Baseband digital synthesis and analysis for high-frequency software radio applications

Software-defined radio (SDR) employs digital modulation and demodulation techniques to solve traditionally analogue communications problems. To achieve this, the SDR must be capable of synthesising and analysing high-frequency analogue signals. However, sampling frequencies are limited by the capabilities of digital-to- analogue and analogue-to-digital converter technology. This paper presents quadrature synthesis and analysis techniques that cause the sampling rate, filtering frequencies and processing requirements to become functions of the signal bandwidth rather than the highest signal frequency component. A new investigation of the inaccuracies inherent to quadrature mixing is presented, and new techniques for digital compensation are suggested. It is shown that these proposed techniques allow all mixing artefacts to be suppressed to the level of the system´s quantisation noise.