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 its 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 communication (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced CordlessTelecommunications(DECT) standard for portable phones. TDMA was first used in satellite communication systems by Western Union in its Westar 3 communications satellite in 1979. It is now used extensively in satellite communications,combat-net radio systems, and  passive optical network (PON) networks for upstream traffic from premises to the operator. For usage of Dynamic TDMA packet mode communication, see below.

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.

# Advantages of TDMA :-

# TDMA allows the operator to do services like fax, voice band data, and SMS as well as bandwidth-intensive application such as multimedia and video conferencing. 

# Since TDMA technology separates users according to time, it ensures that there will be no interference from simultaneous transmissions.

# Disadvantages of TDMA:-

# Disadvantage using TDMA technology is that the users has a predefined time slot. When moving from one cell site to other, if all the time slots in this cell are full the user might be disconnected.

# Another problem in TDMA is that it is subjected to multipath distortion.

# Application :- 

# 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.

# 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.

# Dynamic TDMA:-

In dynamic time-division multiple access (dynamic TDMA), a scheduling algorithm dynamically reserves a variable number of time slots in each frame to variable bit-rate data streams, based on the traffic demand of each data stream. Dynamic TDMA is used in

HIPERLAN/2 broadband radio access network.

IEEE 802.16a WiMax

Bluetooth

Military Radios / Tactical Data Link

TD-SCDMA

ITU-T G.hn

Simulation of TDMA / DTMA links.