This paper addresses the problem of disseminating multiple live videos to mobile users by using a hybrid cellular and ad hoc network. Specifically, we develop techniques to optimize the overall quality of video delivery by: (a) exploiting the flexibility of layered videos for in-network adaptation to reduce the gap between video coding rate and network capacity, and (b) alleviating the load of individually handling a large number of flows at the cell tower by using deviceto-device ad hoc connectivity to deliver videos. We study the problem of optimally choosing the mobile devices that will serve as gateways from the cellular to the ad hoc network, the ad hoc routes from the gateway to individual devices, and the layers to deliver on these ad hoc routes. We develop a Mixed Integer Linear Program (MILP) based solution to the considered problem. We also develop a heuristic algorithm to select the devices, routes, and layers more efficiently than the ideal, but potentially time-consuming MILP-based algorithm. We evaluate the proposed techniques via through simulations. The simulation results show that the proposed algorithms significantly outperform the current solution in terms of overall video quality, transmission latency, delivery ratio, and missed frame ratio. For example, compared to the current cellular network, the MILP-based and the heuristic algorithms result in up to 20 dB higher video quality. Furthermore, the heuristic algorithm runs efficiently yet achieves near-optimal quality: at most 2.3 dB gap across all experiments.

Abstract. In this paper, we consider the problem of efficient social media access on mobile devices, and propose an Offline Online Social Media (O 2 SM) Middleware to: (i) rank the social media streams based the probability that a given user views a given content item, and (ii) invest the limited resources (network, energy, and storage) on prefetching only those social media streams that are most likely to be watched when mobile devices have good Internet connectivity. The ranking scheme leverages social network information to drive a logistic regression based technique that is subsequently exploited to design an utility based content prefetching mechanism. We implemented O 2 SM and a corresponding app, oFacebook, on Android platforms. We evaluated O 2 SM via trace data gathered from a user study with real world users executing oFacebook. Our experimental results indicate that O 2 SM exhibits superior viewing performance and energy efficiency for mobile social media apps; its lightweight nature makes it easily deployable on mobile platforms.

We design, implement, and evaluate a middleware system, HybCAST, that leverages a hybrid cellular and ad hoc network to disseminate rich contents from a source to all mobile devices in a predetermined region. HybCAST targets information dissemination over a range of scenarios (e.g., military operations, crisis alerting, and popular sporting events) in which high reliability and low latency are critical and existing fixed infrastructures such as wired networks, 802.11 access points are heavily loaded or partially destroyed. HybCAST implements a suite of protocols that: (i) structures the hybrid network into a hierarchy of two-level ad hoc clusters for better scalability, (ii) employ both data push and pull mechanisms for high reliability and low latency dissemination of rich content, and (iii) implement a near-optimal gateway selection algorithm to minimize the transmission redundancy. To demonstrate its practicality and efficiency, we have implemented and deployed the HybCAST middleware on several Android smartphones and an in-network Linux machine that acts as a dissemination server. The system is evaluated via real experiments using a UMTS network and extensive packet-level simulations. Our experimental results from a live network show that HybCAST achieves 100% reliability with shorter latencies and lower overall energy consumption. Simulation results confirm that HybCAST outperforms other state-of-the-art systems in the literature. For example, HybCAST exhibits a 5 times reduction in the dissemination latencies as compared to other hybrid dissemination protocols, while its energy consumption is a third of a cellular-only dissemination system. Furthermore, the simulation results demonstrate that HybCAST scales well and maintains good performance under varying numbers of mobile devices, diverse content sizes, and device mobility.

In this paper, we explore the problem of supporting efficient access to social media contents on social network sites for mobile devices without requiring mobile users to be online all the time. We propose and implement a broker/proxy based architecture that stages data at a broker/proxy, and selectively downloads to the mobile device only those contents that have a high likelihood of being viewed. The system determines the relevance of social media updates that continuously arrive (e.g., Facebook friend updates) for each user. Using knowledge of this relevance and current network/system conditions, we develop scheduling algorithms that determine which social contents are sent to the devices. We develop an Android app providing offline access to Facebook. Our experimental results indicate that our system is energy efficient, which saves energy by 6.9 times for WiFi and 9.1 times for cellular connections. We also use data traces gathered from our app to further drive extensive simulation based evaluations which show that our proposed algorithms provide efficient facilities for tuning the system's performance. 1

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A stability of routing path is of a great importance for a reliable communication in mobile ad hoc networks. We propose a novel source routing protocol that establishes a group path with virtual multiple paths to enable a robust communication. The entire mobile nodes form a disjoint set of clusters: Each has its clusterhead as a cluster leader and all the members in the same cluster are assigned an identical cluster label by its clusterhead. A group path is a sequence of cluster labels instead of nodes and the nodes with the same label collaborate to deliver packets to a node with next label on the group path. We prove by resorting to simulation that our proposed protocol outperforms the existing key routing protocols, even for a network with a high mobility of node and a high traffic.