China DJI's Inspire 1 drone

Videos shot using drones are easily accessible through the media, and drone toys for children have been on the market for a long time. Farmers spray pesticides and architects survey with drones. Amazon, an e-commerce company in the U.S., and CJ Logistics, the number one domestic delivery company, are continuing research and development to commercialize delivery using drones. The three domestic mobile carriers are actively developing drones that perform special disaster response missions and the 5G infrastructure that supports them. At the opening ceremony of the 2018 Pyeongchang Winter Olympics, 1,218 drones dazzled the night sky, capturing the attention of people around the world.

Drones used for delivery, broadcasting, entertainment, and rescue purposes

According to a survey by the Korea Aerospace Research Institute, the commercial drone market size is expected to grow from $2.6 billion in 2017 to $8.7 billion in 2021.

In July 2016, the Ministry of Land, Infrastructure and Transport revised the Aviation Act in response to the increasing use of drones. The drone flight approval standard, which was previously over 12 kg, was raised to over 25 kg. This means that drones weighing less than 25 kg can be flown without reporting to the authorities. Most commercial drones currently on the market can be flown without a separate permit. Regulations will be further relaxed in the future. The Ministry of Land, Infrastructure and Transport plans to establish new drone standards by September of this year, which will also reduce the certification burden on drone companies.

Drones used for crime

However, as drone use increases, cases of drone abuse are also increasing.

In January 2015, a drone flew into the White House. The White House's radar system, which is designed to detect flying objects such as airplanes and missiles, failed to detect the small drone.

In April 2015, a man in his 40s who flew a so-called “caesium drone” onto the roof of the Prime Minister’s Office in Japan surrendered himself to the police. The drone, which was carrying a container of Fukushima sand containing caesium, was left on the roof of the Prime Minister’s Office for a full 13 days before it was discovered.

The radical Sunni militant group Islamic State (IS) has been carrying out bombing attacks using civilian drones since late 2015. In October 2016, two French special forces soldiers and two Kurdish militiamen were killed when IS dropped a bomb from a drone on a Kurdish militia base in northern Iraq.

Iraqi government soldiers fire at drone

In April 2017, New York Times reporter Ben Solomon was covering the Iraqi government’s operation to retake Mosul when he encountered a drone flown by ISIS. The drone was a Phantom, a civilian drone manufactured by China’s DJI, and it dropped bombs without being shot down by Iraqi government forces. Soldiers and reporters were seriously injured when a bomb fell on an Iraqi government camp.

On July 2, 2018, Yemeni rebels released a video through the media showing drones dropping bombs on United Arab Emirates (UAE) troops.

Drones are already a headache for correctional authorities around the world, as the number of unauthorized items being smuggled into prisons using drones continues to increase.

In Korea, drone-based hidden camera crimes are on the rise. In August 2017, a man in his 30s was arrested by the police for flying a drone over Gwakji Beach in Jeju and taking hidden camera photos.


How to respond to drones

On July 19, Keysight’s Kim Gyu-il, who held a seminar on drone detection technology, divided drone response methods into three major stages. The first is drone detection (Detection), which is the stage of finding out that there is a drone. The second is drone detection (Location), which is the stage of finding out where the drone is. The third is drone mitigation, which is the stage of making the drone inoperable. We will introduce the first two stages of the three stages, drone detection and detection methods, focusing on Keysight’s solutions.


Drone signal collection and analysis hardware and software

Drone detection can only be done by capturing signals coming from drones. For this, hardware such as a receiver or antenna to receive signals and software to analyze the signals received by the hardware are required.

Keysight's N6841A

Keysight's N6841A is an indoor and outdoor RF (Radio Frequency) receiver. The signals received by the N6841A can be analyzed with software installed on a PC. The N6850A omnidirectional wideband antenna, which will be released in September, can be connected to the N6841A using an N type cable, expanding the signal analysis range.

SPOT (Sensor Placement and Optimization Tool) is a software used to view RF signal propagation. It provides the signal detection range based on the location where the receiver is installed.

N6820ES Signal Surveyor 4D is a high-speed signal monitoring software for finding and collecting various information in wireless communication environments. It is possible to monitor signals coming from multiple antennas and receivers simultaneously. It includes various functions so that users can apply it flexibly according to the situation.

N6854A RF Geolocation Server Software is software that can check the actual location of where RF signals are coming from on a map. Location can be determined using TDOA, RSS, or a hybrid method that uses both, with multiple receivers installed at different locations.

TDOA (Time difference of Arrival) refers to the time difference between the signal from the signal source and the arrival at each receiver. RSS (Received signal strength) refers to the strength of the received signal. Since the installed multiple receivers are all synchronized with the GPS, the location of the signal source can be determined by the time the signal arrived and the strength of the signal.

Identifying drone location using TDOA method

The essence of the TDOA method is to accurately determine the time at which a signal from an unknown location arrives at receivers installed at two or more locations. Since we do not know where the signal source is and when it sent the signal, the arrival time difference is very important. Since we know the location of the receiver and the distance between the signal source and the receiver, the location of the signal source can be calculated using trigonometry.

At least two receivers are absolutely necessary, but if there are two receivers, a line in the form of a hyperbola can be drawn from each receiver to predict where the signal received from the source is.

The black dot is the drone, and R1 and R2 are receivers.

If the distance between the drone and both receivers is the same, the drone signal will be received at the same time at both receivers. In this case, the TDOA, or time difference, is 0. However, since the absolute time of the drone signal is unknown, there is no way to determine the exact location. If the TDOA is 0, the drone can be anywhere that is the same distance from the two receivers, that is, anywhere on the pink line shown in the figure.

If the distance from the drone is different for both receivers, the TDOA will not be 0. Then, it could be anywhere on any of the hyperbolas depicted in the figure. Therefore, it is not easy to accurately determine where the drone is with only two receivers.

If you add one more receiver, the combination of receivers will be three (R1-R2, R1-R3, R2-R3). In this case, there will be more hyperbolas than when two receivers were used, so theoretically they will meet at one point. If a fourth receiver is added, the combination of receivers will increase to six, which will allow you to more effectively and accurately determine the drone's location.


Portable measuring equipment is essential to determine the drone's final location.

Once you have determined the approximate location of the drone using the hardware and software described above, you can go out into the field and use portable equipment to determine its exact location.

Fieldfox is Keysight's portable equipment. It is easy to carry because it is about the size of A4 paper and weighs 3.2kg. It can measure up to 50GHz frequency. Recently, Real-Time Spectrum Analyzers (RTSA) have been added as an option, enabling measurement of signals that appear and disappear at high speeds. The RTSA specification supported by Fieldfox is 100% POI of 12us. This means that it can detect 100% of a 12us pulse width signal.

Keysight's Fieldfox enhances user mobility with its portability.

The biggest advantage of Fieldfox is that it has various measurement functions in one device. It provides network analyzer, power meter, vector voltmeter, and TDR(Time-domain reflectometer) measurement functions depending on the option. It is convenient not only for drone detection, but also outdoors or in situations where it is difficult to carry general bench top equipment. Fieldfox satisfies IP53 standard, so it provides a certain degree of waterproof function. It also satisfies US Army MIL-STD-810 standard, so it is guaranteed to be usable in extreme situations.


3 Tips for Identifying a Drone's Unique Frequency

Drones use the ISM (Industry-Sience-Medical) frequency band. This frequency band is a band used jointly worldwide, and no separate frequency usage fee is charged. Also, since it is based on the premise of shared use, it tolerates a certain degree of mutual interference and uses low output as the default to minimize interference between each other.

The most commonly used ISM bands are 400MHz, 2.4GHz, and 5.8GHz. The output specifications of various equipment using this band are limited by purpose and vary by country. Wi-Fi and Bluetooth use this band. In order to detect signals from drones, it is necessary to distinguish which of the many signals coming from the ISM band are coming from drones.

There are three ways.

The first is to specify a specific band. The frequency range used by commercial drones is limited to about three or four bands. Therefore, rather than analyzing the signal in a wide band, the probability of finding a signal increases when you specify a specific frequency range in a few narrow bands. The N6820ES Signal Surveyor 4D provides this function.

The second is to set a threshold in the software. Since the only signal you need to see is the drone signal, you record the energy history and process the signal that always exists as a limit line. Then, all signals below the line are filtered out, so you can only see the signals that come up above. Conversely, you can use the spectral shape detection function, which puts the rough shape or size of the signal you are looking for into the software and gives the user an alarm whenever a similar signal appears.

The third is to limit the range of signal capture. If you specify a range on the map, you can only capture signals coming from the area within that range.

You can specify a range in the shape of a circle by entering a radius centered on a certain point, or you can specify an area in the shape of a box by specifying latitude and longitude. Signals outside the selected range are automatically filtered out by the software.


Double-edged sword: catching drones

Drones are miniaturized and have good mobility, so they can go anywhere freely. Therefore, the potential uses of drones are endless. However, the usefulness of these drones changes into danger depending on their use. Drones can have a good or bad influence on the public depending on the user's positive or negative intentions. They can save people, but they can also kill them. This is why the need for drone detection and detection technology to prevent drones from being used with negative intentions is growing day by day.

Drone detection and detection technology requires hardware to receive signals and software to analyze the received signals. In addition, portable measuring equipment must be used as an auxiliary device to determine the location of the drone. To do this, it is necessary to be able to capture the drone's unique frequency in the ISM band. There are three ways to do this. Specify a specific frequency band, exclude other frequency signals other than the frequency you are looking for in the software, and limit the signal analysis area to a specific area.