Criteria for spectrum sharing
We identified 5 criteria that spectrum options would have to satisfy
• It must not already have been allocated to mobile
• It must not already have been identified as a candidate mobile band and unlikely to be
so in the medium to long term
• The incumbent use of the candidate band must be harmonised at least Europe wide
– Allows the sharing option to be adopted by other administrations
• It must provide a substantial block of contiguous spectrum
• Must be below 2 GHz
In addition to the above we also recognised that the spectrum would have to be usable by
PMSE
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Compatibility assessment
We carried out theoretical and practical compatibility studies
• Desk based analysis which showed that sharing is possible
• Practical coexistence measurements carried out by JCSys Ltd
(http://stakeholders.ofcom.org.uk/binaries/consultations/new-spectrum-audioPMSE/annexes/annex6.pdf)
– Studies considered both PMSE into aero and aero into PMSE (to see if spectrum
was usable by PMSE)
• Measurements provided interference thresholds into aero systems and coexistence
criteria for satisfactory PMSE operation
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Compatibility assessment
Important points to note
• C/I (to degrade audio quality) is less than 2 dB (both analogue and digital)
• DME channels are 1 MHz wide
• Offsetting PMSE frequency by 300 kHz from DME centre frequency gives additional
20dB+ of isolation
• No airborne DME transmissions below 1025 and above 1150 MHz
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Interference scenarios
Plane ‘interrogates’ ground station on one
frequency and receives response on a different
frequency (separated by 63 MHz) e.g on channel
30X (1054 MHz and 991 MHz)
Air tx limited to
1025-1150 MHz
2
1
4
3
DME Transponder
Time taken for the signal to get from the plane to
the transponder and back is used to calculate the
distance from the ground station
Four interference scenarios:
1. PMSE Tx to DME airborne Rx
2. DME Airborne Tx to PMSE Rx
3. PMSE Tx to DME ground Rx
4. DME ground Tx to PMSE Rx
Limiting scenarios are to and from the air i.e. 1 and 2 as no clutter or
terrain to attenuate signals
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DME overview
* These channels are
reserved exclusively for
national allotments.
** These channels may
be used for national
allotment on a
secondary basis.
The primary reason
for reserving these
channels is to provide
protection for the
secondary
surveillance radar
(SSR) system
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DME overview
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DME overview
PMSE in Liverpool could
operate on channels:
• 44Y, 83X, 89X
The coverage area (DOC) of a DME ground station is
defined as a cylinder of airspace with distance in
nautical miles and height in hundreds of feet e.g.
100/350 would be 100 nautical miles and 35,000 feet.
Some DME are small e.g. 25 nm when used for
landing aids
DME Transponder
Lands End – channel 89X
London – channel 83X
Southampton – channel 44Y
Liverpool – channel 54Y
PMSE in London could operate on
channels:
• 54Y and 89X but not 44Y or
83X due to overlapping
coverage areas
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DME overview
Many overlapping coverage areas
which makes deriving spectrum
availability complex
Amount of spectrum available varies
depending on location
DME beacons around London
DME UK DOCs
(small circles are DME paired with ILS)
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DME – Spectrum availability
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Monitoring – Cambridge Theatre
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Monitoring – Baldock
• 24 hour monitoring of the band 960-1164 MHz (in 12
hour time periods)
• Two sets of measurements – one looking skyward
and one horizontal
• Signal levels recorded every 1 second (43200
samples every 12 hours)
• Levels and spectrum availability compare favourably
with modelled results
• Spectrum analyser details:
– Type FSW-26
– Span 100 MHz
– Ref Level -30 dBm
– RBW 1MHz
– Detector MAXPEAK
– Noisefloor measured at -90dBm
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Modelling
Different approaches to terrestrial and airborne paths
Different approach to interference into DME and into PMSE
IF77 (airborne scenario)
ITU-R Recommendation
P.452 (terrestrial scenario)
Percentage time
1%
1%
Percentage location
50%
50%
Clutter loss (Urban)
n/a
22.9 dB (Note 1)
Clutter loss (Rural)
n/a
17.9 dB (Note 1)
Building entry loss
0 dB
11 dB
Terrain path profile
n/a
Applied
• For interference into airborne DME no building clutter is assumed and minimum height
is 100 m
• For interference into PMSE from airborne DME we assume building clutter (11 dB) and
apply radio horizon
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