Transcript Polar Encoding

‫به ن ـ ـ ـ ــام خدا‬
‫شبکه های کامپیوتری‬
‫جلسه ششم‬
Telephone system
 Public Switched Telephone Network (PSTN)
 Originally designed to transmit human voice
 Telephone system organization: hierarchical network with
three important components:
 Local loops
 Switching centers
 Trunks: connecting switching offices using various transmission
technologies
2
Telephone Modem
 Modem: A device that receives a stream of digital bits and
sends/receives it properly from the transmission medium (such as
twisted pair)
 Transmission problems:
 Attenuation
 Noise (Thermal Noise, Impulse Noise,…)
 Delay Distortion
 Attenuation and Distortion which are frequency dependent
3
4
Baseband Transmission
Line Coding
UniPolar
5
Polar
BiPolar
Unipolar Encoding
 In unipolar encoding, the polarity is assigned to ‘1’ bit, while
the ‘0’ bit is represented by zero voltage.
6
Polar Encoding
 Polar encoding uses two voltage levels (positive and negative).
Polar Encoding
NRZ
7
RZ
Manchester
Differential Manchester
Polar Encoding
 In NRZ-Level (NRZ-L), a positive voltage
 A 1 bit is represented by positive-to-zero
and a 0 bit by negative-to-zero.
means ‘0’ bit, while a negative voltage
means ‘1’ bit.
 Manchester Encoding
 In NRZ-Invert (NRZ-I), it is the transition  Differential Manchester Encoding
between positive and negative voltage, not
the voltage itself, that represents a ‘1’ bit. A
‘0’ bit is represented by no change.
 Return to Zero (RZ) uses three values:
positive, negative and zero.
8
Bipolar AMI Encoding
• in bipolar encoding is used to represent binary 0. The 1s are
represented by alternating positive and negative voltages
9
Passband Transmission
10
Amplitude-Shift Keying (ASK)
0
1
0
11
1
1
0
1
Frequency-shift keying (FSK)
0
1
0
1
0
12
1
1
0
1
Phase-shift keying (PSK)
• No change
• Change
0
1
0
13
0°
180°
1
1
0
1
QPSK-QAM16-QAM64
64-QAM
14
Local Loop, Broadband Access -ADSL
 Objective: Offering data
services without impacting the
voice service on twisted pair
 Central Office (CO) side:
 Use splitter to feed low pass
part to the voice switch while
the higher frequencies to the
feed the DSLAM
 Customer Premise End (CPE)
 Use splitter or in-line filters to
feed the low pass part of the
spectrum to the telephone and
the high pass part to the CPE
ADSL modem
15
Multiplexing
 In telecommunications and computer networks multiplexing is a
method by which multiple analog message signals or digital data
streams are combined into one signal over a shared medium. The
aim is to share an expensive resource.
16
Frequency Division Multiplexing
 Information from multiple sources can be multiplexed in
frequency domain by assigning different carriers to different
sources.
 Usually there is a guard band between different frequency bands
17
Wavelength Division Multiplexing
 Several independent streams of data each carried in a different
wavelength can be multiplexed in optical domain and
transmitted over a single fiber.
 This technology has drastically increased the capacity and
lowered to cost of transmission networks
18
Time Division Multiplexing
 Different sources of data can be transmitted by dividing time into
different slots
 TDM is used widely in telephone and cellular networks
19