Research On Modulation Classification In Fading Channels Under The Non-cooperative Reception Conditions

The modulation recognition technique, which is widely used in various occasions, has important applications and great theoretical values. Although a great progress have been made, there are still many key issues needed to be researched and solved, with the increasing complexity of channel and the appearance of new modulation schemes. The efficiency of existing classification methods need to improve under non-cooperative reception conditions in fading channel, with limited prior information and low precision of preprocessing. Aiming at the effective classification under non-cooperative reception conditions in fading channel, the modulation recognition technique are researched in this paper and the main contents and contributions are listed as follows.The first part: progress of modulation classification research is indicated in detail. Existing modulation classification methods are summed up by channel conditions or pretreatment complexity. Common methods are analyzed from performance, computation complexity to pretreatment requirement, which provides reference to choosing algorithm under different conditions.The second part: processing model of non-cooperative reception in fading channel is proposed, modulation characteristics under the model are analyzed. The modulation types include the common single carrier and multicarrier modulations, such as orthogonal frequency division multiplexing (OFDM) and offset quadrature amplitude modulation (OQAM). These characteristics, extracted directly from the received baseband signal, are hardly distortion to the fading channel and noise.1. The spectral correlation functions (SCFs) of OFDM and OQAM baseband signal in fading channel are analyzed, SCF models of multicarrier signal such as OFDM and OQAM are corrected. The theoretical derivations confirm the SCF of multicarrier signal existing cyclostationarity induced by periodicity of the modulated sequences.2. The second order cyclic cumulants of zero-padding OFDM (ZPOFDM) and OQAM baseband signal under fading channel are explored,cyclostationarity analyses are presented and expressions related to them are proposed and testified.3. Cyclic cumulant characteristics of common digital modulated signals are analyzed, combined with the existing achievements. The related conclusions under non-cooperative reception fading channel model are proposed and proved.The third part: the algorithms about parameter estimation under non-cooperative reception conditions in fading channel are proposed.1. An improved fast algorithm is proposed for cyclic spectral estimation, considering the variance of original cyclic spectral estimation is unsatisfactory. Compared with the existing methods, the proposed algorithm brings the windowed overlapped data processing into the frequency smooth algorithm to improve the estimation quality, which decreases the requirement of data quantity without reducing the performance. 2. Based on the cyclic cumulant of ZPOFDM signals, a blind parameter estimation algorithm is proposed to estimate parameters such as symbol period, zero-padding time guard interval. Compared with the existing algorithm, the employed features of proposed algorithm is insensitive to the fading channels or the noise and lead to an efficient estimation in frequency selective channels.3. A blind parameter estimation algorithm is proposed to estimate OQAM signal parameters such as symbol period, subcarrier number under the environment of fading channel, which exploited the second order cyclic cumulant and SCF of OQAM signal. The estimated performance is validated by experimental results, which indicate that the algorithm can achieve an efficient estimation under blind reception environments in the fading channel.The fourth part: aiming at solving the problems of the existing signal recognition methods under fading conditions, such as high demand of pretreatment, limited recognizable modulation formats that are unsuitable to non-cooperation situation, some other recognition methods are proposed as follow.1. For the limited recognizable modulation formats of the existing multicarrier signal classification methods, an improved OFDM signal recognition algorithm is put forward. This method has widened the recognition set with the ZPOFDM signal, and the recognition performance of the multicarrier signals in frequency selective fading channel is improved.2. An algorithm is proposed in order to overcome the problem of high pretreatment requirements when classifying common digital modulated signals under non-cooperative reception conditions in fading channel. The algorithm combines cyclostationary detection with cyclic frequency distribution characteristics of cyclic cumulant, which accomplishes effectively recognition of common digital modulated signals.3. A classification algorithm based on support vector machine (SVM) and cyclostationary properties is proposed after synthesizing the features and SVM classifiers, which can widen the recognition set and improve the classification effect.Finally the related engineering implementations are also presented. The whole work of the dissertation is summarized, the shortcomings of the researches are pointed, and some suggestions on future researches are given.