衛星授時存在多種方式，如單向授時和雙向授時。在單向授時中，衛星授時終端可自主完(wan)成定(ding)時(shi)。授(shou)時(shi)終端接收衛星(xing)廣(guang)播(bo)的導(dao)航(hang)電(dian)文，其中含(han)有時(shi)間(jian)基準(zhun)信(xin)息、導(dao)航(hang)衛星(xing)星(xing)歷、電(dian)文發(fa)播(bo)時(shi)刻等。之后，解算出(chu)基本觀測量及導(dao)航(hang)電(dian)文信(xin)息，得(de)到鐘差以修正(zheng)本地時(shi)間(jian)，實現本地時(shi)間(jian)與UTC同(tong)步。同(tong)時(shi)，用(yong)戶至少要接收四顆導(dao)航(hang)衛星(xing)的信(xin)號，通過綜合解析(xi)來確定(ding)三維位(wei)置和接收機本地時(shi)間(jian)這(zhe)四個(ge)變量。
一、單向授時的兩種模式
1、RNSS單(dan)向授時
授(shou)時(shi)(shi)終端通過(guo)自主(zhu)解算(suan)獲得自身位置(zhi)(zhi)信息(xi)或者(zhe)根據已(yi)知坐(zuo)標位置(zhi)(zhi)信息(xi)獲得定時(shi)(shi)信息(xi)，衛(wei)星(xing)導航(hang)(hang)電文信息(xi)包括整周秒計數、周內秒計數、鐘(zhong)差參數、與(yu)UTC時(shi)(shi)間(jian)(jian)(jian)(jian)同步參數等信息(xi)，RNSS授(shou)時(shi)(shi)終端通過(guo)接收衛(wei)星(xing)導航(hang)(hang)信號并自主(zhu)解算(suan)出本地時(shi)(shi)間(jian)(jian)(jian)(jian)和GNSS系統時(shi)(shi)間(jian)(jian)(jian)(jian)差?TJST-GNT，并且根據衛(wei)星(xing)導航(hang)(hang)系統與(yu)UTC的時(shi)(shi)間(jian)(jian)(jian)(jian)差值?TGNT-UTC修(xiu)正本地時(shi)(shi)鐘(zhong)，從(cong)而使本地時(shi)(shi)間(jian)(jian)(jian)(jian)與(yu)UTC時(shi)(shi)間(jian)(jian)(jian)(jian)同步。
2、RDSS單向(xiang)授時
原理與RNSS類似，但由于(yu)RDSS衛(wei)星(xing)對于(yu)出站信(xin)號(hao)為透明轉(zhuan)發，因此通過(guo)授時(shi)終端獲得本地時(shi)刻與UTC時(shi)間差值(zhi)中還包括了上行信(xin)號(hao)傳(chuan)播時(shi)延及衛(wei)星(xing)轉(zhuan)發器(qi)的零值(zhi)。其(qi)中上行傳(chuan)播時(shi)延從RDSS出站電文中獲得。
二、RDSS雙向授時
1、RDSS雙向授(shou)時：雙向授(shou)時設(she)備具備出站信號接收(shou)和(he)應答發射入(ru)站信號的能(neng)力，通過與地面(mian)(mian)中心站進行(xing)往返(fan)測量，由(you)中心站獲得授(shou)時終(zhong)端(duan)與地面(mian)(mian)中心站的時間(jian)差(cha)值，可以避免授(shou)時終(zhong)端(duan)天線位置(zhi)誤(wu)差(cha)、電離層(ceng)/對(dui)(dui)流(liu)層(ceng)改造殘(can)差(cha)等諸(zhu)多不確定(ding)因(yin)素引起的單向授(shou)時偏差(cha)，相對(dui)(dui)于RDSS單向授(shou)時，雙向授(shou)時具有較(jiao)高的授(shou)時精度。
2、RDSS雙向(xiang)(xiang)授時(shi)(shi)(shi)(shi)(shi)由授時(shi)(shi)(shi)(shi)(shi)終(zhong)端發起授時(shi)(shi)(shi)(shi)(shi)申請，授時(shi)(shi)(shi)(shi)(shi)終(zhong)端與(yu)(yu)地(di)面中(zhong)心(xin)站(zhan)進行交互，向(xiang)(xiang)地(di)面中(zhong)心(xin)站(zhan)發送定時(shi)(shi)(shi)(shi)(shi)申請，地(di)面中(zhong)心(xin)站(zhan)計算其(qi)與(yu)(yu)授時(shi)(shi)(shi)(shi)(shi)終(zhong)端的時(shi)(shi)(shi)(shi)(shi)間差，并通過出站(zhan)信(xin)號播(bo)發給該授時(shi)(shi)(shi)(shi)(shi)終(zhong)端，授時(shi)(shi)(shi)(shi)(shi)終(zhong)端返回的正(zheng)向(xiang)(xiang)傳播(bo)時(shi)(shi)(shi)(shi)(shi)延信(xin)息T正(zheng)向(xiang)(xiang)及出站(zhan)電文獲得的RDSS系統時(shi)(shi)(shi)(shi)(shi)間與(yu)(yu)UTC時(shi)(shi)(shi)(shi)(shi)間差值?T(GNT-UTC)，修正(zheng)本(ben)地(di)時(shi)(shi)(shi)(shi)(shi)間使其(qi)與(yu)(yu)UTC時(shi)(shi)(shi)(shi)(shi)間同步完成雙向(xiang)(xiang)授時(shi)(shi)(shi)(shi)(shi)。
三、衛星單向授時的常見應用
衛(wei)星單(dan)向授(shou)時(shi)相對較為常見，可滿足大(da)部分中低精(jing)度(du)授(shou)時(shi)要求(qiu)。GPS導航的(de)基本原(yuan)理是(shi)通過用戶終端實時(shi)與衛(wei)星終端進(jin)(jin)行(xing)導航電文的(de)交互(hu)，通過定(ding)位(wei)計算方法，實時(shi)的(de)更新用戶的(de)位(wei)置信(xin)息(xi)(xi)并規劃路徑指引(yin)行(xing)進(jin)(jin)方向，需(xu)要利用到(dao)時(shi)鐘(zhong)記錄的(de)時(shi)間、電文收發的(de)時(shi)間戳信(xin)息(xi)(xi)形成位(wei)置信(xin)息(xi)(xi)。
衛星(xing)單向(xiang)(xiang)授時(shi)(shi)較為常(chang)見，人們平時(shi)(shi)使(shi)用(yong)(yong)(yong)(yong)的(de)(de)手(shou)機GPS授時(shi)(shi)導(dao)航定位(wei)、北斗授時(shi)(shi)定位(wei)、車(che)載GPS授時(shi)(shi)導(dao)航定位(wei)以及能接收軍碼(ma)(ma)的(de)(de)軍用(yong)(yong)(yong)(yong)設施授時(shi)(shi)定位(wei)都是衛星(xing)單向(xiang)(xiang)法(fa)的(de)(de)典型應(ying)用(yong)(yong)(yong)(yong)。衛星(xing)單向(xiang)(xiang)授時(shi)(shi)能夠滿足(zu)大多(duo)數中(zhong)低同(tong)步(bu)精度(du)的(de)(de)要求，應(ying)用(yong)(yong)(yong)(yong)最為廣泛(fan)(fan)。北斗授時(shi)(shi)終端中(zhong)，利用(yong)(yong)(yong)(yong)所(suo)接收導(dao)航信(xin)號解(jie)算的(de)(de)高精度(du)時(shi)(shi)間信(xin)息綜合實現NTP、B碼(ma)(ma)、PTP和(he)串口等的(de)(de)高精度(du)授時(shi)(shi)服務。B碼(ma)(ma)是其中(zhong)一種應(ying)用(yong)(yong)(yong)(yong)最為廣泛(fan)(fan)的(de)(de)專用(yong)(yong)(yong)(yong)時(shi)(shi)間碼(ma)(ma)，其特點是速率適(shi)中(zhong)、編碼(ma)(ma)信(xin)息量豐(feng)富、通用(yong)(yong)(yong)(yong)規范及使(shi)用(yong)(yong)(yong)(yong)靈活方便。基于北斗授時(shi)(shi)的(de)(de)B碼(ma)(ma)終端在靶場測量、控制(zhi)、計算、通信(xin)、氣象和(he)電力等領域得到了(le)越來越廣泛(fan)(fan)的(de)(de)應(ying)用(yong)(yong)(yong)(yong)。
四、北斗衛星授時模塊推薦
高精度授時模塊SKG121T
GPS北斗授時模塊SKG178T
北斗授時模塊SKG09DT
