Link Control Research Articles

A General Self-Adaptive DC Current Control of LCC-HVDC for Eliminating Subsequent Commutation Failure

With more renewable resources are integrated into the receiving-end AC grid through the LCC-HVDC link, a single-infeed LCC-HVDC (SIDC) system is facing a critical subsequent commutation failure (SCF), which stems from the poor dynamic reactive power support capability of the existing LCC-HVDC link's control strategies. This letter proposes a general self-adaptive DC current control (GSDC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of LCC-HVDC to eliminate the SCF, based on the dynamic reactive power interaction mechanism. Then, multiple comparative studies with the existing control strategies are implemented to verify the validation of the proposed control strategy by PSCAD/EMTDC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sup> . A fast evaluation index, called general commutation failure immunity index (GCFII), is also defined to show the performance of the proposed control strategy in eliminating the SCF.

The Role of Informal Control for Volunteer Satisfaction and Turnover in Volunteer Work Teams

Informal organizational control's role, while not extensively studied, has been said to be increasingly important - especially in contexts in which formal power, formal incentives and rewards are not prevalent - in volunteer teams. We are interested in how non-governmental organizations (NGOs) can reduce volunteers' turnover by inducing an informal clan control in their organization. We propose that clan control positively influences both volunteer job satisfaction and satisfaction of relatedness of needs, argued to be important indicators of how likely these volunteers will remain engaged in the organization - and that these links are partly mediated by the induced behavior of volunteers in teams, specifically, the lateral monitoring, i.e. the informal peer control that results. We selected volunteers in a children's rights NGO with almost 3,000 volunteers in Germany to empirically test our model. This NGO organizes its volunteer work in 175 regional volunteer groups, each headed by a group leader. Test results of structural equation modeling provide evidence that direct and indirect peer control indeed act as partial mediators of clan control's link to satisfaction and thereby turnover intention in our sample of more than 600 volunteers. While direct peer control partly mediates clan control's link to job satisfaction and satisfaction of relatedness needs, indirect peer control partly mediates clan control's link to satisfaction of relatedness needs. Implications for NGOs building on volunteer work and future research are discussed.

SOA-Based WDM Metro Ring Networks With Link Control Technologies

We experimentally study the performance of wavelength-division-multiplexing (WDM) metro/access ring networks, based on semiconductor optical amplifiers (SOAs), considering several gain control techniques. We show that gain control through link-control (LC) channel or amplified spontaneous emission (ASE) power recirculation, effectively used in erbium-doped fiber amplifier-based WDM ring networks, introduces serious penalties due to intensity noise transfer, and cannot be used in short-span SOA-based WDM rings. On the other hand, we observe a net benefit using LC channel and ASE extraction for short span rings and a limited WDM channel number, compared with linear operating conditions. An effective optical signal-to-noise ratio improvement of 2.1 dB has been achieved with LC channel extraction with respect to linear operation, for a 4 x 13.5 dB span ring with eight WDM channels. For spans longer than 15 dB, system performance in gain-controlled rings is found to be similar to noncontrolled ones.

Packet level acknowledgement and Go‐Back‐N protocol performance in infrared wireless LANs

AbstractInfrared wireless LANs may employ repetition rate (RR) coding to increase the symbol capture probability at the receiver. This paper examines the effectiveness of RR coding to utilization for infrared LANs using the physical and link layer parameter values proposed in the Advanced Infrared (AIr) protocol standard, which is developed by the Infrared Data Association (IrDA). Infrared LANs employ a Go‐Back‐N (GBN) automatic repeat request (ARQ) retransmission scheme at the Link Control (LC) layer to ensure reliable information transfer. To efficiently implement RR coding, the receiver may return after every DATA packet a suggestion for the suitable RR value to be used by the transmitter and implement a Stop‐and‐Wait (SW) ARQ scheme at the medium access control (MAC) layer. The effectiveness of employing this optional SW ARQ scheme at the MAC layer is discussed. Analytical models for the ARQ retransmission schemes are developed and employed to compare protocol utilization for different link parameter values such as window size, packet length and LC time out periods. This analysis identifies the ARQ protocol that maximizes performance for the specific link quality and the implemented link layer parameters. The effectiveness of the proposed RR coding to LAN utilization for different ARQ scheme implementation is finally explored. This analysis identifies the link quality level at which RR should be adjusted for maximum performance. It is concluded that if the packet error rate is higher than 0.1–0.4 (depending on the implemented ARQ protocol), the receiver should advise the transmitter to double the implemented RR for maximum performance. These error rate values are high and can be effectively estimated by the transmitter based on packet retransmissions. Thus, the usefulness of the receiver indicating to the transmitter to adjust RR is questionable, as the transmitter can effectively implement the suitable RR value based on packet retransmissions. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Suppression of detrimental effects caused by a link control channel in 16×10 Gbit/s wavelength division multiplexing optical network

The detrimental effects caused by a link control (LC) channel have been investigated when most channels are dropped in the LC-based wavelength division multiplexing (WDM) optical network with 16 signal channels. The use of the LC control channel with longer wavelength than the signal-channel band mitigates the gain degradation of surviving channel caused by spectral hole burning in the erbium-doped fiber amplifier (EDFA) and avoids the gain amplification caused by stimulated Raman scattering in the optical fiber. Spectral broadening of the LC channel increases its threshold power of stimulated Brilluoin scattering in the optical fiber. By using a frequency-dithered LC channel with longer wavelength than the signal channels in the SMF 240 km, 16×10 Gbit/s WDM optical network, no degradation is observed in the received optical power whatever the channel count and the surviving channel power excursion is less than 1 dB up to 10 dropped channels.