The Experts below are selected from a list of 6198 Experts worldwide ranked by ideXlab platform
Vaduvur Bharghavan - One of the best experts on this subject based on the ideXlab platform.
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Robust rate adaptation for 802.11 wireless networks
2006Co-Authors: Starsky H.y. Wong, Songwu Lu, Hao Yang, Vaduvur BharghavanAbstract:Rate adaptation is a mechanism unspecified by the 802.11 standards, yet critical to the system performance by exploit- ing themulti-rate capability at the physical layer. In this pa- per, we conduct a systematic and experimental study on rate adaptation over 802.11 wireless networks. Our main contri- butions are two-fold. First, we critique five design guidelines adopted bymost existing algorithms. Our study reveals that these seemingly correct guidelines can bemisleading in prac- tice, thus incur significant performance penalty in certain scenarios. The fundamental challenge is that rate adapta- tion must accurately estimate the channel condition despite the presence of various dynamics caused by fading, mobility and hidden terminals. Second, we design and implement a new Robust Rate Adaptation Algorithm (RRAA) that ad- dresses the above challenge. RRAA uses short-term loss ra- tio to opportunistically guide its rate change decisions, and an adaptive RTS filter to Prevent Collision losses from trig- gering rate decrease. Our extensive experiments have shown that RRAA outperforms three well-known rate adaptation solutions (ARF, AARF, and SampleRate) in all tested sce- narios, with throughput improvement up to 143%.
Chongkwon Kim - One of the best experts on this subject based on the ideXlab platform.
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Collision aware design of rate adaptation for multi rate 802 11 wlans
2008Co-Authors: Jaehyuk Choi, Yeonsup Lim, Kihong Park, Chongkwon KimAbstract:One of the key challenges in designing a rate adaptation scheme for IEEE 802.11 wireless LANs (WLANs) is to differentiate bit errors from link-layer Collisions. Many recent rate adaptation schemes adopt the RTS/CTS mechanism to Prevent Collision losses from triggering unnecessary rate decrease. However, the RTS/CTS handshake incurs significant overhead and is rarely activated in today's infrastructure WLANs. In this paper we propose a new rate adaptation scheme that mitigates the Collision effect on the operation of rate adaptation. In contrast to previous approaches adopting fixed rate-increasing and decreasing thresholds, our scheme varies threshold values based on the measured network status. Using the "retry" information in 802.11 MAC headers as feedback, we enable the transmitter to gauge current network state. The proposed rate adaptation scheme does not require additional probing overhead incurred by RTS/CTS exchanges and can be easily deployed without changes in firmware. We demonstrate the effectiveness of our solution by comparing with existing approaches through extensive simulations.
Starsky H.y. Wong - One of the best experts on this subject based on the ideXlab platform.
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Robust rate adaptation for 802.11 wireless networks
2006Co-Authors: Starsky H.y. Wong, Songwu Lu, Hao Yang, Vaduvur BharghavanAbstract:Rate adaptation is a mechanism unspecified by the 802.11 standards, yet critical to the system performance by exploit- ing themulti-rate capability at the physical layer. In this pa- per, we conduct a systematic and experimental study on rate adaptation over 802.11 wireless networks. Our main contri- butions are two-fold. First, we critique five design guidelines adopted bymost existing algorithms. Our study reveals that these seemingly correct guidelines can bemisleading in prac- tice, thus incur significant performance penalty in certain scenarios. The fundamental challenge is that rate adapta- tion must accurately estimate the channel condition despite the presence of various dynamics caused by fading, mobility and hidden terminals. Second, we design and implement a new Robust Rate Adaptation Algorithm (RRAA) that ad- dresses the above challenge. RRAA uses short-term loss ra- tio to opportunistically guide its rate change decisions, and an adaptive RTS filter to Prevent Collision losses from trig- gering rate decrease. Our extensive experiments have shown that RRAA outperforms three well-known rate adaptation solutions (ARF, AARF, and SampleRate) in all tested sce- narios, with throughput improvement up to 143%.
Do-keun Kim - One of the best experts on this subject based on the ideXlab platform.
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Robust Construction Safety System (RCSS) for Collision Accidents Prevention on Construction Sites
2019Co-Authors: Byung-wan Jo, Yun Sung Lee, Rana Muhammad Asad Khan, Jung-hoon Kim, Do-keun KimAbstract:A proximity warning system to detect the presence of a worker/workers and to warn heavy equipment operators is highly needed to Prevent Collision accidents at construction sites. In this paper, we developed a robust construction safety system (RCSS), which can activate warning devices and automatically halt heavy equipment, simultaneously, to Prevent possible Collision accidents. The proximity detection of this proposed system mainly relies on ultra-wideband (UWB) sensing technologies, which enable instantaneous and simultaneous alarms on (a) a worker’s personal safety (personal protection unit (PPU)) device and (b) hazard area device (zone alert unit (ZAU)). This system also communicates with electronic control sensors (ECSs) installed on the heavy equipment to stop its maneuvering. Moreover, the RCSS has been interfaced with a global positioning system communication unit (GCU) to acquire real-time information of construction site resources and warning events. This enables effective management of construction site resources using an online user interface. The performance and effectiveness of the RCSS have been validated at laboratory scale as well as at real field (construction site and steel factory). Conclusively, the RCSS can significantly enhance construction site safety by pro-actively Preventing Collision of a worker/workers with heavy equipment.
Jaehyuk Choi - One of the best experts on this subject based on the ideXlab platform.
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Collision aware design of rate adaptation for multi rate 802 11 wlans
2008Co-Authors: Jaehyuk Choi, Yeonsup Lim, Kihong Park, Chongkwon KimAbstract:One of the key challenges in designing a rate adaptation scheme for IEEE 802.11 wireless LANs (WLANs) is to differentiate bit errors from link-layer Collisions. Many recent rate adaptation schemes adopt the RTS/CTS mechanism to Prevent Collision losses from triggering unnecessary rate decrease. However, the RTS/CTS handshake incurs significant overhead and is rarely activated in today's infrastructure WLANs. In this paper we propose a new rate adaptation scheme that mitigates the Collision effect on the operation of rate adaptation. In contrast to previous approaches adopting fixed rate-increasing and decreasing thresholds, our scheme varies threshold values based on the measured network status. Using the "retry" information in 802.11 MAC headers as feedback, we enable the transmitter to gauge current network state. The proposed rate adaptation scheme does not require additional probing overhead incurred by RTS/CTS exchanges and can be easily deployed without changes in firmware. We demonstrate the effectiveness of our solution by comparing with existing approaches through extensive simulations.