Module 5: Digital Techniques and Electronic Instrument Systems

5.9 Multiplexing

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.

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.

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

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!

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.

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.

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.

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