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EE 552/452, Spring, 2008

Wireless Communications(and Networks)

Zhu Han

Department of Electrical and Computer Engineering

Class 26

May 6th, 2008

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GSM System Arch i tecture

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GSM interface

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GSM Network Structure

MSC/VLR

HLR/

AUC EIR SC/VM

OMC

BSC

BTS

PSTNISDNPSPDN

MS

BSS

MSS

Um

Abis

BIE

A

F

C

H

MSC/VLR

E

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Base Transceiver Station ( BTS )

Base Transceiver Station (BTS)

–Wireless transmission

– Wireless diversity

– Wireless channel encryption

– Conversion between wired and wireless signals

– Frequency Hopping

BaseBand Unit:

– voice and data speed adapting and channel coding

RF Unit: – modulating/demodulating, transmitter and receiver

Common Control Unit:

– BTS operation and maintenance

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Base Station Controller ( BSC )

Managing Wireless network-BSS

Monitoring BTS

Controls:– Wireless link distribution between MS and BTS

– Communication connection and disconnection

– MS location, handover and paging

– Voice encoding, transecoding (TC), rate, adaptation,

–

The operation and maintenance functions of BSS.

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Mobile Service Switching Center ( MSC )

holds all the switching functions

manages the necessary radio resources,

– updating the location registration

– carrying out the inter-BSC and inter-MSC tender

Inter-working with other networks (IWF).

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Home Location Register ( HLR )

Manages the mobile subscribers database

subscriber information

part of the mobile location information

3 identities essential

– the International Mobile subscriber Identity

– the Mobile station ISDN Number

– the visitor location register (VLR) address

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Visitor Location Register ( VLR )

Dynamically stores subscriber information needed to handle

incoming/outgoing calls

Mobile Station Roaming Number

– When a roaming mobile enters an MSC area. This MSC warns

the associated VLR of this situation; the mobile enters a

registration procedure through which it is assigned a mobilesubscriber roaming number (MSRN)

Temporary Mobile Subscriber Identity, if applicable

The location area in which the mobile has been registered

Data related to supplementary service parameters

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AUC/EIR

Authentication Center(s) (AUC)

– Providing the authentication key used for authorizing the

subscriber access to the associated GSM PLMN.

Equipment Identity Register(s) (EIR)

– Handling Mobile Station Equipment Identity

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Overview: Function Layers of GSM-1

OAM

S ervice carrie r

CM

MM

RR

Subsc riber

Tran smissi on

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Protocol Stack Structure of GSM

CM

MM

RR

LAPDm

MS

RR

LAPDm

Um

LAPD

BTSM

LAPD

Abis

RR

BTSM SCCP

MTP3

BSSAP

BTS BSC

MTP2

SCCP

MTP3

BSSAP

MTP2

CM

MM

MSC

A

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TDMA

Concept:

– channel is composed of a series of timeslots of periodicity.

Different signal energies are distributed into different timeslots.

The adjacent channel interference is restricted by connection

choosing from time to time. So the useful signal is passed only in

the specified timeslot.

GSM adopts TDMA/FDMA mode

channel width: 200KHz,

each channel has 8 timeslots

User 1

User 2

User 3

Frequency

time

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GSM Timeslot and Frame structure

time

Frequency

BP

15/26ms

200KHz

interval

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GSM Spec

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Frequency Resource

GSM900 :

up: 890~915MHz

down: 935~960MHz

duplex interval: 45MHz

bandwidth: 25MHz，

frequency interval: 200KHz

GSM1800 :

up: 1710-1785MHz

down: 1805-1880MHz

duplex interval: 95MHz，

working bandwidth: 75MHz，


EGSM900 :up: 880~890MHz

down: 925~935MHz

duplex interval: 45MHz

bandwidth: 10MHz，


GSM1900MHz:

up:1850~1910MHz

down:1930~1990MHz

duplex interval: 80MHz， working bandwidth: 60MHz，


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Frequency Resource

1800MHz

1900MHz

900MHzWhich one?

Single Band Network General Priority

High

Low

Reason

For Subscriber For Operator

Propagation

Characteristic

New Operator

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Single Band Network

1800MHz

1900MHz

900MHzSingle Band

Dual Band

Triple Band

In a sense, the network determines the handsetscan be selected.

But nowadays, most handsets support dual band.

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Single Band Network

Propagation characteristic

Cell coverage radius :

The higher the propagation

frequency

The higher the propagation loss

The smaller the cell coverage radius.

900MHz

1800MHz

1900MHz

We know

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Timeslot and Frame structure

0 2045 2046 2047321 2044

3210 4947 48 50

0 24 251

1 super high frame = 2048 super frame = 2715648 TDMA frame

1 super frame = 1326 TDMA frame（6.12s）

0 1 2524 504910

1 multiplex frame = 26 TDMA frames（120ms） 1 multiplex frame = 51 TDMA frame

0 1 765432

1 TDMA frame = 8 timeslot（120/26 = 4.615ms）

BCCH

CCCH

SDCHSACCH/TCH

FACCH

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GSM Frame

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Contro l Channel Frame

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Time Slot Data Bursts

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GSM Frame Structu re

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Physical Channel

The physical channel adopts FDMA and TDMA techs. On the time domain, a

specified channel occupies the same timeslots in each TDMA frame, so it canbe identified by the timeslot number and frame number.

0 1 765432

8 9 151413121110

16 17 232221201918

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GSM Speech

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Channel Type-Summary

channel

TCH

CCH

Voice CH

Data CH

FR Voice Traffic Channel (TCH/FS)

HR Traffic Channel (TCH/HS)

4.8Kbit/s HR TCH (TCH/H4.8)

9.6Kbit/s FR TCH(TCH/F9.6)

4.8Kbit/s FR TCH (TCH/F4.8)

BCH

FCCH (down)SCH (down)

BCCH (down)

CCCHRACH (up)AGCH (down)

PCH (down)

DCCH

SDCCH

FACCH

SACCH

14.4Kbit/s FR TCH (TCH/F14.4)

Enhanced FR Traffic Channel (TCH/EFR)

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Channel Type

Traffic Channel

–Transmit voice and data

Signaling Channel

– transmit the signaling and synchronous data between BTS and MS.

BCH :

– Frequency Correction CHannel（FCCH）

-- for MS error correction

– Synchronous Channel（SCH)

-- for MS frame synchronization and BTS recognization

– Broadcasting Control CHannel（BCCH）

-- broadcasting information(cell selection information, etc..)

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Cell Mode Layout

O

Omni-directional cell

Adopt omni-directional antenna，

the overall directional propagation

characteristic is the same.

Directional cell

In general, cell with multi-sector is in

common use. Every directional celladopts directional antenna.

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BTS Mode

Capacity

– When the traffic is very low, and no possibility for quick

increment, Omni-directional cell is used in common. Otherwise,

we suggest to adopt the sector cell.

Note: TRX-transceiver,each TRX handles 1 frequency.

Coverage Area

– Sector cell is often used to enlarge the cell coverage radius

because of the higher antenna gain.

– For special coverage ,such as road coverage, two-sector cell is

adopted firstly.

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System capacity

Erlang :

– the traffic intensity of a totally occupied channel (i.e. the call hour

of a unit hour or the call minute of a unit minute). For example,

the traffic of a channel occupied for 30 minutes in an hour is 0.5

Erlang)

GOS: – defined as the probability of call blocking or the probability when

the call delay time is longer than a given queuing time.

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Reasons for Interference

The transmission path is very complex, ranging from the simple line-of-

sight transmission to encountering such terrain as buildings, hills and trees.Wireless channels are extremely unpredictable.

Abrupt drop, or fading, of signal strength in the land mobile wireless channelis quite common. The fading feature of the mobile channel depends on theradio wave propagation environment.

Environmental factors:

– Terrain (mountains, hills, plains, water bodies, etc.);

– The quantity, heights, distribution and materials of buildings;

– The vegetation of the region;

– Weather conditions; – Natural and artificial electromagnetic noises;

– Frequency;

– How MS is moved.

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Interference

Co-Channel Interference

– Conception: the interference among the signals of co-channel cells is called co-channel interference.

– Result from : Frequency reuse

– Reduction method: co-channel cells must physically be spaced ata minimum interval to ensure adequate isolation of transmissions.

Adjacent Channel Interference

– Conception: The signal interference from the frequency adjacentto that of the signal used is called adjacent channel

interference. – Reduction method: accurate filtering and channel allocation

(maximizing channel intervals of the cell). Interval of frequencyreuse inter-cell interference, such as C/I, C/A

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Solution -Anti-interference

FH technology

Dynamic power control (DPC)

Discontinuous Transceiving (DTX)

Diversity receiving technique

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Frequency Hopping Technique

Reason:

– counteract Rayleigh Fading

– scatter interference among multiple calls

Types:

– Base band frequency hopping

keeps the transmission and receiving frequency of each carrier unit unchanged, but merely sends FU transmission data todifferent carrier units at different FN moments.

– radio frequency hopping

controls the frequency synthesizer of each transceiver, making ithop according to different schemes in different time slots.

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Discontinuous Speech Transmission (DTX)

Two aims can be achieved by adopting DTX mode:

– lower the total interference electric level in the air

– save transmitter power.

TRAU BTS

BTS MS

Speech frame

480 ms

comfort noise frame

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Diversi ty Recept ion Technique

The multi-path propagation of radio signals causes

magnitude fading and delay time. – Space Diversity (antenna diversity)

– Polarization Diversity

orthogonal polarization diversity.

horizontal polarization and vertical polarization.

– Frequency Diversity

The working principle of this technology is that such

fading won’t take place on the frequency outside thecoherence bandwidth of the channel.

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Frequency Reuse

“4 ´ 3” reuse mode:

one group includes 3 sectors /site ,12 frequency which are

distributed to 4 sites. Every site owns 3 frequency.

A3

D2B1

C3

B2D1

D3

A2C1

B3

C2A1

B3

C2A1

A3

A1B1

D1

D3D2

C3

B2A1

C3D2

C3

C1

D2B1C2A1

A2C1

D3

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Frequency Reuse

“3 ´ 3” reuse mode:

– one group includes 3 sectors /site ,9 frequency which aredistributed to 3 sites. Every site owns 3 frequency.

A3

C2B1

B3

A2C1

C3

B2A1

A3

C2B1

B3

A2C1

B3

A1C1

A1

A3A2

C3

B2A1

A3A3

C3

C1

B2A1B2A1

A2C1

B3

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Numbering Arrangement

International Mobile Subscriber Identification number

(IMSI) It identifies a unique international universal number of a

mobile subscriber, which consists of MCC+MNC+MSIN.

1) MCC: country code, 460

2）MNC: network code, 00 or 01

3）MSIN: subscriber identification, H1H2H3H4 9XXXXXX,H1H2H3H4: subscriber registering place

H1H2: assigned by the P&T Administrative Bureau(operator )to different provinces, to each province

H3H4: assigned by each province/city

the IMSI of user will be written into the SIM card by specificdevice and software and be stored into the HLR with otheruser information.

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Mobile Subscriber ISDN Number （MSISDN）

It is the subscriber number commonly used. China uses the

TDMA independent numbering plan:

CC+NDC+ H1H2H3H4 +ABC

CC: country code, 86

NDC: network code, 135 — 139, 130

H1H2H3H4: HLR identification code

ABCD: mobile subscriber number inside each HLR

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International Mobile Equipment Identification code (IMEI)

It will uniquely identify a mobile station. It is a decimal number

of 15 digits. Its structure is:

TAC+FAC+SNR+SP

TAC=model ratification code, 6 digits

FAC=factory assembling code, 2 digits

SNR=sequence code, 6 digits

SP=reserved, 1 digit

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Mobile Subscriber Roaming Number (MSRN)

The MSRN is temporarily distributed to the subscriber by the

VLR according to the request by the HLR when this subscriber is called. The MSRN is released and can be assigned to other

subscriber later.

CC + NDC + 00 + M1M2M3 + ABC

CC: country code, 86 NDC: mobile network code, 135 — 139, 130

M1M2: same as the H2H3 of MSISDN

ABC: 000 -- 999

Temporarily Mobile Subscriber Identification Number (TMSI)

– To insure the IMSI security, the VLR will assign an unique TMSI number for the accessed subscriber. It is used locally only and is a4-byte TMSI number BCD code.

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Main Features Of IS-95 (cdmaone)

Modulation is performed using DSSS.

Employs variable rate coders.

Powerful low rate forward error-correcting codes.

Fast power control is employed to over come the near-far

problem. Soft handoff is employed.

Qualcomm code excited linear predictive (QCELP): 13.4 kbps

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Frequency and Channel Spec

Reverse: 824-849MHz, forward: 869-894MHz; PCS version 1800-2000MHz

Data rate 9.6kb/s; chip rate 1.2288Mchips/s, spreading factor 128.

Power Control:

Close-loop/open-loop

Rake receiver;

Soft handoff

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Forward CDMA channel

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Spec

Convolution code ½. Repetition circuit depending on speech

Block interleaver

Long PN sequence:

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Power Con tro l

Open Loop

Close Loop

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Orthogonal Cover ing and modulat ion

Walsh function: page 574

Quadrature modulation

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Upl ink

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Reverse Link Spec

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CT2

CT2 is a cordless

telephony standard thatwas used in the earlynineties to provide short-range proto-mobile

phone service in somecountries in Europe. It is

considered the precursor to the popular DECT

system.

http://en.wikipedia.org/wiki/DECT

http://en.wikipedia.org/wiki/DECT

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DECT

Digital Enhanced (formerly European) Cordless Telecommunications is

an ETSI standard for digital portable phones, commonly used for domesticor corporate purposes. DECT can also be used for wireless data transfers.DECT is recognised by the ITU as

fullfilling the IMT-2000

requirements and thus

qualifies as a 3G system,

as a part of the IMT-2000

group of technologies,

http://en.wikipedia.org/wiki/ETSI

http://en.wikipedia.org/wiki/Portable_phone

http://en.wikipedia.org/wiki/ITU

http://en.wikipedia.org/wiki/IMT-2000

http://en.wikipedia.org/wiki/3G





http://en.wikipedia.org/wiki/3G




http://en.wikipedia.org/wiki/ITU

http://en.wikipedia.org/wiki/Portable_phone

http://en.wikipedia.org/wiki/ETSI

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DECT func t ional concept

Portable handset

Radio fixed part

Cordless controller

Network-specific

interface unit

Supplementary

services

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DEC spec

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PACS

type of wireless telephone network compatible with telephone sets,answering machines, fax machines, and computers. A PACS can be used like

a local area network (LAN) with voice capability and can be part of a larger network or can be connected into the telephone system.

http://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci213380,00.html

http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci212495,00.html

http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci212495,00.html

http://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci213380,00.html

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PACS Spec

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PACS Frame Structu re

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Other issues

Pacific Digital Cellular: Japan, similar to IS-54

Personal Handyphone System: Japan, like DECT

Industrial, Scientific and Medical (ISM) band: Free

US PCS:

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Analog overv iew

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Digi tal Co rdless

2G

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2G

PCS

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PCS

T P j t

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Term Project

For presentator

– Presentation Clearness

– Timing

– Preparation for the slides

– Do you study something

– Ability to answer questions

For audience

– Bonus on asking good questions

13 minutes + 2 minutes questions

Fi l C t

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Final Comments

Final 60% why, why and why. 3 big questions. Control your

time.

Hope you can get something that can ring a bell to yousometime in the future

Evaluation form: I would appreciate if you can fill. It is

important for me

– https://coeneval.boisestate.edu/index.htm

If you get A, you can ask me for reference in the future.

After graduation, you will all be decent guys. Best wishes toyour career. After success, do not forget BSU.

ppt3675

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