Optimum Digital Modulation/Demodulation Techniques for Mobile Satellite Communications Systems

(1)总结了数字调制/解调和编码技术的发展趋势。为移动卫星通信系统提供了资金。在LEO （Low Fmfl orbit）卫星系统中，由于接收到的信号功率降低，移动站规模的减小会导致传输性能的下降。此外，低轨道卫星快速运动带来的多普勒频移对探测性能影响很大。然后，有必要研究利用多普勒频移快速跟踪载波频率波动的AFG/PLL电路。(2)提出了一种新的相位和频率估计器，作为相干检测系统中的AFC/PLL电路。Ibis估计算子是基于卡尔曼算法来估计载波频率的一阶导数和二阶导数。从而可以准确地估计和跟踪载波相位。采用该估计器的相干检测系统在多普勒频移加性高斯噪声信道和梯度衰落信道中均具有良好的误码率性能。(3)星间通信链路传输技术是利用LED卫星构建全球移动卫星通信系统的关键技术。提出了一种偏振调制/光相干检测系统。并对该系统的性能进行了评价。此外，还提出了一种光学外差空间跟踪系统。

(1) A summary of the trends of digital modulation/demodulation and coding techniques. for mobile satellite communications systems has been provided. In LEO (Low Fmfl Orbiting) satellites symm, reduction of mobile station size introduces the degradation of transmission performance, since the received signal power decreases. Moreover, the detection performance is mwh affected by Doppler frequency shift associated with the rapid motion of LEO satellite. Then, it is necessary to investigate the AFG/PLL circuit which can rapidly track the fluctuation of carrier frequency by Doppler shift.(2) A novel phase and frequency estimator which works as an AFC/PLL circuit in coherent detection systems has been proposed. Ibis estimator operation is based on Kalman algorithm which estimates the first and second derivatives of the carrier frequency. so that it can estimate and track the carrier phase accurately. The coherent detection system with the proposed estimator recieves good bit error rate performance in both an additive Gaussian noise channel with Doppler frequency shift and a Rician fading channel.(3) Transmission techniques in inter-satellite comomication link are key technologies in order to construct worldwide mobile satellite communications systems using LED satellites. A polarization modulation/optical coherent detection system has been proposed. atid the performance of the proposed system has been evaluated. Also, an optical heterodyne spatial tracking system has been proposed.