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Fog Radio Access Network (F-RAN) exploits cached contents at edge nodes (ENs) and fronthaul connection to the cloud for content delivery. Assuming dedicated fronthaul links between cloud and each EN, previous works focused on analyses of F-RANs using offline or online caching depending whether the content popularity is time-invariant or time-variant. Extension has been done for multicast fronthaul link connecting cloud to only two ENs and time-invariant popularity. In contrast, the scope of this work is on the case where multicast fronthaul link connects arbitrary number of ENs to the cloud and content popularity is time-variant. Normalized Delivery Time (NDT) is used as a performance measure and by investigating proactive online caching, analytical results reveal that the power scaling of fronthaul transmission sets a limit on the performance of F-RAN. [ABSTRACT FROM AUTHOR]

Fog radio access network (F-RAN) architectures can leverage both cloud processing and edge caching for content delivery to the users. To this end, F-RAN utilizes caches at the edge nodes (ENs) and fronthaul links connecting a cloud processor to ENs. Assuming time-invariant content popularity, existing information-theoretic analyses of content delivery in F-RANs rely on offline caching with separate content placement and delivery phases. In contrast, this paper focuses on the scenario in which the set of popular content is time-varying, hence necessitating the online replenishment of the ENs’ caches along with the delivery of the requested files. The analysis is centered on the characterization of the long-term normalized delivery time (NDT), which captures the temporal dependence of the coding latencies accrued across multiple time slots in the high signal-to-noise ratio regime. Online edge caching and delivery schemes are investigated for both serial and pipelined transmission modes across fronthaul and edge segments. Analytical results demonstrate that, in the presence of a time-varying content popularity, the rate of fronthaul links sets a fundamental limit on the long-term NDT of F-RAN system. Analytical results are further verified by numerical simulation, yielding important design insights. [ABSTRACT FROM AUTHOR]

The storage of frequently requested multimedia content at small-cell base stations (BSs) can reduce the load of macro-BSs without relying on high-speed backhaul links. In this work, the optimal operation of a system consisting of a cache-aided small-cell BS and a macro-BS is investigated for both offline and online caching settings. In particular, a binary fading one-sided interference channel is considered in which the small-cell BS, whose transmission is interfered by the macro-BS, has a limited-capacity cache. The delivery time per bit (DTB) is adopted as a measure of the coding latency, that is, the duration of the transmission block, required for reliable delivery. For offline caching, assuming a static set of popular contents, the minimum achievable DTB is characterized through information-theoretic achievability and converse arguments as a function of the cache capacity and of the capacity of the backhaul link connecting cloud and small-cell BS. For online caching, under a time-varying set of popular contents, the long-term (average) DTB is evaluated for both proactive and reactive caching policies. Furthermore, a converse argument is developed to characterize the minimum achievable long-term DTB for online caching in terms of the minimum achievable DTB for offline caching. The performance of both online and offline caching is finally compared using numerical results. [ABSTRACT FROM AUTHOR]

To combat erasure channels, multiple description coding (MDC) introduces diversity at source coding level. Each description provides a coarse reconstruction of source information at destination. As the number of received description increases, the reconstruction quality would be improved. Rate region of MDC is the set of achievable rates for a given set of expected distortions. In this paper, coalitional game theory is proposed as a nontrivial approach for determining rate region of MDC. To this end, elaborate game theoretic analysis is provided. Moreover, Shapley value is utilized to determine each description's rate. As a result, a fair rate adjustment is obtained that comprises entropy and mutual information of original and reconstructed descriptions. [ABSTRACT FROM PUBLISHER]

Multiple description coding (MDC) provides a means to combat erasure channels. Both rate and packet delay have significant contributions to end-to-end distortion of delay-sensitive sources. The previous works just considered exponential and fixed packet length distributions to evaluate the packet delay. In this letter, assuming a general (unknown) distribution with known average and variance of packet length, it is showed that average distortions of MDC and Single description coding (SDC) are upper bounded. Derived bounds are determined by encoding rate, packet arrival rate of network, acceptable delay threshold and first and second moments of packet length distribution. [ABSTRACT FROM PUBLISHER]