Ultra-wideband outdoor communication characteristics with and without traffic
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RESEARCH
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Ultra-wideband outdoor communication characteristics with and without traffic Chien-Ching Chiu1*, Chien-Hung Chen2, Shu-Han Liao1 and Ting-Chieh Tu1
Abstract The BER performance for ultra-wideband (UWB) outdoor communication in LOS and NLOS environments with and without traffic is investigated. We obtain the impulse responses of the UWB outdoor environment by both 2.5D SBR-Image method and inverse Fourier transform techniques. The 2.5D SBR-Image method is first considered for two-dimensional environment simulated without heights of obstacles by ray tubes. Then, heights of the obstacles are taken into consideration between the transmitters and receivers. If the height of ray is lower than that of obstacles, the ray is neglected for the receivers. This effectively reduces the simulating time. By using the impulse response of multipath channels, the BER performance for binary pulse amplitude modulation communications over the radio UWB system is evaluated. We have performed computer simulations in LOS and NLOS environments with and without traffic in dense building areas. Numerical results have shown that the multipath effect caused by moving vehicles in the outdoor LOS and NLOS environments has a great impact on BER performance. Rake receivers are used to improve the outage probability. The relationship between traffic and BER performance is investigated; meanwhile, the characteristics of LOS and NLOS outdoor UWB environments are analyzed. Our investigation results can help improve planning and design of the UWB system. Keywords: UWB, multipath, BER, outage probability, RMS delay spread
1. Introduction When the Federal Communications Commission agreed in February 2002 to allocate the 7500 MHz bandwidth for unlicensed use of ultra-wideband (UWB) communications in the 3.1-10.6 GHz frequency region [1], the UWB technology has received wide research attention ever since. There are two task groups for Ultra UWB systems. One is the 802.15.3a for high data rate (100 M/ bps) and short operation distance (10 m). The other one is 802.15.4a for lower data rate (2 M/bps) and longer propagation distance (up to 100 m) [2]. UWB system offers many potential advantages, such as high resolution in multipath, reducing fading margins in link budget analysis, allowing for low transmit powers and low complexity [3,4]. All wireless systems must be able to deal with the challenges of operating over a multipath propagation channel, where objects in outdoor environment can cause multiple reflections and shadow
effect. The bit error rate (BER) degradation is caused by intersymbol interference (ISI) due to a multipath propagation arising from radio wave reflections by buildings, vehicles, trees, and even pedestrians. Recently, UWB has become an alternative physical layer candidate for TG4a in 802.15. In this task group, the emphasis is on lower data rates with larger propagation range in outdoor environment. In this study, we shall focus on this task group and investigate the outdoor environment performance [5,6]. We s
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