According to the mathematic models of pulse with modulation (PWM)-based and pulse position modulation-based multiple phase shift keying (MPSK) signals, the authors analyze the frequency spectrum distribution of MPSK signals. The impacts of drilling fluid channel parameter and modulation methods on the data transmission are researched. Numerical calculation results show that the relative power in the main lobe of the frequency spectrum of PWM-based MPSK signal is too low; only the MPSK modulation based on pulse position could be used for data frequency-band transmission, yet its requirements for signal detection, treatment, and speed control of the rotary valve are relatively higher.

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