Research On Key Technology Of Efficient Spectrum Utilization Based On Entropy

With the rapid development of wirless communication technology and the expansion of wirless communication market, the controdictions is outstanding between the high data transmition and large coverage range required by subscriber and increasing scarce spectrum resources. Which causes that the overlaping and collision of spectrum is more and more serious. The imbalance between supply and demand will cause seriously interference, collision and interrupt of communication. In order to solve the problem, the resourch on key technology of efficient spectrum utilization is made by many academics and engineers. There are two ways to improve spectrum efficiency. One is to enhance the exising systems' capability to make them can transmit more information in the same bandwidth by utilizing the more efficient transmission technique. The other is cognitive radio, which is the emergying technique that reuses the lisensed but underutilized spectrum without causing harmful interference to licensed systems by spectrum sensing. But because of complexity of wirless spectrum, all of these resourch always face many difficulties. Therefore, how to overcome these difficulties is a important resourch using the theory tool from interdisciplinary collaboration.Entropy measures the uncertainty about the value that might be assumed by the variable, and it roughly means disorder, chaos, decay of diversity or tendency toward uniform distribution of kinds. The term entropy is now used in many other sciences. The sequences complexity measure theory based on entropy can measure the disorder(or the complexity) of system by calculation of the data sequences, and the disorder is an essential aspect of the system. Therefore as a measure theory, the entropy can be used in many aspects of the key technology of efficient spectrum utilization, especially in security performance analysis for spectrum used, spectrum sensing for cognitive radio, dynamic spectrum access and so on. Based on the entropy, we investigate the key technology of efficient spectrum utilization, and contributions are summarized as follows:Fristly, the overview of the entropy measure theory used in the key technology of efficient spectrum utilization is introduced, and the novel entropy concept and complexity metric are presented. With consideration of the problems of existing complexity measure theory, The complexity mtric based on Fuzzy Entropy(FuzzyEn) is study, and two basic properties of it are proved. On this condition, the concept of Fuzzy Relation Entropy(F-REn) is presented, and the its properties and essential aspect is discused. FuzzyEn and F-REn works have obvious advantages in the applicability of symbolic space, the sensitivity of vector dimension, the robustness of resolution parameter and the dependence to observation length.Secondly, a novel security performance analysis method for frequency-hopping/ spread-spectrum(FH/SS) sequences is presented. the membership function is constructed for the FH/SS sequences, and fuzzy metric module is embedded into statistic metric for improving performance of complexity metric. the definition of the Fuzzy Approximate Entropy(F-AEn) as a complexity metric of FH/SS sequences is given, and two basic properties of it are proved. The FuzzyEn scheme has obvious advantages in the robustness to resolution parameter, the dependence to observation length and the sensitivity to vector dimension.Thirdly, By introducing the nonuniform quantization, the spectrum entropy-based spectrum sensing scheme is proposed. With consideration of the problems of the energy sensing technology is influenced by noise uncertainty. The validity of entropy-based and spectrum entropy-based detection using uniform quantization are analysed. On this basis, the optimality of spectrum entropy-based detection using uniform quantization is proved using Maximum Entropy Theory. The simulation results verify the robustness against noise uncertainty, and show that the proposed scheme outperforms energy detection under noise uncertainty situation.Finally, the prediction mechanism for channel state parameters and dynamic change mechod for sensing period is presented in dynamic spectrum access of cognitive radio based on entropy measure theory. The model of dynamic spectrum access baed on Partially Observable Markov Decision Process (POMDP) is constructed in the condition of dynamic parameter. On this basis, the prediction mechanism for channel state parameters and dynamic change mechod for sensing period is embedded into the POMDP model. The model have obvious advantages in the normalized throughout and the collision probablity.