Question 1(a) [3 marks]#
Compare Analog Signal and Digital Signal.
Answer:
Parameter | Analog Signal | Digital Signal |
---|---|---|
Nature | Continuous waveform | Discrete values (0 and 1) |
Amplitude | Infinite variations | Fixed discrete levels |
Noise Effect | More susceptible | Less susceptible |
Bandwidth | Requires less bandwidth | Requires more bandwidth |
Security | Less secure | More 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:
Parameter | PAM | PWM | PPM |
---|---|---|---|
Full Form | Pulse Amplitude Modulation | Pulse Width Modulation | Pulse Position Modulation |
Modulated Parameter | Amplitude | Width/Duration | Position/Time |
Noise Immunity | Poor | Good | Excellent |
Bandwidth | Minimum | Medium | Maximum |
Power Consumption | High | Medium | Low |
Diagram:
- 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:
Reason | Explanation |
---|---|
Antenna Size Reduction | Makes practical antenna sizes possible |
Frequency Translation | Shifts signal to suitable frequency range |
Multiplexing | Allows multiple signals on same medium |
Noise Reduction | Improves signal-to-noise ratio |
Power Efficiency | Better 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:
Band | Frequency Range | Wavelength | Applications |
---|---|---|---|
ELF | 30-300 Hz | 10⁶-10⁷ m | Submarine communication |
VLF | 3-30 kHz | 10⁴-10⁵ m | Navigation, time signals |
LF | 30-300 kHz | 10³-10⁴ m | AM broadcasting |
MF | 300 kHz-3 MHz | 100-1000 m | AM radio |
HF | 3-30 MHz | 10-100 m | Short 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:
Parameter | AM | FM |
---|---|---|
Modulated Parameter | Amplitude | Frequency |
Bandwidth | 2fm | 2(Δf + fm) |
Noise Immunity | Poor | Good |
Power Efficiency | Low (33.33%) | High |
Circuit Complexity | Simple | Complex |
- 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:
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:
Parameter | Pre-emphasis | De-emphasis |
---|---|---|
Location | At transmitter | At receiver |
Function | Boosts high frequencies | Attenuates high frequencies |
Frequency Response | High pass characteristic | Low pass characteristic |
Purpose | Improve S/N ratio | Restore original signal |
Time Constant | 75 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:
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:
Characteristic | Definition | Importance |
---|---|---|
Sensitivity | Minimum input signal for satisfactory output | Better weak signal reception |
Selectivity | Ability to select desired signal and reject others | Reduces interference |
Fidelity | Faithfulness of reproduction | Better audio quality |
Image Frequency Rejection | Rejection of image frequency | Prevents 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:
Working Principle:
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:
Type | Condition | Result |
---|---|---|
Under Sampling | fs < 2fm | Aliasing occurs |
Critical Sampling | fs = 2fm | Just adequate, no margin |
Over Sampling | fs > 2fm | No aliasing, safe margin |
Diagram:
- 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:
Term | Definition | Formula |
---|---|---|
Nyquist Rate | Minimum sampling frequency | fs = 2fm |
Nyquist Interval | Maximum sampling interval | Ts = 1/(2fm) |
Aliasing Error | Frequency overlap due to under sampling | fa = |
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:
Type | Characteristics | Mathematical Expression |
---|---|---|
Ideal Sampling | Impulse train multiplication | xs(t) = x(t)·δT(t) |
Natural Sampling | Variable width pulses | Top follows signal |
Flat Top Sampling | Constant amplitude pulses | Sample and hold |
Waveforms:
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:
Disadvantage | Explanation | Solution |
---|---|---|
Slope Overload | Cannot track fast changes | Increase step size |
Granular Noise | Quantization noise in flat regions | Decrease step size |
High Bit Rate | Requires high sampling rate | Use ADPCM |
Limited Dynamic Range | Fixed step size limitation | Adaptive techniques |
Slope Overload Condition: When |dx/dt| > Δfs, slope overload occurs
Granular Noise: Occurs when input signal changes slowly or remains constant
Waveforms:
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:
Block | Function |
---|---|
LPF | Anti-aliasing filter, removes frequencies > fm |
Sample & Hold | Samples at fs ≥ 2fm and holds value |
Quantizer | Converts to discrete amplitude levels |
Encoder | Converts quantized samples to binary code |
Receiver Block Functions:
Block | Function |
---|---|
Decoder | Converts binary code to quantized levels |
DAC | Digital to Analog conversion |
LPF | Reconstruction 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:
Characteristics:
Coding Type | Logic 1 | Logic 0 | Bandwidth |
---|---|---|---|
NRZ Unipolar | +V | 0V | fb |
RZ Unipolar | +V for T/2, 0V for T/2 | 0V | 2fb |
Manchester | High-to-Low transition | Low-to-High transition | 2fb |
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:
Working Principle:
Component | Function |
---|---|
Time Slots | Fixed duration allocated to each channel |
Frame | Complete cycle containing all channels |
Synchronization | Maintains proper channel separation |
Multiplexer | Combines 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:
Type | Formula | Application |
---|---|---|
Zero Order | x̂(n) = x(n-1) | Simple predictor |
First Order | x̂(n) = ax(n-1) | Better prediction |
Higher Order | x̂(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:
Level | Name | Bit Rate | Voice Channels | Application |
---|---|---|---|---|
Level 0 | DS-0 | 64 kbps | 1 | Basic voice channel |
Level 1 | DS-1/T1 | 1.544 Mbps | 24 | Primary multiplex |
Level 2 | DS-2/T2 | 6.312 Mbps | 96 | Secondary multiplex |
Level 3 | DS-3/T3 | 44.736 Mbps | 672 | Tertiary 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:
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”