Ultrareliable Wireless Communication with Message Splitting

Deep fading and multicell interference are the two main limiting factors for the practical realization of ultrareliable wireless transmissions. A recently proposed solution for achieving ultrareliability builds upon the idea of combining the user messages as a single packet, then transmitting the packet using a two-phase relaying strategy in order to harvest diversity. A potential problem with such a strategy is that it may be overly optimistic about the ability of the device to decode the entire message in the first phase. This work devises an alternative approach that splits the per-cell message into the broadcast part and the relay part, thereby enabling layered data transmissions to the receivers of various channel conditions. We first analyze the information theoretic achievable rate of a channel with one sender and two receivers, and show that rate-splitting attains the optimal generalized degree-of-freedom (GDoF) whereas the existing method is suboptimal. Furthermore, we combine rate splitting with successive cancellation to handle the case with multiple cells interfering with each other. Numerical examples show a significant advantage of the proposed rate-splitting method over the existing approaches.