Tham khảo tài liệu 'development and implementation of rfid technology part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Remotely UHF-Powered Ultra Wideband RFID for Ubiquitous Wireless Identification and Sensing 111 band for different applications 11 such as indoor and outdoor communication vehicle radar ground penetrating radar wall imaging systems medical imaging systems surveillance systems and law enforcements. Figure 1 shows the FCC emission mask for indoor and outdoor applications. Ultra Wide Band has been defined by the FCC as a radio or wireless device where the occupied bandwith is greater than 20 of the center frequency or has a bandwidth higher than 500MHz. Two possible techniques for implementing UWB are Impulse Radio IR and multi-carrier UWB. Multi-carrier or multi-band UWB systems use orthogonal frequency division multiplexing OFDM techniques to transmit the information on each of the subbands. OFDM has several good properties including high spectral efficiency robustness to RF interference and to multi-path. It also has been proven in other commercial technologies such as IEEE g. However it has several drawbacks. Up and down conversion is required and it is very sensitive to frequency clock and phase inaccuracy. On the other hand nonlinear amplification destroys the orthogonality of OFDM. With these drawbacks MB-UWB is not suitable for low-power and low cost application. Frequency GHz Fig. 1. FCC regulation mask for indoor and outdoor communications. The main advantage of UWB-IR compared with narrowband systems can be described with Shannon s capacity equation Eq. 1 where B is bandwidth S is the signal power and N the noise power . The channel capacity is directly proportional to the bandwidth and has a logarithmic relation with the signal power. This means that increasing the Bandwidth higher data rates can be achieved keeping a small signal power. .S c 510gJ 1 1 Information in impulse UWB techniques is send by modulating short pulses. In the literature is possible to find many waveforms that fulfill the spectral and power emission regulations stated in .
