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Evaluation of the Effects of a Grouping Algorithm on IEEE 802.15.4 Networks with Hidden Nodes
엄진영,안종석,이강우 한국통신학회 2014 Journal of communications and networks Vol.16 No.1
This paper proposes hidden-node aware grouping (HAG)algorithm to enhance the performance of institute of electricaland electronics engineers (IEEE) 802.15.4 networks when they undergoeither severe collisions or frequent interferences by hiddennodes. According to the degree of measured collisions and interferences,HAG algorithm dynamically transforms IEEE 802.15.4protocol between a contention algorithm and a contention-limitedone. As a way to reduce the degree of contentions, it organizesnodes into some number of groups and assigns each group an exclusiveper-group time slot during which only its member nodescompete to grab the channel. To eliminate harmful disruptions byhidden nodes, especially, it identifies hidden nodes by analyzing thereceived signal powers that each node reports and then places theminto distinct groups. For load balancing, finally it flexibly adaptseach per-group time according to the periodic average collision rateof each group. This paper also extends a conventional Markov chain model ofIEEE 802.15.4 by including the deferment technique and a trafficsource to more accurately evaluate the throughput of HAG algorithmunder both saturated and unsaturated environments. Thismathematical model and corresponding simulations predict with6%discrepancy that HAG algorithm can improve the performanceof the legacy IEEE 802.15.4 protocol, for example, even by 95% ina network that contains two hidden nodes, resulting in creation ofthree groups.
엄진영 한국농촌경제연구원 2021 농촌경제 Vol.44 No.2
In agricultural fields, unregistered foreign workers who illegally reside in Korea with illegal work status takes a larger portion than registered foreign workers. This paper conducts quantitative and qualitative surveys and analyses on the scale of unregistered foreign workers in the agricultural sector and how they are employed. It presents the results and their implications on how to improve related policies and systems. Then, it suggests measures to improve the problem of unregistered foreign workers. First, it is necessary to establish a statistical basis for the agricultural labor force. Second, it is essential to identify the causes for the employment of unregistered foreign workers and improve the system accordingly. Third, there is a need to prepare a plan to move the organized and systemized supply channels of unregistered foreign workers to the institutional sphere.