Table of Contents

1. Introduction to Cellular Systems

 

2. Architecture Overview

 

 3. GSM Services

 

4. The Air Interface

 

5. Protocols

 

6. Speech and Channel Coding

 

7. Mobility Management

 

8. Radio Resource Management

 

9. Call Management

 

10. GSM Security

 

11. Billing Procedures Overview

 

12. GSM Evolution

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Course Objectives and Structure

Courrse Objjeeccttiivveess

• Be familiar with the development of 2G mobile systems
• Describe the architecture of a GSM network
• Appreciate the main services provided within a GSM network
• Understand the various facets of the GSM air interface including, Access
structures, frequency allocations, physical and logical channels
• Appreciate GSM transmission and signalling protocols
• Describe the methods of speech and error coding on the air interface
• Understand the principals mobility management
• Understand the principles of radio resource management
• Describe the processes involved in connection management
• Appreciate the security measures implemented by GSM
• Understand GSM mechanisms for customer billing
• Be familiar with the future evolution of GSM including 2G+ technologies
• Describe the evolution of GSM towards 3G systems

1. Introduction to Cellular Systems

1.1 Introduction

This section reviews the characteristics of first and second generation cellular systems and is
followed by an overview of the functional blocks of GSM architecture, and its functional
entities. Topics covered include:
· Cellular Radio
· 1st generation cellular characteristics and systems
· 2nd generation cellular characteristics and non-GSM systems
· GSM development and characteristics
· Worldwide roll-out of cellular systems and subscriber distribution



1.2 Cellular Radio

Mobile Radio Networks

• There are three major types of terrestrial
mobile communications technologies:
PSTN
Cordless
• Cordless Communication:
Users are provided limited mobility from a
dedicated base station

• Paging:

Brief numeric, alphanumeric or voice messages
are sent to the subscriber typically using
simultaneous broadcasting.

• Cellular:

Users are provided wide area mobility from
multiple base stations with handover
permitted
MSC

Cellular

Users are provided wide area mobility from
multiple base stations with handover
permitted

Cellular Radio Network Characteristics

• Mobile Radio Network based on cellular structure for areas
coverage
• Frequency reuse required due to limited frequency availability
(frequency re-use patterns)
• Mobility between cell areas possible (handover)

1.3 1st Generation Cellular Systems

1st Generrattion Cellllullarr Charractterriisttiics

• Widespread Introduction in early 1980s
• Analogue modulation
• Frequency Division Multiple Access
• Voice traffic only
• No inter-network roaming possible
• Insecure air interface
The 1st Generation of Cellular
Technology makes use of analogue
modulation techniques such as FM
1.3 1st Generation Cellular Systems
1. Introduction to Cellular Systems

In early networks, the emphasis was to provide radio coverage with little consideration for
the number of calls to be carried. As the subscriber base grew, the need to provide greater
traffic capacity had to be addressed.

1stt Generation Standards

• AMPS (Analogue Advanced Mobile Phone System)
• North American Standard in cellular band (800MHz)
• TACS (Total Access Communications System)
• UK originated Standard based on AMPS in 900MHz band
• NMT (Nordic Mobile Telephony System)
• Scandinavian Standard in 450MHz and 900MHz bands
• C-450
• German Standard in 450MHz band
• JTACS (Japanese Total Access Communications System)
• Japanese Standard in 900MHz band
Analogue/AMPS
Nokia 252

1st Generation Planning

• Macrocellular
• High sites for coverage driven planning
• Antennas above roof height
• Frequency planning required
• For networks with more cells than frequencies
these must be planned
• Large cell size
• Order 30km
• Hard handover
• Mobile only ever connected to a single cell
• Hexagonal Grid Representation

1.4 2nd Generation Cellular Systems

Digital systems offer considerable advantages in terms of capacity and security and introduce
new possibilities for data traffic.

2nd Generation Characteristics

• Widespread Introduction in 1990’s
• Uses digital modulation
• Variety of multiple access strategies
• More efficient use of radio spectrum
• Voice and low rate circuit switched data
• International roaming capability
• Secure air interface
• Compatibility with ISDN
While first generation systems used a cellular structure and frequency re-use patterns, digital
systems developed this concept to include multi-layer cellular patterns (microcells and
macrocells). The greater immunity to interference inherent in digital transmission allowed
tighter frequency re-use patterns to be implemented.

cdmaOne Characteristics

• First networks in 1996
• Derived from Qualcomm IS-95 air
interface
• Largely American subscriber base with
some Asian networks
• Code Division Multiple Access
• The closest 2nd generation standard to
many of the 3rd generation standards
• ANSI-41 core network
• Chip rate of 1.2288Mcps
cdmaOne phones

D-AMPS/PDC Characteristics

• TDMA (D-AMPS)
• North American TDMA/FDMA based
standard based upon AMPS
• Predominantly used in North and
South America
• ANSI-41 Core Network
• Planning Similar to GSM
• PDC
• Japanese TDMA/FDMA based
standard
• Predominantly used in Asia
• Planning Similar to GSM

1.5 GSM Development and Characteristics

Originally GSM referred to the European working party set up to establish a new standard
(‘Groupe Speciale Mobile’) but was later amended to reflect a more global application (Global
System for Mobile communications).

Cellular Structure

• The aim of a cellular system is to make best use of the
available frequencies (spectrum)
• The cellular structure allows the re-use of
frequencies across the network
• Planning the pattern of this frequency re-use is a
key part of the system design
• Hexagonal pattern best represents interlocking grid of cells

GSM Planning

• Key Network planning parameters

• Coverage – getting a usable radio signal to all areas in the
network
• Capacity – handling the call traffic generated by the subscribers
• Quality – low interference, few calls dropped etc.

• Optional parameters requiring planning

• Hierarchical Cell Structures (macrocell/microcell)
• Frequency Hopping
• Discontinuous Transmission
• Power Control

• Subscriber/traffic analysis

• Capacity limited by number of TRX’s
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