Loop Filter

The default loop filter are provided by TrackingLoopFilters.jl. This includes

• first order loop filter FirstOrderLF
• second order biliner loop filter SecondOrderBilinearLF
• second order boxcar loop filter SecondOrderBoxcarLF
• third order bilinear loop filter ThirdOrderBilinarLF
• third order boxcar loop filter ThirdOrderBoxcarLF

The default loop filter for the carrier loop is ThirdOrderBilinarLF and the default loop filter for the code loop is SecondOrderBilinearLF. This is set by the initialization of the TrackingState and can be changed by:

state = TrackingState(
  GPSL1,
  carrier_doppler,
  code_phase,
  carrier_loop_filter = ThirdOrderBilinearLF(),
  code_loop_filter = SecondOrderBilinearLF()
)

The bandwidth of the loop filter is set by the track function:

next_results = track(
  next_signal,
  get_state(results),
  prn,
  sample_frequency,
  carrier_loop_filter_bandwidth = 18Hz,
  code_loop_filter_bandwidth = 1Hz
)

You can easily implement a custom loop filter MyLoopFilter <: AbstractLoopFilter. In this case, a specialized propagate and get_filter_output is needed. For more information refer to TrackingLoopFilters.jl.