Evaluation of Free Space Link Budget in UWB Impusle Radio

Recently, an ultra wideband (UWB) impulse radio draws much attention due to its potential low cost and low power consumption properties. The Federal Communications Commission (FCC) is currently working on setting emission limits that would allow UWB communication systems to be deployed on an unlicensed band following the Part 15 rules for radiated emissions of intentional radiators [1]. The UWB radio channel bandwidth for handheld wireless communications isfrom 3.1 GHz to 10.6 GHz. The UWB transmitter sends a pulse with a channel bandwidth of this wide and the receiver collects the power of the received signal for rebuilding the pulse. Since the power spectrum density level of UWB signal may be below the noise level of the receivers for other systems, UWB radio technology can exist with other RF technology without interference. The narrowband wireless systems, Friis’ transmission formula is used for the line-of-sight (LOS) link budget evaluation [2]. However, it is not directly applicable to the UWB-IR system as the bandwidth of the pulse is extremely wide. Moreover, the effect of the waveform distortion shall be quantitatively considered in the link budget evaluation. In this paper, we discuss the free space link budget evaluation scheme in the term of transmission channel for the UWB systems that takes into account the transmitted waveform, its distortion due to the antennas, the channel and the correlation receiver. This scheme is based on the Friis’ transmission formula, adapted to the UWB-IR, in the sense that we derive the equivalent transmission gain of the UWB systems. The transmission is the keys for the extension of the Friis’ transmission formula for the UWB systems [3, 4]. Experimental investigations are done for different types of the antennas.