96 

    97 

    98 WifiMode

    99 WifiPhy::GetPlcpHeaderMode (WifiMode payloadMode, WifiPreamble preamble)

   100 {

   101   switch (payloadMode.GetModulationClass ())

   102     {

   103     case WIFI_MOD_CLASS_OFDM:

   104       {

   105         switch (payloadMode.GetBandwidth ())

   106           {

   107           case 5000000:

   108             return WifiPhy::GetOfdmRate1_5MbpsBW5MHz ();

   109           case 10000000:

   110             return WifiPhy::GetOfdmRate3MbpsBW10MHz ();

   111           default:

   112             // IEEE Std 802.11-2007, 17.3.2

   113             // actually this is only the first part of the PlcpHeader,

   114             // because the last 16 bits of the PlcpHeader are using the

   115             // same mode of the payload

   116             return WifiPhy::GetOfdmRate6Mbps ();

   117           }

   118       }

   119 

   120     case WIFI_MOD_CLASS_ERP_OFDM:

   121       return WifiPhy::GetErpOfdmRate6Mbps ();

   122 

   123     case WIFI_MOD_CLASS_DSSS:

   124       if (preamble == WIFI_PREAMBLE_LONG)

   125         {

   126           // IEEE Std 802.11-2007, sections 15.2.3 and 18.2.2.1

   127           return WifiPhy::GetDsssRate1Mbps ();

   128         }

   129       else  //  WIFI_PREAMBLE_SHORT

   130         {

   131           // IEEE Std 802.11-2007, section 18.2.2.2

   132           return WifiPhy::GetDsssRate2Mbps ();

   133         }

   134 

   135     default:

   136       NS_FATAL_ERROR ("unsupported modulation class");

   137       return WifiMode ();

   138     }

   139 }

   140 

   141 uint32_t

   142 WifiPhy::GetPlcpHeaderDurationMicroSeconds (WifiMode payloadMode, WifiPreamble preamble)

   143 {

   144   switch (payloadMode.GetModulationClass ())

   145     {

   146     case WIFI_MOD_CLASS_OFDM:

   147       {

   148         switch (payloadMode.GetBandwidth ())

   149           {

   150           case 20000000:

   151           default:

   152             // IEEE Std 802.11-2007, section 17.3.3 and figure 17-4

   153             // also section 17.3.2.3, table 17-4

   154             // We return the duration of the SIGNAL field only, since the

   155             // SERVICE field (which strictly speaking belongs to the PLCP

   156             // header, see section 17.3.2 and figure 17-1) is sent using the

   157             // payload mode.

   158             return 4;

   159           case 10000000:

   160             // IEEE Std 802.11-2007, section 17.3.2.3, table 17-4

   161             return 8;

   162           case 5000000:

   163             // IEEE Std 802.11-2007, section 17.3.2.3, table 17-4

   164             return 16;

   165           }

   166       }

   167 

   168     case WIFI_MOD_CLASS_ERP_OFDM:

   169       return 16;

   170 

   171     case WIFI_MOD_CLASS_DSSS:

   172       if (preamble == WIFI_PREAMBLE_SHORT)

   173         {

   174           // IEEE Std 802.11-2007, section 18.2.2.2 and figure 18-2

   175           return 24;

   176         }

   177       else // WIFI_PREAMBLE_LONG

   178         {

   179           // IEEE Std 802.11-2007, sections 18.2.2.1 and figure 18-1

   180           return 48;

   181         }

   182 

   183     default:

   184       NS_FATAL_ERROR ("unsupported modulation class");

   185       return 0;

   186     }

   187 }

   188 

   189 uint32_t

   190 WifiPhy::GetPlcpPreambleDurationMicroSeconds (WifiMode payloadMode, WifiPreamble preamble)

   191 {

   192   switch (payloadMode.GetModulationClass ())

   193     {

   194     case WIFI_MOD_CLASS_OFDM:

   195       {

   196         switch (payloadMode.GetBandwidth ())

   197           {

   198           case 20000000:

   199           default:

   200             // IEEE Std 802.11-2007, section 17.3.3,  figure 17-4

   201             // also section 17.3.2.3, table 17-4

   202             return 16;

   203           case 10000000:

   204             // IEEE Std 802.11-2007, section 17.3.3, table 17-4

   205             // also section 17.3.2.3, table 17-4

   206             return 32;

   207           case 5000000:

   208             // IEEE Std 802.11-2007, section 17.3.3

   209             // also section 17.3.2.3, table 17-4

   210             return 64;

   211           }

   212       }

   213 

   214     case WIFI_MOD_CLASS_ERP_OFDM:

   215       return 4;

   216 

   217     case WIFI_MOD_CLASS_DSSS:

   218       if (preamble == WIFI_PREAMBLE_SHORT)

   219         {

   220           // IEEE Std 802.11-2007, section 18.2.2.2 and figure 18-2

   221           return 72;

   222         }

   223       else // WIFI_PREAMBLE_LONG

   224         {

   225           // IEEE Std 802.11-2007, sections 18.2.2.1 and figure 18-1

   226           return 144;

   227         }

   228 

   229     default:

   230       NS_FATAL_ERROR ("unsupported modulation class");

   231       return 0;

   232     }

   233 }

   234 

   235 uint32_t

   236 WifiPhy::GetPayloadDurationMicroSeconds (uint32_t size, WifiMode payloadMode)

   237 {

   238   NS_LOG_FUNCTION (size << payloadMode);

   239 

   240   switch (payloadMode.GetModulationClass ())

   241     {

   242     case WIFI_MOD_CLASS_OFDM:

   243     case WIFI_MOD_CLASS_ERP_OFDM:

   244       {

   245         // IEEE Std 802.11-2007, section 17.3.2.3, table 17-4

   246         // corresponds to T_{SYM} in the table

   247         uint32_t symbolDurationUs;

   248 

   249         switch (payloadMode.GetBandwidth ())

   250           {

   251           case 20000000:

   252           default:

   253             symbolDurationUs = 4;

   254             break;

   255           case 10000000:

   256             symbolDurationUs = 8;

   257             break;

   258           case 5000000:

   259             symbolDurationUs = 16;

   260             break;

   261           }

   262 

   263         // IEEE Std 802.11-2007, section 17.3.2.2, table 17-3

   264         // corresponds to N_{DBPS} in the table

   265         double numDataBitsPerSymbol = payloadMode.GetDataRate ()  * symbolDurationUs / 1e6;

   266 

   267         // IEEE Std 802.11-2007, section 17.3.5.3, equation (17-11)

   268         uint32_t numSymbols = lrint (ceil ((16 + size * 8.0 + 6.0) / numDataBitsPerSymbol));

   269 

   270         // Add signal extension for ERP PHY

   271         if (payloadMode.GetModulationClass () == WIFI_MOD_CLASS_ERP_OFDM)

   272           {

   273             return numSymbols * symbolDurationUs + 6;

   274           }

   275         else

   276           {

   277             return numSymbols * symbolDurationUs;

   278           }

   279       }

   280 

   281     case WIFI_MOD_CLASS_DSSS:

   282       // IEEE Std 802.11-2007, section 18.2.3.5

   283       NS_LOG_LOGIC (" size=" << size

   284                              << " mode=" << payloadMode

   285                              << " rate=" << payloadMode.GetDataRate () );

   286       return lrint (ceil ((size * 8.0) / (payloadMode.GetDataRate () / 1.0e6)));

   287 

   288     default:

   289       NS_FATAL_ERROR ("unsupported modulation class");

   290       return 0;

   291     }

   292 }

   293 

   294 Time

   295 WifiPhy::CalculateTxDuration (uint32_t size, WifiMode payloadMode, WifiPreamble preamble)

   296 {

   297   uint32_t duration = GetPlcpPreambleDurationMicroSeconds (payloadMode, preamble)

   298     + GetPlcpHeaderDurationMicroSeconds (payloadMode, preamble)

   299     + GetPayloadDurationMicroSeconds (size, payloadMode);

   300   return MicroSeconds (duration);

   301 }

   302