Chapter 3: Data Communication Fundamentals By: Bhargavi Goswami, Sunshine Group of Institutions, Rajkot. Sub: FON, Email: [email protected]Page 1 Topic List: • Topic List, Introduction • Bandwidth & Data Rate • Analog & Digital Signalling • Analog & Digital Transmission • Coding Mechanism • Modulation • Modulation in Practice A. Bandwidth & Data Rate: (a) Bandwidth: Represents the range of frequencies that can pass thru a medium. More the bandwidth larger the data it can transmit. Fixed Eg. Wider the road, larger #Vehicles accommodated. (b) Data Rate: Data rate is the actual traffic passing at given time. Purely depends on bandwidth. Variable. Eg: Driver asking for infinite speed (bandwidth) for transmission. Data Rate depends on: o Bandwidth utilization o If Analog, #constellation points o If Digital, Number of levels o Receiver’s sensitivity o Media resistance and temperature B. Frequency & Band: • Signal travels thru a medium in range of frequencies. • This range of frequencies is called frequency band. • If we try to accommodate more radio stations in a band, they become too noisy. • Similarly for LANs, limits the #users. C. Media Effect on Bandwidth • Distortion: Due to elimination of higher frequency components from signal results to distortion. • Attenuation: Adding more number of different frequency causes attenuation. • Swimmer’s lane: Middle lanes provide less resistance than outer lanes. Larger the frequency, more the noise, smaller the frequency, larger the data transmission rate. D. Harmonics and composite wave: • Fourier Component : Components of a composite signal are known as Fourier Component. • Composite Signals : When a signal contains multiple frequencies, it is called composite signals. • Fundamental Frequency : Frequency of first harmonic (Fourier Component) is knows as Fundamental Frequency. • If first component is f, 2 nd is 3f and 3 rd is 5f. • Frequency is inversely proportional to amplitude. • Large amplitude signals cover smaller distance.
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Chapter 3: Data Communication Fundamentals
By: Bhargavi Goswami, Sunshine Group of Institutions, Rajkot. Sub: FON, Email: [email protected] Page 1
Topic List:
• Topic List, Introduction
• Bandwidth & Data Rate
• Analog & Digital Signalling
• Analog & Digital Transmission
• Coding Mechanism
• Modulation
• Modulation in Practice
A. Bandwidth & Data Rate:
(a) Bandwidth:
Represents the range of frequencies that can pass thru a medium.
More the bandwidth larger the data it can transmit.
Fixed
Eg. Wider the road, larger #Vehicles accommodated.
(b) Data Rate:
Data rate is the actual traffic passing at given time.
Purely depends on bandwidth.
Variable.
Eg: Driver asking for infinite speed (bandwidth) for transmission.
Data Rate depends on:
o Bandwidth utilization
o If Analog, #constellation points
o If Digital, Number of levels
o Receiver’s sensitivity
o Media resistance and temperature
B. Frequency & Band:
• Signal travels thru a medium in range of frequencies.
• This range of frequencies is called frequency band.
• If we try to accommodate more radio stations in a band, they become too noisy.
• Similarly for LANs, limits the #users.
C. Media Effect on Bandwidth
• Distortion: Due to elimination of higher frequency components from signal results to distortion.
• Attenuation: Adding more number of different frequency causes attenuation.
• Swimmer’s lane: Middle lanes provide less resistance than outer lanes. Larger the frequency, more
the noise, smaller the frequency, larger the data transmission rate.
D. Harmonics and composite wave:
• Fourier Component: Components of a composite signal are known as Fourier Component.
• Composite Signals: When a signal contains multiple frequencies, it is called composite signals.
• Fundamental Frequency: Frequency of first harmonic (Fourier Component) is knows as Fundamental
Frequency.
• If first component is f, 2nd
is 3f and 3rd
is 5f.
• Frequency is inversely proportional to amplitude.
• Large amplitude signals cover smaller distance.
Chapter 3: Data Communication Fundamentals
By: Bhargavi Goswami, Sunshine Group of Institutions, Rajkot. Sub: FON, Email: [email protected] Page 2
E. Properties of Channel:
• More the bandwidth of the media, more the number of harmonics that can pass through the media.
• Higher the data rate, less will be the number of harmonics that can pass through the media.
• Baud Rate: #signals that passes thru media in unit time, usually in seconds. As bandwidth is fixed,
Baud Rate is also fixed.
• Bit Rate: #bits that passes thru a media in unit time, usually in seconds. If 1 signal carry n bits then
Baud Rate is 1 and Bit Rate is n.
• Signal: Combination of zeros and ones.
• Maximum Baud Rate: No of harmonics that can be accommodated in a given bandwidth.
• We can obtain Maximum Data Rate (MDR) if we know bandwidth and sensitivity of receiver
(#harmonics recognized correctly).
• Data rate is doubled when baud rate is quadrupled, tripled when baud rate is 8 times, and so on….
F. Baud Rate & Bit Rate Relation:
Nyquist:
• MDR of a channel = 2 × Bandwidth
• MDR of a channel = 2 × Bandwidth × log2 (signal levels)
Claude Shannon:
• MDR of a channel = Bandwidth × log2 (1 + S/N)
Signal to noise ratio (decibel):
• When signal to noice ratio is equal:
• S/N =10 log (Ps/Pn)
• Where, Ps – Signal Power, Pn – Noise Power
• When Ps/Pn becomes 1
• MDR = Bandwidth × log2 (1+10 × log e 1)
= Bandwidth × log 2 (1+0)
= Bandwidth × log 2 1
= 0 (as log21 = 0)
Chapter 3: Data Communication Fundamentals
By: Bhargavi Goswami, Sunshine Group of Institutions, Rajkot. Sub: FON, Email: [email protected] Page 3
G. Filtering a specific frequency:
• Filter is a device used for restricting bandwidth of a medium to specified limit.
• Used with telephone lines,
▫ Actual bandwidth = 1.1 MHz
▫ Using filter reduced to = 4 kHz
▫ Remaining channel can be used for other telephone connections data transmission at a time.
▫ Remaining channel can also be used for broadband.
▫ That’s y we feel voice interference in laneline phone when internet is on.
• DSL (Digital Subscriber’s Line) removes the filter from line to use entire bandwidth for internet
access.
• Filter Types:
• 1. Low Pass Filter: Such filters keep only lower part of frequency out of given range.
• 2. Band Pass Filter: keeps middle part of frequency.
• 3. High Pass Filter: eliminates lower parts to keep only higher part of frequency.
• Widely used is low pass filter.
H. Analog Signals:
• Used to transmit video and audio signals.
• Higher error rate.
• Continuous by nature.
• Uses curved wave forms.
• Used when we don’t have large bandwidth.
• High error rate due to sine property.
• Amplifiers are used which gives strength to signal but can’t correct the signals.
• Three different properties:
▫ Amplitude: signal’s max voltage value.
▫ Frequency: #oscillations per second.
▫ Phase: direction of a signal
• Can be used to transmit digital data also.
• Also supports modulation techniques.
• Technique to represent zeros and ones using one or more properties of wave is called modulation.
Chapter 3: Data Communication Fundamentals
By: Bhargavi Goswami, Sunshine Group of Institutions, Rajkot. Sub: FON, Email: [email protected] Page 4
I. Digital Signals:
• Used when we have large bandwidth.
• Used to transfer (0,1) bits generally for file transfer.
• Low error rate.
• Discrete by nature.
• Square wave forms.
• Repeaters are used to give strength to signal which can also correct signals.
• How to transfer digital data over wire?
▫ Using electromagnetic waves
▫ Using light
• MP3 (Music Player), MPEG (Moving Picture Expert Group) are the types where audio video signals
are converted from analog to digital.
• These signals can be of two types: Periodic and A periodic.
• Periodic Signals: Continuously repeats its shape after a specified interval. Used for data
transmission.
• A-Periodic Signals: does not follow pattern.
Digital signaling and bit rate:
• Baud Rate: #voltage signals we send per second is known as baud rate.
• Bit Rate: #bits sent per second are known as bit rate.
• If we use 2n different voltage signals, then
• bit rate = baud rate × n
• If we use n voltage signals, then
• bit rate = baud rate × log2 n
• n is number of levels.
• Suppose we have 4 different voltage levels, say, 1,2,-1,-2.
• 1v = 10, 2v=11, -1v=01, -2v=00.
• This means, 4(voltage) levels can represent 8(combination of 2) bits of data.
• Suppose it takes 0.1 msec then voltage transmitted are 10 Mbps, but total bits transmitted is 20
Mbps.
Characteristics:
• Square waveforms
• Limited discrete values of voltage levels
Chapter 3: Data Communication Fundamentals
By: Bhargavi Goswami, Sunshine Group of Institutions, Rajkot. Sub: FON, Email: [email protected] Page 5