Broadband Access Fixed Wireless Solutions

Dr. I. J. WassellLaboratory for Communication Engineering

Cambridge University Engineering Dept.

Laboratory for Communication Engineering Consulting and Research

What is Broadband Fixed Wireless Access?

Aim of Broadband Fixed Wireless Access (BFWA) is to deliver broadband data services to homes and businesses in a flexible and efficient manner

Main driver is to provide Internet access for applications such as E-mail Web-browsing File downloading and transfer Streaming audio and video Voice over Internet protocol (VoIP) services

Broadband Options

Developed economies ADSL and cable TV in urban areas Options more limited in rural areas

Developing economies Little existing infrastructure BFWA offers fast deployment Can be used to backhaul traffic from

cellular Base Stations

Typical BFWA Network Topology

Point-to-multipoint AP-Access PointSU-Subscriber Unit

SU

SU

SUAP

History In Cambridge Wireless ATM project begun in early 1990s

at ORL, later AT&T Labs Project spun-out in 1999 as Adaptive

Broadband Ltd. (ABL) First BFWA trial conducted 1999/2000 using

ABL equipment Cambridge Broadband Ltd. (CBL) formed in

2000 by senior staff from ABL CBL Vectastar equipment recently deployed

in Cambridge as part of Radiocommunications Agencys (RAs) Spectrum Efficiency Scheme

Project Title - Efficient Dimensioning of BFWA Networks

Part of the RAs Spectrum Efficiency Scheme

A joint project between Cotares Ltd. (Lead contractor) CBL (Equipment and support provider) LCE (Propagation characterisation and

modelling)

Project Aim To investigate the spectral efficiency of

a FBWA network To achieve this

A near commercial scale FBWA network has been deployed in and around Cambridge

4 Base sites (each with 4 APs) in or near Cambridge

1 Base site in a semi-rural location (Cambourne)

50 SUs at customer premises 2 WiFi hotspots in a semi-rural location ISP connection to attract trial users

FDD/TDMA

High order modulation (up to 64 QAM)

Maximum 60 Mb/s full duplex per sectorwith 14 MHz pair of channels and 64 QAM

2.5 MS/s full duplex in 3.5 MHz pair of channels5 Mb/s full duplex with QPSKmax 15 Mb/s duplex with 64 QAM

High efficiency MAC ( > 80% )ATM packet based frame structureARQ rather than FEC for low overheadstatistical multiplexingvery low delay

Priority scheduling, combining ATM & IP QoS

Dynamic support for very low to very high bandwidths within a single sector

Non Line of Sight support using advanced equalisation

VectaStar 3.5 GHz BFWA Equipment Specifications

Network Interface

Subscriber Unit Standard 4 Sector Base Station

AP AP AP AP

0

30

60

90

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180

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240

270

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15

12

9

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AP

APAP

AP

256 x CPE

256 x CPE256 x CPE

256 x CPE

90 x 8antenna

23 x 23antenna

3 options for user interfaces100 BaseT100 BaseT & E1100 BaseT & 2x POTS

SDH / ATMNetwork

VectaStar System Configuration

VectaStar Base Station Configuration

STM-1

STM-1network interface

The Out Door Unit comprises: Antenna (90 x 8) Radio (controlled by APC) Modem (controlled by APC) Medium Access Control (controlled by APC)

The Out Door Unit comprises: Antenna (90 x 8) Radio (controlled by APC) Modem (controlled by APC) Medium Access Control (controlled by APC)

Multiplexer low cost ATM switch ATM 155 OC3c / STM1

Multiplexer low cost ATM switch ATM 155 OC3c / STM1

Standard 1-4 Sector Base StationStandard 1-4 Sector Base Station

AP Mux

AP Controller

AP ODU

other AP ODU

SDH / ATMNetwork

The Access Point Controller comprise: Radio, Modem & MAC management functionality SNMP Agent

The Access Point Controller comprise: Radio, Modem & MAC management functionality SNMP Agent

STM-1

Physical interface:1300 nm multi-mode fibre, 1.5km reachSONET OC-3 (SDH STM-1)

Two transport options:SONET: ATM / STS-3cSDH: ATM / VC4

Cambridge Trial Network Diagram

CISCOCore

Router

Addenbrookes Base Station

Lime Kiln Hill Base Station

Gates Building Base Station

UoC Gates Building (Network Core)

Gates Buildingto

Lime Kiln HillRadio Backhaul

APU Base Station

Core ATM Switch

Cambourne Base Station

Lime Kiln Hillto

CambourneRadio Backhaul

Lime Kiln Hill

Bourne Water Tower

Internet

Cambridge Trial Frequency Plan

5 Base Stations - 2 using wireless backhaul

Furthest SU 15 km from Base Site

0

Addenbrookes Hospital

Addenbrookes Hospital

Anglia PolytechnicUniversity (APU)

Anglia PolytechnicUniversity (APU)

UoC Gates Building

UoC Gates Building

Bourne Water Toweroverlooking Cambourne 17 km link

Bourne Water Toweroverlooking Cambourne 17 km link

Lime Kiln Hill

Lime Kiln Hill

3.4 GHz 3.5 GHz 3.6 GHz

AP Tx / SU RxAP Rx / SU TxBH AP TxBH SU Rx

BH AP RxBH SU Tx

5 MHz channels for each sector i.e. 4 colour frequency re-use pattern

Two 5 MHz channels for Point to Point backhaul (BH) links.

BH AP

BH AP

Equipment Installation at Lime Kiln Hill Site

Histon WiFi Hot Spot

Experiments

To enable quantitative results to be obtained All APs and SUs will be polled once per second

and key system information will be written to a large database

Data generators at key SUs and in the network core can be set-up to deliver known traffic flows on demand

Traffic monitoring is also performed at the network core

Experiments

Consequently the system can be configured to investigate the effects on system throughput and spectral efficiency of Various frequency reuse plans The effect of radio based backhaul of traffic from

APs compared with the use of fibre backhaul Infrastructure sharing by multiple operators, i.e.,

various QoS and data rate scenarios Response of the system to varying traffic levels

Throughput at an example SU

Time (days)Wed. Thu.

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SNR at an example SU

Time (days)Wed. Thu.

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Co-channel Interference

Receive power at example SU for 2 different interferer AP Tx powers; red- co-channel AP power 20 dBm blue- co-channel AP power 30 dBm

SNR at example SU for 2 different interferer AP Tx powers; red- co-channel AP power 20 dBm blue- co-channel AP power 30 dBm

0 10 20 30 40 50 60 70 80 90-70

-69

-68

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-60LKHW at 30dBm (mean Rxpow=-65dBm)LKHW at 20dBm (mean Rxpow=-65dBm)

time

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time0 10 20 30 40 50 60 70 80 90 100

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30LKHW at 30dBm (mean SNR=9.8dB)LKHW at 20dBm (mean SNR=20.9dB)

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Propagation Experiments

Detailed propagation measurements are being performed at various SU antenna heights using a vehicle equipped with a pump-up mast

Comparison with predictions from a ray tracing based model

Temporal monitoring Development of a statistical propagation model

Path-loss And delay spread

Measurement Vehicle

Mobile test vehicle with pump-up mast (max 18m)

Ability to capture data for further analysis

SU antenna height between 5.5 m and 10 m

GPS location system

Channel Impulse Response

0 5 0 1 0 0 1 5 00

5

1 0

1 5

2 0

2 5

3 0a ve r a g e P o w e r D e la y P r o fi l e

x 5 0 0 n s

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C h a n n e l i m p u l s e r e s p o n s e

- 9 0

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Path Loss

10 -1 10 0 10 180

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Distance (km)

P

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Path Loss vs. AP Distance (Based on mean recorded PL) - Gates All APs

5.5

Path Loss Temporal VariationR

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Time (days)Thu. Wed.

Issues to Date Frequency planning has proved difficult with

only four channels owing to the number APs deployed in a relatively small area

Difficulties compounded by having the back-haul channels adjacent to the 4 main channels

A couple of sectors (APs) have been turned-off to reduce unwanted interference

An 8 channel scheme will be tried to see how its performance compares with the current frequency plan.

Concluding Remarks

A near commercial scale BFWA network has been installed in Cambridge

The quantity of data gathered concerning its performance is unprecedented

Will make a major contribution concerning the planning and deployment of BFWA networks

The preliminary results are encouraging and promise that BFWA can compete with other broadband solutions