## 5 Conclusions  
This work looks at the pseudo range measurement of open loop tracking for GNSS and proposes the Adaptive Correlation Space Adjusted Open Loop Tracking Approach (ACSA-OLTA) to improve the measurement accuracy of open loop tracking for vehicle positioning in urban area. A novel expression to obtain the code search grid size which can bring the best measuring accuracy, named Equivalent Weighed Pseudo Range Error is presented in Section 3.1. Using the new expression, the optimal code search grid sizes for different \(C/N_{0}\) are computed. Following a thorough analysis, the accuracy of the code phase measurement calculated from the early-minus-late discriminator and that directly extracted from the grid is evaluated for different grid sizes when \(C/N_{0}\) varies. The computational costs are also assessed. Based on the analysis results, the measurement calculation strategy is developed. ACSA-OLTA adaptively adjusts the correlation space to the optimal code search grid size and switches the measurement calculation methods as the developed strategy according to \(C/N_{0}\). With the help of the Monte Carlo simulation, the mean code phase measuring errors for different \(C/N_{0}\) and grid sizes are evaluated. The results verify that the proposed EWPRE can indicate the measuring error level for open loop tracking with different grid sizes. The optimal code search grid size obtained according to EWPRE for the corresponding \(C/N_{0}\) is valid. Data was collected in the campus of Beijing Institute of Technology and Zhongguancun, Beijing and processed using various configurations. For the data analyzed herein, based on the positioning results computed with the Least Square method, which is directly related to the code phase measurement accuracy, the main conclusions are as follows:  
Figure 16: Position error cumulative distribution of the positioning results in Segment 2. * In open air area where the \(C/N_{0}\) of most satellites are larger than 30 dBHz, the errors of most positioning results calculated from the code phase measurements that are gained from the EMLD is smaller than 10 m. It outperforms those directly extracted from the grid with the sizes of 0.05 chip, 0.1 chip and 0.2 chip and it is similar to that with the grid size of 0.02 chip. The results validate the analysis in Section 3.2 that the early-minus-late discriminator can keep the measurement accuracy but reduce the correlator utilized when \(C/N_{0}\) is high. It also indicates that narrowing down grid size can help to improve the accuracy in this case which is the same as that EWPRE shows. * In urban canyon area where the \(C/N_{0}\) of a number of satellites is lower than 20 dBHz, the performance of the EMLD based measurement calculation method is greatly degraded. At the same time, the accuracy of the measurements directly extracted from the grids with size of 0.02 chip and 0.05 chip are also deteriorated. On the contrary, the accuracy of the measurements directly extracted from grids with larger grid sizes is better. When the grid sizes are 0.1 chip and 0.2 chip, the positioning errors are much less than those with smaller grid sizes. It verifies that properly enlarging the search grid size can improve the measurement accuracy when \(C/N_{0}\) is low as the EWPRE shows in Section 3.1. * In both the two scenarios, ACSA-OLTA can greatly improve the measurement accuracy compared with the traditional open loop tracking method with fixed search grid sizes and measurement calculation methods. The results of the test in the paper show that when \(C/N_{0}\) is high, the EMLD is utilized and 90% positioning results have the error smaller than 10 m. When \(C/N_{0}\) is low, the search grid size is adjusted and 70% positioning results have the error smaller than 20 m. The results also validate that the grid sizes gained from EWPRE are preferable.