1. Time Division Multiplexing
Chapter 3
Time Division Multiplexing
The concept of Time Division Multiplexing
TDM Examples
Frame Synchronization
TDM Hierarchy
Packet Transmission
Huseyin Bilgekul
Eeng360 Communication Systems I
Department of Electrical and Electronic Engineering
Eastern Mediterranean University

2. Time Division Multiplexing
Definition: Time Division Multiplexing (TDM) is the time interleaving of samples from several sources so that the information from these sources can be transmitted serially over a single communication channel.
At the Transmitter
Simultaneous transmission of several signals on a time-sharing basis.
Each signal occupies its own distinct time slot, using all frequencies, for the duration of the transmission.
Slots may be permanently assigned on demand.
At the Receiver
Decommutator (sampler) has to be synchronized with the incoming waveform  Frame Synchronization
Low pass filter
ISI – poor channel filtering
Feedthrough of one channel's signal into another channel -- Crosstalk
Applications of TDM: Digital Telephony, Data communications, Satellite Access,
Cellular radio.

3. Time Division Multiplexing
Conceptual diagram of multiplexing-demultiplexing.
PAM TDM System

4. Block diagram of TDM system.
PAM TDM System
A Typical Framing Structure for TDM

5. Time Division Multiplexing
Frame structure of a certain TDM signal
Composite Signal Format

6. Time Division Multiplexing
Pulse width of TDM PAM:
Pulse width of TDM PCM:

7. Pulse Stuffing in TDM
Stuff bits, which are dummy bits are inserted in the TDM output data when the different inputs are not completeley synchronized or the different input rates are not related by a ratinal number.

8. Pulse Stuffing in TDM
Stuff bits, which are dummy bits are inserted in the TDM output data when the different inputs are not completeley synchronized or the different input rates are not related by a ratinal number.
Multiplexing of two data streams with bit stuffing

9. TDM Example Source 1: 2 kHz bandwidth.
Source 4-11: Digital 7200 bits/sec.
16 ksam/s
64 kb/s
8x7.2=57.6 kb/s Use stuff bits to complete 7.2 to 8 kb/s. Now 8 and 64 rates are complete multıples
128 kb/s

10. Frame Synchronization
To sort and direct the received multiplexed data to the appropriate output channel
Two ways to provide frame sync to the demultiplexer circuit
- Over a separate channel
- Deriving from the TDM signal itself
Frame sync (unique k-bits) +Information words of an N-channel TDM system

11. TDM PAM for Radio Telemetry

12. CCITT Digital TDM Hierarchy

13. Packet Transmission System
TDM is Synchronous Transfer Mode (STM) technology
- Data source is assigned a specific time slot – fixed data rate
- More efficient when sources have a fixed data rate
- Inefficient to accommodate bursty data source
Solution?
Packet Transmission System
- Partitions source data into data packets (destination address, header)
- Efficiently assigns network resources when the sources have bursty data
- Examples : Internet TCP/IP technology and the Asynchronous Transfer Mode (ATM) technology.

14. Summary How to compute the spectra for line codes
How information in analog waveforms can be represented by digital signaling
How to compute the spectra for line codes
How filtering of the digital signal, due to the communication channel affects our ability to recover the digital information at the receiver [ISI]
How we can merge information from several sources into one digital signal by using time division multiplexing (TDM)