CDMA+FDMA非差非组合区域PPP-RTK

Regional PPP-RTK with CDMA+FDMA data at undifferenced and uncombined level

为顺应多频多模发展趋势,PPP-RTK技术正逐步由传统的消电离层组合数据处理模式发展为非差非组合模式。现有非差非组合PPP-RTK研究多针对码分多址(CDMA)系统,而频分多址(FDMA)PPP-RTK受频率间偏差的影响难以实现。本文针对区域参考网,提出了一种CDMA+FDMA多系统非差非组合PPP-RTK模型,该模型能灵活处理多频多模两类信号体制的数据。为了实现FDMA PPP-RTK,本文利用整数可估理论保证了模糊度固定的严密性,该FDMA PPP-RTK模型适用于同款接收机的参考网。本文采集了香港地区连续运行参考网的GPS、BDS、Galileo、GLONASS数据进行试验,数据采样率为30 s。服务端结果表明,由于各产品之间高度相关,对组合产品进行精度评估是有必要的。组合卫星钟差、卫星相位偏差和电离层产品后,精度达到毫米级,满足用户精密改正的要求。用户端仿动态定位结果表明,GPS、BDS和Galileo单系统PPP-RTK分别在5、1和3 min实现了模糊度首次固定,定位误差收敛至厘米级。GLONASS组合GPS实现了首历元模糊度固定,定位精度比GPS单系统提升了9%、12%、14%(东、北、天3个方向)。BDS组合GPS同样能实现首历元模糊度固定,定位精度比GPS单系统提升了29%、22%、18%,额外加入Galileo观测值,定位精度进一步提升了12%、8%、16%。再加入GLONASS观测值,定位精度仍有小幅提升(4%、3%、8%)。

To conform to the trend of multi-frequency and multi-GNSS,PPP-RTK is gradually transforming its data processing mode from the ionosphere-free method to the undifferenced and uncombined one.Existing studies on undifferenced and uncombined PPP-RTK mainly focus on the code division multiple access(CDMA)systems,whereas conducting frequency division multiple access(FDMA)PPP-RTK is challenging due to the effects of inter-frequency bias.This work proposes a regional PPP-RTK model which is capable of processing multi-frequency CDMA and FDMA data at undifferenced and uncombined level.The model adopts the recently proposed integer estimability theory to realize FDMA PPP-RTK in a network of homogeneous receivers,thereby ensuring the rigor of ambiguity resolution.We carry out experiments by collecting GPS,BDS,Galileo,GLONASS data with a sampling rate of 30 seconds from the Hong Kong continuously operating reference stations.Results on the network side indicate that,due to the strong correlation between different products,it is not wise to assess the precision of individual product,but necessary to analyze the combined product.After forming the combined product of satellite clock,satellite phase bias,and ionospheric delay,the precision reaches to millimeter level,thus precise enough for user correction.Results on the user side indicate that the time to first fix of GPS,BDS,and Galileo single-system PPP-RTK is 5,1,and 3 minutes,respectively.Once the ambiguities are successfully fixed,the positioning errors converge to centimeter level.Instantaneous ambiguity resolution is achievable when combining GLONASS and GPS,and the positioning accuracy is improved by,as compared to GPS-only case,9%,12%,14%(on the east,north,up component).Integrating BDS with GPS also achieves instantaneous ambiguity resolution and obtains an accuracy improvement of 29%,22%,18%compared to GPS-only case.Combining additionally Galileo observables further improves the accuracy by 12%,8%,16%.A slight improvement of 4%,3%,8%is obtained by adding GLONASS observables to carry out quad-system PPP-RTK.