2. Fixed Wireless

8/3/2019 2. Fixed Wireless

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2. Fixed wireless

2. Fixed wireless


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2001,

TelindusHigh-TechInstitute

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2. Fixed wireless

Fixed radio access

Endpoints are stationary and therefore less susceptible to the bandwidth andquality limitations associated with mobile wireless networks

Different configurations

Point to point

Point to multipoint (WLL = Wireless Local Loop)

Local Multipoint Distribution System (LMDS) > 10 GHz

Multichannel Multipoint Distribution System (MMDS) < 10 GHz

Wireless broadband access useful

In (rural) areas where you can't get high-speed access over the traditional

telecommunications infrastructure

In urban areas where the operator doesnt have his own access network


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2001,


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2. Fixed wireless

P2P vs P2MP

P2Pdedicatedbandwidth

P2MPshared

bandwidth

P2MP Sector


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2. Fixed wireless

Cost per subscriber by network

CostP

erSubscriber

CPE Cost

PTP

PMP

# of Subscribers


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2. Fixed wireless

Architecture

Base Station (BS) connected to public networks

BS serves Subscriber Stations (SS)

To backbone

MUXDACS

STM-1

HUB IDU

ODU/ANTENNA

Remote

IDU

E1

RemoteODU/Antenna

PayphonePOTS

ACCESSMUX

TM

VAXstation 3100


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2. Fixed wireless

Fresnel Zone

Line of Sight (LOS) required

Obstructions might obscure a link

Topographic features, such as mountains

The curvature of the earth Buildings and other man-made objects

Trees, water

Radio LOS is not the same as visual LOS

Fresnel zoneis an elliptical area immediately surrounding the visual path. It varies

depending on the length of the signal path and the frequency of the signal


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2. Fixed wireless

Point to point: Wi-Fi @ 2.4 GHz

Performance

Small bandwidth up to 11 Mbps

Long distance up to 20 Km

Different technologies

11Mbit DSSS (Direct Sequence Spread Spectrum)

3Mbit FH (Frequency Hopping)

Applications

Best used for IP

Not good for telecom (E1)


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2. Fixed wireless

Point to point: >10 GHz

Performance

High bandwidth up to 622 Mbit

Long distance up to 30 Km Interference

Rain dependable solution (to overcome by design)

Important technologies

Compression (


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2001,


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2. Fixed wireless

Laser

Performance

High Bandwidth up to 1 GB

Short Distance up to 4 km Interference

Fog

No license required / no radio spectrum to purchase

Rapid deployment

Low maintenance

Applications

IP networks 10, 100 and 1000 Mb/sec

Telecom : E1/E2/E3, STM

2Mb/s 34 Mb/s 155 Mb/s 622Mb/s SDH and SONET support

Video


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2001,


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2. Fixed wireless

Laser

There is no typical application

Temporary deployment

Disaster recovery Broadcast applications

Security

Impossible to tap the signal

Modulated light

No reflections

Narrow beam


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2001,


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2. Fixed wireless

Laser and microwave compared

Bandwidth Distance License Frequency

PAV/Opticalaccess

1 Gbps 4 km No

Witcom 54 Mbps 20 km Yes 15, 18, 23, 26, 38

Ceragon 622 Mbps 30 km Yes 7.5, 10, 15, 18, 23, 26,38


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2001,


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2. Fixed wireless

Point to multipoint

(Formerly) often referred to as

LMDS: >10 GHz

MMDS:


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2001,


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2. Fixed wireless

WiMAX (1/2)

IEEE 802.16 is a groupof WMAN standards

Latest wireless hype

Published in december 2001, in 10 60 GHz spectrum

Amendment 802.16a, approved in January 2003

Non-line-of-sight extensions in the 2 11 GHz spectrum

Up to 70 Mbps at distances up to ~50 km

Initially WiMAX is to be used as a backhaul technology to feed emerging Wi-Fihotspots (and possibly 3G base stations)

In the near future WiMAX claims to offer metro-area mobility for Internetaccess


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2001,


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2. Fixed wireless

Wi-MAX (2/2)

Technology Freq. Band Distance Speed Features

802.16 10-66 Ghz 31 miles 70 MbsRequires Line-of-Sight

(approved 2002)

802.16a 2-11 Ghz 31 miles 70 MbsNo line-of-sight reqd

(approved Mar03)

Intel promises WiMax versions of Centrino for 2004Nokia will launch a WiMax cell phone in 2005


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2001,


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2. Fixed wireless

Overview

Point to point

2.4 GHz

Other frequencies

Laser

Point to multipoint

WiMAX

Annex: multi-carrier modulation


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2001,


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2. Fixed wireless

Multi carrier modulation

Basic idea is to send signal over multiple low-rate carriers instead of a singlehigh-rate carrier

Longer symbol duration on individual carriers causes less inter symbol interference

Multipath effects can be compensated with a much simpler equaliser

OFDM abandoned the use of steep bandpass filters that completely separatedthe spectrum of individual subcarriers

Common practice in older Frequency Division Multiplex (FDM) systems

Instead OFDM uses orthogonal frequencies

Multicarrier technology used in

802.11a (COFDM, WLAN)

802.16 (OFDM, WMAN)

DAB, DVB-T (COFDM)

BWIF (VOFDM) xDSL (DMT)

M lti i d l ti ff ti d l d


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2001,


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2. Fixed wireless

Multi carrier modulation: effective delay spread

Delay spread depends on difference in path lengths

Single carrier modulation

Symbol interval becomes shorter than delay spread as symbol rate is increased

Time dispersion causes intersymbol interference

Equalisation can mitigate this to some extent (number of taps required is

proportional to the delay spread)

Cell size Max Delay Spread

Pico cell 100m 300nsMicro cell 5km 15us

Macro cell 20km 40us

Ts Channel taps Application

802.11a 50ns 6 WLANDVB-T 160ns 90 Audio

DAB 600ns 60 TV broadcast

M lti i d l ti th lit b t b i


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Multi carrier modulation: orthogonality between subcarriers

Frequency spectra of various subcarriers overlap

At the center frequency of any particular subcarrier all other subcarriers attain

a null point Demodulator does not see modulation of the others

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