New Approaches to Highly Bandwidth-Efficient Satellite Communications
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 ?