# AVSS: Airborne Video Surveillance System
## 1 Introduction  
Surveillance systems have always been of a great importance. Typical surveillance systems are implemented with multiple closed circuit televisions (CCTV) installed around the area that requires surveillance. While the traditional method provides highly cost effect method regarding the hardware, it has limitations in many ways. First, they are location bound. With a CCTV, a camera is installed to monitor a location, possibly moving a camera direction is provided at most. Second, it requires significant human labor to install and remove the system. To overcome such issues, we propose AVSS, an aerial video surveillance system that uses a fleet of unmanned aerial vehicles (UAVs). AVSS overcomes aforementioned shortcomings as follows. By adopting UAVs as surveillance probes instead of fixed cameras, the probes can move freely in the sky to adjust the captured region. This provides basic adjustments to the change in target areas. Also, with the fleet platform we designed and implemented, a fleet of UAVs can be deployed and retrieved with a click of a button. Therefore, a short term deployment becomes viable, as opposed to traditional systems. In AVSS, UAVs, specifically multi-rotors, are used as surveillance probes. Single-rotor UAVs can serve the same purpose, but they are not yet widely popular for the danger it causes with their much larger blade wings. Multi-rotors have performance advantages over other types of UAVs, as well aslimitations. As a means to replace CCTV, the video captured by the UAV needs to be still. In many cases, the target area requires constant surveillance, and other forms of UAVs cannot provide such still image capturing. Even capturing the same area will require the UAV to constantly tilt/pan the camera, which will require an image processing technique to keep the camera on the same point, but it is not easily doable on a UAV environment. Furthermore, when a target moves in a specific direction, being quickly responsive or following the target with exact speed may not be doable at all with fixed wing UAVs. On the contrary, these are no issues for multi-rotors as long as the object is not faster than its maximum speed. In this aspect, a multi-rotor UAV is a better fit than most of the other options, including but not limited to, fixed wing UAVs, ground vehicle surveillance, and portable towers. In AVSS, operator can freely set and modify the surveillance area. Operator can setup and modify the surveillance area by simply moving UAVsto an area of interest. Further, scalability can also be supported by utilizing more UAVs. However, there are limitations for UAVs, especially multi-rotors (From this point on, we will refer to multi-rotors as UAVs, non inclusive of other UAV types), to be addressed for practical deployment. First, the flight duration of a UAV is very limited. A commercial UAV can fly at most 30-40 m. It is also to be mentioned that the 30-40 m is the top end of the flight time, and most commercial UAVs can only fly 20-25 m including the ones we use. The time is shortened when the UAVs are equipped with auxiliary devices. Also, UAVs have limited battery life and computing power. The limited computing power makes expensive computing such as high-level image processing implausible. By using a fleet of UAVs as well as light weight algorithms and storage optimization, AVSS has resolved the above challenges. We consider the following characteristics as the key features of the proposed system, and our focus is on implementing the characteristics into the surveillance system: deployable with minimal effort without consideration of the surveillance area, easy modification of the surveillance area, and rate adaptation to the network status for video streaming. As briefly mentioned, the existing CCTV surveillance system requires much work on installing and maintaining the system. Using a surveillance system with UAVs, the deployment and maintenance process of the system can be simplified.