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Data Transmission
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1Data Transmission &
Transmission Media
Chapter Two
Outline Signal
Analog Digital
Transmission Mode Parallel Transmission Serial Transmission
Digital Transmission Digital to digital Modulation Analog to digital Modulation
Analog Transmission Digital to analog transmission Analog to analog transmission
Transmission Media Guided Unguided - wireless
NetworkingNetworking
.
Transmission of data across network connections
To be transmitted, data must be transformed to electromagneticsignals
2Position of the Physical LayerPosition of the Physical Layer
Service send stream data from sender to receiverNode-to-node deliveryTransmission medium control on the direction of data flow
ServicesServices
convert data (bit pattern) to signal
Determines maximum limit of data rate transmission depend on the design of physical hardware and software
providing clocking mechanism to control sender and receiver timing of the transfer
set of techniques that allows the simultaneous transmission of multiple signals across a single data link
Create direct connection two devices such as phones or computers
Analog Signal
3Analog and Digital DataAnalog data human voice
captured by a microphone and converted to an analog signal
Digital data form 0s and 1s
converted to a digital signal when transferred from one position to another
Analog Signal
Analog and Digital SignalsAnalog and Digital Signals
Analog signals can have an infinite number of values in a
range
Digital signals can have only a limited number of values.
Analog Signal
Analog and Digital Signals
Means by which data are propagatedAnalog Continuously variable Various media wire, fiber optic, space
Speech bandwidth 100Hz to 7kHz Telephone bandwidth 300Hz to 3400Hz Video bandwidth 4MHz
Digital Use two DC components
4Comparison of Analog and Digital Signals
Analog Signal
Periodic and Periodic and AperiodicAperiodic SignalsSignalsIn data communication, we commonly use
periodic analog signals and aperiodic (non-periodic) digital signals.
Periodic signal completes a pattern within a measurable time frame, called a period and repeats that pattern over subsequent identical periods.
Pattern repeated over time Completion of one full pattern cycle
Aperiodic signal changes without exhibiting a pattern or cycle that repeats over time
Pattern not repeated over time
Analog Signal
Analog Signals
Classified as: Simple (Sine Wave) cannot be decomposed into smaller signals
Composite composed of multiple sine waves
Analog Signal
5A sine waveA sine wave
Changes over the course of a cycle is smooth and consistent, continuous, rolling flowEach cycle consist of a single arc above the time axis and followed by a single arc below itMathematically describe:
s(t) = A sin (2ft + )
Analog Signal
Sine WaveCan be described by 3 characteristics:
Peak Amplitude (A) maximum strength of signal volts
Frequency (f) Rate of change of signal Hertz (Hz) or cycles per second Period = time for one repetition (T) T = 1/f
Phase () Relative position in time
Analog Signal
AmplitudeAmplitude
Represents the absolute value of its highest intensity, proportional to the energy it carries
For electrical signal, peak amplitude measured in volts
Analog Signal
6Period and frequency
Frequency and period are inverses of each other.
f = 1/T ; T = 1/f
Period amount of time, in seconds, a signal needs to complete one cycleFrequency no. of periods in one second.
Analog Signal
1012 Hzterahertz (THz)1012 sPicoseconds (ps)
109 Hzgigahertz (GHz)109 sNanoseconds (ns)
106 s
103 s
1 s
EQUIVALENT
106 Hzmegahertz (MHz)Microseconds (ms)
103 Hzkilohertz (KHz)Milliseconds (ms)
1 Hzhertz (Hz)Seconds (s)
EQUIVALENTUNITUNIT
Units of periods and frequencies
Period Frequency
Analog Signal
Example 1Example 1Express a period of 100 ms in microseconds, and express the corresponding frequency in kilohertz.
SolutionSolution
From Table 3.1 we find the equivalent of 1 ms.We make the following substitutions:100 ms = 100 10-3 s = 100 10-3 106 ms = 105 ms Now we use the inverse relationship to find the frequency, changing hertz to kilohertz100 ms = 100 10-3 s = 10-1 s f = 1/10-1 Hz = 10 10-3 KHz = 10-2 KHz
Analog Signal
7FrequencyFrequency
is the rate of change with respect to time.
Change in a short span of time means HIGH FREQUENCY.
Change over a loooooonnnnggg span of time means LOW FREQUENCY.
Analog Signal
More about Frequency..More about Frequency..
If a signal does not change at all, its frequency is ZERO.
If a signal changes instantaneously, its frequency is INFINITE. (1/0)
Analog Signal
Components of Speech
Frequency range (of hearing) 20Hz-20kHz Speech 100Hz-7kHz
Easily converted into electromagnetic signal for transmissionSound frequencies with varying volume converted into electromagnetic frequencies with varying voltageLimit frequency range for voice channel 300-3400Hz
Analog Signal
8Conversion of Voice Input into Analog Signal
Analog Signal
PhasePhase describes the position of the waveform relative to time zero.
measured in degrees or radians 360 = 2 rad; 1 = 2/360 rad; 1 rad = 360/(2)
Relationships between different phasesAnalog Signal
9Example 2Example 2A sine wave is offset one-sixth of a cycle with respect to time zero. What is its phase in degrees and radians?
SolutionSolution
We know that one complete cycle is 360 degrees.
Therefore, 1/6 cycle is
(1/6) 360 = 60 degrees = 60 x 2p /360 rad = 1.046 rad
Analog Signal
Sine wave examplesAnalog Signal
Sine wave examples (continued)Analog Signal
10
Sine wave examples (continued)Analog Signal
Time and Frequency DomainTime and Frequency Domain
Time-domain (instantaneous amplitude with respect to time)
Frequency domain (peak amplitude with respect to frequency)
An analog signal is best represented in the frequency domain.
Analog Signal
Time and frequency domains
Analog Signal
11
Time and frequency domains (cont.)Analog Signal
Time and frequency domains (cont.)
Analog Signal
Composite SignalComposite Signal A single-frequency sine wave is not useful in data communications.
e.g.: Electric energy distribution, burglar alarm.
Phone conversation if use single signal it just yield a buzz
Changes of one or more of its characteristicsneed to be done to make it useful.
The signal will become a Composite Signal(which made of many simple sine waves)
Analog Signal
12
Fourier AnalysisFourier Analysis
According to Fourier analysis, any composite signal can be
represented as a combination of simple sine waves with different
frequencies, phases, and amplitudes.
Analog Signal
Square wave
Fundamental frequency frequency f is dominant
Analog Signal
Three harmonics (frequency 3f)Analog Signal
13
Adding first three harmonicsAnalog Signal
Frequency spectrum comparisonFrequency spectrum comparisonFrequency spectrum description of a signal using the frequency domain and containing all its components
Analog Signal
Composite Signal and Transmission Composite Signal and Transmission MediumMedium
Figure 3.12 Signal corruption
no transmission medium is perfect each medium passes some frequencies; weaken others; blocks still others. That will give this result
Analog Signal
14
BandwidthBandwidth range of frequencies that a medium can pass;
without losing one-half of the power contained in that signal.
It is a property of a medium: the difference between the highest and the lowest frequencies that the medium can satisfactorily pass.
Analog Signal
BandwidthAnalog Signal
Example 3Example 3If a periodic signal is decomposed into five sine waves with frequencies of 100, 300, 500, 700, and 900 Hz, what is the bandwidth? Draw the spectrum, assuming all components have a maximum amplitude of 10 V.
SolutionSolutionB = fh - fl = 900 - 100 = 800 HzThe spectrum has only five spikes, at 100, 300, 500, 700, and 900
Analog Signal
15
Example: Frequency spectrumAnalog Signal
Example 4Example 4A signal has a bandwidth of 20 Hz. The highest frequency is 60 Hz. What is the lowest frequency? Draw the spectrum if the signal contains all integral frequencies of the same amplitude.
SolutionSolutionB = B = ffhh -- ffll20 = 60 20 = 60 -- ffllffll = 60 = 60 -- 20 = 40 Hz20 = 40 Hz
Analog Signal
Example: Frequency spectrumAnalog Signal
16
Example 5 A signal has a spectrum with frequencies between 1000 and 2000 Hz (bandwidth of 1000 Hz). A medium can pass frequencies from 3000 to 4000 Hz (a bandwidth of 1000 Hz). Can this signal faithfully pass through this medium?
SolutionSolutionThe answer is definitely no. Although the signal can have the same bandwidth (1000 Hz), the range does not overlap. The medium can only pass the frequencies between 3000 and 4000 Hz; the signal is totally lost.
Analog Signal
Digital Signal
Digital Signals
Bit Interval and Bit Rate As a Composite Analog Signal Through Wide-Bandwidth Medium Through Band-Limited Medium Versus Analog Bandwidth Higher Bit Rate
Digital Signal
17
A digital signal
+ve voltage
zero voltage
Digital Signal
Bit Interval and Bit Rate
Figure 3.17 Bit rate and bit interval
Bit interval time required to send one single bitBit rate no. of bit intervals per second (bps)
Digital Signal
Example 6A digital signal has a bit rate of 2000 bps. What is the duration of each bit (bit interval)
SolutionSolution
The bit interval is the inverse of the bit rate.
Bit interval = 1/ 2000 s = 0.000500 s = 0.000500 x 106 ms = 500 ms
Digital Signal
18
Digital versus analogDigital Signal
50 KHz
5 KHz
500 Hz
Harmonic1
800 KHz450 KHz200 KHz100 Kbps
80 KHz45 KHz20 KHz10 Kbps
8 KHz4.5 KHz2 KHz1 Kbps
Harmonics1, 3, 5, 7
Harmonics1, 3, 5
Harmonics1, 3
BitRate
Bandwidth Requirement
The bit rate and the bandwidth are proportional to each other.
Bandwidth (B) = n(bit rate) , third harmonic: Bandwidth,B = n + 3n2 2 2
Digital Signal
Analog Bandwidth range of frequencies that a medium can pass; in Hertz
Digital Bandwidth maximum bit rate that a medium can pass; in bps
Digital versus Analog BandwidthDigital Signal
19
i.e:- using a modem with modulation techniques that
allow a representation of multiple bits in one single
period of an analog signal
Higher Bit RateDigital Signal
Advantages & Disadvantages of Digital
AdvantagesCheaperLess susceptible to noise
DisadvantageGreater attenuation Pulses become rounded and smaller Leads to loss of information
Digital Signal
Attenuation of Digital Signals
Digital Signal
20
Transmission ModeParallel Transmission
& Serial Transmission
Parallel TransmissionMultiples bits are sent with each clock tickOnly one way to sent data
Serial Transmission1 bit is sent with each clock tickTwo subclasses :Synchronousasynchronous
Transmission ModeTransmission Mode
Data TransmissionTransmission Mode
21
Parallel Transmission
This mechanism is conceptually simple oneUse n wires to send n bits at one timeAdvantages
speed can increase the transmission speed by the factor of nover serial transmission
Drawback: cost requires n communication line to transmit the data
stream- expensive- usually use for limited or short distance
Transmission Mode
Serial Transmission
Transmission based on bit by bit at one time therefore only need one communication lineAdvantages :
reduce cost of transmissionSince communication within devices is parallel, need conversion between
the sender and the line (parallel -to-serial) and ,between the line and the receiver (serial -to- parallel)
Transmission Mode
In asynchronous transmission, we send 1 start bit (0) at the
beginning and 1 or more stop bits (1s) at the end of each byte.
There may be a gap between each byte.
Asynchronous TransmissionTransmission Mode
22
Asynchronous Transmission (cont)Asynchronous here means asynchronous
at the byte level, but the bits are still synchronized; their durations are the same.
Transmission Mode
Synchronous TransmissionIn synchronous transmission,
we send bits one after another without start/stop bits or gaps.
It is the responsibility of the receiver to group the bits.
Transmission Mode
Asynchronous Slower transmission or low-speed
communication Cheap and effective E.g: Keyboard only one character at
one time and leave unpredictable gap of time between each character
Synchronous Faster transmission useful for high speed
application
Asynchronous vs. SynchronousTransmission Mode
23
Digital Transmission
Encoding Techniques
Digital transmissionDigital data, digital signalAnalog data, digital signal
Analog TransmissionDigital data, analog signalAnalog data, analog signal
Digital Transmission
Digital data to digital signalLine Coding technique to convert binary data to digital signalsBlock Coding method to improve the efficiency of line coding
Analog data to digital signalDigitization - Conversion of analog data into digital data Sampling technique for changing
analog data to binary data Pulse Amplitude Modulation (PAM) Pulse Code Modulation (PCM) -
Quantization
Topics Covered:-Digital Transmission
24
Digital Data, Digital Signal
Digital signal Discrete, discontinuous voltage pulses Each pulse is a signal element Binary data encoded into signal
elementsUse a conversion technique Line coding
Digital Transmission
Conversion of PC Input to Digital Signal
Digital Transmission
Digital Signals Carrying Analog and Digital Data
Digital Transmission
25
Line Coding
Define the process of converting binary data to a digital signalIn line coding, we will discuss about the:
Some Characteristics Line Coding Schemes Some Other Schemes
Digital Data, Digital Signal
Line Coding: Characteristics
Signal Level VS Data Level Pulse Rate VS Bit Rate DC Components Self-synchronization
Digital Data, Digital Signal
Signal Level VS Data Level
no. of signal levels no. of values allowed in a particular signalno. of data levels no. of values used to represent
data
Digital Data, Digital Signal
26
Pulse Rate no. of pulses per secondPulse minimum amount of time
required to transmit a symbolBit rate no. of bits per secondMathematically, describe as:
Pulse Rate VS Bit Rate
BitRate = PulseRate x Log2 L
Digital Data, Digital Signal
Data and Signals
Usually use digital signals for digital data and analog signals for analog dataCan use analog signal to carry digital data ModemCan use digital signal to carry analog data Compact Disc audio
DC ComponentsSome line coding leave a residual direct-current (dc) componentThis component is an undesirable components with reasons:-
signal is distorted / create errors in the output when pass through a system that does not allow passage of a dc component (i.e: transformer) extra energy residing on the line and useless
Digital Data, Digital Signal
27
Self-Synchronization includes timing information in the data being transmitted can be achieved if there are transitions in the signal that alert the receiver to the beginning, middle or end of the pulse if the receivers clock is out of synchronization, the alerting points can resetthe clock
Digital Data, Digital Signal
Line Coding SchemesDigital Data, Digital Signal
Unipolar simple and primitive use only one voltage level 1 - +ve value; 0 zero value inexpensive to implement 2 problems:-
dc component lack of synchronization
Digital Data, Digital Signal
28
Polar use two voltage level (+ve and ve)
Digital Data, Digital Signal
NRZ encoding the value of the signal is always either +ve or ve
NRZ-L (Nonreturn Zero-level) the level of the signal depends on the type of bit that it
represents 0 = positive voltage (+ve); 1 = negative voltage (-ve)
NRZ-I (Nonreturn Zero-invert) inversion of the voltage level represents a 1 bit 0 = no changes; 1 = have transition between +ve and
ve voltage Inverted if a 1 is encountered
NRZ (Nonreturn to Zero)Digital Data, Digital Signal
NRZ-L and NRZ-I encodingDigital Data, Digital Signal
29
Return to Zero (RZ) use three values: +ve, -ve and zero i.e: 1 bit positive to zero, 0 bit negative to zero disadvantage occupies more bandwidth (requires two signal changes to encode 1 bit)the most effective compare within these three alternative encoding schemes.
Digital Data, Digital Signal
Manchester use an inversion at the middle of each bit interval for both
synchronization and bit representation. binary 1 negative to positive, binary 0 positive to negative Consider achieve same level of synchronization as RZ but only
involve two levels of amplitude
Digital Data, Digital Signal
Differential Manchester Encoding the inversion at the middle of the bit interval is used for
synchronization, BUT the presence or absence of an additional transition at the beginning of the interval is used to identify the bit.
binary 0 transition; binary 1 no transition
Digital Data, Digital Signal
30
Bipolar use three voltage levels (+ve, -ve and zero) a common bipolar encoding known as Bipolar Alternate Mark
Inversion (AMI) alternate 1 inversionmeans : 0 = 0 voltage; 1 = alternation +ve and ve voltage
Modification of bipolar AMI to solve the problem of synchronizing sequential 0s, especially for long-distance transmission known as BnZS (Bipolar n-zero substitution) Bipolar n-zero substitution (BnZS) wherever n consecutive zeros
occur in the sequence, some of the bits in these n bits become +ve or ve (to help synchronization)
Digital Data, Digital Signal
Other Schemes: 2B1Q 2 binary, one quaternary (2B1Q): uses 4 voltage levels each pulse can represent 2 bits (more efficient)
Digital Data, Digital Signal
Other Schemes: MLT-3Multiline transmission, three level (MLT-3): ~ NRZ-I use three levels signals (+1, 0, -1) signal transit at the beginning of a 1 bit; no transition at the beginning of 0 bit
Digital Data, Digital Signal
31
Block Coding to improve the performance of line coding Need some kind of redundancy to ensure synchronization Need to include other redundant bits to detect errors.
Digital Data, Digital Signal
Step 1 Division Sequence of bits is divided into groups of m bits
Step 2 Substitution substitute an m-bit code for an n-bit group E.g: 4B/5B encoding refer Figure 4.16
Step 3 Line Coding use one of the line coding schemes to create a
signal sometimes step 2 and 3 can be combined
Steps in TransformationDigital Data, Digital Signal
Substitution in block codingDigital Data, Digital Signal
32
1101011010110001010010100100
1101111011110101011010110101
1110011100111001110011100110
1110111101111101111011110111
1011110111101110101101010011
1010010100
0100101001
1111011110
Code
101101011010100010
100111001110010001
10010100101000 0000
CodeDataData
Some Common Block Codes: 4B/5BDigital Data, Digital Signal
Some Common Block Codes: 4B/5B (cont.)
1000110001K (start delimiter)
0110101101T (end delimiter)
1100111001S (Set)
0011100111R (Reset)
1100011000J (start delimiter)
0010000100
1111111111
0000000000
Code
H (Halt)
I (Idle)
Q (Quiet)
Data
Digital Data, Digital Signal
Similar to 4B/5B;Group of 8 bits of data is substituted
by a 10-bit codeMore error detection capability
than 4B/5B
Some Common Block Codes: 8B/10B
Digital Data, Digital Signal
33
Some Common Block Codes: 8B/6T
designed to substitute an 8-bit group with a six symbol code; each symbol is ternary, having one of three signal levels each block of 8-bit data is encoded as units of ternary signals (three levels)
Digital Data, Digital Signal
Pulse Amplitude ModulationPulse Code ModulationSampling Rate: NyquistTheoremHow Many Bits per Sample?Bit Rate
SamplingAnalog Data, Digital Signal
Line coding and block coding use for convert binary data to digital signalVoice or video created as analog signal in order to store the recording in the computer or send it digitalized; need to change it through process sampling
Sampling
Analog Data, Digital Signal
34
Pulse Amplitude Modulation (PAM) analog to digital conversion methodTechnique : take analog signal samples it generate the series of
pulse based on the result of the sampling sampling means measuring the amplitude of the signal at equal intervalsUse technique sample and holdPAM has some application, but is not use in data communication. However, it is the first step in aother popular conversion method call Pulse Code Modulatiom (PCM)
Analog Data, Digital Signal
Pulse Code Modulationmodifies the pulses created by PAM to create a completely digital signal Quantization: method of assigning integral values in a specific range to sampled instances
Analog Data, Digital Signal
Quantization by using sign and magnitude
This figure illustrate a simple method of assigning sign and magnitude to quantized Sample. Each value translate into its 7-bit binary equivalent. The eighth bit indicates the sign
Analog Data, Digital Signal
35
PCM
This figure shows the result of PCM of the original signal encoded into unipolar signal
PCM is made up of PAM, quantization, binary encoding and line coding
Analog Data, Digital Signal
From analog signal to PCM digital codeAnalog Data, Digital Signal
Sampling Rate: Nyquist TheoremAccording to the Nyquist theorem, the sampling rate must
be at least 2 times the highest frequency.
Analog Data, Digital Signal
36
Example 4What sampling rate is needed for a signal with a bandwidth of 10,000 Hz (1000 to 11,000 Hz)?
SolutionSolution
The sampling rate must be twice the highest frequency in the signal:
Sampling rate = 2 x (11,000) = 22,000 samples/s
Analog Data, Digital Signal
Example 5A signal is sampled. Each sample requires at least 12 levels of precision (+0 to +5 and -0 to -5). How many bits should be sent for each sample?
SolutionSolutionWe need 4 bits; 1 bit for the sign and 3 bits for the value. A 3-bit value can represent 23 = 8 levels (000 to 111), which is more than what we need. A 2-bit value is not enough since 22 = 4. A 4-bit value is too much because 24 = 16.
Analog Data, Digital Signal
We want to digitize the human voice. What is the bit rate, assuming 8 bits per sample?
SolutionSolution
The human voice normally contains frequencies from 0 to 4000 Hz. Sampling rate = 4000 x 2 = 8000 samples/sSampling rate = 4000 x 2 = 8000 samples/s
Bit rate = sampling rate x number of bits per sample Bit rate = sampling rate x number of bits per sample = 8000 x 8 = 64,000 bps = 64 Kbps= 8000 x 8 = 64,000 bps = 64 Kbps
Example 6
Analog Data, Digital Signal
37
Advantages of Digital Transmission
Digital technology Low cost LSI/VLSI technology
Data integrity Longer distances over lower quality lines
Capacity utilization High bandwidth links economical High degree of multiplexing easier with digital
techniquesSecurity & Privacy Encryption
Integration Can treat analog and digital data similarly
?Identify and present next lecture
Digital-to-Analog ConversionAmplitude Shift Keying (ASK)Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)Quadrature Amplitude Modulation
Bit/Baud Comparison
Digital-to-Analog
38
Analog Signals Carrying Analog and Digital Data
Analog Transmission
Analog Transmission
Analog signal transmitted without regard to content Represent analog or digital data Attenuated over distance Use amplifiers to boost signal Also amplifies noise
Analog Transmission
Digital Data with Analog Signals This method is used to send computer information over
transmission channels that require analog signals, like a fiber optic networks, computer modems, cellular phone networks, and satellite systems.
An electromagnetic carrier wave is used to carry the informationover great distances and connect digital information users at remote locations.
The digital data is used to modulate one or more of the parameters of the carrier wave (carrier signal)
Carrier signal refers to high frequency signal acts as a basis for the information signal produce by the sending device or source signal
4 possible combinations of data and signal types
Analog data, analog signalDigital data, analog signalAnalog data, digital signal Digital data, digital signal
Digital-to-Analog
39
Digital-to-Analog
Modulationa process converting binary data (low-pass analog signal) to a band pass analog signal or the process of modifying some characteristic of a wave (the carrier) so that it varies synchronized with the instantaneous value of another wave (the modulating wave) in order to transmit a message. The modified characteristic may be frequency, phase, and/or amplitude.
Digital-to-analog modulationa process of changing one of the analog signal characteristic based on the information in a digital signal
Digital-to-Analog
A signal is composed of 1 or more bits In data transmission more concern about the efficiency of data
movement from one destination to another Signal required system efficient bandwidth required to
transmit bits The baud rate determine the bandwidth required to send signal Defines as
Bit rate=baud rate x number of bits per signal Bit rate baud rate
Bit rate is the number of bits per second.Baud rate is the number of signal units per second.
Baud rate is less than or equal to the bit rate
Digital-to-Analog
40
An analog signal carries 4 bits in each signal unit. If 1000 signal units are sent per second, find the baud rate and
the bit rate
Baud rate = 1000 bauds per second (baud/s)Baud rate = 1000 bauds per second (baud/s)Bit rate = 1000 x 4 = 4000 bpsBit rate = 1000 x 4 = 4000 bps
Digital-to-Analog
The bit rate of a signal is 3000. If each signal unit carries 6 bits, what is the baud rate?
Baud rate = 3000 / 6 = 500 baud/sBaud rate = 3000 / 6 = 500 baud/s
Digital-to-Analog
Amplitude changing while frequency and phase remain constant The presence of a carrier wave to indicate a binary one and its absence to
indicate a binary zero. A popular ASK technique called on-off keying (OOK), for example it is used at
radio frequencies to transmit Morse code (referred to as continuous waveoperation).
Drawback :highly susceptible to noise interference refer to unintentional voltageprobably affected by heat or electromagnetic induction created by other sources
Advantages:reduction in the amount of energy required to transmit information
Digital-to-Analog
41
Digital-to-Analog
Find the minimum bandwidth for an ASK signal transmitting at 2000 bps. The transmission mode is half-duplex.
In ASK the baud rate and bit rate are the same. The baud rate is therefore 2000. An ASK signal requires a minimum bandwidth equal to its baud rate. Therefore, the minimum bandwidth is 2000 Hz.
Digital-to-Analog
In ASK the baud rate is the same as the bandwidth, which means the baud rate is 5000. But because the baud rate and the bit rate are also the same for ASK, the bit rate is 5000 bps.
Given a bandwidth of 5000 Hz for an ASK signal, what are the baud rate and bit rate?
Digital-to-Analog
42
Given a bandwidth of 10,000 Hz (1000 to 11,000 Hz), draw the full-duplex ASK diagram of the system. Find the carriers and the bandwidths in each direction. Assume there is no gap between the bands in the two directions.
For full-duplex ASK, the bandwidth for each direction isBW = 10000 / 2 = 5000 Hz
The carrier frequencies can be chosen at the middle of each band(see Fig. 5.5).
fc (forward) = 1000 + 5000/2 = 3500 Hzfc (backward) = 11000 5000/2 = 8500 Hz
Digital-to-Analog
Digital-to-Analog
In Frequency Shift keying (FSK) frequency of the carrier signal is varied to represent binary 0 and 1
Peak amplitude and phase remain constant FSK not affected noise because receiving device focus on the
specific frequency change over a number of period and ignore the voltage
The common FSK is Binary Frequency Shift Keying (BFSK)
Digital-to-Analog
43
In FSK, easier to analyze as two different coexisting frequenciesFSK spectrum is a combination of two ASK spectra centered on fc0 and fc1
Digital-to-Analog
Find the minimum bandwidth for an FSK signal transmitting at 2000 bps. Transmission is in half-duplex mode, and the carriers are separated by 3000 Hz.
For FSKBW = baud rate + fc1 - fc0
BW = bit rate + fc1 - fc0 = 2000 + 3000 = 5000 Hz
Digital-to-Analog
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 is 2000 Hz. Transmission is in full-duplex mode.
Because the transmission is full duplex, only 6000 Hz is allocated for each direction. BW = baud rate + fc1 BW = baud rate + fc1 -- fc0 fc0 Baud rate = BW Baud rate = BW -- (fc1 (fc1 -- fc0 ) = 6000 fc0 ) = 6000 -- 2000 = 40002000 = 4000But because the baud rate is the same as the bit rate, the bit rate is 4000 bps.
Digital-to-Analog
44
In Phase Shift Keying the phase of the carrier signal is shifted to represent data Both peak amplitude and frequency remain constant while the phase tend to change. e.g.: if the phase begin with 0 will represent binary 0, then it can change to binary 1 if begin with a phase 180 The common technique is 2-PSK or Binary PSK used two different phase not susceptible to the noise degradation that affects ASK or bandwidth
limitations of FSK
Digital-to-Analog
Note: The figure illustrate the same relationship showing only the phase
A constellation diagram is a representation of a digital modulationscheme in the complex plane A constellation diagram can perform in some methods approach depend on the variation of phase changes such as 2-PSK, 4-PSK and 8-PSK
Digital-to-Analog
Four variationand each phase shift represent 2 bits
This technique also known as Quadrature PSK (QPSK)
A pair of bits represented by each phase = dibit
more efficient coz able to transmit data twice
Digital-to-Analog
45
000
001
010
011
100
101
110
111
In 8-PSK each phase shift represent 3 bit (tribit) 8-PSK contribute 3 time efficiency compared to 2-PSK
Digital-to-Analog
In PSK, minimum bandwidth minimum bandwidth in ASKMaximum bit rate in PSK Maximum bit rate in ASK
Digital-to-Analog
For 4-PSK baud rate is the same as the bandwidth. 4-PSK carried dibit, therefore bid rate = 2 x baud rate.So:
2000bps = 2 x N baud rateN baud rate = 2000/2Baud rate = 1000Baud rate = bandwidth = 1000Hz
Find the bandwidth for a 4-PSK signal transmitting at 2000 bps. Transmission is in half-duplex mode.
Digital-to-Analog
46
Given a bandwidth of 5000 Hz for an 8-PSK signal, what are the baud rate and bit rate?
For PSK the baud rate is the same as the bandwidth, which means the baud rate is 5000. But in 8-PSK the bit rate is 3 times the baud rate, so the bit rate is 15,000 bps.
Digital-to-Analog
Quadrature amplitude modulation is a combination of
ASK and PSK so that a maximum contrast between each signal unit
(bit, dibit, tribit, and so on) is achieved.
Digital-to-Analog
The number of amplitude shift < the number of phase shift The reason : amplitude change is susceptible to noise and
require greater shift differences rather than phase changes
Digital-to-Analog
47
Digital-to-Analog
The bandwidth for QAM = bandwidth required for ASK and PSK
ITU-T ISO
Digital-to-Analog
Digital-to-Analog
48
8N
7N
6N
5N
4N
3N
2N
N
Bit Rate
N5Pentabit32-QAM
N6Hexabit64-QAM
N7Septabit128-QAM
N8Octabit256-QAM
N4Quadbit16-QAM
Tribit
Dibit
Bit
Units
N38-PSK, 8-QAM
N24-PSK, 4-QAM
N1ASK, FSK, 2-PSK
Baud rateBits/BaudModulation
Digital-to-Analog
A constellation diagram consists of eight equally spaced points on a circle. If the bit rate is 4800 bps, what is the baud rate?
The constellation indicates 8-PSK with the points 45 degrees apart. Since 23 = 8, 3 bits are transmitted with each signal unit. Therefore, the baud rate is
4800 / 3 = 1600 baud
Digital-to-Analog
Compute the bit rate for a 1000-baud 16-QAM signal.
A 16-QAM signal has 4 bits per signal unit since log216 = 4.
Thus, (1000)(4) = 4000 bps
Digital-to-Analog
49
Compute the baud rate for a 72,000-bps 64-QAM signal.
A 64-QAM signal has 6 bits per signal unit since log2 64 = 6.
Thus, 72000 / 6 = 12,000 baud
Digital-to-Analog
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)
Analog-to-Analog
This modulation is to represent analog data to analog signal e.g.: radio each radio station has been assigned a
baseband bandwidth. The analog signal produced by each radio station is low-pass signal, all in same range. To ensure different stations able to listen, the low-pass signal need to be shifted to a different range
Analog-to-Analog
50
AmplitudeModulation
Frequencymodulation
PhaseModulation
Analog-to-Analog
The total bandwidth required for AM can be determined from the bandwidth of the audio signal:
BWt = 2 x BWm.
AMtransmission
Carrier signal
modulated
Amplitude varies
Changing amplitude of the Modulating signal
Analog-to-Analog
Analog-to-Analog
51
Analog-to-Analog
Note:Bandwidth of audio signal (speech and music)5 KHz, therefore, minimum bandwidth for AM radio station = 10KHz. Basically, for AM, allocate carrier frequency = 530Hz 1700KHz. Each Station Radio frequency must have minimum distance 10Khz among each other
Analog-to-Analog
We have an audio signal with a bandwidth of 4 KHz. What is the bandwidth needed if we modulate the signal using AM? Ignore FCC regulations.
An AM signal requires twice the bandwidth of the original signal:
BW = 2 x 4 KHz = 8 KHz
Analog-to-Analog
52
The total bandwidth required for FM can be determined from the bandwidth of the
audio signal: BWt = 10 x BWm
Analog-to-Analog
Analog-to-Analog
Analog-to-Analog
53
The bandwidth of a stereo audio signal is usually 15 KHz. Therefore, an FM station needs at least a bandwidth of 150 KHz. The FCC requires the minimum bandwidth
to be at least 200 KHz (0.2 MHz).
Analog-to-Analog
Analog-to-Analog
We have an audio signal with a bandwidth of 4 MHz. What is the bandwidth needed if we modulate the signal using FM? Ignore FCC regulations.
An FM signal requires 10 times the bandwidth of the original signal:
BW = 10 x 4 MHz = 40 MHz
Analog-to-Analog
54
Transmission Impairments
Signal received may differ from signal transmitted Analog - degradation of signal quality Digital - bit errors Caused by Attenuation and attenuation distortion Delay distortion Noise
Transmission Impairments
Attenuation Signal strength falls off with distance Depends on medium Received signal strength: must be enough to be detected must be sufficiently higher than noise to
be received without error Attenuation is an increasing function
of frequency
Transmission Impairments
Delay Distortion
Only in guided mediaOccurs because velocity of
propagation varies with frequencyVelocity tend to be higher at the
center frequency and fall off toward the two edges of the bandCritical for digital data
Transmission Impairments
55
Noise (1)
Additional signals inserted between transmitter and receiver Divided into 4 categories Thermal Due to thermal agitation of electrons Uniformly distributed across the bandwidth referred
as White noise Significant for satellite communication
Intermodulation Signals that are the sum and difference of original
frequencies sharing a medium
Transmission Impairments
Noise (2)
Crosstalk A signal from one line is picked up by another
Impulse Consist of irregular pulses or spikes of short
duration and high amplitude Generated by external electromagnetic
interference like lightning, fault and flaws in communication system
Transmission Impairments
Transmission Media
56
Guided Media. Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable
Unguided Media : Wireless Radio Waves Microwaves Infrared.
Topic CoveredTransmission Media
Introduction
located below physical layer but controlled by layer 1
Assume that belong to Layer 0
Physical Layer Physical Layer
Sender ReceiverTransmission Media
Cable or air
Transmission Media
Notes Data transmission thru electromagnetic ~ combination of electricand magnetic fieldWired media ~ Signal traveling is directed and having physical limitationTwisted pair and coaxial cable use metallic (copper) conductors ~ accept and transport signal in form of electric current
Transmission MediaTransmission Media
57
OverviewGuided - wireUnguided - wirelessCharacteristics and quality determined by medium and signalFor guided, the medium is more importantFor unguided, the bandwidth produced by the antenna is more importantKey concerns are data rate and distance
Transmission Media
Design Factors
Bandwidth Higher bandwidth gives higher data rate
Transmission impairments Attenuation
InterferenceNumber of receivers In guided media More receivers (multi-point) introduce more
attenuation
Transmission Media
Electromagnetic SpectrumTransmission Media
58
Twisted-Pair Cable
Coaxial Cable
Fiber-Optic Cable
Guided MediaTransmission Media
Transmission Characteristics of Guided Media
Frequency Range
Typical Attenuation
Typical Delay
Repeater Spacing
Twisted pair (with loading)
0 to 3.5 kHz 0.2 dB/km @ 1 kHz
50 s/km 2 km
Twisted pairs (multi-pair cables)
0 to 1 MHz 0.7 dB/km @ 1 kHz
5 s/km 2 km
Coaxial cable
0 to 500 MHz 7 dB/km @ 10 MHz
4 s/km 1 to 9 km
Optical fiber 186 to 370THz
0.2 to 0.5 dB/km
5 s/km 40 km
Guided Media
Twisted pair of coppers with plastic insulation
To carry signals for ground reference
The receiver uses the difference between 2 levels Signal send on one wire
~ Interference & crosstalk may affect both wire and created unwanted signals~ If two are affected equally, receiver is immune
2 wires are parallel ~ the effect of unwanted signals is not same coz different location Twisting balances exposure of interferenceNo of Twist per unit length will influence cable quality, therefore more twist mean better quality.
12
2 Wires
Twisted-Pair CableGuided Media
59
Twisted Pair - Transmission Characteristics
Analog Amplifiers every 5km to 6km
Digital Use either analog or digital signals repeater every 2km or 3km
Limited distanceLimited bandwidth (1MHz)Limited data rate (100MHz)Susceptible to interference and noise
Guided Media
Unshielded Twisted Pair (UTP) Common cable for
communicationOrdinary telephone wireCheapestEasiest to installSuffers from external EM
interference
Unshielded(UTP) vs. Shielded Twisted-Pair(STP)Guided Media
Shielded Twisted Pair (STP)IBMmetal foil OR braided mesh covering each pairimprove noise tolerance ~ preventing the penetration of noise or crosstalk bulky & expensiveharder to handle (thick,heavy)
Several categories of UTP cable exist:Category 1Used for telephone communications; not suitable for transmitting dataCategory 2Capable of transmitting data at speeds of up to 4 MbpsCategory 3Used in 10BASE-T networks; can transmit data at speeds up to 10 MbpsCategory 4Used in Token Ring networks; can transmit data at speeds up to 16 MbpsCategory 5Capable of transmitting data at speeds up to 100 MbpsCategory 5eUsed in networks running at speeds up to 1000 Mbps (1 Gbps)Category 6Consists of four pairs of 24-gauge copper wires that can transmit data at speeds up to 1000 Mbps
UTP CategoriesGuided Media
60
600 MHz
200 MHz
100 MHz
20 MHz
16 MHz
< 2 MHz
very low
Bandwidth
LANsDigital600 Mbps7 (draft)
LANsDigital200 Mbps6 (draft)
LANsDigital100 Mbps5
LANsDigital20 Mbps4
LANsDigital10 Mbps3
T-1 linesAnalog/digital2 Mbps2
TelephoneAnalog< 100 kbps1
UseDigital/AnalogData RateCategory
UTP Cable - Categories
Table 6.1 Categories of UTP cables
Guided Media
UTP Connector
Common connector RJ45 (Registered Jack)~Keyed Connector (connector can be inserted
only one way)
Guided Media
UTP Performance
Compare Attenuation vs. frequency & distanceCan pass a wide range of frequencyAttenuation sharply increases with frequency > 100 KHzGauge is the measure of the thickness of the wire
Guided Media
61
UTP Application
1. To provide voice & Data Channel in telephone line
2. To provide high data rate (use high bandwidth capability of UTP) in DSL line
3. For LAN Network (10Base-T & 100Base-T)
Guided Media
Carries higher frequency ranges than UTPHas central core conductor of solid or stranded wire enclosed in an insulating sheath and encased in outer conductor of metal foil, braid or a combination of twoOuter metallic wrapping
shield against noise second conductor to complete the circuitenclosed in an insulating sheath
Protected by a plastic cover
Coaxial Cable (Coax)Guided Media
Coaxial Cable StandardTable 6.2 Categories of coaxial cables
50 50 75
Impedance
Thick EthernetRG-11
Thin EthernetRG-58
Cable TVRG-59
UseCategory
categorized by radio government (RG) rating. Each RG denote unique set of physical specification consist:
wire gauge, type & thickness of insulation (inner conductor)construction of the shieldsize & type of outer casing
Guided Media
62
Coaxial Cable Connector
common type is BNC - Bayone-Neill-Concelman Type of BNC Connector
a. BNC Connector - end of cable to deviceb. BNC T Connector - branch out of a cable c. BNC Terminator use the end of the cable to
prevent signal reflection
Guided Media
Coaxial Cable Performance
Can be determined by the comparison of attenuation, its higher in coaxial cable require more repeaters but more bandwidth
Guided Media
Coaxial Cable Application
1. Most versatile medium2. Analog telephone line / long distance telephone
transmission could carry 10 000 voice signals Being replaced by fiber optic
3. Digital telephone line can carry up to 600 Mbps data4. Cable TV network/Television Distribution entire network use
coax cable, common use is RG59 Ariel to TV Cable TV
5. Ethernet LAN (10Base2 or Thinnet) - RG58 TX data at 10 Mbps range 185m
6. Thicknet (10Base5) - RG11 TX data at 10Mbps range 5000m
Guided Media
63
Coaxial Cable - Transmission Characteristics
Analog Amplifiers every few km Closer if higher frequency Up to 500MHz
Digital Repeater every 1km Closer for higher data rates
Guided Media
Made of glass or plastic for the core and surrounded by a cladding of lesser dense glass or plastic and transmit signals in the form of lightPrinciple of light
I = Angle of IncidenceCritical Angle = property of substanceUses reflection to guide light through optical
fibers
Fiber Optic CableGuided Media
Design of Density of core and cladding- reflected beam of light remained inside the core
Fiber Optic Cable (cont.)Guided Media
64
Optical Fiber - Transmission Characteristics
Act as wave guide for 1014 to 1015 Hz Portions of infrared and visible spectrum
Light Emitting Diode (LED) Cheaper Wider operating temp range Last longer
Injection Laser Diode (ILD) More efficient Greater data rate
Wavelength Division Multiplexing
Guided Media
Fiber Optic Cable
Propagation Mode
Guided Media
Multimode Modemultiple beams at different pathsthe light direction depend on the structure of the core
Multimode Step-Index fiber Density of Core remains constant from center to edge Lower density at the interface of the core & the cladding change in density alters the angle of the beams motionStep index refer to suddenness changes
Fiber Optic Cable (cont.)Guided Media
65
Multimode Graded-Index fiberDecreases distortion in step-index fiberTerm index refers t index of refractionThe index refraction is related to densityDensity decreases gradually with highest at the center of core & lowest at the edge
Fiber Optic Cable (cont.)Guided Media
Uses step index fiber & highly focused source beam to a small range of angles closed to horizontalmanufactured with smaller diameter & lower density than in multimode fiber Propagation of different beam is almost identical and delays are negligibleAll beams reach at destination are together and can be recombined with minor distortion.
Single ModeGuided Media
Fiber Optic Standard
defined by the ratio of the core diameter to the cladding
Table 6.3 Fiber types
7/1257/125
100/125100/125
62.5/12562.5/125
50/12550/125
Type
7
100
62.5
50
Core
Single-mode125
Multimode, graded-index125
Multimode, graded-index125
Multimode, graded-index125
ModeCladding
Guided Media
66
Figure 6.14 Fiber construction
Outer Jacket PVC or TeflonInner Jacket Kevlar strands material to strengthen the cable Plastic cushion the fiber
Cable CompositionGuided Media
Fiber Optic Cable Connector
Type of Fiber Optic Connectora. Subscriber Channel(SC) - cable TV~ uses a PUSH/PULL
locking systemb. Straight-Tip Connector(ST) connection to networking
devices, uses bayonet locking, more reliable than SC c. MT-RJ new connector & same size as RJ45
Guided Media
Fiber Optic Performance
Measurement of attenuation vs. wavelength Attenuation is flatter than Twisted pair & Coaxial Cable -
require less repeaters
Guided Media
67
Fiber Optic Cable Application1. Backbone Network
wide bandwidth and cost effective2. LAN Network
100Base-FX(Fast Ethernet) & 1000BaseX3. WDM
transfer at data rate 1600Gbps4. Cable TV
combination of fiber optic and coax5. Long-haul trunks
telephone network covered 1500KM capacity 20K 60K voice channel
6. Metropolitan trunks covered 12KM have 100K voice channels in a trunk group
7. Rural exchange trunks between exchanges for average length 40 160KM link towns and villages
8. Subscriber loops Directly from exchange to a subscriber May displace twisted pair and coax cable links
Guided Media
Fiber Optic Cable : Pros and Cons
ADVANTAGE1. High bandwidth2. Less signal attenuation can run
50km not require regeneration but for coax and twisted pair need repeater for each 5km
3. Immune to EMV interference ~ not effected to noise
4. Non-corrosive materials glass more resistant than copper
5. Light weight6. Immune to tapping
Guided Media
DISADVANTAGE
1. Expertise in installation2. Unidirectional Channel 3. Expensive cable &
interfaces
Figure 7.17 Electromagnetic spectrum for wireless communication
Unguided Media / Wireless CommunicationUnGuided Media
68
Antennas Defined as electrical conductor (or system of..) used to
radiate electromagnetic energy or collect electromagnetic energy
Transmission Radio frequency energy from transmitter Converted to electromagnetic energy by antenna Radiated into surrounding environment
Reception Electromagnetic energy impinging on antenna Converted to radio frequency electrical energy Fed to receiver
Same antenna often used for both
UnGuided Media
Wireless Propagation Signal travels along three routes Ground wave Follows contour of earth Up to 2MHz E.g: AM radio
Sky wave Used for amateur radio, BBC world service, Voice of
America Signal reflected from ionosphere layer of upper
atmosphere (Actually refracted)
Line of sight Above 30Mhz signal is not reflected by the
ionosphere May be further than optical line of sight due to
refraction
UnGuided Media
Propagation Method
Radio wave travel through the lowest portion of atmosphere
low frequency omnidirectionalsignal follows the earths curvature
Distance depends on power of the signal
Ground Propagation
UnGuided Media
69
Ground Wave Propagation
UnGuided Media
HF radiates upwards into the ionosphere, reflected back to earth
Allow greater distance with low power signal
Propagation Method (cont.)
Sky Propagation
UnGuided Media
Sky Wave Propagation
UnGuided Media
70
Very HF transmitted in straight lines from antenna to antenna (directly)
Radio transmission cannot be completely focused
Propagation Method (cont.)Line of Sight Propagation
UnGuided Media
Line of Sight Propagation
UnGuided Media
Line of Sight Transmission Free space loss Signal disperses with distance Greater for lower frequencies (longer wavelengths)
Atmospheric Absorption Water vapour and oxygen absorb radio signals Water greatest at 22GHz, less below 15GHz Oxygen greater at 60GHz, less below 30GHz Rain and fog scatter radio waves
Multipath Better to get line of sight if possible Signal can be reflected causing multiple copies to be
received May be no direct signal at all May reinforce or cancel direct signal
Refraction May result in partial or total loss of signal at receiver
UnGuided Media
71
Refraction
Velocity of electromagnetic wave is a function of density of material ~3 x 108 m/s in vacuum, less in anything else
As wave moves from one medium to another, its speed changes Causes bending of direction of wave at boundary Towards more dense medium
Index of refraction (refractive index) is Sin(angle of incidence)/sin(angle of refraction) Varies with wavelength
May cause sudden change of direction at transition between media
May cause gradual bending if medium density is varying Density of atmosphere decreases with height Results in bending towards earth of radio waves
UnGuided Media
Multipath Interference
UnGuided Media
Electromagnetic Spectrum (Bands)Table 7.4 Bands
VHF TV, FM radio
Sky andline-of-sight30300 MHzVHF
UHF TV, cellular phones, paging, satelliteLine-of-sight300 MHz3 GHzUHF
Satellite communicationLine-of-sight330 GHzSHF
Long-range radio navigationLine-of-sight30300 GHzEHF
330 MHz
300 KHz3 MHz
30300 KHz
330 KHz
Range
Citizens band (CB),ship/aircraft communicationSkyHF
AM radioSkyMF
Radio beacons andnavigational locatorsGroundLF
Long-range radio navigationGroundVLF
ApplicationPropagationBand
UnGuided Media
72
Radio frequency 3 KHz to 1 GHz (low & medium)Ominidirectional (propagate in all direction) susceptible to signal interferenceRadio waves in sky mode can travel long distance, good for long distance broadcasting (e.g. AM radio)Long or short distance has ability to penetrate wall
Application - Multicasting-E.g Cordless phone, Paging, AM & FM radio, television
Figure 7.20 Omnidirectional antennas
Radio WavesUnGuided Media
frequency 1 GHz to 300 GHz, microwave band is wide and high data rate is possibleunidirectional narrowly focused, antenna must be alignedline of sight propagation, tower need to be direct sight of each other and cannot penetrate through wallrepeater required for long distanceApplication Unicasting CommunicationE.g cell phone, satelite network & wireless LAN
MicrowavesUnGuided Media
2 type of antenna are parabolic dish and the hornParabolic dish
Based on the geometry of a parabolaWorks as a funnel, catching a wide range of waves and directing to a common pointMore signal recovered rather than single point receiver
Horn antennaLooks like gigantic scoopOutgoing transmission ~ broadcast thru a stem and deflect a series of beam by the curved headIncoming transmission ~ collect by the scoop shape (horn) and deflect down into the stem
Microwaves (cont.)
Figure 7.21 Unidirectional antennas
UnGuided Media
73
Terrestrial Microwave
Parabolic dish Focused beam Line of sight Long haul telecommunications Higher frequencies give higher data
rates
UnGuided Media
Satellite Microwave Satellite is relay station Satellite receives on one frequency,
amplifies or repeats signal and transmits on another frequency Requires geo-stationary orbit Height of 35,784km
Television Long distance telephone Private business networks
UnGuided Media
Satellite Point to Point LinkUnGuided Media
74
Satellite Broadcast Link
UnGuided Media
Broadcast Radio
Omnidirectional FM radio UHF and VHF television Line of sight Suffers from multipath interference Reflections
UnGuided Media
frequency 300 GHz to 400 THz (wavelength from 1 mm to 770nm)short range communication Have frequency but cannot penetrate wallAdvantages : not effected by other systemUseless for long range communication
ApplicationInfrared Data Association (IrDA) sponsoring & promoting use of infrared though line of sight; like keyboard, mouse, PCs and printers.The standard define ~ data rate 75Kbps covered 8m distance.Recent standard, data rate of 4 Mbps
InfraredUnGuided Media
75
LeCtUrE eNd
If you still blur about this chapter, please do revision.