[ 1 ]

　　China launches last BDS satellite to complete global navigation constellation [Internet]. Beijing: China Xinhua News; 2020 Jun 23 [cited 2021 Jan 31]. Available from: http://www.xinhuanet.com/english/2020-06/23/c_ 139161359.htm.

　　链接1

　　[ 2 ]

　　GLONASS history [Internet]. Korolev: Information and Analysis Center for Positioning, Navigation and Timing; [cited 2021 Jan 31]. Available from: https://www.glonass-iac.ru/en/guide/.

　　链接1

　　[ 3 ]

　　Paziewski J, Crespi M. High-precision multi-constellation GNSS: methods, selected applications and challenges. Meas Sci Technol 2020;31:010101.

　　链接1

　　[ 4 ]

　　Parkinson BW, Powers ST华体会最新地址. Part 1: the origins of GPS and the pioneers who launched the system [Internet]. Santa Ana: GPS World; 2010 May 1 [cited 2021 Jan 31]. Available from: https://www.gpsworld.com/origins-gps-part-1/.

　　链接1

　　[ 5 ]

　　Weiss P. The Global Positioning System (GPS): creating satellite beacons in space, engineers transformed daily life on Earth. Engineering 2021;7(3):290–303.

　　[ 6 ]

　　Expert opinions: challenges faced by multi-constellation GNSS receiver designers [Internet]. Santa Ana: GPS World; 2018 Feb 8 [cited 2021 Jan 31]. Available from: https://www.gpsworld.com/expert-opinions-challengesfaced-by-multi-constellation-gnss-receiver-designers/.

　　链接1

　　[ 7 ]

　　Aven T. Implications of black swans to the foundations and practice of risk assesent and management. Reliab Eng Syst Saf 2015;134:83–91.

　　链接1

　　[ 8 ]

　　Parkinson B. Assured PNT for our future: PTA [Internet]. Santa Ana: GPS World; 2014 Sep 1 [cited 2021 Feb 3]. Available from: http://digital.gpsworld.com/ September2014#&pageSet=39.

　　链接1

　　[ 9 ]

　　International committee on global navigation satellite systems (ICG) [Internet]. Vienna: United Nations Office for Outer Space Affairs; [cited 2021 Feb 1]. Available from: https://www.unoosa.org/oosa/en/ourwork/icg/icg. html.

　　链接1

　　[10]

　　Wang W, Wang Y, Yu C, Xu F, Dou X. Spaceborne atomic clock performance review of BDS-3 MEO satellites. Measurement 2021. In press.

　　链接1

　　[11]

　　Jaduszliwer B, Camparo J. Past, present, and future of atomic clocks for GNSS. GPS Solut 2021;25:27.

　　链接1

　　[12]

　　Directorate-General for Defence Industry and Space. EU Space investments to the rescue [Internet]. Brussels: European Commission; 2020 Dec 2 [cited 2021 Feb 1]. Available from: https://ec.europa.eu/defence-industry-space/eu-spaceinvestments-rescue-2020-12-02_en.

　　链接1

　　[13]

　　Li G, Guo S, Lv J, Zhao K, He Z. Introduction to global short message communication service of BeiDou-3 navigation satellite system. Adv Space Res 2021;67:1701–8.

　　链接1

　　[14]

　　Parkinson BW, Powers ST. The origins of GPS: fighting to survive, part 2 [Internet]. Santa Ana: GPS World; 2020 Jun 1 [cited 2021 Feb 1]. Available from: https://www.gpsworld.com/origins-gps-part-2-fighting-survive/.

　　链接1

　　[15]

　　BeiDou completes inter-satellite link testing; only GNSS with this accuracyimproving feature [Internet]. Red Bank: Inside GNSS Media & Research; 2020 Jun 18 [cited 2021 Jan 31]. Available from: https://insidegnss.com/BeiDoucompletes-inter-satellite-link-testing-only-gnss-with-this-accuracy-improvingfeature/.

　　链接1

　　[16]

　　Development of the BeiDou navigation satellite system (version 4.0). Report. Beijing: China Satellite Navigation Office; 2019 Dec.

　　[17]

　　New civil signals [Internet]. Washington, DC: GPS; [cited 2021 Jan 31]. Available from: https://www.gps.gov/systems/gps/modernization/civilsignals/ #L1C.

　　链接1

　　[18]

　　Market understands value of dual frequency [Internet]. Prague: European Global Navigation Satellite System Agency (GSA); 2020 Jan 28 [cited 2021 Feb 1]. Available from: https://www.gsa.europa.eu/newsroom/news/marketunderstands-value-dual-frequency.

　　链接1

　　[19]

　　Carlson EK. What will 5G bring? Engineering 2020;6(7):725–7.

　　链接1

　　[20]

　　Carlson EK. New standards release sets stage for 5G future. Engineering 2021;7 (3):273–4.

　　链接1