john pahl and steve munday transfinite systems ltd

BFWAtg - BFWA sharing with RAS at 43 GHzSlide 1

Re-examination of the protection requirements for the Radio Astronomy Service in light of the Broadband Fixed Wireless Access Multimedia Wireless

Systems proposed for the 42.5 - 43.5 GHz frequency band

John Pahl and Steve Munday

Transfinite Systems Ltd


Presentation Structure

• Project objectives and approach• System parameters used• Approach to analysis• Results of runs• Conclusions


Project objectives

• To analyse the feasibility of BFWA operating in the 42.5 - 43.5 GHz band, taking into account the need to protect the RAS

• Determine the conditions that would facilitate sharing, such as operating restrictions

• Evaluate existing work and approaches to sharing such as in ERC Report 36

• Derive, where necessary, methodologies to model interference and assist in sharing


System Parameters• Obtained from review of previous studies, current literature

and discussion with operators • Data sets developed for different types of BFWA systems:

– 3 types of Mesh system - low, medium and high density– 6 types of Point-to-Multipoint system

• Urban Symmetric and Asymmetric models• Sub-urban Symmetric and Asymmetric models• Rural Symmetric and Asymmetric models

– 2 types of Feeder link

• Variations to analyse impact of modeling assumptions and mitigation


BFWA Baseline Models

• From the data sets, the following were selected as baseline reference models for use in the analysis:– P-MP Urban, Commercial, Symmetric Model (UCS)

– P-MP Rural, Residential, Asymmetric Model (RRA)

– Low Density Mesh Model

– High Density Mesh Model

– Feeder Link Model

• P-MP models included both BS and UT transmit, giving a total of 7 BFWA models


BFWA Mitigation

• Study alternative modeling assumptions and to facilitate sharing

• BFWA mitigation models included:– Realistic model

• Baseline model with antenna modeled as Bessel function

– Pointing model• Realistic model with restriction to avoid pointing at RAS

site

– Full Mitigation• Pointing model with antenna height restriction, shielding

and spreading loss


RAS Reference Models-1

8 potential sites that could operate RAS at 43 GHz


RAS Reference Models-2• Three RAS sites considered - Jodrell Bank,

Defford and Cambridge• Protection criteria obtained from ITU-R Rec.

RA.769 for three types of observation:

ObservationType

Harmful Interference not to beexceeded for 10% of time

Continuum -220.6 dBW/MHz

Spectral Line -204.1 dBW/MHz

VLBI -178.6 dBW/MHz

RAS protection criteria / 1 MHz


RAS Reference Models-3

• Baseline model:– Gain pattern Rec. SA 509-2, ie 32-25log()

– Minimum elevation 5°

• Realistic model:– Baseline model with antenna modeled as Bessel

function

• Pointing model:– Realistic model with minimum elevation of 19°

In all cases observation time 2000 seconds


RAS gain patterns

Bessel

Rec 465

dB

Off Axis Angle

-20

-40

-60

0

20

40

60

80

100

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Up to 35 dB difference !


Summary

Summary of Baseline and Mitigation Models

Model Baseline Realistic Pointing mitigation Full mitigationP-MP UCS BS Tx EN 301 215 CS2

20m antenna heightBessel antenna Bessel antenna

45 pointing restrictionBessel antenna45 pointing restriction15m antenna height3 dB Spreading loss

P-MP UCS UT Tx EN 301 215 TS15m antenna height

Bessel antenna Bessel antenna45 pointing restriction

Bessel antenna45 pointing restriction2.5m antenna height3 dB Spreading loss

P-MP RRA BS Tx Toroidal antenna40m antenna height

n/a n/a 30m antenna height3 dB Spreading loss

P-MP RRA UT Tx Toroidal antenna5m antenna height

n/a n/a 2.5m antenna height3 dB Spreading loss

Low density mesh EN 301 215 TS115m antenna height


Bessel antenna10 pointing restriction10m antenna height18.5 dB Shielding loss3 dB Spreading loss

High density mesh EN 301 215 TS15m antenna height


Bessel antenna10 pointing restriction2.5m antenna height19.7 Shielding loss3 dB Spreading loss

Feeder Rec. F.1245 ant20m antenna height


Bessel antenna10 pointing restriction3 dB Spreading loss

Radio Astronomy Rec. S.465 ant5 min ant elev

Bessel antenna Bessel antenna19 min ant elev

n/a


Approach to Analysis

• Start from ERC Report 36• Analyse its assumptions and models• Develop new modelling methodology to

calculate interference• Develop methods to facilitate sharing• Study impact of implementation details such as:

– RAS operational methods

– potential distribution of BFWA systems


ERC Report 36

• Proposes co-ordination distance of 50 km• Based upon:

– single FS transmitter

– smooth earth ITU-R Rec. P.452 propagation

– antenna heights of 5-10m

• None of these realistic, eg: using RAS & BFWA heights of 30m 36 dB worse


Single vs Aggregate Interference

• ERC Report based upon single transmitter• Analysed impact of large numbers of

transmitters• Simulated impact of adding rings of

transmitters every 4 km from 50 - 110 km• Interference increased:

– ~12 dB single station to all stations in 50 km ring

– ~17.5 dB single station to all rings 50 - 110 km


Single Entry vs Aggregate Interference by distance

-205

-200

-195

-190

-185

-180

50 60 70 80 90 100 110

Distance

5m 20m 5m Worst single 20m Worst single


Modelling Conclusions1. Analysis of BFWA sharing with RAS using ITU-R Rec.

P.452 propagation should be based upon realistic antenna heights.

2. Analysis of BFWA sharing with RAS should be based upon aggregate interference from all potential transmitters.

3. The calculation of aggregate interference need not include transmitters at a distance of more than 110 km from the RAS site.

4. Accurate modelling of interference from BFWA into RAS should include the impact of terrain on propagation loss.


Methodology• Needed to develop methodology to analyse

interference from large numbers of BFWA transmitters

• Methodology included impact of:– terrain– mitigation– variation in BFWA cell configurations– type of RAS observation

• Approach based on cells as Building Blocks, using Monte Carlo techniques to aggregate interference


Example Building Block


Example EIRP Distribution

Random test point.Forward.I

% ti

me

EIR

P e

xcee

ded

EIRP at horizon (dBW/MHz)

0.001

0.01

0.1

1

10

100

-15-20-25-30-35-40 -10


Example distribution of test stations


B F W A B S B F W A U T R A S S ite

In terference = TX(ga in , po in ting, power ...) + P ropagation(Terra in , % , ...) + R X(ga in , po in ting, ...)

P D F P D F P D F

TX E IR P P rop.Loss R X G ain

+ + =P D F

Interference

Monte Carlo Approach


Analysis and Results-1

• Based upon ERC Report exclusion distance of 50 km

• Study impact of input parameters:– Compare modelling assumptions

– Compare impact mitigation methods

– Compare BFWA architectures

– Compare RAS sites


Baseline results: EZ=50km no mitigation

Runs exceeding limit: all

Interference from BFWA systems into Jodrell Bank

0.1

1

10

100

-250 -240 -230 -220 -210 -200 -190 -180 -170 -160 -150

I (dBW)

feeder 1 ant

feeder 2 ant

mesh LD

mesh HD

UCS BS

UCS UT

RRA BS

RRA UT

Criteria


Baseline results: EZ=50km with mitigation

Runs exceeding limit: Mesh LD, Mesh HD, RRA BS

Interference from BFWA systems with pointing mitigation into Jodrell Bank

0.1

1

10

100

-250 -240 -230 -220 -210 -200 -190 -180 -170 -160 -150

I (dBW)

feeder 1 ant

mesh LD

mesh HD

UCS BS

UCS UT

Criteria


Results of initial runs• 50 km exclusion distance in ERC Report is not

sufficient to protect RAS site• Modeling gain patterns using Bessel functions

significantly reduces interference (25 - 30 dB)• Imposing pointing restrictions on BFWA

reduced interference by further 12 - 30 dB• Results between RAS sites similar - variation 0 -

10 dB. Jodrell Bank and Defford most alike as similar terrain profile.


Implications• No one BFWA architecture was worse under

all situations, e.g.:– Mesh worst without mitigation, but has more

ability to decrease interference

– P-MT RRA best without mitigation, but limited ability to decrease interference

• Most important factors are:– use of pointing mitigation

– gain pattern assumed - in particular for RAS


Methods to facilitate sharing

• BFWA operating restrictions– Combining mitigation with Exclusion Zones (EZs)

• BFWA cell distribution and architectures based upon UK census data

• RAS operational considerations– observation types


Exclusion Zone Methods

• Traditionally based upon distance, D• Not appropriate when including terrain:

– azimuth dependent

– does not linearly increase along azimuth

• Propose use of new EZ method:– Exclude all locations where L452(10%) < X

• Compare these two EZ methods• Change size of EZ (D or X) using iteration

until just meet RAS criteria


EZ for RRA BS smooth earth analysis D=66km

EZ based upon distance


EZ for RRA BS with terrain L452(10%) < -176 dB

EZ based upon L452(10%) < X


Impact of L452(10%) method

• Easy to define and implement• Reduces area excluded

– e.g. from 13,872 km2 to 2,816 km2

• Excludes points such as tops of mountains unlikely to be used anyhow

Note: L452(10%) is height dependent, so must specify maximum tx/rx antenna heights


Multi-Zone approach

R estric ted Zone

E xclusionZone

S m ooth E arth m odel used toca lcu la te exclusion d istance

U nrestric ted Zone


Analysis and Results-3

• Following Multi-Zone approach:– EZ: no BFWA operation– RZ: BFWA operating with pointing mitigation– UZ: BFWA operating unrestricted

• Boundaries EZ/RZ and RZ/UZ based upon where L452(10%) = X1, X2 (derived in analysis)

• Distribution of BFWA cells based upon UK Census data

• Multiple runs for alternative RAS assumptions


Production of realistic BFWA distribution

• Mapped 1991 UK Census data to BFWA types based on populated weighted density (persons / km2) :

UK Census Density Group BFWA System Type

3027 or over P-MP UCS

1669 to 3027 P-MP UCS

913 to 1669 Mesh LD

502 to 913 Mesh LD

200 to 502 uneconomic

under 200 uneconomic

• Mesh LD rather than P-MP RRA used for low population areas as needed ability to mitigate


Key: circles = P-MP in urban areas, crosses = mesh LD in rural areas

Realistic BFWA distribution


Worst case: RAS mask gain pattern + no BFWA mitigation

Single EZ - RAS Baseline and BFWA Realistic


Improvement due to use of MZ and Bessel gain pattern

Key: circles = BFWA cells in UZ, crosses = BFWA cells in RZMulti-Zone - RAS Realistic


RAS observing method

• Analysis above based upon RAS most stringent criteria -220.6 dBW/MHz

• This is to protect a single RAS site making Continuum observations

• Criteria to protect VLBI and Spectral line observations are higher

• Analysis was also done against these thresholds


Results: VLBI• Based upon:

– BFWA using MZ (EZ/RZ/UZ)

– RAS modelled using higher elevations and Bessel gain patterns

– Comparing against VLBI threshold

• Conclusion:– BFWA can operate close (~10 km) of RAS site


Locations of EZ/RZ/UZ for VLBI

Key: circles = BFWA cells in UZ, crosses = BFWA cells in RZ


Best case sharing scenarioRAS:• operates only as VLBI and SL (single site)• antenna gain pattern similar to Bessel function• generally operates at elevations 19°

BFWA:• uses multiple zones EZ/RZ/UZ

• zones based upon L452(10%)

• at least pointing mitigation used within RZ• frequency plan takes account of SL frequencies


Impact of RAS assumptions• Worst case - sharing very difficult with large areas

excluded:– RAS single site Continuum observations, gain pattern 32-

25log()

• Intermediate case - sharing possible but significant areas excluded:– RAS single site Continuum observations, gain similar to Bessel

• Best case - sharing possible almost everywhere except very close to RAS site:– RAS VLBI & Spectral line observations, gain pattern similar to

Bessel, elevation angles 19°


Conclusions• On its own, an exclusion zone of 50 km as in ERC Report 36 is

insufficient to protect the RAS• The methodology and assumptions used to derive this figure are

inappropriate for BFWA scenarios• New methodology described here can be used to calculate aggregate

interference BFWA RAS

• Use of Exclusion Zones based upon L452(10%) are more efficient than using distance

• Multiple zones can be used to improve coverage without requiring mitigation everywhere

• The characteristics of RAS operating in this band will determine the extent for which BFWA can be deployed


Areas for Further Study• The following require further study:

– whether the RAS will use the 43 GHz band to make Continuum observations from single sites

– what is the average gain pattern of RAS antennas towards the horizon over typical observation time

From above can determine EZs to protect RAS for specified BFWA systems

Further work also needed to define how to model correlation of propagation effects using Rec. 452.

• More runs could analyse wider range of scenarios

john pahl and steve munday transfinite systems ltd

Documents

model interference

modelrealistic model

realistic modelbaseline

baseline reference models

symmetric model ucspmp

bessel functionpointing

antenna height restriction

lossras reference models