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Communication system. Source encoding. Channel encoding. Line encoding. Source. Modulation. Channel. Source decoding. Channel decoding. Line decoding. Receiver. Demodulation. Distortion. Amplitude distortion Phase distortion. Insertion loss=10log 10 P 0 /P 2 - PowerPoint PPT Presentation
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Communication system
SourceSource
encoding
Channel
encoding
Line
encoding
Modulation
Channel
ReceiverSource
decoding
Channel
decoding
Line
decoding
Demodulation
Distortion
Amplitude distortion Phase distortion
Amplitude response of a telephone channel
Insertion loss=10log10P0/P2
P2=Power delivered to a load by the channel
P0=Power delivered to the same load without channel
Envelope delay and Phase response of a telephone channel
Envelope delay is the derivative of the phase shift
Tx
Rx
Equalizer
Threshold detector
Data
Clock (Trig ขาข��น)
Tx Channel Equalizer ThresholdDetector
RetimingCircuit
ClockExtraction
AB C D
E
F
Communication system
SourceSource
encoding
Channel
encoding
Line
encoding
Modulation
Channel
ReceiverSource
decoding
Channel
decoding
Line
decoding
Demodulation
Data transmission
Communication modes
Simplex Half-Duplex Duplex or Full-duplex
Transmission modesAsynchronous transmission Feature : unnecessary to perfectly
synchronized Encoding Technique Used : NRZ Components : Start Bit (1 : transition from
1 to 0), Data (5-8), stop bit(1, 1.5, 2 : binary 1)
Merit : Easy-to-build Demerit : High overhead e.g. start, stop bit
1 bit, data 8 bit -> overhead = 2/10 = 20 %START BIT
5-8 BITS STOP BIT
START BIT
idle0
1
Transmission modesSynchronous Transmission Feature : synchronized by sending timing
information via separate clock line or embedding in data signal
Line coding: Manchester, AMI Component : preamble (8-bit flag), Control, Data,
Control, postamble (8-bit flag) Merit : Low overhead comparing to Asynchronous
transmission. Example : preamble + control + postamble 48 bits data 1000 bits -> overhead = 48/1048 = 4.6 % data 8000 bits -> overhead = 48/8048 = 0.6 %
8-bitflag
8-bitflag
Control ControlData
Transmission media
Transmission medium is the physical path between transmitter and receiver in a data transmission system.
Guided vs unguided (wireless transmission)
Characteristics and quality of data communication depend on characteristics of both media and signal.
Key concern in design is data rate and distance.
Guided Transmission media Two-wire open Twisted pair Coaxial cable Fiber optic
Twisted pair
&
Coaxial cable & connectors
&
&
Guided transmission media
Data rate Distance Typical use
Two-wire open 19.2 kbps 50 m Telephone
Twisted pair Category1-2
<2 Mbps 2-3 miles Telephone
Twisted pair Category3-6
200 Mbps 100 m LANs
Coaxial cable, ThinBaseband Single Ch.
10 Mbps 100 m LANs
Coaxial cable, ThickBroadband Multi Ch.
10 Mbps 2-3 miles LANs, Cable TV
Fiber optic 10 Gbps 100 miles Data, video, LANs, WANs
Unguided transmission media
Transport electromagnetic waves without using a physical conductor
Geostationary satellites The satellite must move at the same speed as
the earth so that it seems to be fixed above a certain spot.
Orbital speed is based on distance from the planet.
This orbit occurs at the equatorial plane and is approximately 22,000 miles from the surface of the earth.
At least 3 Satellite to cover all areas.
Satellite frequency bands
Band DownlinkSat. to earth
UplinkEarth to Sat.
C 3.7-4.2 GHz 5.925-6.425 GHz
Ku 11.7-12.2 GHz 14-14.5 GHz
Ka 17.7-21 GHz 27.5-31 GHz
Unguided transmission media
Data rate
Distance Typical use
Microwave
n-Gbps 20-30 miles
Building to building
Satellite n-Gbps Worldwide
Long distance
Infrared 16 Mbps 1.5 Miles Short distance
ModulationsAmplitude Shift Keying ASK (OOK)
BW for ASK
Nbaud is baud rate
Ex. Given a BW of 10,000 Hz (1,000-11,000) for a full-duplex ASK. Find the carriers and the BW in each direction. Assume there is no gap between the bands in two directions. What is the maximum baud rate and bit rate?
Frequency Shift Keying (FSK)
BW for FSK
EXample: Find the maximum bit rates for an FSK signal if the bandwidth of the medium is 12,000 Hz, and the difference between the two carriers must be at least 2000 Hz. Transmission is in full-duplex mode.
Phase Shift Keying (PSK)
PSK Constellation diagram
4-PSK
4-PSK Constellation diagram
8-PSK
BW for PSK
The same as ASK Ex. Given a bandwidth of 5000 Hz
for an 8-PSK signal, what are the baud rate and bit rate?
PSK is not susceptible to the noise degradation that affects ASK, nor the BW limitations of FSK.
Quadrature amplitude modulation (QAM)
BW for QAM
The same as ASK and PSK.
Multiplexing
multiple links on 1 physical line common on long-haul, high capacity,
links have FDM and TDM alternatives
Frequency Division Multiplexing
FDMSystem Overview
FDM Voiceband Example
Wavelength Division Multiplexing
FDM with multiple beams of light at different freq
carried over optical fiber links
Synchronous Time Division Multiplexing
TDM SystemOverview
Data communication interfacing
DTE : Data Terminal Equipment is any device that is a source of or destination for binary digital data (PC)
DCE : Data Circuit-terminating Equipment is any device that transmits or receives data in the form of an analog or digital signal through a network (Modem)
DTE DCE PSTN DTEDCE
Data communication interfacing DTE -DCE InterfacingRequirement : Use the same encoding
scheme and have common standards Mechanical characteristics : plugs,
circuits Electrical characteristics : voltage-level,
timing Functional characteristics : meaning of
each interchange circuits เช่�นขา 7 คือ Ground
V.24/EIA-232 (RS 232)
Electronic Industries Association (EIA)
(ISO 2110) 25-pin connector (but can be substituted by 9-pin (DB-9) : 8, 3, 2, 20, 7, 6, 4, 5, 22)
Mechanical characteristics
Electrical characteristics -3 to -15 V=binary 1 or OFF condition +3 to 15 V =binary 0 or ON condition Maximum bit rate 20 kbps
0
1 1
Functional specification
Control SignalName To Function
Request to send
DCE DTE wishes to transmit
Clear to send DTE DCE is ready to receive
DCE ready DTE DCE is ready to operate
DTE ready DCE DTE is ready to operate
Ring indicator DTE DCE is receiving a ringing signal
Received line signal detector
DTE DCE is receiving a signal(carrier)
Null modem
PSTN
MODEMS MOdulator/DEModulator
Bandwidth 600 Hz to 3000 Hz
Dial-up operation
20
DTE