THEORY EXAMINATION (SEM–VIII) 2016-17 WIRELESS & MOBILE COMMUNICATION

SECTION A – Basic Concepts of Wireless & Mobile Communication

Section A contains short questions related to cellular communication, wireless technologies, GSM features, and mobile networking concepts. 

(a) If I = 3 and J = 0, Find Cluster Size

In cellular systems, cluster size is calculated using the formula:

N=i2+ij+j2N = i^2 + ij + j^2N=i2+ij+j2

Given:

i=3,j=0i = 3, \quad j = 0i=3,j=0 N=32+(3×0)+02N = 3^2 + (3×0) + 0^2N=32+(3×0)+02 N=9N = 9N=9

Therefore, the cluster size = 9.

(b) What is Frequency Reuse?

Frequency reuse is a technique used in cellular networks where the same frequency channels are reused in different cells that are sufficiently far apart to avoid interference.

This method increases the number of users that can be supported by the system without requiring additional spectrum.

Frequency reuse improves network capacity and efficient use of available bandwidth.

(c) Define Brewster Angle

The Brewster angle is the angle of incidence at which a reflected electromagnetic wave becomes completely polarized and the reflection coefficient becomes zero.

It is calculated using:

θB=tan⁡−1(εr)\theta_B = \tan^{-1}(\sqrt{\varepsilon_r})θB​=tan−1(εr​​)

Where:
εr = relative permittivity of the medium.

This concept is important in wireless propagation and antenna design.

(d) What is Handoff?

Handoff (or handover) is the process of transferring an ongoing call or data session from one cell base station to another as a user moves across cell boundaries.

Handoff ensures uninterrupted communication for mobile users.

There are two main types:

Hard handoff

Soft handoff

(e) Two Service Aspects in IS-95

IS-95 is a CDMA-based mobile communication standard.

Two important service aspects are:

Voice communication services

Data transmission services

It supports digital voice and limited data communication.

(f) Signalling Features in GSM

GSM signalling provides communication between mobile stations and network infrastructure.

Important signalling features include:

Call setup and termination

Mobility management

Location updating

Authentication and security

Signalling ensures efficient network management and communication control.

(g) Reason Behind the Name Bluetooth

The name Bluetooth comes from a Danish king named Harald Bluetooth, who united Denmark and Norway.

Similarly, Bluetooth technology was named to represent its goal of unifying communication protocols between different devices.

Bluetooth is used for short-range wireless communication.

(h) Examples of Wi-Fi Technology

Wi-Fi technology enables wireless internet access.

Two common Wi-Fi standards include:

IEEE 802.11a

IEEE 802.11b

Other examples include 802.11g and 802.11n.

(i) Demerit of Ad Hoc Network

A major disadvantage of ad hoc networks is the lack of centralized control, which can lead to network management difficulties.

Other disadvantages include:

Limited security

Frequent route changes due to node mobility

Limited scalability

(j) Three Main Wireless Technologies

The three major wireless technologies are:

Wi-Fi – used for wireless local area networks.

Bluetooth – used for short-range communication between devices.

Cellular networks – used for wide-area mobile communication.

These technologies enable wireless connectivity in modern communication systems.

SECTION B – Intermediate Concepts of Wireless Communication

Section B focuses on cellular network design, diversity techniques, mobile communication evolution, and fading effects. 

(a) Channel Assignment Strategies

Channel assignment determines how frequency channels are allocated to cells in a cellular network.

The main strategies include:

Fixed Channel Assignment

Each cell is assigned a fixed number of channels. If all channels are in use, new calls are blocked.

Dynamic Channel Assignment

Channels are assigned dynamically based on demand and availability.

Hybrid Channel Assignment

A combination of fixed and dynamic assignment techniques.

These strategies help manage network traffic efficiently.

(b) Diversity Techniques in Wireless Communication

Diversity techniques improve signal reliability by using multiple signal paths.

Types include:

Space Diversity

Uses multiple antennas separated in space.

Frequency Diversity

Uses different frequency channels to transmit the same signal.

Time Diversity

Transmits the same signal at different time intervals.

Polarization Diversity

Uses antennas with different polarization orientations.

These techniques help reduce fading and signal loss.

(c) Evolution of Mobile Radio Communication

Mobile communication evolved through several generations:

1G – Analog communication systems such as AMPS.

2G – Digital communication systems such as GSM and CDMA.

3G – Introduced multimedia services and high-speed data.

4G – Provided broadband internet and high data rates.

5G – Supports IoT devices, ultra-low latency, and very high data speeds.

(d) Next Generation Network (NGN)

Next Generation Networks integrate voice, data, and multimedia services using packet-switched networks.

Features include:

High-speed data communication

Internet-based services

Convergence of telecom and internet networks

Improved network flexibility

NGN provides efficient communication infrastructure for modern applications.

(e) Mobile Ad Hoc Networks (MANET)

Mobile Ad Hoc Networks are decentralized wireless networks where mobile devices communicate directly without fixed infrastructure.

Features include:

Self-configuring network

Dynamic topology

Peer-to-peer communication

Applications include disaster recovery, military communication, and emergency networks.

(f) RAKE Receiver

A RAKE receiver is used in CDMA systems to combine signals received through multiple paths.

Multipath signals arrive at the receiver with different delays. The RAKE receiver processes these signals separately and combines them constructively.

This improves signal strength and reduces fading effects.

(g) Frequency Hopped Multiple Access and CDMA

Frequency Hopping Multiple Access (FHMA)
Users transmit signals by rapidly switching between different frequency channels.

Code Division Multiple Access (CDMA)
Users share the same frequency band but use different spreading codes to separate signals.

CDMA improves spectrum efficiency and reduces interference.

(h) Types of Fading in Wireless Communication

Fading refers to variations in signal strength due to propagation conditions.

Types include:

Fast fading

Slow fading

Flat fading

Frequency selective fading

Understanding fading helps improve wireless communication system design.

SECTION C – Advanced Concepts of Wireless Communication

Section C questions focus on advanced topics such as vocoders, equalization techniques, and GSM architecture. 

(1) Types of Vocoders

A vocoder (voice coder) is a device used to compress voice signals for efficient transmission.

Types include:

Channel Vocoder

Divides speech into frequency bands and transmits parameters.

LPC Vocoder

Uses linear predictive coding to model the vocal tract.

CELP Vocoder

Code Excited Linear Prediction provides high-quality speech compression.

Vocoders are widely used in digital communication systems.

(2) Equalization Techniques

Equalization is used to reduce inter-symbol interference caused by multipath propagation.

Types of equalizers include:

Linear equalizer

Decision feedback equalizer

Adaptive equalizer

Equalizers restore distorted signals and improve communication reliability.

(3) GSM Architecture

The GSM system architecture consists of three major components:

Mobile Station (MS)

Includes the mobile phone and SIM card used by subscribers.

Base Station Subsystem (BSS)

Includes:

Base Transceiver Station (BTS)

Base Station Controller (BSC)

Responsible for radio communication with mobile devices.

Network Switching Subsystem (NSS)

Includes:

Mobile Switching Center (MSC)

Home Location Register (HLR)

Visitor Location Register (VLR)

This subsystem manages call routing and subscriber information.

Conclusion

Wireless and mobile communication technologies form the foundation of modern telecommunications. Concepts such as cellular networks, diversity techniques, fading, GSM architecture, and vocoders help engineers design efficient and reliable communication systems.

These technologies enable mobile connectivity, wireless internet, and advanced communication services used worldwide.