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The SWANS physical layer components are responsible for modeling signal propagation among radios as well as the mobility of nodes. Radios make transmission downcalls to the simulation ``field'' and other radios on the ``field'' receive reception upcalls from it, if they are within range of the signal. Both the pathloss and fading models are functions that depend on the source and destination radio locations. Pathloss models include free-space, two-ray and table-driven pathloss. Fading models include none, Raleigh and Rician fading. Node mobility is implemented as an interface-based discretized model. Upon each node movement, the model is queried to schedule the next movement. The mobility models that are implemented include static and random-waypoint.

interface class description
FieldInterface Field centralized node container that performs mobility and signal propagation with fading and pathloss
Fading Fading.None zero fading model
  Fading.Raleigh Raleigh fading model
  Fading.Rician Rician fading model
Pathloss Pathloss.FreeSpace pathloss model based purely on distance
  Pathloss.TwoRay pathloss model that incorporates ground reflection
Spatial Spatial.Linear signal propagation and location update performed via linked list of radios
  Spatial.Grid as above, but performed using a more efficient flat grid structure of small ``Linear'' bins
  Spatial.HierGrid as above, but performed using a more consistently efficient hierarchical grid structure
  ...TiledWraparound tile inner spatial structure in 3x3 grid so as to wrap field edges around into a torus
Placement Placement.Random uniformly random initial node placement
Mobility Mobility.Static no mobility
  ...RandomWaypoint pick a random ``waypoint'' and walk towards it with some random velocity, then pause and repeat.
  ...RandomWalk pick a direction, walk a certain distance in that direction, with some fixed and random component, reflecting off walls as necessary, then pause for some time and repeat.
  Mobility.Teleport pick a random location and teleport to it, then pause for some time, and repeat.

The SWANS radio receives upcalls from the field entity and passes successfully received packets on to the link layer. It also receives downcalls from the link layer entity and passes them on to the field for propagation. We have implemented an independent interference radio, as in ns2, as well as an additive interference radio, as in GloMoSim. The independent interference model considers only signals destined for the target radio as interference. The additive model correctly considers all signals as contributing to the interference. Both radios are half-duplex, as in 802.11b. Radios are parameterized by frequency, transmission power, reception sensitivity and threshold, antenna gain, bandwidth and error model. Error models include bit-error rate and signal-to-noise threshold.*
interface class description
RadioInterface RadioNoiseIndep interference at radio consists only of other signals above a threshold that are destined for that same radio
  RadioNoiseAdditive interference consists of all signals above a threshold
none RadioInfo unique and shared radio parameters

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