Continuous Wave Mode

Description

This mode simulates a continuous wave (CW) radar signal. It is configured in the XML by setting the type="continuous" attribute within a <transmitter> or <monostatic> element. Internally, FERS simulates this by treating the CW transmission as a single, very long logical "pulse". The specific shape and characteristics of this continuous waveform (e.g., its constant amplitude and phase) are defined externally and loaded via a RadarSignal object, similar to how pulsed waveforms are handled.

Assumptions

• Assumes that treating the CW signal as one continuous logical pulse within the simulation framework is sufficient for modeling its behavior.
• Assumes the external data loaded into the Signal object accurately represents the desired complex baseband CW signal (this is typically a constant complex value for basic CW).
• Assumes the RadarSignal::_length parameter correctly corresponds to the desired duration of the CW transmission interval being simulated.
• Assumes the params::cwSampleRate parameter is set to a value high enough to adequately sample the relevant changes in the simulation environment (like target movement causing Doppler shifts or phase changes) during the CW interval. This rate determines how often the channel state (InterpPoint) is captured.
• Assumes the RadarSignal::_carrierfreq parameter correctly represents the carrier frequency of the CW signal.
• Assumes the associated Timing source is correctly configured for the simulation.
• Assumes the Signal::render function can handle potentially very long effective signal durations (as defined by RadarSignal::_length) without excessive performance degradation or memory issues.

Limitations

• Implementation Approach: The primary distinction between CW and Pulsed modes within FERS is in the scheduling (CW sends one logical "pulse" at time=0) and the internal channel sampling rate (params::cwSampleRate is used for CW dynamics). The core waveform rendering relies on the same mechanisms as pulsed mode.
• Channel Sampling Fidelity: The accuracy of representing the evolution of Doppler shift and phase during the CW transmission depends critically on the params::cwSampleRate, which dictates the temporal resolution of the saved channel state (InterpPoints). This is distinct from the Signal::_rate which relates to the sample rate of the loaded baseband waveform data itself.
• External Waveform Dependency: FERS does not internally generate a CW signal. It relies entirely on the user providing the appropriate complex baseband representation (usually a constant value) via an external file loaded into the Signal object.
• Lack of CW-Specific Post-Processing: The simulation renders the received CW signal (including Doppler, delay, phase effects) as IQ data. However, FERS does not include built-in processing steps commonly associated with CW radar post-rendering, such as long-term integration for detection or specific CW interference mitigation techniques. These must be performed externally on the output data.

Related Components

• XML Configuration: type="continuous" attribute in <transmitter> / <monostatic>
• Scheduling: Transmitter class (specifically _pulsed flag being false), Transmitter::getPulseCount(), Transmitter::setPulse()
• Internal Sampling: sim_threading module (e.g., simulateTarget, addDirect), params::cwSampleRate, InterpPoint class
• Waveform Definition/Rendering: RadarSignal class, Signal class (methods load, render), Pulsed Radar Mode (shares rendering logic)
• Timing

Validation Status

• Needs Verification: The assumptions and limitations listed above require verification through targeted testing.
• Key Areas for Validation:
  • Confirm that Doppler shifts and phase evolution over the CW duration are accurately captured and depend correctly on params::cwSampleRate.
  • Assess performance and memory usage when simulating very long CW durations (RadarSignal::_length).
  • Verify that loading a simple constant complex value as the external waveform results in the expected rendered output (subject to channel effects).
  • Compare results of a short CW simulation to a single pulse simulation using the same waveform data for consistency checks.
• Priority: Medium