John Pahl and Steve Munday Transfinite Systems Ltd
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Transcript of 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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 2
Presentation Structure
• Project objectives and approach• System parameters used• Approach to analysis• Results of runs• Conclusions
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 3
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 4
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 5
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 6
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 7
RAS Reference Models-1
8 potential sites that could operate RAS at 43 GHz
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 8
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 9
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 10
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 !
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 11
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 antenna Bessel antenna10 pointing restriction
Bessel antenna10 pointing restriction10m antenna height18.5 dB Shielding loss3 dB Spreading loss
High density mesh EN 301 215 TS15m antenna height
Bessel antenna Bessel antenna10 pointing restriction
Bessel antenna10 pointing restriction2.5m antenna height19.7 Shielding loss3 dB Spreading loss
Feeder Rec. F.1245 ant20m antenna height
Bessel antenna Bessel antenna10 pointing restriction
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 12
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 13
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 14
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 15
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 16
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.
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 17
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 18
Example Building Block
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 19
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 20
Example distribution of test stations
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 21
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 22
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 23
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 24
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 25
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.
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 26
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 27
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 28
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 29
EZ for RRA BS smooth earth analysis D=66km
EZ based upon distance
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 30
EZ for RRA BS with terrain L452(10%) < -176 dB
EZ based upon L452(10%) < X
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 31
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 32
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 33
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 34
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 35
Key: circles = P-MP in urban areas, crosses = mesh LD in rural areas
Realistic BFWA distribution
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 36
Worst case: RAS mask gain pattern + no BFWA mitigation
Single EZ - RAS Baseline and BFWA Realistic
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 37
Improvement due to use of MZ and Bessel gain pattern
Key: circles = BFWA cells in UZ, crosses = BFWA cells in RZMulti-Zone - RAS Realistic
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 38
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 39
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 40
Locations of EZ/RZ/UZ for VLBI
Key: circles = BFWA cells in UZ, crosses = BFWA cells in RZ
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 41
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 42
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°
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 43
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
BFWAtg - BFWA sharing with RAS at 43 GHzSlide 44
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