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21.2 Using the Wimax models

The main way that users who write simulation scripts will typically interact with the Wimax models is through the helper API and through the publicly visible attributes of the model.

The helper API is defined in src/helper/wimax-helper.{cc,h.

The example examples/wimax/wimax-simple.cc contains some basic code that shows how to set up the model:

 
 
  switch (schedType)
    {
    case 0:
      scheduler = WimaxHelper::SCHED_TYPE_SIMPLE;
      break;
    case 1:
      scheduler = WimaxHelper::SCHED_TYPE_MBQOS;
      break;
    case 2:
      scheduler = WimaxHelper::SCHED_TYPE_RTPS;
      break;
    default:
      scheduler = WimaxHelper::SCHED_TYPE_SIMPLE;
    

  NodeContainer ssNodes;
  NodeContainer bsNodes;

  ssNodes.Create (2);
  bsNodes.Create (1);

  WimaxHelper wimax;

  NetDeviceContainer ssDevs, bsDevs;

  ssDevs = wimax.Install (ssNodes,
                          WimaxHelper::DEVICE_TYPE_SUBSCRIBER_STATION,
                          WimaxHelper::SIMPLE_PHY_TYPE_OFDM,
                          scheduler);
  bsDevs = wimax.Install (bsNodes, WimaxHelper::DEVICE_TYPE_BASE_STATION, WimaxHelper::SIMPLE_PHY_TYPE_OFDM, scheduler);

This example shows that there are two subscriber stations and one base station created. The helper method Install allows the user to specify the scheduler type, the physical layer type, and the device type.

Different variants of Install are available; for instance, the example examples/wimax/wimax-multicast.cc shows how to specify a non-default channel or propagation model:

 
 
  channel = CreateObject<SimpleOfdmWimaxChannel> ();
  channel->SetPropagationModel (SimpleOfdmWimaxChannel::COST231_PROPAGATION);
  ssDevs = wimax.Install (ssNodes,
                          WimaxHelper::DEVICE_TYPE_SUBSCRIBER_STATION,
                          WimaxHelper::SIMPLE_PHY_TYPE_OFDM,
                          channel,
                          scheduler);
  Ptr<WimaxNetDevice> dev = wimax.Install (bsNodes.Get (0),
                                           WimaxHelper::DEVICE_TYPE_BASE_STATION,
                                           WimaxHelper::SIMPLE_PHY_TYPE_OFDM,
                                           channel,
                                           scheduler);

Mobility is also supported in the same way as in Wifi models; see the examples/wimax/wimax-multicast.cc.

Another important concept in WiMAX is that of a service flow. This is a unidirectional flow of packets with a set of QoS parameters such as traffic priority, rate, scheduling type, etc. The base station is responsible for issuing service flow identifiers and mapping them to WiMAX connections. The following code from examples/wimax/wimax-multicast.cc shows how this is configured from a helper level:

 
 
 ServiceFlow MulticastServiceFlow = wimax.CreateServiceFlow (ServiceFlow::SF_DIRECTION_DOWN,
                                                              ServiceFlow::SF_TYPE_UGS,
                                                              MulticastClassifier);

  bs->GetServiceFlowManager ()->AddMulticastServiceFlow (MulticastServiceFlow, WimaxPhy::MODULATION_TYPE_QPSK_12);
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