**1. Introduction**

Ultra-wideband (UWB) technology has developed rapidly over the past several years due to its high date rate with small current consumption in short range communication. According to Shannon-Hartley theorem, the maximum rate of clean (or arbitrarily low bit error rate) date through an AWGN (Additive white Gaussian Noise) channel, is limited to

$$C = BW \cdot \log\_2 \left( 1 + SNR \right) \tag{1}$$

Where, C is the channel capacity, BW is the bandwidth, SNR is the ratio of average received signal power to the noise spectral density. It can be seen from (1), channel capacity increases linearly with bandwidth but only logarithmically with SNR which means capacity increases as a function of BW faster than as a function of SNR and with a wide bandwidth, high data rate can be achieved with a low transmitted power. Its main applications include imaging systems, vehicular radar systems and communications and measurement systems. Ever since, the FCC released unlicensed spectrum of 3.1-10.6 GHz for UWB application in 2002, UWB has received significant interest from both industry and academia. Mutli-Band OFDM (MB-OFDM) and Direct-Sequence UWB (DS-UWB) are two existing competing proposals for UWB; each gained multiple supports from industry. The MB-OFMD divides the 3 ~ 10 GHz UWB spectrum into fourteen sub-bands which has a 528 MHz bandwidth. Due to incompatible of these two proposals, it experiences huge difficulties in commercialization of UWB technology. On the other hand, Impulse Radio UWB (IR-UWB) has become a hot research area in academia due to its low complexity and low power.
