Coding on demand by an informed source (ISCOD) for efficient broadcast of different supplemental data to caching clients

The Informed-Source Coding On Demand (ISCOD) approach for efficiently supplying nonidentical data from a central server to multiple caching clients over a broadcast channel is presented. The key idea underlying ISCOD is the joint exploitation of the data blocks already cached by each client, the server´s full knowledge of client-cache contents and client requests, and the fact that each client only needs to be able to derive the blocks requested by it rather than all the blocks ever transmitted or even the union of the blocks requested by the different clients. We present two-phase ISCOD algorithms: the server first creates ad-hoc error-correction sets based on its knowledge of client states; next, it uses erasure-correction codes to construct the data for transmission. Each client uses its cached data and the received supplemental data to derive its requested blocks. The result is up to a several-fold reduction in the amount of transmitted supplemental data. Also, we define k-partial cliques in a directed graph and cast ISCOD in terms of partial-clique covers.