Multi-frequency time-division multiple access
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MF-TDMA ("Multi-frequency time-division multiple access") is the leading technology for dynamically sharing bandwidth resources in an over-the-air two-way communications network. Many variations of MF-TDMA technology (including simple TDMA) exist and are commonly used in multiple types of networks, including:
- Most two-way communication satellite networks,
- The most common cellular telephony networks (e.g., GSM),
- Some metro-wireless data access networks (e.g., WiMax).
Some alternatives to MF-TDMA are code-division multiple access (CDMA) and carrier-sense multiple access (CSMA). It is also possible to combine MF-TDMA technology with these other technologies. For satellite networks MF-TDMA is the dominant technology because it provides the most bandwidth and the greatest overall efficiency and service quality, while also allowing the dynamic sharing of that bandwidth among many (tens of thousands) of transmitters in a two-way communication mode. MF-TDMA networks can have either a star topology, fully meshed or partially meshed topologies.
A multi-frequency time-division multiple access (MF-TDMA) system has been developed for a thin route satellite communication network, which has most of the desirable features of both FDMA and time-division multiple access (TDMA) systems. It is shown that when the network downlink is power-limited (with negligible uplink noise) and consists of mixed Earth station sizes with different rain margin requirements, the MF-TDMA and FDMA systems can have greater throughput capacity compared to TDMA. This improvement depends on the amount of satellite transponder backoff required to keep the intermodulation effects small, and is the result of the TDMA downlink having been sized for the smallest station and largest rain margin. In the case where the Earth station must provide circuits to more than one station simultaneously, MF-TDMA is advantageous over FDMA because fewer modems are required. Use of MFTDMA can lead to lower Earth station costs by requiring lower transmitter power compared to TDMA and fewer modems compared to FDMA. Even though the control algorithm for a MFTDMA network is somewhat more complicated, a high degree of flexibility in channel assignment is retained.