69 research outputs found
Power-Optimal Feedback-Based Random Spectrum Access for an Energy Harvesting Cognitive User
In this paper, we study and analyze cognitive radio networks in which
secondary users (SUs) are equipped with Energy Harvesting (EH) capability. We
design a random spectrum sensing and access protocol for the SU that exploits
the primary link's feedback and requires less average sensing time. Unlike
previous works proposed earlier in literature, we do not assume perfect
feedback. Instead, we take into account the more practical possibilities of
overhearing unreliable feedback signals and accommodate spectrum sensing
errors. Moreover, we assume an interference-based channel model where the
receivers are equipped with multi-packet reception (MPR) capability.
Furthermore, we perform power allocation at the SU with the objective of
maximizing the secondary throughput under constraints that maintain certain
quality-of-service (QoS) measures for the primary user (PU)
Energy Efficient Delay Sensitive Optimization in SWIPT-MIMO
In this paper, we consider joint antenna selection and optimal beamforming
for energy efficient delay minimization. We assume multiple-input multi-output
(MIMO) system with full duplex simultaneous wireless information and power
transfer (FD-SWIPT) where each sensor is equipped with a power splitting (PS)
system and can simultaneously receive both energy and information from the
aggregator (AGG). We show that the antenna selection and beamforming power
control policies are adaptive to the energy state information (ESI), the queue
state information (QSI) and the channel state information (CSI). We develop an
analytical framework for energy efficient delay-optimal control problem based
on the theory of infinite horizon partially observable Markov decision process
(POMDP). The infinite-horizon POMDP problem is transformed into an equivalent
value Bellman program and solved by near-optimal point-based Heuristic Search
Value Iteration (PB-HSVI) method under specific standard conditions. The
proposed solution outcome is a set of sub-optimal antenna selection and
beamforming control policies. Simulation results reveal an effective trade-off
between the contradictory objectives (i.e. delay and power consumption) and
show the enhancement in delay by using FD-SWIPT systems in comparison to Half
Duplex (HD)-SWIPT systems
Wireless Power Transfer and Data Collection in Wireless Sensor Networks
In a rechargeable wireless sensor network, the data packets are generated by
sensor nodes at a specific data rate, and transmitted to a base station.
Moreover, the base station transfers power to the nodes by using Wireless Power
Transfer (WPT) to extend their battery life. However, inadequately scheduling
WPT and data collection causes some of the nodes to drain their battery and
have their data buffer overflow, while the other nodes waste their harvested
energy, which is more than they need to transmit their packets. In this paper,
we investigate a novel optimal scheduling strategy, called EHMDP, aiming to
minimize data packet loss from a network of sensor nodes in terms of the nodes'
energy consumption and data queue state information. The scheduling problem is
first formulated by a centralized MDP model, assuming that the complete states
of each node are well known by the base station. This presents the upper bound
of the data that can be collected in a rechargeable wireless sensor network.
Next, we relax the assumption of the availability of full state information so
that the data transmission and WPT can be semi-decentralized. The simulation
results show that, in terms of network throughput and packet loss rate, the
proposed algorithm significantly improves the network performance.Comment: 30 pages, 8 figures, accepted to IEEE Transactions on Vehicular
Technolog
Optimal Random Access and Random Spectrum Sensing for an Energy Harvesting Cognitive Radio
We consider a secondary user with energy harvesting capability. We design
access schemes for the secondary user which incorporate random spectrum sensing
and random access, and which make use of the primary automatic repeat request
(ARQ) feedback. The sensing and access probabilities are obtained such that the
secondary throughput is maximized under the constraints that both the primary
and secondary queues are stable and that the primary queueing delay is kept
lower than a specified value needed to guarantee a certain quality of service
(QoS) for the primary user. We consider spectrum sensing errors and assume
multipacket reception (MPR) capabilities. Numerical results are presented to
show the enhanced performance of our proposed system over a random access
system, and to demonstrate the benefit of leveraging the primary feedback.Comment: in WiMob 201
On the Stability of Random Multiple Access with Stochastic Energy Harvesting
In this paper, we consider the random access of nodes having energy
harvesting capability and a battery to store the harvested energy. Each node
attempts to transmit the head-of-line packet in the queue if its battery is
nonempty. The packet and energy arrivals into the queue and the battery are all
modeled as a discrete-time stochastic process. The main contribution of this
paper is the exact characterization of the stability region of the packet
queues given the energy harvesting rates when a pair of nodes are randomly
accessing a common channel having multipacket reception (MPR) capability. The
channel with MPR capability is a generalized form of the wireless channel
modeling which allows probabilistic receptions of the simultaneously
transmitted packets. The results obtained in this paper are fairly general as
the cases with unlimited energy for transmissions both with the collision
channel and the channel with MPR capability can be derived from ours as special
cases. Furthermore, we study the impact of the finiteness of the batteries on
the achievable stability region.Comment: The material in this paper was presented in part at the IEEE
International Symposium on Information Theory, Saint Petersburg, Russia, Aug.
201
Energy Harvesting Wireless Communications: A Review of Recent Advances
This article summarizes recent contributions in the broad area of energy
harvesting wireless communications. In particular, we provide the current state
of the art for wireless networks composed of energy harvesting nodes, starting
from the information-theoretic performance limits to transmission scheduling
policies and resource allocation, medium access and networking issues. The
emerging related area of energy transfer for self-sustaining energy harvesting
wireless networks is considered in detail covering both energy cooperation
aspects and simultaneous energy and information transfer. Various potential
models with energy harvesting nodes at different network scales are reviewed as
well as models for energy consumption at the nodes.Comment: To appear in the IEEE Journal of Selected Areas in Communications
(Special Issue: Wireless Communications Powered by Energy Harvesting and
Wireless Energy Transfer
Spatial Throughput of Mobile Ad Hoc Networks Powered by Energy Harvesting
Designing mobiles to harvest ambient energy such as kinetic activities or
electromagnetic radiation will enable wireless networks to be self sustaining
besides alleviating global warming. In this paper, the spatial throughput of a
mobile ad hoc network powered by energy harvesting is analyzed using a
stochastic-geometry model. In this model, transmitters are distributed as a
Poisson point process and energy arrives at each transmitter randomly with a
uniform average rate called the energy arrival rate; upon harvesting sufficient
energy, each transmitter transmits with fixed power to an intended receiver
under an outage-probability constraint for a target
signal-to-interference-and-noise ratio. It is assumed that transmitters store
energy in batteries with infinite capacity. By applying the random-walk theory,
the probability that a transmitter transmits, called the transmission
probability, is proved to be equal to one if the energy-arrival rate exceeds
transmission power or otherwise is equal to their ratio. This result and tools
from stochastic geometry are applied to maximize the network throughput for a
given energy-arrival rate by optimizing transmission power. The maximum network
throughput is shown to be proportional to the optimal transmission probability,
which is equal to one if the transmitter density is below a derived function of
the energy-arrival rate or otherwise is smaller than one and solves a given
polynomial equation. Last, the limits of the maximum network throughput are
obtained for the extreme cases of high energy-arrival rates and dense networks.Comment: This paper has been presented in part at Asilomar Conf. on Signals,
Systems, and Computers 2011 and at IEEE Intl. Conf. on Communications (ICC)
2013. The full version will appear in IEEE Transactions on Information Theor
COOPERATIVE NETWORKING AND RELATED ISSUES: STABILITY, ENERGY HARVESTING, AND NEIGHBOR DISCOVERY
This dissertation deals with various newly emerging topics in the context of cooperative networking. The first part is about the cognitive radio. To guarantee the performance of high priority users, it is important to know the activity of the high priority communication system but the knowledge is usually imperfect due to randomness in the observed signal. In such a context, the stability property of cognitive radio systems in the presence of sensing errors is studied. General guidelines on controlling the operating point of the sensing device over its receiver operating characteristics are also given. We then consider the hybrid of different modes of operation for cognitive radio systems with time-varying connectivity. The random connectivity gives additional chances that can be utilized by the low priority communication system.
The second part of this dissertation is about the random access. We are specifically interested in the scenario when the nodes are harvesting energy from the environment. For such a system, we accurately assess the effect of limited, but renewable, energy availability on the stability region. The effect of finite capacity batteries is also studied. We next consider the exploitation of diversity amongst users under random access framework. That is, each user adapts its transmission probability based on the local channel state information in a decentralized manner. The impact of imperfect channel state information on the stability region is investigated. Furthermore, it is compared to the class of stationary scheduling policies that make centralized decisions based on the channel state feedback.
The backpressure policy for cross-layer control of wireless multi-hop networks is known to be throughput-optimal for i.i.d. arrivals. The third part of this dissertation is about the backpressure-based control for networks with time-correlated arrivals that may exhibit long-range dependency. It is shown that the original backpressure policy is still throughput-optimal but with increased average network delay. The case when the arrival rate vector is possibly outside the stability region is also studied by augmenting the backpressure policy with the flow control mechanism.
Lastly, the problem of neighbor discovery in a wireless sensor network is dealt. We first introduce the realistic effect of physical layer considerations in the evaluation of the performance of logical discovery algorithms by incorporating physical layer parameters. Secondly, given the lack of knowledge of the number of neighbors along with the lack of knowledge of the individual signal parameters, we adopt the viewpoint of random set theory to the problem of detecting the transmitting neighbors. Random set theory is a generalization of standard probability theory by assigning sets, rather than values, to random outcomes and it has been applied to multi-user detection problem when the set of transmitters are unknown and dynamically changing
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