ΑΣΥΡΜΑΤΕΣ-ΔΟΡΥΦΟΡΙΚΕΣ_διάλεξη 6η

ΑΣΥΡΜΑΤΕΣ-ΔΟΡΥΦΟΡΙΚΕΣΕΠΙΚΟΙΝΩΝΙΕΣ

Διδάσκων

Λούβρος Σπυρίδων

Επίκουρος Καθηγητής - ΤΕΣΥΔ

ΔΙΑΛΕΞΗ 6

ΕΠΙΓΕΙΑ ΜΙΚΡΟΚΥΜΑΤΙΚΗ ΖΕΥΞΗ (MW LINK) – ΒΑΣΙΚΕΣ ΕΝΝΟΙΕΣ

ΕΙΣΑΓΩΓΗ ΣΤΑ ΜΙΚΡΟΚΥΜΑΤΙΚΑ ΣΥΣΤΗΜΑΤΑ ΜΕΤΑΔΟΣΗΣ

Telecommunication

PDH, Plesiochronous Digital HierarchyDeveloped in the 1950s and 1960s when voice was predominant and digital transmission was only small isolated islands in an analog ocean.

SDH, Synchronous Digital HierarchyDeveloped in the 1980s. Offers a more efficient transmission technique,higher capacities and embedded network management data.

PDH and SDH…

CablesElectrical or Optical

Satellite

Radio link

Media

64kbit/s

64kbit/s

Where it all started, the 64kbit/s PCM channel• Originally used to transport one phone call.• Developed during the sixties when a technology

change from analogue to digital was necessary

PCM = Pulse Coded Modulation

A

D

D

A

Clock/timing Clock/timing

Digital Analogue

Where digital transmission started...

Where digital transmission started...

When 64kbit/s isn’t enough…

Clock

PCM-frame

64kbit/s

64kbit/s“European” standard: 32 x 64kbit/s = 2.048Mbit/s, E1

“American” standard: 24 x 64kbit/s = 1.544Mbit/s, T1

E1 frame (“PCM frame”, “2Mbit frame”, “Primary rate”…)

Structured E1One 64kbit/s channel = One Time Slot (TS)Time Slot 0 used for synchronization of the E1 itselfRemaining 31 time slots used to carry payload such as:• 30 landline telephone calls (1 call/TS, TS16 used for signaling)• Approx. 100 GSM telephone calls.• Data traffic at 64kbit/s level.

TS 0

TS 31

TS 16

… A3, A2, A1

… B3, B2, B1

… C3, C2, C1

… D3, D2, D1

…C2, B2, A2, D1, C1, B1, A1...

Multiplexer

… A3, A2, A1

… B3, B2, B1

… C3, C2, C1

… D3, D2, D1

Demultiplexer

Multiplexing in generalWhen higher capacity is needed…

Bit rate = n times y kbit/s(+ possible extra stuffing bits)

Bit rate = y kbit/s

Multiplexing in SDH

2.048Mbit/s 155.52Mbit/s 622.08Mbit/s

x 63

PDH SDH

STM-1

E1

STM-1

STM-1

STM-1

STM-4

STM-4

STM-4

STM-16

STM-4

E1

2488.32Mbit/s

STM-1 frame structure

=155.52 Mbit/s

1 9 270Columns

1

9

Row

s PayloadMax effective approx. 150Mbit/s

For example 63 x E1

OverheadNetwork

supervision

64kbit/s

10

Summary, ETSI “containers”

MINI-LINK

MINI-LINK MINI-LINK

MINI-LINKMarconi LH, MDRS

64kbit/s x32x4

x4 x4

E1

E2 E3 E4

x63x4 x4

STM-1 STM-4 STM-16

PDH

SDH

x3 x12Mbit/s

8Mbit/s 34Mbit/s 140Mbit/s

155Mbit/s 622Mbit/s 2.5Gbit/s

Marconi LH

Circuit switched, connection oriented

• A fixed path is set up at the beginning of a connection/conversation, • The path is maintained the same during the entire connection,

no matter any variations in the traffic.+ Fixed short delay- Occupies the same capacity even when the connection is “silent”.

PDH or SDH as carrierRadio link/optical fibre/copper as media

64kbit/s

• Traffic divided into small packages (ATM cells)• An address field added.• “Any” type of traffic, voice, video, data…• Only generated when there is “something to be said”.+ Very good for bursty capacity demands (data)+ Occupies no capacity when the connection is “silent”.- Can give unpredicted delay during “busy hours”

Address fieldPayload

ATM,Connection oriented packet switched

ATM over PDH/SDH

• PDH and SDH can be used to carry the ATM cells.• ATM switches reading the destination field of each cell and sends

it in the correct direction.• Gives compared to circuit switched more efficient utilization of

available carrier resources (PDH/SDH/…) by statistical multiplexing

ATM over PDH/SDHPDH or SDH as carrier

Radio link/optical fibre/copper as media

ATM ATMATM

ΑΤΜ Quality of Service

ATM ATMATM

CE

Quality of Service classes (QoS), “priority classes”:

Class AConstant Bit Rate (CBR)Circuit Emulation (CE) trafficEnd to end synchronizationNon compressed voice and video

Class BVariable Bit Rate-Real Time (VBR-RT)End to end synchronizationCompressed voice and video

Class CVariable Bit Rate-Non Real Time (VBR-NRT)LAN interconnectX.25, Frame relay

Class DAvailable Bit Rate (ABR)LAN interconnectInternet, TCP/IP

Class XUndefined Bit Rate (UBR)LAN interconnectInternet, TCP/IPNo

Transmission network - general

Access Network

PDH

PDH

Core/Trunk Network

SDHAccess Network

SDH

Trend

From: Circuit switched To: Packet switched

Point to multipoint network

Hub site

Access TerminalsSector

PABX

CellularRadio Base Station Data Communication

(LAN)

ΠΑΡΑΔΕΙΓΜΑ – ΣΧΕΔΙΑΣΜΟΣ ΜΙΚΡΟΚΥΜΑΤΙΚΗΣ

PSTN(via telephone exchange)

PSTN = Public Switched Telephone Network

Public, fixed networks

Private, corporate networks

PSTN(via PBX)

PBX = Private Branch Exchange

Head Office

Branch Office

Branch Office


Cellular networks

MSC/BSC

BTS

BTS

BTSPSTN

MSC = Mobile Switching CenterBSC = Base Station ControllerBTS = Base Transceiver Station


Cellular networks


From BTSantennas

To the Radio link radio

Radio linkRadio Base

Station 2Mbit/s

Cellular networks


Traffic rate: 2 Mbit/s

Cellular networks


MSC / BSC

BTS2Mbit/s

BTS2Mbit/s

BTS2Mbit/s

BTS2Mbit/s

BTS2Mbit/s

2Mbit/s

2Mbit/s

2x2Mbit/s

2x2M

bit/s

2x8Mbit/s

Cellular networks


ΒΑΣΙΚΕΣ ΑΡΧΕΣ ΡΑΔΙΟΔΙΑΔΟΣΗΣ

ΒΑΣΙΚΕΣ ΑΡΧΕΣ ΡΑΔΙΟΔΙΑΔΟΣΗΣ

A microwave transmission network can be considered to consist of four different subnetworks.

• Traffic network; traffic distribution and traffic related equipment for the transport from BSC/RNC to ”the last site”

• Syncronization network; transport of synchronization signal from BSC/RNC to transmission equipment and radio base stations.

• Management network; for the supervision of every node in the transmission network.

• Radio network; microwave radio communication to carry traffic, synchronization and management.

Radio communication

VoiceVideoData

VoiceVideoData

• Broadcast radio• Television• Mobile phones• Bluetooth• Wireless LAN• Radio links• etc

Carriergenerator

Modulator PowerAmplifier

Transmitter (Tx)

PreAmplifier

De-modulator

Localoscillator

Receiver (Rx)Modulated carrier

Radio path

Equipment properties• Carrier frequency• Bandwidth• Modulation type• Transmitter output power• Receiver sensitivity• Antenna gain/directivity• Antenna mounting position• Diversity

Path properties• Information density

• Coverage area• Interference

• Obstacles• Climate

• Atmospheric properties

Give

Radio communication

Hop (or Link)

Radio pathTerminal Terminal

Digital bit stream in each direction e.g. …100110101…Capacity in Mbit/s

Radio linksΧρειαζόμαστε δύο συχνότητες (carriers) για να έχουμε Full Duplex σύστημα επικοινωνίας

Radio pathAntennaRadio•Transmitter•Receiver

AntennaRadio•Transmitter•Receiver

Two different frequencies, f and f’,used as carriers. Together forming one duplex channel.

f

f’Bandwidth/Capacity

Bandwidth/Capacity

Radio links

Am

plitu

deS

igna

l stre

ngth

, pow

er[d

Bm

]

Frequency, the number of oscillations per second [Hz]

t

Frequency and power

Frequency and power are chosen to give optimum performancesfor the intended radio communication use

The numbers of oscillations per second (the frequency), measured in Hertz [Hz].

By changing the frequency different things are achieved:• Steady large changes will give different propagation properties• Steady small changes will give separate channels• Fast small changes are used to carry the information (modulation)

Frequency

• In radio communication the signal strength is usually measured in Watt or in the logarithmic unit dBm

• The reference for dBm is 1mW 0dBm = 1mW

• Negative dBm values power below 1mWPositive dBm values power above 1mW

Power

Radio link typical transmitter power: 20dBm=0.1WRadio link typical receiver threshold: -80dBm=0.00000000001WGSM 900 cell phone transmitter power: 2W (33dBm)GSM 900 radio base station transmitter power: 20W (43dBm)Broadcast transmitter power: 60 000W (78dBm)

Examples of different carrier power levels

Power

Basic free space loss

d1 d2

• The energy within a certain area will be less as the distance increases.• Frequency dependency,

“Low” frequency → low loss over distance“High” frequency → high loss over distance

ΑΠΩΛΕΙΕΣ ΕΛΕΥΘΕΡΟΥ ΧΩΡΟΥ - link budget

Transmitteroutput power

Input power to

the receiver

Receiver threshold level

Distance [km]

PowerLevel[dBm]

7 GHz

Basic free space loss23 GHz38 GHz

0 km n km

Basic free space loss

Generally frequency licenses shall be applied for from national administrations

“High” frequencyEasier to get licenseShort rangeUrban use in general

“Low” frequencyLong rangeGenerally used in rural areas

Channel spacing/bandwidth

3.5 MHz3.5 MHz

7 MHz

7 MHz14 MHz

14 MHz28 MHz

28 MHz

International regulations divides the frequency bands into channels with different bandwidths, defined as channel spacing.

• Wide bandwidth: high traffic capacity• Narrow bandwidth: more and longer paths

ETSI Channel spacing

40 MHz

40 MHz

Frequency plan, 15GHz band14925 M

Hz

15343 MH

z

28 MHz1D 15D

3.5 MHz1A 3A 5A 7A 114A 116A 118A 120A

7 MHz1B 2B 3B 4B 57B 58B 59B 60B

14 MHz1C 2C 29C 30C

14500 MH

z

28 MHz1’D 15’D

3.5 MHz1’A 3’A 5’A 7’A 114’A 116’A 118’A 120’A

7 MHz1’B 2’B 3’B 4’B 57’B 58’B 59’B 60’B

14 MHz1’C 2’C 29’C 30’C

14924 MH

z

High band

Low band

Modulation techniques, examplesC-QPSK (4QAM)

4 symbols2 bit/symbol

Phase

128QAM

128 symbols7 bit/symbol

Phase and amplitude

Low modulation order: + long hops, fairly uncomplicated techniqueHigh modulation order: + high traffic capacity per bandwidth

Channel spacing/modulation/capacity

Channel spacing [MHz]

3.5714284056

C-QPSK2x28

2x834+2

16QAM

2x834+22x34

STM-1

64QAM

STM-1

Available ETSI combinations in MINI-LINK and Marconi

C-QPSK16QAM

128QAM

Distance [km]Traffic capacity

128QAM

STM-1

64QAM

Antenna

Parabolic 0.6 m

Parabolic 0.2 m

Parabolic antennas • gives high directivity

(well focused beam).• are referred to

by the diameter.• in diameters from 0.2 to 3.7m

Low radio frequency Large antennaLong path length Large antenna

A “small” antenna gives: Less windload, less visibility and lower cost for antenna and installation

A “large” antenna gives: Higher gain, thereby longer hopand/or higher transmissionquality

Antenna

Antenna gain

Transmitteroutput power

Input power to

the receiver

Receiver threshold level

Distance [km]

PowerLevel[dBm] Antenna

Gain[dBi]

0.3m antenna

0.6m antenna

1.2m antenna

0 km n km

Antenna polarization

Different polarization can be used to reduce interference between neighboring paths when using the same or nearby frequencies

V (Default)

H

Point to multipoint antenna

Hub: 0.2m 90º sector antenna

AT: Point to point antenna

Line of sightRadio optical line of sight

Geometrical line of sight

• Το ύψος του Ιστίου τοποθέτησης της κεραίας πρέπει να σχεδιαστείΠροσεκτικά ώστε να δώσει καθαρό line of sight.• Ο σχεδιαστής θα πρέπει να ενθυμείται ότι λόγω ατμοσφαιρικών συνθηκών ράδιο διάδοσης (ο μεταβλητός δείκτης διάθλασης της ατμόσφαιρας) η ράδιο δέσμη της ζεύξης καμπυλώνει ελαφρώς προς τα κάτω….

Ground clearance

BER = Ratio of bits not possible to detect correctlyBER 10-3 = One bit out of 1000 bits corrupted – καλό για φωνή

BER 10-6 = One bit out of 1000 000 bits corrupted - καλό για data

BER 10-9 = One bit out of 1000 000 000 bits corrupted

Two bits out of 8 corrupted

Sent bitstream

Detected bitstream

P

D

…0 0 0 1 1 0 1 0… …0 0 0 0 1 1 1 0…

Transmission quality

Terminal Terminal

Transmitter Receiver

Receiver

Switch Switch

1+1 protection

Quality & Availability targets

• All links are designed to meet a certain transmission Quality & Availability.• Internationally accepted recommendations from:

- ITU-T (media independent)- ITU-R (radio-link specific)

• Quality = the ratio of errors in the bit stream giving short term cuts.• Availability = long term cuts• Limiting factors for radio links

- Distance, - Rain- Multipath fading- Hardware errors

• It is the role of the Planner to design individual links and network to meet the Q&A targets.

ΑΣΥΡΜΑΤΕΣ-ΔΟΡΥΦΟΡΙΚΕΣ_διάλεξη 6η

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