by 0.09%. The mean of balance index of conventional method is and the mean of balance index for mobile priority multi-criteria method is The distribution of balance index for mobile priority multi criteria is presented in Figure 5. Figure 4: Number of Handoff Distribution Figure 5: Balance Index Distribution Balance index is a network related performance metric, thus larger proportion of network criterion should be given to improve the balance index. In the same way, mobile priority multi criteria also degrade blocking probability. Mean value of average blocking probability increased by 8.69%. Mean value for conventional method is 0.11 and 0.12 for mobile priority multi-criteria method. The distribution is presented in Figure 6.

7 152 Mean value of average blocking probability for conventional method is 0.11 meanwhile mean value of average blocking probability for network priority multi-criteria method is Average blocking probability is linked to network occupancy, and in network priority multi-criteria method, the weightage of network occupancy is higher compared to other criteria (RSSI, traffic type and speed class) thus it successfully reduced the average blocking probability. Figure 7 shows a simulation scenario in 3G, WLAN and WiMAX heterogeneous networks. The transmission radiuses of the AP and BS are 50 meters and 500 meters respectively, which are covered completely in 3G signal range. 1. The MS (Mobile station) moves at time 5sec with moving speed 3 m/s. The CN sends out CBR TCP packets, with data rate 1Kbps, to the MS starting at time 5sec. The total simulation time is 400s. The MS connects with the CN initially via the UMTS network. 2. When the MS moves slowly and enters the transmission range of WLAN/WiMAX at time 50s, it handovers form UMTS BS to WLAN AP because the WLAN networks provide higher transmission rate than the UMTS and WiMAX networks in our simulation scenario. 3. Then, the MS handovers form WLAN AP to WiMAX BS at time 83s. 4. Finally, the MS returns to UMTS networks from WiMAX networks at time 340s. Figure 6: Average Blocking Probability Distribution, Fig.7 WLAN, 3G, and WiMAX heterogeneous Ntw 5. CONCLUSIONS Compared to single-criteria decision making, multi-criteria may increase the handover delay as it considers several parameter to decide the handover. However, the implementation of multicriteria decision making in the vertical handover decision algorithm of a heterogeneous network increases the network performance in terms of number of handoff and load balance index REFERENCES [1] A. Jain and S. Tokekar, Optimization of vertical handoff in UMTSWLAN heterogeneous networks, in Proceedings of the International Conference on Emerging Trends in Communication, Control, Signal Processing & Computing Applications (C2SPCA 13), pp. 1 5, Bangalore, India, [2] R. Trestian, O. Ormond, and G.-M. Muntean, Energy-quality cost tradeoff in a multimedia-based heterogeneous wireless network environment, IEEE Transactions on Broadcasting, vol.59, no. 2, pp , [3] O. M. Eshanta, M. Ismail, K. Jumari, and P. Yahaya, "VHO Strategy for QoS Provisioning in the WiMAX/WLAN Interworking System," Asian Journal of Applied Sciences, vol. 2, pp , [4] H. Bing, C. He, and L. Jiang, "Performance analysis of vertical handover in a UMTSWLAN integrated network," in The 14th IEEE 2003 International Symposium on Persona1,lndoor and Mobile Radio Communication Proceedings, 2003, pp [5] Kim T, Han S W, Han Y, A Qos-Aware Vertical Handoff Algorithm Based on Service History Information, IEEE Communication Letter,Vol. 14, No. 6, pp , June [6] Wu Y, Yang K, Zhao L, Cheng X, Congestion-Aware Proactive Vertical Handoff Algorithm in Heterogeneous Wireless Networks, IET Communications,Vol.3,No. 7, pp , [7] Ali R B, Pierre S, On The Impact of Mobility and Soft Vertical Handoff on Voice Admission Control in Loosely Coupled 3G/WLAN Networks, IEEE Communication Letter,Vol.13, No.5, pp , May 2009.

8 153 [8] Sharma M, Khola R K, Pre Decision Based Handoff in Multi Network Environment, Advances in Intelligent and Soft Computing, Vol.167, pp , [9] M. Kassar, B. Kervella, and G. Pujolle, "An overview of vertical handover decision strategies in heterogeneous wireless networks," Computer Communications, vol. 31, pp , [10] D. Manjaiah and P. Payaswini, "A review of vertical handoff algorithms based on Multi Attribute Decision Method," International Journal of Advanced Research in Computer Engineering and Technology (IJARCET), vol. 2, pp , [11] E. Stevens-Navarro and V. W. S. Wong, "Comparison between Vertical Handoff Decision Algorithms for Heterogeneous Wireless Networks," in Vehicular Technology Conference, VTC 2006-Spring. IEEE 63rd, 2006, pp AUTHOR BIOGRAPHY Salavadi Ananda Kumar has received B.Tech Degree from J.N.T.U Hyderabad in 2004, the M.Tech Degree from S.K.University, Ananthapur, India in 2006 and Research Scholar in JNTU, Hyderabad. Previously he worked as an Assistant Professor in SECT Kurnool. His Research areas include implementation of routing protocols in wireless heterogeneous networks, Design & implementation of dynamic models for wired and wireless N/W s. Analysis and their applications in communication networks and their reliability. S.A.Kumar guided M.Tech students. He organized national level workshops and technical events & presented papers in National and International, Journals conferences. K.E.Sreenivasa Murthy received the B.Tech degree from S.V. University, Tirupathi, India in 1989, and M.Tech from S.V.University, Tirupathi, India in 1992, and the Ph.D. degree from Sri Krishnadevaraya University, Ananthapur, India in Dr.K.E.S.Murthy is a professor in the department of ECE at Brahmas Institute of Engg & Tech., Nellore. He is ratified as Principal by JNTU, Ananthapur.Previously he was a professor and HOD of ECE at G.Pulla Reddy Engineering College, Kurnool, India. His Research Interest are in the Microprocessor based Technologies, design of filters using FPGA s, Implementing routing algorithms of Data N/W s and Mobile Adhoc N/W s. Dr.K.E.S. Murthy has published 31 research papers in various International journals. He is giving Ph.D. guidance to 8 candidates out of them 3 were awarded Ph.D. degree and also giving guidance to 3 M.Phil candidates. Dr.K.E.S.Murthy is a life member of ISTE, Instrumentation Society of India and also member of IEE & IETE. He organized many national level workshops & symposiums during his tenure.