Bugzilla – Bug 2770
Simulation fails if multiple stations support different number of spatial streams
Last modified: 2017-09-25 14:27:51 UTC
Hello, I have encountered a problem and I summarized it also in ns-3-users group: https://groups.google.com/forum/#!searchin/ns-3-users/txvector.SetPreambleType$20(WIFI_PREAMBLE_HT_MF)$3B%7Csort:relevance/ns-3-users/fD8zUS5QICI/g6GqZ0SDBAAJ I had the problem that with 3 antenna AP and 3 antenna STA, the number of streams in good channel conditions was not going up to 3 streams. It used to stay constant at 2 streams. After long investigations I found out that the throughput calculated for 2 streams was higher than 3 streams. The problem has to do with the preamble type set in CalculateFirstMpduTxDuration. txvector.SetPreambleType (WIFI_PREAMBLE_HT_MF); I am using the 802.11ac standard, maybe this header is old. Changing it this line to txvector.SetPreambleType (WIFI_PREAMBLE_NONE); fixes the problem but maybe it should be the WIFI_PREAMBLE_VHT type? I have not seen this preamble setting in ns-3.26 but it exists in ns-3-dev. Therefore, I have selected the version as 3.26.
Is this your proposed fix? MinstrelHtWifiManager::CalculateFirstMpduTxDuration (Ptr<WifiPhy> phy, uint8_t s txvector.SetGuardInterval (sgi ? 400 : 800); txvector.SetChannelWidth (chWidth); txvector.SetNess (0); txvector.SetStbc (phy->GetStbc ()); txvector.SetMode (mode); - txvector.SetPreambleType (WIFI_PREAMBLE_HT_MF); + txvector.SetPreambleType (WIFI_PREAMBLE_NONE); return phy->CalculateTxDuration (m_frameLength, txvector, phy->GetFrequency (), MPDU_IN_AGGREGATE, 0); } I would like the view of Mathias before pushing this, because I do not see a link between the preamble type and your issue. Did you enabled Greenfield mode?
Hi. I don't think that is a bug. You have to consider the preamble when calculating the TX time. Akin can you share a test case? I have just tested MinstrelHt with wifi-manager-example and it uses 3 streams correctly.
Back in the time, possibly around June, even though the SINR was high, it was not switching to 3 antennas. If it does with your most recent, then this bug is obsolete.
Akin, Do you mind giving a try with the latest ns-3-dev so that this bug can be closed? Thanks!
Sebastien, I have new errors with the script I used to test. Not sure if it is because of substantially modified code. run it with: ./waf --run 'scratch/vht_network_from_omer --nWifiAp=1 --nWifiSta=2 --udp=1 --ideal=2 --nssAp=3 --nssSta1=2 --nssSta2=1 --speed=0.0 --simulationTime=10.0 --fading=0 --distance=5' and you get the following error: msg="Reception ends in failure because of an unsupported number of spatial streams", file=../src/wifi/model/wifi-phy.cc, line=2399 terminate called without an active exception
Created attachment 2920 [details] test script
I think I got it. The assert is not correct: all stations receive the frame at PHY, it is only at MAC layer that it gets dropped if it is not the recipient. So, even the station with a single antenna received the frame sent with NSS=2. IMO, it should be dropped at PHY since it cannot decode it. I will work on a solution.
Created attachment 2921 [details] proposed solution
Please confirm this solves the issue, so I can push the solution.
OK, the simulation did not fail this time, so this bug is fixed.
Fixed in changeset 13079:a9e130d43da8