1[1].Gsm Overview

7/29/2019 1[1].Gsm Overview

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ZTE University univ.zte.com.cnuniv.zte.com.cnuniv.zte.com.cnThe information contained in the file is solely property of ZTE corporation. Any kind of disclosing without permission is prohibited.

Welcome to ZTE University


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The information contained in the file is solely property of ZTE corporation. Any kind of disclosing without permission is prohibited.ZTE University univ.zte.com.cnuniv.zte.com.cnuniv.zte.com.cn

Global System for Mobile

System Overview


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Mobile communication existed half a century

ago, but it was in the 1980s that it was reallydeveloped.

The main goal of mobile communication is torealize communication among any objects at

any time, and in any place.


4/77The information contained in the file is solely property of ZTE corporation. Any kind of disclosing without permission is prohibited.ZTE University univ.zte.com.cnuniv.zte.com.cnuniv.zte.com.cn

Evolution of Mobile Communication

Land cellular mobile communication system

(PLMN) has gone through 3 stages:

1. First Generation ---Analog Mobile

Telephone System

2. Second Generation---Digital Mobile

Communication System3. Third Generation---IMT-2000



First Generation Analog Mobile Telephone System

Adopts cellular networking technology.

Currently practical, high capacity systems worldwide

includes:

1North-AmericansAMPS2North Europeans NMT-450/9003Britains TACS

Operating frequency bands locate around 450MHz

and 900MHz with carrier spacing less than 30 kHz.



Analog cellular mobile communication system

has following fatal weaknesses:

A) There is no public air interface between various

systems;

B) It can not adapt itself to the digitization of fixed

networks, and digital bearer services are hard to

develop;



C) It has a low frequency availability, thus unable to

meet large capacity requirements;

D) It has a low degree of safety, thus easy to be

eavesdropped, and easy to be copied with false

handsets.

Analog cellular mobile communication system

has been replaced by digital cellular mobile

communication in China.



Second Generation Digital Mobile Comm. System

Due to the various defects of analog systems such as

TACS, mobile telephone systems were developed in

the 1990s embodied by digital transmission, TDMA

and narrow-band CDMA, which are called the

Second generation mobile telephone system.



Types of TDMA Systems

The comparatively mature and most typical system in

the TDMA series are: the pan-European GSM,

American D-AMPS and the Japanese PDC.

1DAMPS was formally launched into commercialapplication in 1993 after the American Electronic

Industry Association (EIA) completed its technical

standardization in 1989).



2Japanese JDC (now renamed as PDC) had itstechnical standards completed in 1990. It was putinto service in 1993, but is restricted to Japan only.

3The special mobile communication group (SMG)of CEPT laid down the phase 1 standard ofGSM in1988, with the working frequency band around

900MHz. It was launched into commercial use in

1990.



Main Features of GSM (1)

(1) Spectrum efficiency: due to the adoption of high-

efficiency modulator, channel coding, interleaving,equalization and voice coding technologies, the system

has a high spectrum efficiency.

(2) Capacity: due to the increase of the transmission

bandwidth of each channel, the requirement of co-

channel reuse carrier-to-interference ratio is lowered to9dB,



So,the cofrequency reuse mode of the GSM system

can be narrowed down to 4/12 or 3/9 or even less

(for a analog system, it is 7/21).

GSM system capacity is 3~5 times higher than thatof a TACS system.


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(3) Voice quality: due to digital transmission

technology, GSM system has a strong anti-

interference capability compared with analog system,thus the voice quality is guaranteed.

(4) Interfaces openness: the open interfaces providedby GSM standards refer not only to air interface (Um),

but alsoA interface.


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(5) Security: security is guaranteed with authentification,

encryption and TMSI.

(6) Interconnection with ISDN, PSTN, etc.:

interconnections with other networks normally use theexisting standard interfaces, such as ISUP or TUP.

(7) Roaming: roaming is realized on basis of SIM cards.


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Summary of TDMA System

The common features of the above three types ofproducts are digitization/TDMA, good voice quality,

good security, ability to transmit data, and automaticroaming.

Each of these 3 types of systems has its own merits.The PDC system has a high spectrum availability,and the DAMPS system has the greatest capacity,while GSM is the most mature of all technologies.

Besides, it is based on OSI, with open technicalstandards, thus have been applied on the greatestscale in the world.


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N-CDMA System

The NCDMA (Narrow band Code Division Multiple

Access) system is a mobile communication systemdeveloped mainly by companies leaded by the

Quacomm Co. on basis of IS95. The specifications of

North American digital cellular systems are drawn up by

the American Telecom Industry Association (TIA).

This system has been adopted by China Unicom in2001.


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Third Generation - IMT-2000

With the ever-lasting increase in subscribers and the

development of digital communications, the second

generation mobile telephone systems has graduallyexposed its shortcomings:

Narrow bandwidth: unable to provide variousbroadband information services such as high-speed

data and television pictures.


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With the development of sciences and technologies

as well as communication services, what is needed is

an integrated service system that can integrate allcurrent mobile telephone system functions and

provide multiple services.


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Features of IMT-2000

Including multiple systems;

With a high degree of consistency in worldwide

design;

Compatibility between IMT-2000 services and fixed

networks;

High quality;

Small portable terminals used worldwide.


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GSM System Architecture


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Block Diagram of GSM System

BSC

B

T

S

B

T

S

HLR/AUC EIR SC

ISDN

PLMN

PSTN

PSPDN

OMC

BSS(1)

BSS n

MS

A interface

Abis interfaceUm interface

Fig.1-1 GSM Mobile Communication Network Structure

MSC/VLR


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BSS: Base Station Subsystem

BSC: Base Station Controller

BTS: Base Transceiver Station

MSC: Mobile Services Switching Center

OMC: Operation and Maintenance Center AUC: Authentication Center

EIR: Equipment Identification Register


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HLR: Home Location Register

VLR: Visitor Location Register

MS: Mobile Station

ISDN: Integrated Services Digital Network

PSTN: Public Switched Telephone Network

PSPDN: Packet Switched Public DataNetwork

PLMN: Public Land Mobile Network


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Mobile Station

Mobile stations are not fixed to one subscriber. On

any mobile station in the system, we can identify thesubscriber with the SIM card (Subscriber Identity

Module). The personal identification number (PIN)

can be used to prevent unauthorized use of the SIMcard.


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Each mobile station has its own identification

number, i.e., the International Mobile Equipment

Identifier (IMEI).

IMEI mainly consists of the type permission code

and the related manufacturer product number.

Each mobile subscriber has its own international

mobile subscriber identifier (IMSI), which is stored in

the SIM card and in HLR.


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Network and Switching Subsystem (NSS)

The Network and Switching Sub-system mainly includes

switching functions of the GSM system, and databasefunctions used for subscriber data and mobility

management as well as safety management. It

manages the communications among GSM mobile

subscribers and those between GSM mobile

subscribers and other communication network

subscribers.


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M S C

V L R

B

M S C

V L R

B

GE

E IR

H L R / A U C

B S CB T S

N S S

A

B S S

F

C

D

Network and Switching Subsystem (NSS)


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The network sub-system is divided into six function

units:

Mobile Service Switching Center (MSC)

Home Location Register (HLR)

Visitor Location Register (VLR)

Authentification Center (AUC)

Equipment Identification Register (EIR) Operation and Maintenance Center (OMC)

NSS Architecture


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Mobile Services Switching Center (MSC)

As the core of a network, MSC provides switching

functions, and connects mobile subscribers with fixed

network subscribers, or with mobile subscribers.

Thus, it provides interfaces to fixed networks (such as

PSTN, ISDN, etc.) and interfaces for interconnectionwith other MSCs.


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Functions of MSC

MSC obtains all the data for processing subscriber

call requests from 3 types of databases: HLR, VLR

and AUC.

MSC can provides a series of services for subscribers:

- Telecom services, such as phone, fax, and emergency calls

- Bearer services

- Supplementary services, such as call transfer, call restriction.


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Visitor Location RegisterVLR

VLR stores all related information of mobile

subscribers having entering into its coverage area,which enables MSC to set up incoming/outgoing calls.

It can be taken as a dynamic subscriber database.

VLR obtains and stores necessary data from the HLR

of a mobile subscriber. Once a mobile subscriber

leaves the coverage area of this VLR, it will be re-

registered in another VLR, the temporarily recorded

data of this mobile subscriber stored in the original

VLR will be deleted.


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Home Location RegisterHLR

As the central database of the GSM system, HLRstores the related data of all existing mobile

subscribers controlled by the same HLR. One HLRcan control several mobile switching areas or thewhole mobile communication network and theimportant static data of all subscribers are stored in

the HLR, including IMSI, access capability,subscriber type and supplementary services.Furthermore, HLR also stores and provides MSC(A)with (dynamic) information of the MSC(B) area intowhich a mobile station has roamed, so that anyincoming call is immediately sent to the calledsubscriber on a selected path.


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Authentication CenterAUC

As a function unit of HLR, AUC is specially used for

security management of the GSM system.

AUC stores authentication information and

encryption keys for subscriber authentication,

encryption of voice, data, signaling messages onradio interfaces, preventing unauthorized

subscribers access and guaranteeing the safety of

mobile subscriber communication.


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Equipment Identification RegisterEIR

EIR stores the international mobile equipment

identifier(IMEI) of mobile equipment.

By checking 3 types of lists, i.e., white lists, black lists,

and gray lists, it respectively lists the mobile

equipment identifiers that are authorized, that shouldbe monitored in case of faults, and that are

unauthorized in case of theft.

Service operators can use such information to locate

the location of a stolen mobile station and block it.


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GSM service area

PLMN service area

MSC Service area

cell

Location area

Wireless Coverage Area Structure


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BSS System Architecture

ZXG 10 BSS St t


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ZXG-10 BSS Structure

MS

Ater interfaceBS inte rface

Um inte rface

BSC

BIE

BTS

BTS

BIE

Abis

interface

SM SM TC

A interface

MSC

OMC

Q3 interface

Fig.1-3 BSS Structure

TC: TransCoder

SM: SubMultiplexing

BIE: Base station

Interface Equipment


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Base Transceiver Station (BTS)

It is the radio tranmission part of the base station

system.

Controlled by BSC, it serves cell radio transceiver

equipment, handles conversion between BSC and

radio channels, and performs radio transmissionbetween BTS and MS via air interfaces as well as

related control functions.

B St ti C t ll (BSC)


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Base Station Controller (BSC)

As the control part of BSS, BSC performs theswitching function in BSS.

BSC may be connected with multiple BTSs at oneend, and MSC and OMC at the other end.

BSC mainly manages radio network and radioresources, supervises and manages radio basestation, controls the establishment, connection anddisconnection of radio links in MS and BTS and the

location updating, hand-over and paging of mobilestation, provides functions such as voice encoding,transcoding, rate adaptation, as well as the operationand maintenance functions of BSS.


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TransCoder (TC)

TC mainly completes voice conversion between the

16kbit/s RPE-LTP (Regular Pulse Excited Long-Term

Prediction) codes and 64kbit/s A-law PCM codes.

In a typical application pattern, ZXG10-TC is located

between MSC and BSC.

Functional Layers of GSM


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Functional Layers of GSM

OAM

Service carrier

CM

MM

RR

Subscriber

Transmission


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Transmission: data transmission function, providing

methods of carrying subscriber data and transmitting

signalings between different entities in varioussegments along the communication path.

RR: radio resources management, setting up andreleasing stable connections between mobile stations

and MSC at the call setup stage, which is mainly

performed by MS and BSC;


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MM: refers to mobility and safety management,

mobile station processing -- environment changing,

making choices of cells possibly belonging todifferent networks, so that the calling subscriber is

able to set up a valid process; infrastructures are

required to manage subscriber location data (locationupdating);


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CM: refers to communication management, i.e., under

subscriber requests, setting up connections between

subscribers, maintaining and releasing calls (which can bedivided into CC - call control, SSM - supplementary

service management, and SMS - short messages service);

OAM: Operation, Administration and Maintenance

platform, providing operation methods for operators. The

service is supplied by the transmission layer directly.

GSM Wi l O ti B d


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GSM900890~915MHZ (upward)

935~960MHZ (downward)Duplex interval is 45MHZ, working bandwidth is 25MHZ, and

carrier frequency interval is 200KHZ.

GSMDCS18001710-1785MHZ (upward)

1805-1880MHZ (downward)Duplex interval is 95MHZ, working bandwidth is 75MHZ, andcarrier frequency interval is 200kHZ.

EGSM900:

880~915MHZ (upward)925~960MHZ (downward)

GSM Wireless Operating Band

Timeslot in Time domain and Frequency domain


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Timeslot in Time-domain and Frequency-domain


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Training Sequence of GSM


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BinaryTSC Hexadecimal

BN61 - BN86

0 970897 00100101110000100010010111

1 B778B7 00101101110111100010110111

2 10EE90E 01000011101110100100001110

3 11ED11E 010001111011010001000111104 6B906B 00011010111001000001101011

5 13AC13A 01001110101100000100111010

6 29F629F 1010011110110001010011111

7 3BC4BBC 11101111000100101110111100

Training Sequence of GSM

Types of Burst Pulse


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Types of Burst Pulse

NB(Normal Burst): used for traffic channel and

control channels except for RACH, SCH, FCCH.

AB(Access Burst): Transmitted on RACH channel

and used as access request made by MS to BTS. AB

is the sole short BP sequence defined by GSMprotocol.


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SB (Synchronization Burst): Transmitted on SCH

channel and used for initial synchronization seizing

by MS.

FB (Frequency Correction Burst) : Used for

carrierfrequency correction of MS.

DB (Dummy Burst): Has the same format with NB,mainly used for bit filling

Channel types


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yp

In a GSM system, channels are divided into logical and

physical channels. Time slots are basic physical

channels; thus each carrier frequency contains 8physical channels. Physical channels of radio sub-

systems support logical channels which can be

subdivided funcationally into Traffic Channels (TCH)and Control Channels (CCH).

Traffic Channel (TCH)


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Traffic Channel (TCH)

Traffic channel carries encoded speech or

subscriber data, including full-rate traffic channel

and half-rate traffic channel: Full-rate traffic channel (TCH/F): total rate is 22.8kbit/s Half-rate traffic channel (TCH/H): total rate is 11.4kbit/s

1) Speech channel TCH/FS: full-rate speech traffic channel

TCH/HS: half-rate speech traffic channel

2) Data channel

TCH/F9.6: 9.6kbit/s full-rate data traffic channel

Control Channel


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Control channel carries signaling or synchronized

data.

There are three types of control channels:

1) Broadcasting Channels (BCH)

Broadcasting channels are used only as downwardchannels, i.e., one-way transmission from the base

station to mobile stations.

Control Channel-BCH


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BCH can be divided into three types of channels:

FCCH: Frequency Correction Channel,

carrying information used in MS frequency calibration.SCH: Synchronization Channel,

carrying information of MS frame synchronization and

Base Transceiver Station (BTS) identification.BCCH: Broadcasting Control Channel;

this channel broadcasts general BTS information.

Among transceivers at each base station, there isalways one transceiver that contains such a channel, so

as to broadcast system information to mobile stations.

Common Control ChannelCCCH


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2) Common Control ChannelCCCHare shared by all mobile stations in the network.

There are 3 types of such channels:

PCH: paging channels,

used by a base station to page mobile stations (downward).

RACH: random access channel,used by mobile stations for random access network application,

i.e.,requesting the allocation of SDCCH channels (upward).

AGCH: access granted channel, used by a base station to

respond to random access requests of mobile stations, i.e., toassign one SDCCH or directly assign one TCH (downward).

Dedicated Control Channel (DCCH)


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( )

3) Dedicated Control Channel (DCCH)

In application, the base station will assign it to a

mobile station, so as to make point-to-pointtransmission between the base station and the

mobile station.

There are 3 types of such channels:

SDCCH: a stand-alone dedicated control channel,

used to transmit such information as channelassignment.

Dedicated Control Channel (DCCH)


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SACCH: slow-speed associated control channel,

Used in combination with one traffic channel or one SDCCH,

to send some specific subscriber information, e.g.,power and

frame adjustment control information, measurement data, etc.

FACCH: fast associated control channel, combining with one

traffic channel to carry the same signals as SDCCH, but it is

assigned only when SDCCH has not been assigned. Call

connection is realized via frames borrowed from traffic

channels to transmit such commands as handover.

( )

Channel Combination


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1) tCHFull TCH/F + FACCH/F + SACCH/TF

2) tCHHalf TCH/H(0,1)+FACCH/H(0,1)+ SACCH/TH(0,1)

3) tCHHalf2 TCH/H(0,0)+FACCH/H(0,1)+SACCH/TH(0,1)+

TCH/H(1,1)4) mainBCCH FCCH + SCH + BCCH + CCCH

5) bCCHCombined FCCH+SCH+BCCH+CCCH+

SDCCH/4(0..3)+ SACCH/C4(0..3)6) bCH BCCH + CCCH

7) sDCCH SDCCH/8(0..7)+ SACCH/C8(0..7)

8) bCCHwithCBCH FCCH+SCH+BCCH+CCCH+ SDCCH/4

+ SACCH/C4 + CBCH9) sDCCHwithCBCH SDCCH/8+SACCH/C8+CBCH

Structure of 26-Frame Traffic Channel


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SF B

C

51

SF C C SF C C SF C

C I

SF C C

BCCH+CCCH

Structure of 51-Frame Control Channel


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SF B C

R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

SF C C SF C C SF C C I

R R R R R R R R R R

D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 A3

SF C C

R R R R R R R R R R

III

D0 D1 D2 D3 D4 D5 D6 D7 A4 A5 A6 A7 III

A1 A2 A3 III

A5 A6 A7 III

D0 D1 D2 D3 D4 D5 D6 D7 A0

D0 D1 D2 D3 D4 D5 D6 D7 A4

SF B C SF C C SF D0 D1 SF D2 D3 ISF A0 A1

SF B C SF C C SF D0 D1 SF D2 D3 ISF A2 A3

D3

D3

R R

R R

A2 A3

A0 A1

D2

D2

SF

SF

D0 D1

D0 D1

R R R R R R R R R R R R R R R R R R R R R R R

R R R R R R R R R R R R R R R R R R R R R R R

FFCCH SSCH

BBCCH CCCCHCCCH=PCH+AGCH+RACH

RRACH DSDCCH

ASACCH/C Iidle

BCCH CCCH

BCCH+CCCH

8 SDCCH/8

8 SDCCH/8

BCCH+CCCH+4SDCCH/4

BCCH+CCCH

+4SDCCH/4

(a) FCCH+SCH+BCCH+CCCH

(b) SDCCH/8(0,...,7)+SACCH/C8(0,...,7)

(c) FCCH+SCH+CCCH+SDCCH/4(0,...,3)+SACCH/C4(0,...,3)

Channel Assignment inside Cells


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Small capacity cell with only 1 TRX

TN0:FCCH+SCH+CCCH+BCCH+SDCCH/4(0,_,3)+

SACCH/C4(0,_,3);TN1_7: TCH/F+FACCH/F+SACCH/TF

The medium-size cell with 4 TRXs

1TN0 group: FCCH+SCH+BCCH+CCCH;

2 SDCCH/8(0,_,7)+SACCH/C8(0,_,7);

29 TCH/F+FACCH/F+SACCH/TF


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Large-size cell with 12 TRXs1 TN0 group: FCCH+SCH+BCCH+CCCH;

1 TN2 group, 1 TN4 group and 1 TN6 group:

BCCH+CCCH;

5 SDCCH/8(0,_,7)+SACCH/C8(0,_,7);

87 TCH/F+FACCH/F+SACCH/TF

Traffic


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Traffic refers to the numbers of subscribers the network cansupport and is usually described as follows:

A=n

T/3600where,

n- calls made by a subscriber within an hour

T- average duration of each call(in seconds)

A - Traffic, in Erlang

If one call is made by a subscriber within an hour and last 120

seconds, the traffic is calculated as: A=1120/3600=33mErl

For convenience of engineering calculation, the traffic is usually

defined as 25mErl per subscriber.

GOS


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Grade of ServiceGOSGOS refers to the degree ofnetwork congestion or call loss rate.

GOS=2% means that 98% of subscribers can make calls

successfully and 2% of subscribers will end up with

unsuccessfulness.For network operators, 2-5% of GoS is adopted.

Erlang-B Traffic Tables

Abbreviated - For P.02 Grade of Service Only


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#TrunksErlangs #TrunksErlangs #Trunks #TrunksErlangs #TrunksErlangs #TrunksErlangs #TrunksErlangs #TrunksErlangs

1 0.0204 26 18.4 51 41.2 76 64.9 100 88 150 136.8 200 186.2 250 235.8

2 0.223 27 19.3 52 42.1 77 65.8 102 89.9 152 138.8 202 188.1 300 285.7

3 0.602 28 20.2 53 43.1 78 66.8 104 91.9 154 140.7 204 190.1 350 335.7

4 1.09 29 21 54 44 79 67.7 106 93.8 156 142.7 206 192.1 400 385.9

5 1.66 30 21.9 55 44.9 80 68.7 108 95.7 158 144.7 208 194.1 450 436.1

6 2.28 31 22.8 56 45.9 81 69.6 110 97.7 160 146.6 210 196.1 500 486.4

7 2.94 32 23.7 57 46.8 82 70.6 112 99.6 162 148.6 212 198.1 600 587.2

8 3.63 33 24.6 58 47.8 83 71.6 114 101.6 164 150.6 214 200 700 688.2

9 4.34 34 25.5 59 48.7 84 72.5 116 103.5 166 152.6 216 202 800 789.3

10 5.08 35 26.4 60 49.6 85 73.5 118 105.5 168 154.5 218 204 900 890.6

11 5.84 36 27.3 61 50.6 86 74.5 120 107.4 170 156.5 220 206 1000 999.112 6.61 37 28.3 62 51.5 87 75.4 122 109.4 172 158.5 222 208 1100 1093

13 7.4 38 29.2 63 52.5 88 76.4 124 111.3 174 160.4 224 210

14 8.2 39 30.1 64 53.4 89 77.3 126 113.3 176 162.4 226 212

15 9.01 40 31 65 54.4 90 78.3 128 115.2 178 164.4 228 213.9

16 9.83 41 31.9 66 55.3 91 79.3 130 117.2 180 166.4 230 215.9

17 10.7 42 32.8 67 56.3 92 80.2 132 119.1 182 168.3 232 217.9

18 11.5 43 33.8 68 57.2 93 81.2 134 121.1 184 170.3 234 219.9

19 12.3 44 34.7 69 58.2 94 82.2 136 123.1 186 172.4 236 221.9

20 13.2 45 35.6 70 59.1 95 83.1 138 125 188 174.3 238 223.9

21 14 46 36.5 71 60.1 96 84.1 140 127 190 176.3 240 225.9

22 14.9 47 37.5 72 61 97 85.1 142 128.9 192 178.2 242 227.9

23 15.8 48 38.4 73 62 98 86 144 130.9 194 180.2 244 229.9

24 16.6 49 39.3 74 62.9 99 87 146 132.9 196 182.2 246 231.8

25 17.5 50 40.3 75 63.9 100 88 148 134.8 198 184.2 248 233.8

Erlangs

Suggested Channel Configuration


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Based on 2% GoS, Zhongxing adopts

followed traffic model.

TRXs 1 2 3 4 5 6 7

CCHs 1 2 2 2 3 3 3TCHs 7 14 22 30 37 45 53

Traffic(Erl) 2.94 8.2 14.9 22 28 35.5 43

Channel Encoding


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In order to enhance channel anti-interference capacityand transmission quality, special redundancytechnologies should be adopted to increase the bulk

of transmitted information which can be inserted at acertain pattern (encoding) at the sending end andextracted at an agreed pattern (decoding) at thereceiving end. This is called the encoding/decoding

process of channels.

Commonly used channel coding methods are: 1)

convolutional coding; 2) Fire coding; 3) parity checkcoding.

Convolutional Coding


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50bit(Ia) 132bit(Ib) 78bit(Ic)

50 3 132 4

1

78

260bit/20ms

X 2 X3 X 4

Fire code

+

+

Protection

bits

456bit

78bit

378bit

Block

coding

Convolutional

coder

G0

G1

136bit

189bit

53bit

O/E

Channel Interleaving


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In radio telecommunication, error bits often occurs inthe burst pulse sequence because of deep signal

fading. Check and correction of errors cannot be

efficiently done merely by means of channelencoding mentioned above. Interleaving technique is

thus adopted, by which the continuous bits in an

information block are segmented and transmittedindividually according to certain rules. That is, the

originally continuous block in the transmission

process becomes discontinuous, forming a group of

interwoven message transmitting blocks, which are tobe recovered (de-interleaving) into the original

information blocks at the receiving end.

Block A

Block B

Block A+1

Block B+1


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456bit

Block A

0

8

1

1

9

2

2

10

3

3

11

4

4

12

5

5

13

6

6

14

7

7

15

8

456bit

Block B

0

8

1

1

9

2

2

10

3

3

11

4

4

12

5

5

13

6

6

14

7

7

15

8

456bit

Block A+1

0

8

1

1

9

2

2

10

3

3

11

4

4

12

5

5

13

6

6

14

7

7

15

8

456bit

Block B+1

0

8

1

1

9

2

2

10

3

3

11

4

4

12

5

5

13

6

6

14

7

7

15

8

57 1 57 1 57 1 57 1 57 1 57 1 57 1 57 1

Even N+3Even N+2Even N+1

Even N

Odd N+4Odd N+5

Odd N+6 Odd N+7

116-bit block 116-bit block 116-bit block 116-bit block

DTX


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Two aims can be achieved by adopting DTX mode. One is to

lower the total interference level in the air, and the other is to

save transmitter power. The DTX mode and the normal mode

are optional, since the former will slightly lower the transmissionquality.

TA


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Signals sent by a base station on the broadcasting

channel help mobile stations to synchronize with the base

station. After connection is set up between a mobilestation and the base station, the base station will make

continuous tests, and provide the time advance (TA) on

the SACCH channel to all mobile stations twice every

second according to the BS-MS-BS broadcasting delay.

Mobile stations will make self-adaptive frame adjustment

according to time advance so that the time of mobile

station transmission to the base station matches that ofbase station reception.

Frequency Hopping


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To enhance system anti-interference ability, the GSM

system adopts the frequency hopping technology.

Frequency hopping refers to the hopping of carrier wave

frequencies according to a certain sequence in a very

wide frequency range. Data of control information are

converted into base band signals after modulation, which

are then sent into carrier wave modulation. Afterwards,the carrier frequency changes under the control of

pseudo-random codes, the sequence of which is

frequency-hopping sequence. Finally, when filtered byradio filter, the carrier is transmitted to and radiated by

antenna.


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Frequency hopping is to avoid external interference.

In other words, it is to prevent or greatly reduce co-

channel interference and frequency selective fadingeffect by converting frequencies to an extent that

interference cannot catch up with.

There are two frequency hopping modes: base band

frequency hopping and radio frequency hopping.


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Baseband frequency hopping


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Radio frequency hopping


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1[1].Gsm Overview

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Transcript of 1[1].Gsm Overview