WIRELESS LOCAL LOOP AN OVERVIEW Mian Ahmed Yaser DE (Computer & Data Services)
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
WIRELESS LOCAL LOOP
AN OVERVIEW
Mian Ahmed YaserDE (Computer & Data Services)
Definition
• WLL is a system that connects the subscribers to the PSTN using radio system as a substitute for the copper for all or part of the connection between subscriber and switch.
Wireless local loop
• Replaces:– Traditional twisted pair
• Also called:– Fixed wireless access
WLL alternatives
• Narrowband– Replaces existing telephony services
• Broadband – Provides high speed two way voice and data
WHY WLL?
• Congested urban areas
• Far flung rural areas
• Fast installation
• Less maintenance
• Easy operation
• Less establishment problems
Role of WLL
• WLL services one or two cells• A cell has a base station antenna installed on
the top of a tall building or a tower• Customers’ antennas are installed atop their
houses or separate poles such that there is an unobstructed line of sight with the base station
• Base station is linked to the switching center wirelessly or wired
• An ISP is linked to the switch using a high speed link
Advantages of WLL1. Cost of installation and maintenance of WLL is lower
than cable network
2. Installation time is less in case of WLL
3. Selective installation: Installation for those who require connection at a certain time
4. Quality of wireless technologies have improved to nearly equal the contemporary wired options which do face problems like longer distances in xDSL and lack of infrastructure, so WLL offers tough competition
5. Cellular systems are too expensive with lesser signal quality than fixed broadband wireless which uses directional antennas
SPECIFICATIONS FROM PTCL
• Technologies and Standards Wing PTCL HQ
• No. T&S / TR-133B/03
• CDMA 2000 1x based on– TIA/EIA/IS-2000 standard– 3GPP2 standard– ITU-RM 1457 standard
Requirements of Specifications
• To Provide– Toll Quality Voice service
– Wireless Pay Phone– Internet access
– Maximum rate of 144 Kbps and at least 30 Kbps packet mode data
– 14.4 Kbps of voice band data in circuit mode
Main Parts of the system
• MSC- Main Switching Center
• BSC- Base Station Controller
• BTS- Base Transceiver Station
• FWT (Fixed Wireless Terminal) or Mobile terminal
Frequency Spectrum
• Rural Areas– 450 MHz band i.e.
• 452.5-457.475 MHz :Uplink
• 462.5-467.475 MHz :Downlink– 1-3 RF carriers 1.25 MHz each
• Urban Areas – 1900 MHz band (If available) i.e.
• 1890-1895 MHz : Uplink
• 1970- 1975 MHz: Downlink– 1-4 RF carriers 1.25 MHz each
Standards
• Air Interface Standard– TIA/EIA/IS-2000
• Frame st. standard– TIA/EIA/IS-2000
Compatibility
• Backward Compatibility– IS-95
• Forward Compatibility– CDMA 2000 1x EV DO
• 2.4 Mbps Multimedia
Vocoders
• Codec (EVRC) (EIA/TIA ISO 127-2)
• 3GPP2 standard CS0014-0-2
• 13.4 Kbps QCELP (IS-733) vocoder
• SMV (Selective Multirate Vocoders)
– Dynamic allocation of Vocoders required – Should also be software configurable
Duplexing method
FDD/TDD
Frequency division duplex/Time division duplex
Traffic Capacity of system
• In Erlangs/sector/MHz for 1% GOS with 98% active voice calls and 2% active data calls at 144 Kbps to be specified by the vendor:
Traffic Capacity of a BSC
• Capacity of BSC for an average traffic of 0.05 Er./Subscriber and 1%GOS. BHCA/sub shall be 4.
Capacity of Base Station
• Minimum 110 Erlang /FA / 3 sectors assuming all Remote Stations are FWTs using voice only.
Coverage Radius of BTS
• 20 to 25 Km, extendable to double this value
BTS sensitivity
-125 dBm
BSC
• The BSC should adopt ATM or IP platform.
• Switching capability of BSC is in Gbps
Power Supply
• To BTS, BSC and MSC is
-48 V (-44 V - -56.4 V)
Requirements from FWT
• Voice supporting RJ-11 Interface
• Group 3 fax at RJ-11 Interface
• Voice band data upto 14.4.kbps in circuit mode
• 144 kbps data in packet mode
• Subscriber’s Call Charge Meter (Home Meter)
Requirements from Handheld terminal
• Voice
• Voice band data upto 14.4.kbps in circuit mode
• 144 kbps data in packet mode
• Extended antenna support
• SMS
• Address book
Generic Model of CDMA 2000 1x WLL
HLR
IWF
OMC-S
AAA
OMC-P
BTSRS
PDSN
BSC MSC
NMC
Core Network (CN)
Radio Network (RN)
OMC-R
Packet SwitchedCore Network(PCN)
Um
Abis
A10/A11
A1/A2
L
HLR
IWF
OMC-S
AAA
OMC-P
BTSRS
PDSN
BSC MSC
NMC
Core Network (CN)
Radio Network (RN)
OMC-R
Packet SwitchedCore Network(PCN)
Um
Abis
A10/A11
A1/A2
L
WLL solution by Huawei
BSC Capabilty
• ATM broadband packet platform with switching capacity of 25Gbps
• Convenient to upgrade to 1x EV only by upgrading the software of BSS and adding 1x EV channel board to BTS;
Evolution to EV-DO
• Patent radio resource management algorithm
• Variable step length power control technique to improve receiving sensitivity and fulfill the performance requirements for future evolution to EV-DO
CDMA 2000 1x and EV-DO mixed Networking
CDMA IS-95 Standard
• Introduced in: 1993• Access Method: CDMA• Uplink band: 869 to 894 MHz• Downlink band: 824 to 849 MHz• Forward rev. spacing: 45 MHz• Channel Bandwidth: 1250 MHz• No. of duplex channels: 20• Max. power of mobile: 0.2 Watts• Users per channel: 35
CDMA IS-95 Standard (Contd.)
• Modulation: QPSK
• Carrier bit rate: 9.6 Kbps
• Speech coder: QCELP
• Speech coding bit rate: 8,4,2,1 Kbps
• Frame size : 20 m sec
• Error control coding: Convolutional1/2 rate forward; 1/3 rate reverse
Example IS-95
Lucent Airloop System
System Elements
.
STRU: Subscriber TRansceiver Unit
ITS: Intelligent Telephone Socket
WLT NIU
CTRUCATU ITSSTRU
OMC
LE
OMC: Operations & Maintenance Centre
System Boundary
WLT: Wireless Line Transceiver
CATU: Central Access and Transcoding Unit
CTRU: Central TRansceiver Unit
NIU: Network Interface Unit
System elements
• .
• Provides the interface to the local exchange (E1 links) non-concentrating
• Provides connection to subscribers over air interface
• Provides connection to OA&M facilities Local
Exchange
WLT
E1 Links(Trunks)
Air Interface
Wireless Line Transceiver (WLT)
OMC
Wireless line transceiver
• .
• Central Access and Transcoding Unit (CATU)
– Interface to the local exchange
• Central TRansceiver Unit (CTRU)
– Access to the Air Interface
The WLT comprises two sub-elements
Local Exchange
CATU
Up to 16 E1 Links
CTRU
Copper, fibre or microwave E1 linkconcentrating
• .
• Provides the Subscriber
interface to the telephone
network over the Air
Interface
• Provides the interface to
subscriber terminal
equipment (telephones,
faxes, modems, etc.) LocalExchange
WLTE1 Links
Air Interface
Network Interface Unit (NIU)
NIU
.
• Subscriber TRansceiver Unit
– Interfaces to the WLT via the Air Interface.
The NIU comprises of two sub-elements
ITS
STRU
– Intelligent Telephone Socket–Subscriber equipment interface
System elements
• .
• Provides all the management functions necessary to maintain the system
Operations and Maintenance Centre (OMC)
OMC• The OMC LAN connects to
AirLoop® via the CATU• The OMC provides OA&M
functionality for up to 250 WLTs
Local Exchange
CATU
Up to 16 E1 Links
CTRU
System interfaces
LE CATU CTRU STRU
ITS
A B C
D
EOMC
F G
LMT
System Deployment
CATU
Exchange
CTRU
4x2Mbps E1
4x2MbpsE1 NIU
STRU
ITS
FixedAccessSystem
OMC
PSTN
System Features
• Wired-Equivalent Service• High Data Rate, 144kbps for ISDN , and 512
kbps and above for packet data• High-End Calling Services• Clear Connections, ensured by CDMA • Signal Security• Modular and easy to expand• Easy to use Graphical User Interface (GUI) for
the Operation and Maintenance Center
System Services•Analogue Services
– POTS
– Voice band data up to 28.8 Kbps
– Emergency calls
– Supplementary services supported by hook-flash and DTMF
•Digital Services– EURO ISDN
– Circuit Mode– CLIP– CLIR
‘A Interface’
and
Central Access &
Transcoding Unit
LE CTRU STRU
ITS
B C
D
EOMC
F G
CATUA
LMT
CATUA
Local Exchange
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
Standard Switch InterconnectionProviding:
Up to 16 E1 links to each CATUTransparency for all services offered by the Local Exchange
All switching is carried out at Local Exchange
The ‘A’ Interface
• Connects the CATU to the Local Exchange• Supports CAS, V5.1, V5.2r1 & Q931 Protocols• Subscriber concentration possible using V5.2• Subscriber capacity varies depending on which protocol is used• V5.2r1 or V5.1* is Lucent proprietary
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
CATU
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
19” or ETSI RackAccepts - 48V DCIndoor Environment:-25°C to +55C °Safety & EMC to European standards
CATU - Interfaces
• A The Central Access & Transcoding Unit Provides
LE
The Local Exchange Interface
The CTRU Interface
CATUA
CTRUB
Router
Router
OMC
The OMC Interface
WAN/LAN
F
CATU - Hardware
The rack houses the following:-
• Up to 4 VME Card Shelves (VCS)
• Power and Alarm Distribution Shelf
• Auxiliary Shelf
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
4
3
2
1
CATU - Circuit Pack Layout
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
• PSU
CATU Shelf Comprises:-
HardDiskUnit
Co
ntr
ol P
roce
sso
r C
ard
Cable Duct
Po
we
r S
upp
ly U
nit
Ala
rm &
Rad
io C
ontr
ol C
ard
Lin
e In
terf
ace
Car
d
Lin
e In
terf
ace
Car
d
Lin
e In
terf
ace
Car
d
Lin
e In
terf
ace
Car
d
Cha
nne
l Ass
ocia
ted
Sig
nal
ing
Car
d
ET
EC
Fan 1 Module Fan 2 Module
Sign
alli
ng
Inte
rfac
e C
ard
Lin
e In
terf
ace
Car
d
ET
EC
ET
EC
ET
EC
ET
EC
ET
EC
ET
EC
• CPC
• HDU
• SIC
• CAS (optional)
• ETEC - 1 to 8
• LIC - 1 to 5
• ARCC 1/2 3 4-6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
CATU - Card Architecture
Central
Processing
Card
Hard Disk
Unit
Alarm and
Radio Control
Card
Signalling LineAInterface
FInterface
BInterface
Control Bus
Traffic and Timing Bus
ExternalAlarms
(WAN/LAN)
(E1 Links)(E1 Link)
ChannelAssociatedSignalling
Card
InterfaceCard
InterfaceCard
LineInterface
Card
Enhanced
Encryptionand
Card
Transcoding
Interface(WAN/LAN)
F
Summary
• Provides Interface to Local Exchange (A)• Supports CAS, V5.1, V5.2r1 & Q931 Protocols
• Supports up to 16 x E1 Links
• Provides an Interface to the CTRU (B)
• Provides an Interface to the OMC (F)
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
•B Interface and Central TRansceiver Unit
System Interfaces
LE CATU STRU
ITS
A C
D
EOMC
F G
CTRUB
LMT
CTRUB
B Interface
• Proprietary Interface• 1 x E1 Link• 128 x 16 kbps channels• 13 channels reserved for system use
• 115 channels available to support subscriber traffic
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
B Interface - E1 Structure
32 Timeslots / E1
= 1 Time Slot Channel16kb 128 TSCs / E1
13 TSCs Reserved for System Use
115 TSCs Available for User Traffic
= 1 Timeslot64Kb
System Capacity• Single Transceiver••• Traffic/Subscriber 0.2E 0.1E 0.1E• Blocking/GoS 0.1% 1.0% 2.0%• Coding Bandwidth Circuits Subs Subs Subs• LD-CELP 16kbps 115 443 982* 1025*• ADPCM 32kbps 57 191 442 468• A-Law 64kbps 28 76 186 201• ISDN (B+D) 80kbps 23 58 145 158• ISDN (2B+D) 144kbps 12 21 59 66
• Systems supporting more than 480 subs/ transceiver need V5.2 or V5.1*
CTRU - Features
CTRU
WLT NIU
OMC
ITSSTRUCATU
LECentral TRansceiver Unit
Outdoor Environment: -45° to +55°C
19” or ETSI rack, req’s 90V-264V AC @ 50/60Hz
Safety & EMCto European Standards
Floor, wall, or pole mounted
CTRU - Function
The CTRU provides the following functionality:-
• Terminates the B interface from the CATU• Provides the Air Interface• “Base Station”• Demodulation of all reverse link bearers
• Allows use of the Local Maintenance Terminal
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
CTRU - Hardware
• VME Shelf
CTRU Outdoor cabinet comprises:-
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
• CTRU Radio
• Optional E1 radio
• Power & Alarm distribution shelf
CTRU - Circuit Pack Layout
Con
tro
l P
roc
ess
or
Car
d
Pow
er S
up
ply
Un
it
Ala
rm &
Rad
io C
ont
rol
Car
d
Lin
e In
terf
ace
Ca
rd
Dem
od
ula
tor
Ca
rd
Dem
od
ula
tor
Ca
rd
Dem
od
ula
tor
Ca
rd
Dem
od
ula
tor
Ca
rd
Dem
od
ula
tor
Ca
rd
Dem
od
ula
tor
Ca
rd
Dem
od
ula
tor
Ca
rd
Dem
od
ula
tor
Ca
rd
Cable DuctFan 1 Module Fan 2 Module
Bla
nk
VM
E F
ace
pla
te
Bla
nk
VM
E F
ace
pla
te
Bla
nk
VM
E F
ace
pla
te
Bla
nk
VM
E F
ace
pla
te
Co
mm
on
Mo
du
lato
r C
ard
Sam
pli
ng &
Me
asu
rem
en
t C
ard
CTRU Shelf comprises:-
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
• PSU ( 90-264vAC)
• CPC
• SMC
• CMC
• DMC (up to 8)
• LIC
• ARCC1 - 4 5 6/7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
CTRU - Card ArchitectureLocal
MaintenanceTerminal
CentralProcessing
Card
LineInterface
Card
CommonModulator
Card
Sampling &Measurement
Card
Alarm &Radio Control
Card
DemodulatorCard
G
Control Bus
Traffic and Timing Bus
Radio Module
C
ExternalAlarm
B
Summary
• Proprietary B Interface (1 x E1 )
• 128 x 16 kbps time-slot channels
• CTRU = Outdoor cabinet
• Supports - Air, B and G interfaces
• Provides demodulation for all reverse link bearers
• Allows use of the Local Maintenance Terminal
AirLoop→ System
The Air Interface
The C InterfaceThe C Interface
Air Interface ObjectivesAir Interface Objectives
An introduction to CDMA
The function of the Air Interface
The Air Interface protocol
Describe:
AirLoop®: System Interfaces
LE CATU CTRU STRU
ITS
A B
D
EOMC
F G
C
LMT
C
Multiple Access TechniquesMultiple Access Techniques
FDMABroadcast
Early cellular (TACS)
Frequency
Tim
e
TDMA
Digital cellular (GSM)
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
Frequency
Tim
e
CDMALatest cellular (IS-95)
AirLoopAirLoop®®
Code
Frequency
Tim
e
Why CDMA ?Why CDMA ?
• Flexible– ability to support multiple basic rate users: (16, 32, 64Kbps)
• High performance – Inherent resistance to narrow-band interference & fading
• High Security – Spreading PN code, with Random Assignment
– Proprietary Interface
• Low Frequency Re-use – N=2
• Range/Capacity Tradeoff– Larger Cells In Low Capacity Areas
The Air Interface• Wideband CDMA
– 4096 kchips, 5MHz bandwidth– Inherent resistance to narrowband fading & RF interference– Power control in simple 2dB steps– Error correction using advanced algorithm
• 2 Frequency Bands 1.9 GHz - 3.4 GHz
• Physical– Base station: 90° sectors– Subscribers: narrow beam antenna
• Designed after UK propagation trial– Urban, sub-urban & rural environments
CDMA Technology - Transmit
Source andChannelCoding
RFModulator
CodeGenerator
X
Multiplier
Code Bits (Chips)
Digital Signal (Bits)
FrequencySpectrum
f
“Spread” FrequencySpectrum
f
• Information signal is multiplied by a unique, high rate digital code which spreads its bandwidth before transmission. Code bits are called “Chips”.
• At the base station, many signals can be combined in one radio transmitter, since all users have same frequency channel.
CDMA Technology - Receive
RFDemodulator
Channeland
SourceDecoding
CodeGenerator
X
Correlator
Code Bits (Chips)
De-SpreadSignal
f
“Spread” FrequencySpectrum
f
Digital Signal (Bits)
• At the receiver, the spread signal is correlated again by a synchronised replica of the same code, and is “de-spread” and recovered
• Even if multiple users share the channel, the signal can be recovered since the other codes are different:
G = processing gain = number of chips per information bit
Recovered SignalOtherUsers
f
G{
DS-CDMA (Spread Spectrum)• Direct Sequence Code Division Multiple Access
Tra
nsm
itte
r
16kbps data
gives
multiplied by
1 of 128 wideband spreading codes
low power, wide band RF signal
Rec
eiv e
r
multiply the received signal with the same, synchronised, spreading code
16kbps data
and
spreads other signals & interference
CDMA
•AirLoop DS-CDMA uses:– Rademacher-Walsch code to differentiate
between the 128 bearers – Pseudo-noise (PN) to differentiate between
WLTs
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
CDMACTRU
WLT NIU
OMC
ITSSTRUCATU
LE
128 x 16kbps channels (bearers)• 115 available for user traffic
aggregated to give required subscriber capacityhard channel limit ensures low Bit Error Rates (BERs)
• centrally configured
115 circuits 982 lines POTS LD-CELP @ 16kbps
57 circuits 442 lines POTS ADPCM @ 32kbps
28 circuits 186 lines POTS PCM @ 64kbps
23 circuits 145 ports ISDN B+D @ 80kbps
(1% blocking, 0.1Erlang/ line)
CDMA: AirLoop® and IS-95
AirLoop IS-95
Fixed Access target services Mobile
No mobility Yes
5MHz RF bandwidth 1.25MHz
115 x 16kbps traffic channels soft limit
10-6 BER 10-3
16-144kbps data bandwidth 8-13kbps
RF Frequency BandRF Frequency Band
3.400GHz 3.500GHz 3.550GHz3.450GHz
Forward LinkReverse Link Guard Band
50MHz
• 2 RF Frequencies in Development
• 5 MHz Forward & Reverse inks
• ETSI TM4 Wireless Access BandplanFrequency Transmit Duplex Receive RF Channels 3.4 GHz 34525-34975 100 35525-35975 10
• Other FrequenciesFrequency Transmit Duplex Receive RF Channels1.9 GHz 18525-19075 80 19325-19875 12
• Base assumption:2 x 5MHz up link2 x 5MHz down link4 x 90° sectors1 WLT/ sector
Frequency Re-Use
f 1 f 1
f 2
f 2
•Additional spectrumlower cell countwithin area coverage constraints
higher final capacity/ celllower initial costsimplifies backhaul1 WLT/ sector/ frequency
Bit Error Rate Effects Range and Capacity versus BER
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
0 10 20 30 40 50 60 70 80 90 100 110 120Number of Bearers
Ra
ng
e
1 E-3 BER
1 E-6 BER
1 E-5 BER
1 E-4 BER
Cell Patterns• Square or Hexagonal Grid
• 4 x 90º
• 1 WLT/sector
• 4 WLTS/cell– or n x 4 depending on
frequency allocations
•Cell radius rural 5.2 km suburban 3.4 km urban 2.1 km
Based on: 95% coverage, 10-6 BER, L-o-S not mandatory, ‘typical’ environment.
Full RF planning should ALWAYS be used to define actual coverage in required areas.
Summary
• DS-CDMA
• Proprietary Interface
• Rademacher-Walsch codes
• Pseudo Noise codes
• Available in 2 frequency bands
AirLoop→ System
The
Subscriber Interface
The
Network Interface Unit
NIU Objectives
Describe:-
The function of the ‘D’ and ‘E’ Interface
The function of the Subscriber Transceiver Unit
The function of the Intelligent Telephone Socket
AirLoop®: System Interfaces
LE CATU CTRUA B C
OMC
F G
STRU
ITS
D
ELMT
STRU
ITS
D
E
NIU
The Subscriber TRansceiver Unit (STRU)
The Network Interface Unit consists of 2 Sub-assemblies
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
andThe Intelligent Telephone Socket (ITS)
STRU - Features
Subscriber TRansceiver Unit– Outdoor Unit (environment: -45 to +55C)
– Wall, or pole mounted
Houses:– Integrated flatplate antenna
– Modem
– Transceiver
– Interface to the ITS - ‘D’ Interface
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
STRU - Function
• The function of the STRU – is to receive and transmit
signals at the subscriber’s premises
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
STRU - Modes of Operation
The STRU has 2 modes of operation;
Idle Mode&
Call Mode
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
STRU - Modes of Operation
• Idle Mode– the STRU enters idle mode when no calls are
being handled. Whilst in this state, the STRU constantly monitors channels to determine if action is required
• Call Mode– the STRU will enter call mode when
calls are being processed
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
ITS Features
Intelligent Telephone Socket:– Requires 90-264V @ 50/60Hz
– Offers battery backup2hrs Standby/1hr Talk Time (optional unit provides 8hrs standby)
– Provides STRU with 54Vdc
– Has smartcard facility
– Can be Wall or Table Mounted
– Offers LED Control/Status Indication
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
ITS - Function
• The function of the ITS– is to provide the
subscriber with either analogue or ISDN access to the local exchange via the STRU, Air Interface and the WLT
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
ITS - Status Indications
The ITS has 3 Status LED’s ;
ITS - Modes of Operation
The ITS has 3 modes of operation;
Installation Mode
Minimum Configuration Mode
Fully Operational Mode
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
ITS - Modes of Operation
• Installation Mode
– is entered when the ITS is powered up during installation. After successful installation the ITS goes into fully operational mode
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
ITS - Modes of Operation
• Minimum Configuration Mode – is entered if during installation
an error is detected or if a major alarm is reported during normal operation.
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
During this mode no call processing takes place.
ITS - Modes of Operation
• Fully Operational Mode – in this mode the ITS is fully
functional, performing maintenance tasks and call processing
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
Other Features
The ITS Also Provides;
– 2 x POTS Subscriber Lines (RJ11)
– 1 x ISDN BRA Interface (RJ45)
– 8 POTS Subscriber Lines (R3)
– Group 3 Fax Capability
– 28.8Kbps Modem Capability
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
Security
• Subscriber authentication– Cell & WLT sector– Range (± 40m)– NIU i/d
• Air interface traffic protection– CDMA inherently difficult to intercept
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
Smartcard
• Contains the following information– NIU i/d - assigned to the smartcard
– PN Code Index
– Frequency Band Channel
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
Engineers Smartcard
NIU Summary
STRU ITS
• Integrated flatplate antenna
• Modem
• Transceiver• ‘D’ Interface
to the ITS• Wall or Pole Mounted
• ‘E’ Interface - 2 x POTS or 1 x ISDN BRA
• LED Control/Status Indication
• Modem and Fax Capability
• Smartcard Facility
• Battery Back-Up
AirLoop® System
Operations and Maintenance Centre
&Local Maintenance Terminal
OMC and LMT Objectives
Identify the Main OMC Applications
Describe the functions achieved by the software applications on the OMC
Describe the function of the LMT
G
AirLoop®: System Interfaces
LE CATU CTRU STRU
ITS
A B C
D
EOMC
F G
LMT
OMC
F
LMT
AirLoop→ System
The Operations, Administration and Maintenance of the AirLoop System is
performed primarily at the
Operations and Maintenance Centreusing the ‘F’ Interface
OMC
There are 2 Main Applications at the OMC
Service Provisioning
Network Management&
Alarm Monitoring
OMCOMC
The Operations & Maintenance Centre provides:-
– Configuration of Equipment and Software– Subscriber Service Provisioning– Alarm Monitoring– Security Management– Performance Monitoring
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
OMC Software Platform
•UNIX (HP-UX)
•HP - Common Desktop Environment•ObjectStore•OpenView (SNMP)
•Network Node Managers
•MIB (Managed Information Base)
OMC
• Service Provisioning Allows the user to:-
– Create, Modify or Delete a service group– Create, Modify or Delete subscribers– Create, View or Delete E1 links on ‘B’ Interface
• Network Management and Alarm Monitoringenables the user to:
– Develop and maintain the AirLoop SystemAccess Network using a Graphical User Interface
CTRU
WLT NIU
OMC
ITSSTRUCATU
LE
OMC Network Architecture
The server can either be a workstation or a full size business server.
The OMC server holds the database used by the applications software, and supports multiple users using X-Terminals.
The user interfaces connect via a hub to the Main OMC Server, the number of which depends on the Network Operator’s requirements of the AirLoop System.
Network Size
• Depends on the customer’s requirements and the size
of the AirLoop System Network to be managed
The Network is scaleable
• The OMC can provide OA&M facilities for up to 250 WLT’s, each supporting up to 480 subscribers
Local Maintenance Terminal
• Portable PC that connectsdirectly into the CTRUvia an RS232 interface.
‘G’Interface • Provides on-site
diagnostics and maintenance functions for the CTRU
CTRU
WLT NIU
ITSSTRUCATU
LE
LMT
7
LMT
• The LMT software is held within the CTRU
• Activity on the RS232 port activates a local maintenance process
• The LMT provides 2 levels of Functionality
• Password Protection allowing:-– View only
– View and Configure
CTRU
WLT NIU
ITSSTRUCATU
LE
LMT
LMT
The Top Level Menu provides options to:-
– Configure Equipment– Data Menu– Display Alarms– CTRU Board Config– Commit Changes– Connect to CATU– Enable ‘Pilot only’CTRU
WLT NIU
ITSSTRUCATU
LE
LMT
7
Summary
• OMC:-– Service Provisioning
– Network Management & Alarm Monitoring
– Performance Monitoring
• LMT:-– On-site diagnostics and maintenance
functions for the CTRU
Frequency bands
• 15 frequency bands allocated by FCC
• 2 GHz-40 GHz i.e. higher than cellular systems
i.e. millimeter wave frequencies
Freq (GHz) Usage
2.15-2.162 Licensed MDS and MMDS, two bands 6MHz each
2.4-2.483 Unlicensed ISM
2.596-2.644 Licensed MMDS, eight bands of 6MHz each
2.65-2.656 Licensed MMDS
2.662-2.668 Licensed MMDS
2.674-2.68 Licensed MMDS
5.725-5.875 Unlicensed ISM-UNII
24-24.25 Unlicensed ISM
24.25-25.25 Licensed
27.5-28.35 Licensed LMDS (Block A)
29.1-29.25 Licensed LMDS (Block A)
31-31.075 Licensed LMDS (Block B)
31.075-31.225 Licensed LMDS (Block A)
31.225-31.3 Licensed LMDS (Block B)
38.6-40.0 Licensed
Propagation considerations
• Millimeter wave range used is defined as frequencies above 10 GHz up to 300 GHz
• Because:
– Availability of wide unused frequency bands above 25 GHz
– Wide channel bandwidths available for high data rates at higher frequencies
– Small size transceivers with adaptive antennas can be used
Disadvantages of millimeter range
• Free space loss increases with the square of frequency
• Attenuation due to rainfall and atmospheric absorption is significant after 10 GHz
• Multi-path losses are high because:
Because:
• Reflection occurs when an EM signal encounters a surface larger relative to the wavelength of the signal
• Scattering occurs if the size of obstacle is of the order of the wavelength of the signal
• Diffraction occurs if wave front encounters the edge of the obstacle that is large compared to wavelength
Fresnel zone
• Space around the direct path between transmitter and receiver that should be clear of obstacles
• Basis:– Any small element of space in the path of EM
wave may be considered as the source of a secondary wavelet. Radiated field is build up by superposition of these wavelets
Fresnel zone (contd.)
• Objects lying within a series of concentric circles around the direct line of sight between two transceivers have constructive or destructive effects on communication
• Objects falling in the first circle have the most negative effect
Fresnel zone (contd.)
R= λSD√ S+D
S=Distance from transmitterD=Distance from receiver λ=Wavelength of signal
S,R and D are in same units
or
Rm =17.3 Skm Dkm
√ fGHz (Skm +Dkm )
S and D are distances in Km,R is in metersf is in Giga Hertz
Attenuation due to Fresnel zone is negligible if :
• Obstruction does not lie within 0.6 times the radius of first Fresnel
zone
ATMOSPHERIC ABSORPTION
• Molecular absorption significant above 10 GHz• Peak of water vapor absorption at 22 GHz• Oxygen absorption peak is at 60 GHz• So, favorable window is in between 28-42 GHz
with attenuation of the order of 0.13dB/km• Another favorable window is between 75 GHz-
95 GHz with attenuation of the order of 0.4dB/km
Effect of rain
• Rain severely degrades the performance of communication links
• It out-weighs all other factors
• Depends upon drop shape, size, rain rate and frequencyA=aRb
R= rate of rain
A=attenuation measured in dB/km
a & b depend upon distribution of drop sizes and frequency
Temperature dependency of air absorption at 28 GHz
0% 50% 100%
00 0.02 0.05 0.08
100 0.02 0.08 0.14
200 0.02 0.12 0.25
300 0.02 0.2 0.44
400 0.01 0.33 0.79
Relative humidity
Temp (0C)
Values of a and b for horizontal and vertically polarized EM waves
Freq(GHz) ah av bh bv
1 .0000387 .0000352 0.912 0.880
2 0.000154 .000138 0.963 0.923
6 0.00175 0.00155 1.308 1.265
10 0.0101 0.00887 1.276 1.264
20 0.0751 0.0691 1.099 1.065
30 0.187 0.167 1.021 1.000
40 0.350 0.310 0.939 0.929
50 0.536 0.479 0.873 0.868
Effect of vegitation
• Trees can cause multipath fading due to diffraction and scattering
• Attenuation of:– Regularly planted orchards is 12-20dB
– Deciduous trees up to 40dBs
– Conifer trees 1 to 3dBs• If foliage lies within 60% of first fresnel zone
Presence of trees does not preclude communication,
• So methods like forward error correction should be employed
WLL SYSTEM TECHNOLOGIES
1. ANALOG CELLULAR
2. DIGITAL CELLULAR
3. PERSONAL COMMUNCATIONS SERVICES / NETWORK (PCS/PCN)
4. DIGITAL CORDLESS SYSTEMS
5. PROPRIETARY IMPLEMENTATIONS
1. Analog Cellular
• Three of its system types operating in the world, AMPS and NAMPS with 69% of
subscribers, while TACS has 23% and NMT has only 8%.
• These systems use conventional FM on either 25 or 30 kHz channels in 800 or
900MHz mobile bands. Most recently AMPS operate in 1800-2000MHz band.
• Best suited to serve low or medium density markets, with long range up to 70km, with
fixed units having high gain antennas.
• Narrow band analog transmission results in low speed.
• Since the access method is FDMA, the subscriber unit cannot support more than one
line per radio tranceiver.
• Relatively low capacity in terms of number of channels.
2. Digital Cellular
• Major worldwide digital cellular standards include GSM, D-AMPS (American) & GSM/DCS
(European), TDMA and CDMA.
• It is forecasted that approximately one-third of the installed WLL will use digital cellular
technology in the year 2000. • Digital cellular can support higher capacity and better functionality than analog cellular and
wireline networks.
• Digital cellular systems are encrypted and provide high speech security with no impact on quality.
• Both DAMPS and GSM use TDMA and support multiple lines from a single subscriber unit.
• Some of these systems has general confusion over industry standards.
• GSM currently dominates mobile cellular industry, but there has been little activity in using GSM
as a WLL platform.
TDMA and Point to Multipoint Systems
• These System are relatively well suited for rural use, because they provides
service coverage over a wide area.
• TDMA standards are IS-54 and IS-136, triples the capacity of cellular
frequencies, by dividing a 30 kHz cellular channel into 3 timeslots.
• Proven and reliable technology.
• Designed to support subscribers in sparsely populated rural areas.
• A typical base station has 30 or 60 traffic channels and could support 256 to
1800 residential subscribers respectively.
• Relatively long range (over 70km) but requires a line-of-sight path between
RBS and all subscriber units.
CDMA (Code Division Multiple Access)
• CDMA is a "spread spectrum" technology, it spreads the information contained in a particular signal over a much greater bandwidth than the original signal.
• A CDMA call starts with a standard rate of 9.6kb/s. This is then spread to a transmitted rate of about 1.23 Mb/s.
• It offers 3-6 times more capacity than the other digital standards and 10-15 times greater than analog cellular.
• Improved spectral efficiency in a multi-cell environment - mainly due to interferer diversity.
• Flexible cell sizes and service provisions - for a given data rate, range is increased as traffic density is reduced.
• Speech delay can be minimized - fast power control tracks and minimize fading.
• Multi-path fading is reduced due to inherent frequency diversity, which is common in mountainous terrain and dense urban areas.
• CDMA-WLL based on new US cdma-One (IS-95) standard is presently used.
3. Personal Communications Services/ Network (PCS/PCN)
• PCS starts to operate in the 1800 MHz frequency band. PCS/PCN incorporates
elements of digital cellular and cordless standards as well as newly developed RF
protocols.
• Its purpose is to offer low-mobility wireless service using low-power antennas.
• The main weakness of PCS/PCN is that it is not yet commercially available.
• The candidate standards are CDMA, TDMA, GSM, personal access communication
systems (PACS), Personal handyphone system (PHS), and digital cordless telephone
United States (DCT-U).
• PHS technology and terminal equipment reduces the WLL system cost as it uses
32kb/s ADPCM voice coding system.
• PHS-WLL system is superior in terms of speech quality and economy for urban and
suburban applications. It also offers extensibility to mobile service in the future.
4. Digital Cordless Systems
• CT2 (Cordless telephone 2nd generation) and DECT (Digital Enhanced / European
cordless telephone systems are its types.
• CT2 provides the user with a single 32kb/s duplex channel, but it has not been
universally adopted.
DECT• DECT is a picocellular wireless system for very dense subscriber environments
where demand per km is high and cell coverage area is not a critical requirement.
• DECT supports ISDN services and also comprehensive security provisions including
authentication and encryption.
• The DECT radio interface is based on TDMA technology. It operates over 10 radio
carriers in the 1880 to 1900 MHz band. • It uses dynamic channel selection, an automated frequency-planning mechanism,
which provides least interference from neighboring cells.
Comparison of DECT and PWT
• DECT• 20 MHz bandwidth• 1.88 to 1.9 GHz band• TDD/TDMA/FDMA• 1.728 MHZ carrier
bandwidth• 10 number of carriers• 12 channels per carrier• Number of channels,120• Transmitted data rate:
1.152Mbps• Speech rate:32 Kbps
• PWT• 20 MHz bandwidth• 1.91 to 1.92GHz band• TDD/TDMA/FDMA• 1.25 MHz
• 8• 12• 120• 1.152
• 32 Kbps
Comparison of DECT and PWT
• Speech coding: ADPCM
• Modulation: Gaussian FSK
• Peak output power: 250 mW
• Maximum cell radius: 30 to 100 meters
• ADPCM
• Pi/4 DQPSK
• 90 mW
• 30 to 100 meters
DECT
• System has frequency reuse limitations, so the maximum number of voice channels
available for a single cell site in a multi-cell environment is 60.
• DECT system transmits at low power using low antenna heights.
• DECT does not appear to be ideally suited for long range rural or low-density
applications.
• Its normal range is 3-5 Km with a capacity up to 100,000 subscribers per km2.
• As compared to cellular technology, DECT is capable of carrying higher levels of
traffic and data.
• The micro-cell architecture of DECT allows it to be deployed in smaller increments
that more closely match the subscriber demand, with reduced initial capital
requirements.
5. Proprietary Implementations
• These systems are considered proprietary because they are not available
on public wireless networks and are typically customized for a specific
application.
• They generally do not provide mobility, and are most effective in terms of
time and cost. • Proprietary systems like broadband CDMA and fixed radio access are
designed from vendors like Interdigital, Ionica and NORTEL. Equipment
providers include corporate giants such as Motorola, Ericsson, Lucent,
Siemens, NEC, Qualcomm and Hughes Network Systems as well as many
other smaller companies
Scope of WLL System application in terms of the Subscriber density
WLL Technologies by Market Segment
Developed Emerging
Urban/Suburban Digital CellularDECTPHSProprietary
DECTPHSDigital CellularProprietary
Rural Digital CellularProprietary
Digital CellularAnalog CellularProprietary
OFDM
• Orthogonal frequency division multiplexing
• Also called Multi carrier modulation
• Sending some of the bits on each channel
• All sub channels are dedicated to a single data source
Suppose we have:
• Data stream operating at R bps
• Available bandwidth is N∆f centered at f0
• Entire bandwidth used to send data stream for which each bit duration is 1/R
• Alternatively split the data stream to N sub-streams using serial to parallel converter
• Each sub-stream has a data rate of R/N bps transmitted on a separate carrier
• Spacing between individual sub-carriers is ∆f
• Now the bit duration is N/R
Advantages of OFDM:
• Frequency selective fading only affects a few channels and not the whole signal so it can be easily handled by forward error correction techniques
• OFDM can handle Inter-symbol interference in multipath environment– ISI is more effective at higher bit rates as the distance
between the bits is smaller– OFDM reduces the data rate by a factor of N thus symbol
period increases by the factor N so effect of ISI is reduced– So equalizers do not remain essential
Modulation scheme for OFDM
• QPSK– There are two bits representing one symbol
MMDS
• Multichannel multipoint Distribution service
• Occupies 6 MHz made up of 512 individual carriers with carrier saparation of 12 kHz
• Data transmitted in bursts
• Cyclic prefix attached to each burst to reduce transients from previous bursts caused by multipath
MMDS (contd.)
• 64 symbols constitute cyclic prefix • Followed by 512 QPSK symbols per burst• So on each sub-channel, QPSK symbols are
separated by a prefix of duration 64/512 symbol times
• By the time prefix is over, the resulting waveform is independent of the previous burst
• So ISI is nil
MMDS contd.
• Frequency range 2.15 GHz to 2.68 GHz– 2.15-2.162 and 2.4-2.4835 GHz bands called
Multipoint distribution service for 6MHz TV broadcast.
– In 1996 FCC increased the allocation up to 2.68 GHz for MMDS
– MMDS is used to provide TV service where broadcast TV or cable can not reach in rural areas
– So, MMDS is also called wireless cable
MMDS contd.
• Range: 50km
• MMDS also used for two-way broad band data services and Internet access
Disadvantages of MMDS
• Lesser bandwidth than LMDS• Data rates:
– 27 Mbps for up-stream per channel– 300kbps to 3 Mbps individual subscriber rates
Used by residential or small business customers
Advantages of MMDS over LMDS
• Larger wavelengths i.e.10cm or more, so travel farther, so larger cells
• Less expensive equipment than LMDS• Signals more susceptible to rain
absorption• Signals do not get easily blocked by
objects
LMDS
• Local Multipoint Distribution service
• TV and two way broadband communication
• Millimeter frequencies
• At 30 GHz in USA and 40 GHz in Europe
Advantages of LMDS
• High data rates i.e. in Mbps
• Capability of video, telephony and data
• Lower cost than cable alternatives
Disadvantage
• SHORT RANGE
Antenna coverage
• 600 to 900 coverage sector so 4 to 6 antennas required for full coverage
• Typical radius of 2 to 4 km• Per customer data rates:
– 1 Mbps upstream– 36 Mbps down stream
• Buildings, trees and foliage affect the communication too much so overlapping cells or the use of repeaters and reflectors is required
FIXED WIRELESS BROADBAND ACCESS
• STANDARD
– IEEE 802.16
• Working group developed in 1999
CHARTER OF IEEE 802.16
• Use of microwave or millimeter wave radio for wireless links
• Use of licensed spectrum• Standards of metropolitan scale• Provide public network service to fee paying
customers• Point to multipoint architecture for roof top or
tower mounted antennas• Efficient transport of heterogeneous traffic with
QoS• Broad band capability i.e. >2 Mbps
IEEE 802.16 working groups
• IEEE 802.16.1:• Air Interface for 10 to 66 GHz
• IEEE 802.16.2:• Co-existance of Broadband wireless access
systems
• IEEE 802.16.3:• Air Interface for licensed frequencies 2 GHz to 11
GHz
IEEE 802.16 system architecture
• Provision of communication path between core network and subscriber’s premises
• IEEE 802.16 is concerned with the air interface
Related Documents
