Digital Modulation, its types, and related terms like bit rate 📘 Example:

and baud rate, with a simple example. If each signal (symbol) carries 2 bits:
 Bit rate = 1000 bps
🟦 What is Digital Modulation?  Baud rate = 500 baud
Digital Modulation is a method used to send digital data (0s ------------------------------------------------------------------------------------
and 1s) using an analog signal (a continuous wave). We do this 🔷 Amplitude Shift Keying (ASK) – Simple Explanation
by changing (modulating) certain properties of the analog 🟩 Definition:
signal (called the carrier) based on the digital bits. ASK is a type of digital modulation where we change the
We usually change: amplitude of a high-frequency analog carrier signal to
 Amplitude (height of the wave), represent digital data (0s and 1s).
 Amplitude changes → based on digital input (1 or 0)
 Frequency (how fast the wave oscillates), or
 Frequency and phase → stay the same
 Phase (position or angle of the wave).

🔸 How ASK Works:

🟩 What is Binary Modulation?  When the digital input is 1 → the analog carrier signal
Binary modulation means the analog carrier is changed based is turned ON)
on only two states – usually 0 and 1.  When the digital input is 0 → the carrier signal is
turned OFF (zero)
🟨 Types of Digital Modulation: This is why ASK is also called On-Off Keying (OOK).
Let’s assume you want to send this digital data:
1010 🧮 Mathematical Expressed as :
You’ll use a carrier wave: a high-frequency analog sine wave Let:
like:  Vc = maximum amplitude of the carrier (volts)
c(t) = Vc × sin(2πfct + θ)  Fc= carrier frequency (Hz)
 cos(2πfct) = the carrier wave
Where:
ASK signal Vask(t) isc
 Vc = amplitude (height),
vASK(t) = Vc × cos(2πfct) → for binary 1
 fc = frequency (speed),
vASK(t) = 0 → for binary 0
 θ = phase (angle shift) 1.
1. ✅ ASK (Amplitude Shift Keying): 1.
 Only amplitude changes. 1.
 Binary 1 = wave is ON (high amplitude), 1.
Binary 0 = wave is OFF (zero or low amplitude). 1.
📘 Example: 1.
If 1 = high wave, 0 = no wave 1.
So for 1010: wave, no wave, wave, no wave 1.
2. ✅ FSK (Frequency Shift Keying): 1.
 Only frequency changes. 1.
1.
 Binary 1 = one frequency,
1.
Binary 0 = another frequency.
1.
📘 Example:
1.
If 1 = fast wave (high freq), 0 = slow wave (low freq) 1.
So for 1010: fast, slow, fast, slow For every bit change (1→0 or 0→1), there is a corresponding
3. ✅ PSK (Phase Shift Keying): change in the ASK waveform.
 Only phase changes. 2. During logic 1, the carrier wave continues with constant
 Binary values are sent by changing the wave's angle. amplitude and frequency.
📘 Example: 3. During logic 0, the waveform is completely off — no
If 1 = wave starts at 0°, 0 = wave starts at 180° wave is present.
So for 1010: 0°, 180°, 0°, 180° 4. The result is a signal that switches between ON and OFF
Bit Rate vs Baud Rate: – just like a flashlight signaling Morse code.
Term Meaning Unit
🧠 Real-Life Analogy:
bits per second Think of a torch:
Bit Rate Number of bits sent per second  You turn it ON for 1
(bps)
 You turn it OFF for 0
Baud Number of symbols (signal symbols per The light turning ON and OFF based on your binary message is
Rate changes) per second second similar to how ASK sends digital data over analog signals.
ask bandwidth and psd waveform Block Components and Function:
The bandwidth of ASK signal is dependent on the bit rate of 1. Balance Modulator
input data.  This part multiplies the received ASK signal with a
reference carrier signal (generated locally).
 This is just like reversing what the ASK modulator did.
1. Bit Duration (Tb): tb=1/fb  It helps bring the signal back to baseband (low
Time to send one bit frequency) for analysis.
2. Bit Rate (fb): 2. Integrator
Number of bits per second (bps) fb = 1/ Tb  This acts like a low-pass filter.
3. Baud Rate = Bit Rate  It looks at the signal over a short time (one bit interval)
In binary ASK, 1 bit = 1 signal change, so baud = bit and averages the energy in the signal.
rate.  If the received signal is strong (like a sine wave), the
integrator gives a higher output.
🔷 ASK Power Spectral Density (PSD)  If no signal (bit 0) is received, the integrator output is
🧠 Understanding PSD: near zero.
 The ASK signal is the product of the binary data 3. Decision Device
(square pulses) and a sinusoidal carrier.  This compares the integrator output to a preset
 When you modulate like this, it shifts the baseband
o If output > threshold ⇒ bit 1
threshold.
spectrum of the data around the carrier frequency ±fc
------------------------------------------------------------------------------------ o If output ≤ threshold ⇒ bit 0
------------------------------------------------------------------------------------
🔷 What is an ASK Modulator? What is a Non-Coherent ASK Demodulator?
An ASK modulator creates an ASK signal by combining a digital A non-coherent ASK demodulator extracts the original binary
signal (made of 1s and 0s) with a high-frequency carrier signal data (1s and 0s) from the received ASK signal without using a
(a sine wave). reference carrier (i.e., no need to match the phase of the
carrier).
🔧 Components Used:
1. Digital Input – This is your binary data like: 1011001 �
It’s in unipolar NRZ format, which means: �
o 1 is represented as positive voltage
o 0 is represented as zero voltage
2. Carrier Signal – A continuous sine wave:
3. Balanced Modulator – This is the main block that How It Works (Easy Steps):
multiplies the digital data with the sine wave. 1. Input = Received ASK signal (sine wave for 1, nothing
for 0)
2. Envelope Detector (like a diode and capacitor):
o Detects the amplitude (strength) of the
incoming signal.
o Converts the high-frequency wave into a
smooth voltage signal.
3. Low-Pass Filter:
o Removes high-frequency ripples.
------------------------------------------------------------------------------------ o Keeps only the slow-changing envelope (i.e.,
Coherent ASK Demodulator: A coherent ASK demodulator is a the outline of the wave).
circuit that receives an ASK signal (the one we transmitted), 4. Decision Device:
and extracts the original binary data (1s and 0s) from it using a o Compares the filtered signal to a threshold.
known (synchronized) carrier signal. o If above threshold → bit 1
o If below threshold → bit 0
✅ Advantages of ASK:
2. Simple to Implement
o Easy circuit design for both modulation and
demodulation.
3. Low Bandwidth Requirement
o Requires less bandwidth compared to some
other modulation techniques like FSK.
4. Cost-Effective
o Since the hardware is simple, it is inexpensive
to build and maintain.

1. Good for Short-Distance Communication

o Works well in systems where the signal doesn’t
 travel too far, like remote controls or optical
communication.

❌ Disadvantages of ASK:
1. Very Sensitive to Noise
o Any small change in signal amplitude due to
noise can cause bit errors.
2. Low Power Efficiency
o Not suitable for power-limited systems (like
satellites or wireless sensors).
3. Poor Performance in Long-Distance or Wireless ------------------------------------------------------------------------------------
Transmission
o Amplitude can be easily distorted by fading or
interference, making it unreliable in such
environments.
4. Not Ideal for High-Speed Data
o Because of its noise sensitivity, ASK is not good
for transmitting fast-changing data over noisy
channels.
------------------------------------------------------------------------------------
🔹 What is Frequency Shift Keying (FSK)?
FSK is a digital modulation technique where the frequency of a
high-frequency carrier signal is changed depending on the
binary input data (1s and 0s).
 Amplitude and phase stay constant How Does the BFSK Modulator Work?
 Only frequency changes 1. Binary Data Input:
o You start with a stream of 1s and 0s (e.g.,
💡 Example: 10110).
Let’s say: 2. NRZ Encoding:
 Binary 1 = use a higher frequency (e.g., f₁ = 1200 Hz) o Convert the 1s and 0s into a signal where:
 Binary 0 = use a lower frequency (e.g., f₂ = 1000 Hz)  1 = +1 (high)
So, the output waveform will “shift” between 1200 Hz and  0 = –1 (low)
1000 Hz depending on the input data. 3. Two Modulators (M1 & M2):
o The encoded signal is sent to two balance
modulators:
 M1 uses frequency f1 (for binary 1)
 M2 uses frequency f2 (for binary 0)
4. Carrier Inputs:
o M1 gets a carrier wave of f1
o M2 gets a carrier wave of f2
5. Linear Adder:
o The outputs from M1 and M2 are added.
o But only one of them is active at a time
(depending on the input bit).
o So, the final output is a wave with frequency f1
or f2, depending on the input bit.

✅ Advantages of BFSK:
🔸 Mathematical Expression (Binary FSK or BFSK):
1. More reliable than ASK – Less affected by noise
and signal amplitude variations.
2. Good for long-distance transmission – Performs
better in wireless and radio systems.
3. Simple to implement – Especially for non-
coherent demodulation.
4. Constant amplitude – Helps reduce distortion in
power amplifiers.
❌ Disadvantages of BFSK: Channel Coding Theorem
1. Takes more bandwidth – BFSK requires more
bandwidth compared to ASK or PSK.
2. Less power-efficient than PSK – It needs more power
to achieve the same error performance.
3. Needs two carriers – Two separate frequencies must
be generated and switched.
4. More complex than ASK – Requires more circuitry for
modulation and demodulation.
------------------------------------------------------------------------------------

🎯 What is Source Coding?

Source coding means converting the original data (from a
voice, image, video, or sensor) into a more compact and
efficient digital form, so it uses less bandwidth and fewer bits
— without losing important information.

✅ Definition (in simple words):

Source coding is the process of removing unnecessary or
redundant bits from the data, and compressing it for efficient
transmission or storage.

🎯 Objectives of Source Coding:

1. ✅ Efficient Use of Bandwidth
→ Reduce the number of bits needed to send the same
message.
2. ✅ Faster Data Transmission
→ Smaller data means it can be sent faster through the
channel.
3. ✅ Reduced Cost & Power
→ Less data to send means saving on energy, time, and
cost.
4. ✅ Maintain Acceptable Quality
→ Even after compression, the output should be
understandable and useful.

💡 Why Source Coding is Needed?

🔸 For Analog Sources (e.g. microphone):
 The audio signal may have repeating patterns or
silence — source coding removes such unnecessary
amplitude details.
 It uses knowledge like autocorrelation (repeating parts
of the waveform).
🔸 For Discrete Sources (e.g. computer data):
 Text or symbols may repeat or follow patterns.
 Source coding removes this symbol redundancy using
compression techniques (like Huffman coding).

🧠 Real-Life Example:
 When you zip a file or compress an image (like JPG),
you're doing source coding.
 It makes the file smaller without losing quality (or with
minimal acceptable loss).

📌 Why Error-Control is Important in Data Communication

In real-world communication systems, errors naturally occur due to noise or interference.
To make sure the data received is correct, we use error-control techniques and coding.

⚠️Causes of Data Transmission Errors

 🌩 Natural interference (lightning, static, etc.)

 🚗 Man-made noise (engines, electronics)
 📶 Imperfect channels (cables, wireless)

So, errors can happen in any medium: wired, wireless, or optical.

💡 Types of Errors

Type Meaning Impact

Single-bit error Only one bit changes (e.g., 1 ➝ 0 or 0 ➝ 1) Affects only one character
Two or more bits change, but not necessarily
Multiple-bit error Affects multiple characters
together
Very common in real channels and harder to
Burst error Two or more bits in a row are wrong
fix

📉 What is BER (Bit Error Rate)?

 BER = Bit Error Rate

 It’s the ratio of wrong bits to total bits sent.

Example:
If 1 wrong bit in 1000 sent →
BER = 1 / 1000 = 10⁻³

✅ Why We Use Error-Control Coding

 To detect errors (Error Detection)

 To correct errors (Error Correction)
 To improve reliability of digital communication

✅ Error Detection Techniques

These techniques help identify if any error has occurred during data transmission. They don’t correct the error—only
detect it.
1. Parity Bit

🧠 Idea: Add one extra bit (parity bit) to make the number of 1s either even or odd.

 Even parity: Total number of 1s (including the parity bit) = even

 Odd parity: Total number of 1s = odd

📦 Example:
Data = 1010001 → has 3 ones
Using even parity → add 1 to make it even → 10100011

✔️Good for detecting single-bit errors, but not reliable for multiple-bit errors.

2. Checksum

🧠 Idea:

 Add all data bytes (or words) using binary addition.

 Send the sum (checksum) along with the data.
 Receiver adds again to verify.

📦 Example:

 Send: 1001, 1100, 0101 → Sum = 10010 → Checksum = 0010 (lower bits)
 Receiver adds: If total = 0 → No error

✔️Good for burst errors, used in TCP/IP networks.

3. Cyclic Redundancy Check (CRC)

🧠 Idea: Treat data as a long binary number.

Divide by a fixed binary divisor (polynomial).
Send remainder (CRC bits) with the data.

📦 Example:

 Data: 1101011011
 Generator: 1011
 Remainder = CRC bits → Send: Data + CRC

✔️Very powerful, used in Ethernet, USB, HDLC etc.

LRC – Longitudinal Redundancy Check

📌 Concept:

 LRC works across multiple rows of data.

 Adds a parity byte (LRC byte) vertically over all the columns.
 This means you check each bit position in all bytes, column by column.
📦 Example:

Data Bytes
10110010
01001101
11011000
LRC Byte: ?

→ LRC is calculated by taking the parity of each column and forming a new byte.
→ This LRC byte is added at the end for checking at the receiver.

MODULE 5
🔟 Top Applications of Wireless Communication:

1️⃣ Mobile Communication (Cell Phones)

 The most common use of wireless communication.

  It allows people to make calls, send messages, and use the internet from anywhere.

📱 Example: Calling or using WhatsApp on your mobile phone.

2️⃣ Wi-Fi (Wireless LAN)

 Wi-Fi provides wireless internet access in homes, schools, offices, and cafes.
 It connects devices like laptops, phones, and smart TVs without cables.

📶 Example: Using your laptop to browse the internet over home Wi-Fi.

3️⃣ Bluetooth

 Short-range wireless communication between devices.

 Mainly used for file sharing, connecting headphones, or other peripherals.

🎧 Example: Listening to music using Bluetooth headphones.

4️⃣ Satellite Communication

 Uses satellites orbiting the Earth to send and receive signals.

 Used in TV broadcasting, GPS navigation, and military operations.

Example: Watching live cricket match via satellite TV (like Tata Sky, Airtel DTH).

7️⃣ GPS (Global Positioning System)

 Provides real-time location tracking using satellite signals.

📍 Example: Using Google Maps to find directions.

5️⃣ Remote Control Systems

 Wireless technology is used in remote controls for TVs, ACs, drones, etc.

🎮 Example: Controlling a drone with a remote or mobile app.

6️⃣ Radio Broadcasting

 Transmits audio signals wirelessly over long distances.

 People can tune into radio channels without wires.

📻 Example: Listening to FM radio in your car or on your phone.

8️⃣ Medical Applications

  Wireless technology helps in remote patient monitoring, body-worn health devices, and emergency
communication in hospitals.

🏥 Example: A heart patient wearing a wireless ECG monitor that sends reports to the doctor’s phone.

9️⃣ Military and Defense

 Used for secure communication, surveillance, radar, and missile guidance.

Example: Soldiers using wireless headsets and encrypted radios in the battlefield.

🔟 Smart Homes / IoT (Internet of Things)

 Devices like lights, fans, door locks, and cameras are connected wirelessly and controlled via mobile apps.

🏠 Example: Turning on lights at home using Alexa or Google Assistant.

✅ Advantages of Wireless Communication

Advantage Explanation
📶 No physical cables No need for wires, which saves cost and reduces mess.
🚀 Mobility Allows users to move freely while staying connected (e.g., mobile phones, Wi-Fi).
Signals can be transmitted over long distances, even to remote areas (e.g., satellite
🌍 Wider Coverage
communication).
🧰 Easy Installation Faster and simpler to set up compared to wired systems.
🔄 Flexibility Easy to upgrade, expand, or shift devices without major changes.
💬 Real-time Communication Enables instant voice, video, and data sharing.

❌ Disadvantages of Wireless Communication

Disadvantage Explanation
📡 Signal Interference Can be affected by weather, walls, other signals, etc.
🔒 Security Risks Wireless signals can be intercepted or hacked if not properly secured.
🧱 Limited Bandwidth Wireless systems often have less bandwidth than wired systems.
🔋 Power Consumption Devices like phones, routers, and Bluetooth gadgets need batteries or power.
📉 Slower Speed Wireless networks can be slower than high-speed wired connections.
📶 Signal Drop/Dead Zones Connection may be weak or lost in certain areas (basements, elevators, etc.)

📶 Evolution of Next Generation Networks (NGN) – Simple Explanation

✅ What is NGN?
Next Generation Network (NGN) is a modern communication network that combines voice, video, and data services
over a single network, mainly using the Internet (IP).

📜 Evolution – Step-by-step:
Generation Features Example
1G – Analog Only voice calls using analog signals Old brick-type mobile phones
2G – Digital Voice + SMS (digital signals) Basic phones with keypad (Nokia 1100)
3G – Internet Voice + SMS + Internet Phones with internet browsing (3G data)
4G – High-
Fast Internet + Video calls + Apps Smartphones with YouTube, Zoom
speed
5G – Smart
Ultra-fast + Smart Devices + Low delay Self-driving cars, smart cities, 5G mobile
World
Combines all services (voice, data, video) on Using one internet connection for everything – calls,
NGN – Future
one IP-based network YouTube, Zoom, IoT devices

🔍 Comparison of Wireless Systems

Feature 2G 3G 4G 5G
Speed Up to 64 kbps Up to 2 Mbps Up to 100 Mbps 1–10 Gbps
Data Support Basic (SMS) Internet, Email HD video, VoLTE 8K video, IoT
Technology GSM/CDMA WCDMA/HSPA LTE mmWave, OFDM
Latency High Medium Low Very low (<1 ms)
Use Cases Voice calls Browsing, video Streaming, apps AI, VR, automation

📶 Cell Structure and Cluster – Simple Explanation

🧩 What is a Cell in Mobile Networks?
 A cell is a small area of coverage served by a mobile tower (called a base station).
 Each cell has its own antenna and radio equipment to provide network service (like calling or internet) to mobile
users in that area.
 The center of a cell is called the cell site – where the tower is placed.

⚪ Why Not Circular Cells?

 Ideally, signals spread like a circle (from antennas).
 But if we use circles to cover the whole city, there will be overlaps (too much signal) or gaps (no signal).
 Circles cannot fit tightly without leaving space or overlapping.

🔷 So What Shape is Used?

 We use Hexagons (like honeycomb patterns) to represent cells.
 Hexagons:
o Fit tightly with no overlaps or gaps
o Cover maximum area for a given radius
o Are easy to calculate and plan for designing networks
🔼 Other Shapes?
 Triangle and square shapes are also possible.
 But hexagon is best for mobile networks – closest to a circle and forms a neat tiling pattern.

📡 What is a Cluster?
 A cluster is a group of cells where each cell uses different frequencies.
 Within one cluster, no two cells use the same frequency to avoid interference.
📌 Why?
To avoid signal clash or interference between nearby towers.

🔁 Reuse of Frequencies (Reuse Pattern)

 Once a cluster is formed, it can be repeated in other locations with the same frequency set because enough
distance keeps interference low.
🧠 Example:
 Let’s say a 7-cell cluster is formed using 7 different frequency sets (F1 to F7).
 This cluster can be repeated in another city block, far enough to avoid signal clash.

🔢 Common Cluster Sizes:

+ Cluster Size (K) Meaning
1 All cells use same frequency (not practical)
3 3 different frequency groups
4, 7, 9, 12, 13 Common in real networks for good balance between reuse and interference

🧠 Real-Life Example:
Imagine you are in a city.
The mobile network divides the city into small hexagonal zones (cells).
 Each zone has its own tower giving strong signal.
 A group of zones (cells) form a cluster – they use different frequencies to avoid confusion.
 These clusters are repeated throughout the city or country to cover the whole area.

✅ Summary:
 Cell = A small service area with its own antenna.
 Hexagon shape is used for perfect coverage and planning.
 Cluster = Group of cells with unique frequencies.
 Cluster Reuse = Same set of frequencies reused in other areas safely.

📡 Reuse of Frequencies – Easy Explanation with Example

Definition:
Frequency reuse is a technique used in cellular systems where the same set of frequencies (or channels) is reused in
different cells that are far apart from each other. This increases spectrum efficiency without causing interference.

🧠 Why is it needed?
The radio frequency spectrum is limited. To serve more users with the available frequencies, we reuse frequencies in a
smart way by separating them with enough distance.

🧱 How does it work?

 In a cluster of cells, each cell is assigned a unique frequency set (so no interference inside the cluster).
 The same frequency set is reused in another cluster that is sufficiently far to avoid interference.
 This helps cover large areas using limited frequency bands.