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Principles of Electronic Communication (4331104) - Summer 2025 Complete Solution

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Study-Material Solutions Electronic-Communication 4331104 2025 Summer
Milav Dabgar
Author
Milav Dabgar
Experienced lecturer in the electrical and electronic manufacturing industry. Skilled in Embedded Systems, Image Processing, Data Science, MATLAB, Python, STM32. Strong education professional with a Master’s degree in Communication Systems Engineering from L.D. College of Engineering - Ahmedabad.
Table of Contents

Question 1(a) [3 marks]
#

Compare Analog Signal and Digital Signal.

Answer:

ParameterAnalog SignalDigital Signal
NatureContinuous waveformDiscrete values (0 and 1)
AmplitudeInfinite variationsFixed discrete levels
Noise EffectMore susceptibleLess susceptible
BandwidthRequires less bandwidthRequires more bandwidth
SecurityLess secureMore secure
  • Signal Type: Analog signals are continuous, Digital signals are discrete
  • Noise Resistance: Digital signals have better noise immunity

Mnemonic: “ABCD - Analog Bad for noise, Continuous; Digital Discrete, Clean signals”


Question 1(b) [4 marks]
#

Compare PAM, PWM and PPM.

Answer:

ParameterPAMPWMPPM
Full FormPulse Amplitude ModulationPulse Width ModulationPulse Position Modulation
Modulated ParameterAmplitudeWidth/DurationPosition/Time
Noise ImmunityPoorGoodExcellent
BandwidthMinimumMediumMaximum
Power ConsumptionHighMediumLow

Diagram:

PPPAWPMMM:::|||||||||||AWPmiopdsltiihttiuvodanerivveaasrriieess
  • Modulation Parameter: Each type modulates different pulse characteristics
  • Applications: PWM used in motor control, PPM in radio control systems

Mnemonic: “PAM-Amplitude, PWM-Width, PPM-Position - AWP”


Question 1(c) [7 marks]
#

Indicate the need of Modulation in detail. Calculate the height of antenna if the frequency of Carrier signal is 1 MHz.

Answer:

Need for Modulation:

ReasonExplanation
Antenna Size ReductionMakes practical antenna sizes possible
Frequency TranslationShifts signal to suitable frequency range
MultiplexingAllows multiple signals on same medium
Noise ReductionImproves signal-to-noise ratio
Power EfficiencyBetter power utilization

Antenna Height Calculation: For efficient radiation, antenna height = λ/4

λ = c/f = (3 × 10⁸)/(1 × 10⁶) = 300 meters

Antenna height = λ/4 = 300/4 = 75 meters

  • Practical Antenna: Without modulation, antenna would be impractically large
  • Frequency Shifting: Allows better propagation characteristics

Mnemonic: “AFMNP - Antenna, Frequency, Multiplexing, Noise, Power”


Question 1(c) OR [7 marks]
#

Write frequency bands with applications domains of EM Wave spectrum. Calculate Wavelength range of ELF band.

Answer:

BandFrequency RangeWavelengthApplications
ELF30-300 Hz10⁶-10⁷ mSubmarine communication
VLF3-30 kHz10⁴-10⁵ mNavigation, time signals
LF30-300 kHz10³-10⁴ mAM broadcasting
MF300 kHz-3 MHz100-1000 mAM radio
HF3-30 MHz10-100 mShort wave radio

ELF Wavelength Calculation:

  • Lower frequency: f₁ = 30 Hz, λ₁ = c/f₁ = (3×10⁸)/30 = 10⁷ meters
  • Upper frequency: f₂ = 300 Hz, λ₂ = c/f₂ = (3×10⁸)/300 = 10⁶ meters

ELF Wavelength range: 10⁶ to 10⁷ meters

  • Application Domain: Each band suited for specific applications
  • Propagation: Lower frequencies have better ground wave propagation

Mnemonic: “Every Valuable Learning Makes Happiness - ELF to HF bands”


Question 2(a) [3 marks]
#

Compare AM and FM.

Answer:

ParameterAMFM
Modulated ParameterAmplitudeFrequency
Bandwidth2fm2(Δf + fm)
Noise ImmunityPoorGood
Power EfficiencyLow (33.33%)High
Circuit ComplexitySimpleComplex
  • Bandwidth: FM requires much wider bandwidth than AM
  • Quality: FM provides better audio quality

Mnemonic: “AM-Amplitude simple, FM-Frequency complex but better quality”


Question 2(b) [4 marks]
#

Draw waveform of Amplitude Modulated wave.

Answer:

Diagram:

CMAaoMrdruWilaeavrtei:SniggnSailg:nal:..Emno.vdeulloapt.ein.fgols.liogwnsal

Characteristics:

  • Envelope: The envelope follows the modulating signal
  • Carrier Frequency: Remains constant throughout
  • Amplitude Variation: Amplitude varies with modulating signal

Mnemonic: “Envelope Follows Message - EFM”


Question 2(c) [7 marks]
#

Define Amplitude Modulation and Derive mathematical expression for Double Sideband Full Carrier (DSBFC) Amplitude Modulation (AM) signal.

Answer:

Definition: Amplitude Modulation is the process where amplitude of carrier signal varies according to instantaneous amplitude of modulating signal.

Mathematical Derivation:

Let carrier signal: ec(t) = Ec cos(ωct) Let modulating signal: em(t) = Em cos(ωmt)

AM Signal Expression: eAM(t) = [Ec + Em cos(ωmt)] cos(ωct) eAM(t) = Ec cos(ωct) + Em cos(ωmt) cos(ωct)

Using trigonometric identity: cos A cos B = ½[cos(A+B) + cos(A-B)]

Final AM Expression: eAM(t) = Ec cos(ωct) + (Em/2) cos(ωc + ωm)t + (Em/2) cos(ωc - ωm)t

Components:

  • Carrier Component: Ec cos(ωct)
  • Upper Sideband: (Em/2) cos(ωc + ωm)t
  • Lower Sideband: (Em/2) cos(ωc - ωm)t

Mnemonic: “Carrier Plus Upper Lower Sidebands - CPULS”


Question 2(a) OR [3 marks]
#

Compare Pre-emphasis and De-emphasis.

Answer:

ParameterPre-emphasisDe-emphasis
LocationAt transmitterAt receiver
FunctionBoosts high frequenciesAttenuates high frequencies
Frequency ResponseHigh pass characteristicLow pass characteristic
PurposeImprove S/N ratioRestore original signal
Time Constant75 μs (FM broadcasting)75 μs (FM broadcasting)
  • Noise Reduction: Combined effect reduces noise in received signal
  • Frequency Response: Complementary characteristics

Mnemonic: “Pre-Boost, De-Cut - Noise Reduction Circuit”


Question 2(b) OR [4 marks]
#

Draw waveform of Frequency Modulated wave.

Answer:

Diagram:

MCFoaMdrurWliaaevtrei:nSgigSniagln:al:HwihgehnermofdreqveLwohweenrmfordeqve

Characteristics:

  • Constant Amplitude: Amplitude remains constant
  • Frequency Variation: Frequency varies with modulating signal
  • Phase Continuity: Phase remains continuous

Mnemonic: “Constant Amplitude, Variable Frequency - CAVF”


Question 2(c) OR [7 marks]
#

Define Frequency Modulation and Derive mathematical expression for FM wave.

Answer:

Definition: Frequency Modulation is the process where frequency of carrier signal varies according to instantaneous amplitude of modulating signal.

Mathematical Derivation:

Let modulating signal: em(t) = Em cos(ωmt) Instantaneous frequency: fi = fc + kf × Em cos(ωmt)

Where kf = frequency sensitivity

Instantaneous angular frequency: ωi = 2π[fc + kf Em cos(ωmt)] ωi = ωc + 2πkf Em cos(ωmt)

Phase calculation: θ(t) = ∫ωi dt = ωct + (2πkf Em/ωm) sin(ωmt)

Let modulation index: mf = 2πkf Em/ωm = Δf/fm

Final FM Expression: eFM(t) = Ec cos[ωct + mf sin(ωmt)]

Parameters:

  • Modulation Index: mf = Δf/fm
  • Frequency Deviation: Δf = kf Em
  • Bandwidth: BW = 2(Δf + fm) (Carson’s rule)

Mnemonic: “Frequency Varies with Message - FVM”


Question 3(a) [3 marks]
#

Illustrate Slope detection method of FM demodulation.

Answer:

Slope Detection Principle:

graph LR
    A[FM Signal] --> B[Tuned Circuit]
    B --> C[Envelope Detector]
    C --> D[Audio Output]

Working:

  • Tuned Circuit: Converts frequency variations to amplitude variations
  • Slope Operation: Uses slope of resonance curve
  • Envelope Detection: Extracts amplitude variations

Characteristics:

  • Simple Circuit: Easy to implement
  • Linear Range: Limited linear range
  • Output Distortion: Higher distortion compared to other methods

Mnemonic: “Slope Converts Frequency to Amplitude - SCFA”


Question 3(b) [4 marks]
#

Explain different Characteristics of radio receiver.

Answer:

CharacteristicDefinitionImportance
SensitivityMinimum input signal for satisfactory outputBetter weak signal reception
SelectivityAbility to select desired signal and reject othersReduces interference
FidelityFaithfulness of reproductionBetter audio quality
Image Frequency RejectionRejection of image frequencyPrevents false signals

Mathematical Relations:

  • Sensitivity: Measured in μV for standard output
  • Selectivity: Q = f₀/BW
  • Image Rejection Ratio: IRR = 1 + (2πfIFRC)²

Mnemonic: “Sensitive Selective Faithful Image-free - SSFI”


Question 3(c) [7 marks]
#

Write short note on Super heterodyne receiver with suitable block diagram.

Answer:

Block Diagram:

graph LR
    A[Antenna] --> B[RF Amplifier]
    B --> C[Mixer]
    D[Local Oscillator] --> C
    C --> E[IF Amplifier]
    E --> F[Detector]
    F --> G[AF Amplifier]
    G --> H[Speaker]
    E --> I[AGC]
    I --> B
    I --> E

Working Principle:

  • RF Amplifier: Amplifies received RF signal
  • Mixer: Converts RF to fixed IF frequency
  • Local Oscillator: Provides mixing frequency
  • IF Amplifier: Main amplification at fixed frequency
  • Detector: Recovers modulated signal
  • AGC: Maintains constant output level

Advantages:

  • High Sensitivity: Better sensitivity than TRF
  • Good Selectivity: Better selectivity
  • Stable Gain: Stable gain characteristics

IF Frequency Selection: Standard IF: 455 kHz for AM, 10.7 MHz for FM

Mnemonic: “Mix RF to IF for Better Selectivity - MRIBS”


Question 3(a) OR [3 marks]
#

Illustrate working of FM demodulator using Phase Locked Loop.

Answer:

PLL FM Demodulator:

graph LR
    A[FM Input] --> B[Phase Detector]
    C[VCO] --> B
    B --> D[Loop Filter]
    D --> C
    D --> E[Audio Output]

Working Principle:

  • Phase Detector: Compares input FM with VCO output
  • VCO: Voltage Controlled Oscillator tracks input frequency
  • Loop Filter: Removes high frequency components
  • Lock Condition: VCO frequency equals input frequency

Advantages:

  • Linear Demodulation: Excellent linearity
  • Low Distortion: Minimum distortion
  • Good Tracking: Excellent frequency tracking

Mnemonic: “Phase Lock Tracks Frequency - PLTF”


Question 3(b) OR [4 marks]
#

Discuss Block diagram of basic FM receiver.

Answer:

FM Receiver Block Diagram:

graph LR
    A[FM Antenna] --> B[RF Amplifier]
    B --> C[Mixer]
    D[Local Oscillator] --> C
    C --> E[IF Amplifier 10.7MHz]
    E --> F[Limiter]
    F --> G[FM Detector]
    G --> H[De-emphasis]
    H --> I[AF Amplifier]
    I --> J[Speaker]

Block Functions:

  • RF Amplifier: Amplifies weak FM signal (88-108 MHz)
  • Mixer: Converts to IF frequency (10.7 MHz)
  • Limiter: Removes amplitude variations
  • FM Detector: Recovers audio signal
  • De-emphasis: Restores original frequency response

Key Differences from AM Receiver:

  • Higher IF: 10.7 MHz vs 455 kHz
  • Limiter Stage: Additional limiter stage
  • De-emphasis: Pre/de-emphasis network

Mnemonic: “FM needs Higher IF and Limiting - FHIL”


Question 3(c) OR [7 marks]
#

Write short note on Envelope detector using diode with suitable circuit diagram and waveform.

Answer:

Circuit Diagram:

AMGNDD1GRCNDAudioOutput

Working Principle:

AD(AMiAuofdIdtineeopruOOtufu:titplpututet:r:.ing.)....

Operation:

  • Diode Conduction: Conducts during positive half cycles
  • Capacitor Charging: Charges to peak value
  • RC Discharge: Discharges through RC circuit
  • Envelope Following: Output follows envelope

Design Considerations:

  • Time Constant: RC » 1/fc but RC « 1/fm
  • Diode Selection: Fast recovery diode preferred
  • Load Resistance: Should be much larger than diode resistance

Advantages:

  • Simplicity: Very simple circuit
  • Low Cost: Economical solution
  • High Efficiency: Good detection efficiency

Mnemonic: “Diode Charges, RC Follows Envelope - DCRF”


Question 4(a) [3 marks]
#

Illustrate under sampling, over sampling and critical sampling.

Answer:

TypeConditionResult
Under Samplingfs < 2fmAliasing occurs
Critical Samplingfs = 2fmJust adequate, no margin
Over Samplingfs > 2fmNo aliasing, safe margin

Diagram:

OUCOrnrvidiegetririncSaSaalalmmpSpSlilaigimnnnpgagl:l:i:ng:.......AJSluaisfatesiOnKg
  • Aliasing Effect: Under sampling causes frequency overlap
  • Nyquist Rate: Minimum sampling rate = 2fm
  • Practical Rate: Usually 2.5 to 5 times message frequency

Mnemonic: “Under-Alias, Critical-Just, Over-Safe - UCO”


Question 4(b) [4 marks]
#

State Sampling theorem and define Nyquist rate, Nyquist interval and aliasing error.

Answer:

Sampling Theorem: “A continuous signal can be completely recovered from its samples if sampling frequency is at least twice the highest frequency component of the signal.”

Definitions:

TermDefinitionFormula
Nyquist RateMinimum sampling frequencyfs = 2fm
Nyquist IntervalMaximum sampling intervalTs = 1/(2fm)
Aliasing ErrorFrequency overlap due to under samplingfa =

Mathematical Expression:

  • Sampling Frequency: fs ≥ 2fm (Nyquist criterion)
  • Sampling Period: Ts = 1/fs
  • Aliasing Condition: fs < 2fm

Practical Applications:

  • Digital Audio: fs = 44.1 kHz for fm = 20 kHz
  • Telephone System: fs = 8 kHz for fm = 4 kHz

Mnemonic: “Sample at twice message frequency - S2M”


Question 4(c) [7 marks]
#

Discuss Ideal, Natural and Flat top sampling.

Answer:

Types of Sampling:

TypeCharacteristicsMathematical Expression
Ideal SamplingImpulse train multiplicationxs(t) = x(t)·δT(t)
Natural SamplingVariable width pulsesTop follows signal
Flat Top SamplingConstant amplitude pulsesSample and hold

Waveforms:

OINFrdalietagautilrn:aTalol:p::||||||||||||IVCmaoprnuislatsbaelnsetwwiiddtthh

Frequency Spectrum:

  • Ideal Sampling: Exact spectral replication
  • Natural Sampling: Slight spectral modification
  • Flat Top Sampling: Aperture effect present

Practical Implementation:

  • Ideal: Theoretical only
  • Natural: Used in PAM systems
  • Flat Top: Sample-and-hold circuits, ADC systems

Aperture Effect: In flat-top sampling: |Sa(πfT/2)| = |sin(πfT/2)/(πfT/2)|

Mnemonic: “Ideal-Impulse, Natural-Variable, Flat-Constant - IVF”


Question 4(a) OR [3 marks]
#

Illustrate the working of Delta modulator with suitable block diagram.

Answer:

Delta Modulator Block Diagram:

graph LR
    A[Input Signal] --> B[Comparator]
    B --> C[1-bit Quantizer]
    C --> D[Output]
    C --> E[Integrator]
    E --> F[Delay]
    F --> B

Working Principle:

  • Comparison: Input compared with previous integrated output
  • 1-bit Quantization: Output is +Δ or -Δ
  • Integration: Integrator approximates input signal
  • Feedback: Previous output fed back for comparison

Output Characteristics:

  • Binary Output: Only 1 bit per sample
  • Step Size: Fixed step size Δ
  • Tracking: Output tracks input in steps

Mnemonic: “Compare, Quantize, Integrate, Feedback - CQIF”


Question 4(b) OR [4 marks]
#

Write disadvantages of Delta modulation (DM) with suitable explanation.

Answer:

Major Disadvantages:

DisadvantageExplanationSolution
Slope OverloadCannot track fast changesIncrease step size
Granular NoiseQuantization noise in flat regionsDecrease step size
High Bit RateRequires high sampling rateUse ADPCM
Limited Dynamic RangeFixed step size limitationAdaptive techniques

Slope Overload Condition: When |dx/dt| > Δfs, slope overload occurs

Granular Noise: Occurs when input signal changes slowly or remains constant

Waveforms:

SGlroapneulOavrerNlooiasde::IDFDnMlMpauototustictpniouplotultafltaaesgsts

Performance Parameters:

  • Slope Overload: Maximum slope = Δfs
  • Granular Noise: Depends on step size
  • SNR: Limited by both effects

Mnemonic: “Slope-Overload, Granular-Noise, High-Bitrate - SOG-H”


Question 4(c) OR [7 marks]
#

Describe functions of each block of pulse code modulation (PCM) transmitter and receiver.

Answer:

PCM Transmitter Block Diagram:

graph LR
    A[Analog Input] --> B[LPF]
    B --> C[Sample & Hold]
    C --> D[Quantizer]
    D --> E[Encoder]
    E --> F[Digital Output]

PCM Receiver Block Diagram:

graph LR
    G[Digital Input] --> H[Decoder]
    H --> I[DAC]
    I --> J[LPF]
    J --> K[Analog Output]

Transmitter Block Functions:

BlockFunction
LPFAnti-aliasing filter, removes frequencies > fm
Sample & HoldSamples at fs ≥ 2fm and holds value
QuantizerConverts to discrete amplitude levels
EncoderConverts quantized samples to binary code

Receiver Block Functions:

BlockFunction
DecoderConverts binary code to quantized levels
DACDigital to Analog conversion
LPFReconstruction filter, removes sampling frequency

Technical Specifications:

  • Quantization Levels: L = 2ⁿ (n = number of bits)
  • Quantization Error: Δ/2 maximum
  • Bit Rate: fb = n × fs

PCM Advantages:

  • Noise Immunity: Excellent noise performance
  • Regeneration: Can be regenerated without error accumulation
  • Multiplexing: Easy to multiplex multiple channels

Mnemonic: “Low-pass, Sample, Quantize, Encode - LSQE for TX; Decode, Convert, Filter - DCF for RX”


Question 5(a) [3 marks]
#

Discuss block diagram of TDM-PCM system in brief.

Answer:

TDM-PCM System Block Diagram:

graph LR
    A[Channel 1] --> D[Commutator]
    B[Channel 2] --> D
    C[Channel 3] --> D
    D --> E[PCM Encoder]
    E --> F[Transmission]
    F --> G[PCM Decoder]
    G --> H[Decommutator]
    H --> I[Channel 1]
    H --> J[Channel 2]
    H --> K[Channel 3]

System Operation:

  • Commutator: Sequential sampling of multiple channels
  • PCM Encoder: Converts samples to digital format
  • Time Division: Each channel gets fixed time slot
  • Decommutator: Separates channels at receiver

Frame Structure:

  • Time Slot: Each channel assigned specific time
  • Frame Period: Complete cycle for all channels
  • Synchronization: Frame synchronization bits added

Advantages:

  • Bandwidth Efficiency: Efficient spectrum utilization
  • Multiple Channels: Multiple channels on single link

Mnemonic: “Time Division Multiple Access - TDMA”


Question 5(b) [4 marks]
#

Write short note on Adaptive delta modulation (ADM).

Answer:

ADM Block Diagram:

graph LR
    A[Input] --> B[Comparator]
    B --> C[Logic Circuit]
    C --> D[Step Size Control]
    D --> E[Integrator]
    E --> F[Delay]
    F --> B
    C --> G[Output]

Working Principle:

  • Adaptive Step Size: Step size changes based on input characteristics
  • Slope Overload Prevention: Increases step size for fast changes
  • Granular Noise Reduction: Decreases step size for slow changes
  • Logic Control: Algorithm controls step size adaptation

Step Size Control:

  • Increase: When consecutive bits are same (slope overload detected)
  • Decrease: When alternate pattern occurs (granular region)

Advantages over Standard DM:

  • Better SNR: Improved signal-to-noise ratio
  • Dynamic Range: Better dynamic range
  • Automatic Adaptation: Self-adjusting characteristics

Mnemonic: “Adaptive Step size Reduces both Slope-overload and Granular noise - ASRSG”


Question 5(c) [7 marks]
#

Define Line coding. Draw NRZ (unipolar), RZ (unipolar), Manchester coding waveforms for “1 0 1 1 1 0 1 1”.

Answer:

Definition: Line coding is the process of converting digital data into digital signals suitable for transmission over communication channels.

Waveform Diagrams:

DNRMaRZatZnaUc:Unhnieipspotolelarar:r::1Tra0nsi1tio1na1tm0idd1le1ofeachbit

Characteristics:

Coding TypeLogic 1Logic 0Bandwidth
NRZ Unipolar+V0Vfb
RZ Unipolar+V for T/2, 0V for T/20V2fb
ManchesterHigh-to-Low transitionLow-to-High transition2fb

Properties:

  • NRZ: No return to zero, simple but no self-synchronization
  • RZ: Return to zero, easy clock recovery but double bandwidth
  • Manchester: Self-synchronizing, used in Ethernet

Applications:

  • NRZ: Simple digital systems
  • RZ: Magnetic recording
  • Manchester: Ethernet, some wireless standards

Mnemonic: “NRZ-Simple, RZ-Return, Manchester-Transition - SRT”


Question 5(a) OR [3 marks]
#

Describe concept of Time division digital multiplexing.

Answer:

TDM Concept: Time Division Multiplexing is a technique where multiple digital signals are transmitted over a single channel by allocating different time slots to each signal.

TDM Frame Structure:

Frame:|CH1|CH2F|rCaHm3e|CPHe4r|iSoYdNC|CH1|CH2|CH3|CH4|SYNC|

Working Principle:

ComponentFunction
Time SlotsFixed duration allocated to each channel
FrameComplete cycle containing all channels
SynchronizationMaintains proper channel separation
MultiplexerCombines multiple inputs sequentially

Key Features:

  • Fixed Time Slot: Each channel gets predetermined time
  • Sequential Sampling: Channels sampled one after another
  • Digital Transmission: Suitable for digital signals
  • Bandwidth Sharing: Efficient spectrum utilization

Applications:

  • Telephone System: T1, E1 systems
  • Digital Hierarchy: PDH, SDH systems

Mnemonic: “Time slots Share Single Channel - TSSC”


Question 5(b) OR [4 marks]
#

Write short note on Differential PCM (DPCM).

Answer:

DPCM Block Diagram:

graph LR
    A[Input] --> B[Difference]
    C[Predictor] --> B
    B --> D[Quantizer]
    D --> E[Encoder]
    E --> F[Output]
    D --> G[Local Decoder]
    G --> H[Adder]
    C --> H
    H --> C

Working Principle:

  • Prediction: Predicts current sample from previous samples
  • Difference Signal: Transmits difference between actual and predicted
  • Quantization: Quantizes difference signal only
  • Local Decoder: Maintains same reference as receiver

Prediction Algorithms:

TypeFormulaApplication
Zero Orderx̂(n) = x(n-1)Simple predictor
First Orderx̂(n) = ax(n-1)Better prediction
Higher Orderx̂(n) = Σai×x(n-i)Optimum prediction

Advantages:

  • Reduced Bit Rate: Lower bit rate than PCM
  • Better SNR: Better SNR for same bit rate
  • Predictive Coding: Exploits signal correlation

Applications:

  • Image Compression: JPEG standards
  • Video Coding: Motion compensation
  • Speech Coding: Speech compression systems

Comparison with PCM:

  • Bit Rate: DPCM requires fewer bits
  • Complexity: More complex than PCM
  • Quality: Better quality at same bit rate

Mnemonic: “Predict Difference, Quantize Less - PDQL”


Question 5(c) OR [7 marks]
#

Write short note on 4 level digital multiplexing Hierarchy.

Answer:

Digital Multiplexing Hierarchy:

Level Structure:

LevelNameBit RateVoice ChannelsApplication
Level 0DS-064 kbps1Basic voice channel
Level 1DS-1/T11.544 Mbps24Primary multiplex
Level 2DS-2/T26.312 Mbps96Secondary multiplex
Level 3DS-3/T344.736 Mbps672Tertiary multiplex

Multiplexing Structure:

graph TD
    A[24 × DS-0] --> B[DS-1]
    C[4 × DS-1] --> D[DS-2]
    E[7 × DS-2] --> F[DS-3]
    G[6 × DS-3] --> H[DS-4]

Frame Structure for T1:

  • Frame Length: 193 bits (192 data + 1 framing)
  • Frame Rate: 8000 frames/second
  • Time Slot: 8 bits per channel
  • Framing Bit: Synchronization pattern

T1 Frame Format:

|FFr|aCmHi1n|gCH2|...|1C9H324b|iFt|sCHt1o|tCaHl2|...|CH24|

Multiplexing Process:

  • Level 1: 24 voice channels × 64 kbps + overhead = 1.544 Mbps
  • Level 2: 4 T1 streams + overhead = 6.312 Mbps
  • Level 3: 7 T2 streams + overhead = 44.736 Mbps
  • Synchronization: Each level adds synchronization bits

Applications:

  • Telephone Network: Primary application in telephone systems
  • Data Communication: High-speed data transmission
  • Internet Backbone: Internet service provider connections

International Standards:

  • North American: T1/T3 hierarchy (DS series)
  • European: E1/E3 hierarchy (different bit rates)
  • ITU-T: International recommendations

Advantages:

  • Standardization: Well-defined international standards
  • Scalability: Easy to scale up capacity
  • Interoperability: Compatible across different vendors

Mnemonic: “Digital Signal hierarchy: 0-1-2-3 levels Build Communication Systems - DS-BCS”

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