# Presentation: 110689

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**UAT-WP-6-11**
**31 July 2001**
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_**RTCA Special Committee 186, Working Group 5**_
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_**ADS-B UAT MOPS**_
_**Meeting #6**_

**Performance of Enhanced UAT in Multi-Aircraft Scenarios**
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**Presented by James Higbie, Johns Hopkins University/Applied Physics Laboratory**
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**SUMMARY**
**A computer simulation of UAT reception was run to predict the performance of an**
**“****enhanced” receiver using RS(48,34) decoding and 1.26 MHz or 0.8 MHz filter bandwidth.**
**Interference scenarios included other co-site transmissions and external UAT and Link 16**
**transmitters, and DME transponders. The simulation conditions are described and**
**simulation results are presented.**** **

## Performance of Enhanced UATin Multi-Aircraft ScenariosPresentation to UAT MOPS WG531 July 2001

- Larry Bachman
- 240-228-6339
- larry.bachman@jhuapl.edu
- as told to James Higbie,
- Al Muaddi & Paul Vichot

## Outline

- UAT Receiver Model
- Simulation Details
- Performance Results:
- Baseline (no DME or Link 16)
- Loaded (DME & Link 16)
- Link 16 & DME Excursions
- Altitude of Receiving Aircraft
- Airspace Restrictions
- Single Switched Receiver

## UAT Receiver Model (1 of 4)

- A new UAT receiver model was needed to handle narrower receiver bandwidths
- 1.2 MHz and 0.8 MHz nominal
- Comparing results of new model to previous results uncovered ***a bug in previous UAT model***
- Goes back to earliest results (TLAT)
- Performance is actually better than we thought
- Difference is substantial
- Other-UAT interference impact was ~ 9 dB too strong
- All results presented here are for corrected model
***All previous multi-aircraft UAT simulation results were conservative***

## UAT Receiver Model (2 of 4)

- Incorporates all empirical data available for receiver noise and other-UAT interference:
- New UPS-AT measurements on narrower bandwidth receiver
***1.2 MHz and 0.8 MHz bandwidths***
- Reported in WP-4-13 and WP-5-08
- Old (TLAT) JHU/APL measurements & simulation results on prototype (3 MHz) UAT
- Impact of ***mixed interference environments***
*Gaussian noise + single UAT interferer*
*Multiple UAT interferers*
- Bit-level model, documented in WP-6-06

## UAT Receiver Model (3 of 4)

- Impact of Link 16 interference:
- Assumed same as white Gaussian noise for the same power in the receiver bandwidth
- TX power spectrum = MITRE model in WP-2-03
*Without -73 dB broadband noise component*
* **(<= -117 dBm/MHz, = ~8 dB or more below receiver noise floor)*
- RX response spectrum modeled as butterworth filter
*1.2 MHz nominal:*
- 9-pole
- 3 dB bw = **1.27 MHz vice 1.26 MHz Sawtek (“typical”) spec**
- 40 dB bw = 2.11 MHz = Sawtek spec
*0.8 MHz nominal:*
- 7-pole
- 3 dB bw = **0.89 MHz vice 0.82 MHz Sawtek spec**
- 40 dB bw = 1.71 MHz = Sawtek spec

## UAT Receiver Model (4 of 4)

- Impact of (external) DME interference:
- On-channel: Assumed equivalent to UAT interferer at same power (averaged over each bit)
- Adjacent-channel: Reduced by
***20 dB for 1.2 MHz***
***40 dB for 0.8 MHz***

## Simulation Details (1 of 7)

- Assumed characteristics of each equipage class:
- A0:
- TX power = 37 - 41 dBm (5 - 12.5 W)
- 50% basic messages, 50% extended messages
***Maximum altitude increased to 18,000 ft.***
- A1:
- TX power = 37 - 41 dBm (5 - 12.5 W)
- 50% basic messages, 50% extended messages
***Maximum altitude increased to 40,000 ft.***
- A2:
- TX power = 41 - 45 dBm (12.5 - 32 W)
- All extended messages
- Maximum altitude = 40,000 ft.
- A3:
- TX power = 50 - 54 dBm (100 - 250 W)
- All extended messages
- Maximum altitude = 40,000 ft.

**Basic Message:**
**RS(30,18), TX lasts 273 usec**
**Extended Message:**
**RS(48,34), TX lasts 411 usec**

## Simulation Details (2 of 7)

- Two receiver bandwidths:
- 1.2 MHz
- 0.8 MHz
- 3 traffic density scenarios from TLAT:
- “Low-Density”
- Core Europe 2015
- LA Basin 2020

## Simulation Details (3 of 7)

- 2 types of interference scenarios:
- “Unloaded” = UAT + co-site
- “Loaded”  =  UAT + co-site + Link 16 + DME
- Default scenarios:
*UAT = Low-Density*
- JTIDS “heavy” scenario [b]: 50% at –50 dBm, +350%
- 1 on-channel DME
- 1 adjacent-channel DME
*UAT = CE 2015*
- JTIDS “light” scenario
- 1 adjacent-channel DME
*UAT = LA 2020*
- JTIDS “baseline” scenario [a]: 50% at –50 dBm, +350%
- 1 on-channel DME
- 1 adjacent-channel DME
- Excursions:
*Other JTIDS / DME combinations to determine individual impacts*

## Simulation Details (4 of 7)

- JTIDS Received Levels
- Includes receiver azimuthal antenna pattern
- Random bearing recomputed every second
- DME source modeling
- On-channel DME--	Assumed received power levels:
***-60 dBm at 40,000 ft.***
***-53 dBm at 18,000 ft.***
***-40 dBm on Ground***
- Adjacent-channel DME
- Power reduced (20/40 dB) according to receiver bandwidth
***3600 pulse-pairs per second*** per DME
- cos2 pulse shape designed to meet DME MOPS
- 12 usec pulse-to-pulse spacing
- Poisson + 60-usec pulse-pair separation statistics

## Simulation Details (5 of 7)

- 3 receiving altitudes
- 40,000 ft. (default)
- “Standard” altitude used for earlier runs
- Receiver = aircraft with largest number of interferers in view
***18,000 ft.*** (excursion)
- Larger number of nearby interferers than 40,000 ft.
- Receiver is closer to A0/A1 transmitters
- Uses same horizontal location as aircraft at 40,000 ft.
- Applies to reception by all equipage classes
***On the ground*** (excursion)
- Center of scenario
- RX antenna pattern assumed same as DME ground antenna

## Simulation Details (6 of 7)

- As an excursion, analysis was restricted to receptions from aircraft in close-in airspace (default = analyze transmissions from aircraft at all altitudes)
- “Close-in airspace” defined as altitude difference no more than:
***3,000 ft. for range < 3 nm*** (vice 1,500 ft. discussed at last WG mtg.)
***10,000 ft. for range 3-10 nm*** (vice 6,000 ft.)
***20,000 ft. for range 10-20 nm*** (vice 15,000 ft.)
- Restrictions were loosened because with the original restrictions there were very few data points for the A0/A1 class

## Simulation Details (7 of 7)

- Single Switched Receiver (excursion) vice 2 independent Receivers (default)
- Antenna switching once per second = T, B, T, B, T, ...
- Note: Only one instantiation of each scenario was run
- Vice 4 instantiations for TLAT runs
- Done to limit simulation run times
- Results in greater statistical fluctuations

## Performance Results

## Core Europe 2015 Unloaded

## LA Basin 2020 Unloaded

## Unloaded Performance Results

- Either 1.2 MHz or 0.8 MHz filter meets MASPS / Eurocontrol synch vector update criteria in absence of DME / Link 16
***Out to 150 nm (A3), and at close ranges***
- Criteria met for Core Europe 2015, LA Basin 2020, (and Low-Density) scenarios
- 1.2 MHz slightly better than 0.8 MHz in these scenarios at ranges covered by MASPS

## Low Density Unloaded Vs. Loaded (JTIDS heavy [a] + on & adj DMEs)—A3

## Core Europe 2015 Loaded (JTIDS light + adj DME)

## LA Basin 2020 Loaded (JTIDS baseline [b] + on & adj DMEs)

## Loaded ScenarioPerformance Impact Results

***MASPS are met in Low-Density and Core Europe Loaded Scenarios for 0.8 MHz bandwidth***
- For transmissions from all aircraft classes
***MASPS are not met in Low-Density and Core Europe Loaded Scenarios for 1.2 MHz bandwidth***
- Transmissions from A3 exceed MASPS at ~120 to ~130 nm
- MASPS are not met in LA Basin Loaded Scenario for either bandwidth
- A0/A1 exceeds at ~15 nm
- A2 exceeds at ~30 nm
- A3 exceeds at ~70 nm (1.2 MHz) or ~90 nm (0.8 MHz)

## 1.2 MHz, Low Density Loaded Excursions (JTIDS heavy, light, or off; on-channel DME on or off)

## 0.8 MHz, Low Density Loaded Excursions (JTIDS heavy, light, or off; on-channel DME on or off)

## 1.2 MHz, Core Europe 2015 Loaded Excursions (JTIDS light or heavy; 1 or 2 adj-channel DMEs)

## 0.8 MHz, Core Europe 2015 Loaded Excursions (JTIDS light or heavy; 1 or 2 adj-channel DMEs)

## 1.2 MHz, LA Basin 2020 Loaded Excursions (JTIDS on or off; on-channel DME on or off)

## 0.8 MHz, LA Basin 2020 Loaded Excursions (JTIDS on or off; on-channel DME on or off)

## Link 16 & DME Excursion Results

***Little difference in impact is observed between light and heavy JTIDS scenarios***
- Evaluations may only need to use “baseline” JTIDS
- An on-channel DME causes more degradation than JTIDS
- Removing JTIDS or the on-channel DME from the Low-Density loaded scenario allows the 1.2 MHz bandwidth to pass MASPS
- A3 only considered
- Removing the on-channel DME from the LA Basin loaded scenario allows the 0.8 MHz bandwidth to pass MASPS
- 1.2 MHz exceeds MASPS at ~130 nm

## Core Europe 2015 Loaded, 1.2 MHzA0/A1/A2 at 3 Reception Altitudes

## Core Europe 2015 Loaded, 1.2 MHzA3 at 3 Reception Altitudes

## Core Europe 2015 Loaded, 0.8 MHzA0/A1/A2 at 3 Reception Altitudes

## Core Europe 2015 Loaded, 0.8 MHzA3 at 3 Reception Altitudes

## LA Basin 2020 Loaded, 1.2 MHzA0/A1/A2 at 3 Reception Altitudes

## LA Basin 2020 Loaded, 1.2 MHzA3 at 3 Reception Altitudes

## LA Basin 2020 Loaded, 0.8 MHzA0/A1/A2 at 3 Reception Altitudes

## LA Basin 2020 Loaded, 0.8 MHzA3 at 3 Reception Altitudes

## Reception AltitudePerformance Impact Results

***Performance at 18,000 ft. receive altitude is comparable to performance at 40,000 ft.***
- A0/A1 reception slightly better (as expected)
- For the loaded scenarios evaluated, an aircraft on the ground meets 12-sec SV update time out to:
- A0/A1:	~20 nm for CE2015, ~40 nm for LA2020
- 0.8 MHz slightly better than 1.2 MHz bandwidth
- A2:	~45 nm for 1.2 MHz bandwidth, ~60 nm for 0.8 MHz
- Loaded LA2020 somewhat more severe than Loaded CE2015
- A3:	>150 nm for CE2015, ~135 for LA2020
- 0.8 MHz slightly better than 1.2 MHz bandwidth

## LA Basin 2020 Loaded, 18K altitude, 1.2 MHzImpact of Airspace Restriction

## LA Basin 2020 Loaded, 18K altitude, 0.8 MHzImpact of Airspace Restriction

## Airspace Restriction Performance Impact Results

- Airspace Restriction, at least the loose ones evaluated, do not affect SV Update Times
- The restrictions on receptions from nearby altitudes were not observed to have any impact on 95% SV Update Time in the Core Europe 2015 Loaded Scenario at 18K altitude
- The restrictions were observed to have negligible impact in the LA Basin 2020 Loaded Scenario at 18K altitude, and only on the A3 aircraft
- Both receiver bandwidths were looked at
- Tighter restrictions may require very long simulation runs to evaluate

## MSR Performance:Core Europe 2015 Loaded, 1.2 MHz, 40,000 ft.Impact of Single Switched Receiver

## State Vector Update Performance:Core Europe 2015 Loaded, 1.2 MHz, 40,000 ft.Impact of Single Switched Receiver

## Core Europe 2015 Loaded, 0.8 MHz, 40,000 ft.Impact of Single Switched Receiver

## Core Europe 2015 Loaded, 1.2 MHz, 18,000 ft.Impact of Single Switched Receiver

## LA Basin 2020 Loaded, 0.8 MHz, 18,000 ft.Impact of Single Switched Receiver

## Single Switched ReceiverPerformance Impact Results

- A Top/Bottom Diversity Receiver performs considerable better than a Single Switched Receiver
- 25% to 50% more messages received under most conditions evaluated
- As far as meeting MASPS is concerned:
- A3 [Diversity Receiver] is roughly the same as
- 	 A0/A1/A2 [Switched Receiver]
- For the scenarios evaluated
- For the A0/A1/A2/A3 TX powers assumed