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10-07-2006 Manish Das, DGM(CMTS), Kolkata

GSM

An O & M overview

Manish Das

Deputy General Manager (CMTS)

Calcutta Telephones

Dimapur 10-07-2006

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GSM GPRS Network Architecture

BSCBSC

BSCBSC

MSCMSC

MSCMSC

EIREIR

AUCAUC

HLRHLR

VLRVLR

BTS

BTS

Backhaul

Internet

SGSNSGSN

GGSNGGSN

Transit

Net

Transit

Net

NSS

NSS Network & Switching Subsystem

VLR Visitor Location RegisterHLR Home Location Register

AUC Authentication Center

EIR Equipment Identity Center

MSC Mobile Switching Center

BSS

BSS Base Station Subsystem

BSC Base Station Controller

BTS Base Transceiver Stations

GSN GPRS Support Node

SGSN Serving GSN

GGSN Gateway GSN

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BASE STATION SUB-SYSTEM

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Base Transceiver Station (BTS)/ Base Station

Responsible for communication to and fromMobile sets via air interface

BTS comprises radio transmission and reception

devices BTS separates the speech and control signaling

associated with a Mobile set and sends them to

the BSC on separate channels

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Base Station Controller (BSC)

Monitor and Control several base stations

Frequency administration, control of BTSs Responsible for all the radio interface

management

Channel allocation and release, handovermanagement

BSC is the interface between MSC and BTS

BSC is connected on one side to several BTSsand on the other side to the MSC

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RF Interface

Also known as Air Interface

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Air Interface

Radio Transmission Techniques

FDMA

TDMA

CDMA

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FDMA

Time

Frequency

Channel

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TDMA

Time

Frequency

0 1 2 3 4 5 6 7

Channel

Time Slot

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CDMAFrequency

Time

Code

Code 1

Code 2

Code 3

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Frequency Spectrum in GSM

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The Frequency Spectrum

1

2

123

124

960MHz

959.8MHz

200KHz

935.2MHz

935MHz

1

2

123

124

915MHz

914.8MHz

200KHz

890.2MHz

890MHz

45MHz

Separation

76543210

76543210

Data Burst, 156.25 bit periods = 15/26 msec = 576.9sec

Down Link

Up Link

TDMA Frame

TDMA Frame

Time Slot

Delay

FDMA

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UP / Down-Link

Down-link: the transmission path from Base

Station to Mobile Station

Up-link: the transmission path from Mobile

Station to Base Station

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Channels

Physical Channels

Associated with frequency bands, time slots, codes

Physical channels transfer bits from one network element

to another

Logical Channels

Distinguished by the nature of carried information and theway to assemble bits into data units

Three types

one-to-one: traffic channels between a BTS and a MS

one-to-many: synchronization signals from BTS to MSs in acell

many-to-one: from MSs to the same BTS

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Trafficchannels(TCH)

Signaling

channel

TCH/F: Full-rate Traffic Channel

TCH/H: Half-rate Traffic Channel

FCCH: Frequency correction

SCH: Synchronization

BCCH: Broadcast control

PCH: Paging

AGCH: Access grant

RACH: Random access

SDCCH: Stand-alone dedicated control

SACCH: Slow associated control

FACCH: Fast associated control

Two-way

Base-to-mobile

Two-way

Logical Channel List

BCH

CCCH

DCCH

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Control Channels Broadcast Channels (BCH)

Frequency Correction Channel (FCCH)

Synchronization Channel (SCH) Broadcast Control Channel (BCCH)

Common Control Channels (CCCH) Paging Channel (PCH)

Random Access Channel (RACH) Access Grant Channel (AGCH)

Dedicated Control Channels (DCCH) Stand alone Dedicated Control Channel (SDCCH)

Cell Broadcast Channel (CBCH)

Slow Associated Control Channel (SACCH)

Fast Associated Control Channel (FACCH)

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Broadcast Channels (BCH)

To help the Mobile set (Mobile Handset)

measures to turn to a BTS

to listen for the cell information

to start roaming, waiting for calls to arrive, making calls

Because BTSs are not synchronized with each

other, every time a Mobile set decides to camp to

another cell, its FCCH, SCH, and BCCH must beread.

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Frequency Correction Channel(FCCH)

Provide Mobile set with the frequencyreference of the system

To enable the Mobile Handset (Mobile set) to

synchronize with the frequency Transmission properties

Transmit on the down-link

Point to multi-point.

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Synchronization Channel (SCH)

Mobile set synchronize with the structure within

the located cell Mobile set can receive information from the proper time

slots on the TDMA structure

To ensure a GSM BTS is chose The Base Station Identity Code (BSIC) can only be

decoded by a GSM BTS

Transmission properties

Transmit on down-link Point to multi-point.

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Broadcast Control Channel (BCCH)

BTS broadcast cell information to Mobile

set LAI ( Location Area Identity), to start roaming,

waiting for calls to arrive, making calls

maximum output power allowed in the cell information about BCCH carriers for the

neighboring cells Mobile set will perform measurement to BTS

Transmission properties Transmit on down-link

Point to multi-point

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Common Control Channels (CCCH)

CCCH support the establishment of a

dedicated communication path (dedicatedchannel) between the Mobile set and the BTS

Three types of CCCH

Paging Channel (PCH)

Random Access Channel (RACH)

Access Grant Channel (AGCH)

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Paging Channel (PCH) Used by BTS to page particular Mobile set in

the cell Mobile set actively listen to PCH to check contact

info within certain time

Contact could be incoming call or short message

Contact info on PCH include IMSI (Mobile sets identity number), or

TMSI (temporary number)


point to point

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Random Access Channel (RACH)

Used by Mobile set to request a dedicated

channel for call setup

Shared by any Mobile set attempts to access

the network

Channel request message contains the reason

for the access attempt

Transmission properties

Transmit on up-link

Point to pint.

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Access Grant Channel (AGCH)

The network assigns a signaling channelvia AGCH

A Stand alone Dedicated Control Channel

(SDCCH) is assigned Transmission properties

Transmit on down-link

Point to point

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Dedicated Control Channels (DCCH)

DCCH are used for transferring nonuser

information between the network and the Mobileset Messages on DCCH Including

channel maintenance

mobility management

radio resource management

Four kinds of DCCH

Stand alone Dedicated Control Channel (SDCCH) Cell Broadcast Channel (CBCH)

Slow Associated Control Channel (SACCH)

Fast Associated Control Channel (FACCH)

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Stand alone Dedicated ControlChannel (SDCCH)

Transfer signaling information between theBTS and the Mobile set

Typically used for location updating prior to

use of a traffic channel Transmission properties

Bidirectional channel, transmit on both up and

down-link

Point to point.

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Cell Broadcast Channel (CBCH)

To carry Short Message Service CellBroadcast (SMSCB)

Use the same physical channel as SDCCH


Point to multi-point

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Slow Associated Control Channel(SACCH) Carries control and measurement parameters

along with routine data necessary to maintain aradio link between the Mobile set and the BTS On the uplink, MS sends averaged measurements

(signal strength and quality) of current and neighboring

BCCH On downlink, MS receives information about

transmitting power to use and an instruction with timeadvance/retard

Transmission properties Bidirection channel, transmit on both up and down link

Point to point

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Fast Associated Control Channel(FACCH)

An FACCH is used over a TCH where itsteals time slots from a TCH

a 20 ms segment of speech is stolen to carry

handover signaling information Appears on demand

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Traffic Channels (TCH)

TCH transport user information (speech/data)

TCH are bidirectional dedicated channels

between the network and the Mobile set

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Geographical Network Structure

Location Units

Cell Location Area (LA)

MSC/VLR Service Area

PLMN (Public Land Mobile Network) Service Area

GSM Service Area

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Location Information --GSM Service Area Hierarchy

Cell

Location Area

MSC/VLR

PLMN Service Area(one per operator)

GSM Service Area

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Cell Characteristics

The Basic Union In The System

defined as the area where radio coverage is givenby one base station.

Addressed by Cell Global Identity (CGI)

A cell has one or several frequencies,depending on traffic load.

Frequencies are reused, but not used in

neighboring cells due to interference.

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ID-Numbers CGI = MCC + MNC + LAC + CI

CGI Cell Global Identity CI Cell Identity

BSIC = NCC + BCC BSIC Base Station Identity Code

NCC Network Color Code (3bits)

BCC Base Station Color Code (3bits)

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Location Registry

Registration Message Flow

Inter-LA movement In the same MSC

Inter-MSC movement

In the same GSM Operator Inter-VLR movement

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Mobile call scenario.

Mobile terminating call

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GPRS

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Gb between SGSN-PCUSN uses Frame Relay protocols

Gn between SGSN-GGSN uses IP routing, GPRS TunnelProtocol

Gr between SGSN-HLR is an extension of MAP

Gi between GGSN and PDNs uses IP and X.25

Gd between SGSN-SMSC delivers SMS messages using MAP

Gc between GGSN-HLR is optional, uses MAP

Gs between SGSN-MSC/VLR is optional, uses BSSMAP

VLR

SMSC

MSC

GGSN SGSNPCUSN

BTSBase

Transceiver

Station

SIM

MobileEqpmt

PSPDN

PLMNPSTNISDN

MobileStation

UmInterface

TCU

GbGnGi

SGSNof a

different

PLMNG

p

A

EIRHLR

Gd

Gs

GfGrGc

New GPRS elements and interfaces

Existing GSM Core Network elements

User data & signaling

Signaling only

LEGEND

FRAME RELAY

IP or X.25

BSCBase

StationController

Ater

Agprs

Abis

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GPRS Architecture - Components

New components introduced for GPRS services:

SGSN (Serving GPRS Support Node) GGSN (Gateway GPRS Support Node)

IP-based backbone network

Old components in GSM upgraded for GPRS

services:

HLR

MSC/VLR

Mobile Station

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Salient Features

High Data Rates up to 172 kpbs an order of

magnitude higher than GSM The setup time is negligible less than a

second

Resource utilization as per requirements airinterface is assigned temporarily on per-

packet basis

Hosts can remain always on

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GPRS Coding Schemes GPRS defines four codingschemes

Only CS-1 is mandatory for theBTS

All coding schemes are

mandatory for the MS The higher the coding scheme,

the higher the throughput

The higher the throughput, thelower protection against errors

Encoded 456 bits interleavedover 4 TDMA bursts

RLC

HeaderRLC Data

160 Data Bits (depends on size RLC header)

RLCHeader RLC Data


RLC

HeaderRLC Data


RLCHeader RLC Data


CS-1

CS-2

CS-3

CS-4

1 TS 2 TS 3 TS 4 TS 8 TS

CS-1 9.05 kbps 18.1 kbps 27.15 kbps 36.2 kbps 72.4 kbpsCS-2 13.4 kbps 26.8 kbps 40.2 kbps 53.6 kbps 107.2 kbps

CS-3 15.6 kbps 31.2 kbps 46.8 kbps 62.4 kbps 124.8 kbps

CS-4 21.4 kbps 42.8 kbps 64.2 kbps 85.6 kbps 171.2 kbps

T i l D C ll S i

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Typical Data Call Scenario

BTS BSC MSC

SGSN

GGSN

GPRS

Register

RouterUser LAN

PSPDN

b

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GPRS Mobile Station Classes

Class

Type

GSM and GPRS

Simultaneously

GSM or GPRS

Sequentially

GSM Only

GPRS Only

Class A Yes Yes Yes

Class B No Yes Yes

Class C No No Yes

Class A supports simultaneous circuit and packet switched Class B supports packet and circuit switched sequentially

Currently only Class B mobiles being developed

Class C does not support parallel operation

Operates in either packet or circuit mode only

Low cost unit available for mass market deployment

EDGE

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EDGE

Enhanced Data rate for Global Evolution GSM/GPRS-Network Enhancement

Data rate comparable to UMTS Network

(384 kBit/s and more) Based on GSM Multiplexmethod (TDMA/FDMA)

Changing GSM Modulation from GPSK to 8PSK

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Introduce new methods at the physical layer

new form of modulation: 8PSK(phrase Shift Keying)

introduced as a complement to GMSK (Gaussian FilterMinimum Shift Keying)

8PSK: use 8 phrases to carry signals

High radio interface data rates (up to 384kbps)

EDGE Features

EDGE F

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EDGE Features cont.

Provides an evolutionary migration path from

GPRS to UMTS Only one EDGE transceiver unit need to be added to

each cell.

Software upgrades to BSC and Base Stations canbe carried out remotely.

Higher layer protocols (GGSN, SGSN) stay the

same

Can be introduced smoothly in GPRS(doesnt

require any new elements)

A li i

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Applications.

Web browsing

Email

File Transfer Banking Transactions

Stock Market Updates

News

Online Video clips/ sports clippings Gaming

Multimedia Greetings card exchange

Polyphonic ring tone download

Weather & Traffic reports

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Network Monitoringand

Troubleshooting

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Net ork monitoring

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Network monitoring

Routine HW check

Call test Customers complaints

Traffic report study

Drive test and remedial actions

Common Problems and Causes

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Common Problems and Causes

No CoverageBTS Power Settings

Antenna Problem

BTS Site

Poor Speech Quality

& Drop Calls

RF Coverage

Interference

- Co, Adjacent and Multipath

Transcoder and Switching Equipment's

Handover Discrepancies

Link Imbalance

RF Coverage

Resource Unavailability

Cell Traffic LoadingRF Coverage

Interference

Link Imbalance

Blocked Calls

Troubleshooting Problems

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Troubleshooting Problems

Blocked Calls

Poor Quality and Drop calls

Abnormal Handovers

Interference

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Blocked Call

Troubleshooting

Blocked Call Analysis

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Blocked Call Analysis

1 3

Channel Request Channel Request

RACH .

: Imm Assignment

RACH

max_retrans Service Request

NO RESPONSE FROM N/W

ACCESS FAILURE ! Signalling

:Signalling

2

NO TCH ASSIGNMENT

Channel Request Mobile Returns To Idle

RACH TCH BLOCKED !

Imm Assign Reject

SDCCH BLOCKED !

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Blocked Call Cause troubleshooting

Access Failures- CCCH Overload at the Base Station

- Uplink Interference at the Base Station

- Low Rxlev at the Base Station

- Base Station TRX decoder malfunctioning

- Downlink Low Rxlev ( Coverage Hole )

- Downlink Interference

- Excess Cell Range

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Blocked Call AnalysisSDCCH Congestion CauseLocation Updates

- Use OMC Statistics

- Drive Test of optimizing Location Areas

Interference

- OMC statistics forIdle Channel Interference

- Uplink Interference Measurements

Heavy Traffic

- OMC traffic statistics

- Call Setup time verification

- CCCH control parameters

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Blocked Call

Solutions To Blocked CallsOptimize coverage

Optimize Cell loading

Interference management

Channel configurations

Optimize neighbors

TCH Blocked - Causes

Interference

-- Idle Channel Interference reports from OMC

--Uplink Interference measurements

Heavy Traffic

-- TCH Holding time and attempts traffic statistics

-- Time Slot testing.

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Dropped Call

Troubleshooting

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Drop Calls Analysis1 2Channel Request Channel Request

Imm Assignment Imm Assignment

Service Request Service Request

Signalling SDCCH Signalling

: :

Signalling Speech

TCH

RLT = 0 ; DROPS RLT = 0 ; DROPS

SDCCH DROP ! TCH DROP !

3 SDCCH / TCH

Handover Command

Hand Access

Handover Failure

HANDOVER FAILURE DROP !

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Dropped Call Analysis SDCCH Drops - Causes

Coverage

Interference & Multipath

BTS performance

TCH Drops - Causes Coverage

Interference & Multipath BTS performance

Handover Failure - Causes

Threshold parameters Missing neighbors

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Poor QualityPoor Speech Quality could be due to

Patchy Coverage ( holes)

No Target cell for HandoverEcho , Audio holes, Voice ClippingInterference ---:

Co-channel

Adjacent channel

External

Multipath

Noise

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Speech Quality ParametersRxQUAL

FER

Echo and distortion

Audio holes

Voice Clipping

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Traffic report analysis

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Any Question ? ?

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Thank You

GSM_LEC_100706

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