Medium access control deals with issues such as addressing, assigning multiplex channels to different users and avoiding collisions.
For example, Daniel Minoli (2009)[2] identifies five principal types of multiple-access schemes: FDMA, TDMA, CDMA, SDMA, and random access.
A related technique is wavelength division multiple access (WDMA), based on wavelength-division multiplexing (WDM), where different data streams get different colors in fiber-optical communications.
[7] An advanced form of FDMA is the orthogonal frequency-division multiple access (OFDMA) scheme, for example, used in 4G cellular communication systems.
The assignment of sub-carriers to users may be changed dynamically, based on the current radio channel conditions and traffic load.
An advanced form is dynamic TDMA (DTDMA), where an assignment of transmitters to time slots varies on each frame.
Due to its random character, it can be categorized as statistical multiplexing methods and capable of dynamic bandwidth allocation.
This requires a media access control (MAC) protocol, i.e. a principle for the nodes to take turns on the channel and to avoid collisions.
The code-division multiple access (CDMA) scheme is based on spread spectrum, meaning that a wider radio channel bandwidth is used than the data rate of individual bit streams requires, and several message signals are transferred simultaneously over the same carrier frequency, utilizing different spreading codes.
Examples include multiple SCPC modems on a satellite transponder, where users get on demand a larger share of the power budget to transmit at higher data rates.
[1] Common statistical time-division multiplexing multiple access protocols for wired multi-drop networks include: Common multiple access protocols that may be used in packet radio wireless networks include: Where these methods are used for dividing forward and reverse communication channels, they are known as duplexing methods.
A walkie-talkie is an example of a half-duplex system because both users can communicate with one another, but not at the same time, someone has to finish transmitting before the next person can begin.
TDMA technology works by identifying natural breaks in speech and utilizing one radio wave to support multiple transmissions in turn.
In CDMA technology, each individual packet receives a unique code that is broken up over a wide frequency spectrum and is then reassembled on the other end.
[9] The origins of CDMA can be traced back to the 1940s where it was patented by the United States government and used throughout World War II to transmit messages.
[10] At the time Qualcomm was founded, Jacobs had already been working on addressing telecommunications problems for the military using digital technology to increase the capacity of spectrum.