millimeter wave (MM wave)
Millimeter wave (MM wave), also known as millimeter band, is the band of spectrum with wavelengths between 10 millimeters (30 GHz) and 1 millimeter (300 GHz). It is also known as the extremely high frequency (EHF) band by the International Telecommunication Union (ITU).
Advantages of millimeter wave
Millimeter wave is a band of electromagnetic spectrum that can be used in a broad range of products and services, such as high-speed, point-to-point wireless local area networks (WLANs) and broadband access. In telecommunications, millimeter wave is used for a variety of services on mobile and wireless networks, as it enables higher data rates than at lower frequencies, such as those used for Wi-Fi and current cellular networks.
Propagation restrictions dictate the use of small cell sizes for Wi-Fi and cellular networks. The short propagation distance can increase the number of access points (APs) to cover a large area but also means fewer client devices will share the bandwidth in each cell. Small cells also facilitate the reuse of channels across the WLAN coverage area.
Antennas for millimeter wave devices are smaller than for other frequencies, making them more suitable for small internet of things (IoT) devices.
Disadvantages of millimeter wave
Millimeter waves are absorbed by gases and moisture in the atmosphere, which reduces the range and strength of the waves. Rain and humidity reduce their signal strength and propagation distance, a condition known as rain fade. The propagation distance at the lower frequencies is up to a kilometer, while the higher frequencies travel only a few meters.
A millimeter wave travels by line of sight and is blocked or degraded by physical objects like trees, walls and buildings. Its propagation is also affected by proximity to humans and animals, primarily due to their water content.
Millimeter wave uses
Millimeter wave has numerous uses, including telecommunications, short-range radar and airport security scanners. In telecommunications, it is used for high-bandwidth WLANs and short-range personal area networks (PANs). Its high bandwidth capacity is ideal for applications like short-distance wireless transmission of ultra-high definition video and communications from small, low-power IoT devices. The limited propagation distance -- small cell size -- and high data rates make millimeter wave ideal for communications between autonomous vehicles.
Portions of the millimeter wave bands are being used for the following use cases:
- Institute of Electrical and Electronics Engineers (IEEE) 802.15 wireless PAN (WPAN);
- IEEE 802.16 wireless metropolitan area network (WMAN), also known as WiMAX> (Worldwide Interoperability for Microwave Access);
- IEEE 802.11ad multiple gigabit wireless system (MGWS) at 60 GHz; and
- 5G cellular telecommunications in the 24 GHz to 39 GHz bands.
Comparison with other spectrums
In comparison, Wi-Fi currently uses frequencies in the 2.4 GHz, 5 GHz and 6 GHz bands, which are known as microwave bands. Cellular networks use frequencies in the 600 MHz to 700 MHz and 2.5 GHz to 3.7 GHz bands. These bands propagate farther than millimeter wave but support lower bandwidths. Frequencies above millimeter wave are in the low infrared spectrum and are limited to short, line-of-sight communications.