Uplink oblivious cloud radio access networks: An information theoretic overview

In this work, we consider transmission over a Cloud Radio Access Network (CRAN) in which the relay nodes (radio units) are constrained to operate without knowledge of the users' codebooks, i.e., are oblivious (nomadic), and only know time- or frequency-sharing protocols. The model is shown in Figure 1. Focusing on a class of discrete memoryless channels in which the relay outputs are independent conditionally on the users' inputs, we establish a single-letter characterization of the capacity region of this class of channels. We show that both relaying à-la Cover-El Gamal [1], i.e., compress-and-forward with joint decompression and decoding, as suggested in [2], are optimal. This is equivalent to noisy notwork coding [3]. For the proof of the converse part, we utilize useful connections with the Chief Executive Officer (CEO) source coding problem under logarithmic loss distortion measure [4]. For memoryless Gaussian channels, we provide a full characterization of the capacity region under Gaussian signaling, i.e., when the users' channel inputs are restricted to be Gaussian. In doing so, we also discuss the suboptimality of separate decompression-decoding and the role of time-sharing. Furthermore, we elaborate on meaningful connections with the problem of distributed information bottleneck problem [5]-[7]. Finally, we evaluate and compare the performance of some oblivious, including the recent scheme [8], and non-oblivious schemes, such as [9] and [10], and cut-set bounds.