SINR Based Vertical Handoff Scheme for QoS in ... - Semantic Scholar

2009 International Conference on Future Computer and Communication

SINR Based Vertical Handoff Scheme for QoS in Heterogeneous Wireless Networks K.Ayyappan

K.Narasimman and P. Dananjayan

Department of Electronics and Communication Engineering, Rajiv Gandhi College of Engineering and Technology Pondicherry-605007, India e-mail: [email protected]

Department of Electronics and Communication Engineering, Pondicherry Engineering College Pondicherry-605014, India [email protected]

Abstract— Next generation wireless network is envisioned as a convergence of different wireless access technologies providing the user enhanced connection any where any time to improve the systems resource utilization. In such converged systems, co- existence of heterogeneous access technologies with largely different characteristics like data rate for wideband code division multiple access (WCDMA), wireless local area network (WLAN) results in handoff asymmetry that differs from the traditional intra-network handoff (horizontal handoff). Thus handoff between different access technologies (vertical handoff) is essential and remains a challenging issue. The vertical handoff (VHO) algorithm must be quality of service (QoS) aware. Conventionally, handoff analysis is performed using well known vertical handoff metric, received signal strength (RSS). In this paper, a more appropriate handoff parameter, signal to interference and noise ratio (SINR) is used to assess the system performance in terms of dropping probabilities in addition to throughput. Simulation results prove that the proposed SINR based vertical handoff scheme offers enhanced system throughput and relatively low dropping probabilities when compared to the existing RSS based handoff scheme.

vertical handoff (DVH). When the mobile user moves out of its serving higher bandwidth network to the network with low bandwidth the handoff request initiated is called upward vertical handoff (UVH). Therefore seamless and efficient handoff between different access technologies known as vertical handoff is essential. All previous studies on vertical handoff [1-6] are based on received signal strength (RSS), in which handoff decisions are made by comparing the RSS with the preset threshold values. The RSS based vertical handoff in integrated WLAN and WCDMA networks cannot provide better quality of service to user to support multimedia services. This degradation in QoS results in premature handoff from a WLAN to WCDMA, even though the user achievable data rate from WLAN is higher than WCDMA. However, the achievable data rate of a mobile device is a function of received signal to interference and noise ratio (SINR), which is proportional to the distance between access point (AP) or base station (BS) to the mobile user and its current interference level. To provide seamless handover between WLAN and WCDMA, a SINR based vertical handoff that can support multimedia QoS with adaptive data rate is desirable. The vertical handoff algorithm not only can support the user with multimedia QoS and also achieving the maximum throughputs and minimum dropping probability. Moreover, the SINR based horizontal handoff [7] is already used within WCDMA systems, to have a unified radio resource management strategy for the heterogeneous wireless network, it is also essential to have a SINR based vertical handoff. In this paper, vertical handoff algorithms consider the received SINR as the handoff criterion. The SINR based vertical handoff is compared with the RSS based vertical handoff with various thresholds settings for different network conditions, such as noise level and load factor. The overall system throughputs and the number of dropped users in SINR based vertical handoff and RSS based vertical handoff for the heterogeneous network is evaluated. This paper is organized as follows; section 2 describes the SINR based vertical handoff strategy. Section 3 explains about the system model and section 4 discusses the performance of RSS, SINR based vertical handoff schemes. Section 5 concludes the paper.

Keywords- Vertical handoff, SINR, Heterogeneous wireless networks, Received signal strength, Quality of service

I.INTRODUCTION For seamless communication, integration of wireless local area network (WLAN) and third generation (3G) cellular networks (CN) such as wideband code division multiple access (WCDMA) system should be error free to achieve the next generation wireless networks (NGWN). These wireless access networks are combined to provide a ubiquitous environment of wireless access for mobile terminals equipped with multiple network interfaces. One of the main issues for the NGWN is the mobility, with which users can benefit continuous services while moving between networks. When mobile user transfers from one network to another the quality of service (QoS) offered by the network decreases under certain predefined quality level. This transfer mechanism is known as vertical handoff (VHO). The vertical handoff occurs in two ways. When the mobile user moves i n t o the netwo r k that h a s h i g h e r bandwith a n d limited coverage, vertical handoff request is initiated. This type of vertical handoff is called downward 978-0-7695-3591-3/09 $25.00 © 2009 IEEE DOI 10.1109/ICFCC.2009.121

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The integration between WLAN and WCDMA use tight coupling [9, 10], in which WLAN is directly connected to RNC via the inter-working unit (IWU), as shown in Fig 1. The SINR based vertical handoff can operate under active mode or passive mode. In active mode, the user continuously seeks for maximum available bandwidth from the integrated networks. The user keeps measuring receiving SINR for WLAN and WCDMA, conducting the γAP to γBS conversion and sending the handoff request to the RNC based on the SINR comparison results. In the passive mode, the measurements of user receiving SINR from both WLAN and WCDMA are periodically sent to RNC directly, in which the handoff decisions are made according to the SINR values, the user specific QoS requirements, as well as the cell congestion conditions.

II.SINR BASED VERTICAL HANDOFF STRATEGY Maximum achievable data rate for the given carrier bandwidth and SINR can be determined with the help of Shannon’s capacity theorem, the maximum achievable data rate R is given by:

⎛ γ⎞ R = Wlog 2 ⎜ 1 + ⎟ ⎝ Γ⎠

(1)

where W is the carrier bandwidth γ is SINR received at user end when associated with WLAN or WCDMA Γ is the dB gap between uncoded Quadrature amplitude modulation (QAM) and channel capacity, minus the coding gain. Let RAP and RBS be the maximum achievable downlink data rate for WLAN and WCDMA respectively while user connected to the respective network. By Shannon’s capacity theorem: ⎛ γ ⎞ R AP = WAP log 2 ⎜1 + AP ⎟ ⎝ Γ AP ⎠

(2)

⎛ γ ⎞ R BS = WBS log 2 ⎜ 1 + BS ⎟ ⎝ Γ BS ⎠

(3)

where γAP and γBS are the receiving SINR from WLAN and WCDMA respectively. Letting RAP = RBS, the relationship between γAP and γBS becomes WBS ⎛ ⎞ ⎛ γ BS ⎞ WAP ⎜ γ AP = Γ AP ⎜ ⎜1 + − 1⎟⎟ (4) ⎟ ⎜ ⎝ Γ BS ⎠ ⎟ ⎝ ⎠ WAP ⎛ ⎞ ⎛ γ ⎞ WBS γ BS = Γ BS ⎜⎜ ⎜1 + AP ⎟ − 1⎟⎟ (5) ⎜ ⎝ Γ AP ⎠ ⎟ ⎝ ⎠

Fig 1 Interworking model

III.SYSTEM MODEL This model considers the end user performance based on the downlink traffic, as they normally require higher bandwidth than uplink, especially for multimedia services such as video streaming using the high speed downlink packet access (HSDPA) channel connected with WCDMA. The SINR γ received by user i from WLAN APj can be represented as

The relationship between the maximum achievable data rate and the receiving SINR from both WLAN and WCDMA makes the SINR based vertical handoff method applicable, in which the receiving SINR from WCDMA is being converted to the equivalent γAP required to achieve the same data rate in WLAN, and compared with the actual receiving SINR from WLAN. Handoff is triggered when the user receives higher equivalent SINR from another access network. It means that the receiver end SINR measurements of both WLAN and WCDMA channel, the handoff mechanism has the estimated maximum possible receiving data rates a user can obtain from either WLAN or WCDMA at the same time. This gives the vertical handoff mechanism the ability to make handoff decision with multimedia QoS consideration, such as the user maximum downlink throughput and minimum dropped user from the integrated network.

γ APj,i =

G APj,i PAPj PB +

∑G

APk,i

PAPk

(6)

k∈AP k≠ j

where PAPj is the transmitting power of APj GAPj,i, is the channel gain between user i and APj PB is the background noise power at user receiver end. The SINR γ received by user i from WCDMA BSj can be represented as:

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γ BSj,i =

G BSj,i PBSj,i

PB +

∑ (G

P

BSk,i BSk

k∈BS

)−G

IV. PERFORMANCE ANALYSIS

(7)

P

The performance of different vertical handoff algorithms are evaluated using the simulation parameters [12, 13] shown in Table1. The performance of SINR based vertical handoff algorithm and RSS based vertical handoff algorithm have been evaluated with simulation model shown in Fig.3. The model consists of 7 BSs, 12 APs and 200 randomly generated UE are placed inside the coverage area of UMTS cell boundary. The UE position changes every time interval, depending on their moving speed and direction. The SINR based vertical handoff algorithm is compared with RSS based vertical handoff algorithm in terms of maximum downlink throughputs and number of dropped user while traveling through heterogeneous network for different network condition.

BSj,i BSj,i

where PBSk is the total transmitting power of BSk PBSj,i is the transmitting power of BSj to user i GBSj,i is the channel gain between user i and BSj A macro-cell propagation model for urban and suburban areas [11] is used, and for an antenna height of 15 meters, the path loss is PL(dB) = 58.8 + 21log(f) + 37.6log(d) + S (8) where f is the carrier frequency d is the distance between the user and the BS or AP S is the shadowing with standard deviation is 10dB In the user end performance analysis, consider a point to point model, in which a user is moving at speed v from AP (X1) to BS (X2), as shown in Fig 2. The vertical handoff is taken place at handoff point Xh.

TABLE I SIMULATION PARAMETERS

Parameters Transmitter power Cell radius Carrier frequency Background noise power Standard deviation

UMTS 40 dBm 1000 m 2 GHz -104 dBm 10 dB

WLAN 20 dBm 100 m 2.4 GHz -96 dBm 10 dB

Fig.2 Point to Point model

The total downlink throughputs θ can be represented as Xh

θ=

∫

X1

R AP ( X ) CRTAP +

X2

∫ R ( X ) CRT BS

BS

(9)

Xh

Fig.3 Location of BS/AP in heterogeneous network

where CRTAP and CRTBS are the cell residence time inside WLAN and WCDMA. RAP and RBS are the maximum bit rate received from WLAN and WCDMA. To determine the user maximum downlink throughput max (θ), the optimum handoff point Xh can be determined. For the RSS based vertical handoff, the Xh for user i is constrained by the receiving power GAPj, i PAPj from APj. In SINR based vertical handoff, the Xh for user i depends on the relationship between receiving SINR γAPj, i from APj and γBSj, i from BSj. Therefore, the average throughputs for different vertical handoff algorithm with different Xh can be compared.

The user’s mean throughputs for different noise power level are shown in Fig.4. The mean throughput lowers with higher noise power and maximum bit rate from WLAN decreases as the interference level increases. In RSS based vertical handoff the user connected to the AP of WLAN for longer period for lower threshold value -90dBm and achieved better throughput with low noise condition than the higher threshold value -80dBm. The performance variations of RSS based vertical handoff for different thresholds values like -90dBm, -85dBm and -80dBm are compared. The SINR based vertical handoff consistently offers the end user with the higher mean throughput for different noise level.

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speeds by varying the noise power. The low speed user access more time in the WLAN AP and achieve higher throughput when compared to high speed user.

Fig.4 Variation of mean throughput with noise power

Fig.6 Variation of mean throughput with noise power

Fig.5 Variation of mean throughput with load factor

In heterogeneous networks, interference power will depend on the user location as well as the density of the users. Therefore, the SINR based vertical handoff can guarantee multimedia QoS and achieve the required data rate for end user inside vertical handover zone. This factor that can adapt to the network conditions and provides consistently maximum available throughputs to the end user better than the RSS based handoff. Fig.5 shows the mean throughput of different handoff schemes for various downlink load factor. In this figure the noise power of WLAN is fixed at its minimum value of -96dBm, which allows the maximum available data rate in WLAN. As the load factor of UMTS network increases, the downlink radio resource become scarce and as a result decreases the maximum achievable data rate of the HSDPA channel. Therefore, the overall user throughput becomes lower for higher load factor, and the variation in the performance of different RSS threshold settings become more apparent. The advantage of SINR based vertical handoff has been confirmed by its highest user mean throughputs over various network conditions. Fig.6 depicts the mean throughput versus noise power. It shows SINR based vertical handoff throughput for different

Fig.7 Variation of mean throughput with data rate

Fig.7 shows the mean throughput versus data rate. It shows that SINR based vertical handoff of varying data rate with different user speed. It describes that low speed user get the higher overall throughput at different data rate compared to high speed user. Fig.8 illustrates that number of dropped handoff user for different time interval versus time. This exhibits the SNIR based vertical handoff gives lower handoff dropped user compared to RSS based vertical handoff. In RSS based handoff, signal level of each user monitor continuously if the signal level below threshold level handoff takes place. In SINR based handoff, SINR level of WLAN network is measured and required SINR value for WCDMA network is calculated. If the required SINR value matches with calculated SINR value of the WCDMA network handoff takes place. The RSS and SINR based vertical handoff strategies are analyzed based on the performance metrics throughput and handoff dropped users. The results are confirmed that SINR based vertical handoff scheme is better than RSS based vertical handoff scheme.

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[6]

[7] [8]

[9]

[10] [11]

Fig.8 Number of dropped users with Time

V. CONCLUSION [12]

The inter-system handover algorithm suggested the successful transfer of mobile user from one network to another, maintaining the minimum QoS requirements. The handoff call quality may drop because of different reasons, such as traffic overloading, coverage shortage, radio propagation effects or location change. In such cases, the user tries to switch to another network that will satisfy the service QoS attributes. The inter-system handover mechanism triggered whenever the user service requirements or quality of the user drops below an acceptable threshold. In order to provide QoS inside the heterogeneous network, the vertical handoff algorithm needs to be QoS aware, which can be achieved by SINR based handoff better than RSS based handoff. Simulation results confirm that SINR based vertical handoff provides higher overall system throughput as well as minimum number of dropped users comparing with the RSS based vertical handoff algorithm for different network conditions.

[13]

M. Ylianttila, M. Pande, J. Makela and P. Mahonen, “Optimization Scheme for Mobile Users Performing Vertical Handoffs between IEEE 802.11 and GPRS/EDGE Networks”, Proceedings of IEEE Global Telecommunications Conference, San Antonio,Texas,USA, Volume 6, pp. 3439-3443, November 2001. H. Holma and A.Toskala, “WCDMA for UMTS”, John Wiley, New York, 2004 S.Toumpis and A.J.Goldsmith, “Capacity Regions for Wireless Ad Hoc Networks”, IEEE Transactions on Wireless Communications, Volume 2, No. 4, pp. 736-748, July 2003. G. Cristache, K. David and M. Hildebrand, “Aspects for the integration of ad-hoc and cellular networks”, Proceedings of 3rd Scandinavian Workshop on Wireless Ad- hoc Networks, Stockholm, 2003. R. Samarasinghe, V. Friderikos and A.H. Aghvami, “Analysis of Intersystem Handover: UMTS FDD and WLAN”, Proceedings of IEEE London Communications Symposium 2003, London, UK, 2003. K.Yang, I.Gondal, B.Qiu and L.S.Dooley, “Combined SINR based Vertical Handoff algorithm for Next generation Heterogeneous wireless networks”, Proceedings of IEEE Global Telecommunications Conference, pp.4483-4487, 2007. K. Premkumar and A. Kumar, “Optimum Association of Mobile Wireless Devices with a WLAN-3G Access Network”, Proceedings of IEEE International Conference on Communication (ICC'06), Istanbul, Turkey, pp. 2002-2008, June 2006. E.L Aguilera, J. Casademont and J. Cotrina, “Outdoor IEEE 802.11g Cellular Network Performance”, Proceedings of IEEE Global Telecommunications Conference, Dallas, Texas USA, pp. 2992-2996, December 2004. K. Ayyappan received the Bachelors Degree from Bharathidasan University in 1989. He completed his Masters degree in Annamalai University in 1991. He is working as a Professor in ECE department of Rajiv Gandhi College of Engineering and Technology, Pondicherry, India. He is pursuing research in the area of internetworking in wireless communication. He has three international publications in journals . His areas of interest include spread spectrum and mobile communication.

K. Narasimman received his B.Tech Degree from Bharathiyar college of Engineering and Technology, Pondicherry University in 2006. He completed his M.Tech from Pondicherry Engineering College, Pondicherry in 2008. His areas of interests include wireless communication and Computer communication.

REFERENCES [1] A. H. Zahran, B. Liang and A. Saleh, “Signal Thresholds Adaptation For Vertical Handoff in Heterogeneous Wireless Networks”,Mobile Networks and Applications, Springer Netherlands, Volume11, No4, pp. 625-640, August 2006. [2] W.Shen and Q.A.Zeng, “A Novel Decision Strategy of Vertical Handoff in Overlay Wireless Networks”, Proceedings of Fifth IEEE International Symposium on Network Computing and Applications (NCA’06), Cambridge, USA, pp. 227-230, July 2006. [3] K.S.Jang, J.S. Kim, H.J.Shin and D.R.Shin, “A Novel Vertical Handoff Strategy for Integrated IEEE 802.11 WLAN/CDMA Networks”, Proceedings of Fourth Annual International Conference on Computer and Information Science, Canes, France, pp.616-621, September 2005. [4] Y.Nkansah Gyekye and J.I.Agbinya, “Vertical Handoff between WWAN and WLAN”, Proceedings of International conference on networking, International conference on systems and International conference on mobile communication and learning technologies (ICN/ICONS/MCL 2006) , pp.132-137, April 2006. [5] J. McNair and F. Zhu, “Vertical Handoffs in Fourth – Generation Multinetworks Environments ”, IEEE Transactions on Wireless Communications, Volume 11, no.3, pp.8-15, June2004.

P. Dananjayan received Bachelor of Science from University of Madras in 1979, Bachelor of Technology in 1982 and Master of Engineering in 1984 from the Madras Institute of Technology, Chennai and Ph.D. degree from Anna University, Chennai in 1998. He is working as a Professor and Head of the Department of Electronics and Communication Engineering, Pondicherry Engineering College, Pondicherry, India. He has more than 60 publications in National and International Journals. He has presented more than 130 papers in National and International conferences. He has produced 6 Ph.D candidates and is currently guiding eight Ph.D students. His areas of interest include Spread spectrum Techniques and Wireless Communication.

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