CE3701 DATA COMMUNICATIONS LAB - PSAU · Experiment 2: PULSE CODE MODULATION (PCM) Objective & Scope To understand the Modulation Process. Experiment deals with basic concepts of

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CE3701

DATA COMMUNICATIONS LAB

Kingdom of Saudi Arabia

Ministry of Education Prince Sattam Bin Abdulaziz University College of Computer Engineering & Sciences

Department of Computer Engineering

اململكة العربية الصعودية

وزارة التعليم

جامعة األمري شطام بن عبدالعسيس

احلاشبكلية هندشة وعلوم

قصم هندشة احلاشب

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Laboratory Safety :

Please read these Safety Guidelines, Safety is a priority at Prince Sattam Bin Abdulaziz

University .While it may seem unlikely that an accident could happen to you, you should know

the accident rate in universities is 10 to 100 times greater than in the chemical industry. To help

prevent accidents, safety notes are included in the lab manual. In addition, any relevant

Material Safety Data Sheets (MSDS) are posted in a laboratory binder and guidelines.

Pay close attention to this information – our goals are:

1. To avoid accidents in the lab, and

2. To respond promptly and appropriately should an accident occur.

Safety depends on you!

It is your responsibility to follow the instructions in the lab

manual and any additional guidelines provided by your

instructor. It is also your responsibility to be familiar with the

location and operation of safety equipment.

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General Laboratory Safety Guidelines

• Wear appropriate protective clothing. Do not wear open-toed shoes, sandals, shorts or shirts

with dangling sleeves. Tie back long hair and avoid dangling jewelry.

• Clean your workstation after each lab period, and return all equipment and

materials to appropriate stations before leaving the lab.

• Always turn off the power before working on any electric circuit or electronic device.

• When operating with electric circuits and electronic devices other than just a computer, you

must work in pairs or teams.

• When in doubt about the operation of any circuit or device in lab, always have an instructor

check your work before connecting power to your system.

• Report any safety issues or violations that you are aware of as soon as possible to your

course instructor and program director.

• Ensure that you have a safe buffer area around you and that you are working on an

appropriate surface when using soldering irons in the lab.

• Always make sure that all lab equipment, soldering irons, project circuits are powered

down before leaving your lab area.

• Ensure that your work environment is clear and free of debris before starting your work AND

after finishing your project.

• Never block walkways in the laboratory with lab equipment, cables, and electrical power

cords.

• Do not eat, drink, smoke, or apply cosmetics in the laboratory.

• Avoid all horseplay in the laboratory.

• Dispose of sharps waste properly — place broken glass in the glass discard container, metal

in the metal waste container, and place other waste materials in the designated container(s).

Secure all sharps, including needles, blades, probes, knives, etc.

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List of Experiments :

1. STUDY OF MODULATION PROCESSES

2. PULSE CODE MODULATION (PCM)

3. PULSE AMPLITUDE MODULATION (PAM)

4. PULSE WIDTH MODULATION(PWM)

5. PULSE POSITION MODULATION (PPM)

6. AMPLITUDE SHIFT KEYING(ASK)

7. FREQUENCY SHIFT KEYING(FSK)

8. PHASE SHIFT KEYING(PSK)

9. TIME DIVISION MULTIPLEXING (TDM)

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Title: Experiment 1: Study of Modulation Processes

Objective & Scope

To understand the Modulation Process.

Experiment deals with basic concepts of modulation and demodulation. Students can get

benefited by studying basic concept of modulation processes.

Background & Terminologies

Knowledge of Digital Communication.

Knowledge of Analog Communication.

Familiar with kits using to perform experiments.

Familiar with Lab equipments like CRO, Function Generator etc.

Safety Issues

• Before start of experiments students should understand the procedure to operate tool

and kits.

• Through understanding of Lab Equipments and Components.

Tools & Equipments

Computer System with at least 40 GB Hard Disk , 1 GB Ram, and windows Operating System

COM3LAB (70071 TX433 Transmitting Technology, 70072 RX433 Receiving Technology,

70073,70074 Modem Technology) Kits are required to perform the Experiments.

Procedure

1. Connections are made as per the circuit diagram. 2. Modulating signal and carrier signal of High frequency is given to aboard. and

switch ON the power supply. 3. Then the modulated output is observed. 4. The output characteristics are plotted on a graph.

Troubleshooting

• While performing experiment instruction given by tool have to be noticed.

• Avoid short circuiting.

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• Connections must be tight.

The width of the signal must be noted carefully.

THEORY:

Modulation procedures are characterized as those having a sinusoidal carrier signal and those with a pulse shaped carrier signal. On the other hand, the modulation signal representing the message can be analog or digital. This course deals with those modulation procedures in which a digital modulation signal is modulated on to a sinusoidal carrier (shown lighter in the adjacent overview). The basics of the various modulation procedures are provided by the corresponding instructional systems. • T 7.2.1.3 Amplitude Modulation • T 7.2.1.5 Frequency and Phase modulation • T 7.2.2.1 Pulse Code Modulation • 700 71 TX 433 Transmission Technique • 700 72 RX 433 Receiving Technique

In pulse Amplitude Modulation the amplitude of the carrier pulses varies in accordance

with the instantaneous values of message signal and the pulse width is fixed, in practice this

is realized by a simple mechanical commutator or by electronic circuit. Natural PAM signal

sampling occurs when finite width is used in the modulators and tops of the pulses are forced

to follow the magnitude of modulating waveform. Flat tapped PAM system is quite often used

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because of the generating the modulating waveform and spectrum. Finite width pulses are

used but they are flat topped after modulation. Reconstruction of original signal is possible by

passing the modulated signal through a low pass filter.

Comment

Quiz

1. What are the classifications of pulse modulation techniques? 2. What is the transmission bandwidth of Pulse amplitude modulation? 3. What are the Draw backs in Pulse amplitude modulated signal? 4. What do you mean by synchronization in PAM? 5. Write the standard equation of a PAM in frequency domain?

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Title: Experiment 2: PULSE CODE MODULATION (PCM)

Objective & Scope


Experiment deals with basic concepts of Pulse CODE modulation and demodulation. Students

can get benefited by studying basic concept of PCM processes.





Familiar with Lab equipments like CRO, Function Generator etc

Safety Issues


and kits.


Tools & Equipments




Procedure 1. Connections are made as per the circuit diagram. 2. Modulating signal and carrier signal of High frequency is given to aboard. and


Troubleshooting


• Avoid short circuiting. • Connections must be tight.

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THEORY:

Pulse code modulation (PCM) is a digital representation of an analog signal that takes samples of

the amplitude of the analog signal at regular intervals. The sampled analog data is changed to,

and then represented by, binary data. PCM requires a very accurate clock. The number of

samples per second, ranging from 8,000 to 192,000, is usually several times the maximum

frequency of the analog waveform in Hertz (Hz), or cycles per second, which ranges from 8 to 192

KHz.

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Results\Graph\

Comments:

Quiz 1. What is meant by Aperture effect? 2. Draw the frequency spectrum of a PAM signal? 3. What is the time domain representation of a PAM signal? 4. What are the major differences between PAM &PWM? 5. Which type of sampling technique is used in PAM signal?

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Title: Experiment 3: Pulse Amplitude Modulation

Objective & Scope


Experiment deals with basic concepts of Pulse Amplitude modulation and demodulation.

Students can get benefited by studying basic concept of PAM processes.






Safety Issues


and kits.


Tools & Equipments




Procedure 5. Connections are made as per the circuit diagram. 6. Modulating signal and carrier signal of High frequency is given to aboard. and


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Troubleshooting




THEORY:

In pulse Amplitude Modulation the amplitude of the carrier pulses varies in accordance

with the instantaneous values of message signal and the pulse width is fixed, in practice this

is realized by a simple mechanical commutator or by electronic circuit. Natural PAM signal

sampling occurs when finite width is used in the modulators and tops of the pulses are forced

to follow the magnitude of modulating waveform. Flat tapped PAM system is quite often used

because of the generating the modulating waveform and spectrum. Finite width pulses are

used but they are flat topped after modulation. Reconstruction of original signal is possible by

passing the modulated signal through a low pass filter.

Results\Graph\

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Comments:

Quiz

1. What are the classifications of pulse modulation techniques? 2. What is the transmission bandwidth of Pulse amplitude modulation? 3. What are the Draw backs in Pulse amplitude modulated signal? 4. What do you mean by synchronization in PAM? 5. Write the standard equation of a PAM in frequency domain? 6. What is meant by Aperture effect? 7. Draw the frequency spectrum of a PAM signal? 8. What is the time domain representation of a PAM signal? 9. What are the major differences between PAM &PWM?

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Title: Experiment 4: Pulse Width Modulation(PWM)

Objective & Scope


Experiment deals with basic concepts of Pulse Width modulation. Students can get benefited

by studying basic concept of PPM processes.






Safety Issues


and kits.


Tools & Equipments




Procedure

1. Connection is made as per the circuit diagram.

2. Vary the control voltage (0-5) v and observe the corresponding change in output square Waveform using CRO.

3. Change in control voltage changes the width of the square wave. 4. Note down the T-ON and T-OFF. 5. Plot the observed waveform.

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Troubleshooting




THEORY:

If the widths of the pulses are varying in accordance with the modulating signal it is

called pulse width modulation. In Pulse width modulation, the amplitude of the pulses is

constant. Generation of PWM the in put modulating signal is given to non - inverting terminal

of op-amp .the op-amp now compares with both the input signals. The output of the

comparator is high only when instantaneous value of input modulating signal is grater then

that of saw tooth waveform. When saw tooth waveform voltage is grater then input modulating

signal at that instant the out put of the comparator remains zero i.e. in negative saturation.

Thus out put of comparator is PWM signal.

OUTPUT WAVEFORMS:

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Results\Graph\

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Comments:

Quiz 1. What are the different types of PTM systems? 2. What is the other name of Pulse width modulation? 3. What do you mean by pulse time modulation? 4. What is the comparison between the PAM and PWM? 5. What is the definition of PWM? 6. What is the transmission bandwidth of PWM signal? 7. Which type sampling technique is used in PWM? What are the applications of PWM

modulation technique?

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Title: Experiment 5: Pulse Position Modulation(PPM)

Objective & Scope


Experiment deals with basic concepts of Pulse Position modulation and demodulation.

Students can get benefited by studying basic concept of PPM processes.






Safety Issues


and kits.


Tools & Equipments




Procedure 1. Connections are made as per circuit diagram.

2. The message signal of 500Hz, 2v pp amp- is applied .

3. The output is observed on CRO

4. The input and output waveforms are rated from CRO and are plotted on graph

sheet.

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Troubleshooting




THEORY:

PPM can be considered version of PDM in PDM, long pulses expend considerable

power during the pulse while bearing no additional information. If an arrangement is made so

that the unused power could be subtracted from the PDM, we get a more efficient pulse

modulation. In PPM the position of a pulse relative to its unmodulated time of occurrence is

varied in accordance with the message signal PPM may be obtained from PWM, in which the

position of PWM pulses are position modulated. Thus these pulses will have time

displacement proportional to the instantaneous value of the signal voltage. The simplest

method of generation of PPM from PWM is to use a monostable multivibrator. It is to be

designed in such away that it triggers the trailing edges of a PWM signal. If a PWM signal is

applied at the inputs, the output will be obviously a pulse position modulated signal whose

duration will be determined by the timing circuit of multivibrator. For demodulation of PPM,

first it converted into PWM with help of flip-flop, and then it is demodulated.

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OUTPUT WAVEFORMS:

Results\Graph\

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Comments:

Quiz 1. Define PPM?

2. What are the differences between PPM & PWM?

3. Which type of sampling technique is used in PPM?

4. The Multivibrator used in PPM is?

5. Pulse duration of PPM is?

6. In PPM the position is proportionally varied in which parameter of the modulating signal?

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Title: Experiment 6: Amplitude Shift Keying

Objective & Scope

To understand the Process of Shift keying.

Experiment deals with basic concepts of shift keying. Students can get benefited by studying

basic concept of ASK process.






Safety Issues


and kits.


Tools & Equipments




Procedure




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Troubleshooting




THEORY:

ASK is one in which the amplitude of a carrier is switched between two values i.e, on

and off. The resultant waveform consists of on pulses representing binary 1 and off pulses

representing binary 0.The binary ASKS signaling scheme was one of the earliest forms of

digital modulation used in wireless telegraphy at the beginning of this century. It is the

simplest form of digital modulation & serves as a useful model for introducing certain

concepts.

In Amplitude Shift Keying (Amplitude Shift Keying ASK1 ) a sinusoidal carrier signal having frequency f0

isturned on and off by the data signal (which is why this procedure is also known as ON/OFF keying). If the data signal has the value logical 1 (HIGH), the carrier signal is turned on, and a data signal of logical 0 (LOW) turns it off. ASK can therefore be implemented by means of a switch. ASK Amplitude Shift Keying is a modulation method whereby the amplitude of a sinusoidal carriers signal is changed as a function of the level of the (digital) modulation signal. The carrier signal is usually turned on and off alternately (ON/OFF Keying).

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In the following experiment you will first study the modulated signal in amplitude shift keying. Periodically a constant data byte will be sent as a data signal and modulated on to the sinusoidal carrier signal. Both signals will be compared using the oscilloscope.

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Result:

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SQ format generates a square-wave signal with a pulse width of 800 μs (upper curve), whereby the pulse width corresponds to the bit width. There are exactly eight oscillations of the carrier signal for each pulse (lower curve). The carrier signal thus has a frequency of f0 = 10 kHz.

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Results\Graph\

Comments:

Quiz 1. What is the other name of ASK signal? 2. Draw the o/p waveform of ASK? 3. What are the demodulation techniques of BASK? 4. Draw the power spectral density of ASK signal? 5. Write the standard equation of ASK signal? 6. What is the transmission BW of an ASK signal? 7. What are the differences between BASK&FSK? 8. What the advantages are of ASK over an AM?

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Title: Experiment 7: Frequency Shift Keying

Objective & Scope



basic concept of FSK process.






Safety Issues


and kits.


Tools & Equipments




Procedure




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Troubleshooting




THEORY:

In FSK, the waveform is generated by switching the frequency of the carrier between

two values corresponding to the binary information which is to be transmitted. Here the carrier

frequency varies from lowest to highest point i.e. carrier swing is known as Frequency shift

keying. FSK signaling schemes find a wide range of applications in low speed digital data

transmission systems.

FSK Demodulation

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In Frequency Shift Keying (FSK1 ) depending on the data signal the shift is made between two

frequencies f0 - Δf (data bit is logical 0) and f0 + Δf (data bit is logical 1). The frequency f0 is termed the

center frequency2 , the frequency Δf the frequency deviation3 . Compared with ASK, FSK is

significantly less noisesensitive. 1 FSK Frequency Shift Keying is a modulation technique whereby the frequency of a sinusoidal carrier signal is changed as a function of the level of the (digital) modulation signal. 2 Center frequency The center frequency f0 = 1/2 (f1 + f2) is the average of the two characteristic frequencies f1 and f2which are alternated in frequency shift keying (FSK). 3 Frequency deviation

The frequency deviation Δf indicates by what value the two characteristic frequencies used in

frequency shift keying (FSK) deviate from the center frequency f0.

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In the following experiment we will first study the modulated signal in frequency shift keying. Periodically a constant data byte will be sent as the data signal and modulated on to the sinusoidal carrier signal. The center frequency and frequency deviation can then be determined from the signals.

Result:

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In SQ data format (symmetrical square-wave signal) alternating LOW and HIGH pulses are sent; each has a duration of 800 μs (upper curve). At logical 0 there are four oscillations during this time, or eight at logical 1.This corresponds to frequencies of 5 kHz and 10 kHz. The center frequency is therefore 7.5 kHz and thefrequency deviation 2.5 kHz.

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Results\Graph\

Comments:

Quiz 1. Define Binary FSK signal?

2. What is meant by carrier swing?

3. Define Frequency deviation of FSK signal?

4. What are the advantages of this FSK signal?

5. Give the differences between FSK & FM?

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Title: Experiment 8:Phase Shift Keying

Objective & Scope



basic concept of PSK process.






Safety Issues


and kits.


Tools & Equipments




Procedure




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Troubleshooting




THEORY:

Phase shift keying or discrete phase modulation is another technique available for

communicating digital information over band pass channels. In PSK signaling schemes the

waveforms s1(t) = -Acoswct & S2(T) = Acoswct are used to convey binary digits 0& 1

respectively. The binary PSK waveform Z (t) can be described by, Z (t) = D (t) Acoswct .

Where D (T) is a random binary waveform with period Tb& levels -1&1. The only difference

b/w the ASK&PSK waveform is that in the ASK scheme the carrier is switched on &off

whereas in the PSK scheme the carrier is switched b/w levels +A & -A.

The differentially coherent PSK signaling scheme makes use of a clever technique

designed to get around the need for a coherent reference signal at the receiver.

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In two-phase shift keying (2PSK1 ) a sinusoidal carrier signal with frequency f0 is toggled between two different phase positions depending on the data signal. Since disturbances generally affect only the amplitude of the signal and not its phase position, Phase Shift Keying is very noise-immune. 1 PSK Phase Shift Keying is a modulation procedure whereby the phase position of a sinusoidal carrier signal is changed depending on the level of the (digital) modulation signal. In 2PSK two and in 4PSK four different phase positions are toggled. There are also variations with more phase positions.

In the following experiment we will first study the modulated signal in two-phase shift keying. A periodic square-wave signal (SQ format) will be sent as the data signal and modulated on to the sinusoidal carrier signal. Both signals will be compared on the oscilloscope. Both the phase positions for logical 0 and logical 1 will be determined from the signals.

Results:

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With the selected square-wave data signal alternating LOW and HIGH pulses are sent; each has a durationof 800 μs (upper curve). The frequency of the carrier is constant at a value of 10 kHz. For a data bit of logical 0 the carrier has a phase shift of 0°, and for a data bit of logical 1 a phase position of 180°.

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Results\Graph\

Comments:

Quiz 1. What is the bandwidth requirement of BPSK?

2. What is the expression for error probability of BPSK reception using coherent

matched filter detection?

3. What are the draw backs of BPSK?

4. Draw the Power spectral density of BPSK?

5. What are the major differences between DPSK&BPSK?

6. What are the advantages of BPSK over a PSK signal?

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Title: Experiment 9:Time Division Multiplexing

Objective & Scope

To understand the Time Division Multiplexing.

Experiment deals with basic concepts of Multiplexing. Students can get benefited by studying

basic concept of Multiplexing.






Safety Issues


and kits.


Tools & Equipments




Procedure

(AT TRANSMITTING BLOCK)

1. Place the duty cycle controlled switch in position-5 2. Turn the potentiometer in function generator block fully in clock wise 3. The following connections are made

250Hz to channel-o

500Hz to channel-1

1kHz to channel-2

2kHz to channel -3 4. The external triggering will be given to the channel-0 terminal. 5. Then multiplexed output is observed across Tx output terminal. 6. Vary the amplitude of input sine wave by varying the potentiometers in function

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generator block to indicate which sample belongs to which output channel and then the outputs are plotted on the graph.

(AT RECEIVER BLOCK)

1. The following connections are made

Tx output to Rx output

Tx clock to Rx clock

Tx t0 to Rx t0 2. Above connections are made sure that the Tx clock signal is used by the Rx to

Synchronize its activity

3. Then de-multiplexed original message signals are available across the low pass

filters at receiver block.

1. .

Troubleshooting




THEORY:

Time division multiplexing is a technique used for transmitting several analog message

signals over a single communication channel, by dividing the time frame in to number of slots,

i.e. one slot for each signal. Here there are four input signals; all are band limited to fx by the

input Low pass filters, and all these are sequentially sampled at the transmitter by using a

rotary switch i.e. commutator. This commutator makes fs revolutions per second and extracts

one sample from each input during each revolution. The out put of the switch is a PAM wave

form containing samples of the input signals periodically interfaced with time.

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CIRCUIT DIAGRAM:

OUTPUT WAVEFORMS: (Transmitting Signals)

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DEMULTIPLEXED OUTPUT:

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Results\Graph\

Comments:

Quiz

1. What is meant by multiplexing technique and what are the different types of

Multiplexers?

2. Briefly explain about TDM&FDM? 3. What is the transmission band width of a PAM/TDM signal? 4. Define crosstalk effect in PAM/TDM system? 5. What are the advantages of TDM system? 6. What are major differences between TDM&FDM? 7. Give the value of Ts in TDM system? 8. What are the applications of TDM system and give some example? 9. What is meant by signal overlapping? 10. Which type of modulation technique will be used in TDM?

CE3701 DATA COMMUNICATIONS LAB - PSAU · Experiment 2: PULSE CODE MODULATION (PCM) Objective & Scope To understand the Modulation Process. Experiment deals with basic concepts of

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