Research On Cognitive Radio Spectrum Sharing Techniques Based On Polarzation Signal Processing

Spectrum is a kind of valuable resource that is non-renewable. It is an eternal topic that the spectrum efficiency should be improved to meet the growing demand for wireless communication services. Although the research of sharing the licensed spectrum utilizing cognitive radio techniques in temporal, frequency and spatial domains has attracted considerable attentions, spectrum sharing realized by utilizing the signals’ polarization characteristics of the primary users and the secondary users deserves more attention. With the potential spectrum opportunities in the polarization domain fully exploited by polarization signal processing, the secondary users can coexist concurrently with the primary users on the same spectrum band and space. Thus the spectrum efficiency can be further improved, which provides new perspectives for alleviating the spectrum scarcity problem.The research work is supported by Chinese National Nature Science Foundation Project:"Research on the theory and technology of spectrum sensing in polarization domain"(60902047), and the National Key Scientific and Technological Project "Research and validation of cognitive radio technology in TD-LTE system"(2012ZX03003006). The research of this thesis concentrates on the spectrum sharing between the secondary users and the primary users based on the signals’polarization information, and the main research work and achievements of this thesis are as follows:(1) The related cognitive radio based spectrum sharing technichs and polarization signal processing technichs are summarized and analyzed. Basically, the spectrum sharing methods in current studies are summarized, and the spectrum opportunities for the secondary users in multiple domains are specially analyzed. Then the research development of polarization signal processing are summarized. Moreover, the feasibility of conducting spectrum sharing in polarization domain is analyzed.(2) For spectrum sharing between a pair of secondary users and a pair of primary users, efficient spectrum sharing algorithm based on polarization adaption is proposed for the problem that current spectrum sharing techniques which utilize temporal or spatial spectrum opportunities are spectrum inefficient. The spectrum sharing model is established based on the users’polarization state and channel depolarization characteristics, then an interference constrained polarization enabled spectrum sharing algorithm is proposed. Furthermore, with the difficulties of acquiring the primary users’priori information taken into account, a semi blind polarization adaptation-polarization enabled spectrum sharing algorithm is proposed. Theoretical and simulation analysis show that, compared with traditional sensing based temporal spectrum sharing algorithms, the proposed algorithms can achieve higher spectrum efficiency.(3) For the issue of spectrum sharing among multiple pairs of secondary users and a pair of primary users, in order to tackle the more complicated interference introduced by additional secondary users, the signal’s spatial information is jointly exploited with polarized information, and a joint polarization adaption and beamforming algorithm is proposed. Furthermore, it is proposed to utilize Markov chain to model the state transition of the licensed spectrum to improve the robustness to the dynamic spectrum environment. Then a weighted throughput optimization problem is modeled and solved, thus multiple pairs of secondary users can coexist with primary users. Analysis and simulation results show that the proposed spectrum sharing approach not only remains robust to the dynamically changing spectrum environment, but also achieves higher spectrum efficiency than traditional sensing based algorithms. (4) For polarization enabled spectrum sharing under circumstances with polarization mode dispersion effect, more interference will be induced to the primary users and the SINR of the secondary users will deteriorate. In order to combat the adverse effect of polarization mode dispersion, the origination polarization mode dispersion is analyzed theoretically, and it is proposed to enable polarized spectrum sharing on a narrower frequency band, that is, a cluster of subcarriers. From the perspectives of combating the polarization mode dispersion effect and reducing environmental learning time overhead, an effective throughput optimization problem with respect to the subcarrier number in per cluster is designed. Simulation results show that, compared with the bandwidth-based and subcarrier-based polarization enabled spectrum sharing algorithms, the secondary users can gain better balance between the environment learning time overhead and avoiding the polarization mode dispersion effect, thus more desirable spectrum efficiency can be achieved.