A new technique for analyzing unknown RF waves

A new technique has been developed for estimating unknown information about quadrature amplitude modulation (QAM) signals. The technique uses RF direct quadrature undersampling to extract individual in-phase and quadrature (I/Q) components of baseband signals from a quadrature-modulated RF carrier. The technique estimates such information as carrier frequency, modulation type, and symbol rate using numerical analysis and the I/Q baseband signal tracks. The measured tracks of I/Q baseband signals correspond to the theoretical ones, demonstrating the validity of this technique. Moreover, the estimated carrier frequencies nearly correspond to the measurement specifications. Furthermore, both modulation types and symbol rates could be estimated by using the waveforms of the vector magnitude. The proposed technique should thus be useful for analyzing unknown information about QAM signals in cognitive radio.