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Spectrum sharing issues for small cells

Michael Fitch – 29th March 2012

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Roadmap of talk

Why small cells

Why spectrum sharing

A bit on TV Whitespace

Spectrum sharing management

Challenges and (potential) solutions to spectrum sharing

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Users are demanding more bandwidth

Orange reported

4,125% increase in

traffic last year, 100%

increase in last 3

months.

Cisco predict demand

doubling every year for

next 5 years.

Nokia Slide – LTE global summit

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10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

2008 2009 2010 2011 2012 2013 2014 2015

sub

scri

pti

on

s (t

ho

usa

nd

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Uk Subscriptions by 2G/3G/4G technology

LTE

3G

GSM

LTE Network Roll-Out

Likely Roll-out:

– Link in with 2G refresh – installation of multi-mode radios

– Start with:

– major cities where most data traffic is generated

– macro-cells; later small outdoor cells and indoor femtocells

– high-end traffic users

Source: Ofcom

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WiFi-LTE Scenarios

Capacity for a given indoor area

Cost

Macro-cells limited by

available spectrum

Small cells limited by

availability of sites

2.4GHz WiFi limited

by interference

Femtocells currently

~$150 each,

ultimately limited by

interference

Relative costs of provisioning indoor coverage

Not to scale:

5GHz WiFi

limited by

coverage

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WiFi-LTE Scenarios

Capacity for a given indoor area

Cost

Relative costs of provisioning indoor coverage

Not to scale:

Time

2013: All

networks will

start roll out

Macro-cellular

networks

2013-2014:

Most

networks will

start roll-out

small cells

2014-2015: When

femto-cells hit the

right price point

networks will

consider large-scale

deployment

2011 onwards: To

varying degrees

MNOs will invest in

WiFi offload

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LTE femtocells may be part of an overall

deployment

• LTE femtocell reference designs announced by vendors.

• LTE femtocells are part of the overall standards. Available closed, hybrid and open

access modes.

• Trials in 2011, Commercial units available in 2012.

• Outdoor femtocells with higher power and more complexity.

• Multi radio femtocells not seen as essential at the moment.

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BT’s 1.5 million hotspots, one billion minutes

1.35m+ enabled Home Hubs

150k+ enabled Business Hubs

3.8k premium hotspots

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BT WiFi cells

BT Infinity is BT Retail broadband service connected using

Openreach NGA

HH3 senses the channels 1 – 11 and chooses one with low

congestion. Noise floor and beacons are sensed

Home Hub 3

BT business and public hotspots

Openzone and HH access points (including Fon access)

are backhauled to the same datacentres

4 datacentres provide authentication, billing, roaming

policies

Hot-spot 2 is work in progress, which will support 802.1x,

roaming for different operators, automated sign-up,

handover to / from 3G networks, operator policy control

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But WiFi is getting congested…

This is what I see in my office….

and there are 3 more below the picture..

Distribution of FTTC / VDSL will

add pressure,

Moving to 5.4GHz has coverage issues

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What are the trends ?

Increasing data traffic, mostly from within buildings

Increasing WiFi offload

Cells are getting smaller

WiFi is ‘loose’

– suffering from increasing congestion and decreasing coverage

LTE is ‘tight’

– suffering from single MNO per BS, lack of spectrum

– planning is increasingly infeasible

Is a solution something in-between unlicensed and licensed, ie smart spectrum sharing ?

– on backhaul and access ?

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Regulators are encouraging a move from binary licensed /

unlicensed towards greater intelligence

and flexibility

Estimate we are here

Planning is becoming infeasible

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(a) 5GHz (b) 2.4GHz (c) 700MHz

Area – 1sq km in London, household density 5k

Coverage of different frequency bands

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(a) 5GHz (b) 2.4GHz (c) 700MHz

Sharing the airwaves with DTV provides coverage similar to a mobile broadband network – with a 20% deployment density, from indoors….

Area – 1sq km in London, household density 5k

Coverage of different frequency bands

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• 16 channels (128MHz) of cleared spectrum for auctions (2012)

• 32 channels (256MHz) interleaved spectrum retained for:

• Licensed Primary Usage for Digital Broadcasting

• Licensed Secondary Usage for Wireless Microphones

• Unlicensed Secondary Usage – sharing-

• 1 channel (8MHz) dedicated to Radio Microphones

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What is TV Whitespace spectrum ? - the UK plan...

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Exploring use of TV Whitespace: Licensed,

unlicensed, primary and secondary

Licensed and unlicensed

in separate spectrum

Licensed and unlicensed

sharing the same spectrum

The order of access priority is Licensed Primary (eg DTV), Licensed Secondary,

(eg wireless microphones), Unlicensed Secondary (everything else)

Sharing is free, but must not cause harmful interference

to systems higher up the pecking order

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Spectrum management using a database

1 Request list

2 Get list

3 Contact a dB with location, uncertainty and

other optional information

4 Get list of available channels / powers and

time to live and other optional information

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1 Request list

2 Get list

3 Contact a dB with location, uncertainty and

other optional information

4 Get list of available channels / powers and

time to live and other optional information

5 Inform database which channels have been

chosen

Need a feedback path

The IETF PAWS WG is defining this protocol

- And use-cases / requirements and security aspects

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We also need fairness etiquette

between secondary systems

Fairness between these guys

- Brokering ? Contention ? SON ?

Regulators are not interested in this critical issue !

Regulators want to certify database algorithms

This, and the issue of fairness, are likely to be the critical lines

to deployment.

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But I think we need even more than this….

To and from repositories

of TV coverage, PMSE usage,

[emergency services etc]

Spectrum portfolio for region,

with quality measures

Spectrum portfolio manager

(centralised)

Resource manager

(distributed) – to cope with many systems Location of BS

Locations of end users

Confidence levels

Antenna characteristics

Sensing information

Quality requests

Mobility requests

What channels and powers are chosen

Others ?

Available channels and powers

Quality of channels

Time of relevance

Others ?

3rd party

database

in two steps

(QoSMOS

approach)

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Regulatory position - briefly

Considerable effort will be needed to establish trust with Ofcom and with primary

users of the spectrum (DTV and Wireless Microphones) – through trials / standards

Ofcom indicate a 2-year process so we may go live in 2013.

A VNS and Interface Specification will be published this year. Vendors will self-certify

against the VNS

An SI is also being drafted to allow unlicensed equipment to operate in the band

Ofcom have started a WI in ETSI BRAN.

Position in other European countries is lumpy:

German / French very cautious for a number of reasons

Swiss /Dutch / Finnish / Polish more open and looking to FCC / Ofcom for lead

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Trials and standards

Isle of Bute and Cambridge trials in UK (rural broadband)

– Proved TV WS can deliver >30Mbit/s and reach 8km with 2Mbit/s with 4W eirp, few users (10)

– Database integration for channel selection and power control (using BT prototype database)

Further trials proposed

– In Suffolk (rural broadband) to evaluate contention and interference, more users (30)

– Indoor networking with small cells (a few houses)

Standards focus

– IETF PAWS

– ETSI RRS and BRAN

– IEEE, especially P1900.7

– SE43

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Challenges and (potential) solutions to sharing

PHY and MAC layer

– Without interfering with adjacent services, needs to be better than OFDM

– To support enough data-rate (30Mbit/s ?), so channel bonding

– Potential solution: FBMC

Protection margins to be agreed

– Sets power within the cells

– Potential solution: measurements from trials and working with stakeholders

Database and sensing algorithms

– Etiquette needed for fairness

– Scalable to large numbers of small cells

– Potential solution: distributed database structure and algorithms with sensing

Eco-system development

– Need to increase confidence in vendors and regulators

– Potential solution: trials and standards activity

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Thank you for listening