Xiao Lu | University of Alberta (original) (raw)

Papers by Xiao Lu

Wireless charging is a technology of transmitting power through an air gap to electrical devices ... more Wireless charging is a technology of transmitting
power through an air gap to electrical devices for the purpose
of energy replenishment. The recent progress in wireless
charging techniques and development of commercial products
have provided a promising alternative way to address the energy
bottleneck of conventionally portable battery-powered devices.
However, the incorporation of wireless charging into the existing
wireless communication systems also brings along a series of
challenging issues with regard to implementation, scheduling, and
power management. In this article, we present a comprehensive
overview of wireless charging techniques, the developments
in technical standards, and their recent advances in network
applications. In particular, with regard to network applications,
we review the static charger scheduling strategies, mobile charger
dispatch strategies and wireless charger deployment strategies.
Additionally, we discuss open issues and challenges in implementing
wireless charging technologies. Finally, we envision some
practical future network applications of wireless charging.

A body area network is a potential application of wireless energy harvesting and transfer to impr... more A body area network is a potential application of
wireless energy harvesting and transfer to improve convenience
and flexibility. However, wireless energy transfer from a wireless
energy source has to be scheduled to minimize energy usage
while meeting quality of service (QoS) requirements of sensor
nodes in the network. In this paper, we consider wireless powered
body area network whose sensor nodes have auxiliary energy
sources in addition to dedicated wireless energy transfer. We
propose a distributed wireless energy transfer scheduling to
achieve the aforementioned objective and meet the requirements.
We formulate a constrained stochastic game model to obtain
a multi-policy constrained Nash equilibrium of wireless energy
transfer request. This equilibrium instructs the sensor node to
request for wireless energy transfer based on its local state. The
performance evaluation shows that the analytical model is well
verified by simulations.

Internet of things (IoT) has been proposed to be a new paradigm of connecting devices and providi... more Internet of things (IoT) has been proposed to be a new paradigm of connecting devices and providing services to
various applications, e.g., transportation, energy, smart city, and healthcare. In this paper, we focus on an important
issue, i.e., economics of IoT, that can have a great impact to the success of IoT applications. In particular, we adopt
and present the information economics approach with its applications in IoT. We first review existing economic
models developed for IoT services. Then, we outline two important topics of information economics which are
pertinent to IoT, i.e., the value of information and information good pricing. Finally, we propose a game theoretic
model to study the price competition of IoT sensing services. Some outlooks on future research directions of
applying information economics to IoT are discussed.

Ambient RF (Radio Frequency) energy harvesting technique has recently been proposed as a potentia... more Ambient RF (Radio Frequency) energy harvesting technique has recently been proposed as a potential solution to provide proactive energy replenishment for wireless devices. This paper aims to analyze the performance of a battery-free wireless sensor powered by ambient RF energy harvesting using a stochastic geometry approach. Specifically, we consider the point-to-point uplink transmission of a wireless sensor in a stochastic geometry network, where ambient RF sources, such as mobile transmit devices, access points and base stations, are distributed as a Ginibre alpha\alphaalpha-determinantal point process (DPP). The DPP is able to capture repulsion among points, and hence, it is more general than the Poisson point process (PPP). We analyze two common receiver architectures: separated receiver and time-switching architectures. For each architecture, we consider the scenarios with and without co-channel interference for information transmission. We derive the expectation of the RF energy harvesting rate in closed form and also compute its variance. Moreover, we perform a worst-case study which derives the upper bound of both power and transmission outage probabilities. Additionally, we provide guidelines on the setting of optimal time-switching coefficient in the case of the time-switching architecture. Numerical results verify the correctness of the analysis and show various tradeoffs between parameter setting. Lastly, we prove that the sensor is more efficient when the distribution of the ambient sources exhibits stronger repulsion.

Wireless charging is a technique of transmitting power through an air gap to an electrical device... more Wireless charging is a technique of transmitting power through an air gap to an electrical device for the purpose of energy replenishment. Recently, the wireless charging technology has been significantly advanced in terms of efficiency and functionality. This article first presents an overview and fundamentals of wireless charging. We then provide the review of standards, i.e., Qi and Alliance for Wireless Power (A4WP), and highlight on their communication protocols. Next, we propose a novel concept of wireless charger networking which allows chargers to be connected to facilitate information collection and control. We demonstrate the application of the wireless charger network in user-charger assignment, which clearly shows the benefit in terms of reduced costs for users to
identify the best chargers to replenish energy for their mobile devices.

Many previous studies have shown that traditional TCP slow-start algorithm suffers performance de... more Many previous studies have shown that traditional TCP slow-start algorithm suffers performance degradation in high-speed and long-delay networks. This paper presents a sender-side enhancement, which makes use of TCP Vegas congestion-detecting scheme to monitor the router queue, and
accordingly refines slow-start window evolution by introducing
a two-phase approach to probe bandwidth more efficiently.
Moreover, it achieves good fairness of bandwidth utilization in
coexistence of multiple connections. Simulation results show that, compared with traditional slow-start and many other enhancements, it is able to significantly improve the startup performance without adversely affecting coexisting TCP connections.

Power line communication (PLC) system refers to the use of power distribution networks for commun... more Power line communication (PLC) system refers
to the use of power distribution networks for communication
purposes. In this paper, we investigate the performance of the
low voltage (LV) power lines for smart grid applications involving data transfer in a specific narrow, low frequency band. We propose an analytical approach to obtain the line’s transfer function and conduct simulation to determine the performance of the LV PLC system in terms of bit error rate. We then evaluate the performance of the medium access control protocol (MAC) for the LV PLC network taking into account its physical characteristic and performance limitation. We show by simulation that packet loss in this network can be significant even with a light traffic condition due to the noisy channel, and the goodput declines sharply once the individual transmission rate is high enough to congest the network. We also show that the channel errors can be reduced by adjusting the MAC parameters to allow the retransmissions recouping losses.

In wireless mesh network (WMN), multiple service providers (SPs) can cooperate to share resources... more In wireless mesh network (WMN), multiple service providers (SPs) can cooperate to share resources (e.g., relay nodes
and spectrum), to serve their collective subscribed customers for better service. As a reward, SPs are able to achieve more individual benefits, i.e., increased revenue or decreased cost, through efficient utilization of shared network resources. However, this cooperation can be realized only if fair allocation of aggregated payoff, which is the sum of the payoff of all the cooperative SPs, can be achieved. We first formulate such cooperation as a coalitional game with transferable utility, specifically, a linear programming game, in which, each SP should obtain the fair share of the aggregated payoff. Then we study the problem of allocating aggregated payoff which leads to stable service coalition of SPs in WMN based on the concepts of dual payoff and Shapley value.

In wireless energy harvesting communication networks, a user receives wireless energy released by... more In wireless energy harvesting communication networks, a user receives wireless energy released by an ambient or dedicated energy source, and uses that energy for delay constrained data transmission. However, such data transmission can be susceptible to a jamming attack from a nearby attacker
also harvesting from the wireless energy source. In this paper, we consider such a scenario and present performance analysis. In particular, we develop an analytical model for the network based on a Markov chain to obtain various performance measures for the user including throughput and delay distribution. The performance evaluation shows some interesting results. For example, under the jamming attack, there is the maximum throughput achievable by the user. We also validate the analytical model using simulation.

Abstract—Device-to-Device (D2D) communications, which al- low direct communication among mobile ... more Abstract—Device-to-Device (D2D) communications, which al-
low direct communication among mobile devices, have been
proposed as an enabler of local services in 3GPP LTE-Advance
(LTE-A) cellular networks. This work investigates a hierarchical
LTE-A network framework consisting of multiple D2D operators
at the upper layer and a group of devices at the lower layer.
We propose a cooperative model that allows the operators to
improve their utility in terms of revenue by sharing their devices, and the devices to improve their payoff in terms of end-to-end throughput by collaboratively performing multi-path routing. To help understanding the interaction among operators and devices, we present a game-theoretic framework to model the cooperation behavior, and further, we propose a layered coalitional game (LCG) to address the decision making problems among them. Specifically, the cooperation of operators is modeled as an overlapping coalition formation game (CFG) in a partition form, in which operators should form a stable coalitional structure. Moreover, the cooperation of devices is modeled as a coalitional graphical game (CGG), in which devices establish links among each other to form a stable network structure for multi-path routing. We adopt the extended recursive core, and Nash network, as the stability concept for the proposed CFG and CGG, respectively. Numerical results demonstrate that the proposed LCG yields notable gains compared to both the non-cooperative case and a LCG variant and achieves good convergence speed.

The advance in RF energy transfer and harvesting technique over the past decade has enabled wirel... more The advance in RF energy transfer and harvesting technique over the past decade has enabled wireless energy replenishment for electronic devices, which is deemed as a
promising alternative to address the energy bottleneck of conventional battery-powered devices. In this paper, by using a
stochastic geometry approach, we aim to analyze the performance of an RF-powered wireless sensor in a downlink simultaneous wireless information and power transfer (SWIPT) system with ambient RF transmitters. Specifically, we consider the point-to-point downlink SWIPT transmission from an access point to a wireless sensor in a network, where ambient RF transmitters are distributed as a Ginibre alpha-determinantal point process (DPP), which becomes the Poisson point process when zero. In the considered network, we focus on analyzing the performance of a sensor equipped with the power-splitting architecture. Under this architecture, we characterize the expected RF energy harvesting rate of the sensor. Moreover, we derive the upper bound of both power and transmission outage probabilities. Numerical results show that our upper bounds are accurate for different value of alpha.

In wireless powered networks, a user can make a request and use the wireless energy transferred f... more In wireless powered networks, a user can make a request and use the wireless energy transferred from an energy source for its data transmission. However, due to broadcast nature of wireless energy transfer (e.g., RF energy), a malicious
node (i.e., an attacker) can also intercept the energy and use it to perform an attack by jamming the data transmission of the user. We consider such a jamming attack where the user and attacker are aware of each other. We formulate a game theoretic model to analyze the energy request and data transmission policy of the user and the attack policy of the attacker when the user and the attacker both want to maximize their own rewards. We use an iterative algorithm designed based on the best response dynamics to obtain the solution defined in terms of the constrained Nash equilibrium. The numerical results show not only the convergence of the proposed algorithm, but also the optimal reward of the
user under different energy cost constraints.

A wireless relay network (WRN) has recently emerged as an effective way to increase communication... more A wireless relay network (WRN) has recently emerged as an effective way to increase communication capacity
and extend a coverage area with a low cost. In the WRN, multiple service providers (SPs) can cooperate to share their resources (e.g., relay nodes and spectrum), to achieve higher utility in terms of revenue. Such cooperation can improve the capacity of the WRN, and thus throughput for terminal devices (TDs). However, this cooperation can be realized only if fair allocation of aggregated utility, which is the sum of the utility of all the cooperative SPs, can be achieved. In this paper, we investigate the WRN consisting of SPs at the upper layer and TDs at the lower layer and present a game theoretic framework to address the cooperation decision making problem in the WRN. Specifically, the cooperation of SPs is modeled as an overlapping coalition formation game, in which SPs should form a stable coalitional structure and obtain a fair share of the aggregated utility. We also study the problem of allocating aggregated utility based on the concept of Shapley value, which stabilizes the cooperation of SPs in the WRN. The cooperation of TDs is modeled as a network formation game, in which TDs establish links among each other to form a stable network structure. Numerical results demonstrate that the proposed distributed algorithm obtains the aggregated utility approximating the optimal solutions and achieves good
convergence speed.

Machine-to-machine (M2M) communications have emerged as a cutting edge technology for next-genera... more Machine-to-machine (M2M) communications have emerged as a cutting edge technology for next-generation communications, and are undergoing rapid development and inspiring numerous
applications. This article presents an investigation of the application of M2M communications in the smart grid. First, an overview of M2M communications is given. The enabling
technologies and open research issues of M2M communications are also discussed. Then we address the network design issue of M2M communications for a home energy management system (HEMS) in the smart grid. The network architecture for HEMS to collect status and
power consumption demand from home appliances
is introduced. Then the optimal HEMS traffic concentration is presented and formulated as the optimal cluster formation. A dynamic programming algorithm is applied to obtain the
optimal solution. The numerical results show that the proposed optimal traffic concentration can minimize the cost of HEMS.

The growing concerns of a global environmental change leads to a revolution in the way energy is ... more The growing concerns of a global environmental change leads to a revolution in the way energy is utilized. In the wireless industry, green wireless communications has recently gained
increasing attention and is expected to play a major role in the reduction of electrical power consumption. Actions to promote energy saving of wireless communications with regard to environmental protection are becoming imperative. To this purpose, we study a green communications system model where a wireless base station is provisioned with a combination of a renewable power source and the electrical grid to minimize the cost of power consumption as well as meet the users’ demand. More specifically, we focus on adaptive power management for a wireless base station under various uncertainties, including renewable power generation,
power price, and wireless traffic load. We believe that demand-side power management solutions based on the studied communication architecture is a major step toward green wireless communications.

Spectrum efficiency and energy efficiency are two critical issues in designing wireless networks.... more Spectrum efficiency and energy efficiency are two critical issues in designing wireless networks. Through dynamic spectrum access, cognitive radios can improve the spectrum efficiency and capacity of wireless networks. On the other hand radio frequency (RF) energy harvesting has emerged as a promising technique to supply energy to wireless networks and thereby increase their energy efficiency. Therefore, to achieve both
spectrum and energy efficiency, the secondary users in a cognitive radio network (CRN) can be equipped with the RF energy harvesting capability, and such a network can be referred to as an RF-powered cognitive radio network. In this article we provide an overview of the RF-powered CRNs and discuss the challenges that arise for dynamic spectrum access in these networks. Focusing on the trade-off among spectrum sensing, data transmission, and RF energy harvesting,
we then discuss the dynamic channel selection problem in a multi-channel RF-powered CRN. In the RF-powered CRN a secondary user can adaptively select a channel to transmit
data when the channel is not occupied by any primary user. Alternatively, the secondary user can harvest RF energy for data transmission if the channel is occupied. The optimal channel selection policy of the secondary user can be obtained
by formulating a Markov decision process (MDP) problem. We present some numerical results obtained by solving this MDP problem.

Radio frequency (RF) energy harvesting and transfer techniques have recently become alternative m... more Radio frequency (RF) energy harvesting and transfer techniques have recently become alternative methods to power the next generation of wireless networks. As this emerging technology enables proactive replenishment of wireless devices, it is advantageous in supporting applications with quality-of-service (QoS) requirement. This article focuses on the resource allocation issues in wireless networks with RF energy harvesting capability, referred to as RF energy harvesting networks (RF-EHNs). First, we present an overview of the RF-EHNs, followed by a review of a variety of issues regarding resource allocation. Then, we present a case study of designing in the receiver operation policy, which is of paramount importance in the RF-EHNs. We focus on QoS support and service differentiation, which have not been addressed by previous literature. Furthermore, we outline some open research directions.

Radio frequency (RF) energy transfer and harvesting techniques have recently become alternative m... more Radio frequency (RF) energy transfer and harvesting techniques have recently become alternative methods to power the next generation wireless networks. As this emerging technology enables proactive energy replenishment of wireless devices, it is advantageous in supporting applications with quality of service (QoS) requirements. In this paper, we present an extensive literature review on the research progresses in wireless networks with RF energy harvesting capability, referred to as
RF energy harvesting networks (RF-EHNs). First, we present
an overview of the RF-EHNs including system architecture, RF
energy harvesting techniques and existing applications. Then, we present the background in circuit design as well as the state-of-the-art circuitry implementations, and review the communication protocols specially designed for RF-EHNs. We also explore various key design issues in the development of RF-EHNs according to the network types, i.e., single-hop networks, multi-antenna networks, relay networks, and cognitive radio networks. Finally, we envision some open research directions.