# Performance Analysis of the Pilot and Data Component of a CSS Signal for LEO-PNT +
## 5 Discussion  
This work has investigated the use of CSS for PNT. This allowed us to show the main challenges and KPIs useful for the design of a CSS-based PNT signal to be operated in LEO constellations and targeting low complexity. Since a PNT signal is equivalent to a joint ranging and communication signal, during the elaboration of the PNT signal design, we are evaluating the ranging and communication capabilities of the signal. Note that today GNSS technology is power hungry in the sense that it needs a high computational load, so the design of a CSS-based PNT signal might provide the solution to this problem. Furthermore, we see a trend of LEO-PNT systems. Unfortunately, the power consumption problem of GNSS is aggravated when moving from MEO to LEO. The reason is that the acquisition search space is increased in LEO due to the increased Doppler frequency with respect to MEO. In this paper, we have shown the different challenges and how to solve them for the design of a low-complexity LEO-PNT signal based on CSS. The first challenge comes when dealing with the estimation of the triple needed for PNT (time delay, Doppler, data) from the CSS signal. To do so, a pilot/data scheme is proposed based on a BOK  
Figure 3: Performance analysis of the data component when linked to the pilot component with the sensitivity performance: (**Left**) bit rate analysis and (**right**) BER analysis.  
CSS and FSK structure for the pilot (i.e., time delay and Doppler estimation) and data (i.e., data demodulation) components, respectively. The second challenge to be dealt with is the design of an MSA scheme useful for PNT. Different schemes can be considered based on two main parameters of the CSS signal: the chirp rate and initial frequency. The performance analysis of the data component is given when linked with the design of the pilot component. The link is given by the design of the chirp period according to the sensitivity performance. The achievable data rate and BER of the considered modulations have been analyzed. Based on the results analyzed in this paper, we see how the proposed CSS signal is a good candidate for a PNT signal. First, it provides valuable results to be operated in a PNT system. For instance, as shown in previous works, it provides accuracies on the level of meters. Furthermore, we show in this paper achievable data rates in the order of tens of kbps. These are metrics of interest for a PNT system. On the other hand, we see that the CSS signal provides a better trade-off between ranging accuracy and achievable data rate than traditional DSSS signals used in GNSS. Note that current GNSSs provide accuracies in the order of meters or tens of meters with just a few tens of bps.  
Conceptualization, methodology, and writing--original draft preparation, D.E.-R.; validation, G.S.-G. and J.A.L.-S.; supervision, G.S.-G. All authors have read and agreed to the published version of the manuscript.  
This research was partly supported by the Spanish Ministry of Science and Innovation under Grant PID2020-118984 GB-I00 and by the TRP programme in the framework of the INNUENDO project, ESA Contract No. AO/1-9585/19/NL/CRS.  
Not applicable.  
Data Availability StatementData are contained within the article.  
The authors declare no conflict of interest.