1、GPS冷啟動(dòng)，暖啟動(dòng)，熱啟動(dòng)的定義–Definition of GPS Cold Start, Warm Start, and Hot Start

GPS定位器的啟動(dòng)時(shí)間比較混亂,達(dá)盟GPS小編搜集外文的一些解釋，希望能夠用比較簡(jiǎn)單的語(yǔ)言讓GPS愛(ài)好者們加深認(rèn)識(shí)。

Hot Start — The GPS receiver remembers its last calculated position and which satellites were in view, the almanac used, and the UTC Time。 It then performs a reset and attempts to acquire satellites and calculate a new position based upon the previous information。 This is the quickest re-acquisition of a GPS lock.

熱啟動(dòng)—-GPS定位器保存有其最后計(jì)算的可視衛(wèi)星的位置、almanac（歷書(shū))和UTC時(shí)間，在重啟以后，GPS定位器以保存的上述內(nèi)容為基礎(chǔ)獲取和計(jì)算當(dāng)前衛(wèi)星的最新位置。

Warm Start – The GPS receiver remembers its last calculated position， almanac used， and knows the UTC Time， but not which satellites were in view. It then performs a reset and attempts to obtain the satellite signals and calculate a new position. The receiver has a general idea of which satellites to look for because it knows its last position and the almanac helps identify which satellites are visible in the sky。 This takes longer than a Hot Start but not as long as a Cold Start。

暖啟動(dòng)——GPS定位器保存有最后計(jì)算的衛(wèi)星的位置、歷書(shū)和UTC時(shí)間，但是沒(méi)保存可視衛(wèi)星的數(shù)據(jù)。GPS定位器重啟以后嘗試去獲得當(dāng)前衛(wèi)星和信號(hào)并計(jì)算其新位置。GPS定位器基于其最后的位置和歷書(shū)得以大概知道當(dāng)前天空中的可視衛(wèi)星。所以暖啟動(dòng)比熱啟動(dòng)慢，但是比冷啟動(dòng)快。

Cold Start – The GPS receiver dumps all information and resets. It then attempts to locate satellites and then calculate a GPS lock. This takes the longest because there is no known information. The GPS receiver has to attempt to lock a satellite signal from all of the satellites， basically like polling， which takes a lot longer than knowing which satellites to look for。 This re-acquisition of a GPS lock takes the longest.

冷啟動(dòng)：GPS定位器清空了所有歷史信息并重啟,然后它嘗試定位并鎖定衛(wèi)星，由于沒(méi)有先前信息，這將花去很長(zhǎng)的時(shí)間。GPS定位器采用類似于輪詢的方法，從所有的衛(wèi)星中鎖定信號(hào)，這將比事前知道該搜索哪些衛(wèi)星要慢不少。這一類重新獲取鎖定要花最長(zhǎng)的時(shí)間.

2、比較和小結(jié)

熱啟動(dòng)就是啟動(dòng)時(shí)可視的衛(wèi)星信息和之前保存的信息是基本一致的.

暖啟動(dòng)和熱啟動(dòng)的區(qū)別在于是否保存了之前的可視衛(wèi)星信息,熱啟動(dòng)保存了可視衛(wèi)星(當(dāng)前衛(wèi)星）而暖啟動(dòng)的可視衛(wèi)星無(wú)效了，所以熱啟動(dòng)比暖啟動(dòng)定位速度快。

冷啟動(dòng)，最好理解,就是在沒(méi)有歷史信息的情況下一個(gè)一個(gè)輪詢的方式搜星定位,所需時(shí)間最長(zhǎng)。

3、關(guān)鍵名詞解釋:Almanac(歷書(shū)） 和 Ephemeris（星歷）

Almanac data is course orbital parameters for all SVs。 Each SV broadcasts Almanac data for ALL SVs。 This Almanac data is not very precise and is considered valid for up to several months。

Almanac 數(shù)據(jù)是反映所有衛(wèi)星狀況的比較粗略的軌道參數(shù)，每一個(gè)衛(wèi)星都會(huì)廣播所有衛(wèi)星的Almanac 數(shù)據(jù)，這類數(shù)據(jù)不是十分精確，有效期長(zhǎng)達(dá)幾個(gè)月。

Ephemeris data by comparison is very precise orbital and clock correction for each SV and is necessary for precise positioning. EACH SV broadcasts ONLY its own Ephemeris data. This data is valid for a period of time （maybe several hours) as determined by information contained in the broadcast。

Ephemeris 數(shù)據(jù)相比之下是十分精確的軌道和時(shí)鐘糾正信息，每一顆衛(wèi)星只會(huì)廣播自己的Ephemeris 數(shù)據(jù)，這類數(shù)據(jù)的有效期或許有幾個(gè)小時(shí)（取決于廣播信息的包含的內(nèi)容）。

下圖是《公開(kāi)服務(wù)性能規(guī)范 (3.0版)》的對(duì)北斗導(dǎo)航電文的描述：

說(shuō)明在北斗系統(tǒng)：Ephemeris的更新周期是1個(gè)小時(shí)，Almanac的更新周期小于7天。

4、GPS冷啟動(dòng)、溫啟動(dòng)和熱啟動(dòng)三種啟動(dòng)條件與啟動(dòng)時(shí)間對(duì)比

冷啟動(dòng)：以下幾種情況開(kāi)機(jī)均屬冷啟動(dòng)。初次使用時(shí)；關(guān)機(jī)后超過(guò)2小時(shí)重新開(kāi)機(jī)；電池耗盡導(dǎo)致星歷信息丟失時(shí)；關(guān)機(jī)狀態(tài)下將GPS定位器移動(dòng)到1000公里以上距離。

冷啟動(dòng)一般在30秒到幾分鐘時(shí)間（決于天氣、AGPS的使用，障礙物、衛(wèi)星信號(hào)強(qiáng)度和GPS芯片性能/設(shè)備性能）。

溫啟動(dòng)：距離上次定位的時(shí)間超過(guò)兩個(gè)小時(shí)的啟動(dòng)。 溫啟動(dòng)一般在3-45秒。（取決于GPS芯片性能/設(shè)備性能，AGPS的使用，環(huán)境等）。

熱啟動(dòng)：距離上次定位的時(shí)間小于兩個(gè)小時(shí)的啟動(dòng)。 熱啟動(dòng)一般在1-10秒。（取決于GPS芯片性能/設(shè)備性能/環(huán)境等）。