CHAP1 dan CHAP2-Dasar pengiriman data.ppt

Transmission Fundamentals
Chapter 2

Electromagnetic Signal
 Function of time
 Can also be expressed as a function
of frequency
 Signal consists of components of
different frequencies

Time-Domain Concepts
 Analog signal - signal intensity varies in a
smooth fashion over time
 No breaks or discontinuities in the signal
 Digital signal - signal intensity maintains a
constant level for some period of time and
then changes to another constant level
 Periodic signal - analog or digital signal
pattern that repeats over time
 s(t +T ) = s(t ) -< t < +

where T is the period of the signal

 Aperiodic signal - analog or digital signal
pattern that doesn't repeat over time
 Peak amplitude (A) - maximum value or
strength of the signal over time; typically
measured in volts
 Frequency (f )
 Rate, in cycles per second, or Hertz (Hz) at
which the signal repeats

 Period (T ) - amount of time it takes for one
repetition of the signal
 T = 1/f
 Phase () - measure of the relative position
in time within a single period of a signal
 Wavelength () - distance occupied by a
single cycle of the signal
 Or, the distance between two points of
corresponding phase of two consecutive cycles

Sine Wave Parameters
 General sine wave
 s(t ) = A sin(2ft + )
 Figure 2.3 shows the effect of varying each
of the three parameters
 (a) A = 1, f = 1 Hz,  = 0; thus T = 1s
 (b) Reduced peak amplitude; A=0.5
 (c) Increased frequency; f = 2, thus T = ½
 (d) Phase shift; = /4 radians (45 degrees)
 note: 2 radians = 360° = 1 period

Time vs. Distance
 When the horizontal axis is time, as in Figure
2.3, graphs display the value of a signal at a
given point in space as a function of time
 With the horizontal axis in space, graphs
display the value of a signal at a given point
in time as a function of distance
 At a particular instant of time, the intensity of the
signal varies as a function of distance from the
source

Frequency-Domain Concepts
 Fundamental frequency - when all frequency
components of a signal are integer multiples of
one frequency, it’s referred to as the
fundamental frequency
 Spectrum - range of frequencies that a signal
contains
 Absolute bandwidth - width of the spectrum of a
signal
 Effective bandwidth (or just bandwidth) - narrow
band of frequencies that most of the signal’s
energy is contained in

Frequency-Domain Concepts
 Any electromagnetic signal can be
shown to consist of a collection of
periodic analog signals (sine waves)
at different amplitudes, frequencies,
and phases
 The period of the total signal is equal
to the period of the fundamental
frequency

Relationship between Data
Rate and Bandwidth
 The greater the bandwidth, the higher the
information-carrying capacity
 Conclusions
 Any digital waveform will have infinite bandwidth
 BUT the transmission system will limit the
bandwidth that can be transmitted
 AND, for any given medium, the greater the
bandwidth transmitted, the greater the cost
 HOWEVER, limiting the bandwidth creates
distortions

Data Communication Terms
 Data - entities that convey meaning,
or information
 Signals - electric or electromagnetic
representations of data
 Transmission - communication of
data by the propagation and
processing of signals

Examples of Analog and
Digital Data
 Analog
 Video
 Audio
 Digital
 Text
 Integers

Analog Signals
 A continuously varying electromagnetic
wave that may be propagated over a
variety of media, depending on frequency
 Examples of media:
 Copper wire media (twisted pair and coaxial
cable)
 Fiber optic cable
 Atmosphere or space propagation
 Analog signals can propagate analog and
digital data

Digital Signals
 A sequence of voltage pulses that may
be transmitted over a copper wire
medium
 Generally cheaper than analog signaling
 Less susceptible to noise interference
 Suffer more from attenuation
 Digital signals can propagate analog
and digital data

Reasons for Choosing Data
and Signal Combinations
 Digital data, digital signal
 Equipment for encoding is less expensive than digital-to-
analog equipment
 Analog data, digital signal
 Conversion permits use of modern digital transmission
and switching equipment
 Digital data, analog signal
 Some transmission media will only propagate analog
signals
 Examples include optical fiber and satellite
 Analog data, analog signal
 Analog data easily converted to analog signal

Analog Transmission
 Transmit analog signals without regard to
content
 Attenuation limits length of transmission
link
 Cascaded amplifiers boost signal’s energy
for longer distances but cause distortion
 Analog data can tolerate distortion
 Introduces errors in digital data

Digital Transmission
 Concerned with the content of the signal
 Attenuation endangers integrity of data
 Digital Signal
 Repeaters achieve greater distance
 Repeaters recover the signal and retransmit
 Analog signal carrying digital data
 Retransmission device recovers the digital data
from analog signal
 Generates new, clean analog signal

About Channel Capacity
 Impairments, such as noise, limit
data rate that can be achieved
 For digital data, to what extent do
impairments limit data rate?
 Channel Capacity – the maximum
rate at which data can be transmitted
over a given communication path, or
channel, under given conditions

Concepts Related to Channel
Capacity
 Data rate - rate at which data can be
communicated (bps)
 Bandwidth - the bandwidth of the transmitted
signal as constrained by the transmitter and
the nature of the transmission medium (Hertz)
 Noise - average level of noise over the
communications path
 Error rate - rate at which errors occur
 Error = transmit 1 and receive 0; transmit 0 and
receive 1

Nyquist Bandwidth
 For binary signals (two voltage levels)
 C = 2B
 With multilevel signaling
 C = 2B log2
M

M = number of discrete signal or voltage
levels

Signal-to-Noise Ratio
 Ratio of the power in a signal to the power
contained in the noise that’s present at a
particular point in the transmission
 Typically measured at a receiver
 Signal-to-noise ratio (SNR, or S/N)
 A high SNR means a high-quality signal, low
number of required intermediate repeaters
 SNR sets upper bound on achievable data rate
power
noise
power
signal
log
10
)
( 10
dB 
SNR

Shannon Capacity Formula
 Equation:
 Represents theoretical maximum that can
be achieved
 In practice, only much lower rates achieved
 Formula assumes white noise (thermal noise)
 Impulse noise is not accounted for
 Attenuation distortion or delay distortion not
accounted for
 
SNR
1
log2 
B
C

Example of Nyquist and
Shannon Formulations
 Spectrum of a channel between 3
MHz and 4 MHz ; SNRdB
= 24 dB
 Using Shannon’s formula
 
251
SNR
SNR
log
10
dB
24
SNR
MHz
1
MHz
3
MHz
4
10
dB






B
  Mbps
8
8
10
251
1
log
10 6
2
6






C

Example of Nyquist and
Shannon Formulations
 How many signaling levels are
required?
 
16
log
4
log
10
2
10
8
log
2
2
2
6
6
2







M
M
M
M
B
C

Classifications of
Transmission Media
 Transmission Medium
 Physical path between transmitter and receiver
 Guided Media
 Waves are guided along a solid medium
 E.g., copper twisted pair, copper coaxial cable,
optical fiber
 Unguided Media
 Provides means of transmission but does not guide
electromagnetic signals
 Usually referred to as wireless transmission
 E.g., atmosphere, outer space

Unguided Media
 Transmission and reception are
achieved by means of an antenna
 Configurations for wireless
transmission
 Directional
 Omnidirectional

General Frequency Ranges
 Microwave frequency range
 1 GHz to 40 GHz
 Directional beams possible
 Suitable for point-to-point transmission
 Used for satellite communications
 Radio frequency range
 30 MHz to 1 GHz
 Suitable for omnidirectional applications
 Infrared frequency range
 Roughly, 3x1011
to 2x1014
Hz
 Useful in local point-to-point multipoint applications within
confined areas

Terrestrial Microwave
 Description of common microwave antenna

Parabolic "dish", 3 m in diameter

Fixed rigidly and focuses a narrow beam

Achieves line-of-sight transmission to receiving
antenna

Located at substantial heights above ground level
 Applications

Long haul telecommunications service

Short point-to-point links between buildings

Satellite Microwave
 Description of communication satellite
 Microwave relay station
 Used to link two or more ground-based microwave
transmitter/receivers
 Receives transmissions on one frequency band
(uplink), amplifies or repeats the signal, and
transmits it on another frequency (downlink)
 Applications
 Television distribution
 Long-distance telephone transmission
 Private business networks

Broadcast Radio
 Description of broadcast radio antennas
 Omnidirectional
 Antennas not required to be dish-shaped
 Antennas need not be rigidly mounted to a
precise alignment
 Applications
 Broadcast radio

VHF and part of the UHF band; 30 MHZ to 1GHz

Covers FM radio and UHF and VHF television

Multiplexing
 Capacity of transmission medium
usually exceeds capacity required for
transmission of a single signal
 Multiplexing - carrying multiple
signals on a single medium
 More efficient use of transmission
medium

Reasons for Widespread Use
of Multiplexing
 Cost per kbps of transmission facility
declines with an increase in the data rate
 Cost of transmission and receiving
equipment declines with increased data
rate
 Most individual data communicating
devices require relatively modest data rate
support

Multiplexing Techniques
 Frequency-division multiplexing (FDM)

Takes advantage of the fact that the useful
bandwidth of the medium exceeds the
required bandwidth of a given signal
 Time-division multiplexing (TDM)

Takes advantage of the fact that the
achievable bit rate of the medium exceeds
the required data rate of a digital signal

Frequency-division
Multiplexing

CHAP1 dan CHAP2-Dasar pengiriman data.ppt

More Related Content

Similar to CHAP1 dan CHAP2-Dasar pengiriman data.ppt (20)

Recently uploaded (20)

CHAP1 dan CHAP2-Dasar pengiriman data.ppt