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
ΠΑΡΑΔΕΙΓΜΑ – ΣΧΕΔΙΑΣΜΟΣ ΜΙΚΡΟΚΥΜΑΤΙΚΗΣ
Cellular networks
MSC/BSC
BTS
BTS
BTSPSTN
MSC = Mobile Switching CenterBSC = Base Station ControllerBTS = Base Transceiver Station
ΠΑΡΑΔΕΙΓΜΑ – ΣΧΕΔΙΑΣΜΟΣ ΜΙΚΡΟΚΥΜΑΤΙΚΗΣ
Cellular networks
ΠΑΡΑΔΕΙΓΜΑ – ΣΧΕΔΙΑΣΜΟΣ ΜΙΚΡΟΚΥΜΑΤΙΚΗΣ
From BTSantennas
To the Radio link radio
Radio linkRadio Base
Station 2Mbit/s
Cellular networks
ΠΑΡΑΔΕΙΓΜΑ – ΣΧΕΔΙΑΣΜΟΣ ΜΙΚΡΟΚΥΜΑΤΙΚΗΣ
Traffic rate: 2 Mbit/s
Cellular networks
ΠΑΡΑΔΕΙΓΜΑ – ΣΧΕΔΙΑΣΜΟΣ ΜΙΚΡΟΚΥΜΑΤΙΚΗΣ
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
ΠΑΡΑΔΕΙΓΜΑ – ΣΧΕΔΙΑΣΜΟΣ ΜΙΚΡΟΚΥΜΑΤΙΚΗΣ
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
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.