The Research Of Signal Recognition Technologies In Wireless Communication System

Along with the rapid development of wireless communications technologies and Internet technologies, wireless spectrum resources become increasingly saturated, in order to improve the utility ratio of spectrum, ensure the different heterogeneous wireless networks to work together and meet the needs of a variety of communication services, in this case, cognitive radio technology is born pregnant, of which the spectrum sensing is one of the key technologies to solve this problem, its objective is to detect and recognize the type of authorized or unauthorized signal exist in various frequency bands, it still belongs to communication signal modulation recognition category. In this dissertation, the signal feature extraction and recognition algorithm suitable for non-cooperative spectrum sensing have been deeply researched, mainly include single-carrier modulation signal feature extraction techniques based on statistical pattern recognition, inter-class recognition technology of single-carrier and multi-carrier modulation signals, as well as the multi-carrier modulation (MCM) signal parameter estimation and intra-class blind recognition technologies.First of all, after the analysis of the traditional statistical pattern recognition algorithm of single-carrier modulation signals, a new signal feature extraction algorithm based on the direction data statistical theory is proposed. This algorithm utilizes the characteristic that signal phase obeys the distribution of circular, take the instantaneous frequency values of single-carrier signal processed by a certain angle transform as data samples to extract the classification features, without any prior knowledge of carrier frequency, bandwidth and modulation index. The features extracted by this algorithm is more stable than conventional algorithms, has little changes with the time or the environment, smaller dependence of the sample length and better degree of inter-class separability. When the signal to noise ratio is greater than lOdB, the feature tends to stabilize and has a high degree of confidence. All of this provides a new way for blind recognition of single-carrier communication signal modulation type in non-cooperative spectrum sensing. Then, the further refinement and improvement are also indicated.Secondly, in order to solve the blind recognition problem of single-carrier signals and multi-carrier signals in Rayleigh fading channel, put forward an improved higher-order cumulants combination feature extraction algorithm and prove that algorithm can effectively suppress the effect on recognition performance caused by multi-path Rayleigh fading and Gaussian noise on the receiving end. Without any a priori knowledge, algorithm avoids tedious process of carrier synchronization and processes the sampling IF signals directly. Simulation shows that the improved features is not sensitive to the number of sub-carrier and have better robustness, compared with traditional algorithm. It also solves the difficulties of determining the recognition threshold caused by the dynamic changes of characteristic parameters. In addition, algorithm not only reduces the probability of misjudgment but also improves the identification accuracy, through the threshold discriminance or combining with simple classifiers it can achieve good recognition effect and lay a good foundation for the recognition of multi-carrier modulation signal next.Thirdly, the estimation of sub-carrier frequencies based high-order cyclic cumulants and bit rate based on multi-scale Haar wavelet transform are discussed about multi-carrier CDMA signal. The research shows that it is feasible to estimate sub-carrier frequencies by detecting the peak position of specific cycle-frequency. After this, bite rate estimation algorithm based on multi-scale Haar wavelet transform and the analysis of its performance under the conditions of existence of carrier frequency offset are simulated. All the experimental results provide the necessary theoretical basis and parameters support for the blind recognition of four kinds multi-carrier modulation signals.Finally, on the basis of the blind parameters estimation of the multi-carrier modulation signal, a new blind identification of. multi-carrier modulation signal algorithm based on the structural data matrix singular value decomposition is proposed, including algorithm model and implementation diagram. Take OFDM, MC-CDMA, MC-DS-CDMA and MT-CDMA four typical kinds of multi-carrier modulation signals based on IFFT implementation for example, which are common but difficult to distinguish. Detailed theoretical analysis and algorithm simulation are made respectively in the ideal Gaussian white noise channel and Rayleigh multi-path channel. Since the number of larger non-zero singular value of the MC-CDMA signal's structure matrix increases linearly with the number of users which leads to the misjudgment caused by the existence of multiple access interference, in one time, so a modified criteria more applicable to the actual channel conditions is presented. Algorithm doesn't need to know any multi-carrier modulation signal data information as well as the type and length of the spreading code. Only by counting the number of large non-zero singular value in gradient sequence of structural matrix singular values, it can accurately determine the type of multi-carrier modulation signal, not only avoids the tedious process of classifier design in traditional recognition algorithms after feature extraction, but also greatly simplifies the identification process. Furthermore, the order of structural data matrix do not have to strictly abide by the relationships that its value is an integer multiple of the number of sub-carriers, so a relative smaller value can be selected to reduce the computational complexity of algorithm. The simulation and analysis verifies that this algorithm can achieve good results in low SNR conditions. All of above providing a new idea for the intra-class recognition of multi-carrier modulation signals, with a high practical value.