Patent Application
20160187488
The disclosed embodiments of the present invention relate to satellite positioning, and more particularly, to a satellite-based positioning method and an associated apparatus.
A Global Navigation Satellite System (GNSS) receiver determines its position by computing arrival times of signals transmitted simultaneously from multiple satellites. Current fully-operational GNSS include the US GPS (Global Positioning System) and the Russian GLONASS (GLObalnaja NAvigatsionnaja Sputnikovaja Sistema). As part of their messages, these satellites transmit both satellite positioning data and satellite clock timing data. The satellite positions and clock timing are represented by almanac or ephemeris data, wherein the ephemeris data provides an extremely accurate estimate (˜1 meter error) of satellite positions and clock bias. The process of searching for and acquiring satellite signals, reading the ephemeris data transmitted by the satellites, and computing the location of the receiver from this data is time consuming, however, often requiring several minutes. In many cases, this lengthy processing time is unacceptable and furthermore, greatly limits battery life in miniaturized portable applications.
For example, a GNSS receiver determines position based on the measurement of the arrival times at a GNSS receiver antenna of the GNSS signals broadcast from orbiting satellites. As stated, one disadvantage of such a system is the relatively long time needed to perform signal acquisition under certain conditions. Satellite signals cannot be tracked until they have first been located by searching in a two-dimensional search “space”, whose dimensions are code-phase delay and observed Doppler frequency shift. The process of the GNSS receiver searching for, acquiring, and demodulating satellite signals is sometimes referred to as a “standalone” mode of operation, which can be contrasted with an “assisted” mode of operation.
In order to reduce the delay associated with a stand-alone mode of operation, information may be provided to aid a GNSS receiver in acquiring a particular signal. Such assistance information permits a receiver to narrow the search space that must be searched in order to locate a signal, by providing bounds on the code and frequency dimensions. A system that employs a GPS receiver augmented with externally sourced GPS assistance data is commonly referred to as an “assisted global positioning system” (AGPS).
AGPS is a system that predicts satellite orbit information and, in many cases, greatly improves the startup performance or time-to-first-fix (TTFF) of a GNSS satellite-based positioning system. Extended Prediction Orbit (EPO) is a prior art example of an AGPS with off-line server based AGPS technology, which is a swift way to obtain specific information of the satellite, such as position and clock, before the receiving of broadcast ephemeris. The specific information aids the GNSS positioning engine (PE) to quickly locate the satellite, and thus obtain a First Fix with a faster speed. Refer to US Patent No. 20110273329 for more details.
EPO supports up to 30 days satellite trajectory prediction using numerical fitting analysis with some models (mathematical, force, etc.), and greatly enhances a user experience by improving TTFF of a GNSS receiver. While providing a prediction of the extended satellite orbit and clock up to many days ahead, however, errors between the predicted and the actual orbit with respect to some satellites may be enormous. The First Fix may be poor since the GNSS PE cannot foretell quality of the orbit and clock prediction for respective satellites in advance.
Therefore, a novel satellite positioning method is desired for aiding a GNSS receiver to derive a First Fix.
One of the objectives of the present invention is to provide a satellite-based positioning method for aiding a GNSS receiver to derive a First Fix, and an apparatus utilizing the same.
According to a first aspect of the present invention, a satellite-based positioning method is disclosed. The satellite-based positioning method comprises: obtaining predicted satellite data for at least one satellite vehicle (SV) in a global navigation satellite system (GNSS); obtaining reference satellite data for the at least one SV; deriving calculating satellite prediction error data for each of the at least one SV according to the predicted satellite data and the reference satellite data; and utilizing a processing unit to calculate a parameter for each of the at least one SV based on the satellite prediction error data.
According to a second aspect of the present invention, a satellite-based positioning apparatus is disclosed. The satellite-based positioning apparatus comprises a prediction unit and a processing unit. The prediction unit is arranged for generating predicted satellite data for at least one satellite vehicles (SVs) in a global navigation satellite system (GNSS). The processing unit is arranged for calculating satellite prediction error data for the at least one SV according to the predicted satellite data and the reference satellite data, and calculating a parameter for each of the at least one SV based on the satellite prediction error data.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is electrically connected to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
Flow 104 is a process to generate at least a confidence index. In 1044, the confidence index is produced based on prediction errors generated by 1042. The prediction errors represent how much the prediction results deviate from the actual orbits and clocks. Specifically, each SV may have a plurality of confidence index sets, which will be described later. By incorporating the confidence index sets obtained by the flow 104 (represented by the dotted line) into the orbit/clock prediction result produced by the flow 102, the GNSS receiver can derive a weight of respective SV (1068). Please note that the processes 1062, 1064, 1066, and 1070 may be replaced by any other First Fix computation mechanism to achieve the same objective. Compared with a conventional flow (bypass 1068), the disclosed method provides a more reliable and precise First Fix by referring to the weight of respective SV while the GNSS receiver computes for the First Fix. This is the spirit of the invention.
The confidence index may be incorporated into the conventional EPO file, or into other types of orbit/clock prediction file. The PE therefore may check the confidence index and appropriately weight a respective SV according to the confidence index, as mentioned in
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
