1,720,971 research outputs found
Energy-Efficient Multi-Tap Single Carrier Hybrid Beamforming in Uplink Wideband Millimeter Wave Systems
No full textMillimeter wave systems are expected to provide several Gbps data rate with large bandwidth. To exploit wideband channels, mitigating inter-symbol interference (ISI) is a challenging problem. Most of the existing approaches employ multi-carrier modulation, in which a baseband beamformer is used per subcarrier, resulting in a significant number of computations. To make an energy-efficient system with a low computational complexity, we propose a single carrier hybrid beamforming scheme equipped with multi-tap analog beamformer that can mitiagte ISI in analog domain so that a simple baseband beamformer can be used. Our design aims to maximize the achievable sum rate of multi-user uplink system, and optimizes the beamforming matrix with a complex circle manifold-based conjugate gradient algorithm with a proposed initialization allowing fast convergence. Considering the baseband and circuit power consumption, the proposed scheme achieves a higher energy efficiency than conventional beamforming schemes in practical transmit power region. In addition, we find a sufficient condition for the numbers of antennas and analog beamformer taps that can completely eliminate both inter-symbol and inter-stream interferences.
A Novel Pilot Design and Channel Estimation in 5G Multi-Numerology Systems
No full textMulti-numerology systems are considered to be promising communication frameworks in 5G new radio (NR) due to their flexibility. However, inter-numerology interference (inter-NI) degrades the quality of communication systems. Hence, techniques for mitigating inter-NI are needed to support multiple numerologies. In particular, the effect of the inter-NI should be considered in channel estimation process. We propose a pilot design which requires relatively short training overhead and mitigates the inter-NI. We stress that inter-NI does not exist in most cases when the proposed pilot signal is used. With taking account of the special case where inter-NI exists, we develop the channel estimation algorithm based on inter-NI cancellation. In addition, we analyze the effect of inter-NI cancellation algorithm which not only eliminates interference but also reduces the variance of noise. The simulation results verify that the performance of channel estimation with the proposed pilot signal is better than the quality of estimation with the case where user equipments transmit their pilot signals in a time division manner
Real-Time Bayesian Neural Networks for 6G Cooperative Positioning and Tracking
No full textIn the evolving landscape of 5G new radio and related 6G evolution, achieving centimeter-level dynamic positioning is pivotal, especially in cooperative intelligent transportation system frameworks. With the challenges posed by higher path loss and blockages in the new frequency bands (i.e., millimeter waves), machine learning (ML) offers new approaches to draw location information from space-time wide-bandwidth radio signals and enable enhanced location-based services. This paper presents an approach to real-time 6G location tracking in urban settings with frequent signal blockages. We introduce a novel teacher-student Bayesian neural network (BNN) method, called Bayesian bright knowledge (BBK), that predicts both the location estimate and the associated uncertainty in real-time. Moreover, we propose a seamless integration of BNNs into a cellular multi-base station tracking system, where more complex channel measurements are taken into account. Our method employs a deep learning (DL)-based autoencoder structure that leverages the complete channel impulse response to deduce location-specific attributes in both line-of-sight and non-line-of-sight environments. Testing in 3GPP specification-compliant urban micro (UMi) scenario with ray-tracing and traffic simulations confirms the BBK’s superiority in estimating uncertainties and handling out-of-distribution testing positions. In dynamic conditions, our BNN-based tracking system surpasses geometric-based tracking techniques and state-of-the-art DL models, localizing a moving target with a median error of 46 cm
Integrated Localization and Communication in 3GPP Industrial Environments
No full textIntegrated localization and communication (ILC) will be a key enabler for providing accurate location information and high data rate in next generation networks. This paper proposes a transmission frame structure and a soft information (SI)-based localization algorithm for position-assisted communications. The proposed ILC achieves improved localization accuracy and enhanced communication rate simultaneously by accounting for the statistical characteristics of the wireless environment. Results in 3rd Generation Partnership Project (3GPP) industrial scenarios show that the SI-based localization algorithm can achieve decimeter-level accuracy. Moreover, the position-assisted communication enhances the achievable rate, especially in scenarios with high mobility
Integrated Localization and Communication for Efficient Millimeter Wave Networks
No full textIntegrated localization and communication (ILC) at millimeter wave (mmWave) frequencies will be a key enabler for providing accurate location information and high data rate communication in beyond fifth generation (B5G) networks. This paper proposes a transmission frame structure and a soft information (SI)-based localization algorithm for position-assisted communications. In accordance with B5G specifications, we consider multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) networks. Theoretical limits are also derived to serve both as performance benchmark and as input for algorithm design. The proposed method enables cooperative ILC with improved localization accuracy and enhanced communication rate simultaneously. In particular, position-assisted communication at mmWave frequencies is explored accounting for the statistical characteristics of the wireless environment. Localization accuracy and communication rate are quantified in 3rd Generation Partnership Project (3GPP) network scenarios. Results show that the SI-based localization algorithm achieves decimeter-level accuracy, approaching the theoretical limit. Moreover, the position-assisted communication can provide higher communication rate with reduced overhead compared to existing techniques, especially in scenarios with high mobility
Joint Beamforming and Resource Allocation for Integrated Satellite-Terrestrial Networks
No full textIntegrated satellite-terrestrial networks (ISTNs) are essential for providing ubiquitous mobile ultra-broadband service in beyond 5G networks. The spectral efficiency and reliability of ISTN depend on the integrated architecture and its operational strategies including interference management and resource allocation. Our view is to integrate terrestrial access and satellite backhaul networks and to develop an optimization technique for their joint operation. This paper proposes an efficient integrated access and backhaul (IAB) architecture for satellite-terrestrial networks (STNs) based on reverse time division duplexing (TDD) considering both uplink (UL) and downlink (DL). In particular, in-band backhauling and gNodeB (gNB) cooperation are considered for high spectral efficiency and reliability. A framework for joint optimization of cooperative beamforming and resource allocation is developed to maximize the UL-DL rate region of the in-band IAB. The proposed scheme is verified using the 3rd Generation Partnership Project (3GPP) standard channel models. Results show that the proposed scheme significantly outperforms the conventional wireless backhauling, while approaching to an outer bound of the UL-DL rate region
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
밀리미터파 다중안테나 통신을 위한 사용자 스케줄링 및 빔포밍 설계
No full text학위논문(박사) - 한국과학기술원 : 전기및전자공학부, 2020.2,[vii, 114 p. :]Millimeter wave (mmWave) beamforming (BF) technique, which uses a large bandwidth, is expected to play a key role in 5G and beyond-5G mobile communications. However, the use of a large number of antennas to compensate the high path-loss of high-frequency channels causes several problems in practice. First, a lot of radio frequency (RF) chains are needed as many as antennas, which requires considerable implementation cost and power consumption. To address this, digital-analog hybrid BF technique, which significantly reduces the number of RF chains by introducing analog BF, should be used. Second, although the mmWave BF systems are expected to increase the areal capacity in ultra-dense network (UDN), the feedback overhead required for channel information exchange may be problematic. In particular, the size of the channel matrix increases depending on the number of antennas, and the amount of resources required for feedback increases along with the number of users or base stations, resulting in a significant overhead which degrades the throughput. This dissertation deals with the BF systems with limited feedback information to reduce implementation complexity and feedback overhead. Also, since all the users in UDN cannot be simultaneously supported by a single transmission, we propose a joint design of user scheduling and hybrid BF, and address different network scenarios. In addition, the performances of the proposed schemes are analyzed for each scenario, and the design guidelines for choosing the system parameters are provided.한국과학기술원 :전기및전자공학부
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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