concepts of multiplexing many input signals to one transmission media reduces the number of channels...

Concepts of Multiplexing

• Many input signals to one transmission media• Reduces the number of channels or conductors running from point A to point B• Added complexity in the muxing and demuxing control

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Frequency Division Multiplexing (FDM)

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Each input signal uses a uniquecarrier frequency.

The different carrier frequenciesare spread across a given frequency spectrum.

The FDM signals can then betransmitted via RF or via somephysical media.

Spectrum of a Frequency Division Multiplexing System

• Bandwidth is divided into smaller channels• Examples: AM or FM radio, Television, Cable and Satellite TV

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FDM Receiver• Note the use of band pass filters (BPF) to select channels or bands

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FDM Telemetry System

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Sensors can bein remote locationsor spread across thefactory floor.

The use of RF in thiscase supports remotedata acquisition.

Data can be sentmany miles usingRF.

FM / FM Telemetry - Receiver

• Multiplexed RF signals are filtered through BPF• PLL’s extract original signal

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FDM Telephone Multiplexing – City to City for example

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Each voice channelis allocated 4 Khz.

Each channelmodulates a uniquecarrier.

The carriers are allmultiplexed into alarger group.

Supports multiple communication channels through asingle media.

FDM Telephone Group

• 4 Khz per channel• 12 channels, 48 Khz bandwidth for the group• Different carrier frequencies for each channel• Multiple carriers in a group

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Telephone Super Group

• Multiplexed groups are then multiplexed to form a super group• 5 groups per super group• 48 Khz per group• Used to support long distance communication

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Demuxing a Super Group

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Each group is recovered bya BPF.

The recovered group is fedthrough a LPF.

Each channel from the specificgroup is recovered by a BPF.

Time Division Multiplexing

• Each user / signal is allocated a certain amount of time• Equal time slots per user / signal• Signals can be grouped into frames or sets

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Time Division Signal or Input Selection Concept

• One user / signal is routed to the output at a time for a fixed amount of time

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4 Channel Time Division Multiplexing Example

• Assume there are 4 different analog signals• Each signal must be sampled and sent to a receiving location

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Using Pulse Amplitude Modulation Time Division Multiplexing• Notice that at each time mark a different signal is sampled• The amplitude of the sampled signal is sent in this case, some other type of modulation scheme could be use• The receiving end must demux the signals and route them to the appropriate output

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TDM Mux Circuit to Produce Pulse Amplitude Modulation

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PAM TDM Timing Graph

• A & B select which input is sampled

• The one shot initiates the sample

• The gate outputs enable the sample to be fed through to the output

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PAM Frame Synchronizing

• Notice how the amplitude of the sync pulse exceeds all other signals• A comparator detects this and synchronizes the receiver

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Analog Input / Pulse Amplitude Modulation – Transmission

• Pulse amplitude modulation to FM – amplitude modulates the transmitted carrier

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Analog Input / Pulse Amplitude Modulation – Transmissions

• Pulse amplitude modulation to FM to PM• PAM signal modulates a sub-carrier• The sub-carriers are summed and they modulate the phase of the carrier

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Demuxing PAM signals from PAM/FM and PAM/FM/PM

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Pulse Code Modulation Multiplexing

• PCM’s for each input are muxed • Resultant output bit stream must be clocked at a higher rate than the data bit rate to support high throughput• Note the use of a sync pulse to separate frames

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Telephone System T-1 Frame – Time Division Multiplexing

• Used to support 8 bit A/D conversion of analog (voice) data• 24 channels • 1 sync bit• 193 bit total frame• 5.2 micro second word time, 125 micro second frame time

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Questions?

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