A radio frequency (RF) signal refers to a wireless electromagnetic signal used as a form of communication if one is discussing wireless electronics. Radio waves are a form of electromagnetic radiation with identified radio frequencies that range from 3kHz to 300 GHz. Frequency refers to the rate of oscillation (of the radio waves.) RF propagation occurs at the speed of light and does not need a medium like air in order to travel. RF waves occur naturally from sun flares, lightning, and stars in space that radiate RF waves as they age. Humankind communicates with artificially created radio waves that oscillate at various chosen frequencies. RF communication is used in many industries including television broadcasting, radar systems, computer and mobile platform networks, remote control, remote metering/monitoring, and many more.
While individual radio components such as mixers, filters, and power amplifiers can be classified according to operating frequency range, they cannot be strictly categorized by wireless standard (e.g. Wi-Fi, Bluetooth, etc.) because these devices only provide a physical layer (PHY) support. In contrast, RF modules, transceivers, and SoCs often include data link layer support for one or more wireless communication protocols.
When working with wireless networks, your neighbors may interfere with your network by generating traffic on the same radio frequencies you are using, or by using devices that encroach on the frequencies that you are using. This issue is especially true when using unlicensed radio frequency (RF) bands, but it is easier to deal with when using the limited licensed radio bands.
All commercial wireless networking solutions operate in the unlicensed RF bands, and the RF bands where wireless networks operate are full of noisy neighbors.
Licensed radio bands
When a national regulatory body (such as the FCC in the United States) allocates a frequency range to be used for a function, it can also specify how the frequency range can be used or shared.
To use licensed radio bands, a license must be obtained from a government agency. This requirement is true of all users of these radio spectrums. A few of the uses of licensed radio bands are as follows:
AM broadcast (short wave between 1.711 MHz–30.0 MHz, medium wave between 520 kHz–1,610 kHz, and the long wave between 148.5 kHz–283.5 kHz )
FM broadcast (87.5 to 108.0 MHz)
- Cellular phones (840 MHz)
In the larger electromagnetic spectrum, which includes the radio spectrum, the licensing of infrared and X-ray spectrums also exists.
Unlicensed radio bands
When hearing the term unlicensed, you may think there are no laws or that unlicensed radio bands are like the Wild West and people can do as they like. However, that is not completely the case: You must follow several regulations that cover the use of unlicensed radio bands.
The big difference between licensed and unlicensed bands is that the licensed bands are allowed to be used only by the company that licensed them, whereas the unlicensed bands are used by anyone who wants to use them.
Unlicensed radio bands have been allocated to certain users by the government, but to be able to use and broadcast on these bands, you do not need to have a license; you only need to create compliant devices that are to be used.
Regulations exist around these bands, so using unlicensed radio bands is not a free-for-all. In the United States, the FCC regulates all the electromagnetic spectrum, but it has set aside several ranges for public use.
Some of the types of unlicensed radio bands are as follows:
Industrial, Scientific, Medical (ISM): This type includes several medical monitors and other devices that operate in the 900-MHZ, 2.4-GHz, and 5-GHz bands.
Unlicensed National Information Infrastructure (U-NII): This type defines the specifications for the use of wireless devices such as WLAN access points and routers in the 5-GHz band.
Unlicensed Personal Communications Services (UPCS): This type defines the specifications for devices operating in the 1.9-GHz band, where DECT6 cordless phones operate.
Wireless phone companies, such as Sprint and Rogers, have specific frequencies that only they are allowed to use by leasing them from the government. IEEE 802.11 networks have several choices of wireless bands that are available to them to use, without the requirement to lease the frequencies from the government.
The downside of the unlicensed frequencies or bands is that anyone else can use the same frequency ranges, which can cause interference for the signals you are trying to transmit.
So users of both licensed and unlicensed bands are required to follow a series of government regulations, but the unlicensed bands may be used by anyone who follows the guidelines and regulations. These guidelines cover issues like encroaching on neighboring frequencies and causing interference; so if everyone follows these rules, they will all be good neighbors, which is not always the case.
Some groups have helped to develop standards so that all users can be good neighbors with others who use those radio bands. These groups and standards bodies include the following:
FCC (Federal Communications Commission): Manages and sets standards with regard to the spectrum use
- IEEE (Institute of Electrical and Electronics Engineers): A leading standards organization which publishes standards that are adopted across industries
Wi-Fi Alliance: An organization that attempts to create a single standard for WLANs, thereby ensuring interoperability
ETSI (European Telecommunications Standards Institute): Another standards organization that has contributed many worldwide standards
ITU-R (International Telecommunication Union, Radiocommunication Sector): With the FCC, defines how WLANs should operate from a regulatory perspective, such as operating frequencies, antenna gain, and transmission power
WLANA (WLAN Association): Provides information resources related to WLANs with regard to industry trends and usage. They are now defunct.