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Medium access and transport protocol aspects in practical 802.11ad networks
Get PDFThe use of directional antennas in millimeter-wave communication promises high spatial reuse at multi-gigabit-persecond data rates in dense wireless networks. Existing work studies such networks using commercial hardware but is limited to individual links. Moreover, such hardware typically allows for little or no control of the lower layers of the protocol stack. In this paper, we study the performance of dense millimeterwave deployments featuring up to eight stations. To this end, we use a practical IEEE 802.11ad millimeter-wave testbed that allows access to the lower layer parameters of each station. This enables us to analyze the impact of these parameters on upper layer performance. We study, for first time to our best knowledge, issues such as the impact of channel contention on the buffer size at the transport layer, the effect of frame aggregation, and the efficiency of spatial sharing. Our results show that using large buffer sizes with TCP is harmful due to channel contention despite the multi-gigabit-per-second data rates. Further, frame aggregation is only beneficial up to a certain level due to higher error rates for large frames. Finally, we also study delay, showing that the regular beacon transmission time can degrade performance.TRUEpu
Unsupervised Scalable Statistical Method for Identifying Influential Users in Online Social Networks
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A Recharging Distance Analysis for Wireless Sensor Networks
No full textEfficient energy consumption is a challenging problem in wireless sensor networks especially close to the sink node, known as the energy hole problem. Various policies for recharging battery exhausted nodes have been proposed using special recharging vehicles. The focus in this paper is on a simple recharging policy that permits a recharging vehicle, stationed at the sink node, to move around and replenish any node’s exhausted battery when a certain recharging threshold is violated. The minimization of the recharging distance covered by the recharging vehicle is shown to be a facility location problem, and particularly a 1-median one. Simulation results investigate various aspects of the recharging policy – including an enhanced version – related to the recharging threshold and the level of the energy left in the network nodes’ batteries. In addition, it is shown that when the sink’s positioning is set to the solution of the particular facility location problem, then the recharging distance is minimized irrespectively of the recharging threshold.pu
A Long Way to the Top: Significance, Structure, and Stability of Internet Top Lists
Get PDFhttps://doi.org/10.1145/3278532.3278574A broad range of research areas including Internet measurement, privacy, and network security rely on lists of target domains to be analysed; researchers make use of target lists for reasons of necessity or efficiency. The popular Alexa list of one million domains is a widely used example. Despite their prevalence in research papers, the soundness of top lists has seldom been questioned by the community: little is known about the lists’ creation, representativity, potential biases, stability, or overlap between lists. In this study we survey the extent, nature, and evolution of top lists used by research communities. We assess the structure and stability of these lists, and show that rank manipulation is possible for some lists. We also reproduce the results of several scientific studies to assess the impact of using a top list at all, which list
specifically, and the date of list creation. We find that (i) top lists generally overestimate results compared to the general population by a significant margin, often even an order of magnitude, and (ii) some top lists have surprising change characteristics, causing high day-to-day fluctuation and leading to result instability. We conclude our paper with specific recommendations on the use of top lists, and how to interpret results based on top lists with caution.TRUEpu
Deep Learning Models for Wireless Signal Classification with Distributed Low-Cost Spectrum Sensors
Get PDFThis paper looks into the modulation classification problem for a distributed wireless spectrum sensing network. First, a new data-driven model for Automatic Modulation Classification (AMC) based on long short term memory (LSTM) is proposed. The model learns from the time domain amplitude and phase information of the modulation schemes present in the training data without requiring expert features like higher order cyclic moments. Analyses show that the proposed model yields an average classification accuracy of close to 90% at varying SNR conditions ranging from 0dB to 20dB. Further, we explore the utility of this LSTM model for a variable symbol rate scenario. We show that a LSTM based model can learn good representations of variable length time domain sequences, which is useful in classifying modulation signals with different symbol rates. The achieved accuracy of 75% on an input sample length of 64 for which it was not trained, substantiates the representation power of the model. To reduce the data communication overhead from distributed sensors, the feasibility of classification using averaged magnitude spectrum data and on-line classification on the low-cost spectrum sensors are studied. Furthermore, quantized realizations of the proposed models are analyzed for deployment on sensors with low processing power.pu
In Light and In Darkness, In Motion and In Stillness: A Reliable and Adaptive Receiver for the Internet of Lights
Get PDFLEDs in our buildings, vehicles and consumer products are rapidly gaining visible light communication capabilities. LED links however are notorious for being unreliable: shadowing, blockage, mobility, external light, all of these issues can disrupt the connectivity easily. Therefore, unless a reliable and cost-efficient data link layer is designed, VLC will be confined to niche applications. In this paper, we reveal a reason for unreliable VLC: a single type of photodetector at the receiver can not establish a reliable link. We show that photodetectors with complementary properties, in terms of optical spectral response and field-of-view, are necessary to handle the wide dynamic range of optical noise (such as the sun and other unwanted light sources) and mobility of users. Motivated by our experimental observations, we design REAL-VLC (a reliable and adaptive receiver for VLC) for low-end communication systems, an inexpensive receiver that senses light with complementary photodetectors and configures itself (Physical and Data Link Layers) dynamically to maintain the communication link. We implement the hardware and the software of REAL-VLC in low-end platforms, and experimentally validate it in representative test scenarios and a proof-of-concept application that consists of mobile nodes maintaining a VLC link under various lighting and path conditions.pu
Addendum to Adaptive Codebook Optimization for Beam Training on Off-The-Shelf IEEE 802.11ad Devices
Get PDFThis technical report is an extension to the paper Adaptive Codebook Optimization for Beam Training on Off-The-Shelf IEEE 802.11ad Devices [1]. It provides additional information and more detailed steps for the mathematical derivations in the paper