Closed-loop Power Control Research Articles

Interference-Aware Uplink Power Control in 3GPP LTE-A HetNet

The latest evolution of cellular network, i.e., the heterogeneous network (HetNet) is a promising technique for facing the explosive data demands that the macro-only network can barely meet. However, unplanned small cell deployments, along with an aggressive frequency reuse scheme, generate severe interference between adjacent cells, degrading system performance. In the conventional homogeneous network, fractional power control (FPC), which consists of open-loop power control (OL-PC) and closed-loop power control (CL-PC), is used to determine adequate transmit power of user equipment (UE) to avoid inter-cell interference. However, setting the UE transmit power requires delicate awareness of uplink interference to properly avoid the severe and complicated inter-cell interference in an uplink HetNet environment. In this paper, we propose an interference-aware uplink power control scheme that considers outgoing and incoming interference in each cell in order to fully take the interference situation of the HetNet into account while setting the OL-PC parameter. By using the proposed scheme, uplink interference existing in a HetNet environment can evidently be reduced; therefore, the total cell capacity of both the macro- and the femtocell is increased by 25.6 %. Furthermore, the simulation results of a CL-PC on a 10 ms basis show that the received signal to interference-plus-noise ratio (SINR) of OL-PC with CL-PC is spread less around the target SINR compared to the case of OL-PC alone. Therefore, it is verified that the CL-PC supports the received SINR of OL-PC to meet the target SINR by compensating the channel variation caused by the fading effect.

A wirelessly-powered homecage with animal behavior analysis and closed-loop power control.

This paper presents a new EnerCage-homecage system, EnerCage-HC2, for longitudinal electrophysiology data acquisition experiments on small freely moving animal subjects, such as rodents. EnerCage-HC2 is equipped with multi-coil wireless power transmission (WPT), closed-loop power control, bidirectional data communication via Bluetooth Low Energy (BLE), and Microsoft Kinect® based animal behavior tracking and analysis. The EnerCage-HC2 achieves a homogeneous power transfer efficiency (PTE) of 14% on average, with ~42 mW power delivered to the load (PDL) at a nominal height of 7 cm by the closed-loop power control mechanism. The Microsoft Kinect® behavioral analysis algorithm can not only track the animal position in real-time but also classify 5 different types of rodent behaviors: standstill, walking, grooming, rearing, and rotating. A proof-of-concept in vivo experiment was conducted on two awake freely behaving rats while successfully operating a one-channel stimulator and generating an ethogram.

Positioning Third-Party Receiver by Exploiting the Close-Loop Power Control in Wireless Networks

In frequency division duplex systems, it is extremely difficult to position the receiver (Rx) that belongs to another system, defined as the third-party Rx, because the sensors usually do not know which band the Rx uses for reverse transmission. In this letter, we propose a new method to position the third-party Rx based on the transmitted signal of the third-party transmitter (Tx). In particular, our method exploits the close-loop power control between the third-party transceivers because the Rx location determines the signal-to-interference-plus-noise ratio (SINR) of the Rx and the SINR further determines the transmission power of the Tx. Therefore, by measuring the transmitted signal of the Tx, the sensors are able to position the Rx. Simulation results indicate the effectiveness of the proposed method.

An Auto-Reconfigurable AC-DC Regulator for Wirelessly Powered Biomedical Implants With 28% Link Efficiency Enhancement

This brief presents an auto-reconfigurable load-dependable ac-dc regulator for wirelessly powered biomedical implants. In wireless power transmission, the peak link efficiency that typically limits the overall system efficiency only occurs at a certain nominal load for a given link design. The proposed reconfigurable ac-dc regulator can automatically switch between doubler and quadrupler rectifier topologies to provide dynamic input impedance matching to the link as the average load current of the regulator varies during system operation, thereby maintaining high-link efficiency over a wide load range. A low-power load modulation signal generator is also developed for closed-loop wireless power control. Implemented in a standard 0.35- $\mu \text{m}$ CMOS process, the proposed rectifier and ac-dc regulator achieve peak power conversion efficiencies of 92.7% and 88.5%, respectively, while operating at 1 MHz. The proposed autoreconfiguration capability of the regulator further provides the link efficiency enhancement of 28% across the wide load power range from 1 to 20 mW.

A DTC Stator Flux Algorithm for the Performance Improvement of Induction Traction Motors

In view of the speed control characteristics of induction traction motors and the problems of direct torque control (DTC) algorithms in current applications, this paper presents a DTC algorithm characterized by a symmetrical polygon flux control and a closed loop power control in the constant-torque base speed region and constant-power field-weakening region of induction traction motors. This algorithm only needs to add a stator flux control algorithm to the traditional DTC structures. This has the benefit of simplicity, while maintaining the features of traditional algorithms such as a rapid dynamic response, uncomplicated control circuit, reduced dependence on motor parameters, etc. In addition, it obtains a smoother flux trajectory that is conducive to improvement of the harmonic elimination capability, the switching frequency utilization as well as the torque and power performance in the field-weakening region. The effectiveness and feasibility of this DTC algorithm are demonstrated by both theoretical analysis and experimental results.

Relay-Assisted Cross-Channel Gain Estimation for Spectrum Sharing

In cognitive radio networks, the cross-channel gain from a cognitive transmitter (CT) to a primary receiver (PR) is critical for spectrum sharing and obtaining the cross-channel gain is very difficult. Even though proactive estimation allows the CT to autonomously estimate the cross-channel gain, it may cause severe interference to the PR. This raises a new issue for spectrum sensing, called spectrum sensing interference . In this paper, we deal with the sensing interference and propose a relay-assisted method to conduct the proactive estimation, which obtains the cross-channel gain with much less interference to the PR. In our method, we let the CT act as a full-duplex amplify-and-forward relay to probe the close-loop power control between primary transceivers. By measuring the power adjustment of the primary signal, the CT estimates the cross-channel gain. Simulation results indicate that our method can reduce the sensing interference to an extremely low level.

A unified framework for adaptive inverse power control

In this paper, a unified framework for adaptive inverse power control is developed. It is based on a modified filtered-x least mean square (MFxLMS) algorithm that is proposed and analyzed. A practical version of the algorithm for closed loop power control is also developed. The filtered-x least mean square (FxLMS) algorithm is widely used for inverse control such as noise cancelation. This is the first paper to apply the algorithm for power control. We have modified the conventional FxLMS algorithm by adding absolute value blocks since power control does not need phase information. The modification makes the algorithm more robust and requires fewer bits to be transmitted in the feedback link. The main contribution of the paper is that the proposed algorithm can be seen as generalized inverse control to be used in power control research. It gives a unified framework for several existing algorithms, linking them to the least mean square (LMS) literature. Numerical results are provided, comparing the performance of the proposed algorithm to existing practical algorithms used, e.g., in Third Generation Partnership Project (3GPP) long-term evolution (LTE) systems.

시변 수중 음향 채널에서 코드 분할 다중 접속 방식의 폐루프 전력 제어 기법

Code division multiple access (CDMA) is one of the promising medium access control scheme for underwater acoustic sensor networks due to its beneficial features such as robustness against frequency-selective fading and high frequency-reuse efficiency. In this paper, we design a closed-loop power control scheme for the underwater CDMA, to adapt time-varying acoustic channel. In the proposed scheme, sink node sends to sensor nodes the associated path loss which is acquired by uplink-channel analysis based on received packets from the sensor nodes. Then, sensor nodes adjust their transmission power in an adaptive manner to time-varying underwater acoustic channel, according to the informations sent by the sink node.

Power headroom report-based uplink power control in 3GPP LTE-A HetNet

In a 3rd Generation Partnership Project Long Term Evolution-Advanced (3GPP LTE-A) uplink, user equipment (UE) has a maximum transmission power limit defined by the UE power class. Generally, the cell edge UE has a higher probability to be constrained by the maximum transmission power level owing to the compensation of the large pathloss. When the UE transmission power is constrained by the maximum level, allocating a higher number of physical resource blocks (PRBs) than the UE power capability can afford will reduce the transmission power to be allocated per PRB, resulting in inefficient use of power resources. To avoid this power inefficiency, the uplink transmission power can be controlled according to the number of PRBs allocated using the power headroom report-based power efficient resource allocation (PHR-PERA) scheme proposed in this paper. Furthermore, adaptive open-loop power control (OL-PC) based on the signal-to-interference-plus-noise ratio (SINR) and the uplink interference is used to improve the cell capacity. By the uplink power control employing the proposed PHR-PERA scheme, the macro and femto UE throughputs were increased by 49.9 and 5 %, respectively, compared to the case of conventional fractional power control (FPC). Additional gains of 21.9 and 4.8 % for macro and femto UE throughputs, respectively, were achieved by adaptive OL-PC. The performance of fast closed-loop power control (CL-PC) based on the received SINR is also evaluated in this paper. The simulation results demonstrate that CL-PC supports OL-PC by compensating the fading effect for the UE uplink SINR to meet the target SINR.

Energy-Efficient Power Control Scheme for Device-to-Device Communications

Device-to-device (D2D) communication permits direct communication between devices and thereby it provides performance gain for the traditional cellular network. In this paper, the problem how to allocate the transmission power efficiently is investigated and a distributed power control scheme is proposed for D2D communications. In this scheme, D2D user equipment (UE) can determine its transmission power dynamically for optimizing the link performance of the D2D link. To achieve this goal, firstly, an upper bound for the D2D transmitter density is derived based on which D2D UE determines its transmission power is on or off to avoid excess interferences and guarantee that each D2D link can achieve the link quality of service (QoS) on generally. In addition, for those D2D UEs transmitting data, the optimal transmission power is derived for a random D2D link which can optimize the successful transmission probability according to the link quality and the interference environment with few signalling exchange. Finally, some non-supported D2D links under hash environment are appropriately removed to reduce unnecessary interferences on other links and guarantee that an optimal power allocation solution exists for each D2D link. Simulation results show that compared with the fixed power scheme and the closed loop power control scheme, the proposed distributed power control scheme can improve the successful transmission probability under different wireless environments. Furthermore, compared with the closed loop power control scheme, the power consumption is reduced significantly (e.g. transmission powers for half of UEs can be reduced by above 84 %) by the proposed scheme.

A Smart Wirelessly Powered Homecage for Long-Term High-Throughput Behavioral Experiments.

A wirelessly powered homecage system, called the EnerCage-HC, that is equipped with multicoil wireless power transfer, closed-loop power control, optical behavioral tracking, and a graphic user interface is presented for longitudinal electrophysiology and behavioral neuroscience experiments. The EnerCage-HC system can wirelessly power a mobile unit attached to a small animal subject and also track its behavior in real-time as it is housed inside a standard homecage. The EnerCage-HC system is equipped with one central and four overlapping slanted wire-wound coils with optimal geometries to form three- and four-coil power transmission links while operating at 13.56 MHz. Utilizing multicoil links increases the power transfer efficiency (PTE) compared with conventional two-coil links and also reduces the number of power amplifiers to only one, which significantly reduces the system complexity, cost, and heat dissipation. A Microsoft Kinect installed 90 cm above the homecage localizes the animal position and orientation with 1.6-cm accuracy. Moreover, a power management ASIC, including a high efficiency active rectifier and automatic coil resonance tuning, was fabricated in a 0.35-μm 4M2P standard CMOS process for the mobile unit. The EnerCage-HC achieves a max/min PTE of 36.3%/16.1% at the nominal height of 7 cm. In vivo experiments were conducted on freely behaving rats by continuously delivering 24 mW to the mobile unit for >7 h inside a standard homecage.

A Closed-Loop Transmission Power Control System Using a Nonlinear Approximation of Power-Time Curve

In wireless communication networks, it is desirable to achieve energy efficiency, while maintaining quality of service. Overall, energy efficiency can be achieved by minimizing the power output for each communication device. This paper presents a novel energy-saving adaptive transmit power control (TPC) algorithm based on bit error rate (BER) feedback (BER-TPC) that outperforms conventional approaches based on signal-to-interference-plus-noise ratio (SINR) feedback (SINR-TPC). It is a distributed algorithm deployed in both transmitting and receiving devices that can be applied for various wireless network topologies and protocols. This paper addresses the power efficiency of adaptive TPC, in terms of reduced total transmit power of the network by smoothing transmit power transients during adaptive iterations. It is achieved using a distributed closed-loop power control system that applies heuristically estimated dual-rate power adjustments during adaptive iterations. Because the proposed system uses a mathematical formula for power adjustment, operational bounds for stability can be provided using simple analysis. It is demonstrated that the proposed system provides adequate tradeoff between performance and complexity, in terms of reduction in sensitivities and better tracking performance in following the desired reference power curves used in the simulations. Case scenarios are simulated demonstrating approximately 1.39-dB transmit power savings compared to conventional methods.

Software-Based Wireless Power Transfer Platform for Various Power Control Experiments

In this paper, we present the design and evaluation of a software-based wireless power transfer platform that enables the development of a prototype involving various open- and closed-loop power control functions. Our platform is based on a loosely coupled planar wireless power transfer circuit that uses a class-E power amplifier. In conjunction with this circuit, we implement flexible control functions using a National Instruments Data Acquisition (NI DAQ) board and algorithms in the MATLAB/Simulink. To verify the effectiveness of our platform, we conduct two types of power-control experiments: a no-load or metal detection using open-loop power control, and an output voltage regulation for different receiver positions using closed-loop power control. The use of the MATLAB/Simulink software as a part of the planar wireless power transfer platform for power control experiments is shown to serve as a useful and inexpensive alternative to conventional hardware-based platforms.

A Hybrid Estimator for Active/Reactive Power Control of Single-Phase Distributed Generation Systems With Energy Storage

This paper presents a new active/reactive power closed-loop control system for a hybrid renewable energy generation system used for single-phase residential/commercial applications. The proposed active/reactive control method includes a hybrid estimator, which is able to quickly and accurately estimate the active/reactive power values. The proposed control system enables the hybrid renewable energy generation system to be able to perform real-time grid interconnection services such as active voltage regulation, active power control, and fault ride-through. Simulation and experimental results demonstrate the superior performance of the proposed closed-loop control system.

Uplink-Oriented Deployment Guidelines and Auto-Configuration Algorithms for Co-Channel W-CDMA Heterogeneous Networks

The operation of wireless cellular networks can be efficiently supported by secondary small cells that are deployed at traffic hotspots within the coverage area of the primary macro cells. To this end, we examine the conditions under which the secondary base stations can share the same communication channel with the primary base stations under the constraint of a predefined quality of service, typical for uplink communications. In particular, requiring a target signal-to-interference-and-noise ratio (SINR) for each transmission accommodated in a common interference-limited channel, we formally assess the impact of the secondary infrastructure in a W-CDMA system on the global achievability of the uplink target SINRs via distributed closed-loop power control. The effects of cell load and inter-cell coupling are distinguished. As a result, we define solutions to the problems of base station placement, cell coverage optimization, and target SINR adaptation in W-CDMA heterogeneous networks, as well as discuss their compatibility with standard downlink-oriented deployment guidelines. Analytical conclusions are validated numerically by 3GPP-compliant simulations of a W-CDMA heterogeneous network.

An Integrated Wireless Power Management and Data Telemetry IC for High-Compliance-Voltage Electrical Stimulation Applications.

This paper describes a 13.56-MHz wireless power recovery system with bidirectional data link for high-compliance-voltage neural/muscle stimulator. The power recovery circuit includes a 2-stage rectifier, 2 LDOs and a high voltage charge pump to provide 3 DC outputs: 1.8 V, 3.3 V and 20 V for the stimulator. A 2-stage time division based rectifier is proposed to provide 3 DC outputs simultaneously. It improves the power efficiency without introducing any impact on the forward data recovery. The 20 V output is generated by a modified low ripple charge pump that reduces the ripple voltage by 40%. The power management system shows 49% peak power efficiency. The data link includes a clock and data recovery (CDR) circuit and a load shift keying (LSK) modulator for bidirectional data telemetry. The forward and backward data rates of the data telemetry are 61.5 kbps and 33.3 kbps, respectively. In addition, a power monitor circuit for closed-loop power control is implemented. The whole system has been fabricated in a 24 V HV LDMOS option 1.8 μ m CMOS process, occupying a core area of around 3.5 mm (2).

A Triple-Loop Inductive Power Transmission System for Biomedical Applications.

A triple-loop wireless power transmission (WPT) system equipped with closed-loop global power control, adaptive transmitter (Tx) resonance compensation (TRC), and automatic receiver (Rx) resonance tuning (ART) is presented. This system not only opposes coupling and load variations but also compensates for changes in the environment surrounding the inductive link to enhance power transfer efficiency (PTE) in applications such as implantable medical devices (IMDs). The Tx was built around a commercial off-the-shelf (COTS) radio-frequency identification (RFID) reader, operating at 13.56 MHz. A local Tx loop finds the optimal capacitance in parallel with the Tx coil by adjusting a varactor. A global power control loop maintains the received power at a desired level in the presence of changes in coupling distance, coil misalignments, and loading. Moreover, a local Rx loop is implemented inside a power management integrated circuit (PMIC) to avoid PTE degradation due to the Rx coil surrounding environment and process variations. The PMIC was fabricated in a 0.35- μm 4M2P standard CMOS process with 2.54 mm(2) active area. Measurement results show that the proposed triple-loop system improves the overall PTE by up to 10.5% and 4.7% compared to a similar open- and single closed-loop system, respectively, at nominal coil distance of 2 cm. The added TRC and ART loops contribute 2.3% and 1.4% to the overall PTE of 13.5%, respectively. This is the first WPT system to include three loops to dynamically compensate for environment and circuit variations and improve the overall power efficiency all the way from the driver output in Tx to the load in Rx.

Research on Digital Controls of Piston Pumps Based on Compound Control Using Feed-Forward and Feedback Controls

Taking the swash plate piston pump as the research plant, the paper introduces the composition of digital control system of variable pump first; Then the mathematical model of variable mechanism is established according to which the closed-loop flow control system and the power control system are worked out. Also, the paper shows the stability margin of the control system and analyzes some response indices to step command under Matlab simulation. Aiming at the shortage of the closed-loop control system, the paper gives an idea of an optimization design of the compound power control system based on both feed-forward and feedback control. Compared with the conventional closed-loop power control method, the compound one gets a 47.2% reduction in the adjusting time and a 38.2% decrease in the overshoot indicating that the adjusting process is obviously shortened and the disturbance effect effectively weakened.

Research on Power Balance Control of Multi-Motor Driving Belt Conveyor System Based on Controlled Transmission Device

According to the existing problems of driving equipment for belt conveyor, a novel design scheme of controlled transmission which uses hydraulic transmission system driving worm gear to control the output speed of planetary gear mechanism is proposed. The control strategy of multi-motor drive power balance which adopts master-slave structure is designed. The master driver adopts speed closed-loop control with current limiting and the slave drivers adopt power closed-loop control. The given power signal of slave pulley is decided by the master motor. The control system offers multiple communication interfaces which enable the belt conveyor to integrate in coal mine information platform and realize information resource sharing. The controlled transmission device and its power balance control system have characteristics of compact, reliable and high efficiency.

Automatic frequency controller for power amplifiers used in bio-implanted applications: issues and challenges.

With the development of communication technologies, the use of wireless systems in biomedical implanted devices has become very useful. Bio-implantable devices are electronic devices which are used for treatment and monitoring brain implants, pacemakers, cochlear implants, retinal implants and so on. The inductive coupling link is used to transmit power and data between the primary and secondary sides of the biomedical implanted system, in which efficient power amplifier is very much needed to ensure the best data transmission rates and low power losses. However, the efficiency of the implanted devices depends on the circuit design, controller, load variation, changes of radio frequency coil's mutual displacement and coupling coefficients. This paper provides a comprehensive survey on various power amplifier classes and their characteristics, efficiency and controller techniques that have been used in bio-implants. The automatic frequency controller used in biomedical implants such as gate drive switching control, closed loop power control, voltage controlled oscillator, capacitor control and microcontroller frequency control have been explained. Most of these techniques keep the resonance frequency stable in transcutaneous power transfer between the external coil and the coil implanted inside the body. Detailed information including carrier frequency, power efficiency, coils displacement, power consumption, supplied voltage and CMOS chip for the controllers techniques are investigated and summarized in the provided tables. From the rigorous review, it is observed that the existing automatic frequency controller technologies are more or less can capable of performing well in the implant devices; however, the systems are still not up to the mark. Accordingly, current challenges and problems of the typical automatic frequency controller techniques for power amplifiers are illustrated, with a brief suggestions and discussion section concerning the progress of implanted device research in the future. This review will hopefully lead to increasing efforts towards the development of low powered, highly efficient, high data rate and reliable automatic frequency controllers for implanted devices.