在深井地震综合观测中实现秒脉冲(Pulse Per Second,PPS)精确、可靠地传输非常重要.针对该需求,设计了一种正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)符号,选择其中的一些频点用来标记PPS,避免了采用单独导线传输PPS,节约了硬件资源,提高了传输可靠性.另外,受传输信道的频带限制,以及接收过程中滤波器的影响,直接传输PPS的时延难以判断,而信道和滤波器相频特性是确定而且可测的,使用正弦波标记传输PPS时,可以基于滤波器相频特性计算出滤波器引起的时延偏差,校正信道及滤波器的影响.实验证明,基于正弦波标记传输PPS的时移计算误差能够达到微秒级,完全能够满足目前地震观测的使用要求.
Design and Implementation of Borehole Comprehensive Observation Timing System
It is very important to realize accurate and reliable transmission of Pulse Per Sec-ond(PPS)in borehole seismic comprehensive observation.Aiming at this requirement,a Orthogonal Frequency Division Multiplexing(OFDM)symbol is designed,and some fre-quency points are selected to mark the second pulse(PPS)for transmission,avoiding the transmission of second pulse(PPS)with a separate wire.It saves hardware resources and improves transmission reliability.In addition,due to the frequency band limitation of the transmission channel and the influence of the filter in the receiving process,the delay of the direct transmission second pulse(PPS)is difficult to judge,and the phase-frequency characteristics of the channel and filter are determined and measurable.When the trans-mission second pulse(PPS)is marked by sine wave,the delay deviation caused by the fil-ter can be calculated based on the phase-frequency characteristics of the filter.Therefore,it is possible to correct the influence of the channel and filter.The calculation error of the time shift based on the sine wave marked transmission second pulse(PPS)can reach the microsecond level,which can fully meet the requirements of the current seismic observa-tion.
Borehole observationDeliver the timePulse per second
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