Wang Weiwei, Tian Ye, Bian Lang, Wang Guoyong, Meng Yansong, Zhang Lixin
China Academy of Space Technology (Xi'an), Xi'an 710100, China.
Sensors (Basel). 2022 Jul 25;22(15):5538. doi: 10.3390/s22155538.
Low Earth Orbit (LEO) satellites have stronger received signals and more rapid geometry changes than Global Navigation Satellite System (GNSS) satellites, making them attractive for positioning, navigation, and timing (PNT) applications. Due to the low altitude, the LEO constellation requires more satellites to cover the entire globe and more Pseudo Random Noise (PRN) codes to realize Code Division Multiple Access (CDMA), which means greater receiver storage resources and receiver acquisition time. In this paper, different from the traditional methods that assign a unique PRN code to each satellite, we propose a novel method in which several satellites share the same PRN code, and simply demonstrate the feasibility and benefits of this method. To determine the minimum number of PRN codes needed for a constellation, we build a mathematical model. After the algorithm comparison, we improve the recursive largest first (RLF) algorithm so that it has a higher running speed and a smaller approximate optimal solution within a certain time period. By studying polar-orbiting and walker constellations, we find that if other satellite parameters remain the same, the higher the orbital altitude is, the more PRN codes are needed, and no matter what the orbital inclination is, the minimum number of PRN codes remains the same. Overall, it is feasible and meaningful for several satellites sharing the same PRN code to save storage resources and reduce the satellite acquisition time of the receiver. If this new technology is applied, the storage resources and the average satellite acquisition time of the receiver will be, at most, one-third of previous ones.
低地球轨道（LEO）卫星比全球导航卫星系统（GNSS）卫星具有更强的接收信号和更快的几何变化，这使得它们在定位、导航和授时（PNT）应用中具有吸引力。由于轨道高度较低，LEO星座需要更多的卫星来覆盖全球，并且需要更多的伪随机噪声（PRN）码来实现码分多址（CDMA），这意味着需要更大的接收机存储资源和接收机捕获时间。在本文中，与传统方法为每颗卫星分配唯一的PRN码不同，我们提出了一种新颖的方法，即几颗卫星共享相同的PRN码，并简单地证明了该方法的可行性和优势。为了确定星座所需的PRN码的最小数量，我们建立了一个数学模型。经过算法比较，我们改进了递归最大优先（RLF）算法，使其在一定时间段内具有更高的运行速度和更小的近似最优解。通过研究极轨星座和沃克星座，我们发现，如果其他卫星参数保持不变，轨道高度越高，所需的PRN码就越多，并且无论轨道倾角如何，PRN码的最小数量保持不变。总体而言，几颗卫星共享相同的PRN码以节省存储资源并减少接收机的卫星捕获时间是可行且有意义的。如果应用这项新技术，接收机的存储资源和平均卫星捕获时间最多将是以前的三分之一。
