Automatic modulation classification of communication signals

The automatic modulation recognition (AMR) plays an important role in various civilian and military applications. Most of the existing AMR algorithms assume that the input signal is only of analog modulation or is only of digital modulation. In blind environments, however, it is impossible to know in advance if the received communication signal is analogue modulated or digitally modulated. Furthermore, it is noted that the applications of the currently existing AMR algorithms designed for handling both analog and digital communication signals are rather restricted in practice. Motivated by this, an AMR algorithm that is able to discriminate between analog communication signals and digital communication signals is developed in this dissertation. The proposed algorithm is able to recognize the concrete modulation type if the input is an analog communication signal and to estimate the number of modulation levels and the frequency deviation if the input is an exponentially modulated digital communication signal. For linearly modulated digital communication signals, the proposed classifier will classify them into one of several nonoverlapping sets of modulation types. In addition, in M-ary FSK (MFSK) signal classification, two classifiers have also been developed. These two classifiers are also capable of providing good estimate of the frequency deviation of a received MFSK signal. For further classification of linearly modulated digital communication signals, it is often necessary to blindly equalize the received signal before performing modulation recognition. This doing generally requires knowing the carrier frequency and symbol rate of the input signal. For this purpose, a blind carrier frequency estimation algorithm and a blind symbol rate estimation algorithm have been developed. The carrier frequency estimator is based on the phases of the autocorrelation functions of the received signal. Unlike the cyclic correlation based estimators, it does not require the transmitted symbols being non-circularly distributed. The symbol rate estimator is based on digital communication signals\u27 cyclostationarity related to the symbol rate. In order to adapt to the unknown symbol rate as well as the unknown excess bandwidth, the received signal is first filtered by using a bank of filters. Symbol rate candidates and their associated confident measurements are extracted from the fourth order cyclic moments of the filtered outputs, and the final estimate of symbol rate is made based on weighted majority voting. A thorough evaluation of some well-known feature based AMR algorithms is also presented in this dissertation

Magnetic field induced bandgap in two dimensional magneto-optical photonic crystals

The photonic bandgap of magneto-optical (MO) photonic crystals (PhCs) induced by an external dc magnetic field is theoretically investigated with the plane-wave expansion method. The effect of PhC lattice shape, MO filling fraction and dc magnetic intensity on such type of bandgap has been studied. It is found that PhC with triangular lattice is superior to PhC with square lattice in term of bandgap width; thus, the one-way waveguide composed by the former PhC has a broader operation band. Moreover, there exists a certain value of external magnetic field at which the bandgap reaches a maximum. These results are found to be in agreement by finite element analysis of transmission property of one-way waveguides

Terahertz spoof plasmonic coaxial microcavity

We theoretically demonstrate a subwavelength spoof surface-plasmon–polariton (SPP) microcavity on a planar metallic surface working at the terahertz regime with a high-quality factor and ultra-small mode volume. The microcavity is based on plasmonic and metamaterial notions, and it consists of an easy-to-manufacture circular aperture and a bell-shaped metallic core. It is shown that such a structure can sustain SPP eigenmodes whose fields are tightly trapped within the microcavity. Using the proposed structure, a total Q factor of 1000 (including losses from metals at low temperatures) and subwavelength mode volume of 0.00018(λ/2)3 can be achieved in the THz range for the fundamental surface-plasmonic eigenmode at room temperature. Moreover, the key figures of merit such as resonance frequency can be flexibly tuned by modifying the geometry of the microcavity, making it attractive for broad applications in filters, light sources, energy storage, and on-chip optical communications.Published versio