What is GNSS Spoofing?
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What is GNSS Spoofing?

How Spoofing Affects Survey and Mapping

With spoofing attacks on the rise, survey-grade GNSS receivers need to be protected by interference mitigation technology utilizing the latest security techniques to ensure reliable positioning.

The survey and mapping industry has been benefiting for years from GPS/GNSS precise positioning technology. While GNSS spoofing is recognized as a real threat for unmanned aerial vehicles (UAVs or ‘drones’), its influence on survey and mapping equipment is still underestimated. Reliable data capture is important across various mapping use cases, from man-based surveying and mobile mapping all the way to UAV photogrammetry. Ensuring dependable positioning requires the use of robust equipment, designed in such a way that alleviates all possible vulnerabilities. The use of GNSS receivers which are robust against jamming and spoofing is key to trustworthy data capture anytime, anywhere.

GPS/GNSS欺骗与干扰

Both jamming and spoofing are a type of GNSS radio interference that happens when weak GNSS signals are overpowered by stronger radio signals on the same frequency. Jamming is a kind of ‘white noise’ interference, causing loss of accuracy and potentially loss of positioning. This type of interference can come from adjacent electronic devices or external sources such as radio amateurs in the area. Spoofing is an intelligent form of interference which fools the user into thinking that he/she is in a false location. During a spoofing attack, a radio transmitter located nearby sends fake GPS signals into the target receiver. For example, even a cheap software-defined radio (SDR) can make a smartphone believe it’s on Mount Everest (see Figure 1)!

GNSS用户正在经历越来越多的干扰案例,并且欺骗事件也在增加 - 尤其是在近年来,由于它变得更容易,更容易创建恶意欺骗系统。从芬兰(芬兰经历了为期一周的欺骗袭击)到中国有很多例子,那里有多艘船是欺骗袭击的目标。因此,干扰和欺骗保护不再是“拥有”功能,而是GNSS接收器的关键组成部分。

Spoofing Incidents are On the Rise

C4ADS, an NGO conducting data-driven analysis of conflict and security matters, concluded that Russia has been extensively using spoofing to divert aerial drones from entering airspace in the vicinity of governmental figures, airports and ports. And some of the most enthusiastic spoofers are fans of the augmented reality mobile game ‘Pokémon Go’, who use SDRs to spoof their GPS position and catch elusive Pokémon without having to leave their rooms.

这种攻击通常目标特定的接收器。However, the spoofing transmission will actually affect all GPS receivers in the vicinity. For example, an SDR can affect all GPS receivers within a 1km radius of the spoofing source, and the signal can be amplified for further propagation. This means that survey or mapping jobs in densely populated areas are at a higher risk of such ‘indirect’ spoofing attacks.

Figure 1: Even a cheap SDR can overpower GNSS signals and spoof a single-frequency smartphone GPS into believing it is on Mount Everest.

How to Spoof-proof a Receiver

A spoofer can either rebroadcast GNSS signals recorded at another place and time, or generate and transmit modified satellite signals. Therefore, to combat spoofing, GNSS receivers need to be able to distinguish spoofed signals from authentic signals. Once a satellite signal is flagged as spoofed, it can be excluded from positioning calculations.

There are various levels of spoofing protection that a receiver can offer. Using the analogy of a home intrusion detection system, it can be based on a simple entry alarm system or a more complex movement detection system. For added security, the home owner could decide to install video image recognition, breaking-glass sound detection or a combination of the above. An unprotected GNSS receiver is like a house with an unlocked door; it is vulnerable to even the simplest forms of spoofing. Secured receivers, on the other hand, can detect spoofing by looking for signal anomalies or by using signals designed to prevent spoofing, such as Galileo OSNMA and E6 or the GPS military code.

高级干扰缓解技术,例如Septentrio AIM+,使用复杂的信号处理算法来减轻干扰和标志欺骗。对于欺骗检测,AIM+检查GNSS信号中的各种异常,例如异常高的信号功率。它还与RAIM+完整性算法一起使用,以通过比较来自各种卫星的范围信息来确保范围(距离卫星)有效性。AIM+甚至不会被先进的GNSS信号发电机Spirent GSS9000所欺骗。即使在信号内使用现实的功率水平和实际导航数据,它仍然可以将其识别为“非真实性”信号。目前正在研究其他先进的抗散热技术,例如使用双极天线。

图2:GNSS欺骗可用于操纵空中无人机的运动。

卫星导航数据身份验证

各个国家通过将安全性直接建立到其GNSS卫星中来投资欺骗韧性。借助开放服务导航消息身份验证(OSNMA),欧洲伽利略是第一个直接在民用GNSS信号上引入反欺骗服务的卫星系统。

OSNMA is a free service on the Galileo E1 frequency that enables authentication of the navigation data on Galileo. Such navigation data carries information about satellite location and, if altered, will result in wrong receiver positioning computation. As a close partner of ESA, the European GNSS manufacturer Septentrio has been contributing to the design and testing of the Galileo system since its inception. Today, as the OSNMA system is entering its testing phase, Septentrio receivers have successfully been used to test the OSNMA signals. The US GPS system is also experimenting with satellite-based anti-spoofing for civil users with its recent authentication system called Chimera.

图3:欧洲伽利略卫星在E1信号和E6信号上的商业身份验证服务上提供了公开的身份验证服务。(图片提供:欧洲航天局)

高级干扰技术

OSNMA is a part of the puzzle comprising the目标+干扰防御系统。抗肢体组件抑制了最广泛的干扰物,从简单,连续的窄带信号到最复杂,宽带和脉冲传输。抗散热成分包括信号异常检测,oSNMA,RAIM+以及其他算法。

未来的防护GNSS接收器

Interference mitigation technology such as AIM+ protects accurate positioning today. To ensure the best protection for tomorrow too, GNSS manufacturers are offering future-proof technology which allows users to take advantage of new GNSS security services like ONSMA and Chimera as soon as they become available. Utilizing future-proof GNSS receivers in survey, mapping and UAV equipment enables integrators to reduce their time to market with resilient products. Secured GNSS means trustworthy precise positioning and peace of mind for everyone who relies on this technology.

Further Reading

https://www.septentrio.com/en/advanced-interference-monitoring-mitigation-aim

https://septentrio-my.sharepoint.com/:b:/p/marketing/EU99N82bWyZPsvd4Dp9g5lwBEwqQLgeT8i7wtW64TEk-tw?e=S0fGFD

This article was featured in

gim-第2-2021期

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