Problems we can solve with a helper

In this work we study source coding problems where a helper provides rate-limited side information to the involved parties. We first consider the Wyner-Ziv problem, where in addition to the memoryless side information available to the decoder, a helper sends common, rate-limited side information to the encoder and decoder. A single letter characterization of the achievable rates is derived, under certain Markov conditions on the source and side information. We then examine the problem of cascade rate distortion with a helper. Partial results are derived also for the case where the side information is not necessarily common, i.e., when the helper can send different streams of coded side information to the involved parties.