Analysis On Bit Error Rate Of The Drilling Fluid Pressure PSK Signals With Wave Form Distortion

Measurement while drilling(MWD)is a kind of technology which can obtain the downhole drilling engineering parameters and the bottom parameters in real time.Up to now,it has become an important part of drilling technology.At present,At present,the underground information telemetry system at home and abroad are used with wireless transmission modes,in which the continuous pressure wave transmission method of drilling fluid is widely used because of its strong anti-interference ability and higher data transmission speed.During drilling,the measured datas are affected by the noise while modulated by the drilling fluid pressure and transmitted by the drilling fluid channel,after crossing the adaptive filtering,most of the noise in the drilling fluid pressure signal will be suppressed,but some distortion will be appered on the waveform,distortion will affect the demodulation of the signal and lead to error.In this paper,the mathematical model of drilling fluid pressure PSK signal is constructed by analyzing the distortion form of the drilling fluid pressure phase shift keying(PSK)signal which has been dealed by adaptive filtering.Based on the study of the effect of distortion on phase demodulation,the phase noise function is established,which is caused by the deviation of carrier amplitude.and the maximum value calculation formula of noise phase is established through mathematical analysis,which changes with the distortion,and the coherent demodulation mathematical model which is affected by the distortion is established.Based on the mathematical analysis of the coherent demodulated signal,the mathematical model of the signal to noise ratio(SNR)of the reconstructed signal isestablished.Based on the analysis theory of the bit error rate of pulse code modulation(PCM)pulse,using the method of theoretical calculation and numerical simulation,the effect of distortion on bit error rate of drilling fluid pressure PSK signal reconstruction pulse is researched.Reaserch results indicates that the waveform distortion of the drilling fluid pressure PSK signal can be regarded as that the amplitude of the PSK signal is modulated by low frequency noise with a bandwidth of 0~4Hz,and the simulation results show that the amplitude of the PSK signal of the drilling fluid pressure established by this theory accords with the corresponding law.Both the distortion of the signal and demodulation system interference affect the bit error rate,in which demodulation system interference plays the main role.The bit error rate of the reconstructed pulses is determined by the maximum distortion of the signal rather than the average distortion.Under the same distortion,the drilling fluid pressure QPSK signal is more error prone than the DPSK signal.In order to reduce the transmission bit error rate of PSK signal in drilling fluid pressure,the feasibility of reducing the PSK signal distortion of drilling fluid pressure is studied by means of mathematical analysis and amplitude compensation method.