Performance and Evaluation of GNSS Receiver Vector Tracking Loop Based on Adaptive Cascade Filter
Round 1
Reviewer 1 Report
The paper is more focused on a method (theory), not on its applications (practice). I recommend to discuss in more detail the practical role of the method. In particular, IoT-oriented sensing technologies and promising IoT applications can be introduced. The key issue is that applications provide model assumptions for the method.
Introduction should be shortened. Details can be moved to the subsequent sections.
There are many umbered formulas. If a formula is numbered then it is significant for the paper. Thus, provide reference to this formular where the formular is applied to construct a result of this paper. If no reference is used then the formular is not important for the paper.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper proposes a method to improve navigation systems using GNSS by using EF and EKF. This paper is useful for technological development.
However, I have an objection to the publication of this paper in Remote Sensing.
In fact, the term "remote sensing" is not used anywhere in the paper,
and there is no mention of how it is related to remote sensing.
This paper should be submitted to another journal.
It is difficult to see what the measurements are, what the system parameters
are, and how and what was calculated, partly due to the fact that many
mathematical symbols are not defined
I would like a clear explanation of those points.
Some math symbols seem to be missing. These are examples of them.
They are not exhaustive.
(1)equation(1) What are alpha and T?
(2)Line 185: 0 is subscript.
(3)Fig.1 What is I & D?
(4)equation(14): What are the subscripts hat and - in X_k?
(5)equation(15) what is tau?
(6)equation(23) Two R_{\rho,k} seem to be the same.
(7)equation(30) P_k is defined from P_{k,k-1}, while P_{k,k-1} is calculated
from P_{k-1}? Is it possible?
(8) Section 4: What is the advantage compared with NovAtel SPAN-CPT
high-precision navigation system?
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
The authors present a new vector tracking algorithm for code delay and Doppler frequency estimation on GNSS receivers. In this type of scheme, the code delay and the Doppler frequency of each satellite is estimated together with that of the other satellites in coverage using a centralized estimation algorithm. It has the advantage that the lack of signal on a satellite does not immediately break the code tracking loop. Authors propose a new vector tracking algorithm for GNSS receiver code lock.
The algorithm, which is an application of typical estimation algorithms (Kalman and Extended Kalman filters) to this problem, seems original. The main contribution lies in the incorporation of an adaptive measurement noise matrix estimation scheme in such a way that the filter is robust to changes in the structure of the measurement noise autocorrelation matrix. The idea is interesting and, together with the results, it seems that the work has enough contributions to be published.
However, the article is not ready to be published. In my opinion the work is not well presented. Especially in sections 2 and 3, where the body of the algorithm is presented. Here are some points that could be corrected in the final wording:
- The title should be changed to indicate that vector tracking is a part of GNSS receivers. As it is written, the title does not clarify paper content.
- The same happens with the abstract, which is only understood after having read the article.
- There are undefined terms and some errors in the equations (line 144, Df should be Da; T is not defined) (Tau needs to be defined in equation (15)) (in eq (16) Qdym, 1 should be Qdym ) (on line 214 “velocity” would be “position”)
- In some expressions the references are missing. For example: equations 1 and 2 that present the dynamic model of the Kalman filter, the model is not explained or a reference is given; equation (5) is not complete; equation (6) needs a reference; It is not clarified which model of correlation between states is used in the covariance matrixQ, a reference is needed in eq. (17).
- The explanation at the beginning of section 3 can be taken to the beginning of section 2. This would improve the intelligibility of the proposed system.
- In section 3, eq (19), where the measurement vector of the EKF filter is expressed, it should be explained how this measurement is obtained from the outputs of the Kalman filter of section 2.
Does eq (29) represent the same magnitude as eq (16)? In addition, this is not an update equation as stated in the text. The equations in (30) should be reviewed.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
There is still no mention of how this work is related to remote sensing.
The author should add this at least in the Introduction.
Author Response
Please see the attachment.Author Response File: Author Response.docx
