Review of code and phase biases in multi-GNSS positioning

Abstract

A review of the research conducted until present on the subject of Global Navigation Satellite System (GNSS) hardware-induced phase and code biases is here provided. Biases in GNSS positioning occur because of imperfections and/or physical limitations in the GNSS hardware. The biases are a result of small delays between events that ideally should be simultaneous in the transmission of the signal from a satellite or in the reception of the signal in a GNSS receiver. Consequently, these biases will also be present in the GNSS code and phase measurements and may there affect the accuracy of positions and other quantities derived from the observations. For instance, biases affect the ability to resolve the integer ambiguities in Precise Point Positioning (PPP), and in relative carrier phase positioning when measurements from multiple GNSSs are used. In addition, code biases affect ionospheric modeling when the Total Electron Content is estimated from GNSS measurements. The paper illustrates how satellite phase biases inhibit the resolution of the phase ambiguity to an integer in PPP, while receiver phase biases affect multi-GNSS positioning. It is also discussed how biases in the receiver channels affect relative GLONASS positioning with baselines of mixed receiver types. In addition, the importance of code biases between signals modulated onto different carriers as is required for modeling the ionosphere from GNSS measurements is discussed. The origin of biases is discussed along with their effect on GNSS positioning, and descriptions of how biases can be estimated or in other ways handled in the positioning process are provided.<p>QC 20170922</p

Investigation on Reference Frames and Time Systems in Multi-GNSS

“…Term dT Rec is the receiver clock offset, which is independent of the GNSS. However we will see later that different receivers measure different TSC X implying receiver biases which are dependent both on the receiver and the GNSS [16]. To monitor the GNSS specific time offset it is convenient to take TSC G as the reference time scale and evaluate the difference (TSC X + dT Rec ) − (TSC G + dT Rec ), with X referring to all the GNSS's different from GPS [17].…”

Nadir-Dependent GNSS Code Biases and Their Effect on 2D and 3D Ionosphere Modeling

“…In this study, STECs were estimated considering only the first-order ionospheric term, derived with Equations (2), (3), and (6). This is acceptable, as the higher-order terms only amount to one centimeter at most [29], which is well below the expected accuracy for ionosphere modeling.…”

“…BeiDou group delay variations were prominent and consistent in the residuals for both the two-dimensional and three-dimensional case of ionosphere modeling, while GPS group delay variations were smaller and could not be confirmed due to the accuracy limitations of the ionospheric models. Group delay variations were, to a larger extent, absorbed by the ionospheric model when three-dimensional ionospheric tomography was performed in comparison with two-dimensional modeling.computerized ionospheric tomography (CIT) [2][3][4], techniques that were inspired by and have emerged from computerized tomography (CT) for medical applications [5].GNSS hardware biases [6], and especially biases in the code observations, are well-known to affect the estimation of TEC from GNSS observations [7][8][9]. These biases, referred to as differential code biases (DCBs), are regarded as constant offsets between code observations associated with two signals transmitted between the same satellite and receiver.…”

“…GNSS hardware biases [6], and especially biases in the code observations, are well-known to affect the estimation of TEC from GNSS observations [7][8][9]. These biases, referred to as differential code biases (DCBs), are regarded as constant offsets between code observations associated with two signals transmitted between the same satellite and receiver.…”

Investigation and Validation of the Time-Varying Characteristic for the GPS Differential Code Bias

“…The GNSS biases are generally analyzed and investigated based on the redundant observations and the geometry-free observations. They can be classified into two types of code and phase observations and have obtained much attention from many authors and this area of research has deeply developed in recent years [1]. The differential code bias (DCB) is one of the biases referring to codes modulated on difference carriers or on the same carrier.…”