Data Downloading in Relay Assisted Mobile Vehicles Helal Chowdhury, Janne Lehtom¨ aki, Jari Iinatti, Pekka Pirinen Centre for Wireless Communications University of Oulu Oulu, Finland Email: helal.chowdhury@ee.oulu.fi Abstract—Traditionally, every mobile station (MS) riding in the mobile vehicle uses conventional connection to the base station (BS). However, in 802.16j mobile multihop relay (MMR) networks, one of the studied usage model is ”coverage on mobile vehicle”. Therein, a relay station (RS) is mounted on a vehicle. The RS provides service to MSs riding on the vehicle by relaying their data to the mobile multihop relay base station (MMR- BS). This brings several benefits compared to the situation where every MS would individually connect to the MMR-BS, including power savings and better channel condition. In this work, we consider a scenario where user is considered sitting in the vehicle and downloading data via relay station which is mounted on top the vehicle. The downloading typically uses the RS mounted on the vehicle but direct communication to the MMR-BS is also allowed. We characterize both the access links (MS-RS, MS-BS) and the relay link (RS-BS) by throughput- distance relationship models. The decision whether to use RS or to communicate directly with the MMR-BS is decided based on comparing the combined throughput distance model. (MS- RS-BS) with the throughput obtained using direct access link. Numerical results are provided using a two-turn mobility model. The results show that mobility and velocity of mobile vehicle have a great impact on the performance of mobile vehicle relay assisted network. I. I NTRODUCTION Wireless connectivity on mobile vehicle by relay station (RS) is emerging as an important mode of communication in future wireless communication systems [1]. In this paradigm of wireless communication RS can serve network access on vehicles for stationary terminal inside the mobile vehicle. As a result, 802.16j has considered coverage on mobile vehicle usage model as one of its four usage models [2], [3]. In this usage model, mobile relay RS is mounted on the vehicle and it connects to the mobile multihop relay base station (MMR-BS) via mobile relay link. Sometimes this application of scenario where mobile relays serving stationary terminals is called moving network hence mobile relays are network elements and are expected to be part of future wireless communication networks [4], [5]. Potential benefits of using mobiles relays are multiplexing gain, saving battery power of the mobile terminal (MT) and better channel condition because of external antenna of mobile RS [2]. There will be other various applications as well of relay based network which will provide services to passenger hand-held devices, vehicle sensors, actuators, and controllers to access heterogeneous wireless networks while the vehicle is in motion [6]. In this work, we consider a scenario where user is considered sitting in the moving mobile vehicle and downloading data via RS mounted on the mobile vehicle. However giving benefits of data downloading in mobile vehicle therein significant key challenges in deployment of such relay based wireless networks. RS is network element and due to the mobility of network element, mobile relaying con- cept is more complex approach in compare to fixed relaying [4]. Network Mobility (NEMO) Basic Support is standardized for moving/mobile networks by extending Mobile IPv6 [6]. This will enable network mobility and wireless connectivity while element of network move [4], [5], [6]. To our best knowledge very few papers have been addressed this usage model described in 802.16j and evaluate the performance of relay based mobile network. In [7], performance evaluation of fixed relay based cellular system has been studied. In [4], [5], solution for power control and allocation has been analyzed for mobile relays. In contrast to the other works, we consider to evaluate the performance of mobile relay network while the user sitting inside the mobile vehicle and download data. In many cases throughput is considered as the performance metric in performance prediction model to evaluate the perfor- mance of wireless network [8]. Throughput is affected by the channel environment such as the distance between transmitter and receiver, fading state of the channel, noise and interference power characteristics and many others [7]. On the other hand, performance of mobile relay assisted network depends also on the link budget evaluation for access link and relay link as well as positions of mobile relay from the MMR-BS [8]. Hence, considering the effects of all above mentioned parameters to the throughput, each link may be described as simplified throughput-distance model [7]. The purpose of using this throughput-distance model is to treat certain aspects in new radio-network solutions in a general way, while modeling other aspects in more great details. II. MATHEMATICAL FRAMEWORK Two co-centric circles are used to represent the different segments of traveling path of a mobile vehicle. The outer tier is used to represent the coverage of multi-hop communication whereas the most inner tier represents the coverage of single- hop communication as shown in Fig. 1. In the outer tier, stationary user in the mobile vehicle connect to MMR-BS via 978-1-4244-4067-2/09/$25.00  2009 IEEE Wireless VITAE’09 361