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This paper presents a novel batteryless wireless sensor that can be embedded in the road and used for the measurement of traffic-flow rate. Compared with existing inductive loop-based traffic sensors, the new sensor is expected to provide increased reliability, easy installation, and low cost. The sensor requires no external power source and has zero idle power loss. Energy to power this sensor is harvested from the short-duration vibrations that result when an automobile passes over the sensor. Since much of the earlier work in literature on vibration energy harvesting has focused on continuous sources of vibration, this paper focuses on short-duration vibrations and on developing low-power control algorithms that can be implemented on the sensor using an analog circuit. To this effect, this paper develops and compares three control algorithms: 1) “fixed threshold switching,” 2) “maximum voltage switching,” and 3) “switched inductor.” The “switched inductor” algorithm is shown to be the most effective at maximizing harvested energy. Experimental results are presented and validate the fact that adequate energy can be harvested from each passing vehicle to enable successful wireless transmission of traffic data. [ABSTRACT FROM PUBLISHER]

A heterogeneous wireless network (HetNet), which combines multiple cooperating radio access technologies in an overlapping structure, is a communication system that has been recognized as an efficient way to meet the increasing traffic demand in broadband wireless networks. In this paper, we exploit the network cooperation in HetNets to propose two joint radio resource management (JRRM) schemes that improve energy savings while satisfying the system quality-of-service (QoS) performance requirements. First, we present an optimal QoS-aware energy-efficient JRRM scheme, which is formulated as a semi-Markov decision process model, and provide the optimal control policy for the HetNet under analysis. Second, we present an implementation-friendly QoS-aware energy-efficient JRRM scheme that utilizes a threshold on the macrocell radio resource occupancy to trigger the switching-on/off procedure of the base transceiver station resources, as well as a load-balancing procedure to minimize the service disruptions that may occur because of radio resource shortage and to reduce power consumption during the HetNet operation. This JRRM scheme is analyzed by means of a multidimensional continuous-time Markov chain model. Third, we devise an algorithm to determine the threshold setting in the implementation-friendly JRRM scheme according to a desirable power saving level that is prespecified by the mobile network operator. Numerical results show that the proposed schemes achieve substantial energy savings while keeping satisfactory performance levels. [ABSTRACT FROM AUTHOR]

The introduction of fourth-generation wireless technologies has fueled the rapid development of cellular networks, significantly increasing the energy consumption and the expenditures of mobile network operators (MNOs). In addition, network underutilization during low-traffic periods (e.g., night zone) has motivated a new business model, namely, infrastructure sharing, which allows the MNOs to have their traffic served by other MNOs in the same geographic area, thus enabling them to switch off part of their network. In this paper, we propose a novel infrastructure-sharing algorithm for multioperator environments, which enables the deactivation of underutilized base stations during low-traffic periods. Motivated by the conflicting interests of the MNOs and the necessity for effective solutions, we introduce a game-theoretic framework that enables the MNOs to individually estimate the switching-off probabilities that reduce their expected financial cost. Our approach reaches dominant strategy equilibrium, which is the strategy that minimizes the cost of each player. Finally, we provide extensive analytical and experimental results to estimate the potential energy and cost savings that can be achieved in multioperator environments, incentivizing the MNOs to apply the proposed scheme. [ABSTRACT FROM AUTHOR]

Selection combining (SC) with full channel state information (CSI) achieves full diversity order in a decode-and-forward (DF) relaying system. However, the estimation of CSI of all the links is a cumbersome process. As an alternative, switched-diversity techniques have been proposed in the literature, in which CSI of all the links are not simultaneously required. In this paper, we compare the variants of the switched-diversity and full-CSI SC schemes through a paired error approach for a multi-DF-relaying-based cooperative diversity system. We derive the exact symbol error probability (SEP) expressions for the full-CSI SC, switch-and-examine combining (SEC), and SEC with post-selection (SECps) schemes, considering $M$-ary phase-shift keying (MPSK) signaling over slow, flat, independent, and nonidentical Nakagami- $m$ fading channels. It is to be noted that the derived SEP expressions are valid for integer values of fading severity parameter $m$. In addition, we also present the closed-form asymptotic SEP expressions for MPSK signaling to evaluate the diversity order. Concisely, from the numerical results, it is observed that the SECps scheme is able to offer the same performance as that of the full-CSI SC scheme. Furthermore, the SECps scheme outperforms the SEC scheme with more CSI. [ABSTRACT FROM AUTHOR]

This paper presents a robust sliding-mode observer (RSMO) for state-of-charge (SOC) estimation of a lithium-polymer battery (LiPB) in electric vehicles (EVs). A radial basis function (RBF) neural network (NN) is employed to adaptively learn an upper bound of system uncertainty. The switching gain of the RSMO is adjusted based on the learned upper bound to achieve asymptotic error convergence of the SOC estimation. A battery equivalent circuit model (BECM) is constructed for battery modeling, and its BECM is identified in real time by using a forgetting-factor recursive least squares (FFRLS) algorithm. The experiments under the discharge current profiles based on EV driving cycles are conducted on the LiPB to validate the effectiveness and accuracy of the proposed framework for the SOC estimation. [ABSTRACT FROM AUTHOR]

Simulation is a valuable way to develop cleaner transportation systems. Nevertheless, the complexity of this kind of system leads to complex models, particularly when taking into account nonlinear aspects of traction power substations (TPSs). Thus, this paper proposes different TPS models based on energetic macroscopic representation. An appropriate model is deduced from comparisons between the different models to realize energetic studies. It is finally applied to the simulation of a simple subway line, which is experimentally validated. [ABSTRACT FROM AUTHOR]

In a cognitive radio network (CRN), two nodes have a rendezvous when they tune to the same channel simultaneously. Providing rendezvous guarantee between any pair of nodes is essential because a rendezvous is necessary for communication. Some existing works claim that rendezvous guarantee can be provided by using a dedicated common control channel to negotiate the channel being used. A serious problem of these mechanisms is that a globally available channel may not exist. Some channel hopping protocols try to provide a rendezvous guarantee without using a common control channel. However, these solutions may suffer from a poor number of rendezvous or uneven channel utilization. In this paper, we propose a novel distributed channel hopping protocol: Quorum and Latin square channel hopping (QLCH). The QLCH scheme efficiently provides rendezvous guarantee by utilizing the concept of quorum systems and Latin squares. The former is utilized to guarantee balanced rendezvous among nodes, whereas the latter is adopted to share the rendezvous among channels. QLCH efficiently provides fast rendezvous guarantee and can cooperate with other channel hopping protocols to enhance network throughput. Analytical and simulation results verify the improvement of QLCH. For example, when there are 30 flows using 11 channels in a CRN, the achieved time to rendezvous of QLCH is 9.84 times lower than that of the existing protocol SYNC-ETCH, whereas the achieved network throughput of QLCH is 362% higher than that of the existing protocol, i.e., Quorum-based channel hopping (L-QCH). [ABSTRACT FROM PUBLISHER]

In this paper, an optimization framework for the calibration of energy management in plug-in hybrid electric vehicles (PHEVs) is proposed. The framework is based on the modeling of hybrid vehicles as hybrid systems in the mathematical sense, i.e., as a system, whose input is composed of continuous and discrete variables. This allows for the flexible integration of discrete decisions, such as drive modes and gear selection. Hybrid optimal control problems are then formulated, which seek optimal continuous and discrete system inputs, and methods for the efficient solution are described. The framework also allows for the incorporation of losses that occur due to a change in a discrete variable. The results can then be used to automatically calculate lookup tables for optimal gear shifts, optimal torque split between the motor/generator and the internal combustion engine, and the determination of the drive mode (electric or hybrid mode). It is demonstrated that when switching cost is disregarded, the main challenge is still finding the initial costate value. Practical strategies for determining the costate value online are described, containing a rule-based method, a \CO2 optimal method, and predictive energy management. The most important implementation issues are discussed, and the results of real-world experiments of predictive energy management are shown. [ABSTRACT FROM PUBLISHER]

It is expected that cognitive machine-to-machine (M2M) communications in smart grid networks will be indispensable in the near future. In this paper, after discussing the motivation of cognitive M2M communications in a smart grid network, we design a cognitive medium access control (MAC) protocol, keeping in view the unique features of M2M devices and smart grid communication requirements. We propose the use of packet reservation multiple access (PRMA), carry out its feasibility study, and adapt and significantly enhance it with modifications particularly tailored for M2M environments. The proposed protocol is centralized in nature and utilizes a specialized frame structure for supporting the coexistence of the cognitive M2M network with the primary network. This frame structure is further optimized, considering different tradeoffs pertaining to primary network protection and the utility of a secondary M2M network. Performance evaluation is carried out by analytical modeling and simulation studies. We also present a case study for application of the proposed protocol in advanced metering infrastructure (AMI) networks under the dynamics of power systems. [ABSTRACT FROM PUBLISHER]

Modern vehicles incorporate an increasing number of distributed compute nodes, resulting in the need for faster and more reliable in-vehicle networks. Time-triggered protocols such as FlexRay have been gaining ground as the standard for high-speed reliable communications in the automotive industry, marking a shift away from the event-triggered medium access used in controller area networks (CANs). These new standards enable the higher levels of determinism and reliability demanded from next-generation safety-critical applications. Advanced applications can benefit from tight coupling of the embedded computing units with the communication interface, thereby providing functionality beyond the FlexRay standard. Such an approach is highly suited to implementation on reconfigurable architectures. This paper describes a field-programmable gate array (FPGA)-based communication controller (CC) that features configurable extensions to provide functionality that is unavailable with standard implementations or off-the-shelf devices. It is implemented and verified on a Xilinx Spartan 6 FPGA, integrated with both a logic-based hardware ECU and a fully fledged processor-based electronic control unit (ECU). Results show that the platform-centric implementation generates a highly efficient core in terms of power, performance, and resource utilization. We demonstrate that the flexible extensions help enable advanced applications that integrate features such as fault tolerance, timeliness, and security, with practical case studies. This tight integration between the controller, computational functions, and flexible extensions on the controller enables enhancements that open the door for exciting applications in future vehicles. [ABSTRACT FROM PUBLISHER]

Recently, the mobile relay technique has been discussed to support communication services for Long-Term Evolution Advanced (LTE-A) high-speed rail networks. In the network, there are several mobile relays in a train. User equipment (UE) devices connect to in-car mobile relays instead of outside evolved NodeBs (eNBs). Mobile relays establish backhaul links with the serving donor eNBs (DeNBs) and coordinate control and data flows for UE devices. Since the train travels in high speed, mobile relays suffer from frequent handovers between DeNBs. We observe that the defined handover procedures in LTE-A specifications may incur message overhead and lengthen handover time. In this paper, we propose an enhanced handover scheme, which contains two procedures. The first procedure is an enhanced measurement procedure, which can accelerate the measurement procedure when the mobile relay knows that the train is moving toward some neighbor DeNBs. The second procedure is a group in-network handover procedure, which can aggregate similar in network handover procedures in the core network. Performance evaluations indicate that our design can conserve both time and messages when handover. [ABSTRACT FROM PUBLISHER]

Although multiple channels are supported in the physical layer, the IEEE 802.11 MAC-layer mechanism is designed for a single channel. Exploiting multiple channels enhances spatial reuse and reduces transmission collisions and, thus, improves network throughput. Designing a multichannel MAC protocol is much more difficult than designing a single-channel MAC protocol. New challenges, such as the channel allocation problem and the missing receiver problem, must be overcome. Existing multichannel MAC protocols suffer from either higher hardware cost (because of applying multiple transceivers) or lower channel utilization (due to limited transmission opportunity). In this paper, a fully distributed channel-hopping solution, i.e., the cyclic-quorum-based multichannel MAC protocol, is proposed. We use the cyclic quorum in a novel way and the proposed protocol has several attractive features. First, only a single transceiver is needed for each node. Second, any sender is guaranteed to meet its receiver in a short time. Third, each node's channel-hopping sequence is derived from its node ID. This avoids exchanging control messages, such as each node's hopping sequence or available channel list. Fourth, multiple transmission pairs can accomplish handshaking simultaneously. The proposed protocol is simple and efficient. Simulation and real system implementation results verify that our mechanism is a promising multichannel MAC protocol for mobile ad hoc networks. [ABSTRACT FROM AUTHOR]

Cell voltage equalization is inevitable to ensure years of safe operation of series-connected energy storage cells, such as lithium-ion batteries and supercapacitors (SCs). Although various kinds of cell voltage equalizers have been proposed, most equalizer topologies require multiple switches and/or a multiwinding transformer, resulting in complex circuitry and poor modularity. In this paper, a single-switch single-transformer equalizer using a forward–flyback resonant inverter (FFRI) with a voltage multiplier is proposed. The required switch count of the proposed equalizer is the minimum without impairing modularity due to the single-switch circuitry with no need for a multiwinding transformer. An experimental equalization test performed for eight SCs connected in series successfully demonstrated the equalization performance of the proposed equalizer. The FFRI can be extended as a “resonant input cell,” and by combining one of resonant input cells and a voltage multiplier, a single-switch resonant equalization charger that is basically a charger with an equalization function is also derived. An experimental charging test using the resonant equalization charger was also performed, and its equalization-charging performance was demonstrated. [ABSTRACT FROM AUTHOR]

This paper deals with a control method that adapts the dc bus voltage of electric traction systems using permanent-magnet synchronous machine (PMSM) fed by bidirectional $Z$-source inverter (ZSI) or other improved topologies. This control allows reducing both the overestimation of the dc bus voltage and losses in the inverter. The sliding-mode control (SMC) method is used to control the $Z$-source converter, whereas flatness-based control is proposed to drive the actuator and generate the peak dc bus voltage reference. Flatness-based control is chosen because the actuator transients are well mastered. Extra shoot-through zero inverter states are inserted by means of implemented algorithm on a space-vector-modulation (SVM) scheme. Different short-circuit strategies are studied and compared according to constraint criteria. Both simulation and experimental results are presented and discussed to validate the proposed voltage adaptation strategy and the improvement on global efficiency. [ABSTRACT FROM AUTHOR]

Frequency-modulated continuous-wave (FMCW) methods and switched antenna arrays (SAAs) are very attractive for application in automotive radar because of their low hardware complexity. In traditional SAA radar, the receiving antenna array elements are successively switched according to their natural spatial order [referred to as sequential SAAs (SSAAs)]. For radars using both SSAA and FMCW methods, the phase difference caused by the target azimuth and time delay will be difficult to distinguish, thus resulting in delay–space coupling, which may lead to degradation of the road target observation. In this paper, randomized SAA (RSAA) FMCW radar is proposed. The new radar scheme has high delay/space resolution for target location detection and character extraction, and can also solve the coupling problem. The signal model of RSAA FMCW radar is derived and compared with that of SSAA radar. The influence of the antenna-array switching mode on the radar performance is also analyzed. A conventional zero-padding algorithm and a new clustering FOCUSS algorithm are both introduced for the signal processing of the new radar scheme. The numerical results illustrate the performance of RSAA FMCW radar in high-resolution target imaging and delay–space decoupling. [ABSTRACT FROM PUBLISHER]

When a mobile operator migrates its network from the third generation (3G) system to Long Term Evolution (LTE), both 3G and LTE will coexist for a period of time. Since the 3G circuit-switched (CS) voice mechanism is more mature and available than that for the LTE Voice over Internet Protocol (VoIP), the operator may consider CS fallback (CSFB) as a solution for providing reliable voice calls. According to the 3G Partnership Project (3GPP) CSFB procedure, when a mobile user in the LTE network has an incoming or an outgoing call, the user equipment (UE) falls back from LTE to Universal Mobile Telecommunications System (UMTS). When the call is complete and released, the UE immediately returns to LTE. If the next activity for the UE is another voice call, immediately switching from UMTS to LTE may not be efficient. In this case, the UE has to perform another CSFB. To resolve this issue, we suggest delaying the returns to avoid unnecessary CSFBs, which is called delayed return (DR). Based on the measurements from the real UMTS and LTE networks, we develop an analytic model for investigating the performance of the CSFB with DR. This paper indicates that the DR scheme can effectively reduce the CSFB costs by up to 60%. [ABSTRACT FROM PUBLISHER]

This paper proposes a generalized interrelay interference cancelation (gIRIC) scheme for a two-path relay model in multisource systems. Both the sources and the relay adopt complex field network coding (CFNC) to remove the interrelay interference (IRI) caused by the two-path relay. Furthermore, we introduce two detecting modes (gIRIC-noSD and gIRIC-SD) for destination in our scheme. Two switching rules are given to select a suitable detecting mode between treating the signal of a direct link as noise (gIRIC-noSD) and utilizing the direct link to assist signal detection (gIRIC-SD). The bounds of average symbol error probability (SEP) and throughput of our scheme are derived. [ABSTRACT FROM PUBLISHER]

This paper presents a six-phase current reconstruction scheme for dual traction inverters in hybrid electric vehicles (HEVs) with a single dc-link current sensor. During the phase current reconstruction, one of the inverters is proposed to operate using active vectors, whereas the other inverter operates using nonactive vectors. An advanced phase-shift scheme for all pulsewidth-modulated (PWM) signals based on the sequence of duty cycles is implemented. PWM signals are considered in three types: large, medium, and small duty cycles. Then, the minimum phase-shift scheme is applied to each type of PWM signal to ensure the minimum duration of the active vector for stable current reconstruction. With this proposed phase-shift scheme, the maximum allowable modulation index and dc-link voltage utilization are improved. In addition, the relationship between the minimum required time for stable phase current reconstruction and the maximum allowable modulation index is derived theoretically. The effectiveness of the proposed method is verified by both simulation and experimental results. With this scheme, cost and volume of dual inverters in HEVs are reduced, considering the lower number of current sensors. [ABSTRACT FROM PUBLISHER]

This paper presents the design guideline of a bidirectional isolated Ćuk converter with an active-snubber circuit, which is used as a cell level tester for multiple automotive dc energy storage devices (ESDs), such as ultracapacitors, Li-ion batteries, and NiMH batteries. The converter interfaces those automotive dc ESD cells with 24-V dc systems, and it realizes bidirectional power flow with two main switches. Based on the ratings of those dc ESD cells, the designed converter operates at a very low voltage range, i.e., from 1.5 to 6 V, with current as high as 300 A. The detailed operation principle and major features, such as soft switching and energy recovery, are analyzed under continuous current mode. Based on the analysis, the design guideline of the dc–dc converter is presented. A 1.2-kW laboratory prototype has been built and tested with full power rating. Both simulation and experimental results are presented to verify the analysis. [ABSTRACT FROM PUBLISHER]

In wireless local area networks (WLANs), switching of the nodes to low-power sleep mode to save energy is common. However, if sleep time is not properly scheduled, significant delays can occur, which is undesirable in delay-constrained applications. In this paper, we propose a novel energy-efficient sleep-scheduling protocol for maximizing the sleep time lengths of each node while satisfying the delay constraints. We first consider the single-user case and present the basic steps that the node takes to decide when and how long it can sleep. For the multiuser scenario, to mitigate channel contention in packet downloading after sleeping, the sleep schedules requested by the nodes are coordinated by the access point (AP) to avoid overlapping active epochs. Simulation results demonstrate that the proposed sleep-scheduling algorithm achieves lower loss rate while achieving higher energy efficiency than that of the existing GreenCall method. [ABSTRACT FROM PUBLISHER]

In this paper, a control strategy is presented for a high-performance capacitively loaded loop (LLC) multiresonant dc–dc converter in a two-stage smart charger for neighborhood electric vehicle (NEV) applications. It addresses several aspects and limitations of LLC resonant dc–dc converters in battery charging applications, such as very wide output voltage range while keeping the efficiency maximized, implementation of the current mode control at the secondary side, and optimization of burst mode operation for current regulation at very low output voltage. The proposed control scheme minimizes both low- and high-frequency current ripples on the battery while maintaining stability of the dc–dc converter, thus maximizing battery life without penalizing the volume of the charger. Experimental results are presented for a prototype unit converting 390 V from the input dc link to an output voltage range of 3–72 V dc at 650 W. The prototype achieves a peak efficiency value of 96%. [ABSTRACT FROM PUBLISHER]

Most existing studies on cognitive-radio networks assume that cognitive users (CUs) can switch to any available channel, regardless of the frequency gap between a target channel and the current channel. However, due to hardware limitations, CUs can actually jump only so far from where the operating frequency of their current channel is. This paper studies the performance of cognitive-radio networks while considering realistic channel handoff agility, where CUs can only switch to their neighboring channels. We use a continuous-time Markov process to derive and analyze the forced termination and blocking probabilities of CUs. Using these derived probabilities, we then study and analyze the impact of limited spectrum handoff agility on cognitive spectrum access efficiency. We show that accounting for realistic spectrum handoff agility reduces performance of cognitive-radio networks in terms of spectrum access capability and efficiency. [ABSTRACT FROM PUBLISHER]

In an earlier paper, a simple and fast bit loading algorithm for orthogonal frequency-division-multiplex (OFDM) systems was presented. A drawback of the algorithm is that the solution obtained is suboptimal. This drawback is removed in this paper, where we show that the algorithm can be improved and turned into an optimal algorithm with a negligible impact on the computational complexity. [ABSTRACT FROM PUBLISHER]

This paper deals with a synthesis of space-vector pulsewidth modulation (SVPWM) control methods applied for an H-bridge inverter feeding a three-phase permanent-magnet synchronous machine (PMSM) in electric-vehicle (EV) applications. First, a short survey of existing architectures of power converters, particularly those adapted to degraded operating modes, is presented. Standard SVPWM control methods are compared with three innovative methods using EV drive specifications in the normal operating mode. Then, a rigorous analysis of the margins left in the control strategy is presented for a semiconductor switch failure to fulfill degraded operating modes. Finally, both classic and innovative strategies are implemented in numerical simulation; their results are analyzed and discussed. [ABSTRACT FROM PUBLISHER]

This paper presents the design and control of a high-efficiency multiphase dc–dc converter for a truck auxiliary power unit (APU) fed by a fuel-cell stack. The power-stage design methodology and the operation of the designed power stage used to achieve high efficiency are described in detail. To operate the designed converter as a truck APU, the mode transfer control scheme, where smooth transitions of the voltage and current control modes are necessary, is proposed, and the current controller design procedure is described. A 5-kW four-phase dc–dc converter prototype is built with the proposed power-stage configuration, and the proposed control strategy is applied to control the dc–dc converter. The efficiency of the converter is more than 99.5% at near 10% load and above 98% from 10% to 100% load range. Simulations and experimental results are provided to verify the feasibilities of dc–dc converter operation and the proposed control strategy in the truck APU application. [ABSTRACT FROM PUBLISHER]

Contact discovery is a fundamental premise of information exchange in delay-tolerant networks (DTNs). However, the intermittent connectivity nature of DTNs makes energy-efficient contact discovery a tough challenge. To save energy, a node should work in low-power mode most of the time since contacts with the other nodes may rarely happen. However, such a strategy will probably fail to detect many contacts with relatively short durations, leading to system performance degradation. In this paper, we consider a specific type of DTN, i.e., the pocket switched networks (PSN), in which the nodes' mobility pattern shows a strong social property. In a PSN, although the end-to-end path may be disconnected for the majority of time, several nodes periodically gather at certain hot spots and form well-connected clusters. Based on such mobility pattern, cooperation among nodes is utilized in our contact discovery design. The nodes that have already joined a cluster collaboratively wake up to discover new contacts. With local synchronization and complementary consideration of possible traffic congestion, both the theoretical analysis and simulation results show that our cooperative duty cycling (CDC) greatly reduces the energy consumption while achieving comparable data delivery performance. [ABSTRACT FROM PUBLISHER]

In this paper, an active suspension system utilizing a low-cost high-performance linear switched reluctance actuator with proportional-derivative (PD) control is presented. With the tracking differentiator (TD) calculating the displacement and its derivatives directly under the presence of noise, velocity and acceleration can be evaluated, and accurate position control can be achieved. Comparison is made between linear and nonlinear PD control methods in terms of various system parameters and road profiles. A nonlinear PD controller with better dynamic responses is evaluated and developed for real-time suspension application. The proposed PD control schemes are simulated, tested, and analyzed to prove its robustness and reliability. Finally, a quarter-car active suspension system prototype is built to demonstrate the effectiveness of the proposed control schemes with experiment results. [ABSTRACT FROM PUBLISHER]

With growing concern about environmental issues and an emerging green communications paradigm, cognitive radio (CR) networks (CRNs) have to be considered from the energy efficiency perspective. In this paper, we focus on scheduling in CRNs, in which a cognitive base station (CBS) makes frequency allocations to the CRs at the beginning of each frame. A cognitive scheduler must consider the diversity among CRs' queues and channel capacities in terms of number of bits and the channel switching cost from one frequency to another. Taking all these into account, we formulate the scheduling problem as an energy efficiency maximization problem, which is a nonlinear integer programming (NLP) problem and is thereby hard to solve. We seek alternate computationally easier solutions. To this aim, we propose a polynomial-time heuristic algorithm, i.e., the energy-efficient heuristic scheduler (EEHS), which allocates each idle frequency to the CR that attains the highest energy efficiency at this frequency. Next, we reformulate the original problem first as a throughput maximization problem subject to energy consumption restrictions and then as an energy consumption minimization problem subject to minimum throughput guarantees. These two schedulers also have the power to provide fairness in resource allocation. We analyze the energy efficiency and successful transmission probability of the proposed schedulers under both contiguous and fragmented spectrum scenarios. Performance studies show that, compared with a pure opportunistic scheduler with a throughput maximization objective, proposed schedulers can attain almost the same throughput performance with better energy efficiency. [ABSTRACT FROM PUBLISHER]

The femtocell is becoming a promising solution to face the explosive growth of mobile broadband usage in cellular networks. Although each femtocell only covers a small area, a massive deployment is expected to form networked femtocells in the near future. One immediate challenge is to provide seamless mobility support for networked femtocells with minimal support from mobile core networks. In this paper, we propose efficient local mobility management schemes for networked femtocells based on X2 traffic forwarding under the Third-Generation Partnership Project Long-Term Evolution Advanced (3GPP LTE-A) framework. Instead of implementing the path switch operation at core network entity for each handover, a local traffic forwarding chain is constructed to use the existing Internet backhaul and the local path between the local anchor femtocell and the target femtocell for ongoing session communications. Both analytical studies and simulation experiments are conducted to evaluate the proposed schemes and compare them with the original 3GPP scheme. The results indicate that the proposed schemes can significantly reduce the signaling cost and relieve the processing burden of mobile core networks with the reasonable distributed cost for local traffic forwarding. In addition, the proposed schemes can enable fast session recovery to adapt to the self-deployment nature of the femtocells. [ABSTRACT FROM PUBLISHER]

Cell voltage equalizers are necessary to ensure years of operation for series-connected supercapacitors (SCs) by eliminating cell voltage imbalance. Conventional equalizers require numerous switches and/or magnetic components; hence, the circuit complexity and size tend to increase. In this paper, a double-switch single-transformer equalizer, which is based on the combination of a half-bridge inverter and a voltage multiplier, is proposed. The operation of the proposed equalizer is analyzed in detail, and a dc equivalent circuit is mathematically derived. Experimental equalization tests were performed for eight SCs connected in series under a voltage-imbalanced condition. The energy of the series-connected SCs was preferentially redistributed to SCs with low voltages, and eventually, the voltage imbalance was eliminated, demonstrating the equalization performance. Simulation-based equalizations using the derived dc equivalent circuit were also performed under the same condition as the experiments. The experimental and simulation results were in good agreement, indicating that the derived dc equivalent circuit can adequately express real equalization profiles. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a diversity combining system with transmit antenna selection at the transmitter and switch-and-examine combining (TAS/SEC) at the receiver. This system has lower processing complexity as compared with the existing TAS systems such as TAS/maximum-ratio combining (TAS/MRC) and TAS/selection combining (TAS/SC). The performance of the TAS/SEC system with different modulation schemes over an independent and nonidentically distributed (i.n.d.) Rayleigh fading channel is investigated. The expressions of the outage probability, average output signal-to-noise ratio (SNR), and symbol error rate (SER) are derived and validated by simulation results. The performance of TAS/SEC is compared with TAS/SC in terms of the SER and the average number of branches to be estimated. It is shown that, as compared with TAS/SC, the TAS/SEC system is able to achieve a lower SER with fewer branches to be estimated. [ABSTRACT FROM PUBLISHER]

Plug-in hybrid electric vehicles (PHEVs) will play a vital role in future sustainable transportation systems due to their potential in terms of energy security, decreased environmental impact, improved fuel economy, and better performance. Moreover, new regulations have been established to improve the collective gas mileage, cut greenhouse gas emissions, and reduce dependence on foreign oil. This paper primarily focuses on two major thrust areas of PHEVs. First, it introduces a grid-friendly bidirectional alternating current/direct current ac/dc–dc/ac rectifier/inverter for facilitating vehicle-to-grid (V2G) integration of PHEVs. Second, it presents an integrated bidirectional noninverted buck–boost converter that interfaces the energy storage device of the PHEV to the dc link in both grid-connected and driving modes. The proposed bidirectional converter has minimal grid-level disruptions in terms of power factor and total harmonic distortion, with less switching noise. The integrated bidirectional dc/dc converter assists the grid interface converter to track the charge/discharge power of the PHEV battery. In addition, while driving, the dc/dc converter provides a regulated dc link voltage to the motor drive and captures the braking energy during regenerative braking. [ABSTRACT FROM PUBLISHER]

A direct instantaneous force control with improved efficiency for the linear switched reluctance actuator (LSRA) is proposed in this paper. Four-quadrant operation is investigated for application in the active suspension system. Force ripple minimization is considered as the primary objective due to the direct impact on passenger ride comfort. An adaptive force distribution function based on the instantaneous force feedback is proposed to achieve a ripple-free system. The choice of switching parameters for improved operation efficiency is examined. The optimal switching positions are online adjusted with respect to the force demand. Simulation and experimental results are presented to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM PUBLISHER]

This paper presents a high-gain boost converter (three-level converter and transformerless converter) for fuel cell (FC) vehicle applications. An original nonlinear control law based on the flatness principle for distributed dc generation is studied. Utilizing the flatness property, we propose simple solutions to the system performance and stabilization problems. The design controller parameters are straightforward and autonomous at the operating point. To validate the proposed method, a prototype FC power converter (1.2-kW three-level boost converter) is developed in the laboratory. The proposed control law is implemented with a digital estimate in a dSPACE 1104 controller card. The experimental results from the laboratory using a 1200-W and 46-A polymer electrolyte membrane FC (PEMFC) verify that this is a good control scheme. [ABSTRACT FROM PUBLISHER]

Fuel consumption of traditional ground vehicles is significantly affected by how the vehicles are driven. This paper focuses on the servo-loop control design of a Pulse-and-Gliding (PnG) strategy to minimize fuel consumption in automated car following. A switching-based framework is proposed for real-time implementation. The corresponding controller was synthesized for ideal conditions and subsequently enhanced to compensate for practical factors such as powertrain dynamics, speed variations, and plant uncertainties. Simulations in both uniform and naturalistic traffic flows demonstrate that, compared with a linear quadratic (LQ)-based benchmark controller, the PnG controller improves fuel economy up to 20%. The significant fuel saving is achieved while maintaining precise range bounds so that the negative impact on safety/traffic flow is contained. The developed algorithm can potentially be embedded in adaptive cruise control systems to achieve fuel-saving function. [ABSTRACT FROM PUBLISHER]

Effective data broadcasting is essential in vehicular networks not only for road-safety message dissemination but also to aid routing and cooperative driving applications through periodic beaconing and to spread network initialization advertisements that are mandatory to support infotainment applications. Broadcast data are neither acknowledged nor retransmitted in case of failure, which raises the possibility of frame loss due to channel errors and collisions with multiple simultaneous broadcasts. This paper aims at modeling periodic broadcasting on the control channel of IEEE Std. 802.11p vehicular networks with multichannel architecture. Unlike previous related work, the proposed novel analytical approach accounts for mutual influence among nodes, frequent periodic updates of broadcasted data, standard network advertisement procedures, and 802.11p prioritized channel access with multichannel-related phenomena under various link quality conditions. [ABSTRACT FROM PUBLISHER]

In this paper, the problem of mode switching in multiple-input–multiple-output (MIMO) broadcast channels utilizing the Per-User Unitary Rate Control (PU2RC) transmission scheme is considered. Since there is no mathematical expression for the achievable rate of the PU2RC systems, it is proposed to approximate them using proper bounds. It is shown that certain simple feedback distributions will lead to tight bounds on the achievable rates of the PU2RC systems. The proposed bounds are used for the calculation of mode-switching points and maximization of the system rate under different multiplexing order conditions. The asymptotic behavior of the preferred modes is also studied under high-signal-to-noise-ratio (SNR) and low-SNR conditions, and it is shown that the single-user transmission mode is the preferred mode for both regimes. [ABSTRACT FROM PUBLISHER]

The cell voltage imbalance of series-connected energy storage cells, such as supercapacitors (SCs) and lithium-ion cells, causes premature deterioration and a decrease in the available energies of the cells. Various equalization techniques have been developed for diminishing such imbalances. However, since the number of switches, sensors, and/or multiwinding transformers present in conventional equalizers is directly proportional to the number of series connections of the cells, the circuit complexity and cost of the equalizers are prone to increase with the number of series connections. In this paper, single-switch cell voltage equalizers using multistacked buck-boost converters, such as the single-ended primary inductor converter (SEPIC), Zeta, and Ćuk converters, are proposed. These equalizers consist of passive components and a single switch, significantly reducing the complexity of the circuit when compared with that of conventional equalizers. In addition, when the proposed equalizers operate in discontinuous conduction mode, feedback control is not required to limit currents flowing through cells and circuit components. The proposed equalizers are compared with conventional topologies in terms of the number of active and passive components required. Operating analyses were conducted under both cell-voltage-balanced and -imbalanced conditions. Experimental equalization tests were performed for four series-connected SCs using the SEPIC-based single-switch equalizer. The energies of the series-connected SCs were preferentially redistributed by the equalizer to the cell(s) having the lowest voltage, resulting in the elimination of the cell voltage imbalance and subsequent uniformity of the cell voltages. [ABSTRACT FROM PUBLISHER]

Multistage sensing is a novel concept that refers to a general class of spectrum sensing algorithms that divide the sensing process into a number of sequential stages. The number of sensing stages and the sensing technique per stage can be used to optimize the performance with respect to secondary user (SU) throughput and the collision probability between primary user (PU) and SU. So far, the impact of multistage sensing on network throughput and collision probability for a realistic network model has been relatively unexplored. Therefore, we present the first analytical framework that enables the performance evaluation of different multichannel multistage spectrum sensing algorithms for opportunistic spectrum access (OSA) networks. The contribution of this paper lies in studying the effect of the following parameters on performance: number of sensing stages, physical layer sensing techniques and durations per each stage, single and parallel channel sensing and access, number of available channels, PU and SU traffic, buffering of incoming SU traffic, and medium access control layer sensing algorithms. The analyzed performance metrics include the average SU throughput and the average collision probability between PU and SU. Our results show that when the probability of PU misdetection is constrained, the performance of multistage sensing is, in most cases, superior to the single-stage sensing counterpart. In addition, prolonged channel observation at the first stage of sensing considerably decreases the collision probability while keeping the throughput at an acceptable level. Finally, in realistic PU traffic scenarios, using two stages of sensing provides a good balance between SU throughput and collision probability while meeting successful detection constraints subjected by OSA communication. [ABSTRACT FROM PUBLISHER]

In high-mobility cognitive radio networks (CRNs), the fast topology changes increase the complexity of the routing scheme. In this paper, we propose a novel CRN routing scheme that considers the path stability and node capacity. First, a realistic mobility model is proposed to describe the movement of highly mobile airborne nodes [e.g., unmanned aerial vehicles (UAVs)] and estimate the link stability performance based on node movement patterns. Second, we propose a CRN topology management scheme based on a clustering model that considers radio link availability, and the cluster heads (CHs) are selected based on the node degree level, the average number of hops, and channel switching from member nodes to the CH. Third, we propose two new common control channel (CCC) selection schemes based on the node contraction concept and the discrete particle swarm optimization algorithm. The intercluster control channels and gateways are selected from the CHs, considering the average delay of control information transmission between two CHs, as well as the total throughput of control channels. Finally, a novel routing scheme is proposed that tightly integrates with the channel assignment scheme based on the node capacity. Our simulation results show that our proposed CCC selection scheme has high throughput and small transmission time. Compared with other popular CRN routing approaches, our proposed routing scheme achieves lower average end-to-end delay and higher packet delivery ratio for high-mobility CRN applications (such as airborne surveillance). [ABSTRACT FROM PUBLISHER]

In this paper, we propose an analytical framework for determining the outage probability of random and best relay selection schemes given a Poisson field of relay nodes and the presence of path loss and fading. For relay selection, relays geographically close to the source and destination are preferred to others. This selection guideline ensures a target quality of service (QoS) and reduces the signaling overhead and the relay selection delay. A spatial region called the QoS region is obtained for the random relay selection and is shown to shrink as the distance between the source and the destination increases and the interfering node density increases. When the QoS region for random relay selection is not large enough and cannot probabilistically ensure a reliable relay therein, the best relay selection is employed since the required relay node density and selection range for a desired QoS can be reduced for the best relay selection. The gain of the best relay selection with respect to the random relay selection is quantified in terms of relay node density reduction and coverage extension due to selection diversity. [ABSTRACT FROM PUBLISHER]

Conventional brake systems using a mechanical-structure-based contact switch with a metal spring suffer from frequent malfunction problems over time caused by unstable contacts stemming from loose tension of the spring, a faulty air gap, and damage to the contact point due to overcurrent from load. In this paper, a novel contactless switch for brake systems using an eddy-current displacement sensor is proposed, fabricated, and verified to have reliable performance that overcomes conventional contact switch problems. A proposed contactless switch was fabricated using automotive-grade surface-mount devices (SMDs) on both sides of an FR-4 printed circuit board for low-cost implementation. The measurement result shows a switching speed of less than 49.7 \mu\s, on average, which is approximately ten times faster than conventional mechanical-structure-based contact switches. The overall dimension of the proposed switch is 36 mm \times 26 mm \times 64 mm, which can fit into most brake switch housings. The operating input voltage range is from +8 V to +22 V, with the temperature ranging from -40\ ^\circ\C to +85\ ^\circ\C, showing reliable performance under harsh environment test for automobile applications. [ABSTRACT FROM PUBLISHER]

Various types of cell voltage equalizers that exchange charges among cells have been proposed for series-connected lithium-ion cells. During equalization, cells are possibly cycled not only over a conventional period that ranges from seconds to hours but at a high frequency that is equal to the operating frequency of the equalizers as well. This paper investigates how the high-frequency cycling occurs and the factor that affects the life performance of the cells during high-frequency cycling. Experiments on charge–discharge cycling at frequencies of 1–100 kHz were performed for lithium-ion cells. The capacity of cells cycled at frequencies below 10 Hz significantly deteriorated, whereas the capacity decay of cells cycled at higher frequencies were identical to the corresponding calendar degradation. Simulation analyses revealed that the cycling current at high frequencies served only to charge and discharge the double-layer capacitance C \rm dl, whereas the current that flows through the charge-transfer resistance Rct, indicating the charge-transfer process, dominated at low frequencies. A correlation between the degradation trend and current distribution to Cdl and Rct was observed, implying that the calendar degradation and the degradation due to the charge-transfer process were the major causes of capacity decay in the frequency range below 10 Hz. [ABSTRACT FROM PUBLISHER]

In this paper, a switched control strategy for an antilock braking system (ABS), which has conventional hydraulic actuators equipped with on/off valves, is presented. The investigated system contains the continuous dynamics of the vehicle and the inherent discontinuous characteristics of the on/off valves. Accordingly, a novel approach based on nonlinear state feedback and a switching strategy renders a controller that assures that the wheel slip converges into the target equilibrium set. Then, the convergence condition of the closed-loop system is analyzed using Lyapunov theory in the Filippov framework, and the influence of controller parameters on the system is also discussed. It is shown that the proposed controller has few tuning parameters, and each parameter has an explicit physical meaning. Both the illustrative hardware-in-the-loop simulation and experimental results show that the switched control approach is robust enough to guarantee a good performance, even if the uncertainties of the actuator characteristics, road-adhesion coefficient, and vehicle speed are considered. [ABSTRACT FROM PUBLISHER]

This paper presents an innovative torque control strategy for a switched reluctance machine (SRM) operating in continuous-conduction mode (CCM). The proposed strategy was first designed to control the torque in discontinuous-conduction mode and then extended to operate in CCM as well. With CCM, the torque can be increased at high speed without modifying the number of turns, the source voltage, or the converter; it is achieved through the control. Reviews of past control strategies, as well as the principle of this mode and its influence on the machine performance, are presented. The advantages and drawbacks of the proposed strategy are outlined. In particular, the power and torque densities of the SRM are improved so that this machine becomes comparable with ac machines without the drawback of field weakening. A new control law has been studied and implemented; simulation and experimental results are provided to demonstrate the effectiveness of the proposed control. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the performance of networks built from single-channel devices that use wireless access in vehicular environment protocols. We consider several traffic combinations, each of which presents a mix of traffic classes, over control and service channels. Our results show that time switching between the channels causes synchronization of backoff processes, which increases the frame collision probability, in particular for small sizes of contention windows. We also evaluate the impact of the interruption of the backoff process by inactive channel time, which gives rise to a probability distribution with repeated tails and a coefficient of variation larger than 1. Our model can also be used to evaluate different sets of enhanced distributed channel access parameters and to select the channel duty cycle according to the policy of the network operator. [ABSTRACT FROM PUBLISHER]

Wireless mesh networking (WMN) is regarded as a low-cost technology for rapid wireless network deployment. However, in a single-channel WMN, the overlapped transmission ranges between relaying mesh points could introduce serious interference. Using multiple radios over multiple channels can decrease the interference and improve the capacity of a WMN, but it increases the cost of a mesh point. One possible solution to balance between interference, hence performance, and cost is utilizing fewer radios that switch among multiple channels instead of using per-channel radios. In this paper, we propose a channel-switching method, called the traffic-aware switching scheme (TRASS), for a mesh point with a limited number of radios. TRASS utilizes the existing IEEE 802.11 mechanisms, i.e., hybrid-coordination-function-controlled channel access and power saving, to avoid packet loss during channel switching. A TRASS mesh point monitors the occupied channel time to schedule radios that switch among channels. The implemented TRASS demonstrates 75% throughput improvement by (2, 1), i.e., two-channel single-radio, over (1, 1). (3, 2) and (3, 1) achieve 69.8% and 39.7%, respectively, of the throughput of (3, 3) in the simulated TRASS. [ABSTRACT FROM PUBLISHER]

Wireless sensor networks are widely adopted in target tracking applications. Wireless sensor nodes are battery-powered devices. These low-cost communication devices have high failure rates and are vulnerable to attacks. To maintain network connectivity and to ensure large network coverage, excessive wireless sensor nodes are usually deployed to provide redundancy. However, these extra wireless sensor nodes would dissipate more power. This problem can be relieved by proper scheduling and putting unnecessary sensor nodes into sleep mode. In this paper, an energy-aware scheduling scheme for wireless sensor networks is proposed. The proposed scheme is a kind of an adaptive/periodic on–off scheduling scheme in which sensor nodes use only local information to make scheduling decisions. The scheme is evaluated in terms of target hit rate, detection delay, and energy consumption per successful target detection. Simulation results show that when comparing with other generic scheduling schemes, the proposed scheme can significantly reduce energy consumption. [ABSTRACT FROM PUBLISHER]

Many incompatible wireless protocols proliferate in unlicensed bands, creating complex coexistence and connectivity problems. If the trend continues, such problems will continue to exist in future unlicensed bands. We take a different approach to spectrum sharing. Instead of proposing a distinct medium-access control (MAC) protocol for each type of application, we propose a family of parameterized MAC protocols called WiFlex, which can be tailored to different application needs, ranging from wireless sensors to media centers. However, these protocols allow communication and spectrum-sharing coordination among different types of devices. We envision this family to be based on a multichannel physical layer. The contributions of this paper include a novel asynchronous split phase (ASP) protocol with dynamic priority support, even in multiple-collision-domain environments. When links are bidirectional, WiFlex resolves the multichannel hidden-node problem, achieving collision-free data exchange in a multihop environment. ASP provides a mechanism for prioritization and fairness. The performance of the protocol is evaluated through analysis and simulation. The coexistence of heterogeneous devices and the support for different applications with high performance are demonstrated. [ABSTRACT FROM PUBLISHER]

This paper presents a theoretical and experimental analysis on the application of power-line communication (PLC) on a cruise ship. The authors have developed an accurate model of the power grid of a ship when it is used as a PLC channel. The model is developed based on a theoretical approach and validated by a thorough measurement campaign. The accuracy of the model is addressed by a comparison between simulation results and measured data, and its use gives an insight into the performance of the power network to be used as PLC channel. [ABSTRACT FROM PUBLISHER]