Why Airlines created a storm against the 5G rollout in USA? And why was it accepted in Europe?
Initially, the FAA banned about 30% of US commercial airplanes from using airports where 5G networks are deployed nearby.
Potential interference of newly deployed 5G networks on airplanes’ altimeters caught the world’s attention. Altimeters are devices that use radio waves (4.2-4.4 GHz) to measure the plane’s altitude to enable safe flight and landing in low visibility.
In Europe, 5G services were rolled out using the (3.4-3.8 GHz) range far from the altimeter band. However, a closer range (3.7-3.98 GHz) in the US was used, increasing the risk of interference. The FAA then mandated retrofitting the altimeters of the affected airplanes with anti-interference measures before using the affected airports.
Figure. 1 5G interference with altimeters [1].
What’s going on?
Wireless communication depends on sending electromagnetic signals that carry information to designated receivers. Each device sends a group of signals over a range of frequencies called a channel. These waves are sent in the open air, which results in unwanted signals (Interference) from multiple sources using the same frequencies arriving at the receiver.
Interference can cause various issues, from reduced network speed to total connectivity loss. The possibility of catastrophic consequences in case the affected equipment performs critical operations should not be ignored.
ISM band
| Freq. | Band\License | Technologies |
| 886-906 MHz | ISM unlicensed | Wireless phones, Wi-Fi. |
| 2.4-2.5 GHz | ISM unlicensed | Wi-Fi, Bluetooth, Wireless USB, SAT, amateur radio. |
| 3.4-3.98 GHz | C-band Licensed (global) Partially licensed (Us) | Mobile 5G, SAT, Mobile, Wi-Fi (US), and Radar |
| 5.15-5.875 GHz | 5GHz-band unlicensed | Wi-Fi, Radars, Weather radars, Amateur radio. |
The Industrial, Scientific, and Medical (ISM) frequency bands are radio ranges initially reserved for non-communication applications. Due to the lack of licensing requirements, many unlicensed and eventually popular communication technologies were developed to operate within the ISM band. This includes Wi-Fi, Wireless USB, Bluetooth, Zigbee, and unlicensed LTE.
Table (1). Important communication bands.
Radio Frequency Interference
Interference is simply unwanted signals or transmissions coming from other nearby devices. Wireless communication depends on transmitting pulses of electromagnetic waves to represent a message. Interference can change the shape of these pulses at the receiver end enough to make the receiver misinterpret the message. Because of multiple technologies and entities within the ISM band, telecommunications devices using these frequencies must tolerate interference from other communication and non-communication technologies. This includes induction heating devices for industrial and home applications,
microwave heating for industrial, medical, and home applications (microwave ovens) and other devices producing electromagnetic interference (EMI).
Devices using the same technology or similar technologies in the same area while transmitting over the same channel will cause some interference depending on the distance and power used. A typical situation is when multiple Wi-Fi, Bluetooth, and Wireless USB devices operate within the same range, i.e. multiple laptops, wireless headsets, cameras, microphones,… etc., are being used. In such a case, you might observe a transmission rate decrease, noise, or loss of connection because of the effect of interference. Sometimes interference is generated by devices operating in adjacent channels due to power leakage. This is mainly due to the complexity of the design of perfect transmitter electronics, bad radio frequency electronics design, or ageing.
Some devices, like heating, for applications other than communication can cause radio frequency interference. Microwave ovens use radio waves (2.5 GHz) to heat food. Water and fats in food absorb the 2.5 GHz waves. These waves induce molecule vibrations which cause heat. If your microwave oven is not shielded well, you might experience a network drop while the oven is used. Radars used for air traffic control, navigation, or military applications, use the 5 GHz band for operation. Wi-Fi operating over the 5 GHz band must have a radar-finding capability (DFS). However, radars might still limit the data rate if there are several Wi-Fi units in the area or the DFS is not working well. Like radars, some motion sensors use radar technology for motion detection. It is much harder for Wi-Fi devices to discover on their own, especially if you use older technologies operating over 2.4 GHz.
Coexistence and mitigation techniques
Coexistence and interference mitigation are mainly achieved through hardware design, protocol design, and deployment planning. Protocols use techniques like collision avoidance and frequency hopping.
Collision-avoidance
Collision-avoidance algorithm is widely used in wireless systems like Wi-Fi and Wireless USB. Typically, the transmitter senses (listens) to the available channel before transmitting. The transmitter then chooses a (quiet) channel for transmission. If a channel becomes noisy, the transmitter stops and listens again. Collision avoidance can also be designed to prioritize one system over the other, like prioritizing radars operating in the 5 GHz band.
Frequency division
Different protocols divide the usable band into multiple channels, so each transmitter can use a separate channel without interfering with another protocol’s channel. (Fig. 2). Wi-Fi divides the 2.4 GHz ISM band into three non-overlapping channels with unusable guard bands between channels to protect against out-of-channel interference. As such, three Wi-Fi hubs can operate within the same area with no interference. Moreover, devices from other technologies, like Bluetooth, which divides the band into 40 channels, can coexist using bands free from Wi-Fi interference.
Figure 2. The 2.4 GHz ISM band channel division [2].
Frequency Hopping
Devices employing this technology, like Bluetooth, continuously and pseudo-randomly change the channel used to minimize using channels overwhelmed with interference. As different devices in the area are constantly altering their frequency of operation, it is improbable that they will use the same frequencies for an extended period.
Dynamic Frequency Selection (DFS)
The regulations mandate that the technologies using the newer 5 GHz band employ channel sensing technologies, like collision avoidance, that are dedicated to detecting radars operating in the area. Since the 5 GHz band is already in use for military applications, channels deemed used by local radars are blocked by the DFS, which moves to other channels.
Frequency reuse
Electromagnetic waves’ power fades with distance. The power deteriorates faster if there are obstacles in the wave path. Generally, the same channel can be reused if there is enough distance or enough barriers that separate the coverage areas with minimal interference between the communicating parties.
Good Planning
All the techniques described are good at reducing interference. However, they might be unable to eliminate it. The reasons are that some devices have no interference coexistence techniques, like radars and amateur radio and the complexity of detecting and achieving zero interference. A good radio frequency planning and device deployment plan can immensely reduce interference. This is done by studying the environment, choosing suitable devices and manufacturers, and choosing the right locations for installations to achieve the best coverage with minimal interference. Some error correction technologies have been developed to overcome the effects of interference and noise in the system. Unfortunately, these techniques affect the data transmission rate. Consequently, interference should be eliminated as much as possible.