Multi Sta - Channel Sharing-AirtimeFairness Problem

[Omer faruk Topal]

Hi ,

I am working to analyze the throughput change in the multi sta case in 802.11ac. In my scenario, there is one AP and its 2 STA which use the same channel. The problem is that  while STA1 is moving away and STA2 is so close to AP, the throughput of STA1 is decreasing as it expected ,However throughput of STA2  decreases at first but increases after a point though the STA1 throughput is still in decrease.
           
Constant    Constant                                                                                    Moving

[    AP  -----  STA2---------------------------------  d  -------------------------------------------------STA1               ]
[             Throughput : decrease                                                    Throughput : decrease       ]
[                                decrease                                                                       decrease        ]
[                                increase                                                                        decrease        ]
[                                increase                                                                        decrease        ]

What is the reason of this abnormal throughput increasing at STA2?

Normally, with DCF mechanism , due to increasing in airtime usage by STA1, the channel gives less airtime to STA2 . Therefore, STA2's throughput should  decrease over distance.

Question : The Airtime Fairness Mechanism was supported in ns3.26?

(Qos-NonQos modes was used but don't solve the problem)
(UDP-802.11ac-MinstrelRateControlAlgorithm)
 


 I would be appreciated if you helping or answering.
Thank You...

[Rediet]

Hi,

It looks very much like a hidden node scenario where STA1 is still in reach of AP but out of reach of STA2. However, your illustration doesn't seem to correspond and this would be the case for UL but not DL (b/c normally AP is still in reach of both STAs).

Regards,

Rediet

[Omer faruk Topal]

Hi Rediet,

I think that it s not in a hidden node case since the CST of the network is at default value(-99 dBm) , hence all the network nodes senses each other. What do you  mean by UL and DL ??  Also I examined the  data traffic from wireshark with pcap traces. The moving away STA has so less data traffic and also contention in network. When the sta moves away ,its channel access reduces a lot.

 Does the access priority effect from rss levels for current Qos or DCF ? Can we comment this as the closest sta has more priority than the other to access the channel?

Thank You for Answering,
Ömer   


28 Şubat 2017 Salı 11:52:31 UTC+3 tarihinde Rediet yazdı:

[Tommaso Pecorella]

Hi,

about the Airtime Fairness Mechanism you should ask the wifi module maintainer.

About your "strange" behaviour, you didn't say how you're calculating or using the channel. If you're using TCP, then the effect could be normal. Try using UDP.

T.

[Omer faruk Topal]

Hi,

 thank you for answering,

I stated them at the first post like (UDP_Minstrelratecontrol)

I am working with UDP 802.11 ac and use Minstrel Rate Control algorithm.Also there is only logdistance pathloss in the channel model.

I dont think that the airtime fairness mechanism is implemented , neverthless , I will contact with the wifi maintainer.

Thank you 

Regards

5 Mar 2017 03:09 tarihinde "Tommaso Pecorella" <tomm...@gmail.com> yazdı:

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[Rediet]

Hello Ömer,

Sorry for the late reply. By UL/DL, I was meaning STA-to-AP/AP-to-STA. It would be very awkward if you had such a behavior with DL (i.e. AP-to-STA) UDP traffic.

Once you contact the maintainer, as per Tommaso's suggestion, could you please consider posting the conclusion? It would be interesting to have it.

Regards,

Rediet

To unsubscribe from this group and all its topics, send an email to ns-3-users+...@googlegroups.com.

[Omer faruk Topal]

Hi,

The problem was solved .The reason of accessing the channel less for STA2 is due to increasing CW. Since the far STA(STA2) has many failure transmissions , it increases its Contention Window size. Therefore it behaves as  the STA1 increases its channel access priority against STA2.Then the throughput of STA1 increases after a point while the STA2 's airtime is in increasing(but its channel access reducing too much.)
 
Regards,

Ömer

6 Mart 2017 Pazartesi 11:43:45 UTC+3 tarihinde Rediet yazdı: