Multi-hop Relay based Coverage Extension in the IEEE802.16j based Mobile WiMAX Systems Se-Jin Kim 1 , Seung-Yeon Kim 2 , Byung-Bog Lee 3 , Seung-Wan Ryu 4 , Hyong-Woo Lee 2 , and Choong-Ho Cho 1 1 Department of Computer and Information Science, Korea University, Korea 2 Department of Electronics and Information Engineering, Korea University, Korea 3 RFID/USN Research Division, ETRI, Korea 4 Department of Information Systems, Chung-Ang University, Korea E-mail: {kimsejin, kimsy8011, hwlee, chcho}@korea.ac.kr, bblee40@etri.re.kr, rush2384@cau.ac.kr Abstract In this paper, we investigate various issues of cost- effective coverage extension in a multi-hop relay based WiBro/WiMAX systems. Since the coverage extension problem may occur in metropolitan areas as well as suburban or rural areas where user density is relatively low or moderate, we fist introduce several topologies and the resulting cost-effective coverage extension methods for each case. Secondly, we propose two cost-effective coverage extension methods using two sectorized cellular approaches, one using the wide-beam tri-sector cell (WBTC) and the other using the narrow-beam tri-sector cell (NBTC). Finally, we present a practical deployment scenario consisting of three phases depending on user traffic density. 1. Introduction Recently, there have been numerous standardization activities for making the IEEE 802.16e system highly effective in supporting mobile users based on orthogonal frequency division multiple access (OFDMA) with TDD mode [1,2]. Standardization activities of the IEEE802.16e system were completed in 2005, and currently enhancements of the IEEE802.16e standard are under discussion. One such enhancement effort is cell coverage extension and link throughput enhancement which is being studied in IEEE802.16j TG. In order to achieve these goals, the IEEE802.16j TG introduces mobile multi-hop relay technology to the IEEE802.16e system. The other enhancement effort is being discussed in IEE802.16m TG. The IEEE802.16m system, called the gigabit WiMAX, mainly aims to enhance system throughput up to 1Gbps. Besides, this system aims to support legacy IEEE802.16 standards including the IEEE802.16j, and to interworking with other wireless systems such as 3GPP LTE and IMT-advanced system [2, 3]. In particular, in Korea, the IEEE802.16e standard- based wireless broadband (WiBro) system was developed in 2005 and WiBro service was launched in 2006 covering isolated areas in Seoul [4]. Since the initial launch, WiBro service providers have been trying to extend service areas from Seoul to regions nationwide. In order to cover the entire region of Korea, however, deployment cost for the traditional infrastructure consisting of only Base Stations (BSs) is estimated to be astronomical. For this reason, it is necessary to adopt a cost-effective service coverage extension method, and the mobile multi-hop relay (MMR) WiBro system is considered as a strong candidate for possible implementation. In this paper, we investigate various issues on multi-hop relay based WiBro/WiMAX systems, i.e., the IEEE802.16j system, with a focus on cost-effective cell coverage extension under various deployment situations. Since the coverage extension problem may occur in both of metropolitan areas and rural areas when the user-traffic density is relatively moderate or low, we first introduce several topologies and the resulting cost-effective coverage extension methods for each case. Secondly, we propose two sectored cellular based cost-effective coverage extension methods, the WBTC and NBTC system based approaches. Finally, we present a practical deployment scenario consisting of three phases depending on the user-traffic density and the number of traffic relaying hops. The remainder of this paper is organized as follows. In the next section, we analyze cost-effective coverage extension methods under various MMR topologies that may occur in metropolitan and rural areas. Then we Fourth International Conference on Networked Computing and Advanced Information Management 978-0-7695-3322-3/08 $25.00 © 2008 IEEE DOI 10.1109/NCM.2008.88 516 Authorized licensed use limited to: Korea University. Downloaded on October 9, 2008 at 07:55 from IEEE Xplore. Restrictions apply.