WiFiMode官方文檔介紹
代表單一傳輸模式
WifiMode由單個(gè)整數(shù)實(shí)現(xiàn)雾消，用于在全局?jǐn)?shù)組中查找相關(guān)傳輸模式的特性友驮。
因此鳍刷，保持WifiMode變量是非常便宜的鱼的。
源碼分析
在/src/wifi/model/wifi-phy.cc中定義了OFDM DSSS HTMCS等一系列模式。
WifiMode
WifiPhy::GetOfdmRate6Mbps ()
{
static WifiMode mode =
WifiModeFactory::CreateWifiMode ("OfdmRate6Mbps",
WIFI_MOD_CLASS_OFDM,
true,
WIFI_CODE_RATE_1_2,
2);
return mode;
}
WifiMode
WifiPhy::GetOfdmRate9Mbps ()
{
static WifiMode mode =
WifiModeFactory::CreateWifiMode ("OfdmRate9Mbps",
WIFI_MOD_CLASS_OFDM,
false,
WIFI_CODE_RATE_3_4,
2);
return mode;
}
在這里就這幾行代碼稍稍分析一下痘煤。
WifiModeFactory的構(gòu)造器函數(shù)如下：
WifiModeFactory::WifiModeFactory ()
{
}
但是這個(gè)構(gòu)造函數(shù)是私有的凑阶，外界無法訪問。
WifiModeFactory 對象的創(chuàng)建衷快，可以通過下面的GetFactory方法：
WifiModeFactory *
WifiModeFactory::GetFactory (void)
{
static bool isFirstTime = true;
static WifiModeFactory factory;
if (isFirstTime)
{
uint32_t uid = factory.AllocateUid ("Invalid-WifiMode");
WifiModeItem *item = factory.Get (uid);
item->uniqueUid = "Invalid-WifiMode";
item->modClass = WIFI_MOD_CLASS_UNKNOWN;
item->constellationSize = 0;
item->codingRate = WIFI_CODE_RATE_UNDEFINED;
item->isMandatory = false;
item->mcsValue = 0;
isFirstTime = false;
}
return &factory;
}
可以發(fā)現(xiàn)宙橱，上面的靜態(tài)方法中factory靜態(tài)變量，僅被初始化一次蘸拔，全局訪問這一個(gè)靜態(tài)變量师郑。
WifiModeItem 是結(jié)構(gòu)體。
struct WifiModeItem
{
std::string uniqueUid;
enum WifiModulationClass modClass;
uint16_t constellationSize;
enum WifiCodeRate codingRate;
bool isMandatory;
uint8_t mcsValue;
};
有了上面的準(zhǔn)備工作调窍，重點(diǎn)看下面的CreateWifiMode 方法：
WifiMode
WifiModeFactory::CreateWifiMode (std::string uniqueName,
enum WifiModulationClass modClass,
bool isMandatory,
enum WifiCodeRate codingRate,
uint16_t constellationSize)
{
WifiModeFactory *factory = GetFactory ();
uint32_t uid = factory->AllocateUid (uniqueName);
WifiModeItem *item = factory->Get (uid);
item->uniqueUid = uniqueName;
item->modClass = modClass;
//The modulation class for this WifiMode must be valid.
NS_ASSERT (modClass != WIFI_MOD_CLASS_UNKNOWN);
item->codingRate = codingRate;
if ((codingRate == WIFI_CODE_RATE_UNDEFINED) &&
modClass != WIFI_MOD_CLASS_DSSS &&
modClass != WIFI_MOD_CLASS_HR_DSSS)
{
NS_FATAL_ERROR ("Error in creation of WifiMode named " << uniqueName << std::endl
<< "Code rate must be WIFI_CODE_RATE_UNDEFINED iff
Modulation Class is WIFI_MOD_CLASS_DSSS or
WIFI_MOD_CLASS_HR_DSSS");
}
item->constellationSize = constellationSize;
item->isMandatory = isMandatory;
NS_ASSERT (modClass != WIFI_MOD_CLASS_HT && modClass != WIFI_MOD_CLASS_VHT);
//fill unused mcs item with a dummy value
item->mcsValue = 0;
return WifiMode (uid);
}
CreateWifiMode 方法首先通過GetFactory 方法創(chuàng)建一個(gè)WifiModeFactory 對象宝冕，利用AllocateUid 方法產(chǎn)生一個(gè)唯一的uid,通過唯一的uid產(chǎn)生一個(gè)WifiModeItem 結(jié)構(gòu)體，結(jié)構(gòu)體對象中保存了WiFimode中的參數(shù)邓萨。
由于uid唯一的地梨，WiFiMode對象只需要保存uid的值，就可以通過uid值傳遞給WifiModeFactory 對象缔恳，得到WifiModeItem 結(jié)構(gòu)體宝剖，而該結(jié)構(gòu)體保存了WiFimode中的參數(shù)。
上面的CreateWifiMode 方法中使用到的AllocateUid 方法和Get 方法如下：
uint32_t
WifiModeFactory::AllocateUid (std::string uniqueUid)
{
uint32_t j = 0;
for (WifiModeItemList::const_iterator i = m_itemList.begin ();
i != m_itemList.end (); i++)
{
if (i->uniqueUid == uniqueUid)
{
return j;
}
j++;
}
uint32_t uid = m_itemList.size ();
m_itemList.push_back (WifiModeItem ());
return uid;
}
struct WifiModeFactory::WifiModeItem *
WifiModeFactory::Get (uint32_t uid)
{
NS_ASSERT (uid < m_itemList.size ());
return &m_itemList[uid];
}
其中的m_itemList對象就是一個(gè)列表歉甚，保存了每一個(gè)結(jié)構(gòu)體對象万细，結(jié)構(gòu)體對象保存了WiFimode的相應(yīng)的參數(shù)。
AllocateUid 方法設(shè)計(jì)的非常巧妙纸泄，返回的uid的值就是對應(yīng)的結(jié)構(gòu)器在m_itemList中的位置赖钞。所以可通過將uid傳遞給Get方法，從m_itemList列表中獲取到對應(yīng)的結(jié)構(gòu)體對象聘裁。
WifiMode::WifiMode (uint32_t uid)
: m_uid (uid)
{
}
WifiMode對象通過這個(gè)構(gòu)造函數(shù)雪营，只需要保存uid的值，就可以通過下面的代碼：
struct WifiModeFactory::WifiModeItem *item = WifiModeFactory::GetFactory ()->Get (m_uid);
僅僅通過這一行代碼就可以獲取到WifiModeItem 結(jié)構(gòu)體對象咧虎，獲取到wifimode的參數(shù)卓缰。
