Closed-loop Power Control Scheme Research Articles

Power control in LTE based on heuristic game theory for interference management

In the conventional LTE homogeneous network, sufficient transmit power of user equipment (UE) is determined by open-loop power control (OL-PC) and closed-loop power control (CL-PC) schemes. However, in a Het-Net environment, setting the UE’s transmit power requires delicate responsiveness to handle the severe and complicated uplink interference. In this paper, an interference-aware uplink power control mechanism based on Heuristic game theory approach is proposed for devices coexisting in a heterogeneous wireless network. Various wireless constraints like channel response, path loss, fading, shadowing, interference and metrics like SNR, SINR, throughput and bit rates are considered. Uplink power is controlled by suitably selecting the penalization factor (β) based on a simple Heuristic game theory approach considering the possible wireless constraints of each user depending on its location in the cell under consideration. The algorithm is framed in such a way to reduce inter-cell interference, limit transmit power, enhance bit rates and throughput of users. A significant improvement of 5.2% in the user coverage/distribution is achieved as a result of interference management compared to conventional power control scheme and power control with convex pricing.

A deep reinforcement learning-based power control scheme for the 5G wireless systems

In the fifth generation (5G) wireless system, a closed-loop power control (CLPC) scheme based on deep Q learning network (DQN) is introduced to intelligently adjust the transmit power of the base station (BS), which can improve the user equipment (UE) received signal to interference plus noise ratio (SINR) to a target threshold range. However, the selected power control (PC) action in DQN is not accurately matched the fluctuations of the wireless environment. Since the experience replay characteristic of the conventional DQN scheme leads to a possibility of insufficient training in the target deep neural network (DNN). As a result, the Q-value of the sub-optimal PC action exceed the optimal one. To solve this problem, we propose the improved DQN scheme. In the proposed scheme, we add an additional DNN to the conventional DQN, and set a shorter training interval to speed up the training of the DNN in order to fully train it. Finally, the proposed scheme can ensure that the Q value of the optimal action remains maximum. After multiple episodes of training, the proposed scheme can generate more accurate PC actions to match the fluctuations of the wireless environment. As a result, the UE received SINR can achieve the target threshold range faster and keep more stable. The simulation results prove that the proposed scheme outperforms the conventional schemes.

Distributed power control based on linear quadratic optimal controller for cognitive radio network

We propose a distributed closed-loop power control scheme for a cognitive radio network (CRN) based on our developed state space model of the CRN. The whole power control process is separated into outer control loop and inner control loop in order to solve different problem. In outer loop, the interference temperature (IT) constraint is transformed to a performance index minimized by a state feedback controller to obtain an appropriate target signal to interference plus noise ratio (SINR) of secondary user (SU). For ideal channel model and random time-varying channel model, our designed controller is a linear quadratic regulator (LQR) and a linear quadratic Gaussian (LQG) regulator respectively. While in inner loop, SU controls its transmit power to make the instantaneous SINR track the corresponding target and ensure the IT constraint under the limited threshold. The closed-loop stability of the CRN is proved and the performance of proposed control scheme is presented by computer simulations, which shows that this scheme can effectively guarantee both the requirement of SINR and IT constraint for all SUs.

Modeling and Control of Quasi Z-source Cascaded H-bridge Multilevel Inverter for Grid Connected Photovoltaic Systems

This paper presents the modeling and controlling the power of Quasi Z-Source cascaded H-bridge multilevel inverter for grid connected photovoltaic systems. The Quasi Z-Source inverter is an inverter that provides buck / boost output along with DC-AC conversion in a single stage. This topology has numerous advantages which makes it reliable and suitable for PV applications. Due to the impedance network and the cascaded H-bridge structure, it provides high gain, reduced total harmonic distortion (THD) and high reliability in PV systems. In this paper, a five level cascaded H-Bridge Quasi Z-source inverter has been considered for which the impedance network has been designed. Phase Shifted Inverted Sine carrier pulse width modulation has been implemented along with shoot- through control for controlling the switches of the inverter. The closed loop power control scheme has been implemented in two stages. In the PV input side, each string voltage is controlled by adjusting the shoot-through states of the inverter using Independent Maximum Power Point Tracking Control. DC link voltage of each bridge has been balanced by using DC link voltage control. Both of these controlling actions result in the control of grid injected power. A 2kVA PV inverter has been designed and built using MATLAB/SIMULINK and the hardware has been completed for the open loop control. The simulation and open loop hardware results are discussed.

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.

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.

Active Harmonic Filtering Using Current-Controlled, Grid-Connected DG Units With Closed-Loop Power Control

The increasing application of nonlinear loads may cause distribution system power quality issues. In order to utilize distributed generation (DG) unit interfacing converters to actively compensate harmonics, this paper proposes an enhanced current control approach, which seamlessly integrates system harmonic mitigation capabilities with the primary DG power generation function. As the proposed current controller has two well-decoupled control branches to independently control fundamental and harmonic DG currents, local nonlinear load harmonic current detection and distribution system harmonic voltage detection are not necessary for the proposed harmonic compensation method. Moreover, a closed-loop power control scheme is employed to directly derive the fundamental current reference without using any phase-locked loops (PLL). The proposed power control scheme effectively eliminates the impacts of steady-state fundamental current tracking errors in the DG units. Thus, an accurate power control is realized even when the harmonic compensation functions are activated. In addition, this paper also briefly discusses the performance of the proposed method when DG unit is connected to a grid with frequency deviation. Simulated and experimental results from a single-phase DG unit validate the correctness of the proposed methods.

A Fabry–Pérot electro-optic sensing system using a drive-current-tuned wavelength laser diode

A Fabry-Pérot enhanced electro-optic sensing system that utilizes a drive-current-tuned wavelength laser diode is presented. An electro-optic prober made of LiNbO(3) crystal with an asymmetric Fabry-Pérot cavity is used in this system. To lock the wavelength of the laser diode at resonant condition, a closed-loop power control scheme is proposed. Experiment results show that the system can keep the electro-optic prober at high sensitivity for a long working time when the closed-loop control function is on. If this function is off, the sensitivity may be fluctuated and only one-third of the best level in the worst case.

Predictive Closed-Loop Power Control for Delay-Prone Burst Transmission Systems in Rayleigh Fading

We present a predictive closed-loop power control scheme for delay-prone burst transmission systems. The scheme has a sample-by-sample predictor compensating burst delay and a built-in channel encoder reducing power control command bit error.

An Improved Power Estimation for Mobile Satellite Communication Systems

In this paper, in order to increase system capacity and reduce the transmitting power of the user's equipment, we propose a efficient power estimation algorithm consisting of a modified open-loop power control (OLPC) and closed-loop power control (CLPC) for mobile satellite communications systems. The improved CLPC scheme, combining delay compensation algorithms and pilot diversity, is mainly applied to the ancillary ter-restrial component (ATC). ATC link in urban areas, because it is more suitable to the short round-trip delay (RTD). In the case of rural areas, where ATCs are not deployed or where a signal is not received from ATCs, transmit power monitoring equipment and OLPC schemes using efficient pilot diversity are combined and ap-plied to the link between the user's equipment and the satellite. Two modified power control schemes are ap-plied equally to the boundary areas where two kinds of signals are received in order to ensure coverage conti-nuity. Simulation results show that the improved power control scheme has good performance compared to conventional power control schemes in a geostationary earth orbit (GEO) satellite system utilizing ATCs.

Predictive Closed-Loop Power Control for CDMA Cellular Networks

In this paper, we present and analyze a predictive closedloop power control (CLPC) scheme which employs a comb-type sample arrangement to effectively compensate multiple power control group (PCG) delays over mobile fading channels. We consider both least squares and recursive least squares filters in our CLPC scheme. The effects of channel estimation error, prediction filter error, and power control bit transmission error on the performance of the proposed CLPC method along with competing non-predictive and predictive CLPC schemes are thoroughly investigated. Our results clearly indicate the superiority of the proposed scheme with its improved robustness under non-ideal conditions. Furthermore, we carry out a Monte-Carlo simulation study of a 5×5 square grid cellular network and evaluate the user capacity. Capacity improvements up to 90% are observed for a typical cellular network scenario.

Predictive closed-loop power control scheme with comb-type sample arrangement for code division multiple access cellular networks

The authors present and analyse a predictive closed-loop power control (CLPC) scheme, which employs a comb-type sample arrangement to effectively compensate multiple power control group delays over mobile fading channels. The authors consider both least squares and recursive least squares filters in our CLPC scheme. The effects of channel estimation error, prediction filter error and power control bit transmission error on the performance of the proposed CLPC method along with competing non-predictive and predictive CLPC schemes are thoroughly investigated. The results clearly indicate the superiority of the proposed scheme with its improved robustness under non-ideal conditions. Furthermore, the authors carry out a Monte-Carlo simulation study of a 5×5 square grid cellular network and evaluate the user capacity. Capacity improvements up to 90% are observed for a typical cellular network scenario.

Robust autoregressive predictive power control method for mobile CDMA systems

A closed-loop power control (CLPC) scheme with a multistep (indicating multiple prediction steps) linear autoregressive predictor is presented. The proposed CLPC relies on low-rate sample vector based autoregressive prediction. Compared to currently available predictive CLCP schemes, it demonstrates particularly robust performance in the presence of large loop delays and channel estimation errors.

Multiphase transfer of control signal for adaptive power control in CDMA systems

Capacity improvment in cellular networks is highly dependent on the effectiveness of power control. A power control procedure is needed to compensate for the fluctuation of a mobile's transmitting power received at a base station and to increase the capacity of the mobile communication system via decreasing intra- and inter-cellular interference. Here we consider fuzzy set theory based delayed adaptive step-size closed loop power control scheme(s). In this scheme transmitters adjust their power step sizes according to the received multiphased power control signals (delayed commands) from base stations. Code division multiple access (CDMA) system standards (cdmaOne, CDMA2000 and ETSI UMTS/UTRAN) limit the number of bits to two for the length of the control command in time slots. Hence, the number of commands is limited to four per time slot (in practise to two: up and down fixed amount, the rest are zero and unused values) when a sign and magnitude binary word format is used. In the developed algorithm, the number of commands is enlarged to 16 per two sequential time slots (four bits) without an increase in the standardized control bit rate by transmitting control commands in two sequential phases (time slots). First two bits of the command are transmitted in the current time slot and a receiver stores them and waits for the next time slot, which includes the last two bits of the control signal. The receiver interprets control command after receiving all 4 bits. Therefore, the control frequency is decreased (delayed control) to half of the original but respectively the dynamic scale is increased to 4 times larger (in practise 7 times: 7 values up and 7 down, 1 value for zero and 1 unused) for the sign and magnitude binary coding. A single transmitter's control results with the developed controller in a frequency selective fading channel in a CDMA network with interfering nodes and Gaussian noise are compared to the predefined step size power control scheme, which is a de facto standard the power control in cellular networks.

Performance Analysis of a Truncated Closed-Loop Power-Control Scheme for DS/CDMA Cellular Systems

This paper analyzes the system performance of a truncated closed-loop power-control (TCPC) scheme for uplinks in direct-sequence/code-division multiple-access cellular systems over frequency-selective fading channels. In this TCPC scheme, a mobile station (MS) suspends its transmission when the short-term fading is less than a preset cutoff threshold; otherwise, the MS transmits with power adapted to compensate for the short-term fading so that the received signal power level remains constant. Closed-form formulas are successfully derived for performance measures, such as system capacity, average system transmission rate, MS average transmission rate, MS power consumption, and MS suspension delay. Numerical results show that the analysis provides reasonable accuracy and that the TCPC scheme can substantially improve the system capacity, the average system transmission rate, and power saving over conventional closed-loop power-control schemes. Moreover, the TCPC scheme under realistic consideration of power-control error due to power-control step size, power-control period, power-control command loop delay, and MS velocity is further investigated. A closed-form formula is obtained to accurately approximate the system capacity of the realistic TCPC scheme.

Filter-shaped LMS algorithm-based predictive power control

A predictive closed-loop power control scheme based on a filter-shaped least-mean-square (FS-LMS) algorithm, which takes into account knowledge of the fading process time-evolution, is proposed. It is demonstrated through simulation, that an FS-LMS-based closed-loop power control scheme performs better than the standard LMS algorithm.

Predictive closed-loop power control in CDMA mobilesystems

An achievable-SIR-based closed-loop power control scheme is proposed to maximise the minimum signal-to-interference power ratio (SIR). The proposed scheme is found to reduce the outage probability and also the dynamic range of the transmission power compared with the conventional power control scheme.

Optimization of power control parameters for DS-CDMA cellular systems

This paper envisages a cellular system based on code-division multiple access and investigates the performance of a strength-based closed-loop power control (CLPC) scheme on the basis of different parameters, such as the number of bits of the power command, the quantization step size, and the user speed. On the basis of a log-linear CLPC model, an analytical approach has been developed that has allowed to determine the optimum quantization step size to be used for each value of the number of power command bits. Simulation results have permitted to support the analytical framework developed in this paper.

On the analytical evaluation of closed-loop power-control error statistics in DS-CDMA cellular systems

This paper proposes an analytical study that aims at evaluating the power-control error statistics in wireless direct-sequence code-division multiple-access (DS-CDMA) cellular systems based on an ideal variable step closed-loop power-control scheme. In particular, the cumulative distribution function and the correlation coefficient of the power-control error are derived through a first-order Taylor expansion of the received signal envelope. A novel power-control scheme that exploits the autocorrelation properties of the fading is also proposed, and its performance is analyzed in terms of power-control error statistics. Rayleigh and Rice frequency-selective channel models, which involve the use of a diversity RAKE receiver at the base station, have been taken into account. The proposed analytical approach specifically applies to CDMA systems. A method that aims at estimating the capacity of a DS-CDMA cellular network is also given.

Performance of closed-loop power control in DS-CDMA cellular systems

In situations where the round-trip delay between the mobile and the base stations is smaller than the correlation time of the channel, power control schemes using feedback from the base station can effectively compensate for the fast fading due to multipath. We study several closed-loop power control (CLPC) algorithms by analysis and detailed simulation. We introduce a new loglinear model for analyzing the received power correlation statistics of a CLPC scheme. The model provides analytical expressions for the temporal correlation of the power controlled channel parameterized by the update rate, loop delay, and vehicle speed. The received power correlation statistics quantify the ability of closed-loop power control to compensate for the time-varying channel. To study more complex update strategies, detailed simulations that estimate the channel bit-error performance are carried out. Simulation results are combined with coding bounds to obtain quasi-analytic estimates of the reverse link capacity in a direct-sequence code-division multiple-access (DS-CDMA) cellular system. The quasi-analytic approach quantifies the performance improvements due to effective power control in both single-cell and multicell DS-CDMA systems operating over both frequency-nonselective and frequency-selective fading channels. The effect of nonstationary base stations on the system performance is also presented.