Software-Defined Radio based Blind Hierarchical Modulation Detector via Second-Order Cyclostationary and Fourth-Order Cumulant

Modulation detection is very important to many communication and electronic warfare applications. Recent developments in cognitive radio (CR) and dynamic spectrum access (DSA) network have also brought much attention to modulation detection of unknown radio frequency (RF) signals. It is well known that using second-order cyclostationary features, e.g., spectral correlation function (SCF) and spectral coherent function (SOF), BPSK modulation can be easily distinguished from higher order modulations such as QPSK and QAM modulations. However, QPSK and higher order modulations exhibit similar second-order cyclostationary features, thus these features cannot be employed to distinguish among higher order modulations. To classify higher order modulations, higher order cumulants are proposed in the literature. In this thesis, we build a blind hierarchical modulation detector to successfully classify the modulations of the RF signals. Moreover, we use software-defined radio (SDR) to implement and demonstrate a practical blind modulation detector which can accurately distinguish among three popular modulations, i.e., BPSK, QPSK and 16-QAM. Specifically, second-order cyclostationary features using detailed SOF are applied to distinguish between BPSK modulation and non-BPSK modulations (e.g., QPSK and 16-QAM modulations) at first level of the hierarchical modulation detector. Then fourth-order cumulant feature is applied to the non-BPSK RF signals: distinguish between QPSK modulation and 16-QAM modulation. In the implementation, we use Universal Software Radio Peripheral (USRP) hardware and GNU Radio software to realize the blind hierarchical modulation detector. Energy based signal detection is implemented to detect the existence of RF signals, and the hierarchical modulation detector will classify the modulation of the detected RF signal. The SDR based blind hierarchical modulation detector does not require any priori information of the RF signal, and performs real-time accurate modulation detection. The performance of the proposed blind hierarchical modulation detector is analyzed under different conditions, such as the number of samples and the number of symbols. Demonstrations in AWGN channel and realistic multi-path fading channel confirm the effectiveness and efficiency of the proposed SDR based blind hierarchical modulation detector