# Detecting and Mitigating Attacks on GPS Devices
## 4 Factors Contributing to GPS-Denied or GPS-Disrupted Environments
### GPS Spoofing
A wide variety of low-cost SDR units are available, such as the HackRF and BladeRF platforms, which are the most popular. There are also open-source signal generation environments that can be leveraged for GPS spoofing, such as the GPS-SDR-SIM GPS signal simulation software package. The authors of [62] presented research in which they constructed a low-cost GPS spoofing system using a HackRF One SDR platform connected to a laptop computer running the GPS-SDR-SIM GPS signal simulator. This GPS spoofing system was tested against a Holystone HS7000 UAS. The authors did not provide results in terms of effective range, but they did demonstrate that spoofed signals are effective. The authors of [50] also used their BladeRF X40 SDR-based system to implement a GPS spoofing attack. The authors of [63] constructed a GPS spoofer utilizing the BladeRF x40 SDR platform with the GPS-SDR-SIM GPS signal simulator. They tested this low-cost GPS spoofer against a Huawei tablet with a GPS receiver and demonstrated that the receiver reported the spoofed GPS position. The authors of [64] presented a low-cost GPS spoofing system based on the HackRF One SDR platform attached to a laptop computer running the GPS-SDR-SIM GPS signal simulator. They tested the effectiveness of this solution against a GPS-enabled smartphone, successfully demonstrating that their low-cost system transmitting a spoofed L1 GPS carrier caused the smartphone to report the incorrect spoofed position. The research presented in these papers clearly illustrates that an effective GPS spoofing system can be implemented easily and inexpensively. Table 8 summarizes low-cost GPS spoofer implementations found in the literature. There are several additional critical insights from existing research. First, unmanned systems can respond erratically and catastrophically to rapidly varying spoofed positions. The authors of [62] noted that a UAS exhibited erratic behavior, rapid speed increases, and a subsequent crash when a very low position altitude was rapidly spoofed. The authors of [65] discussed how rapid or erratic changes in the spoofed position could result in UAS crashes and proposed a GPS spoofing algorithm that implemented slow changes in the spoofed location to create the desired deception trajectory without adverse effects, such as crashing or detection. Second, a GPS spoofer's effectiveness depends on the quality of the authentic GPS signal. Experiments performed in [50] examined attacks against a GPS-enabled smartphone device in indoor and outdoor scenarios. The GPS spoofing system successfully tricked the receiver in both scenarios; however, spoofing took significantly longer outdoors. In some cases, GPS spoofing did not become effective until approximately three minutes later. Spoofing was never effective when the actual GPS signal had a very high DOP. These results suggest that the effectiveness of GPS spoofing might be directly related to the signal's quality in terms of signal strength and system geometry. These results also suggest a temporal aspect to spoofer effectiveness. A spoofed GPS signal does not necessarily have to \"overpower\" the actual GPS signal to be effective. A key result from [63] is that position estimation error begins to grow if the spoofed GPS signal is 8.04 dB weaker than the actual GPS signal. The spoofed signal controlled the position once it was 4.52 dB weaker than the actual GPS signal. There is an example in the literature revealing the ease