About this previous year paper
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.