Điện tử viễn thông c1 4 điện thoại số và truy nhập số khotailieu

NT1 NT2Terminal Adapter Terminal Adapter Terminal Adapter... Belgacom TWIN Network Terminator interface U S bus available for extensions 192 Kb/s Up to 8 terminals Terminal Adapter NT12

TỔNG ĐÀI &

KỸ THUẬT CHUYỂN MẠCH

Chương 1: Lý thuyết tổng quan và cơ sơ

TRƯỜNG ĐẠI HỌC ĐIỆN LỰC KHOA ĐIỆN TỬ - VIỄN THÔNG

Giảng viên: Phan Thị Thanh Ngọc

IV Điện thoại số và truy nhập số trong mạng VT

ABX

I S D N Đặc tính chính

– # simultaneous communications = # B channels

– Calling line identification

The Telephone Network

ISDN Basic Access

twisted pair, average length 2.5 Km

Digital switch

S bus

2 * 64 Kb/s + 16 Kb/s

144Kb/s modem

144Kb/s

modem

A/D converter

in phone

NT1 NT2

Terminal Adapter

Terminal Adapter

Terminal Adapter

Belgacom

TWIN

Network Terminator interface U

S bus available for extensions

192 Kb/s

Up to 8 terminals

Terminal Adapter

NT12ab Terminal

Adapter

ABX

ABX

Digital Cellular Radio

Systems

CT2

864-868

40 0.01 0.2 32

DECT

1880-1890

10 0.25 0.15 32

GSM

890-915 935-960 124 8 30 13

Wireless Local

LoopRadio is sometimes cheaper than digging the streets !

Wireless Local

Loop Planes or balloons could be cheaper

than building towers !

ABX

»Electromagnetic noise sources

»Other radio transmitters

»Multi-path propagation

Reuse of Frequencies

r Pr/s a = P t /r 2

transmitter

Cellular Radio

Cellular Radio

k = number available frequencies per cell

With smaller cells,

- more antenna sites are needed

Cellular Radio

in practice

Cellular Radio

GSTN ISDN

MSC

SS7

NSS

R A D I O

16Kb/s

64Kb/s

MS

GSM acronyms

• MS : Mobile Station

– ME : Mobile Equipment – SIM : Subscriber Identity Module

• BSS : Base Station Sub-system

– BSC : Base Station Controller – BTS : Base Transceiver Station – TRAU : Transcoder / Rate Adapter Unit

• NSS : Network and Switching Sub-system

– MSC: Mobile service Switching Center – HLR : Home Location Register

– VLR : Visitors Location Register

y

• Location Management : 3 options

– Ubiquitous paging :

»call made in all cells.

»No need to know where MS is

»Waste of radio capacity – Systematic location updating

»call made in the single cell where MS is

»Overload of NSS – Location Area

»call made in a group of adjacent cells

»location information transmitted only when leaving the area.

GSM Radio Transmission

• Two transmission modes

– Idle Mode - via a "common channel"

»MS lists to paging messages

»Monitors radio environment to select base

station

»Sends and receives short messages

– Dedicated Mode - via a "Traffic Channel"

»A TCH (13 kb/s full duplex) is assigned to a

specific call for voice/data transmission

»A "Slow Associated Control Channel" is used

for radio measurements

»For "Fast associated signaling" (needed for

rand,sres, Kc

data & signalling

i:Ki

sres = A3(Ki,rand)

Kc = A8(Ki,rand)

Wireless Interference Margins

Cause considerable loss in transmission

capacity

• Considerable room for

improvements by controlling interferences

– Signal hardening – Signal recovery – Signal expansion

= Next generation mobile

networks (UMTS)

Frequency

Space Time

Multi-path Interference

2nd generation (GSM) : interference = noise

3rd generation (UMTS) : add similar input signals with

Different paths have different lengths and different delays

Other Cellular

Protocols

• GSM & UMTS offer a mobile to fixed service

• Some professional users communities need

– Broadcast – Group communications – Mobile to mobile communications – Precise mobile localization

• TErestrial Trunked Radio is the answer !

– Used by police & emergency services in

»Belgium

»The Netherlands

»Germany