IT602 β€’ Wireless and Mobile Computing

Unit 1 Wireless Communication Fundamentals

Complete exam-oriented notes on antennas, propagation, fading, multiple access, cellular systems, handoff, power control, sectorization and traffic engineering.

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Home β€Ί Wireless and Mobile Computing β€Ί Unit 1

1. Introduction to Wireless Communication

Wireless communication is the transfer of information without physical cables by using electromagnetic waves.

Examples include mobile communication, Wi-Fi, Bluetooth, satellite links and radio broadcasting.

Information Source β†’ Transmitter β†’ Wireless Channel β†’ Receiver β†’ Destination

Advantages

  • Mobility
  • Easy installation
  • Wide coverage
  • Flexible expansion

Limitations

  • Interference
  • Fading
  • Limited spectrum
  • Security risks

2. Antenna and Radiation Pattern

An antenna converts electrical signals into electromagnetic waves and received waves back into electrical signals.

Radiation Pattern

A radiation pattern shows antenna radiation strength in different directions.

  • Main lobe: maximum radiation direction.
  • Side lobe: smaller unwanted radiation.
  • Back lobe: radiation opposite to the main lobe.
  • Beamwidth: angular width of the main lobe.
  • Null: minimum-radiation direction.
Main Lobe / Side Lobe/ \Side Lobe -----------------/----\---------------- \__/ Back Lobe

3. Antenna Types and Gain

TypeDescriptionUse
DipoleSimple two-conductor antennaRadio and TV
MonopoleHalf dipole over ground planeMobile and vehicles
Yagi-UdaDirectional, high gainTV reception
ParabolicDish reflectorSatellite and radar
PatchCompact printed antennaMobiles and GPS
HelicalHelix-shaped conductorSatellite links
Antenna gain measures how effectively an antenna directs energy in a chosen direction.
Gain = Efficiency Γ— Directivity

4. Propagation Modes

Ground Wave

Follows the Earth’s surface and is useful at low and medium frequencies.

Sky Wave

Returns to Earth after interaction with the ionosphere and supports long-distance communication.

Line-of-Sight

Requires direct or nearly direct visibility between transmitter and receiver.

ModeTypical UseExample
Ground waveLow/medium frequencyAM radio
Sky waveHigh frequencyShortwave radio
Line of sightVHF and aboveMobile, TV, satellite

5. Types of Fading

Fading is variation in received signal strength due to propagation conditions and multiple signal paths.

Large-Scale Fading

  • Path loss: signal weakens with distance.
  • Shadowing: obstacles block the signal.

Small-Scale Fading

  • Multipath fading
  • Fast fading
  • Slow fading
  • Flat fading
  • Frequency-selective fading
Direct Path -------------------> Reflected Path β†’ Building -----> Diffracted Path β†’ Obstacle ----> Receiver

6. Wireless Digital Communication Model

Information ↓ Source Encoder ↓ Channel Encoder ↓ Digital Modulator ↓ Wireless Channel ↓ Demodulator ↓ Channel Decoder ↓ Destination
  1. Source encoding converts information into efficient digital form.
  2. Channel coding adds error protection.
  3. Modulation maps bits onto a carrier.
  4. The channel introduces noise, interference and fading.
  5. The receiver recovers the original information.

7. Multiple Access Techniques

Multiple access techniques allow many users to share limited wireless resources.

SDMA

Separates users by space using cells, sectors or directional beams.

FDMA

Assigns a separate frequency band to each user.

TDMA

Allows users to share one frequency in different time slots.

CDMA

Allows users to transmit at the same time and frequency using unique spreading codes.

TechniqueSeparationMain Feature
SDMASpaceCells and sectors
FDMAFrequencyDedicated band
TDMATimeDedicated slot
CDMACodeUnique spreading code

8. DAMA, PRMA and MAC/CA

DAMA

Demand Assigned Multiple Access allocates resources only when requested.

PRMA

Packet Reservation Multiple Access combines random access with slot reservation.

MAC/CA

Multiple Access with Collision Avoidance attempts to prevent collisions before transmission.

  1. Sense the channel.
  2. Wait if busy.
  3. Select a random backoff time.
  4. Transmit when idle.
  5. Receive acknowledgement.

9. Cellular Network Organization

A cellular network divides a service area into cells, each served by a base station.
Cells β†’ Base Stations β†’ Mobile Switching Centre β†’ Public Network

Main Components

  • Mobile station
  • Base transceiver station
  • Base station controller
  • Mobile switching centre
  • Location databases

Frequency Reuse

The same frequencies are reused in sufficiently separated cells to increase capacity.

10. Cellular System Operations

  1. The mobile registers with the network.
  2. The network records its location.
  3. For an outgoing call, the mobile requests a channel.
  4. For an incoming call, the network pages the mobile.
  5. The network assigns radio resources.
  6. Handoff occurs when the mobile changes cells.
  7. Resources are released after the call.

11. Mobile Radio Propagation Effects

  • Reflection: waves bounce from large surfaces.
  • Diffraction: waves bend around obstacles.
  • Scattering: waves spread from small objects.
  • Doppler shift: frequency changes because of motion.
  • Multipath: several copies arrive by different paths.
  • Delay spread: signal copies arrive at different times.

12. Handoff

Handoff transfers an active mobile connection from one channel, base station or cell to another.
  • Hard handoff: break before make.
  • Soft handoff: make before break.
  • Horizontal handoff: between similar networks.
  • Vertical handoff: between different technologies.

Decision Factors

  • Signal strength
  • Signal quality
  • Interference
  • Mobile speed
  • Network load

13. Power Control and Sectorization

Power Control

Power control adjusts transmitter power to maintain signal quality, save battery and reduce interference.

  • Open-loop power control
  • Closed-loop power control

Sectorization

Sectorization divides a cell into angular sectors served by directional antennas.

  • Reduces co-channel interference
  • Improves capacity
  • Improves signal quality

14. Traffic Engineering

Traffic engineering estimates the number of calls and channels needed for a desired service level.
Traffic Intensity A = Ξ» Γ— H Erlangs

Ξ» is the average call-arrival rate and H is average holding time.

Infinite Sources

The user population is assumed very large, so arrival rate is approximately independent of active users.

Lost Calls Cleared

A blocked call leaves the system instead of waiting.

Grade of Service

The probability that a call is blocked or delayed beyond an acceptable limit.

Poisson Arrival Process

Models random and independent call arrivals at an average rate.

Note: The syllabus phrase β€œpoison arrival process” refers to the Poisson arrival process.

Unit 1 Summary

  • Antennas transmit and receive electromagnetic waves.
  • Propagation may be ground wave, sky wave or line of sight.
  • Fading changes received signal strength.
  • SDMA, FDMA, TDMA and CDMA separate users by space, frequency, time and code.
  • Cellular systems use cells, frequency reuse and handoff.
  • Power control reduces interference and saves battery.
  • Traffic engineering uses Erlang, Grade of Service and Poisson arrivals.

Important RGPV Exam Questions

Long Answer Questions

  1. Explain antenna, radiation pattern, antenna types and gain.
  2. Explain radio wave propagation modes.
  3. What is fading? Explain its types.
  4. Draw and explain the wireless digital communication model.
  5. Compare SDMA, FDMA, TDMA and CDMA.
  6. Explain DAMA, PRMA and MAC/CA.
  7. Explain cellular network organization and frequency reuse.
  8. Define handoff and explain its types.
  9. Explain power control and sectorization.
  10. Explain traffic intensity, lost calls cleared, Grade of Service and Poisson arrival process.

Short Answer Questions

  1. Define antenna gain.
  2. What is beamwidth?
  3. Define fading.
  4. What is MAC/CA?
  5. What is frequency reuse?
  6. Define hard handoff.
  7. What is Grade of Service?
  8. What is an Erlang?
Exam Strategy: Write definition, neat diagram, working, comparison, advantages and conclusion.

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Frequently Asked Questions

It measures how effectively an antenna directs energy in a selected direction.
Fading is variation in received signal strength due to propagation and multipath.
FDMA separates by frequency, TDMA by time and CDMA by code.
Handoff transfers an active connection from one cell or base station to another.
Yes. It is saved in localStorage.