1. 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

2. 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 (
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

3. 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

4. Interference scenarios
Slant range
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 MHz 2
MHz
991 MHz 1 4 3
DME Transponder
Four interference scenarios:
PMSE Tx to DME airborne Rx
DME Airborne Tx to PMSE Rx
PMSE Tx to DME ground Rx
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
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

5. 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

6. DME overview

7. DME overview
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
PMSE in Liverpool could operate on channels:
44Y, 83X, 89X
DME Transponder
Lands End – channel 89X
PMSE in London could operate on channels:
54Y and 89X but not 44Y or 83X due to overlapping coverage areas
London – channel 83X
Southampton – channel 44Y
Liverpool – channel 54Y

8. 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)

9. DME – Spectrum availability

10. Monitoring – Cambridge Theatre

11. Monitoring – Baldock
24 hour monitoring of the band 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

12. 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%
Percentage location
50%
Clutter loss (Urban)
n/a
22.9 dB (Note 1)
Clutter loss (Rural)
17.9 dB (Note 1)
Building entry loss
0 dB
11 dB
Terrain path profile
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