The characteristics of ultra wideband systems in indoor environments

Abstract

The Ultra Wideband (UWB) systems have recently been proposed for use in a range of RF applications from ground probing radar to wireless communications. The UWB systems use a series of very short pulses in the order of sub-nanosecond. Consequently, the emission bandwidth of such UWB device (so called impulse radio) is extremely wide (1 to 10GHz or more). An UWB signal is directly applied to broad bandwidth antenna to generate RF emission without modulating a carrier (also called carrierless). In this thesis, the UWB technology is shortly introduced at first. The definition of UWB signal and the characteristics of UWB systems are introduced. Various UWB signal waveforms are also overviewed. Because the UWB signals are intrinsically very narrow pulse width, the coexistence between UWB system and conventional narrowband system is inevitable. Today, many researches are performed to decide whether UWB signal gives a harmful interference to conventional narrowband interference or not. The coexistence of UWB system and narrowband system is analyzed in theory and experiment. The conventional narrowband interference on UWB system is analyzed in theory. On the other hand, the effect of UWB system on conventional narrowband system is analyzed in experiment specifically the 2.4GHz WLAN (Wireless Local Area Network) system. The interference effects are measured by the file transferring access time from WLAN AP (Access Point) to WLAN STA (Station) and total throughput degradation. Then, the UWB signal measurement techniques are investigated. Because the UWB signal is very narrow in the order of sub-nanosecond, the successful capturing in the receiver is very difficult. The high minute calibrations in antenna, cable, DSO (Digital Sampling Oscilloscope), etc. are necessary. Based on this UWB signal measurement setup, the characteristics of UWB signal propagation in indoor environments and the feasibility of coexistence between UWB and 2.4GHz WLAN system are investigated. T...