Communication Systems Engineering with GNU Radio

2Using GNU Radio with Signals Collected from SDR Hardware

Having introduced the basics of GNU Radio operations and the design of processing flowcharts using GNU Radio Companion to analyze synthetic signals, we will address in this chapter the acquisition of live signals using hardware receivers. Doing so, we meet the challenge that the emitter and receiver local oscillators are at different locations and at different frequencies – if only because of the Doppler shift introduced by a moving emitter or receiver – and this frequency difference must be compensated for. Hence, the modulation scheme aims at imprinting the transmitted information on all possible carrier variables, the amplitude, the frequency, or the phase. As stated by Mitola [2000], increasing complexity is associated with each one of these modulation schemes due to increasing coherence, namely the need to recover on the receiver side increasingly accurate copies of the transmitted carrier. The increasing complexity however comes with the benefit of increased spectral efficiency and immunity to noise, and hence increased ...