HARQ protocols for cooperative networks

本研究计划的目的是增加我们对在协作通信网络中部署所谓的HARQ协议的基本原理、限制和权衡的理解。网络中终端之间的协作被视为在无线环境中增加通信的覆盖率、速率和可靠性的一种方式。它通常采取中继的形式，终端相互帮助将信息传递到各自的目的地。在无线环境下，传输错误是不可避免的，因此有必要考虑通过所谓的混合自动重复请求（HARQ）协议进行重传。虽然它在点对点通信中是一种众所周知的机制，但在协作网络环境中部署HARQ并非易事，因为由于许多终端的存在，重新传输的可能性大大增加。由于继电器可能使用所谓的网络编码，因此阐明和分析如何将其与基于继电器的HARQ有效地结合起来是很重要的，因此增加了问题的另一个维度。

The objective of this research program is to increase our understanding of the fundamental principles, limitations, and trade-offs related to the deployment of the so-called HARQ protocols in the collaborative communications networks. The collaboration between the terminals in the network is seen as a way to increase the coverage, the rate, and the reliability of the communication in the wireless environment. It usually takes the form of relaying, where the terminals help each other to convey information to their respective destinations. In the wireless context, the transmission errors are unavoidable so it is necessary to consider retransmission via the so-called hybrid automatic repeat request (HARQ) protocol. While it is a well-known mechanism in point-to-point communications, deploying HARQ in the context of collaborative network is not trivial because the number of retransmissions possibilities is significantly increased due to the presence of many terminals. Another dimension to the problem is added since the relays may use the so-called network-coding and thus it is important to elucidate and analyze how to combine it efficiently with the relay-based HARQ. Our goal is to find the most convenient cooperative transmission schemes, which is possible only when we are able to optimize the rate and/or power of the HARQ retransmission rounds. We will also consider the HARQ parameters' adaptation strategies, which rely on the information being exchanged between the communication terminals. Since, in practice, this information may be subject to errors, we will analyze the effects caused by these errors and propose mechanisms to deal with these undesirable effects. Developing the methods to efficiently optimize and characterize the collaborative HARQ is crucial to use them and integrate these transmission strategies into high-level optimization of the network communications.