面向低轨卫星通信的多载波超奈奎斯特速率传输的信号接收技术研究

With the rapid development of terrestrial-satellite integration，the number of users and satellites in the network becomes increasingly large， leading to the severe scarcity for wireless spectrum resource. For higher spectrum efficiency and the increasingly demand for high-speed data transmission, proposed is to apply the multi-carrier faster-than-Nyquist (MFTN) signaling technique into the downlink high-speed rate transmission in low-earth-orbit satellite communications. Comparing with conventional modulation methods, MFTN is a kind of non-orthogonal transmission technique, which has higher spectrum efficiency, more signal design dimensions and can change signal transmission parameters flexibly. Considering Doppler frequency shift and noise in the downlink channel, our main aim is to decrease the effect of carrier frequency offset (CFO) for improving the transmission performance. The main contributions include following three aspects: the first one is to propose the method for deriving the performance bound of CFO estimation, providing an important reference for weighing the estimation performance of different methods. For improving the accuracy of CFO estimation, proposed is the non-data-aided CFO estimation method based on object function fitting, which is the second contribution of our work. The last is to propose a kind of turbo detection method for MFTN signal based on the principle of two dimension linear minimum mean square error, for decreasing the computation complexity and improving the CFO robust. It will provide the important support and reference for the application of MFTN signaling technique.

随着星地一体化的不断发展，用户终端以及卫星数量越来越多，导致稀缺的频谱资源更加紧张。为了进一步提高频谱效率以及满足高速传输的需要，本项目提出将多载波超奈奎斯速率传输技术应用于低轨卫星通信下行链路的高速传输场景。该技术是一种高效的非正交传输方式，比传统正交传输方式具有更高的频谱效率、更多的信号设计维度和更灵活的信号参数调整方式。本项目拟针对存在多普勒频偏、噪声等情况，深入研究如何降低频率偏差影响，以及提高信号接收性能。主要工作包括：1、提出多载波超奈奎斯特速率信号的频偏估计性能界的推导方法，为衡量不同频偏估计方法的性能提供重要参考；2、为提高频偏估计的精度，提出基于目标函数拟合的非数据辅助的频偏估计方法；3、为了降低信号接收的复杂度和提高抗频偏的鲁棒性，提出一种基于二维线性最小均方误差的多载波超奈奎斯特速率传输的迭代信号检测方法。为该技术的实际应用提供重要的理论支撑和参考。

在低轨卫星通信场景中，由于卫星与地面用户之间存在相对运动，通常会导致接收信号与发送信号之间存在多普勒频移。本项目考虑低轨卫星通信中下行链路所存在多普勒频移、多径效应等因素，对频域非正交信号（即多载波超奈奎斯特信号的一个子集）的接收技术进行了研究。研究内容主要集中在载波频偏估计、定时偏差估计等方面，并提出了相应的解决方法。仿真结果表明，所提出的方法比传统方法更具优势。相关研究结果已发表在IEEE Transactions on Aerospace and Electronic Systems、IEEE Transactions on Vehicular Technology、IEEE Photonics Technology Letters等期刊上，并申请了多项国家发明专利。本项目取得的研究成果已达到了预期目标。所提出的方法可以应用在低轨卫星通信的接收端，并降低载波频偏、定时偏差对传输性能的影响，从而尽可能发挥出非正交传输系统所具有的高频谱效率的优势。