Frequency Division Multiple Access (FDMA) is a method of radio frequency utilization in which only one subscriber occupies a given frequency slot, and different subscribers use different frequencies within a cell. Network capacity is determined by the number of allocated frequency channels. It is one of the three main mobile radio communication technologies.
The FDMA method allows achieving comparable (or even better) service area sizes in voice communication compared to analog radio systems over the same distance. This principle is implemented in cellular communication standards such as AMPS, N-AMPS, NMT, and trunking standards like EDACS (U.S. standard), APCO-25, among others.
FDMA (frequency division multiple access) is used in many terrestrial mobile communication systems, for example, in LTR®, SmartNet, and MPT systems. It is also applied in the Project 25 Phase I standard, intended for digital radio systems used by public safety agencies.
The FDMA method is implemented in the license-free dPMR 446 standard, meeting the 6.25 kHz technology requirement. A licensed radio station version is also available (operating only on 12.5 kHz channels).
A synonym for the technology is FDD (frequency division duplex).
The use of FDMA frequency multiplexing technology allows to:
• Improve communication quality. The use of digital technologies for voice transmission ensures accurate reproduction of human speech even at low radio signal levels, providing high-quality audio transmission across the entire coverage area;
• Increase spectral efficiency and save frequency resources. When two logical information channels are organized within one physical radio channel, the need for frequency resources is reduced by half;
• Integrate voice and data transmission within a single radio station. By creating two information channels in one radio channel, one can be used for voice transmission and the other for data transmission;
Advantages of FDMA
To meet the requirement for efficient spectrum use at one voice channel per 6.25 kHz bandwidth, it is possible to use the TDMA - Time Division Multiple Access method with two slots (12.5 kHz channel). However, for large coverage areas and for direct communication between subscriber radios, the FDMA method is better suited. Moreover, FDMA is simpler than TDMA in terms of maintenance and technical support. In direct mode communication using the two-slot TDMA method, essentially only one of these slots is used, so the 6.25 kHz efficiency is not achieved (requiring complex management). TDMA also requires a guard time interval between slots to prevent data conflicts, which reduces coverage area and the actual data rate for each slot. These drawbacks are absent in the FDMA method.