Design of an optical UWB pulse leading to an in-band interference tolerant impulse radio UWB transceiver

Abstract

Impulse-radio UWB (IR-UWB) transceivers are quite interesting since they can achieve high data rate while consuming low power. But UNII Band interferers are a serious problem for using the whole spectrum in IR-UWB. Also the short range of UWB is a serious limitation to this technology. Here we have proposed a solution to overcome both of the above mentioned problems. Matched filter concept shapes the output noise according to its spectrum so it can act as a noise filter. Matched filter is implemented in analog domain by designing an all optical UWB pulse featuring notches that can be tuned to a certain frequency. Therefore, any narrowband interferer can be nulled out passing through the matched filter. Also no transmission is done in the spectrum of the narrow band system so no interference is caused by UWB system. On the other hand since the pulse is implemented fully optically, by using UWB over fiber, the UWB range can be greatly extended. Modified Hermite polynomials have unique properties which are used for designing an optical UWB pulse with frequency nulls in its spectrum. For optical implementation of the proposed UWB pulse, Gaussian laser beams are combined to provide a signal with similar properties of Modified Hermite polynomials. The proposed system consists of a single wave length laser source, optical delay, power splitter/combiner, a length of single mode fiber (SMF) and a photo detector (APD). The simulation results shows that for short range communication the proposed architecture can tolerate large in band interferers up to 30 dBm. For long range the tolerance is degraded to 0dBm interferer power which is still quite high.