Frequency-division multiple access (FDMA) is a

channel access method In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity. Examples of shared physical m ...

used in some multiple-access protocols. FDMA allows multiple users to send data through a single

communication channel A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for informa ...

, such as a coaxial cable or

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...

beam, by dividing the

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

of the channel into separate non-overlapping

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

sub-channels and allocating each sub-channel to a separate user. Users can send data through a subchannel by modulating it on a

carrier wave In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has ...

at the subchannel's frequency. It is used in

satellite communication A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. C ...

systems and telephone trunklines. FDMA splits the total bandwidth into multiple channels. Each ground station on the earth is allocated a particular frequency group (or a range of frequencies). Within each group, the ground station can allocate different frequencies to individual channels, which are used by different stations connected to that ground station. Before the transmission begins, the transmitting ground station looks for an empty channel within the frequency range that is allocated to it and once it finds an empty channel, it allocates it to the particular transmitting station.

Method

Alternatives include time-division multiple access (TDMA),

code-division multiple access Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...

(CDMA), or

space-division multiple access Space-division multiple access (SDMA) is a channel access method based on creating parallel spatial pipes (focused signal beams) using advanced antenna technology next to higher capacity pipes through spatial multiplexing and/or diversity, by ...

(SDMA). These protocols are utilized differently, at different levels of the theoretical

OSI model The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...

. Disadvantage: Crosstalk may cause interference among frequencies and disrupt the transmission. * In FDMA, all users share the satellite transponder or

frequency channel In broadcasting, a channel or frequency channel is a designated radio frequency (or, equivalently, wavelength), assigned by a competent frequency assignment authority for the operation of a particular radio station, television station or televis ...

simultaneously but each user transmits at single frequency. * FDMA can be used with both analog and digital signal but it generally used with analog signal. * FDMA requires high-performing filters in the radio hardware, in contrast to TDMA and

CDMA Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...

. * FDMA is not vulnerable to the timing problems that TDMA has. Since a predetermined frequency band is available for the entire period of communication, stream data (a continuous flow of data that may not be packetized) can easily be used with FDMA. * Due to the frequency filtering, FDMA is not sensitive to

near–far problem The near–far problem or hearability problem is the effect of a strong signal from a near signal source in making it hard for a receiver to hear a weaker signal from a further source due to adjacent-channel interference, co-channel interference, d ...

which is pronounced for

. * Each user transmits and receives at different frequencies as each user gets a unique frequency slot. FDMA is distinct from

frequency division duplexing A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow ...

(FDD). While FDMA allows multiple users simultaneous access to a transmission system, FDD refers to how the radio channel is shared between the

uplink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or sha ...

and

downlink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or shar ...

(for instance, the traffic going back and forth between a mobile-phone and a mobile phone base station).

Frequency-division multiplexing In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separat ...

(FDM) is also distinct from FDMA. FDM is a physical layer technique that combines and transmits low-bandwidth channels through a high-bandwidth channel. FDMA, on the other hand, is an access method in the

data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer ...

. FDMA also supports demand assignment in addition to fixed assignment. ''Demand assignment'' allows all users apparently continuous access of the

radio spectrum The radio spectrum is the part of the electromagnetic spectrum with frequencies from 0 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particula ...

by assigning carrier frequencies on a temporary basis using a statistical assignment process. The first FDMA ''demand-assignment'' system for satellite was developed by

COMSAT COMSAT (Communications Satellite Corporation) is a global telecommunications company based in the United States. By 2007, it had branches in Brazil, Argentina, Colombia, Mexico, Peru, Venezuela and several other countries in the Americas. ...

for use on the '' Intelsat'' series ''IVA'' and ''V'' satellites. There are two main techniques: *Multi-channel per-carrier (

MCPC In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...

) *Single-channel per-carrier (

SCPC Single channel per carrier (SCPC) refers to using a single signal at a given frequency and bandwidth. Most often, this is used on broadcast satellites to indicate that radio stations are not multiplexed as subcarriers onto a single video carrier ...

)

References

* Olenewa, J. & Ciampa, M. (2007). Wireless# Guide to Wireless Communications (2nd ed.). Boston, United States: THOMSON COURSE TECHNOLOGY {{Telecommunications he:ריבוב#xDMA

Method

See also

References