basics of communication unit-i. unit i: basics of communication basics of communication:...

Basics Of Communication

UNIT-I

Unit I: Basics of communication

Basics of communication: Introduction, Mathematical Foundation, Basic Problem Solving, Communication System, Baseband, Broadband and Carrier Communication, transmission modes, Baud rate, bit rate, SNR, Channel Bandwidth and rate of communication. Digital Modulation Techniques: PCM, PCM Encoder and Decoder, DPCM, ADPCM, Delta modulation,Adaptive Delta Modulation, RS-232C,Bandwidth requirement of digital modulation techniques, quantization noise Line Coding techniques: Bipolar, Unipolar, RZ, NRZ, Manchester, AMI, B8ZS,

Block coding techniques. Multiplexing techniques: TDM, FDM, WDM, and CDMA, TD-SCDMA, LTETDD, LTE-FDD,. LAN standards: Ethernet, Wireless LAN, WiMax, ZigBee,

Bluetooth,Infrastructure based (satellite n/w, Cellular n/w) and Infrastructure less (Adhoc n/w) wireless topologies. VLAN, Basics of VPN, VPN tools and

04/21/23 Prof.E. Jayanthi M.Tech (comp N/w) SCOE. 2

Transformation of Information to Signals


Analog and Digital Clocks


Analog and Digital Signals


Figure Periodic Signals


Aperiodic Signals


Figure

Sine Wave


Phases


Amplitude Change


Frequency Change


Figure 4-10

Phase Change


Time and Frequency Domain


Examples



Communication Systems

Digital

Analog


Data Representation

3.17

AUDIO

VIDEO

TEXT NUMBERSNUMBERS IMAGE

SBINARY NUMBERS

ASCIIUNICODEEBCDICISO

DATADATA

Elements of CS

Input TransducerTransmitterCommunication Channel

- Line or RadioReceiverOutput TransducerNoiseInformation


Modulation


Modulation is a process of impressing (applying) a low frequency information signals onto a relatively high frequency carrier signal

Need of ModulationReduction in height of antennaAvoid mixing of signalsIncrease the range of communicationMultiplexing is possibleQuality


Baseband and BroadbandBaseband – wired only – the signal goes

down the wire without any modulationBroadband – wired and wireless – the

signal is modulated on a carrier.

Broadband is a communication carrier or media. Two types of communications.

Traditional communication. Non-traditional communication.

Two types carriers. Broadband. Base band.

For multipurpose. Fast accessing. Enabling convergence.

Largely depends upon a cost Cable modems used mostly for homes DSL and ethernet are used mostly for offices DSL is better one because cable is shared media

High-Speed internet access. Remote LAN access. Desk-Top-Desk video. Interactive CAD. Collaborative working. Military and defense. Mobile video conferencing. Remote monitoring of industrial plants.

BROADBAND OVER ETHERNET CABLE MODEM SETUP DSL SETUP

Simplex


Half-Duplex


Full-Duplex


Characteristics of Data communication SystemDeliveryAccuracyTimeliness


Parallel Transmission


Serial Transmission


Asynchronous Transmission


Synchronous Transmission



Digital Carrier Modulation

(Digital Continuous Wave Modulation Techniques)


Bit Rate

Baud Rate

5.44

Bit rate is the number of bits per second.

Baud rate is the number of signal elements per second.

In the analog transmission of digital data, the baud rate is less than or equal to the bit rate.

Note

04/21/23 Prof.E. Jayanthi M.Tech (comp N/w) SCOE.

4.45

Figure :Signal element versus data element


5.46

An analog signal carries 4 bits per signal element. If 1000 signal elements are sent per second, find the bit rate.

SolutionIn this case, r = 4, S = 1000, and N is unknown. We can find the value of N from


5.47

Example

An analog signal has a bit rate of 8000 bps and a baud rate of 1000 baud. How many data elements are carried by each signal element? How many signal elements do we need?

SolutionIn this example, S = 1000, N = 8000, and r and L are unknown. We find first the value of r and then the value of L.



Different types of Conversion /modulation

Analog to AnalogAnalog to DigitalDigital to AnalogDigital to Digital

Types of Modulation


Analog to Analog Analog to Digital

AmplitudeModulation

Frequency /Phase Modulation

Pulse AnalogModulation

Pulse codeModulation

1. DeltaModulation2. Adaptive Delta Modulation

Differential Pulse code modulation

Types of analog-to-analog modulation


Amplitude modulation


Frequency modulation


Phase modulation



Analog to digital modulation Techniques

1.Pulse Code Modulation2. Differential pulse code modulation3. Adaptive Differential pulse code modulation4. Delta modulation5. Adaptive Delta Modulation

Pulse Code Modulation (PCM)

Pulse code modulation (PCM) is produced by analog-to-digital conversion process. Quantized PAM

As in the case of other pulse modulation techniques, the rate at which samples are taken and encoded must conform to the Nyquist sampling rate.

The sampling rate must be greater than, twice the highest frequency in the analog signal,

fs > 2fA(max) Telegraph time-division multiplex (TDM) was conveyed as early

as 1853, by the American inventor M.B. Farmer. The electrical engineer W.M. Miner, in 1903.

PCM was invented by the British engineer Alec Reeves in 1937 in France.

It was not until about the middle of 1943 that the Bell Labs people became aware of the use of PCM binary coding as already proposed by Alec Reeves.

Pulse Code ModulationPulse modulation

Use discrete time samples of analog signalsTransmission is composed of analog

information sent at different timesVariation of pulse amplitude or pulse timing

allowed to vary continuously over all valuesPCM

Analog signal is quantized into a number of discrete levels

CS 414 - Spring 2012

Figure Figure The basic elements of a PCM system.The basic elements of a PCM system.

Pulse Code Modulation

4.58

Components of PCM encoder

4.59

Three different sampling methods for PCM

4.60

According to the Nyquist theorem, the sampling rate must be

at least 2 times the highest frequency contained in the signal.

Note

4.61

Figure Nyquist sampling rate for low-pass and bandpass signals

4.62

For an intuitive example of the Nyquist theorem, let us sample a simple sine wave at three sampling rates: fs = 4f (2 times the Nyquist rate), fs = 2f (Nyquist rate), and fs = f (one-half the Nyquist rate). Figure 4.24 shows the sampling and the subsequent recovery of the signal.

It can be seen that sampling at the Nyquist rate can create a good approximation of the original sine wave (part a). Oversampling in part b can also create the same approximation, but it is redundant and unnecessary. Sampling below the Nyquist rate (part c) does not produce a signal that looks like the original sine wave.

Example

4.63

Figure Recovery of a sampled sine wave for different sampling rates

4.64

Figure Quantization and encoding of a sampled signal

QuantizationTypically use

8 bits = 256 levels16 bits = 65,536 levels

How should the levels be distributed?Linearly? (PCM)Perceptually? (u-Law)Differential? (DPCM)Adaptively? (ADPCM)


4.66

We want to digitize the human voice. What is the bit rate, assuming 8 bits per sample?

SolutionThe human voice normally contains frequencies from 0 to 4000 Hz. So the sampling rate and bit rate are calculated as follows:

Example

4.67

F Components of a PCM decoder

Advantages of PCM

1. Robustness to noise and interference

2. Efficient regeneration

3. Efficient SNR and bandwidth trade-off

4. Uniform format

5. Ease add and drop

6. Secure

Advantages of PCM


Disdvantages of PCM

Differential Pulse Code Modulation (DPCM)What if we look at sample differences, not the

samples themselves?dt = xt-xt-1

Differences tend to be smaller Use 4 bits instead of 12, maybe?


Differential Pulse Code Modulation (DPCM)Changes between adjacent samples smallSend value, then relative changes

value uses full bits, changes use fewer bitsE.g., 220, 218, 221, 219, 220, 221, 222, 218,..

(all values between 218 and 222)Difference sequence sent: 220, +2, -3, 2, -1, -

1, -1, +4....Result: originally for encoding sequence 0..255

numbers need 8 bits; Difference coding: need only 3 bits


Differential Pulse-Code Modulation (DPCM)


Differential Pulse-Code Modulation (DPCM)

Usually PCM has the sampling rate higher than the Nyquist rate.The encode signal contains redundant information. DPCM can efficiently remove this redundancy.

Adaptive Differential Pulse Code Modulation (ADPCM)Adaptive similar to DPCM, but adjusts the width

of the quantization stepsEncode difference in 4 bits, but vary the mapping

of bits to difference dynamicallyIf rapid change, use large differencesIf slow change, use small differences


Need for coding speech at low bit rates , we have two aims in mind:

1. Remove redundancies from the speech signal as far as possible.

2. Assign the available bits in a perceptually efficient manner.

Adaptive quantization with backward estimation (AQB).

Adaptive Differential Pulse-Code Modulation (ADPCM)

ADPCM

Adaptive prediction with backward estimation (APB).

8-16 kbps with the same quality of PCM

DELTA MODULATION


4.79

Figure The process of delta modulation

4.80

Delta modulation components

4.81

Figure Delta demodulation components

Delta Modulation (DM)

size step theis and , of version quantized the

is ,output quantizer theis where

1

) sgn(

1

is signalerror The

).( of sample a is )( and period sampling theis where

,2,1,0 , )(Let

ne

nenm

nenmnm

nene

nmnmne

tmnTmT

nnTmnm

qq

qqq

q

q

ss

s

The modulator consists of a comparator, a quantizer, and an accumulator. The output of the accumulator is

)sgn(

1

1

n

iq

n

iq

ie

ienm

Slope overload distortion and granular noise

.)( of slope local the torelative large toois

size step when occurs noisegranular hand,other On the

)(

max (slope)

require we, distortion overload-slope avoid To

signalinput theof difference backward

first a isinput quantizer the,1for Except

11

have We

, by error on quantizati theDenote

tm

dt

tdm

T

nq

nqnmnmne

nqnmnm

nq

s

q

Slope Overload Distortion and Granular Noise

( differentiator )

NDSL Copyright@2008 1.85

Adaptive DMAdaptive delta modulation

A better performance can be achieved if the value of δ is not fixed.

The value of δ changes according to the amplitude of the analog signal.

Quantization ErrorDM is not perfect.Quantization error is always introduced in the

process.Much less than that for PCM.

Digital Communication SystemSource: sequence of digitsMultiplexer: FDMA, TDMA, CDMA…Line Coder

Code chosen for use within a communications system for transmission purposes.

Baseband transmissionTwisted wire, cable, fiber communications

Regenerative repeatorDetect incoming signals and regenerate new

clean pulses

4.87

DIGITAL-TO-DIGITAL CONVERSIONDIGITAL-TO-DIGITAL CONVERSION

The conversion involves three techniques: The conversion involves three techniques: line codingline codingblock codingblock codingscramblingscrambling..Line coding is always needed; Line coding is always needed; block coding and scrambling may or may not be block coding and scrambling may or may not be needed.needed.

Data Formats or Line Coding

The analog waveforms are converted to digital signal by PCM, DM ADM, DPCM etc., techniques. This digital data can be represented by different formats or waveforms. These waveforms are commonly known as digital data formats or their represented is called as line coding.

Line coding and decoding

Signal element versus data element

Data Rate Vs. Signal Rate Data rate: the number of data elements (bits) sent in 1s

(bps). It’s also called the bit rate Signal rate: the number of signal elements sent in 1s

(baud). It’s also called the pulse rate, the modulation rate, or the baud rate.

We wish to: increase the data rate (increase the speed of transmission) decrease the signal rate (decrease the bandwidth

requirement) worst case, best case, and average case of r N bit rate c is a constant that depends on different line codes. S = c * N / r baud

Example• A signal is carrying data in which one data element is

encoded as one signal element ( r = 1). If the bit rate is 100 kbps, what is the average value of the baud rate if c is between 0 and 1?

SolutionWe assume that the average value of c is 1/2 . The baud rate is

then

• Although the actual bandwidth of a digital signal is infinite, the effective bandwidth is finite.

• What is the relationship between baud rate, bit rate, and the required bandwidth?

Self-synchronizationReceiver Setting the clock matching the

sender’sEffect of lack of synchronization

Example• In a digital transmission, the receiver clock is 0.1

percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 kbps? How many if the data rate is 1 Mbps?

SolutionAt 1 kbps, the receiver receives 1001 bps instead of

1000 bps.

At 1 Mbps, the receiver receives 1,001,000 bps instead of 1,000,000 bps.

Other propertiesDC componentsTransmission bandwidthPower efficiencyError detection and correction capabilityFavorable power spectral densityAdequate timing contentTransparency

Line coding schemes

Unipolar NRZ scheme

Polar NRZ-L and NRZ-I schemes• In NRZ-L, the level of the voltage determines the

value of the bit. RS232.• In NRZ-I, the inversion or the lack of inversion

determines the value of the bit. USB, Compact CD, and Fast-Ethernet.

• NRZ-L and NRZ-I both have an average signal rate of N/2 Bd.

NRZ-L and NRZ-I both have a DC component problem.

ExampleA system is using NRZ-I to transfer 1-Mbps

data. What are the average signal rate and minimum bandwidth?

SolutionThe average signal rate is S = N/2 = 500

kbaud. The minimum bandwidth for this average baud rate is Bmin = S = 500 kHz.

RZ schemeReturn to zero Self clocking

Polar biphase: Manchester and differential Manchester schemes

In Manchester and differential Manchester encoding, the transition at the middle of the bit is used for synchronization.

The minimum bandwidth of Manchester and differential Manchester is 2 times that of NRZ. 802.3 token bus and

802.4 Ethernet

Bipolar schemes: AMI and pseudoternaryIn bipolar encoding, we use three levels: positive,

zero, and negative.Pseudoternary:

1 represented by absence of line signal0 represented by alternating positive and

negativeDS1, E1

Bipolar 8-Zero Substitution (B8ZS)Adds synchronization for long strings of 0sNorth American systemSame working principle as AMI except for eight

consecutive 0s

EvaluationAdds synchronization without changing the DC

balanceError detection possible

Used in T1/DS1

Amplitude

Time

0 0 0 0 0 0 0 01 0 1

Violation Violation

10000000001 +000+-0-+01 in general 00000000000V(-V)0(-V)V

ECE 4371 Fall 2008

B8ZS uses violations of the Alternate Mark Inversion (AMI) rule to replace a pattern of eight zeros in a row.0 0 0 0 0 0 0 0 0 0 0 V 1 0 V 1Example: (-) 0 0 0 - + 0 + - OR (+) 0 0 0 + - 0 - +

8B6T code table (partial)

Summary of line coding schemes

Plus HDB3 and B8ZS

Homework Draw line codes for 1010 0000 0000 1011 0000

1011 0000NRZNRZ-L, NRZ-IAMI, Pseudoternary, HDB3, B8ZS, CMIManchester and differential Manchester schemes2B1Q, MLT-3If the bit rate is 1Kbps, what are the baud rates

for the above line codes.Matlab plot of spectrum

4.108

Block coding is normally referred to as mB/nB coding;

it replaces each m-bit group with an n-bit group.

Note

4.109

Figure Block coding concept

4.110

Figure Using block coding 4B/5B with NRZ-I line coding scheme

4.111

Table 4B/5B mapping codes

4.112

Figure Substitution in 4B/5B block coding

4.113

We need to send data at a 1-Mbps rate. What is the minimum required bandwidth, using a combination of 4B/5B and NRZ-I or Manchester coding?

SolutionFirst 4B/5B block coding increases the bit rate to 1.25 Mbps. The minimum bandwidth using NRZ-I is N/2 or 625 kHz. The Manchester scheme needs a minimum bandwidth of 1 MHz. The first choice needs a lower bandwidth, but has a DC component problem; the second choice needs a higher bandwidth, but does not have a DC component problem.

Example

4.114

Figure 8B/10B block encoding

4.115

Figure AMI used with scrambling

4.116

Figure Two cases of B8ZS scrambling technique

4.117

B8ZS substitutes eight consecutive zeros with 000VB0VB.

Note

4.118

Figure Different situations in HDB3 scrambling technique

4.119

HDB3 substitutes four consecutive zeros with 000V or B00V depending

on the number of nonzero pulses after the last substitution.

Note

12.120

CHANNELIZATIONCHANNELIZATION

ChannelizationChannelization is a multiple-access method in which the is a multiple-access method in which the available bandwidth of a link is shared in time, available bandwidth of a link is shared in time, frequency, or through code, between different stations. frequency, or through code, between different stations. In this section, we discuss three channelization In this section, we discuss three channelization protocols.protocols.The multiplexing is used to combine a number of The multiplexing is used to combine a number of independent signals into a composite signal suitable for independent signals into a composite signal suitable for transmission over a common channeltransmission over a common channel

Need of MultiplexingUse of available bandwidthEfficiency can be achievedReduce cost of transmission

Types of MultiplexingMULTIPLEXIN

G

ANALOG MULTIPLEXIN

TG

DIGITAL MULTIPLEXING

FREQUENCY DIVISION

MULTIPLEXING

WAVELENGTHDIVISION

MULTIPLEXING

TIMEDIVISION

MULTIPLEXING

STATISTICAL SYNCHRONOUS

123/16

Type of Multiplexing: 1. Frequency-Division Multiple Access (FDMA). 1. Frequency-Division Multiple Access (FDMA).

3. Code-division Multiple-Access (CDMA)3. Code-division Multiple-Access (CDMA)

2. Time-Division Multiple Access (TDMA). 2. Time-Division Multiple Access (TDMA).

124/16

Frequency-Division Multiple Access (FDMA)

It is a communications technique that divides a communications It is a communications technique that divides a communications channel into a number of equally spaced frequency bandschannel into a number of equally spaced frequency bands

12.125

Frequency-division multiple access (FDMA)

12.126

In FDMA, the available bandwidth of the common channel is divided into

bands that are separated by guard bands.

Note

127/16

Time-Division Multiple Access (TDMA) It is a digital transmission technology that allows a number of users to It is a digital transmission technology that allows a number of users to

access a single radio-frequency (RF) channel without interference by access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel. allocating unique time slots to each user within each channel.

12.128

Time-division multiple access (TDMA)

12.129

In TDMA, the bandwidth is just one channel that is timeshared between different

stations.

Note

12.130

In CDMA, one channel carries all transmissions simultaneously.

Note

Code Division Multiple Access (CDMA) is a wireless communications technology that uses the is a wireless communications technology that uses the principle of spread spectrum communication.principle of spread spectrum communication.

There are three ways to spread the bandwidth of the signal: Frequency hopping Time hopping Direct sequence

Code Division Multiple Access (CDMA)

CDMA Features:CDMA Features:

o All users use same frequency and may transmit simultaneouslyAll users use same frequency and may transmit simultaneously

o Narrowband message signal multiplied by wideband spreading Narrowband message signal multiplied by wideband spreading signal, or codewordsignal, or codeword

o Each user has its own pseudo-codeword (orthogonal to others).Each user has its own pseudo-codeword (orthogonal to others).

o Receivers detect only the desired codeword. All others appearReceivers detect only the desired codeword. All others appear

as noise.as noise.

o Receivers must know transmitter’s codeword.Receivers must know transmitter’s codeword.

CDMA is a Direct Sequence Spread Spectrum systemCDMA is a Direct Sequence Spread Spectrum system

Direct Sequence Spread Spectrum System

Prepared By Ibrahim AL-OBIDA 135/16

Code Division Multiple Access (CDMA)Advantages:Advantages:

oIncreased capacityIncreased capacity

oImproved voice qualityImproved voice quality

oEliminating the audible effects of multipath fadingEliminating the audible effects of multipath fading

oEnhanced privacy and securityEnhanced privacy and security

oReduced average transmitted powerReduced average transmitted power

oReduced interference to other electronic devices Reduced interference to other electronic devices

Disadvantages:Disadvantages:oWide bandwidth per user requiredWide bandwidth per user required

oPrecision code synchronization neededPrecision code synchronization needed

12.136

Simple idea of communication with code

12.137

Chip sequences

12.138

Data representation in CDMA

12.139

Sharing channel in CDMA

12.140

Digital signal created by four stations in CDMA

12.141

What is the number of sequences if we have 90 stations in our network?

Example

SolutionThe number of sequences needs to be 2m. We need to choose m = 7 and N = 27 or 128. We can then use 90 of the sequences as the chips.

12.142

Prove that a receiving station can get the data sent by a specific sender if it multiplies the entire data on the channel by the sender’s chip code and then divides it by the number of stations.

Example

SolutionLet us prove this for the first station, using our previous four-station example. We can say that the data on the channel D = (d1 c1 + d2 c2 + d3 c3 + d4 c4). ⋅ ⋅ ⋅ ⋅The receiver which wants to get the data sent by station 1 multiplies these data by c1.

12.143

Example (continued)

When we divide the result by N, we get d1 .

12.144

Find the chips for a network witha. Two stations b. Four stations

Example

SolutionWe can use the rows of W2 and W4 in Figure 12.29:a. For a two-station network, we have [+1 +1] and [+1 −1].

b. For a four-station network we have [+1 +1 +1 +1], [+1 −1 +1 −1], [+1 +1 −1 −1], and [+1 −1 −1 +1].

12.145

What is the number of sequences if we have 90 stations in our network?

Example

SolutionThe number of sequences needs to be 2m. We need to choose m = 7 and N = 27 or 128. We can then use 90 of the sequences as the chips.

12.146

Prove that a receiving station can get the data sent by a specific sender if it multiplies the entire data on the channel by the sender’s chip code and then divides it by the number of stations.

Example

SolutionLet us prove this for the first station, using our previous four-station example. We can say that the data on the channel D = (d1 c1 + d2 c2 + d3 c3 + d4 c4). ⋅ ⋅ ⋅ ⋅The receiver which wants to get the data sent by station 1 multiplies these data by c1.

12.147

Example (continued)

When we divide the result by N, we get d1 .


Advantages of FDM:Simultaneous transmissionDoesn't need synchronization in Transmitter and ReceiverIn narrow band fading only one channel gets affected

Disadvantages of FDM:Crosstalk problemMust have very large B/wDue to Wideband fading all channels get affected

Applications of FDM:Telephone SystemsAM and FM adio broadcastingFirst generation cellular PhoneTV Broadcasting

WDM technique used in Optical N/w

Working on Prism Principle

Higher than metallic trans.

Very complex

Wavelength DM

04/21/23 149Prof.E. Jayanthi M.Tech (comp N/w) SCOE.

Figure: Prisms in wavelength-division multiplexing and demultiplexing

04/21/23 150Prof.E. Jayanthi M.Tech (comp N/w) SCOE.


Advantages of WDM:Simultaneous transmissionDoesn't need synchronization in Transmitter and ReceiverSince B/W of single fiber band is about 25,000 Ghz , great potential for multiplexing channels for long routes. Disadvantages of WDM:Tunnable Filters required at every input stage.Very Complex

Applications of WDM:

SONET


LTE, Long Term Evolution


LTE, Long Term Evolution, the successor to UMTS and HSPA is now being deployed and is the way forwards for high speed cellular services.In its first forms it is a 3G or as some would call it a 3.99G technology, but with further additions the technology can be migrated to a full 4G standard and here it is known as LTE Advanced.There has been a rapid increase in the use of data carried by cellular services, and this increase will only become larger in what has been termed the "data explosion". To cater for this and the increased demands for increased data transmission speeds and lower latency, further development of cellular technology have been required.


Advantages / disadvantages of LTE TDD and LTE FDD for cellular communications


TD-SCDMA

Time Division Synchronous Code Division Multiple Access (TD-SCDMA) or UTRA/UMTS-TDD 1.28 Mcps Low Chip Rate (LCR), is an air interface[ found in UMTSmobile telecommunications networks in China as an alternative to W-CDMA. Together with TD-CDMA, it is also known as UMTS-TDD or IMT 2000 Time-Division (IMT-TD). The term "TD-SCDMA" is misleading. While it suggests covering only a channel access method based on CDMA, it is actually the common name for the whole air interface specification. TD-SCDMA uses the S-CDMA channel access method across multiple time slots.

basics of communication unit-i. unit i: basics of communication basics of communication:...

Documents

tech comp nw scoe

cellular nw

adhoc nw wireless topologies

digital signals

rate of communication

carrier communication

frequency change

multiplexing techniques