National Conference on Communication and Information Security (NCCIS 2009) Daffodil International University, Dhaka, Bangladesh, 14 February 2009. Optimizing the Handover Procedure in IEEE 802.16e Mobile Wimax Network Nafiz Imtiaz Bin Hamid and Adnan Mahmud Department of Electrical and Electronic Engineering (EEE) Islamic University of Technology (IUT), Boardbazar, Gazipur, Bangladesh E-mail: nafiz-imtiaz@hotmail.com, adnan903@yahoo.com Abstract: The mobile WiMAX bearing the IEEE standard 802.16e-2005 brings wireless broadband to a new dimension due to the support of nomadism. As a result, handover has obviously become a very significant factor in the performance of mobile WiMAX. But because of the presence of unnecessary ranging/scanning in Layer 2 along with the network re-entry procedure enormous handover latency occurs. This threatening handover delay is a huge obstacle for the optimum performance of mobile WiMAX. In this paper various problematic scenarios of handover procedure have been shown with the log file analyzer tool along with “SlickEdit” using data from a WiMAX trial network and from that an optimized handoff scheme is proposed associated with suitable pre- scanning algorithm, fast dedicated ranging and pre-registration process. Keywords: IEEE 802.16e, Mobile WiMAX, Scanning, Handover 1. Introduction New and emerging multimedia applications and broadband remote access are driving the need for very high-speed wide area Internet access to mobile devices. Mobile WiMAX based on IEEE 802.16e-2005 [1] standard is an amendment of IEEE STD 802.16-2004 [2] for supporting mobility. It is a key component of broadband wireless strategy for delivering innovative mobile platforms for anytime, anywhere Internet connectivity [6]. The mobile WiMAX air interface adopts Orthogonal Frequency Division Multiple Access (OFDMA) for improved multi-path performance in non-line-of-sight (NLOS) environments. Other advanced features of 802.16e include Adaptive Modulation and Coding (AMC), Hybrid Automatic Repeat Request (HARQ) & Channel Quality Indication Channel (CQICH) for fast feedback channel & smart antenna technology deployment [1, 2, 6, 8]. As in the current standard, there is the support for mobility; handover has become a very vital issue. In IEEE 802.16e standard, three kinds of handover types can be supported- Hard Handover (HHO), Macro Diversity Handover (MDHO) & Fast Base Station Switching (FBSS). HHO is the simplest one among them; whether other two types having more complicacy are regarded as optional. Besides these, handover can be both MS & BS initiated [1, 4]. In this paper, when handover is mentioned, it refers to MS initiated HHO. Handover of IEEE 802.16e broadband wireless network had been studied in several literatures. Up to now several fast handover schemes had been proposed. A solution meeting requirements for micro-and macro- mobility management in Mobile IP based systems as well as those for Mobile BWA systems had been proposed in [9]. It provided a significant level of improvement in handoff latency relative to other Mobile IPv6 schemes. An enhanced fast handover algorithm was proposed to reduce the waste of the wireless channel resources and handover delay in [6, 7]. Target BS estimation using mean CINR and arrival time differences had been proposed for reducing unnecessary neighbor BS scanning & association process in [6]. Single neighbor BS scanning along with modified network re- entering method for fast HO had been proposed in [7]. A delay timer to reduce the initiation of unnecessary handover had been proposed in [5]. In that proposal the timer deals with unnecessary handover caused by inaccurate signal level assessment. Again, a scheme for the reduction of data transmission delay & packet loss probability for real-time downlink service had been proposed in [3]. In our paper an efficient fast HO algorithm is proposed to limit /reduce the redundancies in 24