The critical environment is one of the main insufficient to positioning. Geodetic observing systems such as the global positioning system （GPS） and the global navigation satellite systems （GNSS） are routinely used...The critical environment is one of the main insufficient to positioning. Geodetic observing systems such as the global positioning system （GPS） and the global navigation satellite systems （GNSS） are routinely used to estimate the contaminating effects by critical environment. In an effort to define the accuracy and reliability of GPS/ GNSS positioning, we investigated the data having con- taminating effects due to forestry environment. Some reliability criteria and geometric concepts were defined and then examined by them. Two sets of data were collected in open sky and closed canopy separately. The analysis of the observed data was performed using the reliability criteria and geometric concepts. The accuracy and reliability of positioning strongly depended on the canopy ratio and satellite availability. The minimum detectable error on baseline was estimated about 2.5 mm under closed canopy. The number of observable satellites and minimal detectable errors were computed for each epoch. The minimal biases on estimated baselines, bias-to-noise ratios for estimating baseline components and probability of success of the integer ambiguity solution were defined in case of forest canopy. Finally, geometric quality could be achieved using the factors of dilution of precision. Thus, the presented accuracy and reliability concepts fulfill the requirement proposed by the global geodetic observing system in forest environment.展开更多
A voltage-controlled oscillator（VCO） with dual stages of accumulation mode varactors for a multimode global navigation satellite system（GNSS） application,which adopts sigma-delta fractional-N technology in the syn...A voltage-controlled oscillator（VCO） with dual stages of accumulation mode varactors for a multimode global navigation satellite system（GNSS） application,which adopts sigma-delta fractional-N technology in the synthesizer,is presented.The structure is selected to optimize the frequency coverage and tuning linearity, based on a general analysis of the parasitic capacitance in the coarse tuning switch bank cells,which cover the global positioning system（GPS） and Beidou（BD） bands.The VCO implemented in the 0.18μm CMOS process can cover the GPS L1,BD B1,B2 and B3 bands with sufficient margin,and exhibits low phase noise by using this tuning curve linearization technique.The equalized K_（vco）,characteristic behavior further offers a wide voltage tuning range and improves the stability of the closed loop.展开更多
文摘The critical environment is one of the main insufficient to positioning. Geodetic observing systems such as the global positioning system （GPS） and the global navigation satellite systems （GNSS） are routinely used to estimate the contaminating effects by critical environment. In an effort to define the accuracy and reliability of GPS/ GNSS positioning, we investigated the data having con- taminating effects due to forestry environment. Some reliability criteria and geometric concepts were defined and then examined by them. Two sets of data were collected in open sky and closed canopy separately. The analysis of the observed data was performed using the reliability criteria and geometric concepts. The accuracy and reliability of positioning strongly depended on the canopy ratio and satellite availability. The minimum detectable error on baseline was estimated about 2.5 mm under closed canopy. The number of observable satellites and minimal detectable errors were computed for each epoch. The minimal biases on estimated baselines, bias-to-noise ratios for estimating baseline components and probability of success of the integer ambiguity solution were defined in case of forest canopy. Finally, geometric quality could be achieved using the factors of dilution of precision. Thus, the presented accuracy and reliability concepts fulfill the requirement proposed by the global geodetic observing system in forest environment.
文摘A voltage-controlled oscillator（VCO） with dual stages of accumulation mode varactors for a multimode global navigation satellite system（GNSS） application,which adopts sigma-delta fractional-N technology in the synthesizer,is presented.The structure is selected to optimize the frequency coverage and tuning linearity, based on a general analysis of the parasitic capacitance in the coarse tuning switch bank cells,which cover the global positioning system（GPS） and Beidou（BD） bands.The VCO implemented in the 0.18μm CMOS process can cover the GPS L1,BD B1,B2 and B3 bands with sufficient margin,and exhibits low phase noise by using this tuning curve linearization technique.The equalized K_（vco）,characteristic behavior further offers a wide voltage tuning range and improves the stability of the closed loop.
