给出一个基于NS-3的WIFI性能仿真代码，并说出如何运行

以下是一个基于NS-3的WIFI性能仿真代码示例：

#include "ns3/core-module.h"
#include "ns3/wifi-module.h"
#include "ns3/mobility-module.h"
#include "ns3/internet-module.h"
#include "ns3/applications-module.h"

using namespace ns3;

NS_LOG_COMPONENT_DEFINE ("WifiPerformance");

int main (int argc, char *argv[])
{
  // 设置日志级别
  LogComponentEnable ("WifiPerformance", LOG_LEVEL_INFO);

  // 创建节点
  NodeContainer wifiNodes;
  wifiNodes.Create (2);

  // 配置物理层参数
  WifiHelper wifi;
  wifi.SetStandard (WIFI_PHY_STANDARD_80211n_2_4GHZ);
  wifi.SetRemoteStationManager ("ns3::ConstantRateWifiManager",
                                "DataMode", StringValue ("HtMcs0"),
                                "ControlMode", StringValue ("HtMcs0"));

  // 创建wifi设备
  NetDeviceContainer devices = wifi.Install (WifiPhyHelper::Default (), WifiMacHelper::Default (), wifiNodes);

  // 设置移动模型
  MobilityHelper mobility;
  mobility.SetPositionAllocator ("ns3::GridPositionAllocator",
                                 "MinX", DoubleValue (0.0),
                                 "MinY", DoubleValue (0.0),
                                 "DeltaX", DoubleValue (5.0),
                                 "DeltaY", DoubleValue (10.0),
                                 "GridWidth", UintegerValue (3),
                                 "LayoutType", StringValue ("RowFirst"));
  mobility.SetMobilityModel ("ns3::RandomWalk2dMobilityModel",
                             "Bounds", RectangleValue (Rectangle (-50, 50, -50, 50)));

  mobility.Install (wifiNodes);

  // 安装网络协议栈
  InternetStackHelper stack;
  stack.Install (wifiNodes);

  // 分配IP地址
  Ipv4AddressHelper address;
  address.SetBase ("10.1.1.0", "255.255.255.0");
  Ipv4InterfaceContainer interfaces = address.Assign (devices);

  // 创建流量发生器和接收器
  uint16_t port = 9;
  OnOffHelper onOffHelper ("ns3::UdpSocketFactory", Address (InetSocketAddress (interfaces.GetAddress (1), port)));
  onOffHelper.SetAttribute ("OnTime", StringValue ("ns3::ConstantRandomVariable[Constant=1]"));
  onOffHelper.SetAttribute ("OffTime", StringValue ("ns3::ConstantRandomVariable[Constant=0]"));
  onOffHelper.SetAttribute ("PacketSize", UintegerValue (1024));
  onOffHelper.SetAttribute ("DataRate", StringValue ("50Mbps"));

  ApplicationContainer onOffApps = onOffHelper.Install (wifiNodes.Get (0));
  onOffApps.Start (Seconds (1.0));
  onOffApps.Stop (Seconds (10.0));

  PacketSinkHelper sinkHelper ("ns3::UdpSocketFactory", Address (InetSocketAddress (Ipv4Address::GetAny (), port)));
  ApplicationContainer sinkApps = sinkHelper.Install (wifiNodes.Get (1));
  sinkApps.Start (Seconds (1.0));
  sinkApps.Stop (Seconds (10.0));

  // 启动仿真器
  Simulator::Stop (Seconds (10.0));
  Simulator::Run ();
  Simulator::Destroy ();

  return 0;
}

代码中创建了两个节点，配置了物理层参数，设置了移动模型，安装了网络协议栈并分配了IP地址，创建了流量发生器和接收器，最后启动了仿真器。

要运行该代码，需要安装NS-3并编译该代码。运行命令如下：

./waf --run wifi-performance

其中，`wifi-performance`是代码文件名。在运行过程中，程序会输出日志信息和仿真结果。