Coded caching for reducing CSIT-feedback in wireless communications

Abstract

The work explores the role of caching content at receiving users for the purpose of reducing the need for feedback in wireless communications. In the K-user broadcast channel (BC), we show how caching, when combined with a rate-splitting broadcast approach, can not only improve performance, but can also reduce the need for channel state information at the transmitter (CSIT), in the sense that the identified cache-aided optimal degrees-of-freedom performance, can in fact be achieved with reduced-quality CSIT. These CSIT savings can be traced back to an inherent relationship between caching, performance, and CSIT; caching improves performance by leveraging multicasting of common information, which automatically reduces the need for CSIT, by virtue of the fact that common information is not a cause of interference. At the same time though, too much multicasting of common information can be detrimental, as it does not utilize existing CSIT. Our caching method builds on the Maddah-Ali and Niesen coded caching scheme, by properly balancing multicast and broadcast opportunities, and by combing caching with rate-splitting communication schemes that are specifically designed to operate under imperfect-quality CSIT. The observed achievable CSIT savings here, are more pronounced for smaller values of K users and N files.