339 research outputs found
Optimal Online Transmission Policy for Energy-Constrained Wireless-Powered Communication Networks
This work considers the design of online transmission policy in a
wireless-powered communication system with a given energy budget. The system
design objective is to maximize the long-term throughput of the system
exploiting the energy storage capability at the wireless-powered node. We
formulate the design problem as a constrained Markov decision process (CMDP)
problem and obtain the optimal policy of transmit power and time allocation in
each fading block via the Lagrangian approach. To investigate the system
performance in different scenarios, numerical simulations are conducted with
various system parameters. Our simulation results show that the optimal policy
significantly outperforms a myopic policy which only maximizes the throughput
in the current fading block. Moreover, the optimal allocation of transmit power
and time is shown to be insensitive to the change of modulation and coding
schemes, which facilitates its practical implementation.Comment: 7 pages, accepted by ICC 2019. An extended version of this paper is
accepted by IEEE TW
Quantifying Link Stability in Ad Hoc Wireless Networks Subject to Ornstein-Uhlenbeck Mobility
The performance of mobile ad hoc networks in general and that of the routing
algorithm, in particular, can be heavily affected by the intrinsic dynamic
nature of the underlying topology. In this paper, we build a new
analytical/numerical framework that characterizes nodes' mobility and the
evolution of links between them. This formulation is based on a stationary
Markov chain representation of link connectivity. The existence of a link
between two nodes depends on their distance, which is governed by the mobility
model. In our analysis, nodes move randomly according to an Ornstein-Uhlenbeck
process using one tuning parameter to obtain different levels of randomness in
the mobility pattern. Finally, we propose an entropy-rate-based metric that
quantifies link uncertainty and evaluates its stability. Numerical results show
that the proposed approach can accurately reflect the random mobility in the
network and fully captures the link dynamics. It may thus be considered a
valuable performance metric for the evaluation of the link stability and
connectivity in these networks.Comment: 6 pages, 4 figures, Submitted to IEEE International Conference on
Communications 201
A Unification of LoS, Non-LoS and Quasi-LoS Signal Propagation in Wireless Channels
The modeling of wireless communications channels
is often broken down into two distinct states, defined
according to the optical viewpoints of the transmitter (TX) and
receiver (RX) antennas, namely line-of-sight (LoS) and non-LoS
(NLoS). Movement by the TX, RX, both and/or objects in the
surrounding environment means that channel conditions may
transition between LoS and NLoS leading to a third state of
signal propagation, namely quasi-LoS (QLoS). Unfortunately, this
state is largely ignored in the analysis of signal propagation
in wireless channels. We therefore propose a new statistical
framework that unifies signal propagation for LoS, NLoS, and
QLoS channel conditions, leading to the creation of the Three
State Model (TSM). The TSM has a strong physical motivation,
whereby the signal propagation mechanisms underlying each
state are considered to be similar to those responsible for Rician
fading. However, in the TSM, the dominant signal component, if
present, can be subject to shadowing. To support the use of the
TSM, we develop novel formulations for the probability density
functions of the in-phase and quadrature components of the
complex received signal, the received signal envelope, and the
received signal phase. Additionally, we derive an expression for
the complex autocorrelation function of the TSM, which will be of
particular importance in understanding and simulating its time
correlation properties. Finally, we show that the TSM provides a
good fit to field measurements obtained for two different bodycentric
wireless channels operating at 2.45 GHz, which are known
to be subject to the phenomena underlying the TSM.The State Research Agency (AEI) of SpainThe European
Social Fund under grant RYC2020-030536-IAEI under
grant PID2020-118139RB-I00
Adaptive Transmission Techniques for Mobile Satellite Links
Adapting the transmission rate in an LMS channel is a challenging task
because of the relatively fast time variations, of the long delays involved,
and of the difficulty in mapping the parameters of a time-varying channel into
communication performance. In this paper, we propose two strategies for dealing
with these impairments, namely, multi-layer coding (MLC) in the forward link,
and open-loop adaptation in the return link. Both strategies rely on
physical-layer abstraction tools for predicting the link performance. We will
show that, in both cases, it is possible to increase the average spectral
efficiency while at the same time keeping the outage probability under a given
threshold. To do so, the forward link strategy will rely on introducing some
latency in the data stream by using retransmissions. The return link, on the
other hand, will rely on a statistical characterization of a physical-layer
abstraction measure.Comment: Presented at the 30th AIAA International Communications Satellite
Systems Conference (ICSSC), Ottawa, Canada, 2012. Best Professional Paper
Awar
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