Tham khảo tài liệu 'ultra wideband communications novel trends system, architecture and implementation part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 140 Ultra Wideband Communications Novel Trends - System Architecture and Implementation 2. System analysis and operation principle Transmission power and pulse shaping For the UWB band the FCC limits the maximum transmitting power spectrum mask to MHz. Therefore the maximum allowable transmitted power within 3-5GHz is but no such a pulse can meet the FCC mask in practice assuming a filling coefficient of k 0 k 1 or spectral efficiencyWentzloff 2007 . The filling coefficient spectral efficiency k of a pulse is the loss incurred from incomplete filling of the -10dB channel bandwidth calculated by Ech k n PEIRPBW-10dB 1 where Ech is the pulse energy within the -10dB channel bandwidth PEIRP is the maximum average power spectral density and BW-10dB is the -10dB bandwidth. Due to this filling coefficient the maximum transmission power will be much smaller. To improve this filling coefficient many techniques for baseband pulse shaping have been investigated since the release of the UWB FCC mask First Report and Order . . For example a gaussian pulse is theoretically the ideal pulse shaping technique but it is difficult to implement Wentzloff Chandrakasan 2007 Zheng et al. 2006 . Fig. 4. Rectangular baseband and sine-wave modulated pulses in time and frequency domain Fig. 4Lathi . shows the Fourier transform of a baseband rectangle pulse and a rectangle pulse modulated by a sine wave. Notice that the spectral bandwidth is inversely proportional to the pulse width where for a rectangle pulse of T s pulse width its frequency bandwidth is 2 T Hz . For the 3-5GHz UWB band the maximum bandwidth is 2GHz when the carrier frequency is 4GHz with a minimum pulse width Wpulse of 1ns. Assuming a 1ns pulse width the pulse amplitude will depend on the pulse repetition frequency PRF or data rate limited by the maximum allowed transmission power. For data rates of 500Mbps 250Mbps and 125Mbps with equal probability of 1 and 0 symbols a filling .
