Presentation Note: Agenda Change

• The schedule presentation on “Breaking out Base Station Strategies” has changed

• This new topic, “Who Put This Tower Here Anyway?” has been selected to be more consistent with the technical track on Wireless Backhaul

• If you have interest in the previous topic, please contact today’s speaker at scott.d.nelson@alcatel-lucent.com for assistance in contacting the original presenter.

Who Put This Tower Who Put This Tower Here Anyway?Here Anyway?

Challenges and Options for Rapid Challenges and Options for Rapid Expansion in Wireless BackhaulExpansion in Wireless Backhaul

What we all should know by now…

• Backhaul requirements are growing exponentially• Number and density of cell are sites ramping up• Fiber backhaul will be critical for 4G• Fiber cannot (cost effectively) reach all cell sites• Microwave offers relief for the backhaul bottleneck

What we may be avoiding…• It is easy to talk about, but hard to implement

Side Bar #1 : Old School

• Focus on propagation and obstructions– Terrain, trees & buildings– Availability objective: better than “five nines” (99.999%)

• How we met those challenges– Line of sight clearance analysis– Site selection (with the intent of building LOS paths)– Link by link path design

• Labor intensive and time consuming

How Clear is “Clear”?

• Line of sight clearance is more than just grazing

• Clear LOS has two requirements:

– Freznel zone clearance• From 6/10th F1 to entire F1

– Additional margin for variation in atmospheric refractivity• K-factor from 4/3rd to 2/3rd (or possibly more severe)

Fresnel Zones• Term used to describe path clearance

– Principles introduced by Augustin Fresnel, French Physicist, (1788-1827)

r1= 72.1 [ (d1*d2) / (f *D)]1/2

Where:r1 = first Fresnel zone radius at point P in feetd1 = distance from Tx in milesd2 = distance from Rx in milesD = path length in miles &f = operating frequency in GHz

an + bn = D + n(/ 2 ) &rn = r1 [ n ]1/2

Where:n = the nth Fresnel zonern = the radius of the nth Fresnel zone & = operating frequency wavelength

a2

b2

First Fresnel Zone(n = 1)

Second Fresnel Zone(n = 2)

Tx Rx

d1 d2

D

r1

r2

P

b1a1

F1

F2

Mid-Path Fresnel ZonesRadii For 10 mile Path:@ 6 GHz @ 18 GHz

F1 = 47 ft F1 = 27 ftF2 = 66 ft F2 = 38 ftF3 = 81 ft F3 = 47 ftF4 = 93 ft F4 = 54 ft

Radio Ref. (N)

Normal Atmosphere (K = 4/3)

Normal Atmosphere

Heig

ht

(h)

Radio Ref. (N)

Heig

ht

(h)

Subrefractive, Obstruction (K < 4/3)

Radio Ref. (N)

Heig

ht

(h)

Superrefractive (K > 4/3)

Superrefractive

Radio Ref. (N)

Heig

ht

(h)

Possible Ducting (K varies across beamwidth)

Radio Refractivity Gradients (K Factors)

Subrefractive

Ducting

Path Profile Example

Jun 13 06

Alcatel Canada Inc.

Systonen's Corner NEW

Latitude 48 31 11.00 NLongitude 089 38 55.00 WAzimuth 133.64°Elevation 469 m ASLAntenna CL 95.0 m AGL

Rosslyn

Latitude 48 22 17.00 NLongitude 089 24 56.00 WAzimuth 313.82°Elevation 224 m ASLAntenna CL 23.0 m AGL

Frequency (MHz) = 11200.0K = 1.33

%F1 = 100.00

Path length (23.86 km)

0 2 4 6 8 10 12 14 16 18 20 22

Ele

vation (

m)

200

250

300

350

400

450

500

550

600

Fresnel Zone Clearance

Annual Variations in K-factor

Obstructions (Trees,

Buildings)

Site Selection Process

• Find suitable towers near markets– Height, structure type,

availability

• Line of sight analysis– First Fresnel zone clearance

• Path performance analysis– Objective: 99.99x%

availability

• Iterative process– Several passes, multiple sites,

and typically field surveys

Refugio

Beeville

Skidmore

Private

Towers

Private

Towers

Private

Towers

That Was Then…

• Since the introduction of AMPS cellular service, half of the microwave industry in North America was driven by backhaul to less than 5% of cell sites– The other half was private microwave, largely for public safety and

critical infrastructure protection

• More than 3/4th of microwave deployments were long-haul– Greater than 15 miles– Tall towers– Large antennas (6 to 12 foot diameter)

• Long planning cycles and large-scale construction projects were common

But what about the other 95% of cell sites???

• Low cost and highly ubiquitous T1 backhaul fueled cell site backhaul

• One T1 provided 24 voice circuit trunks, and with PCS and digital voice compression, that capacity per T1 was expanded even further

• Cell sites with more than 4 T1 were uncommon, and typically associated with collocation of multiple base stations and carriers

This lead to a critical development…

Cell Sites Everywhere and Anywhere!

Benefits of Flexible Cell Site Location

• Design process for RF coverage is more flexible and optimized– Fill in critical spots rather than blanket the countryside

• High ground and tall towers less necessary• Lightweight towers & monopoles at tree top level• Alternate structures & moderate elevations

– Rooftops, water tanks, silos, billboards, steeples, and other “stealth” sites

The Dramatic Downside• Cell sites are often in valleys and topographic depressions • Virtually eliminates LOS clearance between many cell sites• Microwave backhaul becomes very challenging

Example – Statewide Broadband Deployment

• Initial requirement for 135 sites to support broadband

• Selection window included all sites within 20 miles of each other

• Terrain and 80’ trees used in LOS clearance analysis and 11 GHz for first Freznel zone

• Using only the targeted cell sites, less than 30% of the sites had a connection to another site

• Even fewer had routes traceable to a fiber-fed tower location

And Not Every Site is “Microwave Ready”

Solutions?Solutions?

Trees and Terrain

Urban Clutter

Interdependent Considerations for MW DesignDistance

•From fiber to cell sites

•Between cell sitesCapacity

Requirements•Individual cell sites

•Aggregate of multiple cells on same

route•(current & growth)

Microwave Reach•Relative to capacity

•Relative to frequency

Spectrum•Congestion•Number of

channels

Site Constraints•Tower/rooftop lease•Existing occupants

Antennas•Size

•Performance

Las Vegas

Dashed Lines = Possible PathsSolid Lines = Actual Paths

(paths that are not blocked)

Very Complex for Large Systems

Computer Aided Path Design Helps Dramatically

The next step involves boots on the ground…The next step involves boots on the ground…

Example of an Initial Feasibility Study

Recommendations

• Consider large scale deployments– more sites in the database = more possible connections

• Look for hub sites outside of those targeted for backhaul– High elevations, room for multiple antennas, convenient fiber access

• Evolve coverage models to include inter-cell LOS– Select new sites that are potential hub locations

• Break out of the 6 GHz mold– 11, 18 & 23 GHz are more available– Consider subleasing other bands such as 38 GHz, 28 GHz and 24 GHz– Take the 60 & 80 GHz plunge – short reach, but very high capacity– All of these can be engineered for better than 99.999%

• Employ or contract personnel focused on backhaul