906 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 24, NO. 4, APRIL 2006 Modeling of Ultra-Wideband Channels Within Vehicles Paul C. Richardson, Weidong Xiang, Member, IEEE, and Wayne Stark, Fellow, IEEE Abstract—This paper aims to lay a solid foundation for the application of ultra-wideband (UWB) radio in vehicle environ- ments by exploring the characteristics of UWB channels within a vehicle. A comprehensive measurement campaign was conducted to gather a set of channel impulse responses of UWB links within and outside an armored vehicle. Based on the experimental data, the channel’s temporal characteristics, path loss, and capacities are analyzed. The distributions of delay spread and amplitudes of multipath signals are also studied, showing correspondence with the IEEE 802.15.3a UWB channel model. The UWB channels within the vehicle are then modeled by extracting relevant cluster and ray arrival rates and cluster and ray decay factors. Index Terms—Channel model, ultra-wideband (UWB). I. INTRODUCTION U LTRA-WIDEBAND (UWB) radio has attracted a great deal of research interest and applied for a variety of com- mercial and military applications recently. The extremely wide bandwidth promises tremendous channel capacity and makes UWB radio immune to conventional narrowband interferences. A major focus on UWB radio applications in the commercial sector has for wireless personal area network (WPAN) offering data rates up to 480 Mb/s over short distances of 4–10 m. Recently, there has been interest in the use of UWB in both military and commercial vehicles. The developers of commer- cial vehicles are interested in replacing certain segments of con- ventional wired control network with a wireless communica- tions system. The amount of cabling required in a modern auto- mobile could exceed 4 km in some cases [7] and the costs asso- ciated with developing, installing, and maintaining this amount of cabling per vehicle is becoming prohibitive. By eliminating a significant percentage of the total signal cables in a vehicle, developers can reap big savings in manufacturing, maintaining, and new model developing. Military users have also expressed an interest in short range m communications in proximity to the vehicle. The goal is to provide the crew with connection to the vehicle when they are dismounted. Dismounted operations in urban and in- dustrialized environments are of special interest because of the hazards associated with them. Manuscript received March 1, 2004; revised September 15, 2005. P. C. Richardson and W. Xiang are with the Department of Electrical and Computer Engineering, University of Michigan, Dearborn, MI 48128 USA (e-mail: richarpc@umich.edu; xwd@umich.edu). W. Stark is with the Department of Electrical Engineering and Com- puter Science, University of Michigan, Ann Arbor, MI 48109 USA (e-mail: stark@eecs.umich.edu). Digital Object Identifier 10.1109/JSAC.2005.863882 The replacement of conventional wired links with wireless connections in vehicular systems presents a number of chal- lenges regarding system reliability and safety. UWB radio is re- garded as a competitive candidate to address these challenges due to its superior properties: resilience to narrowband inter- ference and extremely low radiation power. Similarly, for dis- mounted military operations in proximity to the vehicle, UWB radio is difficult to be jammed and detected. Moreover, the fine delay capability can provide accurate range determination. These emerging applications for UWB presents new channel environments that have not been extensively studied. The new channel environments include the inside of both commercial and military vehicles and various short-range outdoor environ- ments in proximity to the vehicle. The major research focus of UWB channel models has been predominantly in the area of high data rate, short range commercial applications. The IEEE 802.15.3a work group has defined a UWB indoor channel model for the 4–10 m range [5] based on the clustering effects first re- ported by Saleh and Valenzuela [8]. Many efforts have focused on the UWB channel for indoor environments because of the tremendous commercial potential that exists [2]–[12]. The ef- fects of human beings in sparse and dense multipath environ- ments are described in [13]. The propagation of UWB radio sig- nals through different building materials are studied in [14]. The UWB channels in watertight ship compartments are explored in [15] and UWB outdoor channels in forested environments are discussed in [16]. In this paper, we study the UWB channels within a vehicle and outdoors in proximity to the vehicle in an industrial envi- ronment. The objective is to gain the channel impulse responses (CIRs) of UWB channels in these environments and to compare the results with those derived from the IEEE 802.15.3a channel model developed for indoor environments. The paper is arranged as follows. The experiment setup is de- scribed in Section II. In Section III, we measure the temporal characteristics of UWB channels and compare with those from the IEEE 802.15.3a model. Section IV discusses channel ca- pacity and path loss. Conclusions are given in Section V. II. UWB TESTBED AND EXPERIMENTS The vehicle selected for this study is an armored military vehicle. An industrial environment is selected because it is a challenging environment for dismounted military operations. The industrial site selected is a manufacturing building at the U.S. Army Tank-Automotive Research Center (TARDEC), Warren, MI. The PulsON 200 Evaluation Kit (EVK) from the Time Domain Corporation (Huntsville, AL) is adopted in the test. 0733-8716/$20.00 © 2006 IEEE