Coordination Through Shared Randomness
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We study a distributed sampling problem where a set of processors want to output approximately (in the sense of asymptotically vanishing total variation distance) independent and identically distributed samples from a given joint distribution with the help of a coordinator. We consider two settings. In the omniscient coordinator setting, the coordinator has access to several independent sources of randomness and each processor has access to a subset of these sources. The oblivious coordinator setting is similar except that the coordinator does not have access to any of the shared randomness sources. In addition, all processors and the coordinator may privately randomize. In the omniscient coordinator setting, when the subsets at the processors are disjoint (individually shared randomness model), we characterize the rate of communication required from the coordinator to the processors over a multicast link. We also give an upper bound on the communication rate for the randomness-on-the-forehead model where each processor observes all but one source of randomness and we give an achievable strategy in the omniscient coordinator setting for the general case where the processors have access to arbitrary subsets of sources of randomness. Also, we consider a more general model where the processors observe components of correlated sources (with the coordinator observing all the components), where we characterize the communication rate when all the processors wish to output the same random sequence. In the oblivious coordinator setting, we completely characterize the trade-off region between the communication and shared randomness rates for the general case where the processors have access to arbitrary subsets of sources of randomness.
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