Time division multiple access

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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, and combat-net radio systems. For usage of Dynamic TDMA packet mode communication, see below.

TDMA is a type of Time-division multiplexing, with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile phone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.

Contents

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 envelop: Interference with other devices

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