CIF: Small: Efficient Satellite Relaying

通过卫星中继建立数据网络仍然是连接商业和政府应用的全球分布网络终端的重要手段，特别是在偏远地区。现代应用对网络的频谱和功率效率都有要求。这种网络中的原型网络模型是具有希望通过单个卫星应答器交换数据的两个终端的网络模型。相对于传统的双向通信路径分时或分频，信息理论表明，对于给定的链路功率资源集，可以获得高达100%的频谱效率增益。当采用非正交传输方法时，这些增益是可能的，并且解码器利用先前传输信息的侧知识。该项目编纂了适合于这种两端数据交换模型的各种协议，包括放大转发，以及涉及卫星解码/重新编码的协议。可能的增益取决于链路资源以及期望的双向速率目标。现有的研究假设两个终端都有完美的同步和侧信息，但是大的往返延迟、载波相位/频率同步和符号同步等实际问题是实现信息论承诺的重要障碍。因此，研究人员开发了接近理想信息理论极限的现实同步协议设计。此外，该项目还研究了一种新的基于下行链路上嵌套LDPC编码的解码转发中继协议，该协议在速率不对称方面具有灵活性。

Data networking via satellite relays remains an important means of linking globally-distributed network terminals for both commercial and governmental applications, especially in remote regions. Modern applications demand both spectrum and power efficiency in the network. The archetype network model in such networks is one with two terminals wishing to exchange data via a single satellite transponder. Relative to traditional time-sharing or frequency-sharing for the bidirectional communication paths, information-theory reveals that spectrum efficiency gains of up to 100% can be obtained for a given set of link power resources. These gains are possible when non-orthogonal transmission methods are adopted, and the decoders exploit side-knowledge on previously-transmitted information. The project codifies various protocols appropriate to this two-terminal data exchange model, including amplify-forward, as well as protocols that involve satellite decoding/re-encoding. The possible gains depend on link resources as well as the desired bidirectional rate targets. Existing research for this problem presumes perfect synchronization and side-information at both terminals, but practical issues of large round-trip delay, carrier phase/frequency synchronization, and symbol synchronization are important obstacles to achieving the promise of information theory. So the investigators develop realistic synchronization protocol designs that approach the ideal information-theoretic limits. In addition, the project studies a new decode-and-forward relaying protocol based on nested LDPC coding on downlinks that is flexible in terms of rate-asymmetry.