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For BSNL internal circulation only. E2-E3 Consumer Mobility GSM Radio Concept

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Page 1: Marketing Mix - Bharat Sanchar Nigam Limitedtraining.bsnl.co.in/DIGITAL_LIBRARY_SOURCE/upgradation/E2-E3/E2-E3 CM/E2-E3 CM PPT...of 22.8 kbit/s (after channel coding). The net (or

For BSNL internal circulation only.

E2-E3

Consumer Mobility

GSM Radio Concept

Page 2: Marketing Mix - Bharat Sanchar Nigam Limitedtraining.bsnl.co.in/DIGITAL_LIBRARY_SOURCE/upgradation/E2-E3/E2-E3 CM/E2-E3 CM PPT...of 22.8 kbit/s (after channel coding). The net (or

For BSNL internal circulation only.

WELCOME

• This is a presentation for the E2-E3 Consumer

Mobility Module for the Topic: GSM Radio

Concepts

• Eligibility: Those who have got the Upgradation

from E2 to E3.

• This presentation is last updated on 15-3-2011.

• You can also visit the Digital library of BSNL to

see this topic.

Page 3: Marketing Mix - Bharat Sanchar Nigam Limitedtraining.bsnl.co.in/DIGITAL_LIBRARY_SOURCE/upgradation/E2-E3/E2-E3 CM/E2-E3 CM PPT...of 22.8 kbit/s (after channel coding). The net (or

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Learning Objective

Define radio concept

Frequency Spectrum for GSM

The Air Interface

Physical Channels- FDMA &

TDMA

Logical Channels

Frames

Network Attachment Procedure

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1. GSM Radio Concept

GSM Radio interface is an important openinterface which facilitates integration of variousmobiles with GSM networks. Coverage in a cellis provided by means of radio signalstransmitted through BTS.

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GSM Interface

Air interface or U m –interface

The Air Interface is the interface between theBTS (Base Transceiver Station) and the MS(Mobile Station). The air interface is required forsupporting:

Universal use of any compatible mobile stationin a GSM network

A maximum spectral efficiency

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A bis -interface

The A bis -interface is the interface between theBSC and the BTS.

The interface comprises traffic and controlchannels. Functions implemented at the A bis -interfaces are:

Voice-data traffic exchange

Signaling exchange between the BSC and theBTS

Transporting synchronization information fromthe BSC to the BTS

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7

GSM RADIO INTERFACE

Most Important Interface

Full Compatibility between mobile stations ofvarious Manufacturers & Networks of differentvendors to help roaming

To increase spectral efficiency

-- Large number of simultaneous calls in agiven

bandwidth

-- Frequency Reuse

-- Interference

-- Use of Interference Reduction Techniques

Page 8: Marketing Mix - Bharat Sanchar Nigam Limitedtraining.bsnl.co.in/DIGITAL_LIBRARY_SOURCE/upgradation/E2-E3/E2-E3 CM/E2-E3 CM PPT...of 22.8 kbit/s (after channel coding). The net (or

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8

GSM Uplink & Downlink

Frequency Bands

GSM 900 Mhz

DCS 1800 MHz

B

T

S

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9

GSM Specifications

RF Spectrum :

GSM 900

Mobile to BS (UP-LINK) - 890 to 915 MHz

BS to Mobile (DOWN -LINK) - 935 to 960 MHz

Bandwidth - 25 MHz

GSM 1800

Mobile to Cell (UP-LINK) - 1710 to 1785 MHz

Cell to Mobile (DOWN -LINK) - 1805 to 1880 MHz

Bandwidth - 75 MHz

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U m or Air interface

To achieve a high spectral efficiency in the

cellular network a combination of FDMA

(Frequency Division Multiple Access) and TDMA

(Time Division Multiple Access) is used.

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Frequency Division Multiple Access FDMA

It involves the division by frequency of the 25

MHz bandwidth into 124 carrier frequencies

spaced 200 KHz for GSM-900

GSM-1800 the frequency spectrum of the 75

MHz bandwidth is divided into 374 carrier

frequencies spaced 200 KHz.

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Time Division Multiple Access TDMA

To increase the number of channels per carrier

frequency

A carrier frequency channel carries eight time-

division multiplexed signals

A mobile station can transmit speech data only

during its assigned timeslot.

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Physical channel

It is determined by the carrier frequency and the

time slot number

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14

GSM-900 Specifications

Carrier Separation - 200 kHz

No. of RF Carriers - 124

Access Method - TDMA/FDMA

Modulation Method - GMSK

Transmission Rate - 270.833 Kbps

Speech Coding - Full rate 13 Kbps

Half rate 6.5 Kbps

Duplex Distance - 45 MHz

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GSM-1800 Specifications

No. of RF Carriers - 124

Access Method - TDMA/FDMA

Modulation Method - GMSK

Transmission Rate - 270.833 Kbps

Speech Coding - Full rate 13 Kbps

Half rate 6.5 Kbps

Duplex Distance - 95 MHz

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18

GSM-- TDMA STRUCTURE

• TDMA 8 Time Slots / RF Channel

• Time slot duration 0.577m sec or 15 / 26 m sec

• Frame 8 Burst Periods ( Time Slots)

• Multi Frame Traffic 26 4.615 = 120 msec

Control 51 4.615 = 235.365 m sec

• Super Frame 51 Traffic Multi frames

26 Control Multi frames

• Hyper Frame 2048 Super Frames = 3 28 52.76

hr min sec

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Logical Channels

Traffic channel

Broadcast channels

Common control channels

Dedicated control channels

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Traffic channels

The traffic channels are used to send speech or

data services. There are two types of traffic

channels. They are distinguished by their

transmission rates

1. TCH/F (Traffic Channel Full rate )

2. TCH/H (Traffic Channel Half rate)

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TCH/F (Traffic Channel Full rate)

The TCH/F carries information at a gross bit rateof 22.8 kbit/s (after channel coding). The net (oreffective) bit rate at the TCH/F is for speech 13kbit/s and for data 12, 6 or 3.6 kbit/s (beforechannel coding). The transmission rates of thedata services allow services which arecompatible to the existing, respectively, 9.6, 4.8and 2.4 kbit/s PSTN and ISDN services.

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TCH/H (Traffic Channel Half rate)

The TCH/H carries information at a gross bit rateof 11.4 kbit/s. The net bit rate at the TCH/H is forspeech 5.6 kbit/s and for data 6 or 3.6 kbit/s.

A TCH/F or a TCH/H may also be used to sendsignaling information (for example callforwarding and short messages). In that case asmall portion of the time slot is used.

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Broadcast Channels

The information distributed over the broadcast

channels helps the mobile stations to orient

themselves in the mobile radio network.

The broadcast channels are point-to-multipoint

channels which are only defined for the downlink

direction (BTS to the mobile station)

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Types Of Broadcast Channels

BCCH (Broadcast Control Channel)

FCCH (Frequency Correction Channel)

SCH (Synchronization Channel)

CBCH (Cell Broadcast Channel)

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BCCH (Broadcast Control Channel)

Via the BCCH the mobile station is informed

about the system configuration parameters (for

example Local Area Identification, Cell Identity

and Neighbor Cells). Using this information the

mobile stations can choose the best cell to

attach to.

The BCCH is also known as beacon.

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FCCH (Frequency Correction Channel)

To communicate with the BTS the mobile station

must tune to the BTS. The FCC transmits a

constant frequency shift of the radio frequency

carrier that can be used by the mobile station for

frequency correction

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SCH (Synchronization Channel)

The SCH is used to time synchronize the mobile

stations. The data on this channel carries the

TDMA frame number and the BSIC (Base

Station Identity Code).

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CBCH (Cell Broadcast Channel)

The CBCH is used for the transmission of

generally accessible information (Short Message

Service messages) in a cell, which can be polled

by the mobile station.

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Common Control Channel

Common control channels are specified as

point-to-multipoint channels which only operate

in one direction of transmission, either in the

uplink or downlink direction

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Types of Common Control Channel

PCH (Paging Channel)

AGCH (Access Grant Channel)

RACH (Random Access Channel)

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PCH (Paging Channel)

The PCH is used in the downlink direction for

paging the mobile stations

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AGCH (Access Grant Channel)

The AGCH is also used in the downlink direction.

A logical channel for a connection is allocated

via the AGCH if the mobile station has requested

such a Channel via the RACH.

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RACH (Random Access Channel)

The RACH is used in the uplink direction by the

mobile stations for requesting a channel for a

connection. It is an access channel that uses the

slotted Aloha access scheme

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Dedicated Control Channels P-P

Dedicated control channels are full-duplex,

point-to-point Channels. They are used for

signaling between the BTS and a certain mobile

station

34

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Types of Dedicated Control Channels

SACCH (Slow Associated Control Channel)

FACCH (Fast Associated Control Channel)

SDCCH (Stand-alone Dedicated Control Channel)

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SACCH (Slow Associated Control Channel)

The SACCH is a duplex Channel which is

always allocated to a TCH or SDCCH. The

SACCH is used for transmission of signaling

data, radio link supervision measurements,

transmit power control and timing advance data.

Note that the SACCH is only used for non-urgent

procedures.

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FACCH (Fast Associated Control Channel )

The FACCH is used as a main signaling link forthe transmission of signaling data (for examplehandover commands). It is also required forevery call set-up and release. During the call theFACCH data is transmitted over the allocatedTCH instead of traffic data; this is marked by aflag called a stealing flag. The process ofstealing a TCH for FACCH data is called pre-emption.

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SDCCH (Stand-alone Dedicated Control

Channel)

The SDCCH is a duplex, point-to-point Channelwhich is used for signaling in higher layers. Itcarries all signaling between the BTS and themobile station when no TCH is allocated. TheSDCCHs are used for service requests (forexample Short Message Service), locationupdates, subscriber authentication, cipheringinitiation, equipment validation and assignmentto a TCH. The net SDCCH bit rate is about 0.8kbit/s.

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Multiplexing Logical Channels onto

Physical Channels

Several of the above-mentioned types of logicalchannels can be transmitted over one singlephysical channel (timeslot).

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Channel Combination

1.TCH/F + FACCH/F + SACCH/F

2. TCH/H + FACCH/H + SACCH/H

3. (TCH/F + FACCH/F + SACCH/F) or (TCH/H +FACCH/H + SACCH/H)

4. FCCH + SCH + CCCH + BCCH

5. FCCH + SCH + CCCH + BCCH + SDCCH/4 +SACCH/4

6. CCCH + BCCH

7. SDCCH/8 + SACCH/8

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The CCCH is a channel that carries both thePCH and the AGCH on the downlink, and theRACH on the uplink.

The extensions “/4” and “/8” mean, respectively,that four and eight logical channels are mappedonto one physical channel (timeslot).

Note that the BCCH is always transmitted intimeslot 0 on the first defined frequency.

The logical channels FCCH, SCH, BCCH andCCCH are transmitted on the downlink intimeslot 0.

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Frame Types on the Um –interface

TDMA frame

A TDMA frame consists of eight timeslots(physical channels). The length of a timeslot is0.577 ms. The length of a TDMA frame istherefore 4.62 ms.

Data on a timeslot is transmitted in bursts, thelength of a timeslot is often expressed in BP(Burst Period); 1 BP represents the length of 1timeslot.

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26-TDMA multiframe

This multiframe is defined as a succession of 26TDMA frames, and corresponds to the 26 x 8 BPor 120 ms cycle used in the definition of theTCH/F and TCH/H.

51-TDMA multiframe

This multiframe is defined as a succession of 51TDMA frames, and corresponds to the 51 x 8 BPcycle used in the definition of the TCH/F, TCH/Hand of the common channels

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Super frame

The superframe is a succession of 51 x 26 TDMAframes (6.12 sec), and corresponds to the smallestcycle for which the organization of all channels isrepeated.

Hyper frame

The hyper frame is the numbering period. It is 2048 x51 x 26 x 8 BP long, or 3 hours, 28 minutes, 53seconds and 760 milliseconds. It is a multiple of allpreviously cited cycles, and determines all the cyclesin the transmission of the radio path. It is in particularthe smallest cycle for frequency hopping and forciphering.

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45

OPERATIONAL CONCEPTSIDLE MODE

• IDLE MODE

ACCESS PROCDURE DEDICATED MODE

• MS O/G Call

• MS I/C Call

----FCCH

---- SCH

----BCCH

----RACH

----AGCH

----SDCCH

----TCH

----PCH

----RACH----AGCH

----SDCCH

----TCH

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Network Attachment Process:

Network attachment is the process of selectingan appropriate cell (radio frequency) by themobile station to make its location known to thenetwork.

The process starts when the mobile is switchedon, and ends when the mobile station enter theidle mode. In idle mode the mobile station doesnot have a traffic channel allocated to make orreceive a call, but the Public Land MobileNetwork (PLMN) is aware of the existence of themobile station within the chosen cell

46

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The network attachment process

It consists of the following three tasks

Cell Identification

PLMN Selection

Cell selection

47

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Cell Identification

When Mobile Station is switched on, it attemptsto make contact with a GSM PLMN byperforming following actions.

Measure the BCCH channel.

Search for a suitable cell.

The Mobile Station measure the signal strengthof the BCCH (Broadcast Control Channel)Channels received. It stores a list informationabout 30 of these BCCH channels, such assignal strength and the frequencycorresponding.

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PLMN Selection

Automatic mode

In automatic mode, the station will choose which PLMNs to tryby itself. The automatic mode is based on the existence of thepreferred list, which is stored in a non-volatile memory in theSIM. This list includes a number of PLMN identities in order ofpreference and is under control of the user. The most preferredis usually the home PLMN. The list is filled in by the userthrough a mechanism to be specified by the mobile stationmanufacturer. The automatic mode is normally used when themobile station operates on its home PLMN (that is the PLMNthe mobile station is subscribed to).

Manual mode

In manual mode, the user is presented a list containing allfound PLMNs. The user chooses one of the PLMNs from thelist.

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Cell selection

The mobile station attempts to find a suitable cell bypassing through the list in descending order of receivedsignal strength; the first BCCH Channel which satisfies aset of requirements. The requirement that a cell mustsatisfy before a mobile station can be provide servicefrom it, are:

It should be a cell of the selected PLMN.

The mobile station checks whether the cell is part of theselected PLMN.

It should not be “barred”.

The PLMN operator may decide not to allow mobilestations to access certain cells. These cells may, forexample, only be used for handover traffic. Barred cellinformation is broadcast on the BCCH to instruct mobilestations not to access these cells.

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If No suitable cell found MS can only attemptto make emergency calls irrespective of thePLMN identity .

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