Fix VHT short-GI timing and mode-set remapping

Use 3.6 us raw VHT data symbols for short guard intervals and round the aggregate data duration to a 4 us boundary according to IEEE 802.11-2024. Keep VHT signaling intervals and rates independent of the data guard interval.

Add an exact PHY compatibility lookup for mode-set transitions. Preserve bitrate, bandwidth, spatial-stream count, and modeled guard-interval presence, and reject incompatible transitions before mutating transmitter state.

Document radio command precedence and rate-selection guard-interval qualifiers. Extend the focused IEEE 802.11 guard-interval test with VHT rounding boundaries, signaling checks, compatible and rejected mode-set transitions, and atomic state preservation.

Validated with the debug build, the filtered Ieee80211HtGuardInterval_1 unit test, and the lan80211ac Ping1 fingerprint.

Author: mgonzalezlopezudc

src/inet/linklayer/ieee80211/mac/rateselection/QosRateSelection.ned

@@ -33,7 +33,7 @@ simple QosRateSelection extends SimpleModule
         double dataFrameBitrate @unit(bps) = default(-1bps); // Fastest
         double dataFrameBandwidth @unit(Hz) = default(nan Hz); // Explicit mode qualifier when dataFrameBitrate is specified
         int dataFrameNumSpatialStreams = default(-1); // Explicit mode qualifier when dataFrameBitrate is specified
-        double dataFrameGuardInterval @unit(s) = default(-1s); // Explicit mode qualifier when dataFrameBitrate is specified
+        double dataFrameGuardInterval @unit(s) = default(-1s); // Explicit mode qualifier when dataFrameBitrate is specified; negative means unspecified, otherwise it must equal the selected PHY mode's modeled GI
 
         double mgmtFrameBitrate @unit(bps) = default(-1bps); // Fastest
         double controlFrameBitrate @unit(bps) = default(-1bps);

src/inet/linklayer/ieee80211/mac/rateselection/RateSelection.ned

@@ -28,7 +28,7 @@ simple RateSelection extends SimpleModule like IRateSelection
         double dataFrameBitrate @unit(bps) = default(-1bps); // Fastest
         double dataFrameBandwidth @unit(Hz) = default(nan Hz); // Explicit mode qualifier when dataFrameBitrate is specified
         int dataFrameNumSpatialStreams = default(-1); // Explicit mode qualifier when dataFrameBitrate is specified
-        double dataFrameGuardInterval @unit(s) = default(-1s); // Explicit mode qualifier when dataFrameBitrate is specified
+        double dataFrameGuardInterval @unit(s) = default(-1s); // Explicit mode qualifier when dataFrameBitrate is specified; negative means unspecified, otherwise it must equal the selected PHY mode's modeled GI
 
         double mgmtFrameBitrate @unit(bps) = default(-1bps); // Fastest
         double controlFrameBitrate @unit(bps) = default(-1bps);

src/inet/physicallayer/wireless/ieee80211/mode/Ieee80211ModeSet.cc

@@ -520,6 +520,33 @@ bool Ieee80211ModeSet::getIsMandatory(const IIeee80211Mode *mode) const
     return entries[getModeIndex(mode)].isMandatory;
 }
 
+const IIeee80211Mode *Ieee80211ModeSet::findCompatibleMode(const IIeee80211Mode *mode) const
+{
+    if (mode == nullptr)
+        return nullptr;
+
+    const auto sourceDataMode = mode->getDataMode();
+    const auto sourceBitrate = sourceDataMode->getNetBitrate();
+    const auto sourceBandwidth = sourceDataMode->getBandwidth();
+    const auto sourceGuardInterval = sourceDataMode->getGuardInterval();
+    const auto minBitrate = sourceBitrate - Mbps(0.05);
+    const auto maxBitrate = sourceBitrate + Mbps(0.05);
+    for (const auto& entry : entries) {
+        const auto candidateDataMode = entry.mode->getDataMode();
+        const auto candidateBandwidth = candidateDataMode->getBandwidth();
+        const auto candidateGuardInterval = candidateDataMode->getGuardInterval();
+        const bool bandwidthMatches = (std::isnan(sourceBandwidth.get()) && std::isnan(candidateBandwidth.get())) ||
+                (!std::isnan(sourceBandwidth.get()) && !std::isnan(candidateBandwidth.get()) && sourceBandwidth == candidateBandwidth);
+        const bool guardIntervalMatches = (sourceGuardInterval < SIMTIME_ZERO && candidateGuardInterval < SIMTIME_ZERO) ||
+                (sourceGuardInterval >= SIMTIME_ZERO && candidateGuardInterval == sourceGuardInterval);
+        if (minBitrate <= candidateDataMode->getNetBitrate() && candidateDataMode->getNetBitrate() <= maxBitrate &&
+            bandwidthMatches && candidateDataMode->getNumberOfSpatialStreams() == sourceDataMode->getNumberOfSpatialStreams() &&
+            guardIntervalMatches)
+            return entry.mode;
+    }
+    return nullptr;
+}
+
 const IIeee80211Mode *Ieee80211ModeSet::findMode(bps bitrate, Hz bandwidth, int numSpatialStreams, simtime_t guardInterval) const
 {
     return findMode(bitrate - Mbps(0.05), bitrate + Mbps(0.05), bandwidth, numSpatialStreams, guardInterval);

src/inet/physicallayer/wireless/ieee80211/mode/Ieee80211ModeSet.h

@@ -52,6 +52,9 @@ class INET_API Ieee80211ModeSet : public IPrintableObject, public cObject
 
     bool containsMode(const IIeee80211Mode *mode) const { return findModeIndex(mode) != -1; }
     bool getIsMandatory(const IIeee80211Mode *mode) const;
+    // Finds a mode with the same PHY tuple as mode. Unlike findMode(), this
+    // treats an absent guard interval (negative value) as an exact value.
+    const IIeee80211Mode *findCompatibleMode(const IIeee80211Mode *mode) const;
 
     const IIeee80211Mode *findMode(bps bitrate, Hz bandwidth = Hz(NaN), int numSpatialStreams = -1, simtime_t guardInterval = -1) const;
     const IIeee80211Mode *findMode(bps minBitrate, bps maxBitrate, Hz bandwidth = Hz(NaN), int numSpatialStreams = -1, simtime_t guardInterval = -1) const;

src/inet/physicallayer/wireless/ieee80211/mode/Ieee80211VhtMode.cc

@@ -258,12 +258,9 @@ const simtime_t Ieee80211VhtPreambleMode::getDuration() const
 bps Ieee80211VhtSignalMode::computeGrossBitrate() const
 {
     unsigned int numberOfCodedBitsPerSymbol = modulation->getSubcarrierModulation()->getCodeWordSize() * getNumberOfDataSubcarriers();
-    if (guardIntervalType == HT_GUARD_INTERVAL_LONG)
-        return bps(numberOfCodedBitsPerSymbol / getSymbolInterval());
-    else if (guardIntervalType == HT_GUARD_INTERVAL_SHORT)
-        return bps(numberOfCodedBitsPerSymbol / getShortGISymbolInterval());
-    else
-        throw cRuntimeError("Unknown guard interval type");
+    // IEEE Std 802.11-2024, Table 21-5: VHT-SIG fields use TSYML even
+    // when the Data field uses short GI; their signaling rate is GI-independent.
+    return bps(numberOfCodedBitsPerSymbol / getSymbolInterval());
 }
 
 bps Ieee80211VhtSignalMode::computeNetBitrate() const
@@ -646,6 +643,19 @@ const simtime_t Ieee80211VhtDataMode::getDuration(b dataLength) const
     return numberOfSymbols * getSymbolInterval();
 }
 
+const simtime_t Ieee80211VhtMode::getDataDuration(b dataBitLength) const
+{
+    auto dataDuration = dataMode->getDuration(dataBitLength);
+    if (dataMode->getGuardInterval() == dataMode->getShortGIDuration()) {
+        // IEEE Std 802.11-2024, 21.4.3, Eq. (21-109): short-GI VHT data
+        // airtime is the raw TSYMS train rounded up to a TSYML boundary.
+        const auto longGiSymbolInterval = dataMode->getDFTPeriod() + dataMode->getGIDuration();
+        const auto numberOfLongGiSymbols = (dataDuration.raw() + longGiSymbolInterval.raw() - 1) / longGiSymbolInterval.raw();
+        dataDuration = SimTime::fromRaw(numberOfLongGiSymbols * longGiSymbolInterval.raw());
+    }
+    return dataDuration;
+}
+
 const simtime_t Ieee80211VhtMode::getSlotTime() const
 {
     if (centerFrequencyMode == BAND_5GHZ)

src/inet/physicallayer/wireless/ieee80211/mode/Ieee80211VhtMode.h

@@ -96,6 +96,8 @@ class INET_API Ieee80211VhtSignalMode : public IIeee80211HeaderMode, public Ieee
     virtual b getLength() const override;
     virtual bps getNetBitrate() const override { return Ieee80211VhtModeBase::getNetBitrate(); }
     virtual bps getGrossBitrate() const override { return Ieee80211VhtModeBase::getGrossBitrate(); }
+    // IEEE Std 802.11-2024, Table 21-5: VHT-SIG uses the long-GI symbol
+    // interval independently of the data field's selected guard interval.
     virtual const simtime_t getSymbolInterval() const override { return Ieee80211HtTimingRelatedParametersBase::getSymbolInterval(); }
     virtual const Ieee80211OfdmModulation *getModulation() const override { return modulation; }
     virtual const Ieee80211VhtCode *getCode() const { return code; }
@@ -239,7 +241,9 @@ class INET_API Ieee80211VhtDataMode : public IIeee80211DataMode, public Ieee8021
     virtual const Ieee80211Vhtmcs *getModulationAndCodingScheme() const { return modulationAndCodingScheme; }
     virtual const Ieee80211VhtCode *getCode() const { return modulationAndCodingScheme->getCode(); }
     virtual const simtime_t getGuardInterval() const override { return guardIntervalType == HT_GUARD_INTERVAL_LONG ? getGIDuration() : getShortGIDuration(); }
-    virtual const simtime_t getSymbolInterval() const override { return Ieee80211HtTimingRelatedParametersBase::getSymbolInterval(); }
+    // IEEE Std 802.11-2024, Tables 21-5 and 21-8: the VHT Data symbol
+    // interval is TSYML for long GI and TSYMS for short GI.
+    virtual const simtime_t getSymbolInterval() const override { return getDFTPeriod() + getGuardInterval(); }
     virtual const Ieee80211OfdmModulation *getModulation() const override { return modulationAndCodingScheme->getModulation(); }
 };
 
@@ -282,10 +286,10 @@ class INET_API Ieee80211VhtMode : public Ieee80211ModeBase
     virtual int getMpduMaxLength() const override { return 65535; } // in octets
     virtual BandMode getCenterFrequencyMode() const { return centerFrequencyMode; }
 
-    virtual const simtime_t getDuration(b dataBitLength) const override { return preambleMode->getDuration() + dataMode->getDuration(dataBitLength); }
+    virtual const simtime_t getDuration(b dataBitLength) const override { return preambleMode->getDuration() + getDataDuration(dataBitLength); }
     virtual const simtime_t getPreambleDuration() const override { return preambleMode->getDurationBeforeHeader(); }
     virtual const simtime_t getHeaderDuration() const override { return preambleMode->getDuration() - getPreambleDuration(); }
-    virtual const simtime_t getDataDuration(b dataBitLength) const override { return dataMode->getDuration(dataBitLength); }
+    virtual const simtime_t getDataDuration(b dataBitLength) const override;
 };
 
 // A specification of the high-throughput (HT) physical layer (PHY)

src/inet/physicallayer/wireless/ieee80211/packetlevel/Ieee80211ControlInfo.msg

@@ -17,9 +17,9 @@ namespace inet::physicallayer;
 //
 class Ieee80211ConfigureRadioCommand extends ConfigureRadioCommand
 {
-    string opMode;                         // new default operation mode or "" if not set.
-    const Ieee80211ModeSet *modeSet;       // new default mode set or nullptr if not set.
-    const IIeee80211Mode *mode;            // new default transmission mode or nullptr if not set.
+    string opMode;                         // new default operation mode or "" if not set; ignored when modeSet is set.
+    const Ieee80211ModeSet *modeSet;       // new default mode set or nullptr if not set; takes precedence over opMode.
+    const IIeee80211Mode *mode;            // new default transmission mode or nullptr if not set; atomically validated against the resolved mode set.
     IIeee80211Band *band;                  // new default band or nullptr if not set.
     Ieee80211Channel *channel;             // new default band and channel or nullptr if not set.
     int channelNumber = -1;                // new default channel number in the range [0, numChannels] or -1 if not set.

src/inet/physicallayer/wireless/ieee80211/packetlevel/Ieee80211Transmitter.cc

@@ -77,8 +77,9 @@ void Ieee80211Transmitter::setModeSet(const Ieee80211ModeSet *modeSet)
     if (this->modeSet != modeSet) {
         auto newMode = mode;
         if (mode != nullptr && modeSet != nullptr && !modeSet->containsMode(mode)) {
-            auto dataMode = mode->getDataMode();
-            newMode = modeSet->getMode(dataMode->getNetBitrate(), dataMode->getBandwidth(), dataMode->getNumberOfSpatialStreams(), dataMode->getGuardInterval());
+            newMode = modeSet->findCompatibleMode(mode);
+            if (newMode == nullptr)
+                throw cRuntimeError("Cannot map current mode to operation mode '%s' without changing bitrate, bandwidth, spatial streams, or guard interval", modeSet->getName());
         }
         else if (modeSet == nullptr)
             newMode = nullptr;

src/inet/physicallayer/wireless/ieee80211/packetlevel/Ieee80211Transmitter.h

@@ -38,6 +38,8 @@ class INET_API Ieee80211Transmitter : public FlatTransmitterBase
     virtual const IIeee80211Mode *computeTransmissionMode(const Packet *packet) const;
     virtual const Ieee80211Channel *computeTransmissionChannel(const Packet *packet) const;
 
+    // Re-selects the current mode only when bitrate, bandwidth, NSS, and GI
+    // remain compatible. Use setModeSetAndMode for an explicit transition.
     virtual void setModeSet(const Ieee80211ModeSet *modeSet);
     // Applies a mode set and an explicitly selected mode as one validated update.
     virtual void setModeSetAndMode(const Ieee80211ModeSet *modeSet, const IIeee80211Mode *mode);

tests/unit/Ieee80211HtGuardInterval_1.test

@@ -226,6 +226,46 @@ const auto legacyOfdmModeSet = Ieee80211ModeSet::getModeSet("a");
 ASSERT(legacyOfdmModeSet->findMode(Mbps(6), Hz(NaN), -1, SimTime(800, SIMTIME_NS)) != nullptr);
 ASSERT(legacyOfdmModeSet->findMode(Mbps(6), Hz(NaN), -1, SimTime(400, SIMTIME_NS)) == nullptr);
 
+// Mode-set remapping preserves the complete modeled PHY tuple. In
+// particular, a negative GI is an actual absence for compatibility lookup,
+// not findMode()'s public wildcard.
+const auto erpModeSet = Ieee80211ModeSet::getModeSet("g(erp)");
+const auto pModeSet = Ieee80211ModeSet::getModeSet("p");
+const auto aMode = legacyOfdmModeSet->getMode(Mbps(6), MHz(20), 1, SimTime(800, SIMTIME_NS));
+const auto erpMode = erpModeSet->findCompatibleMode(aMode);
+ASSERT(erpMode != nullptr);
+ASSERT(erpMode->getDataMode()->getNetBitrate() == aMode->getDataMode()->getNetBitrate());
+ASSERT(erpMode->getDataMode()->getBandwidth() == aMode->getDataMode()->getBandwidth());
+ASSERT(erpMode->getDataMode()->getGuardInterval() == aMode->getDataMode()->getGuardInterval());
+
+const auto dsssModeSet = Ieee80211ModeSet::getModeSet("b");
+const auto mixedModeSet = Ieee80211ModeSet::getModeSet("g(mixed)");
+const auto dsssMode = dsssModeSet->getMode(Mbps(1));
+ASSERT(dsssMode->getDataMode()->getGuardInterval() < SIMTIME_ZERO);
+ASSERT(mixedModeSet->findCompatibleMode(dsssMode) != nullptr);
+
+TestIeee80211Transmitter legacyTransmitter;
+legacyTransmitter.setModeSet(legacyOfdmModeSet);
+legacyTransmitter.setMode(aMode);
+legacyTransmitter.setModeSet(erpModeSet);
+ASSERT(legacyTransmitter.getSelectedModeSet() == erpModeSet);
+ASSERT(legacyTransmitter.getSelectedMode() == erpMode);
+const auto modeBeforeRejectedTransition = legacyTransmitter.getSelectedMode();
+bool rejectedIncompatibleModeSet = false;
+try {
+    legacyTransmitter.setModeSet(pModeSet);
+}
+catch (cRuntimeError&) {
+    rejectedIncompatibleModeSet = true;
+}
+ASSERT(rejectedIncompatibleModeSet);
+ASSERT(legacyTransmitter.getSelectedModeSet() == erpModeSet);
+ASSERT(legacyTransmitter.getSelectedMode() == modeBeforeRejectedTransition);
+const auto pMode = pModeSet->getMode(2); // the declared 6 Mbps 10 MHz mode
+legacyTransmitter.setModeSetAndMode(pModeSet, pMode);
+ASSERT(legacyTransmitter.getSelectedModeSet() == pModeSet);
+ASSERT(legacyTransmitter.getSelectedMode() == pMode);
+
 Ieee80211VhtCompliantModes::getCompliantMode(&Ieee80211VhtmcsTable::vhtMcs0BW20MHzNss1,
         Ieee80211VhtMode::BAND_5GHZ, Ieee80211VhtPreambleMode::HT_PREAMBLE_MIXED,
         Ieee80211VhtModeBase::HT_GUARD_INTERVAL_LONG);
@@ -240,6 +280,30 @@ catch (cRuntimeError&) {
 }
 ASSERT(rejectedVhtGreenfieldAfterMixed);
 const auto vhtModeSet = Ieee80211ModeSet::getModeSet("ac");
+const auto vhtLongMcs0 = Ieee80211VhtCompliantModes::getCompliantMode(
+        &Ieee80211VhtmcsTable::vhtMcs0BW20MHzNss1, Ieee80211VhtMode::BAND_5GHZ,
+        Ieee80211VhtPreambleMode::HT_PREAMBLE_MIXED, Ieee80211VhtModeBase::HT_GUARD_INTERVAL_LONG);
+const auto vhtShortMcs0 = Ieee80211VhtCompliantModes::getCompliantMode(
+        &Ieee80211VhtmcsTable::vhtMcs0BW20MHzNss1, Ieee80211VhtMode::BAND_5GHZ,
+        Ieee80211VhtPreambleMode::HT_PREAMBLE_MIXED, Ieee80211VhtModeBase::HT_GUARD_INTERVAL_SHORT);
+// IEEE Std 802.11-2024, Tables 21-5/21-8 and 21.4.3, Eqs. (21-109)/(21-110).
+ASSERT(vhtLongMcs0->getDataMode()->getSymbolInterval() == SimTime(4, SIMTIME_US));
+ASSERT(vhtShortMcs0->getDataMode()->getSymbolInterval() == SimTime(3600, SIMTIME_NS));
+ASSERT(vhtLongMcs0->getHeaderMode()->getSymbolInterval() == SimTime(4, SIMTIME_US));
+ASSERT(vhtShortMcs0->getHeaderMode()->getSymbolInterval() == SimTime(4, SIMTIME_US));
+ASSERT(vhtLongMcs0->getHeaderMode()->getNetBitrate() == vhtShortMcs0->getHeaderMode()->getNetBitrate());
+ASSERT(vhtLongMcs0->getHeaderMode()->getGrossBitrate() == vhtShortMcs0->getHeaderMode()->getGrossBitrate());
+ASSERT(vhtShortMcs0->getDataMode()->getDuration(B(24)) == SimTime(32400, SIMTIME_NS));
+ASSERT(vhtShortMcs0->getDataDuration(B(24)) == SimTime(36, SIMTIME_US));
+ASSERT(vhtShortMcs0->getDataMode()->getDuration(B(27)) == SimTime(36, SIMTIME_US));
+ASSERT(vhtShortMcs0->getDataDuration(B(27)) == SimTime(36, SIMTIME_US));
+ASSERT(vhtShortMcs0->getDataMode()->getDuration(B(30)) == SimTime(39600, SIMTIME_NS));
+ASSERT(vhtShortMcs0->getDataDuration(B(30)) == SimTime(40, SIMTIME_US));
+ASSERT(vhtLongMcs0->getDataMode()->getDuration(B(24)) == SimTime(36, SIMTIME_US));
+ASSERT(vhtLongMcs0->getDataDuration(B(24)) == SimTime(36, SIMTIME_US));
+for (auto vhtMode : {vhtLongMcs0, vhtShortMcs0})
+    for (auto dataLength : {B(24), B(27), B(30)})
+        ASSERT(vhtMode->getDuration(dataLength) == vhtMode->getPreambleDuration() + vhtMode->getHeaderDuration() + vhtMode->getDataDuration(dataLength));
 bool foundVhtLongGuardInterval = false;
 bool foundVhtShortGuardInterval = false;
 for (int index = 0; index < vhtModeSet->getNumModes(); index++) {