7 research outputs found
Scheduling to Minimize Age of Synchronization in Wireless Broadcast Networks with Random Updates
In this work, a wireless broadcast network with a base station (BS) sending
random time-sensitive information updates to multiple users with interference
constraints is considered. The Age of Synchronization (AoS), namely the amount
of time elapsed since the information stored at the network user becomes
desynchronized, is adopted to measure data freshness from the perspective of
network users. Compared with the more widely used metric---the Age of
Information (AoI), AoS accounts for the freshness of the randomly changing
content. The AoS minimization scheduling problem is formulated into a discrete
time Markov decision process and the optimal solution is approximated through
structural finite state policy iteration. An index based heuristic scheduling
policy based on restless multi-arm bandit (RMAB) is provided to further reduce
computational complexity. Simulation results show that the proposed index
policy can achieve compatible performance with the MDP and close to the AoS
lower bound. Moreover, theoretic analysis and simulations reveal the
differences between AoS and AoI. AoI minimization scheduling policy cannot
guarantee a good AoS performance.Comment: accepted and to appear, IEEE Transactions on Wireless Communication
Delay Optimal Cross-Layer Scheduling Over Markov Channels with Power Constraint
We consider a scenario where a power constrained transmitter delivers
randomly arriving packets to the destination over Markov time-varying channel
and adapts different transmission power to each channel state in order to
guarantee successful transmission. To minimize the expected average
transmission delay of each packet, we formulate the problem into a constrained
Markov decision process (CMDP). We reveal the queue-length threshold structure
of the optimal policy, i.e., the transmitter sends packets if and only if the
queue length surpasses a threshold and obtain the optimal cross-layer
scheduling strategy through linear programming (LP). Numerical results validate
the performance of the proposed strategy and illustrate a delay-power tradeoff
in such scenario
Age of Information Aware Cache Updating with File- and Age-Dependent Update Durations
We consider a system consisting of a library of time-varying files, a server
that at all times observes the current version of all files, and a cache that
at the beginning stores the current versions of all files but afterwards has to
update %fresh versions of these files from the server. Unlike previous works,
the update duration is not constant but depends on the file and its Age of
Information (AoI), i.e., of the time elapsed since it was last updated. The
goal of this work is to design an update policy that minimizes the average AoI
of all files with respect to a given popularity distribution. Actually a
relaxed problem, close to the original optimization problem, is solved and a
practical update policy is derived. The update policy relies on the file
popularity and on the functions that characterize the update durations of the
files depending on their AoI. Numerical simulations show a significant
improvement of this new update policy compared to the so-called square-root
policy that is optimal under file-independent and constant update durations.Comment: To be submitted to ICC 202
Timely Synchronization with Sporadic Status Changes
In this paper, we consider a status updating system where the transmitter
sends status updates of the signal it monitors to the destination through a
rate-limited link. We consider the scenario where the status of the monitored
signal only changes at discrete time points. The objective is to let the
destination be synchronized with the source in a timely manner once a status
change happens. What complicates the problem is that the transmission takes
multiple time slots due to the link-rate constraint. Thus, the transmitter has
to decide to switch or to skip a new update when the status of the monitored
signal changes and it has not completed the transmission of the previous one
yet. We adopt a metric called "Age of Synchronization" (AoS) to measure the
"dissatisfaction" of the destination when it is desynchronized with the source.
Then, the objective of this paper is to minimize the time-average AoS by
designing optimal transmission policies for the transmitter. We formulate the
problem as a Markov decision process (MDP) and prove the multi-threshold
structure of the optimal policy. Based on that, we propose a low
computational-complexity algorithm for the MDP value iteration. We then
evaluate the performance of the multi-threshold policy through simulations and
compare it with two baseline policies and the AoI-optimal policy
Securing Fresh Data in Wireless Monitoring Networks: Age-of-Information Sensitive Coverage Perspective
With the development of IoT, the sensor usage has been elevated to a new
level, and it becomes more crucial to maintain reliable sensor networks. In
this paper, we provide how to efficiently and reliably manage the sensor
monitoring system for securing fresh data at the data center (DC). A sensor
transmits its sensing information regularly to the DC, and the freshness of the
information at the DC is characterized by the age of information (AoI) that
quantifies the timeliness of information. By considering the effect of the AoI
and the spatial distance from the sensor on the information error at the DC, we
newly define an error-tolerable sensing (ETS) coverage as the area that the
estimated information is with smaller error than the target value. We then
derive the average AoI and the AoI violation probability of the sensor
monitoring system, and finally present the {\eta}-coverage probability, which
is the probability that the ETS coverage is greater than {\eta} ratio of the
maximum sensor coverage. We also provide the optimal transmission power of the
sensor, which minimizes the average energy consumption while guaranteeing
certain level of the {\eta}-coverage probability. Numerical results validate
the theoretical analysis and show the tendency of the optimal transmission
power according to the maximum number of retransmissions. This paper can pave
the way to efficient design of the AoI-sensitive sensor networks for IoT
Minimizing Age of Information with Power Constraints: Multi-user Opportunistic Scheduling in Multi-State Time-Varying Channels
This work is motivated by the need of collecting fresh data from
power-constrained sensors in the industrial Internet of Things (IIoT) network.
A recently proposed metric, the Age of Information (AoI) is adopted to measure
data freshness from the perspective of the central controller in the IIoT
network. We wonder what is the minimum average AoI the network can achieve and
how to design scheduling algorithms to approach it. To answer these questions
when the channel states of the network are Markov time-varying and scheduling
decisions are restricted to bandwidth constraint, we first decouple the
multi-sensor scheduling problem into a single-sensor constrained Markov
decision process (CMDP) through relaxation of the hard bandwidth constraint.
Next we exploit the threshold structure of the optimal policy for the decoupled
single sensor CMDP and obtain the optimum solution through linear programming
(LP). Finally, an asymptotically optimal truncated policy that can satisfy the
hard bandwidth constraint is built upon the optimal solution to each of the
decoupled single-sensor. Our investigation shows that to obtain a small AoI
performance: (1) The scheduler exploits good channels to schedule sensors
supported by limited power; (2) Sensors equipped with enough transmission power
are updated in a timely manner such that the bandwidth constraint can be
satisfied.Comment: accepted and to appear, IEEE JSAC. arXiv admin note: substantial text
overlap with arXiv:1908.0133
The Road Towards 6G: A Comprehensive Survey
As of today, the fifth generation (5G) mobile communication system has been
rolled out in many countries and the number of 5G subscribers already reaches a
very large scale. It is time for academia and industry to shift their attention
towards the next generation. At this crossroad, an overview of the current
state of the art and a vision of future communications are definitely of
interest. This article thus aims to provide a comprehensive survey to draw a
picture of the sixth generation (6G) system in terms of drivers, use cases,
usage scenarios, requirements, key performance indicators (KPIs), architecture,
and enabling technologies. First, we attempt to answer the question of "Is
there any need for 6G?" by shedding light on its key driving factors, in which
we predict the explosive growth of mobile traffic until 2030, and envision
potential use cases and usage scenarios. Second, the technical requirements of
6G are discussed and compared with those of 5G with respect to a set of KPIs in
a quantitative manner. Third, the state-of-the-art 6G research efforts and
activities from representative institutions and countries are summarized, and a
tentative roadmap of definition, specification, standardization, and regulation
is projected. Then, we identify a dozen of potential technologies and introduce
their principles, advantages, challenges, and open research issues. Finally,
the conclusions are drawn to paint a picture of "What 6G may look like?". This
survey is intended to serve as an enlightening guideline to spur interests and
further investigations for subsequent research and development of 6G
communications systems.Comment: 30 Pages, 5 figures, IEEE open Journa