This document discusses multiplexing techniques for transmitting information from multiple transmitters to receivers over a single communication channel. It describes two main types of multiplexing: frequency division multiplexing (FDM), which differentiates signals by allocating different frequency bands to different transmitters, and time division multiplexing (TDM), which allocates discrete time slots to each transmitter in turn. The key components for implementing multiplexing are multiplexers, which combine signals before transmission, and demultiplexers, which separate the signals at the receiving end.

1. Module 5: Digital Techniques and
Electronic Instrument Systems
5.9 Multiplexing

2. Multiplexing
 Simplex bus:
 Data flow always
in one way.
 Half duplex bus:
 Send and receive
but not in the
same.
 Full duplex bus:
 Send and receive
simultaneously.

3. How can a transmitter send information to more than
one receivers through a single wire?
 Multiplexing
 2 types of multiplexing:
 Frequency Division Multiplexing (FDM):
 The information intended to for different receivers is differentiated by
using different frequencies.
 Time Division Multiplexing (TDM):
 Each transmitter has its own time-slot at which he can send
information.

4. Frequency Division Multiplexing
 Each transmitter
modulates the data
using a “carrier” with a
specific frequency.
 The receiver obtains
the original data using
a filter and a
demodulator circuit,
which removes the
“carrier”.
 ADSL example:
 Voice: 0 – 4KHz
 Upstream: 25 – 138KHz.
 Downstream: 138 – 1104KHz

5. Frequency Division Multiplexing
 Signal in time domain
 Signal in time
frequency domain
 OFDM: Orthogonal
carriers overlap, but
data can be still
recovered by the
receiver.
  Bandwidth savings!

6. Time Division Multiplexing
 Each receiver has a
specific timeslot.
 Multiplexer receives
one bit form each
transmitter in order,
combines them to a
TDM frame and
sends them to the
channel.
 Demultiplexer
receives the TDM
frame and gives
each bit the
appropriate receiver
in order.

7. Multiplexer
 a, b: address lines.
 A, B, C & D:
transmitters.
 Q: Output connected
to the channel.
 a & b define from
which transmitter,
data will be
forwarded to the
output.
 Usually a clock is
connected to a & b to
perform TDM.

8. Demultiplexer
 s0, s1: address
lines.
 DATA: data received
from the channel.
 Y0,…, Y3: receivers.
 s0 & s1 will select to
which of receivers
the data will be
forwarded.
 s0 & s1 are usually
connected to a clock
to perform TDM.

9. Symbols