Research On Adaptive Polarization Modulation In Depolarization Channel

Polarization modulation (PM) scheme could let the power amplifier work in its nonlinear region to acquire high effective data rate, in which the polarization state was used as the information bearing parameter, due to that the polarization state in wireless communication are not impacted by power amplifier nonlinear distortion. However, one of the biggest challenges is faced when introducing the polarization state as the information bearer into wireless communication, which is the depolarization effect caused by the multipath and rich-scattering characteristics of wireless channel, such as the polarization dependent loss (PDL) effect and polarization mode dispersion (PMD) effect.1) in single-carrier communication scenario, PDL incurs the polarization state-dependent power attenuation in polarization modulation system;2) in multicarrier communication scenario, the PMD effect causes the frequency dependent fluctuation of the PDL effect level, leading the SER performance of PM to be diverse on each subcarrier. Both of them incur impairment to polarization modulation, which restrict the development and employment of polarization modulation in wireless communication. Therefore, research on the method to mitigate the impact of depolarization effects on the polarization modulation turns out to be very necessary.The research work is supported by "Chinese National Nature Science Foundation Project:Research on power amplifier energy efficiency based on cognitive and polarization signal processing (61271177)". The research of this thesis concentrates on employing adaptive polarization modulation technique to mitigate the impact of polarization dependent loss and polarization mode dispersion to the polarization modulation. And the related algorithms and schemes are analyzed and researched. The main research work and achievements of this thesis are as follows:(1) The related polarization signal processing techniques^polarization modulation techniques、adaptive modulation techniques and the existing research on depolarization effect are summarized and analyzed. Moreover, the dissertation points out the feasibility of using adaptive technology to reduce the influence of PDL and PMD in wireless channel on polarization modulation, and indicates the direction of this research.(2) In order to reduce the influence of PDL on polarization modulation, an adaptive polarization modulation scheme is proposed. Firstly, the polarization dependent loss impairment of the wireless depolarized channel to PM is analyzed, and the corresponding adaptive polarization modulation scheme is presented to mitigate such impairment; finally, as evaluated in simulation, adaptive polarization modulation scheme obtains a better performance in terms of spectral efficiency as compared to the nonadaptive polarization modulation, subject to the same fixed target BER constraint.(3) In order to reduce the influence of PMD on polarization modulation in Orthogonal Frequency Division Multiplexing (OFDM) system, An Adaptive Polarization Modulation in OFDM system is presented to combat the polarization mode dispersion effect, in which the subcarriers are grouped into several subcarrier-groups and independently modulated according to channel characteristics in each subcarrier-group. Simulation results show that, the proposed scheme could effectively mitigate such impairment, to be specific, the BER performance of OFDM system using Adaptive Polarization Modulation is better than nonadaptive polarization modulation.