Wireless Pers Commun (2013) 71:1421–1442 DOI 10.1007/s11277-012-0883-0
Fuzzy Logic Based Self-Adaptive Handover Algorithm for Mobile WiMAX Mohammed A. Ben-Mubarak · Borhanuddin Mohd. Ali · Nor Kamariah Noordin · Alyani Ismail · Chee Kyun Ng
Published online: 25 October 2012 © Springer Science+Business Media New York 2012
Abstract It is well known that WiMAX is a broadband technology that is capable of delivering triple play (voice, data, and video) services. However, mobility in WiMAX system is still a main issue when the mobile station (MS) moves across the base station (BS) coverage and be handed over between BSs. Among the challenging issues in mobile WiMAX handover are unnecessary handover, handover failure and handover delay, which may affect real-time applications. The conventional handover decision algorithm in mobile WiMAX is based on a single criterion, which usually uses the received signal strength indicator (RSSI) as an indicator, with the other fixed handover parameters such as handover threshold and handover margin. In this paper, a fuzzy logic based self-adaptive handover (FuzSAHO) algorithm is introduced. The proposed algorithm is derived from the self-adaptive handover parameters to overcome the mobile WiMAX ping-pong handover and handover delay issues. Hence, the proposed FuzSAHO is initiated to check whether a handover is necessary or not which depends on its fuzzy logic stage. The proposed FuzSAHO algorithm will first self-adapt the handover parameters based on a set of multiple criteria, which includes the RSSI and MS velocity. Then the handover decision will be executed according to the handover parameter values. Simulation results show that the proposed FuzSAHO algorithm reduces the number of ping-pong handover and its delay. When compared with RSSI based handover algorithm and mobility improved handover (MIHO) algorithm, respectively, FuzSAHO reduces the
M. A. Ben-Mubarak (B) · B. Mohd. Ali · N. K. Noordin · A. Ismail · C. K. Ng Department of Computer and Communication Systems Engineering, Faculty of Engineering, Universiti Putra Malaysia, UPM Serdang, Selangor, Malaysia e-mail:
[email protected] B. Mohd. Ali e-mail:
[email protected] N. K. Noordin e-mail:
[email protected] A. Ismail e-mail:
[email protected] C. K. Ng e-mail:
[email protected]
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number of handovers by 12.5 and 7.5 %, respectively, when the MS velocity is 17 m/s, the performance is almost the same for both conventional RSSI based and the proposed FuzSAHO schemes which includes MIHO as well. Moreover, the proposed FuzSAHO algorithm enhances the handover delay performance as shown in Fig. 23. Hence, an improvement in terms of handover delay has been shown in the proposed FuzSAHO algorithm with 27.8 and 8 % compared to the conventional RSSI
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Fig. 23 Handover delay versus MS velocity
RSSI based HO based initiation and decision. 1. RSSI measuring 2. Comparing the nBS RSSI with current BS RSSI+margin Mobility Improvement Handover (MIHO) based initiation and decision. 1. RSSI measuring 2. MS velocity estimation/ measuring 3. Self-tuning the HO threshold using logarithm function 4. Comparing the nBS RSSI with current BS RSSI+margin Fuzzy logic based self-adaptive handover (FuzSAHO) based initiation and decision. 1. RSSI measuring 2. MS velocity estimation/ measuring 3. fuzzifying the RSSI and MS velocity values 4. Self-tuning the HO threshold and HO margin using fuzzy logic 5. Comparing the nBS RSSI with current BS RSSI+margin
Fig. 24 Number of main operations for RSSI-Based HO, MIHO and FuzSAHO algorithms
based handover scheme and MIHO, respectively. This indicates that in conventional handover scheme, when the MS velocity is slow, the MS may perform unnecessary or ping-pong handover, and the number of handover will be reduced when the MS becomes fast. The obtained results show that the MS velocity has an important impact on the handover process. When the velocity of MS gets higher the probability of getting handover will be lower because the TBS information changes quickly and the re-scanning and re-ranging are necessary in MS to get the updated information. Also, in high velocity, the channel condition will change frequently, which makes the pre-obtained information useless. Thus, during the handover, neighbouring
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BSs scanning and contention-based ranging operation must be performed, which causes a long handover delay and wastage of the wireless channel resource [5]. To evaluate the computational overhead, two aspects, the number of operations and the execution time of each algorithm will be considered. Figure 24 shows the number of main operations for RSSI-Based HO, MIHO and FuzSAHO algorithms, respectively. From this figure, it is shown that the FuzzSAHO algorithm has the most number of operations. However, the FuzSAHO algorithm is designed as a simple and quick algorithm. It is only based on two system inputs and all the membership functions, and the rule base is pre-defined. As regards the execution time which may effect real-time application, simulation experiments were performed to measure the execution time of each algorithm. The simulation tool’s clock time is in nano second (ns). The measured execution time of each algorithm results are 0 ns. Thus, although the FuzSAHO algorithm requires more number of operations, it is still fast enough to support real-time application and hence the number of operations could be neglected. Therefore, the computational overhead for all these algorithms could be considered negligible. Simulation results indicate that the proposed FuzSAHO algorithm with self-adaptive handover parameters managed to reduce the number of unnecessary or ping-pong handover. It enhances the overall performance of handover operation in term of reduced overhead signalling, handover delay, which satisfies the network operator and user requirements.
5 Conclusion The conventional mobile WiMAX handover based on fixed handover parameters and single criteria may cause unnecessary or ping-pong handover which will affect the system performances. In this paper, the proposed fuzzy logic based self adaptive handover (FuzSAHO) algorithm has been shown to reduce the number of handovers and handover delay to satisfy network and user requirements. Simulation results show that FuzSAHO algorithm reduces the number of handovers by 12.5 and 7.5 %, compared to the conventional RSSI based handover and MIHO schemes, respectively when the MS velocity increases to 17 m/s. In terms of handover delay, the proposed algorithm shows an improvement by 27.8 and 8 % compared to the conventional RSSI based handover and MIHO schemes, respectively. Thus, it can be concluded that the proposed FuzSAHO algorithm which is a fuzzy logic decision engine based with multi-criteria input, and self-adaptive handover parameters, managed to enhance the overall handover performance in mobile WiMAX. Acknowledgments Mohammed Ben-Mubarak was supported by the Graduate Research Fellowship (GRF) from Universiti Putra Malaysia (UPM).
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Author Biographies Mohammed A. Ben-Mubarak received the B.Sc. degree (first class honor) in Computer Engineering from University of Science and Technology, Sana’a, Yemen, in 2001. He received the M.Sc. degree in IT from Multimedia University, Cyberjaya, Malaysia, in 2008. He is currently a Ph.D. student in Wireless Communication Engineering at Universiti Putra Malaysia (UPM). His main research interests are handover, mobile WiMAX, fuzzy logic, bio-inspired and emerging wireless technologies standard such as IEEE 802.16e and IEEE 802.16m.
Borhanuddin Mohd. Ali obtained his B.Sc. (Hons) Electrical and Electronics Engineering from Loughborough University in 1979; M.Sc. and Ph.D. from University of Wales, UK, in 1981 and 1985, respectively. He became a lecturer at the Faculty of Engineering UPM in 1985, made a Professor in 2002, and Director of Institute of Multimedia and Software, 2001–2006. In 1997 he co founded the national networking testbed project code named Teman, and became Chairman of the MYREN Research Community in 2002, the successor to Teman. His research interest is in Wireless Communications and Networks where he publishes over 80 journal and 200 conference papers. He is a Senior Member of IEEE and a member of IET and a Chartered Engineer, and the present ComSoc Chapter Chair. He is presently on a 2-year secondment term with Mimos as a Principal Researcher, heading the Wireless Networks and Protocol Research Lab.
Nor Kamariah Noordin received her B.Sc. in Electrical Engineering majoring in Telecommunications from University of Alabama, USA, in 1987. She became a tutor at the Department of Computer and Electronics Engineering, Universiti Putra Malaysia, and pursued her Masters Degree at Universiti Teknologi Malaysia and Ph.D. at UPM. She then became a lecturer in 1991 at the same department where she was later appointed as the Head from year 2000 to 2002. She is currently the Director of Corporate Planning Division at the Office of the Vice Chancellor. During her more than 15 years at the department she has been actively involved in teaching, research and administrative activities. She has supervised a number of undergraduate students as well as postgraduate students in the area of wireless communications, which led to receiving some national and UPM research awards. Her research work also led her to publish more than 100 papers in journals and in conferences.
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M. A. Ben-Mubarak et al. Alyani Ismail received her B.Eng. (Hons) Electronic and Information Engineering from University of Huddersfield, United Kingdom in 1999. She received her M.Sc. in Communication, Computer and Human-Centred Systems Engineering in 2001 and her Ph.D. in Electronics Engineering majoring in micromachined microwave devices in 2006 from University of Wales, UK. Her research in micromachined filter design at Birmingham was sponsored by the UK Engineering and Physical Science Research Council. She became a lecturer at the Faculty of Engineering, Universiti Putra Malaysia (UPM) in 2006. Her research interest specializes in the development of microwave devices particularly passive filters and antennas.
Chee Kyun Ng received his Bachelor of Engineering and Master of Science degrees majoring in Computer & Communication Systems from Universiti Putra Malaysia, Serdang, Selangor, Malaysia, in 1999 and 2002, respectively. He has also completed his Ph.D. programme in 2007 majoring in Communications and Network Engineering at the same university. He is currently undertaking his research on wireless multiple access schemes, wireless sensor networks and smart antenna system. His research interests include mobile cellular and satellite communications, digital signal processing, and network security. Along the period of his study programmes, he has published over 100 papers in journals and in conferences.
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