Fundamental Limits of Memory-Latency Tradeoff in Fog Radio Access Networks Under Arbitrary Demands

Abstract

We consider a Fog Radio Access Network (F-RAN) with multiple of transmitters and receivers, where each transmitter is connected to the cloud via a fronthaul link. Each network node has a finite cache, where it fills its cache with portions of the library files in the off-peak hours. In the delivery phase, receivers request each library files according to an arbitrary popularity distribution. The cloud and the transmitters are responsible for satisfying the requests. This paper aims to design content placement and coded delivery schemes for minimizing both the expected normalized delivery time (NDT) and the peak NDT which measures the transmission latency. We propose achievable transmission policies, and derive an information-theoretic bound on the expected NDT under uniform popularity distribution. Analytical results show that the proposed scheme is within a gap of 2.58 from the derived bound for both the expected NDT under uniform popularity distribution and the peak NDT. Next, we investigate the expected NDT under an arbitrary popularity distribution for an F-RAN with transmitter-side caches only. The achievable and information-theoretic bounds on the expected NDT are derived, where we analytically prove that our proposed scheme is optimal within a gap of 2 independent of the popularity distribution.

Coded Caching and Spatial Multiplexing Gains in MIMO Interference Networks

“…The work in [5] has studied an F-RAN with caches at both transmitters and receivers under the assumption that the content placement is applied in a decentralized manner. In [6], the authors have characterized both the peak NDT and the expected NDT under uniform popularity distribution for F-RAN with caches at transmitters and receivers. In addition, the authors in [6] have proposed a coding scheme for the F-RAN with caches only at the transmitters and shown that this scheme is order optimal for any popularity distribution.…”

“…In [6], the authors have characterized both the peak NDT and the expected NDT under uniform popularity distribution for F-RAN with caches at transmitters and receivers. In addition, the authors in [6] have proposed a coding scheme for the F-RAN with caches only at the transmitters and shown that this scheme is order optimal for any popularity distribution. The work in [7]- [9] studied SISO interference networks with caches at both transmitters and receivers.…”

A Converse Bound for Cache-Aided Interference Networks

“…Hence, in the peak hours when the network is congested, caches can be exploited to serve the receivers requests with a significant improvement in the system performance. The rule of caching in interference networks is studied in [1]- [10]. In [1], the degrees of freedom (DoF) of a 3 × 3 interference network with cache-equipped transmitters was studied.…”

“…In [4], the normalized delivery time (NDT) which defines the delivery latency is introduced as a performance metric to study the fog radio access network (F-RAN) with two transmitters and two receivers. The work in [6]- [10] studied interference networks and F-RANs with caches at both transmitters and receivers.…”