ICCAS2004 August 25-27, The Shangri-La Hotel, Bangkok, THAILAND Characterization of Body Shadowing Effects on Ultra-Wideband Propagation Channel Apichit Pradubphon ∗ , Sathaporn Promwong ∗,∗∗ , Monchai Chamchoy ∗ , Pichaya Supanakoon ∗ , and Jun-ichi Takada ∗∗ ∗ Department of Information Engineering, Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang Chalongkrung Rd., Ladkrabang, Bangkok 10520, Thailand Tel: +66 2 7372500-47 Ext. 5140 Fax: +66 2 3264176 E-mail: {s6064613,kcmoncha,kspichay}@kmitl.ac.th ∗∗ Graduate School of Science and Engineering, Tokyo Institute of Technology 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552, Japan E-mail: ken@ap.ide.titech.ac.jp Abstract: There are several factors that disturb an Ultra-Wideband (UWB) radio propagation in an indoor environment such as path loss, shadowing and multipath fading. These factors directly affect the quality of the received signal. In this paper, we investigated the influence of the human body shadowing on UWB propagation based on measured wireless channel in an anechoic chamber. The characteristics of the UWB channel including the transmitter and the receiver antenna effects are acquired over the frequency bandwidth of 3∼11 GHz. The major factors such as the power delay profile (PDP), the angular power distribution (APD), the pulse distortion and the RMS delay spread caused by the human body shadowing are presented. Keywords: Ultra-wideband communication, body shadowing, delay spread, pulse distortion 1. Introduction Recently, the ultra wideband (UWB) radio technology is be- coming an interesting topic for the wireless communication. The UWB system is different from other radio communica- tion technology. Instead of using narrow carrier frequency, the UWB transmits the pulse of power which is in the range of ultra-wide frequency spectrum. The US Federal Commu- nication Commission (FCC) specifies that the UWB signal has the frequency spectrum range from 3.1 GHz to 10.6 GHz [1]. The UWB technology is an ideal candidate that can be utilized for commercial, short-range, low power, and low cost indoor communication systems such as Wireless Per- sonal Area Networks (WPANs) [2], [3]. Hence, the charac- terization of an indoor radio channel is very important if we will use this technology in the realworld. Also, the effect of human body shadowing affecting to the signal level in the re- ceived part are also considered. Research about the influence of the human body on the radio channel has been in progress for several literatures [4]-[6]. A recent example of such a re- search by Welch et al. [4] which detailed the characteristic of the UWB antenna using traditional anechoic-chamber mea- surement techniques and characterize the power pattern of the UWB antenna with as the human body obstacte in the indoor environment. The RF environment is relatively quiet in the frequency range of interest (1-3 GHz)., Sanchez et al.[5]detailed their analytical results of human operator ef- fect on the wideband and narrowband channel and Zasowski et al. [6] detailed their UWB channel measurements from 3∼6 GHz for a body area network (BAN) in the anechoic chamber and an office room. But these researches do not consider the influence of the human body shadowing on the UWB communication channel by statistical process such as the mean excess delay, the RMS delay spread etc. are also an important parameter. In this paper, we investigated the influence of the human body showing on the UWB propagation over the frequency bandwidth of 3∼11 GHz. The experimental channels are taken in the anechoic chamber to avoid the environmental effects. However, the characteristics of the transmitter and receiver antennas are included in the channel. In the ex- periment, a handmade biconical antenna and the commer- cial, small-size, low profile antenna developed by Skycross, are used at the transmitter and receiver, respectively. From the experimental results, the channel parameters such as the power delay profile, the RMS delay spread, the correlation coefficient and the angular power distribution are seen di- rectly to be affected by the human body shadowing. 2. Investigation Parameters 2.1. Time Dispersion In order to investigate the effects of the human body shad- owing, we considered the time delay of the arrived signal at the receiver. Multiple reflections of the transmitted signal may arrive at the receiver at different times, resulting in in- tersymbol interference (ISI, or bits into one another) which the receiver cannot sort out. The time dispersion can be analyzed by using the mean excess delay, τm, and the RMS delay spread, τrms, to illustrate the effects of body shadow- ing. The mean excess delay which is the first central moment of |h(t)| 2 and the RMS delay spread which is the square root of the second central moment of |h(t)| 2 take into account the relative powers of the taps as well as their delays, making it a better indicator of system performance than the other pa- rameters. The mean excess delay, τm, is defined as [6] 219