New Approaches to Highly Bandwidth-Efficient Satellite Communications

由于对数据传输的需求大幅增加，卫星通信系统正面临容量限制。满足需求的方法必须与地面系统中使用的方法有很大的不同，因为在信号处理的可能性和卫星的功率消耗方面存在严重的限制。此外，卫星的操作应该是简单和透明的，因为卫星被设计为在轨道上停留约15年，不容易更新和维修。因此，卫星社区主要采用常规方法。带宽效率的提高通常通过高阶调制方案（APSK）和减少多余带宽的脉冲整形来解决。然而，在卫星系统的严格限制下，不太传统的方法似乎更有希望实现高带宽效率。在提议的项目中，我们打算采用两种非常规的方法：多输入多输出（MIMO）传输，这在地面网络中已经很好地建立了，但由于共同视距信道条件，在卫星网络中并不常见。第二种方法是比奈奎斯特更快的信号，其中使用低阶调制通过违反第一个奈奎斯特条件来提高带宽效率。结合这两种方法，我们将设计和评估卫星场景中非常规应用的传输策略。我们打算在回答这个基本问题上迈出一步：MIMO和比奈奎斯特更快的信号是否可以被认为是提高卫星通信系统频谱效率的合适、创新和卓越的替代方案？

Due to substantially increasing demand for data transmission, satellite communications systems are facing capacity limits. The approaches to satisfy the demands have to be substantially different from the approaches used in terrestrial systems due to severe limitations in terms of signal processing possibilities and power consumption at the satellites. Moreover, the operations at the satellite should be simple and transparent as a satellite is designed to stay in the orbit for about 15 years without easy update and repair possibilities. Therefore, the satellite community mainly adopts conventional approaches. Increase in terms of bandwidth efficiency is typically addressed by higher order modulation schemes (APSK) and pulse shaping with reduced excess bandwidth. Nevertheless, less conventional approaches seem to be more promising to achieve high bandwidth-efficiency under the strict restrictions of satellite systems. In the proposed project, we intend to adopt two unconventional approaches: Multiple-input multiple-output (MIMO) transmission, which is well established in terrestrial networks but unusual in satellite networks due to the common line-of-sight channel conditions. The second approach is Faster-Than-Nyquist signaling, where the bandwidth-efficiency is increased using low-order modulation by violating the first Nyquist condition. Combining both approaches, we will design and evaluate transmission strategies for the unconventional application in satellite scenarios. We intend to make a step forward in answering the fundamental question: Can MIMO and Faster-Than-Nyquist signaling be considered as suitable, innovative and superior alternatives to increase the spectral efficiency of satellite communications systems ?