14-09-2017, 09:17 AM
Frequency division multiple access or FDMA is a channel access method used in multiple access protocols as a channelization protocol. FDMA gives users an individual assignment of one or more frequency bands, or channels. It is particularly common in satellite communication. FDMA, like other multiple access systems, coordinates access between multiple users. Alternatives include TDMA, CDMA or SDMA. These protocols are used differently at different levels of the theoretical OSI model.
Disadvantages:
Crosstalk can cause interference between frequencies and interrupt transmission.
• In FDMA, all users simultaneously share the satellite transponder or the frequency channel, but each user transmits to a single frequency.
• FDMA can be used with both analog and digital signals.
• FDMA requires high performance filters on radio hardware, in contrast to TDMA and CDMA.
• FDMA is not vulnerable to TDMA timing problems. Since a predetermined frequency band is available throughout the period of communication, flow data (a continuous stream of data that can not be packaged) can be easily used with FDMA.
• Due to frequency filtering, FDMA is not sensitive to the problem near the end that is pronounced for CDMA.
• Each user transmits and receives at different frequencies as each user receives a unique frequency.
FDMA is different from frequency division duplexing (FDD). While FDMA allows multiple users simultaneous access to a transmission system, FDD refers to how the radio channel is shared between the uplink and the downlink (eg, traffic coming and going between a mobile phone and a station base of mobile telephony). Frequency division multiplexing (FDM) is also different 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.
FDMA also supports demand allocation in addition to the fixed allocation. Demand allocation allows all users apparently continuous access to the radio spectrum by allocating carrier frequencies on a temporary basis using a statistical allocation process. The first FDMA demand allocation system for satellite was developed by COMSAT for use in the Intelsat series IVA and V series satellites.
There are two main techniques:
• Multi-channel per carrier (MCPC)
• One channel per channel (SCPC)
Disadvantages:
Crosstalk can cause interference between frequencies and interrupt transmission.
• In FDMA, all users simultaneously share the satellite transponder or the frequency channel, but each user transmits to a single frequency.
• FDMA can be used with both analog and digital signals.
• FDMA requires high performance filters on radio hardware, in contrast to TDMA and CDMA.
• FDMA is not vulnerable to TDMA timing problems. Since a predetermined frequency band is available throughout the period of communication, flow data (a continuous stream of data that can not be packaged) can be easily used with FDMA.
• Due to frequency filtering, FDMA is not sensitive to the problem near the end that is pronounced for CDMA.
• Each user transmits and receives at different frequencies as each user receives a unique frequency.
FDMA is different from frequency division duplexing (FDD). While FDMA allows multiple users simultaneous access to a transmission system, FDD refers to how the radio channel is shared between the uplink and the downlink (eg, traffic coming and going between a mobile phone and a station base of mobile telephony). Frequency division multiplexing (FDM) is also different 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.
FDMA also supports demand allocation in addition to the fixed allocation. Demand allocation allows all users apparently continuous access to the radio spectrum by allocating carrier frequencies on a temporary basis using a statistical allocation process. The first FDMA demand allocation system for satellite was developed by COMSAT for use in the Intelsat series IVA and V series satellites.
There are two main techniques:
• Multi-channel per carrier (MCPC)
• One channel per channel (SCPC)