Ultra-wideband (UWB) technology is currently considered the most attractive solution to develop a Local Positioning System. In fact, the IEEE 802.15.4a standard includes a link (MAC) and physical (PHY) layer with indoor positioning capabilities. This paper presents a study of the typical modulations schemes used with UWB and its adaptation to ultrasonic frequencies. Moreover, several tests of the modulation schemes in the ultrasonic frequency range are shown, in order to apply these techniques in a local positioning system. The main goal is to implement the algorithms in FPGAs using UWB radio technology. Therefore, the use of ultrasonic frequencies can be considered as a previous step of the future work.