The frequency-division multiple access (FDMA) channel-access scheme is based on the frequency-division multiplexing (FDM) scheme, which provides different frequency bands to different data-streams. In the FDMA case, the data streams are allocated to different nodes or devices. An example of FDMA systems were the first-generation (1G) cell-phone systems, where each phone call was assigned to a specific uplink frequency channel, and another downlink frequency channel. Each message signal (each phone call) is modulated on a specific carrier frequency.
A related technique is wavelength division multiple access (WDMA), based on wavelength-division multiplexing (WDM), where different datastreams get different colors in fiber-optical communications. In the WDMA case, different network nodes in a bus or hub network get a different color.
An advanced form of FDMA is the orthogonal frequency-division multiple access (OFDMA) scheme, for example used in 4G cellular communication systems. In OFDMA, each node may use several sub-carriers, making it possible to provide different quality of service (different data rates) to different users. The assignment of sub-carriers to users may be changed dynamically, based on the current radio channel conditions and traffic load.
The following are common circuit mode and channelization channel access methods:
Frequency-division multiple access (FDMA), based on frequency-division multiplexing (FDM)
Wavelength division multiple access (WDMA)
Orthogonal frequency-division multiple access (OFDMA), based on Orthogonal frequency-division multiplexing (OFDM)
Single-carrier FDMA (SC-FDMA), a.k.a. linearly-precoded OFDMA (LP-OFDMA), based on single-carrier frequency-domain-equalization (SC-FDE).
Time-division multiple access (TDMA), based on time-division multiplexing (TDM)
Multi-Frequency Time Division Multiple Access (MF-TDMA)
Code division multiple access (CDMA), a.k.a. Spread spectrum multiple access (SSMA)
Direct-sequence CDMA (DS-CDMA), based on Direct-sequence spread spectrum (DSSS)
Frequency-hopping CDMA (FH-CDMA), based on Frequency-hopping spread spectrum (FHSS)
Orthogonal frequency-hopping multiple access (OFHMA)
Multi-carrier code division multiple access (MC-CDMA)
Space-division multiple access (SDMA)
Power-division multiple access (PDMA)
Several ways of categorizing multiple-access schemes and protocols have been used in the literature. For example, Daniel Minoli (2009) identifies five principal types of multiple-access schemes: FDMA, TDMA, CDMA, SDMA, and Random access. R. Rom and M. Sidi (1990) categorize the protocols into Conflict-free access protocols, Aloha protocols, and Carrier Sensing protocols.
The Telecommunications Handbook (Terplan and Morreale, 2000) identifies the following MAC categories:
Fixed assigned: TDMA, FDMA+WDMA, CDMA, SDMA
Demand assigned (DA)
Reservation: DA/TDMA, DA/FDMA+DA/WDMA, DA/CDMA, DA/SDMA
Polling: Generalized polling, Distributed polling, Token Passing, Implicit polling, Slotted access
Random access (RA): Pure RA (ALOHA, GRA), Adaptive RA (TRA), CSMA, CSMA/CD, CSMA/CA