基于PPM(Pulse Position Modulation)硬判决检错的ARQ-FSO(Automatic Repeat Request-Free Space Optical)通信系统结合了PPM硬判决和新的ARQ协议.该系统以PPM硬判决的结果代替了传统ARQ的监督码元作为数据的检错依据,同时只重传数据包里面译码失败部分的PPM符号,消除了传统ARQ中用来检错的信息冗余,提高了系统的效率.理论分析表明该方案能够有效地改善硬判决误码率,其通过率也优于传统ARQ,适用于较低误码率、低复杂度的自由空间光通信场景. 相似文献
In situ stress is not only a vital indicator for selecting explorative regions of coalbed methane (CBM), but also a pivotal factor affecting CBM production. The present study explored whether in situ stress affected the development potential of CBM in western Guizhou, China. To this end, we collected injection/falloff well test data and gas content data from 70 coal seams in 28 wells. The study found that from top to bottom, strike slip fault stress fields (<?500 m), normal fault stress fields (500–1000 m) and strike slip fault stress fields (>?1000 m) were successively developed in western Guizhou. The distribution features of vertical permeability in western Guizhou are consistent with the stress fields' transformation location. The coal permeability in the western part in Guizhou presents a tendency of increase followed by decrease as a result of increased burial depth. The vertical development characteristics of coal seam gas content are controlled mainly by reservoir pressure, and the relationship between reservoir pressure and buried depth shows a linear increase. The CBM in western Guizhou is divided vertically into three development potential regions dependent on the characteristics of burial depth, permeability and gas content of coal seams. The most favorable vertical development potential region in western Guizhou is 500–1000 m. This region exhibits high gas content, high permeability and moderate burial depth, which are favorable for the production of CBM. These research results can provide basis for geological selection and engineering implementation of CBM in western Guizhou.