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Symmetry 2019, 11(1), 71;

CoFi: Coding-Assisted File Distribution over a Wireless LAN

1,2,* and 1
College of Information and Communication Engineering, Harbin Engineering University, Harbin 150001, China
Information and Network Center, Heilongjiang University of Science and Technology, Harbin 150022, China
Author to whom correspondence should be addressed.
Received: 7 November 2018 / Revised: 22 December 2018 / Accepted: 25 December 2018 / Published: 10 January 2019
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The wireless channel is volatile in nature, due to various signal attenuation factors including path-loss, shadowing, and multipath fading. Existing media access control (MAC) protocols, such as the widely adopted 802.11 wireless fidelity (Wi-Fi) family, advocate masking harsh channel conditions with persistent retransmission and backoff, in order to provide a packet-level best-effort service. However, the asymmetry of the network environment of client nodes in space is not fully considered in the method, which leads to the decline of the transmission efficiency of the good ones. In this paper, we propose CoFi, a coding-assisted file distribution protocol for 802.11 based wireless local area networks (LANs). CoFi groups data into batches and transmits a random linear combination of packets within each batch, thereby reducing redundant packet and acknowledgement (ACK) retransmissions when the channel is lossy. In addition, CoFi adopts a MAC layer caching scheme that allows clients to store the overheard coded packets and use such cached packets to assist nearby peers. With this measure, it further improves the effective throughput and shortens the buffering delay when running applications such as bulk data transmission and video streaming. Our trace based simulation demonstrates that CoFi can maintain a similar level of packet delay to 802.11, but increases the throughput performance by a significant margin in a lossy wireless LAN. Furthermore, we perform a reverse-engineering on CoFi and 802.11 using a simple analytical framework, proving that they asymptotically approach different fairness measures, thus resulting in a disparate performance. View Full-Text
Keywords: CoFi distribution protocol; delay; harsh channel condition; hybrid coding scheme; IEEE802.11 standard; internet of things; media access control protocol; throughput; Wi-Fi CoFi distribution protocol; delay; harsh channel condition; hybrid coding scheme; IEEE802.11 standard; internet of things; media access control protocol; throughput; Wi-Fi

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Ma, N.; Diao, M. CoFi: Coding-Assisted File Distribution over a Wireless LAN. Symmetry 2019, 11, 71.

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