看過該網站 即可知道為什麼 俄羅斯的干擾器在伊拉克被JDAM幹掉的原因

這個網站程度稍微深一點 提到一些GPS抗干擾技術
http://www.globalsecurity.org/space/systems/gps.htm
節錄部分內容如下:
......GPS users can combine a variety of demonstrated techniques for a robust battlefield capability, including adaptive nulling antenna arrays, integration and fielding of the numerous receiver upgrades available to provide matched dynamic tracking and increased dynamic range, and airborne UAV-carrying pseudo-satellites (pseudolites which provide high-power and close-in GPS navigational data), which will overpower jammers. Developing and using out-of-band pseudolites with GPS down converters for weapons, developing cheap radiation homing weapons for GPS and military communications frequencies, and developing a joint jamming evaluation group will also counter the effects of jamming. The appropriate combination of these to obtain 30 dB of processing gain will decrease the effectiveness of a 60-mile jammer to 1¼ miles and allow an inertial system to provide the desired weapons accuracy.

The relationship between the jammer size and the GPS receiver antijam capability determines the target protected area. The current military receivers have a jammer tolerance of 54 dB above the received signal levels from the satellites. Using advanced receiver improvements and nulling antennas in the future, it is possible to raise the tolerance level to a combined level of 98 dB. This 44-dB increase in protection will reduce the protected target area against a 1-kW jammer from a 190-km diameter circle to a 1.2-km diameter circle. It is possible to even raise the jamming margin up to 120 dB, reducing the protected circle to a 184-meter diameter. At the 120-dB level, the enemy must use psuedolites and homing weapons to offset this capability. A HARM missile tuned to the antijammer frequency can negate this jamming effort.

As users improves GPS systems, the opposition can increase its effective radiated power up to approximately 100 megawatts before it becomes too costly for the jammer to continue. Thus, antijam weapons provide an effective capability.

介紹了如何在實驗室製造GPS 干擾信號 Continuous Wave, broadband, wideband 三種不同的干擾方式 以測試GPS武器的抗干擾性能

介紹GPS的信號 所代表的意義
1. pseudorandom code: is simply an I.D. code that identifies which satellite is transmitting information. You can view this number on your Garmin GPS units satellite page, as it identifies which satellites its receiving.

2.Ephemeris data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position

3.The almanac data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits almanac data showing the orbital information for that satellite and for every other satellite in the system.

這個網站詳細解釋了下列GPS相關名詞

GPS CAPABILITIES
1.Standard Positioning Service (SPS)
2.Precise Positioning Service (PPS)

GPS SIGNAL CHARACTERISTICS
1. coarse/acquisition (C/A) code
2.precision (P) code
3. Y-code
4.L-band frequencies: L1 = 1575.42 MHz and L2 = 1227.6 MHz.

SELECTIVE AVAILABILITY, ANTI-SPOOFING

GPS SYSTEM SEGMENTS
1.The SPACE segment
2.The CONTROL segment
Monitor Stations
Ground Antennas
Master Control Station (MCS)
3.The USER segment

GPS SYSTEM TIME

1.Composite Clock (CC).

GPS TIME TRANSFER

airborne pseudo-satellites(pseudolite) 的GPS抗干擾概念
http://www.darpa.mil/spo/SPO_handouts/GPX.pdf

第一個網站介紹地面固定的pseudo-satellites 第二個網站則是以UAV為載具的pseudo-satellites
運作概念上不太一樣

節錄第二個網站的部分內容如下
....DARPA is solving the problem of GPS jamming by developing airborne pseudo-satellites (or “pseudolites”) which provide high power GPS signals that overpower jammers. A pseudolite system can be thought of as being a miniature GPS constellation. Four pseudolites are required for a full navigation solution, just like four GPS satellites are required today. The concept is that the airborne pseudolites would find their own position from GPS satellites, even in the presence of jamming. The pseudolites do this through a state-of-the-art beamforming antenna and signal processor that decrease the effects of jamming. Then they transmit a GPS-like signal to the friendly air and ground forces at much higher power and at closer range than the satellites. The pseudolite signal overwhelms the jammer and allows the multitude of users to ignore the jamming and continue to navigate.

簡而言之 4架UAV在干擾的環境下 由GPS得知自身的座標 然後以比干擾器更強的訊號蓋台 以類似GPS的訊號(經由GPS定位後 廣播自己的座標) 供友軍定位

　　目前美國使用的全球定位系統(GPS)是20世紀70年代由美國陸海空三軍聯合研製的太空衛星導航定位系統,由24顆衛星組成，這些衛星分佈在互成120度角的軌道平面上，每個軌道平面平均分佈8顆衛星。其主要目的是為陸、海、空三軍提供實時、全天候和全球性導航服務，並用於情報收集、核爆監測和應急通訊等軍事目的，是美國獨霸全球戰略的重要組成部分。經過20餘年的研究實驗，耗資300億美元，直到1994年3月，24顆GPS衛星才真正布設完成。GPS由三部分構成：地面控制部分、太空部分（由24顆衛星組成）、用戶裝置部分（由GPS接收機和衛星天線組成）。

　　GPS衛星最早是提供P碼（精碼）和C/A碼（粗碼）兩種定位服務。P碼為美國軍方服務，定位精度達到3公尺；C/A碼對國際社會開放，定位精度為14公尺。基於本身安全的考慮，美國先後實施了SA和AS政策。SA政策在C/A碼中人為引入了誤差，使定位精度下降到100公尺；AS則對P碼實行加密。由於GPS對國際社會開放，因此各類接收機被廣泛應用於各行各業，改變了傳統的定位導航方式。

　　目前，美國使用的GPS系統為第一代，但由於衛星的訊號功率較低，抗干擾能力較差，伊拉克戰爭中就發生了不少美軍發射由GPS導引的巡弋飛彈因受到干擾而大幅度偏離航向的事件，有的甚至落在土耳其境內。其實早在幾年前，美國國防部就計劃對當前使用的GPS衛星進行現代化改造，增加發射新的高功率點波束軍用M碼，在戰時美國軍方有權對某地區的其他訊號進行干擾。但目前美國軍方認為這些改進仍無法滿足未來的需要，因此這次推出了GPS—3計劃。

　　據美國軍方介紹，GPS—3將改變舊的GPS體系結構，新研製的衛星解析度比目前衛星高10倍，設計壽命為15—20年。GPS—3的抗干擾能力比現有GPS系統提高了100—500倍，並採用了最先進的加密技術。美軍預計將用20年時間再發射24顆新型衛星，替代目前的24顆舊的GPS系統的衛星。另外，洛克希德·馬丁公司已宣佈，它們為GPS—3研製出了新一代的G—STAR接收機，該機抗干擾能力強、可以設定自動反欺騙模式，對抗敵方的干擾活動，而且該接收機還可以安裝在美軍最先進的長程空對地巡弋飛彈上，引導飛彈精確攻擊目標。

　　當前世界上各個主要的大國都十分重視全球導航系統的建立。以俄羅斯為例，俄國在20世紀70年代初就訂定了“全球導航衛星系統”(Glonass)計劃，並於1995年開始實施，發射24顆在軌衛星構成完整的全球定位系統。但由於經濟原因，該項計劃擱置了5年，直到2001年12月1日俄再次發射3顆Glonass衛星，拉開了Glonass衛星更新計劃的序幕。同時，俄預計2005年開始設計名為Glonass—K的第三代Glonass衛星。另外，西歐國家的“伽利略”計劃也是一項龐大的歐洲版“全球導航系統”，目前也正在加緊實施 ; 德國和法國為了分攤研發經費並擴大歐洲版“全球導航系統--伽利略”的使用國規模，甚至在去年底邀請中國加入“伽利略”計劃 ! 據稱中國目前正在考慮。不過另一方面，中國本身也在部署建構自己的“北斗”衛星導航定位系統，所以是否會參與西歐國家的“伽利略”計劃還須再觀察。