Simulation of the VU Ranging application and the LocalDistanceMap component

[This document is under construction, links may be broken.]

The VU Ranging component is used to determine distances between motes by using radio signals and sounder. The motes emit once every minute a radio signal and a chirping sound at the same time, so that listening motes can determine the time-of-flight of the sound signal and with this the distance to the sound source - the other mote.

How does the VU Ranging simulation work?

The basic scenario of the ranging simulation can roughly be described as follows:

• each n milliseconds a (simulated) radio message containing the own address is broadcasted, which should correspond to the "beacon" consisting of the combination of sound and radio signals in the real VU component. The number n can be configured in RangingSimConfig.h
• if such a "beacon" message is received, the mote determines whether it disregards it or not based on a probability value (see RangingSimConfig.h).
• if the mote "decides" to process the received beacon message it determines the "real" distance to the sender of the message by calling SimCoordinates.getXYDistance().
• in order to get a behaviour closer to the real component a derivation is added/substracted from the "real" distance (the maximal error can be configured in RangingSimConfig.h)
• finally, a distanceEstimated event is signaled

Components/Files

• files with the suffix "M.nc" contain implementation modules
• files with the suffix "C.nc" or just ".nc" contain configurations, i.e. their implementation is realized in terms of other components by connecting provides and uses interfaces.
• files with the suffix just ".nc" may also contain interfaces (sorry)

Components

• RMain: toplevel component; can be ignored for understanding the interplay between localization and ranging. The only purpose of RMain component is to simulate, that the motes are not switched on at the same time by waiting for a random amount of seconds before the start() command of the KLocalizationC component is executed.
  • Main: every application's toplevel component has to use this, initializes, starts, and stops the application
  • RMainM: implementation component of toplevel component. It implements the above mentioned "switch-on" delay by starting a "one-shot" timer initialized with a random amount of milliseconds (see command start())
  • RandomLFSR: used to get the random number for the delay timer
  • TimerC: the delay timer, started as "one-shot" timer in RMainM, i.e. it fires exactly one time after the given amount of milliseconds and then never again thereafter.
  • KLocalizationC: the toplevel component of the localization application, it uses the following components:
    • KLocalizationM: (will) implement(s) the Kestrel localization component; currently only local distance map functionality implemented
    • RangingSim: The toplevel component of the VU ranging simulation, it uses:
      • RangingSimM: This is the most important component for understanding the VU ranging simulation. It implements the above sketched scenario, how distance estimates are determined.
      • SimCoordinatesC: for retrieving distance information from the simulator
      • RandomLSFR: to get random numbers used to make the simulation more realistic (see RangingSimM component)
      • TimerC: for sending out beacons periodically
      • IntToRfm: for sending the radio signal part of the beacon
      • RfmToInt: for receiving the radio signal part of the beacon
    • LocalDistanceMapM: simple data base type of component for storing and retrieving distance information that has been collected from the ranging component.

Interfaces

• AcousticRangingControl for starting and stoping the VU ranging simulation; provided by RangingSimM
• DistanceEstimate for signaling "distanceEstimate" event; provided by RangingSimM
• LocalDistanceMap for storing and retrieving distance information; provided by LocalDistanceMapM
• LocalizationControl for signaling "localizationDone" events; provided by KLocalizationM, but never used in this application (for now)