全球定位系統(tǒng)的介紹外文翻譯-通信工程(存儲(chǔ)版)
【正文】 GPS 接收器之間是多少距離？ 第三章 ：如何確定 GPS 衛(wèi)星當(dāng)前位置 GPS 衛(wèi)星在高度為 11000 公里的軌道繞地球飛行。 國防部不 斷地監(jiān)視衛(wèi)星的軌道預(yù)測(cè)值的偏差。 為了做到這一點(diǎn)，衛(wèi)星和接收機(jī)使用非常精確的同步時(shí)鐘，以便它們?cè)谕耆嗤臅r(shí)間，生成相同的代碼。不幸的是，這兩個(gè)時(shí)鐘是不可能同步的，因?yàn)?GPS接收機(jī)中的時(shí)鐘是不像非常精確和昂貴的衛(wèi)星原子鐘那樣精確的。在數(shù)學(xué)上，解決四個(gè)未知數(shù)（ x， y 和 z，和 t），必須有四個(gè)方程。 正如前面提到的， GPS 信號(hào)包含有關(guān)下列內(nèi)容的信息的星歷表（軌道位置）的錯(cuò)誤，和有關(guān)的廣播衛(wèi)星的時(shí)鐘漂移的速率。雖然上面討論的誤差總是 會(huì)影響精度，確定定位精度的另一個(gè)主要因素是正在接收信號(hào)的一組衛(wèi)星（星座）的排布或幾何分布。 GPS 接收器的另一個(gè)重要的特點(diǎn)是可以忽略或消除超過用戶定義的限制受 DOP 影響的 GPS 讀數(shù)。不同的衛(wèi)星的幾何形狀，可以放大或減少上述誤差預(yù)算中的錯(cuò)誤。 星歷誤差不應(yīng)該與選擇可用性（ SA）混淆， SA 是國防部對(duì)信號(hào)的時(shí)間和星歷的蓄意篡改。這些錯(cuò)誤加在一起可能會(huì)導(dǎo)致實(shí)際 的 GPS 接收器的位置偏差為 + / 50 100 米。從地面關(guān)閉監(jiān)測(cè)每顆衛(wèi)星的時(shí)鐘使得控制站能在每個(gè)衛(wèi)星的信號(hào)中插入精確地描述了該衛(wèi)星的時(shí)鐘漂移率的消息。每秒 186,000 英里的速度乘以這個(gè)時(shí)間間隔就是接收機(jī)位置與衛(wèi)星之間的距離。 第四章 ：計(jì)算你的位置和 GPS 衛(wèi)星之間的距離 GPS 通過測(cè)量衛(wèi)星和接收機(jī)之間無線電信號(hào)（ GPS 信號(hào)）傳輸所花費(fèi)的時(shí)間來確定衛(wèi)星和接收機(jī)的距離。今天的 GPS 接收器存儲(chǔ)所有的 GPS 衛(wèi)星的軌道信息，被稱為星歷。其實(shí)，第四球體可能不是必需的。你會(huì)知道我在一個(gè)以你的房子為圓心，半徑 10 英里的球形邊界的地方。 GPS 會(huì)告訴你，你是在點(diǎn) X， Y， Z，而 GIS 告訴你， X， Y， Z 點(diǎn)是一棵橡樹，或河流中的一個(gè) pH值 的點(diǎn)。 今天，許多行業(yè)都促使國防部改變。s clock. The insertion of the drift rate effectively synchronizes all of the GPS satellite clocks. The same procedure cannot be applied to the clock in a GPS receiver. Therefore, a fourth variable (in addition to x, y and z), time, must be determined in order to calculate a precise location. Mathematically, to solve for four unknowns (x,y,z, and t), there must be four equations. In determining GPS positions, the four equations are represented by signals from four different satellites. Chapter Six: The GPS Error Budget The GPS system has been designed to be as nearly accurate as possible. However, there are still errors. Added together, these errors can cause a deviation of +/ 50 100 meters from the actual GPS receiver position. There are several sources for these errors, the most significant of which are discussed below: Atmospheric Conditions The ionosphere and troposphere both refract the GPS signals. This causes the speed of the GPS signal in the ionosphere and troposphere to be different from the speed of the GPS signal in space. Therefore, the distance calculated from Signal Speed x Time will be different for the portion of the GPS signal path that passes through the ionosphere and troposphere and for the portion that passes through space. As mentioned earlier, GPS signals contain information about ephemeris (orbital position) errors, and about the rate of clock drift for the broadcasting satellite. The data concerning ephemeris errors may not exactly model the true satellite motion or the exact rate of clock drift. Distortion of the signal by measurement noise can further increase positional error. The disparity in ephemeris data can introduce 15 meters of positional error, clock drift disparity can introduce meters of positional error and measurement noise can introduce 010 meters of positional error. Ephemeris errors should not be confused with Selective Availability (SA), which is the intentional alteration of the time and ephemeris signal by the Department of Defense. A GPS signal bouncing off a reflective surface prior to reaching the GPS receiver antenna is referred to as multipath. Because it is difficult to pletely correct multipath error, even in high precision GPS units, multipath error is a serious concern to the GPS user. Chapter Seven: Measuring GPS Accuracy As discussed above, there are several external so
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