# Performance Analysis of the Pilot and Data Component of a CSS Signal for LEO-PNT +
## 1 Introduction  
The extended use of battery-powered devices, such as smartphones, tablets, portable computers, and wearable and IoT devices, is changing the way our technology is designed. In the last decade, there has been a trend of devices with low-power consumption and low-complexity processing. To do so, we must consider simple signal structures leading to simple receiver processing architectures. In addition, there is a trend toward targeting everywhere connectivity by relying on the satellite segment. A proof of that is the extended list of low Earth orbit (LEO) satellite constellations for internet services or IoT connectivity in the NewSpace landscape [1, 2]. The opportunities of LEO constellations deal with the main challenges of IoT communication and localization systems [3, 4]. One clear example joining both communication and localization is a positioning, navigation, and timing (PNT) system [5], and there is a current interest in LEO-PNT. Indeed, the first PNT results from the Starlink constellation were published in [6], and it opened a new era of alternative PNT solutions based on signals of opportunity (SoO) from LEO constellations or by the development of an alternative LEO PNT system [7]. During the past decades, the use of global navigation satellite systems (GNSSs) has become the primary and sometimes only way of providing a global PNT solution for many outdoor applications [8]. Unfortunately, GNSS is a very power-hungry technology that is vulnerable to several threats [9]. Thus, it is important to provide alternative PNT solutions to back up GNSS in case of failure or denial of service [9, 10]. In this sense, the use of LEO constellations has been considered in the literature to provide a global PNT solution, but more importantly, because it will bring some benefits with respect to MEO constellations [6, 7]. In this paper, we focus on the signal design for a LEO-PNTsystem. Different options can be adopted for the LEO-PNT signal, but if we aim to reduce complexity with respect to current GNSS, we should change the current GNSS signal structure [4; 11]. Otherwise, the signal acquisition would be prohibitive for low-complexity devices. Recall that the high dynamic in LEO constellations will produce a large search space for the acquisition process of a direct-sequence spread spectrum (DSSS) signal (i.e., current GNSS signal structure) [4]. One alternative with lower acquisition complexity can be based on a chirp spread spectrum (CSS) signal. The CSS signal has extensively been used in radar [12] since a long time ago, and it is reaching the realm of low-power wide-area networks (LPWANs) by the deployment of LoRa networks [13]. From the analysis of CSS signals in radar and communication applications, we can distinguish the cases of estimating only data or time-delay propagation or Doppler frequency when all the other parameters are known or set to zero. The case of estimating all three parameters at the same time has not been treated in the literature of radar or communications. The first time a CSS signal was considered for a PNT signal was given in [4]. Indeed, the complexity of the CSS signal was analyzed in [4], and it was compared with a DSSS signal. Improvements in terms of complexity from 1 and up to 2 orders of magnitude can be obtained using CSS with respect to DSSS. Furthermore, ref. [11] provides details on the key performance indices (KPIs) for PNT of the CSS signal. We consider in this paper the use of a CSS signal for a LEO-PNT signal, which perfectly fits with the case of estimating the three parameters mentioned above. The goal of this paper is to explain the design of a CSS signal for PNT. This will include the design of the ranging component and the data component. The performance evaluation of both components will also be analyzed and compared. Therefore, the contribution of this paper is to complete the design of a CSS-based PNT signal by analyzing both the ranging and data component.