Design of Fast Positioning GPS Software Receiver
Date Issued
2014
Date
2014
Author(s)
Chen, Hung-Wei
Abstract
There are three processes in traditional GPS positioning algorithm: Signal acquisition, signal tracking and positioning. At least 30 seconds sampled data length are required to complete the reception of navigation messages in the tracking process which is the most time consuming part of positioning. Using the advantage of a software receiver which is flexible architecture of positioning algorithm, we design a new positioning algorithm to achieve fast positioning without the tracking process. In the proposed design, the information of satellite positions is provided by an external source.
The proposed design is divided to two parts: Doppler positioning algorithm and code-phase positioning algorithm. In the first part, we apply the Doppler positioning algorithm with a priori time and the Doppler measurements obtained from signal acquisition process to derive coarse position of receiver which is used as a priori position in the code-phase positioning algorithm. In the second part, the a priori time and position are then used in the code-phase positioning algorithm with the code-phase measurements obtained from signal acquisition process to calculate precise time and position solution. There is a similar combined positioning algorithm named Doppler/code-phase positioning algorithm with tracking process which requires longer length of sampled data for stable measurements addressed in the literature. Using proposed tracking-free design, the required sampled data length can be less than 10 milliseconds. Therefore, time to first fix (TTFF) can be greatly reduced.
There are two different lengths of sampled data used in the dissertation :10 milliseconds(ms) and 1 millisecond. Two extreme time accuracy of a priori time are used: 1 second(s) and 12 hours(h). Therefore, there are four cases which are 1s-10ms, 1s-1ms ,12h-10ms and 12h-1ms. algorithm. Using Doppler/code-phase positioning algorithm, we can only derive the correct receiver position in the first case. The correct position can be obtained using proposed geometric constraint in the Doppler positioning algorithm for the third case. Because of short sampled data length used in the second case, there will be an integer ambiguity problem. Therefore, the time accuracy constraint of 1 ms is introduced in the code-phase positioning algorithm to efficiently search correct integers for deriving correct receiver position. Besides, a dynamic problem was addressed in the literature. If the speed of receiver is over 80-100 km/h, error of positioning results will be several hundreds of kilometers which can also be resolved by the time accuracy constraint.
In other words, the limitations are reduced using the proposed constraints. We can derive the receiver position in the second and third case using the designed algorithm. When the sampled data length is 10ms, the required time accuracy of a priori time can be relaxed to 12 hours with geometric constraint used in the Doppler positioning algorithm. If the time accuracy of a priori time is 1 second, the sampled data length of signal can be as short as 1 ms by using the time accuracy constraint in the code-phase positioning algorithm. The positioning accuracy is about few tens of meters with 1 ms sampled data . However, with 10 ms sampled data, the positioning accuracy can be improved to 10-20 meters which is similar to traditional positioning algorithm with tracking. We set up several static and dynamic experiments using both simulated and real signals to verify the proposed design.
Subjects
快速定位
無追蹤程序
都卜勒定位
粗略時間定位
Type
thesis
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