This paper studies the gains, in terms of served requests, attainable through out-of-band deviceto-device (D2D) video exchanges in large cellular networks. A stochastic framework, in which users are clustered to exchange videos, is introduced, considering several aspects of this problem: the videocaching policy, user matching for exchanges, aspects regarding scheduling and transmissions. A family of admissible protocols is introduced: in each protocol the users are clustered by means of a hard-core point process and, within the clusters, video exchanges take place. Two metrics, quantifying the "local"and "global" fraction of video requests served through D2D are defined, and relevant trade-off regions involving these metrics, as well as quality-of-service constraints, are identified. A simple communication strategy is proposed and analyzed, to obtain inner bounds to the trade-off regions, and draw conclusions on the performance attainable through D2D. To this end, an analysis of the time-varying interference that the nodes experience, and tight approximations of its Laplace transform are derived.

Abstract-This paper investigates the benefits of cooperation and proposes a relay activation strategy for a large wireless network with multiple transmitters. In this framework, some nodes cooperate with a nearby node that acts as a relay, using the decode-and-forward protocol, and others use direct transmission. The network is modeled as an independently marked Poisson point process and the source nodes may choose their relays from the set of inactive nodes. Although cooperation can potentially lead to significant improvements in the performance of a communication pair, relaying causes additional interference in the network, increasing the average noise that other nodes see.We investigate how source nodes should balance cooperation vs. interference to obtain reliable transmissions, and for this purpose we study and optimize a relay activation strategy with respect to the outage probability. Surprisingly, in the high reliability regime, the optimized strategy consists on the activation of all the relays or none at all, depending on network parameters. We provide a simple closed-form expression that indicates when the relays should be active, and we introduce closed form expressions that quantify the performance gains of this scheme with respect to a network that only uses direct transmission.Index Terms-Cooperative communication, interference, network management, outage probability, decode and forward, marked Poisson point processes.

International audienceThis paper introduces a stochastic geometry model of a cellular network in which users exchange videos through out-of-band device-to-device (D2D) communications. Users are grouped into clusters, in which a user-based distributed cache is formed to satisfy in-cluster video requests through D2D, avoiding the base station. This paper studies how many of these requests could be served, considering two service metrics: the global relative density of served requests, and the mean ratio of served requests per cluster. The model considers random user placement, content request statistics, and transmission scheduling and impairments, like fading and path loss. A simple communications strategy to be used in the clusters, involving time-division multiple access and one-hop transmissions, is introduced and the metrics are evaluated in this setup, drawing conclusions on the performance of distributed-caching in large wireless networks

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Consider the communication of a single-user aided by a nearby relay involved in a large wireless network where the nodes form an homogeneous Poisson point process. Since this network is interference-limited the asymptotic error probability is bounded from above by the outage probability experienced by the user. We investigate the outage behavior for the wellknown cooperative schemes, namely, decode-and-forward (DF) and compress-and-forward (CF). In this setting, the outage events are induced by both fading and the spatial proximity of neighbor nodes who generate the strongest interference and hence the worst communication case. Upper and lower bounds on the asymptotic error probability which are tight in some cases are derived. It is shown that there exists a clear trade off between the network density and the benefits of user cooperation. These results are useful to evaluate performances and to optimize relaying schemes in the context of large wireless networks.