Using GNU Radio in a Multipath Environment Practical Application

Abstract

Having used GNU Radio for several years, it has many worthy applications. One such use has been propagating data using ultrasound in a variety of material such as air, water and steel. The modulation protocol used to date has been binary FSK (some ASK/PSK have also been used), however these protocols do not handle multipath well. For this application we would look to use OFDM, however OFDM is normally used in a broadband application, where many subcarriers can be created, using it in an application that has limited bandwidth can be challenging. The bandwidth I have available with standard transducers is less than 1 kilohertz, as such the scaling and management of the subcarriers can be difficult. Sound waves travelling in solids can be made up of transverse and longitudinal waves, the sensors receiving this mixed signal must be able to filter out the unwanted signal so the modulated data can be extracted with the minimum number of errors. In liquids and air, shields can be employed on the receiving sensor to limit the unwanted signal picked up by the transducer, however in solids this is not possible. My objective is to modulate data in steel rail using GNU radio at a data rate that has useful and practical application. This paper explores these issues and how GNU radio can be employed to create duplex channels in ultrasound that can be used for data communications.