EE4367 Telecom. Switching & Transmission Prof. Murat Torlak Voice Transmission Voice Transmission -- -- Basic Concepts Basic Concepts -- -- Voice---is analog in character and moves in the form of waves. 3-important wave-characteristics : Amplitude Frequency Phase EE4367 Telecom. Switching & Transmission Prof. Murat Torlak Telephone Handset (has 2 Telephone Handset (has 2- parts) parts) 1. Transmitter (i.e mouthpiece) consists of a movable speaker diaphragm that is sensitive to both amplitude and frequency The diaphragm contains carbon particles that can conduct electricity. As the human voice spoken into the transmitter varies, the amount of carbon granules that strike the electrical contacts in the mouthpiece also varies—thereby sending varying analog electrical signals out into the voice network.
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EE4367 Telecom. Switching & Transmission Prof. Murat Torlak
Voice TransmissionVoice Transmission
----Basic ConceptsBasic Concepts----
� Voice---is analog in character and moves in the form of waves.
� 3-important wave-characteristics:
� Amplitude
� Frequency
� Phase
EE4367 Telecom. Switching & Transmission Prof. Murat Torlak
� 1. Transmitter (i.e mouthpiece)� consists of a movable speaker diaphragm that is sensitive to both amplitude and frequency
� The diaphragm contains carbon particles that can conduct electricity.
� As the human voice spoken into the transmitter varies, the amount of carbon granules that strike the electrical contacts inthe mouthpiece also varies—thereby sending varying analog electrical signals out into the voice network.
EE4367 Telecom. Switching & Transmission Prof. Murat Torlak
� Acts in an opposite direction to the mouthpiece.
� The electrical signal/waves produced by the transmitter are received at an electromagnet in the receiver.
� Varying levels of electricity produce varying levels of magnetism—that, in turn, cause the diaphragm to move in direct proportion to the magnetic variance.
� The moving diaphragm produces varying sound that corresponds to the sound waves that were input at the transmitter.
EE4367 Telecom. Switching & Transmission Prof. Murat Torlak
Getting Voice Onto and Off the Network
ElectromagnetSpeaker diaphram (moveable)
Permanent magnet
Variable magnetic field
Diaphram (moveable)
Granulated carbon
4 Wires
Sound Waves
Sound Waves
Handset
Transmitter (mouthpiece)
Receiver (earpiece)
Electrical contacts
RJ-22 connector
RJ-22 connector
RJ-11 connectors
2 wires
EE4367 Telecom. Switching & Transmission Prof. Murat Torlak
Voice Bandwidth
Range of human hearing
Full bandwidth of analog
circuit
Guardband
Bandwidth available for analog voice transmission
Guardband
0
20
300
3,400
4,000
20,000
Her
tz (
Hz)
(gra
ph
not t
o sc
ale
)
EE4367 Telecom. Switching & Transmission Prof. Murat Torlak
Voice Digitization in the POTSVoice Digitization in the POTS� Traditional POTS was analog.
� The current telephone system of the POTS combines both analog and digital transmission technologies.
� Why Voice digitization:
� Ensures better quality (than analog)
� Provides higher capacity (than analog)
� Deals with longer distance (than analog)
EE4367 Telecom. Switching & Transmission Prof. Murat Torlak
Voice DigitizationVoice Digitization——How!How!� Digitization is just a discrete electrical voltage.
� Electrical pulses can be varied to represent characteristics of an analog voice signal.
� 5-different VD-techniques:
� PAM = pulse amplitude modulation
� PDM = pulse duration modulation
� PPM = Pulse position modulation
� PCM = Pulse code modulation
� ADPCM = Adaptive differential PCM
EE4367 Telecom. Switching & Transmission Prof. Murat Torlak