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Yonghui Li - One of the best experts on this subject based on the ideXlab platform.
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a novel efficient initial access method for 5g millimeter wave communications using genetic algorithm
IEEE Transactions on Vehicular Technology, 2019Co-Authors: Victoria Dala Pegorara Souto, Richard Demo Souza, Bartolomeu F Uchoafilho, Yonghui LiAbstract:Initial Access (IA) in millimeter wave (mmWave) communications, i.e., the mechanism by which the Base Station (BS) and the User Equipment (UE) establish a Directional communication Link, is a challenging problem. A significant delay can be incurred when the BS and the UE try to find the appropriate beam alignment for obtaining a Directional Link, and solving this problem efficiently has become an important research topic. In this work, we propose a new beam refinement method based on Genetic Algorithms (GAs) which is particularly advantageous when the number of antennas is large. In particular, we consider a scenario where both the BS and the UE are equipped with a single RF chain and multiple antennas, i.e., a single beam analog beamforming is considered at the BS and UE. The efficiency of the proposed method and the effect of several parameters, such as the number of transmit and receive antennas, codebook size, and transmission power are investigated. In the case of small parameters, it is shown that the proposed method achieves the same capacity of Exhaustive Search (ES) but with a much lower complexity. Moreover, in comparison with existing methods, our method has a superior performance in terms of capacity, outage probability, and power consumption.
Aykin Irmak - One of the best experts on this subject based on the ideXlab platform.
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Design and Implementation of Machine-Learning-Based Beam Management Protocols for 5G Millimeter-Wave Networks
The University of Arizona., 2020Co-Authors: Aykin IrmakAbstract:Millimeter-wave (mmWave) communications have recently attracted considerable interest as a key element of next-generation wireless systems, e.g., 5G New Radio (NR) cellular systems and WiGig. The abundant spectrum available in the mmWave bands enables many users to be served by a base station (BS), with significantly higher data rates than what is possible at sub-6 GHz bands. However, wireless transmissions at mmWave frequencies suffer from high propagation losses and poor penetration. At the same time, the small wavelengths allow many antenna elements to be packed into a single portable device without increasing its form factor. With proper processing of signals fed into these antennas, transmissions can be beamed along a desired direction, resulting in high beamforming gain that compensates for the severe signal attenuation. However, beamforming and Directional communications raise various challenges related to beam management. In 4G LTE systems, initial access (IA) procedure, the process by which a user equipment (UE) establishes a connection with a BS, is performed in an omniDirectional fashion, alleviating the complexity of beam alignment. In contrast, the IA procedure in 5G NR is done Directionally to reach more users and support subsequent Directional data transmissions. Specifically, the BS need to sequentially sweep its beams for the UEs to measure their qualities, determine the best beam and report it back to the BS. This Directional procedure incurs significant delay, which lowers the Link throughput and spectral efficiency. Methods that focus on reducing this Link establishment delay often suffer from an unacceptable probability of missing a UE in range, motivating the need for fast and efficient Link establishment techniques. In addition to the IA problem, Directionally tracking a mobile UE efficiently and reliably is also a research challenge. After establishing the initial Directional Link between a BS and a UE, beam misalignments occur frequently due to UE mobility, environmental changes, or wind. These misalignments incur a large beamforming loss, resulting in reduced data rate or even Link outage. Consequently, tracking UEs and maintaining the quality of their Directional Links are quite critical. This can be done via frequent channel probing at the expense of extra control overhead, which lowers the spectral efficiency and increases latency. In this dissertation, we design efficient and reliable initial access and beam tracking protocols for Directional mmWave systems. In designing these protocols, we aim at minimizing the UE finding/tracking overhead, while maintaining a low probability of missing previously undiscovered UEs. We first design an IA protocol called FastLink, which allows the BS and the UE to transmit and receive using the narrowest possible beams, hence providing the highest possible beamforming gain. At the same time, beam sweeping in FastLink is done in such a way that the discovery process is much faster than the beam scanning mechanisms used in both the 802.11ad standard and 5G NR. FastLink exploits compressive sensing (CS) theory to determine the number of measurements (beam probes) needed to identify the `dominant' channel cluster. Inspired by this theory, we design a search algorithm called 3-dimensional peak finding (3DPF) to find the best beam. 3DPF divides the set of beam directions into equally spaced subsets and then finds the beam that achieves the maximum received power in each subset. The number of subsets is a design parameter, determined using CS results. We integrate 3DPF into the FastLink protocol and explain the required control messages that need to be exchanged between the BS and the UE in support of this protocol. Next, we develop a communication protocol called SmartLink that utilizes multiple channel clusters between the BS and the UE to provide an effective mechanism for maintaining communications under random blockage. SmartLink is built on a unique beam scanning technique called multi-lobe beam search (MLBS). Implementing shortest-depth decision trees, MLBS utilizes beam patterns with multiple lobes to simultaneously discover multiple channel clusters. Through rigorous analysis, we show that MLBS reduces the search time from linear to logarithmic with respect to the total number of beam directions. Depending on the discovered channel clusters and their relative gains, we then virtually divide the Tx and the Rx antenna arrays into several sub-arrays. Each sub-array is assigned to a beam that points towards one of the inferred channel clusters. The goal of such antenna partitioning is to maximize the average data rate in a blockage-prone environment. Besides incorporating MLBS and antenna partitioning, the specification of SmartLink also includes the required message exchange between the BS and the UE to establish the multi-Directional Link. Finally, for beam tracking in mmWave systems, we propose a restless multi-armed bandit framework, called MAMBA. In MAMBA, each beam is modeled as an arm of a multi-armed bandit problem. The BS acts as the agent, interacting with these arms to learn the underlying system dynamics, i.e., changes in beam qualities over time. The quality of a beam is quantified by the best modulation and coding scheme (MCS) that can be supported. We develop a reinforcement learning (RL) algorithm called adaptive Thompson sampling (ATS) to determine the optimal beam/MCS pair in MAMBA for each downLink transmission. ATS aims at maximizing the expected transmission rate, taking into account the estimated reward distributions associated with each beam. However, due to the time-varying nature of the environment, keeping track of these reward distributions is nontrivial. To address this issue, ATS uses a priori beam-quality information collected through IA, and updates this information at each iteration based on the feedback obtained from the UE. The beam and MCS for the next downLink transmission are then selected based on the updated posterior distributions of the rewards, i.e., achievable rates of various beams. Due to its model-free nature, ATS can accurately estimate the best beam/MCS pair without making unrealistic assumptions regarding channel dynamics and/or the UE mobility pattern
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SmartLink: Exploiting Channel Clustering Effects for Reliable Millimeter Wave Communications
'Institute of Electrical and Electronics Engineers (IEEE)', 2019Co-Authors: Aykin Irmak, Akgun Berk, Krunz MarwanAbstract:Millimeter wave (mmW) communications have recently attracted considerable attention as a key element of next generation (5G) wireless systems. Despite significant efforts in this domain, establishing and maintaining Directional mmW Links in a dynamic environment are still quite challenging, largely due to the search-time overhead of beam scanning, and the vulnerability of Directional Links to beam misalignment, blockage, and outages. In this paper, we propose SmartLink, a protocol that exploits the multi-cluster scattering phenomenon at mmW frequencies to establish a multi-Directional Link between a base station and a user. By exploiting multiple clusters, SmartLink enables fast initial access and Link maintenance, along with sustained throughput. A search algorithm called multi-lobe beam search (MLBS) is used to discover multiple channel clusters by probing several directions simultaneously using carefully designed multi lobe beam patterns. MLBS reduces the search time from linear to logarithmic with respect to the number of directions. We provide detailed analysis of the false alarm and misdetection probabilities for the designed beam patterns. Following cluster discovery, SmartLink divides antennas into sub-arrays to generate the optimal multi-lobe pattern with respect to cluster powers and blockage probabilities. Finally, extensive trace-driven simulations at 29 GHz frequency using phased-array antennas verify the efficiency of SmartLink.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu
Tongwen Chen - One of the best experts on this subject based on the ideXlab platform.
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finite time consensus in networks of integrator like dynamic agents with Directional Link failure
IEEE Transactions on Automatic Control, 2014Co-Authors: Feng Xiao, Long Wang, Tongwen ChenAbstract:This technical note proposes a general class of nonlinear protocols in the form of continuous state feedbacks for finite-time consensus in networks of integrator-like dynamic agents with Directional Link failure. These protocols, with adjustable terms, are applicable in a wide range of situations, such as with input saturation restrictions and with convergence rate constraints. Based on the assumption of a common positive dwell time for all active information Links, it is shown that if the union of the interaction topology over some fixed length of time always contains a spanning tree, then the system will solve an asymptotical consensus problem; in addition, if the length sum of time intervals, over which the interaction topology contains a spanning tree, is larger than a threshold, determined by the state differences between agents, then the system will solve a finite-time consensus problem. The validity of the protocols is proven in the case with external reference inputs. Finally, simulations are presented to demonstrate the effectiveness of the theoretical results.
Consolato Sergi - One of the best experts on this subject based on the ideXlab platform.
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co ingestion of aspirin and acetaminophen promoting fulminant liver failure a critical review of reye syndrome in the current perspective at the dawn of the 21st century
Clinical and Experimental Pharmacology and Physiology, 2018Co-Authors: Deepak Dinakaran, Consolato SergiAbstract:In the pediatric population, there is some evidence of possible interaction, synergism, and co-toxicity of aspirin and acetaminophen. The toxicity of salicylates such as aspirin in this population is well known and documented, specifically in the form of Reye syndrome. The possible toxic synergism with aspirin and acetaminophen, however, is not previously described; though case reports suggest such co-toxicities with low levels of aspirin and other compounds can exist. In vitro studies into mechanistic processes of salicylate toxicity propose that there are a bi-Directional Link and potentiation with glutathione (GSH) depletion and salicylate toxicity. Data may suggest a plausible explanation for salicylate and acetaminophen toxic synergism. Further studies investigating this potential toxic synergism are warranted. Given the lack of awareness in the clinical community about potential toxic synergism between these relatively common medications, caution is advised in the co-administration of these drugs, particularly in communities using natural or alternative therapy. This article is protected by copyright. All rights reserved.
Victoria Dala Pegorara Souto - One of the best experts on this subject based on the ideXlab platform.
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a novel efficient initial access method for 5g millimeter wave communications using genetic algorithm
IEEE Transactions on Vehicular Technology, 2019Co-Authors: Victoria Dala Pegorara Souto, Richard Demo Souza, Bartolomeu F Uchoafilho, Yonghui LiAbstract:Initial Access (IA) in millimeter wave (mmWave) communications, i.e., the mechanism by which the Base Station (BS) and the User Equipment (UE) establish a Directional communication Link, is a challenging problem. A significant delay can be incurred when the BS and the UE try to find the appropriate beam alignment for obtaining a Directional Link, and solving this problem efficiently has become an important research topic. In this work, we propose a new beam refinement method based on Genetic Algorithms (GAs) which is particularly advantageous when the number of antennas is large. In particular, we consider a scenario where both the BS and the UE are equipped with a single RF chain and multiple antennas, i.e., a single beam analog beamforming is considered at the BS and UE. The efficiency of the proposed method and the effect of several parameters, such as the number of transmit and receive antennas, codebook size, and transmission power are investigated. In the case of small parameters, it is shown that the proposed method achieves the same capacity of Exhaustive Search (ES) but with a much lower complexity. Moreover, in comparison with existing methods, our method has a superior performance in terms of capacity, outage probability, and power consumption.