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Embedded Visible Light Communication: Link Measurements and Interpretation
Get PDFEmbedded visible light communication (VLC) systems built with low-cost commodity hardware are starting to attract the interest of the embedded systems community, but are yet unexplored in many aspects. The performance of VLC channels is not comprehensively studied under different communication settings and scenarios. In this paper we present an experimental characterization of the performance of low-end VLC channels and investigate the impact of various transmitter/receiver settings, protocol-level parameters and deployment aspects using both low-power and high-power LEDs. Our goal is to discover the strengths, weaknesses and limitations of embedded VLC systems.TRUEpu
Evaluating Reliability Techniques in the Master-Worker Paradigm
Get PDFA distributed system is considered that carries out
computational tasks according to the master-worker paradigm.
A master has a set of computational tasks to resolve. She assigns each task to a set of workers over the Internet, instead of computing the task locally. For each task each worker reply to the master with the task result. Since the task was not computed locally, the master can not trust the result for two main reasons: (i) workers might deliberately provide an incorrect result, (ii) the result is corrupted due to some hardware or software failure during the execution of the task. Given the above, we can model our workers as either “altruistic”, always willing to provide the correct result to each task, or “troll” that are trying to provide an incorrect result to each task. Moreover we model the failure of the worker to comply with her intended behavior, as an error probability �. The goal of the master is to compute the correct result of all the tasks with high probability. In the literature two techniques have been used to achieve this goal: (i) “voting”, that determines the correct result of a task given multiple replies of distinct workers; (ii)“challenges”, that are tasks whose result is known and can be used to detect altruistic workers. What separates our work from the current literature is the realistic modelling of the worker’s behavior and the fact that we do not restrict the task result to a binary set of answers; the domain of
possible replies for a task can have multiple correct and multiple incorrect results. Given the above we evaluate the performance of the two techniques described in the literature in the scenario where � = 0 and when � > 0. Performance is measured in terms of: (1) time, i.e., the number of rounds performed by an algorithm for the computation of all the tasks, and (2) work, i.e., the number of total task computations performed by the
workers. The case where � = 0 is used as a best case scenario that provides the optimal time and work bounds of the problem. In the case where � > 0 we propose two “natural” algorithms: one using a combination of both voting and challenges, and a second one using only voting. Both algorithms assume that certain system parameters are known. Since this might not always be the case we also provide an algorithm that estimates correctly these parameters with high probability.TRUEpu
Radical business innovation with machine learning and intelligent optimization
No full textLearning and Intelligent Optimization (LION) is the combination of machine learning from data and optimization to solve challenging and dynamic problems, previously thought to require intelligent human intervention and creativity. Businesses can be run more and more by defining objectives, measuring and collecting data, using data to build models, using models to connect new data directly to decisions and actions, with very limited human intervention. With support of the right software, a huge power is directly in the hands of businesses in a self-service and automated manner. We highlight the scientific principles and mention some notable examples of this radical transformation which can produce wealth for everybody provided that the risk of higher unemployment rate is properly addressed.FALSEpu
Hybrid Analog-Digital Beam Training for mmWave Systems with Low-Resolution RF Phase Shifters
Get PDFMillimeter wave (mmWave) wireless technologies are expected to exploit large-scale multiple-input multiple-output and adaptive antenna arrays at both the transmitter and receiver
to deal with unfavorable radio propagation and realize sufficient link margin. However, the high cost and power consumption of mmWave radio components prohibit the use of fully-digital precoding/combining architectures, which incurs one dedicated RF chain per antenna element. This paper proposes a practical design of multi-beamwidth codebook exploiting hybrid analogdigital architectures with a number of RF chains much lower than the number of antenna elements and 2-bit RF phase shifters. The proposed solution relies on the orthogonal matching pursuit algorithm enhanced by a dynamic dictionary learning mechanism. Simulation results show that the designed hybrid codebooks are able to shape beam patterns very close to those attained by a fully-digital beamforming architecture. Furthermore, when leveraged in the framework of an adaptive, multi-resolution beam training protocol, our hybrid codebooks are able to estimate the most promising angle-of-departure and angle-of-arrival directions with extreme accuracy, yet requiring lower complexity hardware compared to the state of art.TRUEpu
FIB Efficiency in Distributed Platforms
Get PDFThe Internet routing ecosystem is facing substantial scalability challenges due to continuous, significant growth of the state represented in the data plane. Distributed switch architectures introduce additional constraints on efficient implementations from both lookup time and memory footprint perspectives. In this work we explore efficient FIB representations in common distributed switch architectures. Our approach introduces substantial savings in memory footprint transparently for existing hardware. Our results are supported by an extensive simulation study on real IPv4 and IPv6 FIBs.TRUEpu
Intra-Frame Bidirectional Transmission in Networks of Visible LEDs
Get PDFThe optical antenna's directionality of nodes forming a Visible Light Communication (VLC) networks, i.e., their Field-Of-View (FOV), varies greatly from device to device. This encompasses wide FOVs of ambient light infrastructure and directional FOVs of light from low-end embedded devices. This variety of light propagation can severely affect the transmission reliability, despite "pointing" the devices to each other may seem enough for a reliable communication. The presence of interference among nodes with different FOVs makes traditional access protocols in VLC unreliable and it also exacerbates the hidden-node problem. In this paper, we propose a Carrier Sensing Multiple Access/Collision Detection&Hidden Avoidance (CSMA/CD-HA) medium access control protocol for a network where each node solely uses one Light Emitting Diode (LED) to transmit and receive data. The CSMA/CD-HA can enable in-band intra-frame bidirectional transmission with just one optical antenna. The key idea is to exploit the intra-frame data symbols without emission of light to introduce an embedded communication channel. This approach enables the transmission of additional data while receiving in the same optical frequency band and it makes the communication robust to different types of FOVs. We implement the CSMA/CD-HA protocol in a software-defined embedded platform running Linux, and evaluate its performance through analysis and experiments. Results show that collisions caused by hidden nodes can be largely reduced and our protocol can increase the saturation throughput by nearly up to 50% and 100% under the two- and four-node scenarios, respectively.pu
Offloading Cellular Traffic Through Opportunistic Communications: Analysis and Optimization
Get PDFOffloading traffic through opportunistic communications
has been recently proposed as a way to relieve the current overload of cellular networks. Opportunistic communication can occur when mobile device users are (temporarily) in each other’s proximity, such that the devices can establish a local peer-to-peer connection (e.g., via WLAN or Bluetooth). Since opportunistic communication is based on the spontaneous mobility of the participants, it is inherently unreliable. This poses a serious challenge to the design of any cellular offloading solutions, that must meet the applications’ requirements. In this paper, we address this challenge from an optimization analysis perspective, in contrast to the existing heuristic solutions. We first model the dissemination of content (injected through the cellular interface) in an opportunistic network with heterogeneous node mobility. Then, based on this model, we derive the optimal content injection strategy, which minimizes the load of the cellular network while meeting the applications’constraints. Finally, we propose an adaptive algorithmbased on control theory that implements this optimal strategy without requiring any data on the mobility patterns or the mobile nodes’ contact rates. The proposed approach is extensively evaluated with both a heterogeneous mobility model as well as real-world contact traces, showing that it substantially outperforms previous approaches proposed in the literature.pu
Speeding Up mmWave Beam Training through Low-Complexity Hybrid Transceivers
Get PDFMillimeter wave (mmWave) wireless technologies are expected to become key enablers of multi-gigabit wireless access in next-generation cellular and local area networks. Due to unfavorable radio propagation, mmWave systems will exploit large-scale MIMO and adaptive antenna arrays at both the transmitter and receiver to realize sufficient link margin. Unfortunately, power and cost requirements in mmWave radio frontends make the use of fully-digital beamforming very challenging. In this paper, we focus on hybrid analog-digital beamforming and address two relevant aspects of the initial access procedure at mmWave frequencies. First, we propose a beam training protocol which effectively accelerates the link establishment by exploiting the ability of mobile users to simultaneously receive from multiple directions. Second, we deal with practical constraints of mmWave transceivers and propose a novel, geometric approach to synthesize multi-beamwidth beam patterns that can be leveraged for simultaneous multi-direction scanning. Simulation results show that the proposed hybrid codebooks are able to shape beam patterns very close to those attained by a fully-digital beamforming architecture, yet require lower complexity hardware compared
with the state of the art. Furthermore, the reduced duration
of the beam training phase, in turn enabled by the multi-beam characteristics of our hybrid codebooks, provides a 25% to 70% increase in spectral efficiency compared to existing sequential scanning strategies.TRUEpu
Opportunistic Device-To-Device Communication In Cellular Networks: From Theory To Practice
Get PDFCellular service providers have been struggling with users’ demand since the emergence of mobile Internet. As a result, each generation of cellular network prevailed over its predecessors mainly in terms of connection speed. However, the fifth generation (5G) of cellular network promises to go beyond this trend by revolutionizing the network architecture. Device-to- Device (D2D) communication is one of the revolutionary changes that enables mobile users to communicate directly without traversing a base station. This feature is being actively studied in 3GPP with special focus on public safety as it allows mobiles to operate in adhoc mode. Although under the (partial) control of the network, D2D communications open the door to many other use-cases.
This dissertation studies different aspects of D2D communications and its impact on the key performance indicators of the network. We design an architecture for the collaboration of cellular users by means of timely exploited D2D opportunities. We begin by presenting the analytical study on opportunistic outband D2D communications. The study reveals the great potential of opportunistic outband D2D communications for enhancing energy efficiency, fairness, and capacity of cellular networks when groups of D2D users can be form and managed in the cellular network. Then we introduce a protocol that is compatible with the latest release of IEEE and 3GPP standards and allows for implementation of our proposal in a today’s cellular network. To validate our analytical findings, we use our experimental Software Defined Radio (SDR)-based testbed to further study our proposal in a real world scenario. The experimental results confirm the outstanding potential of opportunistic outband D2D communications. Finally, we investigate the performance merits and disadvantages of different D2D “modes”. Our investigation reveals, despite the common belief, that all D2D modes are complementary and their merits are scenario based.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
Power-efficient Assignment of Virtual Machines to Physical Machines
Get PDFMotivated by current trends in cloud computing, we study a version of the generalized assignment problem where a set of virtual processors has to be implemented by a set of identical processors. For literature consistency, we say that a set of virtual machines (VMs) is assigned to a set of physical machines (PMs). The optimization criterion is to minimize the power consumed by all the PMs. We term the problem Virtual Machine Assignment (VMA). Crucial differences with previous work include a variable number of PMs, that each VM must be assigned to exactly one PM (i.e., VMs cannot be implemented fractionally), and a minimum power consumption for each active PM. Such infrastructure may be strictly constrained in the number of PMs or in the PMs' capacity, depending on how costly (in terms of power consumption) it is to add a new PM to the system or to heavily load some of the existing PMs. Low usage or ample budget yields models where PM capacity and/or the number of PMs may be assumed unbounded for all practical purposes.
We study four VMA problems depending on whether the capacity or the number of PMs is bounded or not. Specifically, we study hardness and online competitiveness for a variety of cases. To the best of our knowledge, this is the first comprehensive study of the VMA problem for this cost function.pu