From 7ee21c2cf83602f6eb9da7487a3e903f3d1f49ba Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Deronne?= <sebastien.deronne@gmail.com>
Date: Thu, 22 Aug 2019 13:49:40 +0200
Subject: [PATCH] wifi: Add methods to convert L-SIG length to HE TB PPDU
 duration and vice versa

---
 src/wifi/model/wifi-phy.cc | 31 +++++++++++++++++++++++++++++++
 src/wifi/model/wifi-phy.h  | 17 +++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/src/wifi/model/wifi-phy.cc b/src/wifi/model/wifi-phy.cc
index 188c2c309..434f2888d 100644
--- a/src/wifi/model/wifi-phy.cc
+++ b/src/wifi/model/wifi-phy.cc
@@ -4845,6 +4845,37 @@ WifiPhy::GetBand (uint16_t /*bandWidth*/, uint8_t /*bandIndex*/)
   return band;
 }
 
+uint16_t
+WifiPhy::ConvertHeTbPpduDurationToLSigLength (Time ppduDuration, WifiPhyBand band)
+{
+  uint8_t sigExtension = 0;
+  if (band == WIFI_PHY_BAND_2_4GHZ)
+    {
+      sigExtension = 6;
+    }
+  uint8_t m = 2; //HE TB PPDU so m is set to 2
+  uint16_t length = ((ceil ((static_cast<double> (ppduDuration.GetNanoSeconds () - (20 * 1000) - (sigExtension * 1000)) / 1000) / 4.0) * 3) - 3 - m);
+  return length;
+}
+
+Time
+WifiPhy::ConvertLSigLengthToHeTbPpduDuration (uint16_t length, WifiTxVector txVector, WifiPhyBand band)
+{
+  Time tSymbol = NanoSeconds (12800 + txVector.GetGuardInterval ());
+  Time preambleDuration = CalculatePhyPreambleAndHeaderDuration (txVector);
+  uint8_t sigExtension = 0;
+  if (band == WIFI_PHY_BAND_2_4GHZ)
+    {
+      sigExtension = 6;
+    }
+  uint8_t m = 2; //HE TB PPDU so m is set to 2
+  //Equation 27-11 of IEEE P802.11ax/D4.0
+  Time calculatedDuration = MicroSeconds (((ceil (static_cast<double> (length + 3 + m) / 3)) * 4) + 20 + sigExtension);
+  uint32_t nSymbols = floor (static_cast<double> ((calculatedDuration - preambleDuration).GetNanoSeconds () - (sigExtension * 1000)) / tSymbol.GetNanoSeconds ());
+  Time ppduDuration = preambleDuration + (nSymbols * tSymbol) + MicroSeconds (sigExtension);
+  return ppduDuration;
+}
+
 int64_t
 WifiPhy::AssignStreams (int64_t stream)
 {
diff --git a/src/wifi/model/wifi-phy.h b/src/wifi/model/wifi-phy.h
index 6b4990e74..42869282d 100644
--- a/src/wifi/model/wifi-phy.h
+++ b/src/wifi/model/wifi-phy.h
@@ -340,6 +340,23 @@ public:
    */
   Time GetLastRxEndTime (void) const;
 
+  /**
+   * \param ppduDuration the duration of the HE TB PPDU
+   * \param band the frequency band being used
+   *
+   * \return the L-SIG length value corresponding to that HE TB PPDU duration.
+   */
+  static uint16_t ConvertHeTbPpduDurationToLSigLength (Time ppduDuration, WifiPhyBand band);
+
+  /**
+   * \param length the L-SIG length value
+   * \param txVector the TXVECTOR used for the transmission of this HE TB PPDU
+   * \param band the frequency band being used
+   *
+   * \return the duration of the HE TB PPDU corresponding to that L-SIG length value.
+   */
+  static Time ConvertLSigLengthToHeTbPpduDuration (uint16_t length, WifiTxVector txVector, WifiPhyBand band);
+
   /**
    * \param size the number of bytes in the packet to send
    * \param txVector the TXVECTOR used for the transmission of this packet