780 research outputs found
Average AoI Minimization for Energy Harvesting Relay-aided Status Update Network Using Deep Reinforcement Learning
A dual-hop status update system aided by energy harvesting (EH) relays with
finite data and energy buffers is studied in this work. To achieve timely
status updates, the best relays should be selected to minimize the average age
of information (AoI), which is a recently proposed metric to evaluate
information freshness. The average AoI minimization can be formulated as a
Markov decision process (MDP), but the state space for capturing channel and
buffer evolution grows exponentially with the number of relays, leading to high
solution complexity. We propose a relay selection (RS) scheme based on deep
reinforcement learning (DRL) according to the instantaneous channel packet
freshness and buffer information of each relay. Simulation results show a
significant improvement of the proposed DRL-based RS scheme over state-of-art
approaches.Comment: This article has been accepted for publication in IEEE Wireless
Communications Letters. Citation information: DOI 10.1109/LWC.2023.327886
Design, Modeling, and Analysis for MAC Protocols in Ultra-wideband Networks
Ultra-wideband (UWB) is an appealing transmission technology for
short-range, bandwidth demanded wireless communications. With the
data rate of several hundred megabits per second, UWB demonstrates
great potential in supporting multimedia streams such as
high-definition television (HDTV), voice over Internet Protocol
(VoIP), and console gaming in office or home networks, known as the
wireless personal area network (WPAN). While vast research effort
has been made on the physical layer issues of UWB, the corresponding
medium access control (MAC) protocols that exploit UWB technology
have not been well developed.
Given an extremely wide bandwidth of UWB, a fundamental problem on
how to manage multiple users to efficiently utilize the bandwidth is
a MAC design issue. Without explicitly considering the physical
properties of UWB, existing MAC protocols are not optimized for
UWB-based networks. In addition, the limited processing capability
of UWB devices poses challenges to the design of low-complexity MAC
protocols. In this thesis, we comprehensively investigate the MAC
protocols for UWB networks. The objective is to link the physical
characteristics of UWB with the MAC protocols to fully exploit its
advantage. We consider two themes: centralized and distributed UWB
networks.
For centralized networks, the most critical issue surrounding the
MAC protocol is the resource allocation with fairness and quality of
service (QoS) provisioning. We address this issue by breaking down
into two scenarios: homogeneous and heterogeneous network
configurations. In the homogeneous case, users have the same
bandwidth requirement, and the objective of resource allocation is
to maximize the network throughput. In the heterogeneous case, users
have different bandwidth requirements, and the objective of resource
allocation is to provide differentiated services. For both design
objectives, the optimal scheduling problem is NP-hard. Our
contributions lie in the development of low-complexity scheduling
algorithms that fully exploit the characteristics of UWB.
For distributed networks, the MAC becomes node-based problems,
rather than link-based problems as in centralized networks. Each
node either contends for channel access or reserves transmission
opportunity through negotiation. We investigate two representative
protocols that have been adopted in the WiMedia specification for
future UWB-based WPANs. One is a contention-based protocol called
prioritized channel access (PCA), which employs the same mechanisms
as the enhanced distributed channel access (EDCA) in IEEE 802.11e
for providing differentiated services. The other is a
reservation-based protocol called distributed reservation protocol
(DRP), which allows time slots to be reserved in a distributed
manner. Our goal is to identify the capabilities of these two
protocols in supporting multimedia applications for UWB networks. To
achieve this, we develop analytical models and conduct detailed
analysis for respective protocols. The proposed analytical models
have several merits. They are accurate and provide close-form
expressions with low computational effort. Through a cross-layer
approach, our analytical models can capture the near-realistic
protocol behaviors, thus useful insights into the protocol can be
obtained to improve or fine-tune the protocol operations. The
proposed models can also be readily extended to incorporate more
sophisticated considerations, which should benefit future UWB
network design
Fast generation of arbitrary optical focus array
We report a novel method to generate arbitrary optical focus arrays (OFAs).
Our approach rapidly produces computer-generated holograms (CGHs) to precisely
control the positions and the intensities of the foci. This is achieved by
replacing the fast Fourier transform (FFT) operation in the conventional
iterative Fourier-transform algorithm (IFTA) with a linear algebra one,
identifying/removing zero elements from the matrices, and employing a
generalized weighting strategy. On the premise of accelerating the calculation
speed by >70 times, we demonstrate OFA with 99% intensity precision in the
experiment. Our method proves effective and is applicable for the systems in
which real-time OFA generation is essential
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