FDMA versus TDMA versus CDMA
This page on FDMA versus TDMA versus CDMA provides difference between FDMA,TDMA and CDMA technologies. This page describes various multiple access techniques to make use of common resources by multiple users/subscribers.
FDMA- Frequency Division Multiple Access, here entire band of frequencies is divided into multiple RF channels/carriers. Each carrier is allocated to different users.
For example in GSM entire frequency band of 25 MHz is divided into 124 RF carriers of bandwidth 200 KHz each. In Satellite applications entire transponder band of 500 MHz is divided into 24 channels each of bandwidth 40MHz (36 MHz useful and 4MHz guard band).
There are two main types of FDMA scheme used in satellite network. SCPC(Single channel per carrier) and MCPC(multiple channel per carrier). MCPC uses FDM or TDM as multiplexing scheme.
• FAMA- Fixed Assignment Multiple Access, here frequencies are pre-allocated to users/subscribers/VSATs.
• DAMA- Demand Assignment Multiple Access, here frequencies are dynamically allocated based on requests.
TDMA- Time Division Multiple Access, here entire bandwidth is shared among different subscribers at fixed predetermined or dynamically assigned time intervals/slots. For example in GSM each RF carrier is used/shared by 8 users at different time instants.
TDMA uses TDM multiplexing technique.
CDMA-Code Division Multiple Access, here entire bandwidth is shared among different users by assigning unique codes. For example in CDMA IS-95 standard entire bandwidth of 1.225 MHz is shared by various channels/users using unique 64 Walsh Codes. In CDMA entire bandwidth is being used by users all the time and each have their unique codes to recover the data. The system works based on spread spectrum concept.
FDMA versus FHMA
PAMA vs DAMA vs RMA
To know more on FDMA refer satellite tutorial
To know more on TDMA refer GSM tutorial
To know more on CDMA refer CDMA tutorial
For comparison between FDM and TDM multiplexing techniques, READ MORE
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