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Network Simulator 3 (ns-3.16) Patches (Version 1.0)

for Vehicle-2-Vehicle Broadcast Simulations

Developed 2013-2014

These patches have been developed jointly at WINLAB, Rutgers University and West Virginia

University as part of the V2V safety communications scalability activity of the Interoperability

Issues of Vehicle-to-Vehicle Based Safety Systems (V2V-Interoperability) Project headed by the

Crash Avoidance Metrics Partnership (CAMP) Vehicle Safety Communications 3 (VSC3)

Consortium, in partnership with the United States Department of Transportation (USDOT).

plus one SlotTime before decrementation in the DCF. In the latter case, if the medium becomes

busy again during this slot time, the backoff timer remains unchanged. Therefore, to accurately

implement the EDCA functionality, the backoff timer needs to be changed in ns-3 simulator.

The modification steps are as follows: First, the idle duration of medium is tracked by each station.

Once the idle duration of one station becomes greater than or equal to AIFS, the next step is

triggered. In step two, the slot boundary of AIFS is identified and the potential decrement for the

backoff timer counter is increased by one. Hence, the length of the idle duration after AIFS is

divided by the length of one SlotTime and, in step three, the backoff timer counter is decremented

by the quotient plus one. When the backoff timer reaches zero, the station is allowed to

immediately transmit after the medium becomes idle for one AIFS.

Additional Backoff Timer Trigger

EDCA-mac-fixes-patches.tar.gz

In ns-3, once a frame is generated in the upper layer and ready for transmission, the station requests

to access to the medium immediately. According to the standard, there are two possible situations

for this access request.

• If the medium is busy as indicated by either physical or virtual carrier sensing, and the

counter of backoff timer is equal to zero, the station should invoke a backoff procedure.

• If the counter of backoff timer is equal to zero and the medium is idle for at least one AIFS

(i.e., the medium is not seized by another station), the station should immediately start the

transmission.

Taking into consideration the situation where the counter of backoff timer is zero and the idle

duration is less than one AIFS. There are two options: after AIFS, the station either transmits the

frame immediately, or initiates an additional backoff procedure. Based on the conditions for

initiating a transmission for EDCA in the 802.11 standard: “there is a frame available for

transmission at that Enhanced Distributed Channel Access Function (EDCAF), and the backoff

timer for that EDCAF has a value of 0”. Although the situation fits the condition, the second option

is chosen, since even though the medium is indicated as idle when the station claims its request,

the medium might not be truly idle. In other words, the AIFS is a part of the EDCA function that

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评论1

白嫖客

2021-04-19

全英文的，读的有点累。

Jerry&张

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