Literature Database Entry


Gurjashan Singh Pannu, "Design and Evaluation of Unicast Retransmission Techniques in Vehicular Communications," Master's Thesis, Department of Computer Science, Paderborn University, July 2017. (Advisors: Florian Klingler and Falko Dressler)


Broadcasting is commonly used for exchanging information in Vehicular Ad Hoc Networks (VANETs). However, the source never gets any feedback for the lost broadcasts. For reliability, unicast communication with MAC Acknowledgment (ACK) frames can be used. Missing an ACK frame causes retransmissions of the failed unicast packet. Consequently, the trailing packets enqueued in Enhanced Distributed Channel Access (EDCA) transmit queues momentarily experience head- of-line (HOL) blocking. A previous research [1] demonstrated that highly dynamic VANETs experience frequent unicast packet losses and thereby, frequent HOL blocking on the transmit queues. Under frequent blocking conditions, the queuing time of the safety related broadcast packets in the transmit queues easily crosses the acceptable limits (∼200ms), thereby causing the safety related information to be outdated. We present E2DCA, an enhanced EDCA system in IEEE 802.11p MAC layer, which is robust to failed unicast communications in VANETs. The designed system is capable of creating on-demand backup transmit queues per-destination which hold the failed unicast packets. This removes the HOL blocking on the queue holding the broadcasts and unicast to other destinations. Because of the existence of several transmit queues in E2DCA, a combination of scheduling policies like round robin and priority scheduling is used to select a queue for the next transmission. To investigate the performance of E2DCA in comparison with IEEE 802.11p, we considered two cases: 1) When a malicious app is trying to exploit the IEEE 802.11p unicast loophole and consequently block the broadcast packets. 2) When all apps are genuine and the unicast failure is only due to packet collisions or vehicles moving out of the communication range. For both cases, an extensive simulation study was conducted in a highway, Manhattan Grid and Luxembourg City scenario. We found that by using E2DCA in Luxembourg City scenario, the queuing time of the broadcasts reduced by 95 \% and 83 \% in 1) and 2) respectively in comparison with IEEE 802.11p standard. Additionally, the end-to-end delay for the unicast packets also improved while the other metrics remain comparable.

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Gurjashan Singh Pannu

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    author = {Pannu, Gurjashan Singh},
    advisor = {Klingler, Florian and Dressler, Falko},
    title = {{Design and Evaluation of Unicast Retransmission Techniques in Vehicular Communications}},
    institution = {Department of Computer Science},
    year = {2017},
    month = {July},
    school = {Paderborn University},
    type = {Master's Thesis},

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