band

In wireless communication, a band is a contiguous block of radio frequencies allocated by regulatory bodies like the FCC or ITU for particular applications. A band has defined upper and lower frequency limits, measured in hertz, and everything within those boundaries belongs to that band. The 2.4 GHz industrial, scientific and medical band, for instance, spans 2400 to 2484 MHz and is shared by Wi-Fi, Bluetooth, and microwave ovens. The 5 GHz Wi-Fi band is actually multiple smaller bands stacked together, each 20 to 160 MHz wide depending on channel width.

Bands exist because radio spectrum is finite and prone to interference when signals overlap. Without boundaries, every transmitter would jam every other one. Regulatory agencies divide the spectrum into bands and assign them to uses: maritime communication gets VHF bands around 156 to 162 MHz; amateur radio operators get bands like 3.5 to 4.0 MHz or 144 to 148 MHz; cellular networks operate in licensed bands like the 700 MHz band or 2.1 GHz band depending on the country and carrier.

Licensed versus unlicensed bands

Licensed bands require operators to obtain permission and often pay fees to transmit within them; cellular carriers hold licenses to specific bands in specific geographic regions. Unlicensed bands, such as the 2.4 GHz and 5 GHz bands used for Wi-Fi, are open to anyone but must operate within strict power limits and use spread-spectrum techniques to tolerate interference. The 900 MHz ISM band and 60 GHz band are also unlicensed in many countries. Unlicensed bands are cheaper to enter but crowded and unpredictable.

The physical properties of a band depend on its frequency. Lower frequency bands penetrate buildings and obstacles better but require larger antennas and have less available bandwidth. The 800 MHz cellular band travels farther than 2.4 GHz but carries less data per unit time. Higher frequency bands like 28 GHz or 39 GHz used in millimeter-wave 5G systems offer enormous bandwidth but are easily blocked by walls and rain.

Band selection is a primary design constraint in wireless systems. The choice determines antenna size, propagation distance, regulatory requirements, cost, available device support, and coexistence challenges with other systems. Industrial IoT deployments often choose the unlicensed 915 MHz band in the Americas or 868 MHz in Europe for long range with lower power. Satellite systems occupy bands far above terrestrial uses: L-band (1 to 2 GHz), S-band (2 to 4 GHz), C-band (4 to 8 GHz), and higher.