Contents I. Introduction
To overcome the scarcity of available radio frequency (RF) resource, ultra-wideband (UWB) attracts its attention as one of next generation high-speed radio communication technologies because UWB systems can share the RF band with existing narrowband radio systems [1]–[3]. Although a UWB signal can occupy the bandwidth of over 500 MHz, its spectral density is regulated to be less than-41.3 dBm/MHz [4]. Therefore, it is possible that UWB radio systems share the RF band with existing narrowband radio systems. It is limited to the use in a short distance of around several tens meter due to the small power density, but it is expected to perform high-speed radio communication of more than 100 Mb/s. In addition, if UWB signal is composed of ultra short pulse, which is generally called impulse radio (IR), high-resolution radar ranging is possible. Moreover, low power consumption, low cost, and ease of miniaturization of the device would enable the installation of UWB transmitter and receiver to various equipments. Recently, UWB applications such as high-speed wireless personal area network (WPAN) and short range radar (SRR) built-in vehicle are strenuously studied [2], [3]. If such UWB signal can be delivered through optical networks without distance limitation, various stand-alone UWB applications can be networked widely and become available anywhere on demand.
