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Opp-Relay: Managing Directionality and Mobility Issues of Millimeter-Wave via D2D Communication
Get PDFThe directionality of millimeter-Wave (mm-Wave) communication results in challenging network dynamics and thus complex system design. A key problem with such networks is human blockage, which is highly detrimental since absorption at mm-Wave frequencies is extremely high. This poses a significant challenge for the state-of-the-art technologies in 5G networks such as Device-to-Device (D2D) communication. Essentially, the aforementioned dynamics hinder direct communication between devices. Existing protocols in the mm-Wave band such as IEEE 802.11ad address this problem using relays. However, the complexity relay discovery in these protocols grows linearly with the number of users, Hence, these approaches are infeasible for crowded areas such as malls or busy pedestrian streets. In this paper, we present a lightweight relaying mechanism called Opp-Relay that builds on the existing D2D features of the 3GPP standard to opportunistically discover an mm-Wave enabled relay. Specifically, we provide an algorithm to compute the optimal beamwidth for opportunistic discovery of a relay in dense and dynamic network environments. We validate our approach in practice using our experimental testbed operating in the 60 GHz band. Our experiments demonstrate that choosing a suitable beamwidth to discover and communicate with a relay node is crucial. Moreover, we show that our relaying mechanism significantly reduces the complexity of relay discovery.TRUEpu
Performance of Overlaid MIMO Cellular Networks with TAS/MRC Under Hybrid-Access Small Cells and Poisson Field Interference
Get PDFThis paper presents new approaches to characterize the achieved performance of hybrid control-access small cells in the context of two-tier multi-input multi-output (MIMO) cellular networks with random interference distributions. The hybrids cheme at small cells (such as femtocells) allows for sharing radio resources between the two network tiers according to the densities of small cells and their associated users, as well as the observed interference power levels in the two network tiers. The analysis considers MIMO transceivers at all nodes, for which antenna arrays can be utilized to implement transmit antenna selection (TAS) and receive maximal ratio combining (MRC) under MIMO point-to-point channels. Moreover, it targets network-level models of interference sources inside each tier and between the two tiers, which are assumed to follow Poisson field processes. To fully capture the occasions for Poisson field distribution on MIMO spatial domain. Two practical scenarios of interference sources are addressed including highly-correlated or uncorrelated transmit antenna arrays of the serving macrocell base station. The analysis presents new analytical approaches that can characterize the downlink outage probability performance in any tier. Furthermore, the outage performance in high signal-tonoise (SNR) regime is also obtained, which can be useful to deduce diversity and/or coding gains.TRUEpu
Uncovering Flipped-classroom Problems at an Engineering Course on Systems Architecture through Data-driven Learning Design
No full textFlipped classroom is a student-centered methodology that can help engineering students to acquire the cross-curricular skills demanded by society. However, its effectiveness relies on the commitment of both instructors and students. In particular, this strategy requires students to work on a number of proposed activities before face-to-face classes. Then, in order to follow the most appropriate path in those classes, instructors need a reliable way to know at which degree their students worked on those proposed activities, what issues they encountered while doing them and which concepts need to be reinforced in class. This paper presents a case study of a flipped-classroom undergraduate engineering course. By using data-driven learning design and learning analytics techniques we show that: (1) by delaying their work on the course activities our students actually drove the course towards the traditional approach; (2) despite directly asking students at the beginning of a face-to-face class might seem to be an appropriate way of getting reliable information about their previous work, it may lead instructors to erroneous conclusions; (3) our students were strongly mark- and deadline-oriented, but even a small grade encouraged them to work on the assignments; (4) the gathering and checking of students’ learning data before the class can help instructors to tailor the lesson design; and (5) if students did not work on pre-class activities, dedicating a small amount of time of the in-class lesson to explain the most difficult concepts can help students to be more efficient with their work, at the cost of losing some of the spirit of the flipped classroom.pu
An Advertising Revenue Model for Access ISPs
Get PDFFaced with the unrelenting traffic growth and rising costs, access ISPs (Internet Service Providers) realize that their traditional revenue model of flat subscription fees is unsustainable. Regulatory concerns, e.g., about content-specific charging, constrain the ISPs’ search for new revenue sources. This paper analyzes a revenue model where an access ISP acts as a publisher of ads to users who explicitly opt for an ad-sponsored access plan of the ISP. First, we conduct a survey showing a substantial interest of users in ad-sponsored Internet access. Then, we mathematically characterize the advertising revenue model and asses its economic feasibility based on real data from two access ISPs and an ad publisher. While the ad revenues are tangible, they do not completely cover the costs of the access ISPs. Even in relative terms, a larger access ISP benefits more from the advertising, with the ad revenues covering up to 50% of the ISP’s capital expenditure. Complementing the subscription fees, the access ISPs can leverage the ad revenues to meaningfully incentivize the users with better Internet connectivity, such as 6-9 Mbps in extra data rates or 12-20 GB in extra data caps for the two considered ISPs.TRUEpu
Why Your Smartphone Doesn’t Work in Very Crowded Environments
Get PDFAn experience common to smartphone users is the
difficulty in accessing services in crowded scenarios, such as a rock concert or a football match. In these cases, to (partially) mitigate frustration, users generically claim that network congestion is occurring, and try again and again to access the network with their smartphones: the result is that user frustration and network congestion reinforce each other! This paper investigates the root
causes of poor performance of cellular networks in crowded
environments, and shows that the commonly adopted random
access procedure can prevent full utilization of wireless resources. We develop a simple, yet accurate analytical model, to analyze why attempting random access to wireless resources can become a problem even when access congestion avoidance is enforced, e.g., with the Access Class Barring (ACB) technique. The model we propose suggests that cluster-based network access, leveraging device-to-device communications, significantly alleviates access problems. Moreover, it sheds light on scalability laws that govern
network utilization and quality of experience, in terms of cell capacity, number of access channels, and cluster size.TRUEpu
Millimeter Wave Networking Challenges
No full textState-of-the-art wireless communication already operates close to Shannon capacity and one of the most promising options to further increase data rates is to increase the communication bandwidth. 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, such as IEEE 802.11ad, are already starting to exploit this part of the radio spectrum to achieve data rates of several GBit/s. However, communication at such high frequencies also suffers from high attenuation and signal absorption, often restricting communication to line-of-sight (LOS) 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 turn a collection of such very high speed but brittle links into an efficient, low latency, and reliable network. This talk will highlight some of the challenges of and possible approaches for mm-wave networking.FALSEpu
Algorithms for Sensor Systems - 13th International Symposium on Algorithms and Experiments for Wireless Sensor Networks, ALGOSENSORS 2017, Vienna, Austria, September 7-8, 2017, Revised Selected Papers
No full textThis book constitutes revised selected papers from the 13th International Symposium on Algorithms and Experiments for Wireless Sensor Networks, ALGOSENSORS 2017, held in Vienna, in September 2017.
The 17 full papers presented in this volume were carefully reviewed and selected from 30 submissions. ALGOSENSORS is an international symposium dedicated to the algorithmic aspects of wireless networks. Originally focused on sensor networks, it now covers algorithmic issues arising in wireless networks of all types of computational entities, static or mobile, including sensor networks, sensor-actuator networks, autonomous robots. The focus is on the design and analysis of algorithms, models of computation, and experimental analysis.TRUEpu
Revisiting Source Routing for Underwater Networking: The SUN Protocol
Get PDFWith respect to other routing paradigms, source routing has received comparatively less attention in the underwater acoustic networking domain. The most likely causes of this lack of momentum are the high overhead caused by route discovery and maintenance in typical implementations of the source routing paradigm (e.g., Dynamic Source Routing, DSR) in terrestrial radio networks.
In this paper, we revert this view and argue that Source Routing can in fact be a reliable and convenient routing paradigm in underwater networks, when properly implemented and tailored to the peculiarities of underwater acoustic channels. Our scheme, named SUN, successfully recasts the source routing approach by introducing a number of new features, that improve the routing performance especially in the presence of unstable network links and mobile nodes. SUN is scenario-independent by design: this means that it can work in any connected topology, and does not need any side information (such as the node location and depth, or the channel state) in order to operate correctly.
We evaluate the performance of SUN by means of simulations using the DESERT Underwater framework. Our results show that SUN correctly manages routing in both static and mobile networks, and that in some scenarios it even achieves better performance than a competing flooding-based approach. We also test the performance of SUN in a thorough experimental campaign involving 6 nodes and carried out in a lake near Berlin.
From these results, we conclude that SUN, and the source routing paradigm in general, are in fact feasible options for general-purpose routing in underwater acoustic networks.pu
µNap: Practical micro-sleeps for 802.11 WLANs
Get PDFIn this paper, we revisit the idea of putting interfaces to sleep during packet overhearing (i.e., when there are ongoing transmissions addressed to other stations) from a practical standpoint. To this aim, we perform a robust experimental characterisation of the timing and consumption behaviour of a commercial 802.11 card. We design μNap, a local standard-compliant energy-saving mechanism that leverages micro-sleep opportunities inherent to the CSMA operation of 802.11 WLANs. This mechanism is backwards compatible and incrementally deployable, and takes into account the timing limitations of existing hardware, as well as practical CSMA-related issues (e.g., capture effect). According to the performance assessment carried out through trace-based simulation, the use of our scheme would result in a 57% reduction in the time spent in overhearing, thus leading to an energy saving of 15.8% of the activity time.pu