explain m01- 1 gsm standardisation and technology.pdf

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GSM Standardisation GSM Standardisation and Technologyand Technology


Module objectives

DESCRIBE GSM ARCHITECTURE AND MAIN ELEMENTS

LIST RADIO ACCESS TECHNOLOGIES

DESCRIBE THE PRINCIPLES OF GMSK MODULATION

At the end of this module you will be able to …


Content

TECHNOLOGIES

GSM OVERVIEW

RADIO ACCESS

MODULATION


Introduction

TECHNOLOGIES

GSM OVERVIEW

RADIO ACCESS

MODULATION


GSM Evolutionary Steps


System architecture - GSM, GPRS and UMTS

BTS

RNC

BSCBTS

SGSN

GGSN@GPRS

infrastructure

UMTS infrastructure

MSC


Introduction

TECHNOLOGIES

GSM OVERVIEW

RADIO ACCESS

MODULATION


StandardisationETSI

European Telecommunications Standards Institute• Financed by EU• Co-operation of suppliers and operators• Specification of European telecommunications standards

ETSI- standards :• Cellular GSM 900/1800 - GPRS - UMTS• Cordless DECT• Paging ERMES• Trunked radio TETRA


GSM Bandwidth & Main Parameters900 MHz & 1800 MHz

• GSM 900 :

• GSM 1800 :

• Channel spacing 200kHz

• Usual bandwidth values (GSM900): 5 ..8 MHz per operator in one or more sub-bands

1710 1785 1805 1880

duplex distance: 95 MHz

890 915 935 960


Operator A Operator B Op. BOp. Anot allocated


• GSM 1900 :

• 2 x 60 MHz at channel spacing 200kHz ⇒ ~300 channels

• Band divided into sub-bands A..Fsub-bands A, B, C : 2 x 15 MHz spectrumsub-bands D, E, F : 2 x 5 MHz

1850 1910 1930 1990


Operator A Operator DOp. B Op. EOperator C Op. F

GSM Bandwidth & Main Parameters 1900 MHz


• E-GSM :

• E-GSM band: 880-890 MHz & 925-935 MHz

880 890 925 935


GSM Bandwidth & Main Parameters E-GSM


• GSM 900 and GSM 1800 are twins

GSM 900 GSM 1800• Frequency band 890 - 960 MHz 1710 - 1880 MHz

• Number of channels 124 (125) 372 (375)

• Channel spacing 200 kHz 200 kHz

• Multiplex technologies TDMA/FDMA TDMA/FDMA

• Mobile power 0,8 / 2 / 5 W 0,25 / 1 W

There are no major differences between GSM 900 and GSM 1800

GSM Bandwidth & Main Parameters Summary


NMS

NSSBSS

GSM Architecture & Interfaces

BSCHLR/AC/EIR

TCSM

MSC/VLR

BTS

AbisInterface

AterInterface

AInterface

AirInterface

TC

Ater’Interface

O&M Interface


Introduction

TECHNOLOGIES

GSM OVERVIEW

RADIO ACCESS

MODULATION


Multiple Access TechnologiesBasics

• Multiple access schemes are used to allow many mobile users to share simultaneously a finite amount of radio spectrum

• Multiple access enhances the capacity of the link

• Multiple access technologies can be grouped as narrowband and wideband systems, depending on how the available bandwidth is allocated to the users

ffc


200

100

50

Bandwidth Conventional radio systems

FDMA

Multiple Access TechnologiesFDMA

Frequency Division Multiple Access

• Individual radio channels are allocated to individual users on demand for the time of transaction

• Each radio resource is identified with the carrier frequency and the relative bandwidth

• Amplifiers and combiners may introduce intermodulation effects


Multiple Access TechnologiesTDMA

Time Division Multiple Access• The resource (time slot) is available only to a user for the time of transaction• High synchronization overhead & adaptive equalization are required• TDMA is mainly used in digital systems

T = Allocated time

t

Slot for user 1

Slot for user 2

Slot for user 3

Slot for user 5

Slot for user 7

Slot for user 8

Slot for user 4

Slot for user 6


Ti

0 1 0 0 1 x 0 1 1 1 0 0 1 0

1 1 0 1 1 1 0 0 1 1 0 0x=0

0 0 1 0 0 0 1 1 0 0 1 1x=1

Tc 1 chip

user information

W ≅ d i = 1 / Ti

each data bit is codedwith a chips code sequenceTc ≅ Ti/n ⇒ B ≅ 1/Tc ≅ n * W

W = modulation bandwidth before expansionB = modulation bandwidth after expansion

B >> W ⇒ “spread spectrum”G = “processing gain = bandwidth expansion factor (n = B/W)

Multiple Access TechnologiesCDMA

Code Division Multiple Access• Against near-far problem, power control is used

• Unlike FDMA and TDMA, CDMA has a soft capacity limit


Multiple Access TechnologiesSDMA & PR

Space Division Multiple Access• The radiated energy for each user is controlled in space• Normal application: sectorizedantennas• Future application: adaptive antennas

Packet Radio• The access to the radio channel is uncoordinated• Burst of data• Low spectral efficiency and delays• ALOHA algorithm is used for contentions


Time

Frequency

UL

DL

Time

Frequency

UL

DL

Duplex TechnologiesFDD & TDD

Frequency Division Duplex• UL & DL are divided in Frequency

Time Division Duplex• UL & DL are divided in Time


Channel Types

A to B

B to A

f1f2f3f4

FDMA: e.g. walkie-talkie

A to B B to A A to B B to AX to Y Y to X X to Y Y to X

C to D D to C C to D D to CM to N N to M N to M M to N

f1f2f3f4

FDMA/TDD: e.g. CT2-system

f1f2f3f4

1 2 3 4 5 6 ... 1 2 3 4 5 6

TDMA/TDD : e.g. DECT

Multiple access and Duplex combination

f1f2f3f4

.. 1 2 3 4 5 6 ... 1 2 3 4 5

3 4 5 6 ... 1 2 3 4 5 6 .. 1

FDMA/TDMA/FDD: e.g. GSM


Difference Between Multiple Access and Duplex

• Multiple access allows several users to share simultaneously a part of the radio spectrum

• (full)Duplex allows the user to use Uplink and Downlink simultaneously

• To avoid interference between Uplink and Downlink, Duplex distance is needed e.g. GSM 900 Duplex distance is 45 MHz


Introduction

TECHNOLOGIES

GSM OVERVIEW

RADIO ACCESS

MODULATION


• Modulation is the process of encoding information from a message source in a manner suitable for transmission

• Modulating signal = baseband signal Modulated signal = bandpasssignal

• Demodulation is the process of extracting the baseband message from the modulated carrier

Modulation TechnologiesBasics

Modulation

fc

bandpass

f0

baseband


Modulation TechnologiesModulation in GSM

• GMSK with B3dB*Tb = 0,3• Gaussian Minimum Shift Keying• Simple binary digital phase modulation scheme• Excellent power and bandwidth efficiencies

• Constant envelope & continuous phase • Noise-resistant• Limited bandwidth

• Implementation of transmitters and receivers is easy and cheap

Rb ≅ 270,833 kb/sTb = 1/Rb ≅ 3,692 µs

⇒ B3dB = 0,3/Tb ≅ 81,25 kHz


Modulation TechnologiesGMSK Spectrum


Exercises / Questions

Why is duplex distance needed?

List the GSM interfaces.

Which radio access technology is used in GSM?


References

1. W.C.Y. Lee, “Mobile Communications Design Fundamentals,” John Wiley & Sons, 1993.

2. W.C.Y. Lee, “Mobile Cellular Telecommunication Systems,” McGraw-Hill Book Company, 1990.

3. J. Lempiäinen, M. Manninen, ”Radio Interface System Planningfor GSM/GPRS/UMTS,” Kluwer Academic Publishers 2001.

explain m01- 1 gsm standardisation and technology.pdf

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