| Satellite communication has more unique advantage than other transmission media, but with development of broadband satellite communication, the useful spectral resources become more limited. One of solutions is to raise spectral efficiency, hoping to select appropriate high level modulated signal to transfer over satellites. Spectral efficiency of traditional QAM is a high level modulation, but it doesn't fit satellite channels for its nonlinearity. High level modulation selects APSK constellation for its high power efficiency as near to MPSK and for its high spectral efficiency as rectangle QAM. The aim of studying APSK is selecting appropriate relative radii and relative phase for low SNR and non-linearity over nonlinear satellite channels by maximization of minimum Euclidean distance and calculation of average mutual information.Nonlinearity of HPA brings signal's heavy nonlinear distortion; we should take some of compensation technology. The paper finds by comparison that the scheme of pre-distortion of APSK constellation before HPA and restore excellent constellation after HPA is prior to other compensation ones, and it can combine nonlinear equilibrium to get better effect.APSK and QAM both belong to high level modulations so they are resemble on both modulation and demodulation. The way of APSK modulation and demodulation use reference of QAM. The SNR of satellite channel is low and we should adopt strong Error Correction of Coding, it is possible combining other simple modulation on sometimes asπ/2 BPSK modulation on DVB-S2. For APSK constellation is circle and the way of coding is not the same to QAM, the paper also bring forward a soft demodulation scheme for APSK.
|
PDF Full Text Request