The automatic recognition of the modulation format of a detected signal, the intermediate step between signal detection and demodulation, is a major task of an intelligent receiver, with various civilian and military applications. Obviously, with no knowledge of the transmitted data and many unknown parameters at the receiver, such as the signal power, carrier frequency and phase offsets, timing information, etc., blind identification of the modulation is a difficult task. This becomes even more challenging in real-world scenarios with multipath fading, frequency-selective and time-varying channels. In this paper we provide a comprehensive survey of different modulation recognition techniques, in a systematic way. A unified notation is used to bring in together, under the same umbrella, the vast amount of results and classifiers, developed for different modulations. The two general classes of automatic modulation identification algorithms are discussed in detail, which rely on the likelihood function and features of the received signal, respectively. The contributions of numerous articles are summarized in compact forms. This helps the reader to see the main characteristics of each technique. However, in many cases, the reported results in the literature have been obtained under different conditions. So, we have also simulated some major techniques under the same conditions, which allows a fair comparison among different methodologies. Furthermore, new problems that have appeared as a result of emerging wireless technologies are outlined. At the end, open problems and possible directions for future research are briefly discussed.

__ In this paper we propose a new shadowed Rice model for land mobile satellite channels. In this model, the amplitude of the line-of-sight is characterized by the Nakagami distribution. The major advantage of the model is that it leads to closed-form and mathematically-tractable expressions for the fundamental channel statistics such as the envelope probability density function, moment generating function of the instantaneous power, and the level crossing rate. The model is very convenient for analytical and numerical performance prediction of complicated narrowband and wideband land mobile satellite systems, with different types of uncoded/coded modulations, with or without diversity. Comparison of the first-and the second-order statistics of the proposed model with different sets of published channel data demonstrates the flexibility of the new model in characterizing a variety of channel conditions and propagation mechanisms over satellite links. Interestingly, the proposed model provides a similar fit to the experimental data as the well-accepted Loo's model, but with significantly less computational burden.

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__ One of the main assumptions in the Clarke's classic channel model is isotropic scattering, i.e. uniform distribution for the angle of arrival of multipath components at the mobile station.However, in many mobile radio channels we encounter non-isotropic scattering, which strongly affects the correlation function and power spectrum of the complex envelope at the mobile receiver. In this contribution, we propose the use of the versatile von Mises angular distribution, which includes and/or closely approximates important distributions like uniform, impulse, cardioid, Gaussian, and wrapped Gaussian, for modeling the non-uniform angle of arrivals at the mobile. Based on this distribution, associated correlation function and power spectrum of the complex envelope at the mobile receiver are derived. The utility of the new results is demonstrated by comparison with the correlation function estimates of measured data.

Rayleigh-lognormal distribution, proven useful for modeling fading-shadowing wireless channels, has a complicated integral form. In this paper we have accurately approximated it by the K distribution. This distribution is simpler and thus more appropriate for analysis and design of wireless communication systems.