Bandwidth in (inet::physicallayer::Ieee80211Radio) different from bandwidth in (inet::physicallayer::WirelessSignal). Why?

[arahman33]

I am trying to understand the different opModes of Ieee80211 in Ieee80211ModeSet.cc. I have the following setup in my .ini file

**.opMode = "n(mixed-2.4Ghz)"
**.bandName = "5 GHz (40 MHz)"
**.bandwidth = 40MHz

For this, I can see during the initializations that the bandwidth is set as I wanted. (text in bold)

INFO: Initialized (inet::physicallayer::Ieee80211Radio)radio id=1317, antenna = { IsotropicAntenna }, transmitter = { Ieee80211ScalarTransmitter, modeSet = { Ieee80211ModeSet, name = n(mixed-2.4Ghz) }, band = { Ieee80211Band, name = 5 GHz (40 MHz) }, mode = { object@0x28978aaf308 }, channel = { Ieee80211Channel, band = { Ieee80211Band, name = 5 GHz (40 MHz) }, channelNumber = 0 }, preambleDuration = -1, headerLength = 24 B, bitrate = -1 bps, codeRate = 1, power = 2.5 mW, modulation = { BpskModulation }, centerFrequency = 5.02 GHz, bandwidth = 40 MHz }, receiver = { Ieee80211ScalarReceiver, modeSet = { Ieee80211ModeSet, name = n(mixed-2.4Ghz) }, band = { Ieee80211Band, name = 5 GHz (40 MHz) }, channel = { Ieee80211Channel, band = { Ieee80211Band, name = 5 GHz (40 MHz) }, channelNumber = 0 }, errorModel = { Ieee80211NistErrorModel }, energyDetection = 3.16228 pW, sensitivity = 3.16228 pW, modulation = { BpskModulation }, centerFrequency = 5.02 GHz, bandwidth = 40 MHz, snirThreshold = 2.51189 }

But as the emulation takes place I can see that the bandwidth in WIRELESS SIGNAL changes as the following:

INFO: Transmission started: (inet::physicallayer::WirelessSignal)IABData2-0 (80 us 355 B) (inet::Packet)IABData2-0 (355 B) (inet::SequenceChunk) length = 355 B WHOLE as Ieee80211ScalarTransmission, mode = { object@0x28978aaca18 }, channel = { Ieee80211Channel, channelNumber = 0 }, power = 2.2 mW, bitrate = 65 Mbps, headerLength = 6 B, dataLength = 2814 b, centerFrequency = 5.02 GHz, bandwidth = 20 MHz, modulation = { Ieee80211OfdmModulation }, id = 15, transmitterId = 16, startTime = 0.250056114244, endTime = 0.250136114244, preambleDuration = 0.000036, headerDuration = 0.000008, dataDuration = 0.000036, startPosition = (76.75, 145.695, 0) m, endPosition = (76.75, 145.695, 0) m, startOrientation = (1, 0, 0, 0), endOrientation = (1, 0, 0, 0)

I am not sure why this is happening and what is the physical meaning. From Ieee80211ModeSet.cc I saw that opModes n and ac have bandwidth 20, 40.. 160MHz. How can I get the modes operate in with those bandwidths?

I've updated the post from opMode "p" to "n(mixed-2.4Ghz).

[sadman-siraj]

I am facing a similar issue on my end with the defining the bandwidth. Did you find any solution regarding this?

[arahman33]

@sadman-siraj No I haven't figured it out yet.

@ZoltanBojthe, @levy can you please help us out on this matter?

[levy]

I think the bandwidth parameter is inherited from a base module and it is misleading because it gives you the impression that you can directly control the bandwidth of the signal. In 802.11, the bandwidth of the signal is determined by the mode selected by the MAC. If you dig deep into the 802.11 mode sets, you will see the individual modes have their own bandwidth parameters. For example, see the Ieee80211OfdmCompliantModes, the Ieee80211HtmcsTable class, etc.

[arahman33]

@levy where can I find the tables you have mentioned? I looked through the github repo but couldn't find it. I also looked through the file directories of inet4.5 but still couldn't find it. Is it the one in Ieee80211ModeSet.cc? Thanks in advance.

[levy]

Try searching for those class names in the src folder using the rg Ieee80211OfdmCompliantModes and rg Ieee80211HtmcsTable.

[aarizaq]

This is a quite old problem, I have suffered it about more of 2 years ago.
I solved this problem with this:
temp.patch.txt

[arahman33]

@aarizaq thanks for your reply. Can you walk me through the process? Where should I add the piece of code you have provided?

[aarizaq]

You can add it or you can use inetmanet,