chapter 2 : data transmission

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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Digital Transmission

Encoding Techniques

Digital transmissionDigital data, digital signalAnalog data, digital signal

Analog TransmissionDigital data, analog signalAnalog data, analog signal


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

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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


Conversion of PC Input to Digital Signal


Digital Signals Carrying Analog and Digital Data


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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


Line Coding: Characteristics

Signal Level VS Data Level Pulse Rate VS Bit Rate DC Components Self-synchronization


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


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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


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


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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


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


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Polar use two voltage level (+ve and ve)


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

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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.


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


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


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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)


Other Schemes: 2B1Q 2 binary, one quaternary (2B1Q): uses 4 voltage levels each pulse can represent 2 bits (more efficient)


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


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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.


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

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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


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


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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)


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

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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)


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


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


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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


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.


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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


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.


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


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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

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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

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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

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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


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


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


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


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 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


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


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



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.

chapter 2 : data transmission

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