Coded Caching With Nonuniform Demands

• Published in: IEEE transactions on information theory Vol. 63; no. 2; pp. 1146 - 1158
• Main Authors: Niesen, Urs, Maddah-Ali, Mohammad Ali
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-02-2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Cache; Cache memory; Caching; Channel estimation; coding; content distribution; Data transmission; Decoding; Encoding; Information storage; Information theory; Libraries; Memory management; Optimization; prefetching; Servers
• ISSN: 0018-9448; 1557-9654
• DOI: 10.1109/TIT.2016.2639522

We consider a network consisting of a file server connected through a shared link to a number of users, each equipped with a cache. Knowing the popularity distribution of the files, the goal is to optimally populate the caches, such as to minimize the expected load of the shared link. For a single cache, it is well known that storing the most popular files is optimal in this setting. However, we show here that this is no longer the case for multiple caches. Indeed, caching only the most popular files can be highly suboptimal. Instead, a fundamentally different approach is needed, in which the cache contents are used as side information for coded communication over the shared link. We propose such a coded caching scheme and prove that it is close to optimal.