Coherent detection in signal processing refers to a method where the received signal is mixed (multiplied) with a local oscillator signal that is phase-locked to the transmitted aircraft carrier signal. This approach preserves the phase relationship between transmitted and received signals, allowing accurate recovery of transmitted data. Coherent detection is commonly used in radio communications, radar systems and optical communications to demodulate signals and extract information such as amplitude, phase and frequency. This technique offers high sensitivity and is capable of detecting weak signals but requires precise synchronization between the local oscillator and the received signal.
Noncoherent detection, on the other hand, does not require phase synchronization between the received signal and a local oscillator. Instead, it typically involves techniques such as envelope detection, where variations in amplitude of the received signal are directly detected without reference to its phase. Noncoherent detection is simpler to implement and less sensitive to phase fluctuations or variations, but may have lower detection sensitivity compared to coherent detection. It is commonly used in applications where phase coherence is difficult to maintain or unnecessary, such as in radio modulated (AM) receivers or simple radar systems.
Coherent demodulation refers to a process where the received signal is demodulated using coherent detection techniques, maintaining the phase relationship between the transmitted and received signals. This approach allows precise recovery of the modulation signal (e.g., data or information) encoded on the carrier wave. Coherent demodulation is particularly effective in applications requiring precise measurement of phase, frequency or amplitude variations in the received signal, such as in high-speed digital communications or radar systems.
Noncoherent demodulation, on the other hand, involves demodulating the received signal without maintaining phase coherence between the transmitted and received signals. This method generally relies on techniques such as envelope detection, where only amplitude variations of the received signal are extracted to recover the modulation signal. Noncoherent demodulation is simpler and more robust against phase fluctuations, but may sacrifice some sensitivity and accuracy compared to coherent demodulation. It is often used in applications where phase coherence is difficult to achieve or maintain consistently.
Coherent processing refers to signal processing techniques that rely on maintaining phase coherence between transmitted and received signals. These techniques include coherent integration, coherent detection, and Doppler processing, among others. Coherent processing is crucial in radar systems, communications systems, and other applications requiring precise measurement of signal phase, frequency, or amplitude variations.
Incoherent processing, on the other hand, involves signal processing techniques that do not require maintaining phase consistency between transmitted and received signals. These techniques may include averaging, envelope detection, or amplitude summation. Incoherent processing is simpler to implement and less sensitive to phase variations, but may have limitations in sensitivity and accuracy compared to coherent processing techniques.
In the context of frequency shift capture (FSK), coherent detection refers to the demodulation of FSK signals by maintaining phase coherence between the received signal and a local oscillator tuned to the carrier frequencies corresponding to the FSK modulation. This allows precise recovery of digital data encoded in frequency variations of the FSK signal. Coherent FSK detection is effective in high-speed digital communications systems where precise timing and frequency synchronization are essential for data recovery.
Noncoherent FSK detection involves demolating the FSK signal without maintaining phase coherence between the received signal and a local oscillator. Noncoherent FSK demodulation techniques may include methods such as frequency discriminator circuits or envelope detectors, which detect changes in signal frequency without direct reference to phase. Noncoherent FSK detection is simpler and more robust against phase variations, but may exhibit lower sensitivity and accuracy compared to coherent detection techniques. It is often used in applications where phase coherence is difficult to achieve consistently or where simpler receiver designs are preferred.