Achieving Full Multiplexing and Unbounded Caching Gains with Bounded Feedback Resources

摘要

In the context of the K-user MISO broadcast channel with cache-aided receivers, recent multi-antenna coded-caching techniques have sought to complement the traditional multiplexing gains associated to multiple (L) antennas, with the (potentially unbounded) caching gains (G) associated to coded caching. To date, all known existing efforts to combine the two gains, either resulted in a maximum known DoF L + G that required though CSIT on all (L + G) users served at a time (i.e., that induced potentially unbounded CSIT costs that matched the DoF gains), or resulted in a much compromised DoF where multiplexing gains came at the expense of bounded or vanishing caching gains. We present here a new multi-antenna coded caching algorithm that introduces a new XOR generation structure which completely untangles caching gains from CSIT, delivering the desired sum-DoF of L+G but with a much reduced CSIT cost of only L channel vectors at a time (L × L CSIT matrix). This means that for the first time in multi-antenna coded caching, one can achieve full multiplexing gains and unbounded caching gains, at the mere CSIT cost associated to achieving the multiplexing gains. In the end, the result solidifies the role of coded caching as a method for reducing feedback requirements in multi-antenna environments.