TDMA

TDMA(Time Division Multiple Access

Time division multiple access (TDMA) is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using his own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, combat-net radio systems, and PON networks for upstream traffic from premises to the operator.


TDMA in wired networks

The ITU-T G.hn standard, which provides high-speed local area networking over existing home wiring (power lines, phone lines and coaxial cables) is based on a TDMA scheme. In G.hn, a "master" device allocates "Contention-Free Transmission Opportunities" (CFTXOP) to other "slave" devices in the network. Only one device can use a CFTXOP at a time, thus avoiding collisions. FlexRay protocol which is also a wired network used for Safety Critical communication in modern cars, uses the TDMA method for data transmission control.


TDMA characteristics


Shares single carrier frequency with multiple users

Non-continuous transmission makes handoff simpler

Slots can be assigned on demand in dynamic TDMA

less stringent power control than CDMA due to reduced intra cell interference

Higher synchronization overhead than CDMA

Advanced equalization may be necessary for high data rates if the channel is "frequency

selective" and creates Intersymbol interference

Cell breathing (borrowing resources from adjacent cells) is more complicated than in CDMA

Frequency/slot allocation complexity

Pulsating power envelope: Interference with other devices