WIRELESS LOCAL LOOP15april04

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

REQUIREMENTS FROM PTA

• Radio Frequency bands allocated by PTA– 1.9 GHz– 3.4 to 3.6 GHz– 450 MHz– 479 MHz

Radio Spectrum Band Information sheet 1.9 GHz

Spectrum Block size (Transmit + Receive)

MHz

Number of available blocks

Maximum blocks available per applicant and affiliates

One time fee per block upon lisencing by Region (US $ and Pak Rs)

Annual renewal fee per block per region (US $ and Pak Rs)

Roll out commitment in region

Rollout commitment compliance

5+5

1.25 x3+

1.25 x3

1890-1895

1970-1975

1 1 Area 1

Area 2

US $ 250,000 or Pk Rs. 14,500,000

US $75,000or

Pk Rs. 4,350,000

Area 1

Area 2

US $75,000or

Pk Rs. 4,350,000

US $ 25,000 or Pk Rs. 1,450,000

1.Atleast one base station that is in ongoing operational as part of licensee’s network

2. One or more base stations providing service to atleastt 5 customers

1. Initially by 18 months from effective date. 2. On an ongoing basis thereafter

1.9 GHz band

• 1880-1885 ; 1960-1965 MHz will be available if not used by CMTS– AREA 1

• Karachi, Lahore, Islamabad

– AREA 2• FTR, HTR, GTR, RTR, WTR, STR-I, STR-V, MTR,

NTR-I, NTR-II and CTR

Radio Spectrum Band Information sheet 3.4-3.6 GHz


MHz







10.5+10.5

3.5 x21+

3.5 x21

Blocks located within

3410-3497.5

3510-3597.5

7 1 Area 1

Area 2

US $ 25,000 or Pk Rs. 1,450,000

US $10,000or

Pk Rs. 580,000

Area 1

Area 2

US $ 25,000 or Pk Rs. 1,450,000

US $10,000or

Pk Rs. 580,000




– AREA 1• Karachi, Lahore, Islamabad

– AREA 2• FTR, HTR, GTR, RTR, WTR, STR-I, STR-V, MTR,

NTR-I, NTR-II and CTR

Radio Spectrum Band Information sheet 450 MHz


MHz







5+5

1.25 x3+

1.25 x3

452.5-457.457;

462.5-467.457

1 1 Area 1

Area 2

US $ 75,000 or Pk Rs. 4,350,000

US $37,500or

Pk Rs. 2,175,000

Area 1

Area 2

US $50,000or

Pk Rs. 2,900,000

US $ 25,000 or Pk Rs. 1,450,000




– AREA 1• Karachi, Lahore, Islamabad

– AREA 2• FTR, HTR, GTR, NTR-I,RTR

– AREA 3• WTR, STR-I, STR-V, MTR, NTR-II and CTR

– PTCL has been allocated 1.25 MHz band in this area 3, rest of the 3.75 MHz is available for new LL operators in area 3

– License fee given for area 2 will apply

Radio Spectrum Band Information sheet 479 MHz


MHz







5+5

1.24 x3+

1.24 x3

479-483.48

489-493.48

1 1 Area 1

Area 2

US $ 75,000 or Pk Rs. 4,350,000

US $22,500or

Pk Rs. 1,305,000

Area 1

Area 2

US $50,000or

Pk Rs. 2,900,000

US $ 15,000 or Pk Rs. 870,000




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

CDMA 2000 1x WLL Huawei solution

• Basically this is a complete solution for a PLMN: Public local mobile network

• Only minor changes in the software can change this WLL network into a mobile system

Expected Network in Pakistan

• Islamabad: Centralized control

• Peshawar

• Lahore

• Quetta

• Karachi

• Multan

Equipment to be available at sites

• MSC: Mobile Switching center

• BSC : Base Station Controller

• BTS : Base Transceiver Station

• HLR/AuC : Home Location Register/ Authentication Center

Interfaces

• Between MSC and BSC: V 5.2

• Between BSC and BTS: E1

– No. of max. BTS that can be connected to a BSC: 14

– No. of BSC that can be connected to a MSC:

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 KHz• 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

Development of Mobile Communications

1st Generation 1980s (analog)

2nd Generation 1990s (digital)

3rd Generation current (digital)

3G provides: Complete integrated service solutions High bandwidth Unified air interface Best spectral efficiency and ……………… a step towards PCS

AMPS

Analog to DigitalTACS

NMT

OTHERS

GSM

CDMA IS95

TDMA IS-136

PDC

UMTS WCDMA

CDMA 2000

TD-SCDMA

Voice to Broadband

Transmission TechniquesTraffic channels: different users are assigned unique code and transmitted over the same frequency band, for example, WCDMA and CDMA2000

Traffic channels: different frequency bands are allocated to different users,for example, AMPS and TACS

Traffic channels: different time slots are allocated to different users, for example, DAMPS and GSM

FrequencyTime

Power

FrequencyTime

Power

FrequencyTime

Power

FDMA

TDMA

CDMA

User

User

User

User User

User

TDMA

Frequency

Time

Power

use

r

use

r

use

r

use

r

use

r

3G Objectives

3G is developed to achieve:• Universal frequency band for standard and seamless

global coverage • High spectral efficiency• High quality of service with complete security and

reliability• Easy and smoothly transition from 2G to 3G, compatible

with 2G• Provide multimedia services, with the rates:

– Vehicle environment: 144kbps– Walking environment: 384kbps– Indoor environment: 2Mbps

Standards for 3G

3G system

CDMA2000

3GPP2

FDD mode

WCDMA

3GPP

FDD mode

TD-SCDMA

CWTS

TDD mode

A Comparison b/w 3G standardsWCDMA CDMA2000 TD-SCDMA

Receiver type RAKE RAKE RAKE

Close loop power control Supported Supported Supported

Handoff Soft/hard handoff

Demodulation mode Coherent

Chip rate (Mcps) 3.84 N*1.2288 1.28

Transmission diversity mode

TSTD, STTDFBTD

OTD, STS No

Synchronizationmode

Asynchronous Synchronous Asynchronous

Core network GSM MAP ANSI-41 GSM MAP

CoherentCoherent

Soft/hard handoff Soft/hard handoff

Development of CDMA

IS95A 9.6kbps

IS95A 115.2kbps

CDMA2000 307.2kbps

Heavier voice service capacity ;

Longer period of standby time

CDMA2000 3X

CDMA2000 1X EV

1X EV-DO

1X EV-DV

1995 1998

20002003

• Higher spectrum efficiency and network

capacity

• Higher packet data rate and more diversified

services

• Smooth transit to 3G

CDMA2000 1X Network Structure

• MS: Mobile Station BTS: Base Transceiver Station• BSC: Base Station Controller MSC: Mobile Switching Center• HLR :Home Location Register VLR: Visitor Location Register• PCF: Packet data Control Function PDSN: Packet Data Service Node • HA: Home Agent FA: Foreign Agent • SCP: Service Control Point Radius: Remote Authentication Dial-in User Service

Abis

A1(Signaling)

A2(Traffic)

A11(Signaling)

A10(Traffic)

A3(Signaling &

Traffic)

A7(Singaling)

Correlation

(a)

(b)

+1

-1

+1

-1

+1

-1

+1

Correlation 100% so the functions are parallel

Correlation 0% so the functions are

orthogonal

Orthogonal Function

• Orthogonal functions have zero correlation. Two binary sequences are orthogonal if their “XOR” output contains equal number of 1’s and 0’s

0000

0101

0101

EXAMPLE:

1010

0101

1111

Information spreading over orthogonal codes

1 0 0 1 1

0110 0110 0110 0110 0110

1001 0110 0110 1001 1001

User Input

Orthogonal Sequence

Tx Data

+1

-1

+1

-1

Information recovery

1 0 0 1 1+1

-1

Rx Data 1001 0110 0110 1001 10010110 0110 0110 0110 01101111 0000 0000 1111 1111

Correct Function

? ? ? ? ?

Rx Data 1001 0110 0110 1001 10010101 0101 0101 0101 01011100 0011 0011 1100 1100

Incorrect Function

Spreading and De-spreading

information pulse interference White noise

The improvement of time-domain information rate means that the bandwidth of spectrum-domain

information is spread.

S(f) is the energy density.

f

S （ f）

The spectrum before spreading

information

f0

The spectrum before despreading

informationInterference/noise

S （ f）

f0 f f0

The spectrum after despreading

information

Interference/noise

S （ f）

f

The spectrum after spreading

information

f0

S （ f）

f

Signal flow

InterleavingSource coding

Convolution &Interleaving

Scrambling Spreading Modulation

RF transmission

Source decoding

deinterleavingDecovolution &Deinterleaving

Unscrambling De-spreading Demodulation RF receiving

Common Technical Terms

• Bit, Symbol, Chip:– A bit is the input data which contain information– A symbol is the output of the convolution, encoder, and the

block interleaving– A chip is the output of spreading

• Processing Gain:– Processing gain is the ratio of chip rate to the bit rate. – The processing gain in IS-95 system is 128, about 21dB.

• Forward direction: Information path from base station to mobile station

• Reverse direction: Information path from mobile station to base station

Source Coding

• Vocoder: – 8K QCELP– 13K QCELP– EVRC

• Characteristics– Support voice activity

In a typical duplex call, the duty ratio is less than 35%. To achieve

better capacity and low power consumption, base station reduces its

transmission power.

Channel Coding

Convolution code or TURBO code is used in channel encoding

Constraint length=shift register number+1.

Encoding efficiency= (total input bits / total output symbols)

convolution encoder

Input (bits)

Output (symbols)

Turbo Code

Turbo code is used during the transmission of large data packet.

• Characteristics of the Turbo code: – The input information is encoded twice and the

two output codes can exchange information with each other during decoding.

– The symbol is protected not only by the neighborhood check bits, but also by the separate Check Bits.

The performance of a Turbo code is superior to that of a convolution code.

Interleaving

The direction of the data stream

1 2 873 64 5

1 2 873 64 5

1 2 873 64 5

1 2 873 64 5

1 2 873 64 5

1 2 873 64 5

1 2 873 64 51 2 873 64 51 2 873 64 5

1 2 873 64 5

1 1 111 11 1

2 2222

7 7 777 77 7

6 6 666 66 6

3 3 333 33 3

4 4 444 44 4

1 2 873 64 51 2 873 64 55 5 555 55 5

8 8 888 88 8interleaving

2 2 2

Scrambling (M) sequence

Out

0 0 1

1 1 0

• Two points are important here: – Maximum number of shift register (N)– Mask

• The period of out put sequence is 2N-1 bits• Only sequence offset is change when the mask is

changed• PN stands for Pseudorandom Noise sequence

Long Code

• The long code is a PN sequence with period of 242-1chips

• The functions of a long code: – Scramble the forward CDMA channel– Control the insertion of power control bit– Spread the information on the reverse

CDMA channel to identify the mobile stations

Short Code

• Short code is a PN sequence with period of 215 chips– Sequence with different time offset is used to distinguish different

sectors

– Minimum PN sequence offset used is 64 chips, that is, 512 PN offsets are available to identify the CDMA sectors (215/64=512).

PNa

PNc

PNb

Walsh Code

W2n=Wn Wn

Wn Wn

W1=0

W2= 0 0

0 1

W4 =

0 00 1

0 00 1

0 00 1

Walsh code

64-order Walsh function is used as a spreading function and each Walsh code is orthogonal to other.

Walsh Code is one kind of orthogonal code.

A Walsh can be presented by Wim where ith (row) is the

position and m is the order. For example, W24 means 0101

code in W4 matrix

1 11 0

Walsh Code

• In forward direction, each symbol is spread with Walsh code

• Walsh code is used to distinguish the user in forward link

• For IS95A/B, in the reverse, every 6 symbols correspond to one Walsh code. For example, if the symbol input is 110011,the output after spreading is W51

64 (110011=51).

• For CDMA2000, in the reverse, Walsh function is used to define the type of channel (RC 3-9)

Variable Walsh codes

64

48

16

32

12

9600 19200 38400 76800 153600 307200 614400

Data rate -bps-

W01 =0

W02 =00

W12 =01

W04 =0000

W24 =0011

W14 =0101

W34 =0110

W08 =00000000

W48 =00001111

W28 =00110011

W68 =00111100

W18 =01010101

W58 =01011010

W38 =01100110

W78 =01101001

( W016 ,W8

16)

( W416 ,W12

16 )

( W216 ,W14

16 )

( W616 ,W14

16 )

( W116 ,W9

16 )

( W516 ,W13

16 )

( W316 ,W11

16 )

( W716 ,W15

16 )

The different Walsh codes corresponding to different data rates

Modulation-QPSK

I

Q

I channel PN sequence1.2288Mcps

Q channel PN sequence

1.2288Mcps

Baseband filter

Baseband filter

Cos(2pfct)

Sin(2pfct)

I(t)

Q(t)

s(t)A

1.2288Mcps: the PN chip rate of the system.

After being spread, all the forward channels in the same carrier are

modulated by means of QPSK(OQPSK in the reverse), converted

into simulation signals and transmitted after clustering.

CDMA mobile parameters

Power Control Handoff Diversity and RAKE

Power Control

• Reverse power control– Open loop power control– Closed loop power control

• Inner loop power control: 800 Hz• Outer loop power control

• Forward power control– Message transmission mode:

• threshold transmission• periodic transmission

– Closed loop power control

Reverse Open Loop Power Control• The transmission power required by the mobile station is determined by

the following factors:

Distance from the base station

Load of the cell

Circumstance of the code channels

• The transmission power of the mobile station is relative to its received

power.

BTSMobile

Reverse Open LoopPower Control

BTS

BTS

Transmitting Power

Reverse Closed Loop Power Control

BTS

Power Control Bit

Eb/Nt Value FER Value

Inner Loop Power Control

Outer Loop Power Control

Change in Eb/Nt Value

BSC

BTS

Forward Power Control

MS measures the frame quality and informs the base station to the result i.e. whether it is in the threshold or periodical mode. Base station determines whether to change the forward transmitting power or not.

In IS-95 system, the forward power control is slow but in CDMA2000 system it is fast.

Message Transmission Mode

Forward Closed Loop Power Control

•Compared with IS-95 system,

CDMA2000 the forward quick

power control is fast.Power Control Bit

Eb/Nt Value

BTS

Handoff

• Soft handoff–It is a process of establishing a link with a target sector before breaking the link with the serving sector

• Softer handoff–Like the soft handoff, but the handoff is occurred between multi-sectors in the same base station

• Hard handoff–Hard handoff occurs when the two sectors are not synchronized or are not on the same frequency. Interruption in voice or data communication occurs but this interruption does not effect the user communication

Soft/Softer Handoff• Multi-path combination in the BSC during soft handoff

• Multi-path combination in the BTS during softer handoffs

Combine all the power from each

sector

Power received from a single sector

Pilot Set

ActiveSet

CandidateSet

NeighborSet

Remaining Set

The pilot set, corresponding to the base station being connected

The pilot set, not in the active set but potential to be demodulated

Other pilot sets

the set of the pilots having same frequency but different PN sequence offset

T_ADD,T_DROP,T_TDROP

Time

Ec/Io

Sector A Sector

B

Guard Time(T-TDROP)

Add Threshold (T_ADD)

DropThreshold (T_DROP)

Soft Handoff Region

T_ADD, T_DROP and T_TDROP affect the percentage of MS in handoff.

T_ADD & T_DROP is the standards used to add or drop a pilot.

T_DROP is a timer.

Comparison Threshold

Pilot P1

Pilot P2

t0

T_COMP×0.5dB

t1 t2

T_ADD

P0-Strengh of Pilot P0 in Candidate Set.

P1,P2-Stength of Pilot P1,P2 in Active Set.

t0-Pilot strength Measurement Message Sent, P0>T_ADD

t1-Pilot strength Measurement Message Sent, P0>P1+T_COMP*0.5dB

t2 -Pilot strength Measurement Message Sent, P0>P2+T_COMP*0.5dB

Transition Between Pilot Sets

T_ADD

T_DROP

Pilot 1

Pilot strength

Pilot 2

T_TDROP

T_TDROP

NeighborSet

CandidateSet

ActiveSet

CandidateSet

NeighborSet

TIME1 2 3 4 5 6 7 8

Transmit Diversity

• Time diversity– Block interleaving, error-correction

• Frequency diversity– The CDMA signal energy is distributed on the whole

1.23MHZ bandwidth.

• Space diversity– The introduction of twin receive antennas .– The RAKE receivers of the mobile station and the base

station can combine the signals of different time delay.– During a handoff, the mobile station contacts multiple base

stations and searches for the strongest frame

Transmission Diversity

• The forward transmission diversity types in CDMA2000 1X are– TD (Transmit Diversity)

• OTD (Orthogonal Transmit Diversity)– The data stream is divided into two parts, which will

be spread by the orthogonal code sequence, and transmitted by two antennas.

• STS (Space Time Spreading)– All the forward code channels are transmitted by the

multi-antennas.– Spread with the quasi-orthogonal code

–Non-TD

Transmission DiversityTransmission Diversity

The Transmission Diversity Technology enhances the receive performance of MS.

Transmission diversity

processing

Data stream 1

Data stream 2

Data stream Restoring data stream

Path 1

Path 2

Antenna 2

Antenna 1

The Principle of RAKE Receiver

RAKE antennas help to overcome on the multi-path fading and enhance

the receive performance of the system

Receive set

Correlator 1

Correlator 2

Correlator 3

Searcher correlator Calculate the time delay and signal strength

Combiner The combined signal

tt

s(t) s(t)

A typical CDMA Network

MS BS MSC

HLRAC

EIR

VLR

PSTN

ISDN

MC

Um A

BC

D

E

H

Ai

Di

MSC

F

VLR

MCSMESME

GN

MMM

Q

SCPSCP SSP

Ai

T1T8

IP HLR IP ISDNDi

T2T3T5

T9

CDMA Interfaces

MSC: Mobile-service Switching Center BSC: Base Station ControllerMC: Short Message Center HLR: Home Location RegisterBTS: Base Transceiver Station VM: Voice MailboxVLR: Visitor Location Register OMC: Operation & Maintenance Center AC: Authentication Center SCP: Service Control Point

MSC: Mobile-service Switching Center BSC: Base Station ControllerMC: Short Message Center HLR: Home Location RegisterBTS: Base Transceiver Station VM: Voice MailboxVLR: Visitor Location Register OMC: Operation & Maintenance Center AC: Authentication Center SCP: Service Control Point

Other MSCs

MC/VM

MSC/SSP/VLR

OMC

HLR/AC

SDH

GMSC/SSP

SCP

STP

IOS4.0

SS7

IS-41

IS-41

IS-41

IS-41

Mobile Customer Service Center

SS7

TCP/IP

SS7IS-41

BTS

BTS

BSC

MSINTERNET

Other PLMNs

PSTN/ISDN

Network InterfaceMSC/VLR GMSC

HLR/AuC

PDSN

PSTN

GPRS IP骨干网

SS7

SCPBSS

HA

A1/A2

BSSAP

SCCP

MTP

Physical layer

IP backbon

e network

A10/A11

A11 signaling

UDP

IP

Link layer

Physical layer

A10 service

GRE

IP

Link layer

Physical layer

CN

CDMA Services

Businesses, enterprises•Mobile virtual private network•Mobile high-speed network access•Advertising services•Free phone

Family•Familiarity number•Life & amusement

Schools, groups•Universal account number•Sectorized and time-shared charge•Broadcast news

Individuals•Individualized services•Privacy

CDMA2000---Data Services

0

32

64

9.6

128

144

384

2,000 Video StreamingVideo Streaming

VoiceVoice

Text Text MessagingMessaging

Still ImagingStill Imaging

Audio StreamingAudio Streaming

Electronic newspaper

High-quality videoconference

Telephone (Voice)

Voice Mail

E-MailFax

Electronic book

Sports, news and weather report on

demand

Singing room

Low-quality videoconference

JPEG Still Photos

Mobile Radio

Video Surveillance,Video Mail, Travel

Image

Data

Weather, transportation, news, sports and securities

Mobile TV

E-commerce

RemoteMedical Service

Da

ta r

ate

in

Kb

ps

Da

ta r

ate

in

Kb

ps

Locating Services

3GPP2 uses the following 3 standards for MS location:

• GPS-aided measurement

– Accuracy: suburbs---10m.

City zone---30~70m.

Indoor --unable to locate

– Response time: 3~10s

• Measurement of base station pilot phase

– Accuracy: 50~200m

– Response time: 3~6s

• Locating of a cell ID

– Accuracy: depends on the size of a cell

– Response time: within 3s

Locating Services

110! Bandit!

• The system transfers the alarm to the nearest alarm processing center based on the location.

• An emergency button can be set on a user’s mobile phone to so that an alarm can be reported without any conversation or delay.

Review

• Chips rate: 1.2288Mcps• IS-95A/B is a subset, RC1/RC2 • Apply the coherent demodulation to the reverse pilot channel• Forward transmit diversity: OTD and STS• Forward quick power control at 800HZ rate• Improve the standby time by introducing the quick paging

channel.• Variable frames: 5ms, 20ms, 40ms and 80ms• Introduce TURBO code into channel encoding• The maximum rate of a physical layer is up to 307.2K

A Simple CDMA 1X BSS Network

PSTNMSC

PDSN

Abis A10/A11

A1/A2

A3/A7

BSC

PCF

A8/A9Um

CDMA2000 1X BSS

MS

MS

BTS

BTS

BTS

BTS

BTS

BTS

BSC

Description of Interfaces

• Um interface carries all signaling & services between MS and

BTS over radio links.

• Abis interface carries signaling & services between BTS and

BSC.

• A1 interface carries call control signaling between MSC and

BSC.

• A2 interface provides 64kbit/s PCM speech channels between

MSC and BSC.

• A3 interface has two functions: Signaling and traffic. A3

signaling is used to control and allocate the transmission

channels for user traffic.

Description of Interfaces

• A7 interface carries signaling between source BSC and

target BSC.

• A8 interface carries user traffic between BSC and PCF.

• A9 interface carries signaling between BSC and PCF.

• A10 interface carries user traffic between PCF and PDSN.

• A11 interface caries signaling between PCF and PDSN.

A CDMA Network

BTS: Base Transceiver Station MSC: Mobile Switching Center

BSC: Base Station Controller PDSN: Packet Data Service Node

PCF: Packet data Control Function MS: Mobile Station

Rack Distribution in BSC

Large capacity BSC is divided into following functional blocks. In

general each block corresponds to single subrack. These are:

• CDMA Switch Subrack (CSWS)• CDMA Integrated Processing Subrack (CIPS) • CDMA Resource and Packet Subrack (CRPS) • CDMA Packet Module Subrack (CPMS)• CLocK processing Module (CLKM)• CDMA Integrated Management System (CIMS)

Rack DistributionTo/from MSC

To / from PDSN

Optical fiber

To / from NMSLAN

E1

GE

Ethernet

Optical fiber

Optical fiber

CIPS

CIMS

CPMS

CRPS

CSWS

CLKM

To / from PDSNGE

Configuration for 120,000 Subscribers

• BHCA: 240k• Voice traffic volume: 2,400Erl• Um interface: 54,000TCE (traffic channel element)• A-interface: 38400CIC,1280E1• Abis interface: 960E1

•3840 Sector Carriers•1,200k Voice Subscribers(0.02Erl/sub)•70,000 PPP connections•5,000 active PPP connections•Total flow of packet data: 200Mbps

CCTR (CDMA Controller Rack)

CBUR (CDMA BUsiness Rack)

Overview

Power distribution box

Cabling Through

Air guide subrackFan box

Cable trough

Air guide subrack

Fan boxCable trough

Keyboard

Dummy panel

Lanswitch

Dummy Panel

CLKM

Lanswitch

BAM Server

BAM ServerBAM Server

LCD

CSWS

CRPS/CRMS

CLKM

Cabling though

Dummy panel

Air guide subrackFan box

Cable trough

Power distribution box

Fan boxCable trough

Fan boxCable trough

Air guide subrack

CIPS/CPMS

CIPS/CPMS

CIPS/CPMS

A Wireless Network

BTS3612 Cabinet & Functional Distribution

BC IM

BC IM

BCPM

BCPM

BCPM

BCPM

BCPM

BCPM

BRDM

BRDM

BCKM

BCKM

BRDM

BRDM

BCPM

BCPM

BCPM

BCPM

BCPM

BCPM

BRDM

BRDM

Fan box 1 Fan box 2

Power distribution room

PSU

BHPA

BTRM

RLDU

CDU

PSU

PSU

PSU

PSU

RLDU RLDU

BHPA

BTRM

BHPA

BTRM

BHPA

BTRM

BHPA

BTRM

BHPA

BTRM

BHPA

BTRM

BHPA

BTRM

BHPA

BTRM

BHPA

BTRM

BHPA

BTRM

BHPA

BTRM

CDU/DFU CDU/DFUCDU CDU/DFU CDU

RF subrack

CDU/RLDU subrack

Fan subrack

Baseband subrack

RF subrack

Power subrack

Interface Protocol Stack

Abis signaling

TCP/IP

IPOA

AAL5

ATM

OML signaling

TCP/IP

IPOA

AAL5

ATM

Abis traffic

AAL2

ATM

Abis signaling OML signalingAbis traffic

IS-2000.2

Um

Command line

TELNET

802.3

MMI command

Introduction

• BTS antenna & feeder subsystem consists of two parts:

RF antenna & feeder, and dual-satellite synchronization

antenna & feeder.

• RF antenna & feeder transmits the modulated RF signals

and receives MS signals, while the dual-satellite

synchronization antenna & feeder provides precise

synchronization for CDMA system.

RF Antenna &Feeder

Inner cable

TX/RXMA

NT

RXD

CDU/DFU

Sect

or ¦A

Sect

or¦A

Sect

or¦A

Antenna

Feeder

Jumper

Jumper

BTS cabinet

Dual-satellite Synchronization Antenna & Feeder

Note: BTS3612 receiver is provided by CLK on BCKM.

Inner cable

Receiver on BCKM

GPS/GLONASS receiving antenna

Feeder

Jumper

BTS3612 cabinet

Jumper

Lighting arrester

Lighting arrester

Lighting arrester

Resource Pool 、 Carrier 、 Sector and Frequency

Resource Pool1

BTRM0 BTRM1 BTRM2 BTRM3



SECTOR0

SECTOR1

SECTOR2

CARRIER1 CARRIER2 CARRIER 3 CARRIER 4

BTS3612

Resource Pool2

Resource Pool3

Resource Pool4

Configuration SchemeCabinet Configuration Scheme-01 or S1Cabinet Configuration Scheme-01 or S1

CDU/DFU

RLDURLDU RLDU

BHPA

BTRX

CDU/DFU

PSU

PSU

PSU

PSU

PSU

PSU

F A N F A N

Baseband frame

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BHPA

BHPA

BTRM

BHPA

BTRX

CDU/DFU

CDU/DFU

CDU/DFU

CDU/DFU

CDU/DFU

• 1HPA + 1BTRM• 1 DFU/CDU/DDU• 1RLDU• PSU 1+1 standby

Configuration Scheme

CDU/DFU

RLDU

BHPA

BTRX

CDU/DFU

PSU

PSU

PSU

PSU

PSU

PSU

F A N F A N

Baseband frame

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BHPA

BHPA

BTRM

BHPA

BTRX

CDU/DFU

CDU/DFU

CDU/DFU

CDU/DFU

BHPA

BHPA

BHPA

BTRM

BHPA

BHPA

BHPA

BTRM

RLDURLDU RLDU

Cabinet Configuration Scheme- S111Cabinet Configuration Scheme- S111

• 3HPA + 3BTRM• 3CDU/DFU/DDU• 3RLDU• PSU1+1 standby

Sector 0 Sector 1 Sector 2

Configuration SchemeCabinet Configuration Scheme-S222Cabinet Configuration Scheme-S222

• 6HPA+6BTRM

• 3CDU/DDU• 3RLDU• PSU

2+1backupCDU/DFU

RLDU

BHPA

BTRX

CDU/DFU

PSU

PSU

PSU

PSU

PSU

PSU

F A N F A N

Baseband frame

BHPA

BTRX

BHPA

BTRX

BHPA

BHPA

BHPA

BTRM

CDU/DFU

CDU/DFU

CDU/DFU

CDU/DFU

BHPA

BHPA

BHPA

BTRM

BHPA

BHPA

BHPA

BTRM

RLDURLDU RLDU

BHPA

BTRX

BHPA

BTRX

BHPA

BTRX

BHPA

BHPA

BHPA

BTRM

BHPA

BHPA

BHPA

BTRM

BHPA

BHPA

BHPA

BTRM

Product Performance (1)

• Abis interface– Use the IMA technique and support the E1 interface (16E1s)– Support the E1 mode in SDH– Support ATM over SDH (compatible interface)

• The traffic and control bus adopt CELLBUS.– Switching bus– AAL2 transports the traffic data and AAL5 transports the signaling data– Bus clock is 25MHz

• External interfaces include:– RS485 power monitoring interface– RS485 interface to support the environment monitoring– External time reference interfaces (RS485 and RS232)– 10MHz, PP2S interfaces used for instrument testing


Built-in GPS and GLONASS receiver

Built-in testing functions Perfect heat dissipation: upper and lower ducts

Product Performance (3)Technical Features of Power Supply subrackTechnical Features of Power Supply subrack

• Input voltage: -48V• Output voltage: +25V ± 0.5V ~ +29V±0.5V• Power modules: 1800W each module 9000W in

total• Power efficiency: 85%• Heat dissipation: upper and lower grid with fans• Hot swappable• Provides RS485 monitoring interfaces


Technical Features of RF ModuleTechnical Features of RF Module

•Modular architecture•Each cabinet supports 12 antennas and 6-sectors application•BTRM supports the digital intermediate frequency technology•BTRM offers the fiber interface to support remote RF module•BTRM supports receiving and transmitting diversities•Each sub-module fulfills the blind mate•Provides the power monitoring RS485 interface which is used for remote RF modules

Product Performance (5)Technical Features of RF ModuleTechnical Features of RF Module

• RF front end adopts the CDU/DFU+RLDU mode

• Each cabinet supports 6 sectors

• Each sector supports the 4FA/2 antenna and space receiving

diversity

• Supports the transmitting diversity

• HPA and BTRM modules with fans follows the combination

structure with front and rear ducts

• Front cabling makes installation and maintenance convenient


Thermal Design of Integrated EquipmentThermal Design of Integrated Equipment

•The dissipation power of the integrated equipment is about 7000W.•Thermal design of large power module.•Front/rear duct and independent duct.•The distribution structure is adopted to reduce the heat generation density at certain point.•Holes at both the front and rear doors for ventilation.•The small power modules adopt upper and lower ducts to reduce the number of cascades.•Automatic speed controller to regulate the fans speed.

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



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)


31-31.075 Licensed LMDS (Block B)


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 SkmDkm

√ 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.

AMPS Parameters

• Base Station Transmission band

• Mobile unit transmission band

• Spacing between forward and reverse channels

• Channel bandwidth

• Number of full duplex voice channels

• Mobile unit maximum power

• Cell size, radius

• Modulation voice channel

• Modulation, control channel

• Data transmission rate

• Error control coding

• 869 to 894 MHz

• 824 to 849 MHz

• 45 MHz

• 30 KHz

• 790

• 3 watts

• 2 to 20 Km

• FM, 12 KHz peak deviation

• FSK, 8 KHz peak deviation

• 10 Kbps

• BCH (48,36,5) and (40,28,5)

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.

Digital Cellular GSM IS-136 IS-95

Year Introduced 1990 1991 1993

Access Method TDMA TDMA CDMA

Base Station Transmission band 935 to 960 869 to 894 869 to 894

Mobile Station Transmission band 890 to 915 824 to 849 824 to 849

Spacing between forward and rev. 45 MHz 45 MHz 45 MHz

Channel bandwidth 200 KHz 30 KHz 1250 KHz

Number of duplex channels 125 832 20

Mobile unit maximum power 20 W 3 W 0.2 W

Users per channel 8 3 35

Modulation GMSK Pi/4 DQPSK QPSK

Carrier bit rate 270.8 Kbps 48.6 Kbps 9.6 Kbps

Speech coder RPE-LTP VSELP QCELP

Speech coding bit rate 13 Kbps 8 Kbps 8,4,2,1 K

Frame size 4.6 ms 40 ms 20 ms

Error control coding Conv 1/2 Conv 1/2 Conv 1/2f,1/3r

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

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

WIRELESS LOCAL LOOP15april04

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