Outer Loop Power Control Research Articles

Computer Simulation Research of MMC Control in DC Power Network Using RTDS

With the development of DC power network, MMC has become an important AC/DC converter. MMC adopts the basic double closed-loop control composed of inner loop current control and outer loop power control. The modulation strategy adopts the nearest level approximation modulation and the capacitor voltage sequence method to ensure the capacitor voltage equalization of the sub-modules. The circulation suppression strategy can suppress the internal circulation of MMC. Finally, the simulation model of MMC was built based on RTDS, and the double closed-loop control strategy and circulation suppression strategy of MMC were verified.

Comprehensive control scheme of the interlinking converter in hybrid AC/DC microgrid

This paper presents a comprehensive control scheme for the interlinking converter (ILC) in a hybrid AC/DC microgrid consisting of the outer loop flexible power sharing control and the improved robust inner loop control. The outer loop power control of ILC is presented to achieve flexible power sharing of distributed generations (DGs) in the hybrid microgrid, depending on different power management objectives, which is realized based on the deduced balance state equation, and regulating the frequency and DC voltage at the same time. The improved robust inner loop control of ILC is also presented to suppress external disturbance and system model uncertainties with the improved dynamic response. This improved inner loop control which includes a disturbance observer link, can force the converter current to track the reference value with no steady error and improve the dynamic stability of the microgrid. With the proposed outer loop power sharing control and improved inner loop control, the comprehensive control scheme for the ILC is presented. Simulations cases show the effectiveness and superiority of the proposed comprehensive control scheme.

Optimal implementation of novel WCDMA uplink outer loop power control algorithm

Wideband code division multiple access (WCDMA) uplink outer loop power control has been responsible for changing the signal to interference ratio (SIR) target value according to the SIR target control algorithms. Thus maintains the desired block error rate (BLER) for voice connections and transmission to target error rate (TTE) for data connections. During a call, the SIR target varies between implemented lower (sirMin) and upper boundaries (sirMax), which are fixed values on radio network control station (RNC). As possible solution for WCDMA uplink overload problems, a novel uplink outer loop power control algorithm with dynamic change of sirMax has been proposed. In this paper optimal implementation for dynamic change of sirMax has been investigated. Performance management statistic and general performance event handling (GPEH) data, for current uplink received signal strength indicator (UL RSSI) and required SIR target, have been obtained. Based on analysis from obtained data optimal implementation for dynamic change of sirMax has been proposed.

Flicker transfer for three‐phase voltage source converter in distribution network

Flicker transfer is significantly affected by the dynamic impedance of the three-phase voltage source converter (VSC) in the distribution network. A methodology to determine the flicker transfer coefficient in a distribution system with a VSC is proposed. The formula of VSC dynamic impedance in the phase domain is derived based on the linearisation model of the VSC with the inner-loop current control and outer-loop power control as well as the phase-locked loop block taken into consideration.

소프트 핸드오프 상황에서 상향링크 송신 전력 제어 성능 분석

In a mobile communication system, we analyze the performance of uplink transmit power control mechanisms for various environments when a mobile station is during soft handoff. The quality of data frames at the receiver side can be better at a base station controller (BSC) than at its base stations (BSs) if the BSC combines selectively the data frames transmitted from the BSs. And, in order to achieve the target frame error rate (FER), the outer loop power control should be done at the BSC instead of at the BSs. It can save the energy consumption of a mobile station during the soft handoff.

Joint Physical Layer and Data Link Layer Optimization of CDMA-Based Networks

In CDMA systems, outer loop power control (OLPC) determines the target value of SNR at the receiver, mostly by using look-up tables to map bit error rates (BERs) to SNR-targets. In this contribution, transmission delay and packet loss rate constraints in the data link layer (DLL) are invoked in order to determine the optimum outer loop setpoint analytically, according to the number of active users in cell. Optimality is, in this sense, the maximization of system throughput. Using the optimum SNR-target, the optimal spreading factor is determined. Subsequently, the joint optimization of outer loop and variable spreading factor (VSF), at the physical(PHY)-layer, with truncated automatic repeat request (ARQ) error control mechanism at the data link layer are proposed. Hence, we show that quality of service (QoS) requirements at these layers can be simultaneously satisfied while maximizing throughput. Total and truncated channel inversion strategies are employed in the inner loop to adapt transmit power to short-time channel variations. We propose a system where the number of users in a cell is modeled by a one-dimensional discrete Markov chain, and design the adaptive continuous power and rate mechanism for the worst case packet error rate (PER) condition. The corresponding theoretical throughput, which can be regarded as upper-bound for discrete spreading factor case, is obtained numerically for various settings of system parameters. We have also provided simulation results for a practical channel condition. Our scheme is compared with constant SNR-target and PHY-layer based variable SNR-target cases under continuous power and rate variation to show the achievable gain through the coupling of physical and data link layers parameters.

Study of Rate Assignment on the Downlink of WCDMA

In the paper, firstly we can know the power control is one of the most important technologies of radio resource management in WCDMA system, secondly the base principle of the outer loop power control is analyzed theoretically, and at the same time, both the utility function-based power control algorithm and the power control algorithm with the base station assignment are briefly discussed. The two algorithms are connected according to their advantages and disadvantages, a rate assignment algorithm on the downlink for the data transmission is proposed. The optimization goal of the resource allocation strategy is choosing appropriate utility function. The utility function reflects a flexible tradeoff between total system throughput and fairness. The power is distributed through the control module and the scheduling module. The simulations show the performance of the algorithm.

Jointly optimized rate and outer loop power control with single- and multi-user detection

We propose a technique for enhancing the achievable spectral efficiency of multiuser direct-sequence code-division multiple-access (DS-CDMA) fading channels in the presence of additive white Gaussian noise (AWGN) and multiple access interference (MAI). The proposed scheme involves the joint optimization of outer loop power control (OLPC) and rate control using variable spreading factors (VSFs). The optimality is in the sense of average spectral efficiency maximization. The optimum outer loop target signal-to-noise ratio (SNR-target) and the corresponding spreading factor are derived jointly, in terms of the number of active users. Along with transmit power adaptation in the inner loop, this leads to maximized average spectral efficiency. Total and truncated channel inversion strategies are used in the inner loop. The average spectral efficiency of the joint optimization scheme is derived for the conventional matched-filter and the multiuser decorrelating detectors. Average transmit power and instantaneous bit error rate (BER) constraints are considered and the performance is evaluated over Nakagami-m flat-fading channels. In low SNRs, the proposed scheme can provide a considerable gain in bits/s/Hz for either of the detectors, compared to a VSF-assisted system that does not exploit OLPC and thus the optimum SNR-target.

DS-CDMA system outer loop power control and improvement for multi-service

When a new user accesses the CDMA system, the load will change drastically, and therefore, the advanced outer loop power control (OLPC) technology has to be adopted to enrich the target signal interference ratio (SIR) and improve the system performance. The existing problems about DS-CDMA outer loop power control for multi-service are introduced and the power control theoretical model is analyzed. System simulation is adopted on how to obtain the theoretical performance and parameter optimization of the power control algorithm. The OLPC algorithm is improved and the performance comparisons between the old algorithm and the improved algorithm are given. The results show good performance of the improved OLPC algorithm and prove the validity of the improved method for multi-service.

Outer loop power control in CDMA satellite systems with on-board power constraints

This paper aims at clarifying the role of the outer loop power control for CDMA satellite systems with on-board power constraints. If the inner loop of the power control is perfect, the channel turns into a AWGN channel and there is no need of the outer loop. In satellite CDMA systems, due to the longer propagation delay with respect to a terrestrial system, the inner loop of power control is only partly able to track power variations due to fast fading. Moreover, the Rice factor, which characterizes the channel statistics, can widely vary even if the user does not move but just because of the change of the elevation angle. Because of that, a wide range of target SNIR (and larger than in typical terrestrial systems) may be necessary to get the same BER performance. Therefore, the outer loop power control turns out to be essential to minimize the dynamic of the power link margins and avoid capacity degradations induced by the systematic use of static link margins. A semi-analytical model for the capacity evaluation has been developed, which is specifically intended for the power-limited satellite-to-mobile link with multi satellite reception. We found that the capacity gain with respect to a pure SNIR-based strategy (i.e., only inner loop) can reach the 40% of the total capacity in a single reception scheme. A smaller, but still noticeable capacity gain of the order of 20 - 30% is observed in presence of satellite diversity. Therefore, any dimensioning of CDMA satellite systems should not neglect this component of the power control.

Outer loop power control in CDMA systems with on-board power constraints

This paper aims at clarifying the role of the outer loop power control for CDMA satellite systems with on-board power constraints. If the inner loop of the power control is perfect, the channel turns into a AWGN channel and there is no need of the outer loop. In satellite CDMA sytsems, due to the longer propagation delay with respect to a terrestrial system, the inner loop of power control is only partly able to track power variations due to fast fading. Moreover, the Rice factor, which characterizes the channel statistics, can widely vary even if the user does not move but just because of the change of the elevation angle. Because of that, a wide range of target SNIR (and larger than in typical terrestrial systems) may be necessary to get the same BER performance. Therefore, the outer loop power control turns out to be essential to minimize the dynamic of the power link margins and avoid capacity degradations induced by the systematic use of static link margins. A semi-analytical model for the capacity evaluation has been developed, which is specifically intended for the power-limited satellite-to-mobile link with multi satellite reception. We found that the capacity gain with respect to pure SNIR-based strategy (i.e. only inner loop) can reach the 40% of the total capacity in a single reception scheme. A smaller, but still noticeable capacity gain of the order of 20-30% is observed in the presence of satellite diversity. Therefore, any dimensioning of CDMA satellite systems should neglet this component of the power control.

Benefits of perceptual speech quality metrics in modern cellular systems

Advanced algorithms have become available in recent years that can reliably measure the speech quality as ‘perceived’ by humans. The benefits of applying the perceptual quality measures obtained using these algorithms in the outer loop power control (OLPC) of the Third Generation Universal Mobile Telecommunication System (3G UMTS) are studied. It is shown that 20% capacity improvement compared to the use of conventional measures can be achieved, while an adequate and uniform speech quality is maintained.

WCDMA Uplink Parallel Interference Cancellation—System Simulations and Prototype Field Trials

Interference cancellation (IC) is one identified key technology to enhance WCDMA uplink performance. The goal of this contribution is to highlight the relative uplink system capacity improvement available for WCDMA, especially in realistic typical urban radio environments when employing receiver implementations including realistic channel estimation, searcher, and so forth. The performance of the selected limited-complexity parallel IC receiver is first evaluated with link-level simulations in order to provide input to system-level simulations. The system-level methodology is explained and a 40% system-level uplink capacity increase compared to utilizing the conventional RAKE receiver is found. The limited-complexity parallel IC receiver is then evaluated in a single-cell field trial. The trials show that both the mean and the variance of the outer-loop power control is reduced, which implies an overall increased capacity and an increased battery life of the terminals. Furthermore, the observed capacity gains are in accordance with system simulations.

On the uplink SIR of a mobile in soft handoff with applications to BLER estimation

We focus on the uplink and derive the joint probability density function of the signal to interference (+noise) ratios (SIRs) at the base stations (BSs) for the general case of n BSs supporting a mobile in soft handoff, each using maximal ratio combining with m-fold diversity. We then calculate the correlations between the SIRs for some example cases. The insights gained here lead to a fresh approach to the estimation of the block error rate (BLER) at the output of the frame selector (FS), which is the usual measure of quality of service in UMTS. For low specified BLER (e.g., 0.1%), the method of counting cyclic redundancy code errors requires an impractically large number of data blocks for an accurate estimate of BLER. We propose to estimate the BLER at the FS output based on measurements performed by the individual BSs. The initial setting of the target SIR in the outer loop power control can then be selected in the same way in order to expedite BLER convergence to the desired setting.

QoS based outer loop power control for enhanced reverse links of CDMA systems

Outer loop power control (OLPC) is also an important radio resource management (RRM) algorithm in dedicated channels of code division multiple access (CDMA) systems. Proposed is a new OLPC algorithm that also takes HARQ into consideration. The proposed algorithm can guarantee the QoS and help the system to greatly decrease average physical layer delays with similar relative throughput to the conventional algorithm.

MODELING AND CONTROL OF IP TRANSPORT IN CELLULAR RADIO LINKS

A fundamental assumption of the tcp protocol is that packet losses indicate congestion on the network. This is a problem when using tcp over wireless links, because a noisy radio transmission may erroneously indicate congestion and thereby reduce the tcp sending rate. Two partial solutions, which improve the quality of the radio link, are power control and link-layer retransmissions. We consider a radio channel with multiple users and traffic classes, and investigate how parameters in the radio model influences tcp-related quality measures, such as the average delay and the probability of spurious timeout. The results indicate that the outer loop power control is robust to uncertainties in the radio model. This robustness property supports separation between the radio layer design and the ip and tcp layers.

On the usefulness of outer-loop power control with successive interference cancellation

Multiuser detection (MUD) performance can be significantly better than the conventional matched filter receiver in CDMA systems. Further, since optimal MUD is exponentially complex, research has mainly focused on suboptimal approaches such as successive interference cancellation (SIC). SIC requires a geometric distribution of received powers to achieve equal performance for all received signals. We propose a power control scheme for SIC to achieve this profile (or the profile corresponding to any desired and achievable set of error rates) based on frame-error rate (FER) or bit-error rate (BER). Specifically, we derive the relationship between received power and BER for linear SIC and show that for unlimited mobile powers, a deterministic distributed BER-based outer-loop power control drives the received powers to the optimal power profile. The convergence of the deterministic BER-based algorithm is examined in the absence of inner loop power control errors. The simulated performance of a stochastic version of this algorithm is examined using instantaneous FER measurements. The stochastic algorithm is shown to provide unbiased estimates of the true power updates and converge to the optimal power vector provided the mobiles have unlimited power. We consider power limits for specific mobiles and find that individual mobile limits do not affect the performance of other signals. We examine the impact of system loading, multiple FER targets, error correction, and inner loop power control error on the performance of the algorithm.