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Algorithm Design for Scheduling and Medium Access Control in Heterogeneous Mobile Networks
Get PDFThe rapid growth of wireless mobile devices has led to saturation and congestion of wireless channels – a well-known fact. In the recent years, this issue is further exacerbated by the everincreasing demand for traffic intensed multimedia content applications, which include but are not limited to social media, news and video streaming applications. Therefore the development of highly efficient content distribution technologies is of utmost importance, specifically to cope with the scarcity and the high cost of wireless resources. To this aim, this thesis investigates the challenges and the considerations required to design efficient techniques to improve the performance of wireless networks. Since wireless signals are prone to fluctuations and mobile users are, with high likelihood, have difference channel qualities, we particularly focus on the scenarios with heterogeneous user distribution. Further, this dissertation considers two main techniques to cope with mobile users demand and the limitation of wireless resources. Firstly, we propose an opportunistic multicast scheduling to efficiently distribute or disseminate data to all users with low delay. Secondly, we exploit the Millimeter-Wave (mm-Wave) frequency band that has a high
potential of meeting the high bandwidth demand. In particular, we propose a channel access mechanism and a scheduling algorithm that take into account the limitation of the high frequency band (i.e., high path loss). Multicast scheduling has emerged as one of the most promising techniques for multicast applications
when multiple users require the same content from the base station. Unlike a unicast scheduler which sequentially serves the individual users, a multicast scheduler efficiently utilizes the wireless resources by simultaneously transmitting to multiple users. Precisely, it multiplies the gain in terms of the system throughput compared to unicast transmissions. In spite of the fact that multicast schedulers are more efficient than unicast schedulers, scheduling for multicast transmission is a challenging task. In particular, base station can only chose one rate to transmit to all users. While determining the rate for users with a similar instantaneous channel quality is straight forward, it is non-trivial when users have different instantaneous channel qualities, i.e., when the channel is heterogeneous. In such a scenario, on one hand, transmitting at a low rate results in low throughput. On the other hand, transmitting at a high rate causes some users to fail to receive the transmitted packet while others successfully receive it but with a rate lower
than their maximum rate. The most common and simplest multicasting technique, i.e., broadcasting, transmits to all receivers using the maximum rate that is supported by the worst receiver.
In recent years, opportunistic schedulers have been considered for multicasting. Opportunistic multicast schedulers maximize instantaneous throughput and transmit at a higher rate to serve only a subset of the multicast users. While broadcasting suffers from high delay for all users due to low transmission rate, the latter causes a long delay for the users with worse channel quality as they always favor users with better channel quality. To address these problems, we designed an opportunistic multicast scheduling mechanism that aims to achieve high throughput as well as low delay. Precisely, we are solving the finite horizon problem for multicasting. Our goal is that all multicast users receive the same amount of data within the shortest amount of time. Although our proposed opportunistic multicast scheduling mechanism improves the system throughput and reduces delay, a common problem in multicast scheduling is that its throughput performance is limited by the worst user in the system. To overcome this problem, transmit beamforming can be used to adjust antenna gains to the different receivers. This allows improving the SNR of the receiver with the worst channel SNR at the expense of worsening the SNR of the better channel receivers. In the first part of this thesis, two different versions of the finite horizon problem are considered: (i) opportunistic multicast scheduling and (ii) opportunistic multicast
beamforming. In recent years, many researchers venture into the potential of communication over mm-Wave band as it potentially solves the existing network capacity problem. Since beamforming is capable to concentrate the transmit energy in the direction of interest, this technique is particularly beneficial to improve signal quality of the highly attenuated mm-Wave signal. Although directional beamforming in mm-Wave offers multi-gigabit-per-second data rates, directional communication
severely deteriorates the channel sensing capability of a user. For instance, when a user is not within the transmission coverage or range of the communicating users, it is unable to identify the state of the channel (i.e., busy or free). As a result, this leads to a problem commonly known as the deafness problem. This calls for rethinking of the legacy medium access control and scheduling mechanisms for mm-Wave communication. Further, without omni-directional transmission,
disseminating or broadcasting global information also becomes complex. To cope with these issues, we propose two techniques in the second part of this thesis. First, leveraging that recent mobile devices have multiple wireless interface, we present a dual-band solution. This solution exploits the omni-directional capable lower frequency bands (i.e., 2.4 and 5 GHz) to transmit control messages and the mm-Wave band for high speed data transmission. Second, we develop a decentralized scheduling technique which copes with the deafness problem in mm-Wave through a learning mechanism.
In a nutshell, this thesis explores solutions which (i) improve the utilization of the network resources through multicasting and (ii) meet the mobile user demand with the abundant channel resources available at high frequency bands.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
The DESERT Underwater Framework v2: Improved Capabilities and Extension Tools
Get PDFThe DESERT Underwater emulation system (http://nautilus.dei.unipd.it/desert-underwater), originally designed for testing underwater acoustic networks, has been recently extended. The new framework now includes multi-modal communication functionalities encompassing low rate and high rate acoustics as well as optics, the capability of testing wireless telemetry for underwater equipment, a connection to the most recent version of the World Ocean Simulation System (WOSS), a modification to the RECORDS system for sea trial remote control, and an interface between external tools, e.g., Matlab, and the EvoLogics modem. In addition, experimental activities are now supported by an accurate real-time event scheduler which has been shown to support, among others, long experiments involving time-division multiple-access (TDMA)-based MAC protocols. These additional protocol schemes from the MAC to the application layer (most of which have been tested in controlled environments and sea trials) now make DESERT Underwater a comprehensive tool for underwater network simulation and experimentation. In this paper, we present the new functionalities developed over the last two years.TRUEpu
The Role of Topology and Contracts in Internet Content Delivery
Get PDFThe Internet depends on economic relationships between ASes (Autonomous Systems), which come in different shapes and sizes - transit, content, and access networks. CDNs (Content delivery networks) are also a pivotal part of the Internet ecosystem and construct their overlays for faster content delivery. With the evolving Internet topology
and traffic growth, there is a need to study the cache deployments of CDNs to optimize cost while meeting performance requirements. The bilateral contracts enforce the routing of traffic between neighbouring ASes and are applied recursively: traffic that an AS sends to its neighbour is then controlled by the contracts of that neighbour. The lack of routing flexibility, little control over the quality of the end-to-end path are some of the
limitations with the existing bilateral model, and they need to be overcome for achieving end-to-end performance guarantees. Furthermore, due to general reluctance of ASes to disclose their interconnection agreements, inference of inter-AS economic relationships depend on routing and forwarding data from measurements. Since the inferences are imperfect, this necessitates building robust algorithmic strategies to characterize ASes with a significantly higher accuracy.
In this thesis, we first study the problem of optimizing multi-AS deployments of CDN caches in the Internet core. Our work is of significant practical relevance since it formalizes the planning process that all CDN operators must follow to reduce the operational cost of their overlay networks, while meeting the performance requirements of their end users. Next, we focus on developing a temporal cone (TC) algorithm that detects PFS (Provider-free ASes). By delivering a significant portion of Internet traffic, PFS is highly relevant to the overall resilience of the Internet. We detect PFS from public datasets of inter-AS economic relationships, utilizing topological statistics (customer cones of ASes) and temporal diversity. Finally, we focus on a multilateral contractual arrangement and
develop algorithms for optimizing the cost of transit and access ASes. In particular, we implement Bertsekas auction algorithm for the optimal cost assignment of access ASes
to transit ASes. Furthermore, we implement an epsilon-greedy bandit algorithm for optimizing the price of transit ASes and show its learning potential.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
5G systems: The mmMAGIC project perspective on Use cases and Challenges between 6-100 GHz
Get PDFmmMAGIC (Millimetre-Wave Based Mobile Radio Access Network for Fifth Generation Integrated Communications) is an EU funded 5G-PPP project, whose overall objective is to design and pre-develop a mobile radio access technology (RAT) operating in the 6-100 GHz range, capable of impacting standards and other relevant fora. The focus of the project is on extreme Mobile Broadband, which is expected to drive the 5G requirements for massive increase in capacity and data-rates. This paper elaborates on some 5G key research areas such as: identification of the most compelling use-cases and Key Performance Indicators (KPIs) for future 5G systems, advantages and challenges of millimeter-wave (mmWave) technologies, channel measurements and channel modeling, network architecture; and the design of a new mobile radio interface including multi-node and multi-antenna transceiver architecture.TRUEpu
Optimal configuration of a Resource-on-Demand 802.11 WLAN with Non-Zero Start-Up Times
Get PDFhttp://www.sciencedirect.com/science/article/pii/S014036641630161XResource on Demand in 802.11 Wireless LANs is receiving an increasing attention, with its feasibility already proved in practice and some initial analytical models available. However, while these models have assumed that access points (APs) start up in zero time, experimentation has showed that this is hardly the case. In this work, we provide a new model to account for this time in the simple case of a WLAN formed by two APs where the second AP is switched on/off dynamically to adapt to the traffic load and reduce the overall power consumption, and show that it significantly alters the results when compared to the zero start-up time case, both qualitatively and quantitatively. Our findings show that having a non-zero start up time modifies significantly the trade-offs between power consumption and performance that appears on Resource on Demand solutions. Finally, we propose an algorithm to optimize the energy consumption of the network while guaranteeing a given performance bound.pu
Flipping the classroom to improve learning with MOOCs technology
Get PDFThe use of Massive Open Online Courses (MOOCs) is increasing worldwide and brings a revolution in education. The application of MOOCs has technological but also pedagogical implications. MOOCs are usually driven by short video lessons, automatic correction exercises, and the technological platforms can implement gamification or learning analytics techniques. However, much more analysis is required about the success or failure of these initiatives in order to know if this new MOOCs paradigm is appropriate for different learning situations. This work aims at analyzing and reporting whether the introduction of MOOCs technology was good or not in a case study with the Khan Academy platform at our university with students in a remedial Physics course in engineering education. Results show that students improved their grades significantly when using MOOCs technology, student satisfaction was high regarding the experience and for most of the different provided features, and there were good levels of interaction with the platform (e.g. number of completed videos or proficient exercises), and also the activity distribution for the different topics and types of activities was appropriate.pu
Measuring and Assessing Mobile Broadband Networks with MONROE
Get PDFBest Demo Award.Mobile broadband (MBB) networks underpin numerous vital operations of the society and are arguably becoming the most important piece of the communications infrastructure. In this demo paper, our goal is to showcase the potential of a novel multi-homed MBB platform for measuring, monitoring and assessing the performance of MBB services in an objective manner. Our platform, MONROE, is composed of hundreds of nodes scattered over four European countries and a backend system that collects the measurement results. Through a user-friendly web client, the experimenters can schedule and deploy their experiments. The platform further embeds traffic analysis tools for real-time traffic flow analysis and a powerful visualization tool.TRUEpu
Exploiting Order Independence for Scalable and Expressive Packet Classification
Get PDFEfficient packet classification is a core concern for network services. Traditional multi-field classification approaches, in both software and ternary content-addressable memory (TCAMs), entail tradeoffs between (memory) space and (lookup) time. TCAMs cannot efficiently represent range rules, a common class of classification rules confining values of packet fields to given ranges. The exponential space growth of TCAM entries relative to the number of fields is exacerbated when multiple fields contain ranges.
In this work, we present a novel approach which identifies properties of many classifiers which can be implemented in linear space and with worst-case guaranteed logarithmic time \emph{and} allows the addition of more fields including range constraints without impacting space and time complexities.
On real-life classifiers from Cisco Systems and additional classifiers from ClassBench~\cite{CLASSBENCH} (with real parameters), - of rules are thus handled, and the other - of rules can be stored in TCAM to be processed in parallel.pu
Challenges and Solutions for Millimeter-Wave Wireless Networks
No full textOne of the most promising options to significantly increase data rates in future wireless networks is to vastly increase the communication bandwidth. Such very high bandwidth channels are only available in the extremely high frequency part of the radio spectrum, the millimeter wave band (mm-wave). Upcoming communication technologies, for example IEEE 802.11ad, are already starting to exploit this part of the radio spectrum to achieve data rates of several GBit/s. mm-wave communication is also discussed as key technology for 5G mobile networks. However, communication at such high frequencies also suffers from high attenuation and signal absorption, often restricting communication to line-of-sight scenarios and requiring the use of highly directional antennas. This in turn requires a radical rethinking of wireless network design. On the one hand side, such channels experience little interference, allowing for a high degree of spatial reuse and potentially simpler MAC and interference management mechanisms. On the other hand, such an environment is extremely dynamic and channels may appear and disappear over very short time intervals, in particular for mobile devices. It is essential to take these characteristics into account to design efficient wireless architectures. The talk will highlight main challenges and possible solutions for networking in the mm-wave band.FALSEpu
Computationally Light “Multi-Speed” Atomic Memory
Get PDFCommunication demands are usually the leading factor that defines the efficiency of operations on a read/write shared memory emulation in the message-passing environment. In the quest for minimizing the communication demands, the algorithms proposed either require restrictions in the system or incur high computation demands. As a result, such solutions may be not suitable to be used in practice.
In this paper we focus on the practicality of implementations of atomic read/write shared memory emulation in the message-passing environment. In particular we investigate implementations that reduce both communication and computation demands. We first examine the shortcomings of the best two (in terms of communication demands) known algorithms that implement atomic single-writer multiple-reader (SWMR) atomic memory, [4, 7]. The algorithm ccFast proposed in [4], achieves optimal communication by allowing each operation to complete in one round trip, with light computation requirements. Unfortunately, it relies on strict limitations on the number of readers. On the other hand, algorithm OhSam [7], imposes no restrictions on the system, but provides operations that require one and a half communication rounds. In the light of these shortcomings, we present two algorithms that implement multi-speed operations with light computation, and without imposing any restriction on the system. In particular, algorithm ccHybrid adopts the fast (one-round) writes presented in [4], and makes clients to switch to a slow (two-round) mode whenever the system is congested. On the other hand, algorithm OhFast, pushes the responsibility of deciding for the speed switch to the servers. This allows the algorithm to utilize the fast operations presented in [4], and the slow one-and-a-half-rounds operations of [7], whenever is necessary. We prove that both new algorithms preserve atomicity.
To evaluate the new algorithms we implement five different atomic memory algorithms in the NS3 simulator, and we compare their performance in terms of operation latency, and ratio of slow over fast operations performed. We test the algorithms over different: (i) topologies, and (ii) operation loads. Our results support that the newly presented algorithms increase the practicality of atomic read/write atomic shared memory implementations in the message-passing, asynchronous environment.TRUEpu