一. Helpers
helpers包括：a）较低级别的MAC和PHY channel helpers，以及b）处理基本安全消息（BSM）的发送和接收的较高级application helpers。
较低级别的helpers包括ns3 :: YansWavePhyHelper，ns3 :: NqosWaveMacHelper，ns3 :: QosWaveMacHelper，ns3 :: Wifi80211pHelper和ns3 :: WaveHelper。
Wifi80211pHelper用于创建符合802.11p-2010标准的802.11p设备。 WaveHelper用于创建符合802.11p-2010和1609.4-2010标准（WAVE体系结构的MAC和PHY层）的WAVE设备。
ns3 :: NqosWaveMacHelper，ns3 :: QosWaveMacHelper和ns3 :: Wifi80211pHelper的关系如下所示：
从上面的图中，有两个Mac助手类都从WifiMacHelper继承; 当WAVE模块最初写入时，WifiMacHelper的专用版本（QoS和Nqos）已经从Wifi代码库中删除，但是WAVE助手仍然保留其区别。 WiFi 802.11p设备的功能可以通过WaveNetDevice的ContinuousAccess分配来实现，如果不需要多通道操作，建议使用Wifi80211pHelper。 用法如下：
NodeContainer nodes;
NetDeviceContainer devices;
nodes.Create (2);
YansWifiPhyHelper wifiPhy = YansWifiPhyHelper::Default ();
YansWifiChannelHelper wifiChannel = YansWifiChannelHelper::Default ();
wifiPhy.SetChannel (wifiChannel.Create ());
NqosWave80211pMacHelper wifi80211pMac = NqosWaveMacHelper::Default();
Wifi80211pHelper 80211pHelper = Wifi80211pHelper::Default ();
devices = 80211pHelper.Install (wifiPhy, wifi80211pMac, nodes);
从上图中可以看出，WaveHelper不是WifiHelper的子类，只能使用QosWaveMacHelper，因为WAVE MAC层是基于QoS机制的。 但是如果需要多通道操作的话，WaveHelper是推荐的。 用法如下：
NodeContainer nodes;
NetDeviceContainer devices;
nodes.Create (2);
YansWifiChannelHelper wifiChannel = YansWifiChannelHelper::Default ();
YansWavePhyHelper wavePhy = YansWavePhyHelper::Default ();
wavePhy.SetChannel (wifiChannel.Create ());
QosWaveMacHelper waveMac = QosWaveMacHelper::Default ();
WaveHelper waveHelper = WaveHelper::Default ();
devices = waveHelper.Install (wavePhy, waveMac, nodes);
更高级别的helpers包括ns3 :: WaveBsmStats和ns3 :: WaveBsmHelper。
WaveBsmStats用于收集和管理有关WAVE BSM数据包发送和接收的统计信息，例如数据包和字节数以及数据包传输率（PDR）。 WaveBsmHelper是被希望发送和接收BSM的应用程序使用。
ns3 :: WaveBsmHelper和WaveBsmStats的关系如下所述：
从<Your Vanet Routing Application>，用法如下：
//声明WAVE BSM helper实例
WaveBsmHelper m_waveBsmHelper
//接下来的这些都会被传递给WaveBsmHelpe::Install()
//NodeContainer m_adhocTxNodes(container of network node)
//NetDeviceContainer m_adhocTxDevices((transmitting) devices (1 per node) )
//Ipv4InterfaceContainer m_adhocTxInterfaces(IPv4 interfaces (1 per device))
//double m_TotalSimTime(total simulation time (in seconds))
//double m_waveInterval(WAVE BSM broadcast interval(seconds))
//double m_gpsAccuracyNs(time-synchronization accuracy of GPS devices,E.g., +/- 40ns)
//std::vector <double> m_txSafetyRanges(array of distances (m) at which safety PDR shall be determined)
//int64_t m_streamIndex(used to get consistent random numbers across scenarios)
m_waveBsmHelper.Install (m_adhocTxNodes,m_adhocTxDevices, m_adhocTxInterfaces,Seconds(m_TotalSimTime),m_wavePacketSize, Seconds(m_waveInterval), Time Seconds(m_gpsAccuracyNs / 1000000.0), m_txSafetyRanges);
//fix random number streams
m_streamIndex += m_waveBsmHelper.AssignStreams (m_streamIndex)
BSM statistics的使用方法如下：
//Get the cumulative PDR of the first safety Tx range
double bsm_pdr1 = m_waveBsmHelper.GetWaveBsmStats ()->GetBsmPdr (1);
//total WAVE BSM bytes sent
uint32_t cumulativeWaveBsmBytes = m_waveBsmHelper.GetWaveBsmStats ()->GetTxByteCount ();
//get number of WAVE BSM packets sent
int wavePktsSent = m_waveBsmHelper.GetWaveBsmStats ()->GetTxPktCount ();
// get number of WAVE BSM packets received
int wavePktsReceived = m_waveBsmHelper.GetWaveBsmStats ()->GetRxPktCount ();
// reset count of WAVE BSM packets received
m_waveBsmHelper.GetWaveBsmStats ()->SetRxPktCount (0);
// reset count of WAVE BSM packets sent
m_waveBsmHelper.GetWaveBsmStats ()->SetTxPktCount (0);
// indicate that a node (nodeId) is moving. (set to 0 to “stop” node)
WaveBsmHelper::GetNodesMoving()[nodeId] = 1;
二.APIs
MAC layer
802.11p设备可以通过使用不同的OrganizationIdentifier字段来识别差异，从而允许上层通过VSA管理帧来发送不同的信息。
1.创建一些Node对象和WifiNetDevice对象，例如一个sender一个receiver
2.receiver定义一个OrganizationIdentifier
uint8_t oi_bytes[5] = {0x00, 0x50, 0xC2, 0x4A, 0x40};
OrganizationIdentifier oi(oi_bytes,5);
3.receiver为OrganizationIdentifier定义一个Callback
VscCallback vsccall = MakeCallback(&VsaExample::GetWsaAndOi, this);
4.receiver注册这个标识符和功能
Ptr<WifiNetDevice> device1 = DynamicCast<WifiNetDevice>(nodes.Get (i)->GetDevice (0));
Ptr<OcbWifiMac> ocb1 = DynamicCast<OcbWifiMac>(device->GetMac ());
ocb1->AddReceiveVscCallback (oi, vsccall);
5.sender通过VAS帧传送管理信息
Ptr<Packet> vsc = Create<Packet> ();
ocb2->SendVsc (vsc, Mac48Address::GetBroadcast (), m_16093oi);
6.接着在receiver中被注册的callbacks会被调用。
MAC extension layer
WAVE设备允许上层用不同的控制方式进行路由。但是应遵循专用的API和调用顺序; 否则，报文可能会被设备丢弃。
1.创建一些Node对象和WifiNetDevice对象，例如一个sender一个receiver
2.如果是接受WSMP和IP-based消息，则receiver注册接受callback
// the class ``ns3::WaveNetDeviceExample``here will has a receive method "Receive" to be registered.
receiver->SetReceiveCallback (MakeCallback (&WaveNetDeviceExample::Receive, this));
3.如果是接受WSA帧，则receiver注册callback
// the class ``ns3::WaveNetDeviceExample``here will has a receive method "ReceiveVsa" to be registered.
receiver->SetWaveVsaCallback (MakeCallback (&WaveNetDeviceExample::ReceiveVsa, this));
4.sender和receiver通过StartSch方法安排信道接入
// in this case that alternating access with non-immediate mode is assigned for sender and receiver devices.
//非即时模式的交替访问
const SchInfo schInfo = SchInfo (SCH1, false, EXTENDED_ALTERNATING);
Simulator::Schedule (Seconds (0.0), &WaveNetDevice::StartSch, sender, schInfo);
Simulator::Schedule (Seconds (0.0), &WaveNetDevice::StartSch, receiver, schInfo);
or
// in this case that continuous access with immediate mode is assigned for sender and receiver devices.
//即时模式的连续访问
const SchInfo schInfo = SchInfo (SCH1, true, EXTENDED_CONTINUOUS);
Simulator::Schedule (Seconds (0.0), &WaveNetDevice::StartSch, sender, schInfo);
Simulator::Schedule (Seconds (0.0), &WaveNetDevice::StartSch, receiver, schInfo)
or
// in this case that extended access with non-immediate mode is assigned for sender and receiver devices.
//非即时模式的扩展接入
const SchInfo schInfo = SchInfo (SCH1, false, 100);
Simulator::Schedule (Seconds (0.0), &WaveNetDevice::StartSch, sender, schInfo);
Simulator::Schedule (Seconds (0.0), &WaveNetDevice::StartSch, receiver, schInfo)
5.如果传送对的是IP-based消息，sender注册tx配置文件
// the IP-based packets will be transmitted in SCH1 with 6Mbps and 4 txPowerLevel with adaptable mode.
const TxProfile txProfile = TxProfile (SCH1, true, 4, WifiMode("OfdmRate6MbpsBW10MHz"));
Simulator::Schedule (Seconds (2.0), &WaveNetDevice::RegisterTxProfile, sender, txProfile);
6.sender通过SendX方法传输WSMP包
// the data rate and txPowerLevel is controlled by the high layer which are 6Mbps and 0 level here.
const TxInfo txInfo = TxInfo (CCH, 7, WifiMode("OfdmRate6MbpsBW10MHz"), 0);
// this packet will contain WSMP header when IEEE 1609.3 model is implemented
const static uint16_t WSMP_PROT_NUMBER = 0x88DC;
Ptr<Packet> wsaPacket = Create<Packet> (100);
const Address dest = receiver->GetAddress ();
Simulator::Schedule (Seconds (2.0), &WaveNetDevice::SendX, sender, wsaPacket, dest, WSMP_PROT_NUMBER, txInfo);
or
// the data rate and txPowerLevel is controlled by the MAC layer which are decided by WifiRemoteStationManager
const TxInfo txInfo = TxInfo (CCH, 7, WifiMode(), 8);
// this packet will contain WSMP header when IEEE 1609.3 model is implemented
const static uint16_t WSMP_PROT_NUMBER = 0x88DC;
Ptr<Packet> wsaPacket = Create<Packet> (100);
const Address dest = receiver->GetAddress ();
Simulator::Schedule (Seconds (2.0), &WaveNetDevice::SendX, sender, wsaPacket, dest, WSMP_PROT_NUMBER, txInfo);
7.sender通过Send方法传送IP-based包
const static uint16_t IPv6_PROT_NUMBER = 0x86DD;
Ptr<Packet> packet = Create<Packet> (100);
const Address dest = receiver->GetAddress ();
Simulator::Schedule (Seconds (2.0), &WaveNetDevice::Send, sender, packet, dest, IPv6_PROT_NUMBER);
8.sender通过StartVsa方法重复传送WSA帧
// this packet will contain WSA management information when IEEE 1609.3 model is implemented
Ptr<Packet> wsaPacket = Create<Packet> (100);
Mac48Address dest = Mac48Address::GetBroadcast ();
const VsaInfo vsaInfo = VsaInfo (dest, OrganizationIdentifier (), 0, wsaPacket, SCH1, 100, VSA_TRANSMIT_IN_BOTHI);
Simulator::Schedule (Seconds (2.0), &WaveNetDevice::StartVsa, sender, vsaInfo);
9.sender通过StopVsa方法停止WSA帧的重复传送
Simulator::Schedule (Seconds (3.0), &WaveNetDevice::StopVsa, sender, SCH1);
10.sender和receiver通过StopSch方法释放信道
Simulator::Schedule (Seconds (4.0), &WaveNetDevice::StopSch, sender, SCH1);
Simulator::Schedule (Seconds (4.0), &WaveNetDevice::StopSch, receiver, SCH1);
11.sender和receiver通过ChangeAddress方法改变目前的MAC地址
Address newAddress = Mac48Address::Allocate ();
Simulator::Schedule (Seconds (4.0), &WaveNetDevice::ChangeAddress, sender, newAddress);
12.sender通过CancelTx方法取消特定类别和信道的所有传送
Simulator::Schedule (Seconds (4.0), &WaveNetDevice::CancelTx, sender, CCH, AC_BE);
为了成功发送和接收这些数据包，应该执行正常和适当的调用过程。
A.对于WSMP，信道访问应分配给发送和接收。 如果不需要在另一个通道中传输，则通道访问释放操作可以是可选的。
StartSch -------------> SendX / ReceiveCallback --------------> StopSch
B.对于IP，tx配置文件必须在传送和接收前被注册。如果不需要使用别的tx参数进行传送则删除tx配置文件的操作是可选的。信道接入和释放操作和WSMP是一样的。
StartSch -------------> RegisterTxProfile ----------> Send / ReceiveCallback --------------> DeleteTxProfile -------------> StopSch
C.对于WSA，StartVsa在传送时需要被调用，而StopVsa是用于取消重复发送的可选操作。 频道访问分配和释放可选用法在这里也与WSMP相同。 为了接收VSA，WaveVsaCallback应该被注册; 否则，接收到的VSA帧将被MAC扩展层丢弃，无法传递到上层。
StartSch -------------> StartVsa / WaveVsaCallback --------------> StopVsa ---------------> StopSch
D.如果上层想要在CCH中传递这些包，则不需要通过StartSch方法请求CCH，这意味着StartSch可以是可选的或者这里应该避免。原因是在WAVE设备被创建和初始化之后，默认的连续CCH访问已被自动分配。 因此，如果使用CCH作为参数调用StartSch和StopSch方法，则请求将被设备丢弃，并且方法将返回false以指示失败。
三.Attributes
通道间隔时间的默认值是在标准中定义的。 但是，当前的实现允许用户使用其他值配置这些属性。 这些属性包含在ns3 :: ChannelCoodinator类中，其配置路径如下所示。 建议使用IsValidConfig方法测试新配置是否遵循标准。
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/ChannelCoordinator/$ns3::ChannelCoordinator/CchInterval
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/ChannelCoordinator/$ns3::ChannelCoordinator/SchInterval
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/ChannelCoordinator/$ns3::ChannelCoordinator/GuardInterval
ns3 :: WaveNetDevice是一个包装类，它包含支持多通道操作的类。 要设置或获取这些对象的指针，用户还可以通过下面显示的配置路径来使用它们。
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/Mtu
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/Channel
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/PhyEntities
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/MacEntities
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/ChannelScheduler
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/ChannelManager
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/ChannelCoordinator
/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/VsaManager
四.Output
对于802.11p设备，当前类别提供与WiFi设备相同类型的输出; 即ASCII和pcap跟踪和日志输出。 802.11p日志记录组件可以通过调用:
Wifi80211pHelper::EnableLogComponents ();
WAVE日志记录组件可以通过调用:
WaveHelper::EnableLogComponents ();
五.Advanced Usage
Advanced WaveHelper configuration
如果用户可以明确WAVE设备在哪个信道工作，可以设置明确的信道来节约资源。
// in this case, the MAC entities for SCH2 to SCH6 will not be created
WaveHelper helper = WaveHelper::Default ();
uint32_t channels[] = {CCH, SCH1};
std::vector<uint32_t> channelsVector (channels, channels + 2);
helper.CreateMacForChannel (channelsVector);
如果用户可以创建其他频道访问分配机制，例如 在可能被称为“ns3 :: AnotherScheduler”的更多PHY实体的情况下，他们可以使用这个帮助器来创建具有新分配机制的WAVE设备。 用法如下：
WaveHelper helper = WaveHelper::Default ();
helper.helper.CreateMacForChannel (ChannelManager::GetWaveChannels ()); // create all 7 MAC entites for WAVE
helper.CreatePhys (2); // or other number which should be less than 7
helper.SetChannelScheduler ("ns3::AnotherScheduler"); // The AnotherScheduler should be implemented by users.
helper.SetRemoteStationManager ("ns3::ConstantRateWifiManager"); // or other rate control algorithms
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