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Kim, Eui-Jik,Choi, Hyo Hyun,Kwon, Jung-Hyok MYU K.K. 2018 Sensors and materials Vol.30 No.8
<P>This paper presents a regional density-aware data collection (RDDC) using unmanned aerial vehicles (UAVs) in large-scale wireless sensor networks (WSNs). The RDDC is designed to support fast data collection by adaptively adjusting the value of the minimum contention window (CWmin) of the sensor nodes depending on the regional node density of sensing fields. The operation of RDDC consists of the region-partitioning, node-scanning, and data-collecting phases. In the region-partitioning phase, the RDDC partitions the sensing field into multiple regions and assigns a region ID to each sensor node according to the region to which it belongs. In the node-scanning phase, the RDDC calculates the node density of each region. Finally, in the data-collecting phase, the RDDC assigns different CWmin values to each sensor node considering the regional node density of each region. The experimental simulation results show that the RDDC obtains higher aggregate throughput and shorter delay than the existing data collection method.</P>
Distributed Interference-aware Medium Access Control for IEEE 802.15.7 Visible Light Communications
Kim, Eui-Jik,Kwon, Jung-Hyok,Kim, Dongwan,Lim, Yongseok MYU K.K. 2018 Sensors and materials Vol.30 No.8
<P>In this paper, we present a distributed interference-aware medium access control (DI-MAC) for IEEE 802.15.7 visible light communications (VLCs), which improves the spatial efficiency of VLC devices deployed in specific service areas. The DI-MAC adaptively adjusts the backoff exponent (BE) of each VLC device by considering the number of adjacent VLC devices causing the interference, which are called VLC interferers. Therefore, it reduces interference between the VLC devices and unnecessary waiting time for channel access. To this end, the DI-MAC conducts VLC interferer discovery by using the IDs of VLC interferers obtained via hello messages from adjacent VLC devices and then performing a BE adaptation to determine the BE of each VLC device based on the number of VLC interferers. An experimental simulation was conducted to evaluate the performance of the DI-MAC, and the results show that the DI-MAC obtains a higher aggregate throughput performance than the existing IEEE 802.15.7 VLC.</P>
Kim, Eui-Jik,Kim, Ho-Young,Kim, Daehee,Kim, Dongwan MYU K.K. 2018 Sensors and materials Vol.30 No.8
<P>Concern about energy-efficient medium access control (MAC) protocols for wearable devices is increasing owing to support for healthcare services using wireless body sensor networks (WBSNs). The most popular energy-efficient MAC protocol for WBSNs is the IEEE 802.15.6 standard, which adopts carrier sensing multiple access with collision avoidance (CSMA/CA). The CSMA/CA mechanism of the IEEE 802.15.6 standard allows differentiated channel access by assigning a different size of contention window to the nodes, each of which has a different priority. However, the existing CSMA/CA of IEEE 802.15.6 still cannot guarantee successful data transmission in error-prone channels and congested network environments, which leads to wasted energy owing to data retransmission. In this paper, we propose an adaptive priority-based MAC (AP-MAC) protocol for IEEE 802.15.6 WBSNs, which utilizes transmission opportunities suitable for WBSNs. For this, data types are classified with predefined priorities with each data type having a different opportunity to access the channel. In addition, the priority of each classification is updated adaptively according to the update metrics channel state and congestion level. Simulation results show the enhanced performance of the AP-MAC protocol compared with that of the IEEE 802.15.6 standard.</P>