IMDEA Networks Institute Digital Repository
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Potholes Ahead: Impact of Transient Link Blockage on Beam Steering in Practical mm-Wave Systems
Get PDFThe practical realization of beam steering mechanisms in millimeter wave communications has a large impact on performance. The key challenge is to find a pragmatic trade-off between throughput performance and the overhead of periodic beam sweeping required to improve link quality in case of transient link blockage. This is particularly critical in commercial off-the-shelf devices, which require simple yet efficient solutions. First, we analyze the operation of such a commercial device to understand the impact of link blockage in practice. To this end, we measure TCP throughput for different traffic loads while blocking the link at regular intervals. Second, we derive a Markov model based on our practical insights to compute throughput for the case of transient blockage. We use this model to evaluate the trade-off between throughput and periodic beam sweeping. Finally, we validate our results using throughput traces collected using the aforementioned commercial device. Both our model and our practical measurements show that transient blockage causes significant signal fluctuation due to suboptimal beam realignment. In particular, fluctuations increase with traffic load, limiting the achievable throughput. We show that choosing lower traffic loads allows us to reduce fluctuations by 41% while achieving the same net throughput than with higher traffic loads.TRUEpu
Optimization of an integrated fronthaul/backhaul network for hard real-time traffic
No full textTelematics EngineeringUniversidad Carlos III de Madrid, Spainpu
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
Visible Light and Device-to-Device Communications: System Analysis and Implementation
Get PDFRadio-frequency based wireless communications have revolutionized our society. Thanks to important wireless communication technologies such as Wi-Fi, LTE, and so on, people can enjoy high data rate and pervasive connections while surfing the Internet. However, new challenges are rising in today’s wireless networks. Increasing capacity demands are requiring more bandwidth and various wireless radio technologies are exacerbating the spectrum problem. New technologies and paradigms are needed to meet these demands. In this thesis, I investigate two technologies towards this direction: Visible Light Communication (VLC) and Device-to-Device (D2D) communication systems.
In VLC, transmitters modulate the light intensity of Light Emitting Diodes (LEDs) to send information. Receivers detect these light changes and decode them into data. Although more and more researchers are becoming interested in VLC, the lacking of an open-source platform for VLC research is preventing the fast evolution of VLC. To solve this problem, I design, implement, and evaluate the first open-source platform OpenVLC for embedded VLC research. OpenVLC employs cost-efficient and off-the-shelf optical components and electronics to provide a research platform. The software solutions are developed as a Linux driver and can be easily connected to the TCP/IP layers. This allows for the adoption of various Linux diagnostic tools to evaluate the VLC’s properties and performance. Based on OpenVLC, I propose a new MAC protocol that enables the intra-frame bidirectional transmissions in networks of visible LEDs. The method adopts only a single LED at each node for both transmission and reception. Through this proposed method, the system’s throughput can be greatly improved and the hidden-node problem can be strongly alleviated. Motivated by the envision of the Internet of lights, I study how to provide stable visible light links in VLC. I identify the limitations and trade-off of two different types of optical receivers (photodiode and LED), and design and implement a new optical data link layer
that is resilient to dynamic environments.
On the other hand, to meet the increasing demands, small cells are proposed and deployed in latest cellular networks. As a result, the number of users served by each cell is decreasing.
As the opportunistic gain increases as a concave function of active users, in small cells and when dynamic traffic load are considered, the opportunistic gain will lost. To recoup the opportunistic gain, I propose a base-station transparent method based on D2D communication to dispatch
traffic among devices. Dynamic programming is used to find the optimal dispatching policy. The results show this method can improve the average packet transfer delay greatly. To increase the opportunistic gain by a further step, I propose a base-station initiated policy to solve the same problem. An algorithm is therefore designed and implemented, and its performance shows that it can reduce the frame loss ratio significantly.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
OWL: a Reliable Online Watcher for LTE Control Channel Measurements
Get PDFReliable network measurements are a fundamental component of networking research as they enable network analysis, system debugging, performance evaluation and optimization. In particular, decoding the LTE control channel would give access to the full base station traffic at a 1 ms granularity, thus allowing for traffic profiling and accurate measurements. Although a few open-source implementations of LTE are available, they do not provide tools to reliably decoding the LTE control channel and, thus, accessing the scheduling information. In this paper, we present OWL, an Online Watcher for LTE that is able to decode all the resource blocks in more than 99% of the system frames, significantly outperforming existing non-commercial prior de coders. Compared to previous attempts, OWL grounds the decoding procedure on information obtained from the LTE random access mechanism. This makes it possible to run our software on inexpensive hardware coupled with almost any software defined radio capable of sampling the LTE signal with sufficient accuracy.TRUEpu
An analysis of the use of badges in an educational experiment
Get PDFDOI: 10.1109/FIE.2016.7757424The use of badges in educational contexts its starting to gain popularity. However many studies do not offer an extensive analysis of the results regarding the use of badges after the educational experiment is finished. In this work we offer an evaluation of the results of three courses (physics, chemistry and mathematics) that we have conducted using Khan Academy with a wide badge system and 291 different students. We analyze these results regarding the distribution of badges per student, analyzing also the different badge types and which of them were delivered more often. We also explore the influence of factors such as the difficulty of problems or video length in the amount of badges triggered by exercises and videos respectively. We compare the results among the three courses trying to find possible explanations to these differences. We also put the lessons learned into context and give recommendations so that our findings can be used by instructional designers and other researchers.TRUEpu
Millimeter-Wave Blind Spots: Mitigating Deafness Collisions Using Frame Aggregation
Get PDFMulti-gigabit-per-second data rates in millimeterwave
networks can result in an excessive amount of channel
accesses. Transmitting a single packet at such rates often only requires a few microseconds. In contrast, the medium access control (MAC) overhead is about 20⇥ larger. This is particularly harmful if one or more nodes are deaf due to the use of directional antennas. Deaf nodes cannot overhear ongoing transmissions, and thus cause a high number of collisions, exacerbating MAC overhead even more. In addition, the contention window of deaf nodes becomes very large since their transmissions often fail, resulting in unfairness.
To mitigate this issue, we suggest increasing traffic burstiness deliberately to allow for higher frame aggregation at the physical layer. This reduces the number of medium accesses, and thus decreases the probability of collision in case of deafness. We adapt existing theoretical models to our scenario to show the effectiveness of this strategy. Moreover, we validate our scheme in a practical testbed operating in the 60 GHz
band. In particular, our evaluation shows that our strategy improves fairness by 20% and throughput by 66% compared to a system that does not exploit deliberate burstiness.TRUEpu
Pushing the Frontier: Exploring the African Web Ecosystem (Presented by Gareth Tyson)
No full textTRUEpu
Energy Efficiency in Mixed Access Networks
Get PDFDOI: http://dx.doi.org/10.1145/2988287.2989151This paper tackles the multifaceted challenges of controlling mixed access networks with base stations, access points and D2D relay stations. Mixed access networks are of uncompelling importance since the next generation cellular access networks are envisioned to use different access technologies at once. We propose a unified framework to model throughput, airtime and power consumption of mobile terminals under any workload conditions in SDN-controlled mixed access networks. With our analysis, we formulate an access selection problem to optimize energy efficiency at the terminal side, while providing fair throughput guarantees. We show that the problem is NP-hard and propose an online low-complexity heuristic that largely outperforms legacy access selection policies. Our results indicate that energy efficiency can be traded off for fairness and that D2D relay is key to increase both energy efficiency and fairness.TRUEpu
Enhanced Content Update Dissemination through D2D in 5G Cellular Networks
Get PDFOpportunistic traffic offloading has been proposed
to tackle overload problems in cellular networks.
However, existing proposals only address D2D-based offloading techniques with deadline-based data propagation, and neglect content injection procedures. In contrast, we tackle the offloading issue from another perspective: the base station interference coordination problem during content injection. In particular, we focus on the dissemination of contents, and aim at the minimisation of the total transmission time spent by base stations to inject the contents into the network. We leverage the ABSF technique to keep under control intercell interference in such process. We formulate an optimisation problem, prove that it is NP-Hard and NP-Complete, and propose a near-optimal heuristic to solve it. Our algorithm substantially outperforms classical intercell interference approaches, as we evaluate through the simulation of LTE-A
networks.pu