Francis Lau

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Shengzhong Feng

ubaid abbasi

Imam Abdulrahman bin Faisal University

Hathairat Ketmaneechairat

King Mongkut's University of Technology North Bangkok

Hathairat Ketmaneechairat

King Mongkut's University of Technology North Bangkok

Satoshi Fujita

Benjamin Rainer

AIT Austrian Institute of Technology GmbH

rowayda sadek

Darshan Purandare

University of Central Florida

José Soler Lucas

Tarik Taleb

Aalto University

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Papers by Francis Lau

InstantLeap

Proceedings of the 18th international workshop on Network and operating systems support for digital audio and video, 2009

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Distributed wireless link scheduling in the SINR model

Journal of Combinatorial Optimization, 2015

We present an approximation algorithm for wireless link scheduling under the physical SINR interf... more We present an approximation algorithm for wireless link scheduling under the physical SINR interference model. In the link scheduling problem, it is given a set of n links in a metric space, each of which is a sender-receiver pair, and the objective is to schedule the links using the minimum amount of time. We focus on a variant of this fundamental problem where the power is fixed, i.e., the power assignment of links is given as part of the input. Specifically, we consider an important category of power assignments called length-monotone sublinear power assignment, which includes the widely studied uniform, mean and linear power assignments. We present a distributed B Yuexuan Wang

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Utility-Maximizing Data Dissemination in Socially Selfish Cognitive Radio Networks

2011 IEEE Eighth International Conference on Mobile Ad-Hoc and Sensor Systems, 2011

Socially-optimal multi-hop secondary communication under arbitrary primary user mechanisms

2013 Proceedings IEEE INFOCOM, 2013

In a cognitive radio system, licensed primary users can lease idle spectrum to secondary users fo... more In a cognitive radio system, licensed primary users can lease idle spectrum to secondary users for monetary remuneration. Secondary users acquire available spectrum for their data delivery needs, with the goal of achieving high throughput and low spectrum charges. Maximizing such a net utility (throughput utility minus spectrum cost) is a central problem faced by a multihop secondary network. Optimal decision making is challenging, since it involves multiple data flows, cross-layer coordination, and economic constraints (budgets of sources). The picture is further complicated by the interplay between secondary data communication and primary spectrum leasing mechanisms. This work is the first to investigate the full spectrum of socially optimal secondary user communication. We design a social welfare maximization framework for multi-session multi-hop secondary data dissemination based on Lyapunov optimization techniques. A salient feature of the framework is that it takes any given primary user mechanism as input, and produces correspondingly a dynamic, distributed rate control, routing, and spectrum allocation and pricing protocol that can achieve longterm maximization of the overall system utility. Through rigorous theoretical analysis, we prove that our online protocol can achieve a social welfare that is arbitrarily close to the offline optimum, with only finite buffer space requirement at each secondary user, and guarantee of no buffer overflow. Empirical studies are conducted to examine the performance of the protocol.

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Cost-Minimizing Dynamic Migration of Content Distribution Services into Hybrid Clouds

IEEE Transactions on Parallel and Distributed Systems, 2015

The recent advent of cloud computing technologies has enabled agile and scalable resource access ... more The recent advent of cloud computing technologies has enabled agile and scalable resource access for a variety of applications. Content distribution services are a major category of popular Internet applications. A growing number of content providers are contemplating a switch to cloud-based services, for better scalability and lower cost. Two key tasks are involved for such a move: to migrate their contents to cloud storage, and to distribute their web service load to cloud-based web services. The main challenge is to make the best use of the cloud as well as their existing on-premise server infrastructure, to serve volatile content requests with service response time guarantee at all times, while incurring the minimum operational cost. Employing Lyapunov optimization techniques, we present an optimization framework for dynamic, cost-minimizing migration of content distribution services into a hybrid cloud infrastructure that spans geographically distributed data centers. A dynamic control algorithm is designed, which optimally places contents and dispatches requests in different data centers to minimize overall operational cost over time, subject to service response time constraints. Rigorous analysis shows that the algorithm nicely bounds the response times within the preset QoS target in cases of arbitrary request arrival patterns, and guarantees that the overall cost is within a small constant gap from the optimum achieved by a T-slot lookahead mechanism with known information into the future.

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Distributed local broadcasting algorithms in the physical interference model

2011 International Conference on Distributed Computing in Sensor Systems and Workshops (DCOSS), 2011

An O(log n) Distributed Approximation Algorithm for Local Broadcasting in Unstructured Wireless Networks

2012 IEEE 8th International Conference on Distributed Computing in Sensor Systems, 2012

Distributed Multiple-Message Broadcast in Wireless Ad-Hoc Networks under the SINR Model

Lecture Notes in Computer Science, 2012

In a multiple-message broadcast, an arbitrary number of messages originate at arbitrary nodes in ... more In a multiple-message broadcast, an arbitrary number of messages originate at arbitrary nodes in the network at arbitrary times. The problem is to disseminate all these messages to the whole network. This paper gives the first randomized distributed multiple-message broadcast algorithm with worst-case performance guarantee in wireless ad hoc networks employing the SINR interference model which takes interferences from all the nodes in the network into account. The network model used in this paper also considers the harsh characteristics of wireless ad hoc networks: there is no prior structure, and nodes cannot perform collision detection and have little knowledge of the network topology. Under all these restrictions, our proposed randomized distributed multiple-message broadcast protocol can deliver any message m to all nodes in the network in O (D + k + log 2 n) timeslots with high probability, where D is the network diameter, k is the number of messages whose broadcasts overlap with m, and n is the number of nodes in the network. We also study the lower bound for randomized distributed multiple-message broadcast protocols. In particular, we prove that any uniform randomized algorithm needs Ω(D + k + log 2 n log log log n) timeslots to disseminate k messages initially stored at k nodes.

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Distributed (Δ + 1)-Coloring in the Physical Model

Lecture Notes in Computer Science, 2012

In multi-hop radio networks, such as wireless ad-hoc networks and wireless sensor networks, nodes... more In multi-hop radio networks, such as wireless ad-hoc networks and wireless sensor networks, nodes employ a MAC (Medium Access Control) protocol such as TDMA to coordinate accesses to the shared medium and to avoid interference of close-by transmissions. These protocols can be implemented using standard node coloring. The (Δ + 1)-coloring problem is to color all nodes in as few timeslots as possible using at most Δ +1 colors such that any two nodes within distance R are assigned different colors, where R is a given parameter and Δ is the maximum degree of the modeled unit disk graph using R as a scaling factor. Being one of the most fundamental problems in distributed computing, this problem is well studied and there is a long chain of algorithms prescribed for it. However, all previous works are based on abstract models, such as message passing models and graph based interference models, which limit the utility of these algorithms in practice. In this paper, for the first time, we consider the distributed (Δ + 1)-coloring problem under the more practical SINR interference model. In particular, without requiring any knowledge about the neighborhood, we propose a novel randomized (Δ + 1)-coloring algorithm with time complexity O (Δ log n +log 2 n). For the case where nodes cannot adjust their transmission power, we give an O (Δ log 2 n) randomized algorithm, which only incurs a logarithmic multiplicative factor overhead.

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Minimizing Average Interference through Topology Control

Lecture Notes in Computer Science, 2012

Information exchange with collision detection on multiple channels

Journal of Combinatorial Optimization, 2014

Information exchange is a fundamental communication primitive in radio networks. We study this pr... more Information exchange is a fundamental communication primitive in radio networks. We study this problem in multi-channel singlehop networks. In particular, given k pieces of information, initially stored in k nodes respectively, the task is to broadcast these information pieces to the entire network via a set of F channels. We develop efficient distributed algorithms for this task for the scenario where both the identities and the number k of the initial information holders are unknown to the participating nodes. Assuming nodes with collision detection, we present an efficient randomized algorithm for unrestricted information exchange, where multiple information items can be combined into a single message. The algorithm disseminates all the information items within O(k F + F log 2 n) timeslots with high probability. To the best of our knowledge, this is the first algorithm that breaks the Ω(k) lower bound for unrestricted information exchange if only a single channel is available. This result establishes the superiority of multiple channels for the task of unrestricted information exchange. Moreover, for restricted information exchange, where each message can carry only one information item, we devise a randomized algorithm that completes the task in O(k + log 2 n F + log n) timeslots. When k is large, both algorithms are asymptotically optimal, as they can reach the trivial lower bounds of Ω(k F) and Ω(k) for unrestricted and restricted information exchange, respectively.

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Aggregation Latency-Energy Tradeoff in Wireless Sensor Networks with Successive Interference Cancellation

IEEE Transactions on Parallel and Distributed Systems, 2013

Minimizing latency and energy consumption is the prime objective of the design of data aggregatio... more Minimizing latency and energy consumption is the prime objective of the design of data aggregation in battery-powered wireless networks. A tradeoff exists between the aggregation latency and the energy consumption, which has been widely studied under the protocol interference model. There has been however no investigation of the tradeoff under the physical interference model which is known to capture more accurately the characteristics of wireless interferences. When coupled with the technique of successive interference cancellation, by which a receiver may recover signals from multiple simultaneous senders, the model can lead to much reduced latency but increased energy usage. In this paper, we investigate the latency-energy tradeoff for data aggregation in wireless sensor networks under the physical interference model and using successive interference cancellation. We present theoretical lower bounds on both latency and energy as well as their tradeoff, and give an efficient approximation algorithm that can achieve the asymptotical optimum in both aggregation latency and latency-energy tradeoff. We show that our algorithm can significantly reduce the aggregation latency, for which the energy consumption is kept at its lowest possible level.

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CloudMoV: Cloud-Based Mobile Social TV

IEEE Transactions on Multimedia, 2013

The rapidly increasing power of personal mobile devices (smartphones, tablets, etc.) is providing... more The rapidly increasing power of personal mobile devices (smartphones, tablets, etc.) is providing much richer contents and social interactions to users on the move. This trend however is throttled by the limited battery lifetime of mobile devices and unstable wireless connectivity, making the highest possible quality of service experienced by mobile users not feasible. The recent cloud computing technology, with its rich resources to compensate for the limitations of mobile devices and connections, can potentially provide an ideal platform to support the desired mobile services. Tough challenges arise on how to effectively exploit cloud resources to facilitate mobile services, especially those with stringent interaction delay requirements. In this paper, we propose the design of a Cloud-based, novel Mobile sOcial tV system (CloudMoV). The system effectively utilizes both PaaS (Platform-as-a-Service) and IaaS (Infrastructure-as-a-Service) cloud services to offer the living-room experience of video watching to a group of disparate mobile users who can interact socially while sharing the video. To guarantee good streaming quality as experienced by the mobile users with time-varying wireless connectivity, we employ a surrogate for each user in the IaaS cloud for video downloading and social exchanges on behalf of the user. The surrogate performs efficient stream transcoding that matches the current connectivity quality of the mobile user. Given the battery life as a key performance bottleneck, we advocate the use of burst transmission from the surrogates to the mobile users, and carefully decide the burst size which can lead to high energy efficiency and streaming quality. Social interactions among the users, in terms of spontaneous textual exchanges, are effectively achieved by efficient designs of data storage with BigTable and dynamic handling of large volumes of concurrent messages in a typical PaaS cloud. These various designs for flexible transcoding capabilities, battery efficiency of mobile devices and spontaneous social interactivity together provide an ideal platform for mobile social TV services. We have implemented CloudMoV on Amazon EC2 and Google App Engine and verified its superior performance based on real-world experiments.

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Latency-minimizing data aggregation in wireless sensor networks under physical interference model

Ad Hoc Networks, 2014

Minimizing latency is of primary importance for data aggregation which is an essential applicatio... more Minimizing latency is of primary importance for data aggregation which is an essential application in wireless sensor networks. Many fast data aggregation algorithms under the protocol interference model have been proposed, but the model falls short of being an accurate abstraction of wireless interferences in reality. In contrast, the physical interference model has been shown to be more realistic and has the potential to increase the network capacity when adopted in a design. It is a challenge to derive a distributed solution to latency-minimizing data aggregation under the physical interference model because of the simple fact that global-scale information to compute the cumulative interference is needed at any node. In this paper, we propose a distributed algorithm that aims to minimize aggregation latency under the physical interference model in wireless sensor networks of arbitrary topologies. The algorithm uses O(K) time slots to complete the aggregation task, where K is the logarithm of the ratio between the lengths of the longest and shortest links in the network. The key idea of our distributed algorithm is to partition the network into cells according to the value K, thus obviating the need for global information. We also give a centralized algorithm which can serve as a benchmark for comparison purposes. It constructs the aggregation tree following the nearest-neighbor criterion. The centralized algorithm takes O(log n) and O(log 3 n) time slots when coupled with two existing link scheduling strategies, respectively (where n is the total number of nodes), which represents the current

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Auction-based P2P VoD streaming

ACM Transactions on Multimedia Computing, Communications, and Applications, 2012

Real-world large-scale Peer-to-Peer (P2P) Video-on-Demand (VoD) streaming applications face more ... more Real-world large-scale Peer-to-Peer (P2P) Video-on-Demand (VoD) streaming applications face more design challenges as compared to P2P live streaming, due to higher peer dynamics and less buffer overlap. The situation is further complicated when we consider the selfish nature of peers, who in general wish to download more and upload less, unless otherwise motivated. Taking a new perspective of distributed dynamic auctions, we design efficient P2P VoD streaming algorithms with simultaneous consideration of peer incentives and streaming optimality. In our solution, media block exchanges among peers are carried out through local auctions, in which budget-constrained peers bid for desired blocks from their neighbors, which in turn deliver blocks to the winning bidders and collect revenue. With strategic design of a discriminative second price auction with seller reservation, a supplying peer has full incentive to maximally contribute its bandwidth to increase its budget; requesting peers...

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Orchestrating Bulk Data Transfers across Geo-Distributed Datacenters

IEEE Transactions on Cloud Computing, 2017

As it has become the norm for cloud providers to host multiple datacenters around the globe, sign... more As it has become the norm for cloud providers to host multiple datacenters around the globe, significant demands exist for inter-datacenter data transfers in large volumes, e.g., migration of big data. A challenge arises on how to schedule the bulk data transfers at different urgency levels, in order to fully utilize the available inter-datacenter bandwidth. The Software Defined Networking (SDN) paradigm has emerged recently which decouples the control plane from the data paths, enabling potential global optimization of data routing in a network. This paper aims to design a dynamic, highly efficient bulk data transfer service in a geo-distributed datacenter system, and engineer its design and solution algorithms closely within an SDN architecture. We model data transfer demands as delay tolerant migration requests with different finishing deadlines. Thanks to the flexibility provided by SDN, we enable dynamic, optimal routing of distinct chunks within each bulk data transfer (instead of treating each transfer as an infinite flow), which can be temporarily stored at intermediate datacenters to mitigate bandwidth contention with more urgent transfers. An optimal chunk routing optimization model is formulated to solve for the best chunk transfer schedules over time. To derive the optimal schedules in an online fashion, three algorithms are discussed, namely a bandwidth-reserving algorithm, a dynamically-adjusting algorithm, and a future-demandfriendly algorithm, targeting at different levels of optimality and scalability. We build an SDN system based on the Beacon platform and OpenFlow APIs, and carefully engineer our bulk data transfer algorithms in the system. Extensive real-world experiments are carried out to compare the three algorithms as well as those from the existing literature, in terms of routing optimality, computational delay and overhead.

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The scheduling and energy complexity of strong connectivity in ultra-wideband networks

Proceedings of the 9th ACM international symposium on Modeling analysis and simulation of wireless and mobile systems, 2006

Recently Moscibroda and Wattenhofer came up with the notion of scheduling complexity to capture t... more Recently Moscibroda and Wattenhofer came up with the notion of scheduling complexity to capture the minimum amount of time to successfully schedule all the transmission requests under the physical SINR model. Their algorithm featuring a nonlinear power assignment can schedule strongly connected transmissions in narrowband networks with 4

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A New Bio-inspired Approach to the Traveling Salesman Problem

Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2009

The host-seeking behavior of mosquitoes is very interesting. In this paper, we propose a novel mo... more The host-seeking behavior of mosquitoes is very interesting. In this paper, we propose a novel mosquito host-seeking algorithm (MHSA) as a new branch of biology-inspired algorithms for solving TSP problems. The MHSA is inspired by the host-seeking behavior of mosquitoes. We present the mathematical model, the algorithm, the motivation, and the biological model. The MHSA can work out the theoretical optimum solution, which is important and exciting, and we give the theoretical foundation and present experiment results that verify this fact.

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Exact and approximate link scheduling algorithms under the physical interference model

Proceedings of the fifth international workshop on Foundations of mobile computing - DIAL M-POMC '08, 2008

Given arbitrarily distributed single-hop wireless links, using the physical interference model, t... more

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Joint Link Scheduling and Topology Control for Wireless Sensor Networks with SINR Constraints

From Principle to Practice

This chapter studies the joint link scheduling and topology control problems in wireless sensor n... more This chapter studies the joint link scheduling and topology control problems in wireless sensor networks. Given arbitrarily located sensor nodes on a plane, the task is to schedule all the wireless links (each representing a wireless transmission) between adjacent sensors using a minimum number of timeslots. There are two requirements for these problems: first, all the links must satisfy a certain property, such as that the wireless links form a data gathering tree towards the sink node; second, all the links simultaneously scheduled in the same timeslot must satisfy the SINR constraints. This chapter focuses on various scheduling algorithms for both arbitrarily constructed link topologies and the data gathering tree topology. We also discuss possible research directions.

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InstantLeap

Proceedings of the 18th international workshop on Network and operating systems support for digital audio and video, 2009

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Distributed wireless link scheduling in the SINR model

Journal of Combinatorial Optimization, 2015

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Utility-Maximizing Data Dissemination in Socially Selfish Cognitive Radio Networks

2011 IEEE Eighth International Conference on Mobile Ad-Hoc and Sensor Systems, 2011

Socially-optimal multi-hop secondary communication under arbitrary primary user mechanisms

2013 Proceedings IEEE INFOCOM, 2013

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