【 Notes 】 AGPS or Assisted GPS
Assisted Global Positioning System ( AGPS or Assisted GPS )
GPS operation was summarized in the previous section. Although GPS is a very robust positioning system, there remains the problem of time to first fix ( TTFF ) or “ cold start ” ; that is, GPS receivers are first turned on, they need a long time (on the order of 30 seconds to a few minutes) to acquire satellite signals, to navigate data, and to localize. This time duration varies with the location of the receiver and the surrounding interference. In order to address this problem, AGPS has been developed.
GPS操作在前一節中進行了總結。 盡管GPS是一種非常強大的定位系統，但仍然存在首次定位時間（TTFF）或“冷啟動”的問題; 也就是說，GPS接收器首先打開，它們需要很長時間（大約30秒到幾分鐘）來獲取衛星信號，導航數據和定位。 該持續時間隨接收器的位置和周圍干擾而變化。 為了解決這個問題，已經開發了AGPS。
AGPS consists of
1. a wireless handset with a scaled - down version (with respect to the power requirements, computational capabilities, etc.) of a GPS receiver;
2. an AGPS server with a reference GPS receiver that can simultaneously monitor and track the same satellites as the wireless handset; and
3. a wireless network infrastructure consisting of base stations and a mobile switching center.
AGPS包括
1.具有縮小版本（關于GPS接收器的功率要求，計算能力等）的無線手機;
2.具有參考GPS接收器的AGPS服務器，其可以同時監視和跟蹤與無線手機相同的衛星; 和
3.由基站和移動交換中心組成的無線網絡基礎設施。
The AGPS server obtains handset position from the mobile switching center and can locate the cell of the handset and even the sector of the handset within a set if directional antennas are used at the cell base stations [1] . Because the AGPS server monitors and tracks the GPS satellites, it can predict the satellites that are sending the signals to the handset at any given point of time. Thus, the AGPS server can communicate the satellite information to the handset.
AGPS服務器從移動交換中心獲得手機位置，并且如果在小區基站使用定向天線，則可以定位手機的小區甚至手機的扇區[1]。 由于AGPS服務器監視和跟蹤GPS衛星，它可以預測在任何給定時間點向手機發送信號的衛星。 因此，AGPS服務器可以將衛星信息傳送到手機。
This enables the handset to acquire GPS signals quickly when it is fi rst turned on, reducing TTFF from minutes to less than a second. Once the satellite signals are acquired by the handset, it calculates the distances to satellites without clock synchronization. These satellite distances are sent back to the AGPS server for further computation, as can be seen in Figure 1.3 a. Thus, the AGPS server also shares the computational load of the handset, reducing the handset battery power consumption.
這使得手機能夠在首次開啟時快速獲取GPS信號，從而將TTFF從幾分鐘減少到不到一秒。 一旦手機獲取衛星信號，它就會在沒有時鐘同步的情況下計算到衛星的距離。 這些衛星距離被發送回AGPS服務器以進行進一步計算，如圖1.3a所示。 因此，AGPS服務器還共享手機的計算負荷，降低了手機電池的功耗。
Figure 1.3 a
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