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为了降低OFDM信号的峰平比,提出了一种适应于任意子载波数目OFDM信号PAR降低的冲激脉冲峰值相消的方法.分析了采用此方法的OFDM信号峰平比的概率分布和误码率性能,对冲激脉冲相消法中不同限幅因子和冲激比因子对OFDM信号的峰平比降低的程度进行了仿真.仿真结果表明,当限幅因子一定时,冲激比因子为0.3时,冲激脉冲相消法可以有效地改善OFDM信号的高峰平比特性. 相似文献
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Variability of snow and ice thermal, physical and optical properties pertinent to sea ice algae biomass during spring 总被引:6,自引:2,他引:4
Changes in the thermal, physical and optical properties of the snow–sea ice system and feedbacks between various temporal and spatial scales affect accumulation of microalgae at the sea ice bottom and are the focus of this research. During the spring transition period, May 4 to June 9, 2002, we closely monitored atmospheric conditions and properties of the snow–sea ice system, including thermal, physical and optical properties of the snow cover (e.g., temperature, grain size, light attenuation), ice thickness and salinity, and biomass of bottom ice algae. Results show that snowdrift size averaged 31.2 by 10.6 m with a depth range of 2 to 45 cm. Snowpacks also varied in age, distinguished by coincident peaks of snow salinity and grain size and a lower PAR extinction coefficient. Spatial variability of the snowpack was superimposed by temporal variability associated with seasonal snow–ice melt and wind redistribution of snow. Maximum biomass of ice algae was observed under intermediate snow covers. Under thin snow covers, algae biomass declined steadily coincident with seasonal warming and desalination of the ice cover. Under thick snow covers, algae biomass was negatively correlated with snow depth. These results suggest that thin snow covers were associated with a thermal effect causing sloughing of algae, whereas under deep snow, algae were still light limited and thermally insulated from the warming atmosphere. Our results highlight the importance of snow cover history on the sea ice system operating below. Furthermore, in the context of current climate change scenarios, shifts in snow depth would result in decreases of ice algae biomass. 相似文献
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