Fog-Aided Wireless Networks for Content Delivery: Fundamental Latency Tradeoffs

Avik Sengupta, Ravi Tandon, Osvaldo Simeone

Research output: Contribution to journalArticlepeer-review

87 Scopus citations

Abstract

A fog-aided wireless network architecture is studied in which edge nodes (ENs), such as base stations, are connected to a cloud processor via dedicated fronthaul links while also being endowed with caches. Cloud processing enables the centralized implementation of cooperative transmission strategies at the ENs, albeit at the cost of an increased latency due to fronthaul transfer. In contrast, the proactive caching of popular content at the ENs allows for the low-latency delivery of the cached files, but with generally limited opportunities for cooperative transmission among the ENs. The interplay between cloud processing and edge caching is addressed from an information-theoretic viewpoint by investigating the fundamental limits of a high signal-to-noise-ratio metric, termed normalized delivery time (NDT), which captures the worst case coding latency for delivering any requested content to the users. The NDT is defined under the assumptions of either serial or pipelined fronthaul-edge transmission, and is studied as a function of fronthaul and cache capacity constraints. Placement and delivery strategies across both fronthaul and wireless, or edge, segments are proposed with the aim of minimizing the NDT. Information-theoretic lower bounds on the NDT are also derived. Achievability arguments and lower bounds are leveraged to characterize the minimal NDT in a number of important special cases, including systems with no caching capabilities, as well as to prove that the proposed schemes achieve optimality within a constant multiplicative factor of 2 for all values of the problem parameters.

Original languageEnglish (US)
Article number8002603
Pages (from-to)6650-6678
Number of pages29
JournalIEEE Transactions on Information Theory
Volume63
Issue number10
DOIs
StatePublished - Oct 2017
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Information Systems
  • Computer Science Applications
  • Library and Information Sciences

Keywords

  • 5G
  • Caching
  • cloud radio access network (C-RAN)
  • degrees-of-freedom
  • edge processing
  • fog radio access network
  • interference channel
  • latency
  • wireless networks

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