دانلود کتاب رمزنگاری و ناوبری ماهواره‌ای

Most personal electronic devices give position and time automatically, and from that, navigation easily follows. In practice, satnav systems like a Global Navigation Satellite System (GNSS), infrastructure such as the Global Positioning System (GPS), or a Regional Navigation Satellite System (RNSS) set of satellites such as the Quasi-Zenith Satellite System (QZSS) contribute to that position, navigation, and timing data. As with any other kind of information service, the assumption is that this information is true—that one can believe the position and time are what we are given. That belief is our informal definition of PNT assurance: the degree to which a user can trust that PNT is accurate. This notion is formalized later. Assurance, in general, is achieved by putting protections in place to mitigate anything that would cause the information to deviate from truth. In cybersecurity, the whole subject of system security engineering exists there to develop methods to provide assurance. Adapting that thinking to the PNT world has been considered, as discussed later in this chapter, but delving into those broad areas is beyond our scope.