Tijani Chahed

Trend detection in social networks using Hawkes processes

We develop in this paper a trend detection algorithm, designed to find trendy topics being disseminated in a social network. We assume that the broadcasts of messages in the social network is governed by a self-exciting point process, namely a Hawkes process, which takes into consideration the real broadcasting times of messages and the interaction between users and topics. We formally define trendiness and derive trend indices for each topic being disseminated in the social network. These indices take into consideration the time between the detection and the message broadcasts, the distance between the real broadcast intensity and the maximum expected broadcast intensity, and the social network topology. The proposed trend detection algorithm is simple and uses stochastic control techniques in order to calculate the trend indices. It is also fast and aggregates all the information of the broadcasts into a simple one-dimensional process, thus reducing its complexity and the quantity of data necessary to the detection.

Service-oriented sharing of energy in wireless access networks using shapley value

We investigate in this paper the sharing of energy consumption among service categories in the access of a wireless network. We focus on the fixed component of the energy consumption, which is known to be significantly larger than the load-dependent variable component, and propose its sharing among the service categories based on coalition game concept, the Shapley value. We consider five service categories, two large players: streaming and web browsing, and three smaller ones: download, voice and other minor services, and compare our proposal with two other sharing methods: uniform and proportional which follows the same traffic proportions. Our results, applied on a real dataset extracted from an operational network in Europe, show that our proposal is more fair both towards small services in that it reduces their shares in comparison to the uniform approach and towards larger services as it reduces their shares in comparison with the proportional one. Indeed, our Shapley-based model accommodates both short term network behavior, in which the fixed energy component is independent of the traffic load, and longer term behavior, in which it varies with the load and infrastructure. Uniform sharing accounts only for the short term, and the proportional one only for the longer term.

Performance evaluation of user centric multihoming strategies in LTE/WiFi networks

This paper presents an analytical performance evaluation framework for 4G/WiFi multihoming techniques. Several multihoming flavors have been compared, with a focus on user centric allocation strategies. In these strategies the user splits his packets between two radio interfaces following a policy that depends on the amount of information he gets. First, the simplest policy is considered in which the user sends an amount of traffic on each interface proportional to the latters peak rate. Second, the optimal selfish policy is investigated in which the user has complete information about the traffic intensities. This latter policy has been proved to achieves a global optimum. The numerical results show that an optimized user centric policy achieves good gains for both the system capacity and the user throughput compared to a peak maximization strategy. The results also show that multihoming provides large performance gains for multi-homed users while degrading neither the capacity of the system nor the performance of single-homed users.

Sharing of energy among service categories in wireless access networks using Shapley value

We investigate in this paper the sharing of energy consumption among service categories in the access of a wireless network. We focus on the fixed part of the energy consumption of the network, which is known to be significantly larger than the load-dependent variable part, and propose its sharing among the service categories based on coalition game concept, the Shapley value. We consider five service categories, two large players: streaming and web browsing, and three smaller ones: download, voice and other minor services, and compare our proposal with two other sharing strategies: uniform and proportional which follows the same volume proportions. Our results, applied on a real dataset extracted from an operational network in Europe, show that our proposal is more fair both towards small services in that it reduces their shares in comparison to the uniform approach, and towards larger services as it reduces their shares in comparison with the proportional one. Indeed, our Shapley-based model accommodates both short term network behavior, in which the fixed energy component is independent of the traffic load, and longer term behavior, in which it varies with the load and infrastructure. Uniform sharing accounts only for the short term, and the proportional one only for the longer term.

Performance of Delay Tolerant Mobile Networks and its improvement using mobile relay nodes under buffer constraint

The performance of Delay Tolerant Mobile Networks (DTMNs) depends on the mobility pattern through the nodes encounter process which constitutes opportunities for exchange of information between nodes. However, the exchange of information itself depends also on the routing/replication protocol and the network resources as the node buffer capacity and which determines the effective network performance. We focus in this work on those two concepts: encounter and exchange, and evaluate them along with resulting network performance for different mobility patterns and routing protocols as well as under the limited buffer space constraint. We also propose the use of additional, mobile, dedicated relays so as to enhance the performance of the DTMN in cases of ill-behaved mobility schemes.

Energy efficiency of a network per service

We investigate in this paper the assessment of the energy efficiency of a wireless access network per service category. We consider five categories of service, two categories with high traffic: streaming and web browsing, and three other with lower traffic: download, voice and other minor data services. We introduce two scenarios, one where some services are mandatory, it is typically the case of Voice which is mandatory to be provided due to legal constraints, and another one where there is no mandatory service. We used our Shapley-based sharing model introduced in previous works to share the total energy consumption of the access network among the service categories, and then derive the energy efficiency of each service category as the ratio of its traffic volume (measured in the network) and its energy consumption assessed with our Shapley-based model. We applied the models on a real dataset extracted from an operational network in Europe, and analyze the energy efficiency of each considered service category.

A framework for information dissemination in social networks using Hawkes processes

Abstract We define in this paper a general Hawkes-based framework to model information diffusion in social networks. The proposed framework takes into consideration the hidden interactions between users as well as the interactions between contents and social networks, and can also accommodate dynamic social networks and various temporal effects of the diffusion, which provides a complete analysis of the hidden influences in social networks. This framework can be combined with topic modeling, for which modified collapsed Gibbs sampling and variational Bayes techniques are derived. We provide an estimation algorithm based on nonnegative tensor factorization techniques, which together with a dimensionality reduction argument are able to discover, in addition, the latent community structure of the social network. At last, we provide numerical examples from real-life networks: a Game of Thrones and a MemeTracker datasets.

Impact of Playout Buffering on Mobile TV Performance

We study in this work the quality of experience of live mobile TV users in the presence of a playout buffer at the receiver side. We specifically consider an LTE network delivering both unicast and broadcast services, and study two cases: i. lossless channels where interruptions in mobile TV delivery are due to the absence of resources at the base station because they are totally consumed by higher priority real-time voice services, and ii. lossy channels, where we propose to exploit the existence of feedback channels to request, if possible, retransmission of the lost video frame. We derive in both cases several QoS metrics pertaining to mobile TV performance, such as interruption frequency and duration as well as video frame loss probability. Our results show the trends of these metrics as a function of several system parameters and yield design rules for network planning as well as for the playout buffer so as to enhance efficiently the live TV watching experience.

Performance of Delay Tolerant Mobile Networks under propagation and buffer capacity constraints

The performance of Delay Tolerant Mobile Networks (DTMNs) depends on the mobility pattern through the nodes encounter process which constitutes opportunities for exchange of information between nodes. The effective exchange of information depends also on the routing/replication protocol and on several network resources such as buffer capacity, radio propagation conditions and energy. We focus in this work on those two concepts: encounter and exchange, and evaluate them along with resulting network performance for different synthetic mobility patterns and routing protocols, as well as under several constraints on the radio conditions and buffer space. We also propose the use of additional, mobile, dedicated relays so as to enhance the performance of the DTMN in cases of ill-behaved mobility schemes.

Proposal for access point backhaul resource aggregation and its modeling using one-to-one matching game

In this paper, we propose a new scheme for aggregating access points backhaul bandwidth resources in wireless local area networks. We consider a setting with several access points, some with excess backhaul capacity, and others in shortage of it, and propose a symmetric approach wherein the distribution of resources is managed between providing and beneficiary access points, without involving the direct participation of the users. We then model the proposal using one-to-one matching game theory and make use of the so-called deferred access (DA) algorithm to reach an optimal, stable solution for the problem. In comparison with random distribution of available backhaul resources, the DA scheme offers significantly better performance in terms of overall throughput, reaching up to 40% when compared to random matching.