Evaluating Time Diversity Evaluating Time Diversity Performance on an On-Performance on an On-

Board Processing Satellite Board Processing Satellite in Earth Station Downlink.in Earth Station Downlink.

Kufre Udofia & Ifiok Otung, Kufre Udofia & Ifiok Otung, ICRC, Faculty of Advanced TechnologyICRC, Faculty of Advanced Technology

University of Glamorgan,University of Glamorgan,Pontypridd CF37 1DL, Wales. United KingdomPontypridd CF37 1DL, Wales. United Kingdom

(kmudofia@glam.ac.uk)(kmudofia@glam.ac.uk).

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Content OutlineContent OutlineIntroductionFMT TDEvaluation, Results and AnalysesDiscussions and ConclusionsReferencesQuestions

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IntroductionIntroductionFade Mitigation TechniqueFMT is a reliable and robust way of

overcoming fading in real-timeIncrease development for high data

rate multimedia servicesCongestion of conventional bands X, C

and KuImprove link performanceImplementation necessary at Ka and V

–bands

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Types of FMTTypes of FMT

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Power ControlFrequency DiversitySpatial/Site DiversityTime DiversitySatellite DiversityAntenna DiversitySignal ProcessingAdaptive Coding

Time Diversity (TD)Time Diversity (TD)Re-sending of signal until channel

status allows it to pass through

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SampledTime Series

DelayedTime Series

st min5

st min10

snt min

min1 t

1 to 86400 samples represents seconds

delay

864001 2 3 4 5 6

864001

864001

864001

864001

Based on the idea that events are short-lived

Dependent on the re-transmission delay

More affordable when compared to site diversity and uses a single link unlike others

Provides high quality data rate multimedia services

Provides high quality of service (QoS) and an increase availability.

Able to combat large fading

Time Diversity (TD)Time Diversity (TD)

Problem DefinitionProblem DefinitionEvaluating time diversity performance

on an on-board processing satellite in earth station downlink. A fade mitigation process to combat effects of atmosphere on satellite-earth links at Ka and V bands, a case study is the UK.

7

Properties of Ka BandsProperties of Ka BandsLarger bandwidths and cost efficiencyReduced co-ordination problems due

to decreased wavelengthPropagation impairments are very

prominent 21/04/23 01:26 AM

8

Effects of Propagation Effects of Propagation ImpairmentsImpairments

Rain attenuation, melting layer, cloud, attenuation, tropospheric scintillation, depolarisation due to rain and ice

Propagation Impairments Propagation Impairments FactorsFactors

Fading, signal attenuation, increase in the sky noise temperature and intersystem interference

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Block View of the LinkBlock View of the Link

9

600.2Km

Dundee

Chilbolton

UFO-9 20.7 GHz Beacon Payload

RAIN

Cloud

Aup From Scaled

Frequency

Adown BEACON

Adown From Link

Earth-stations with Beacon Receivers

SignalDirections

Sparsholt is about 7.8Km from Chilbolton21/04/23 01:26 AM

Analysis of Time Series of Analysis of Time Series of SitesSites

10

Rain attenuation time series for three UK sites Rain attenuation time series for three UK sites measured at 20.7GHz on November 11, 2005.measured at 20.7GHz on November 11, 2005.

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0 1 2 3 4 5 6 7 8 9

x 104

-5

0

5Chilbolton

0 1 2 3 4 5 6 7 8 9

x 104

-1

0

1

Att

enuation (

dB

)

Dundee

0 1 2 3 4 5 6 7 8 9

x 104

-5

0

5

Time (seconds)

Sparsholt

Earth location, separation distances, frequency and satellite earth link

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Cumulative distributions of measured Cumulative distributions of measured rain attenuation for Chilbolton compared rain attenuation for Chilbolton compared with the ITU-R 618v9 (predicted) model with the ITU-R 618v9 (predicted) model at 20.7 GHz with an elevation angle of at 20.7 GHz with an elevation angle of 3030..

0 5 10 15 20 25 3010

-3

10-2

10-1

100

101

102

Attenuation (dB)

Tim

e A

bsci

ssa

is E

xcee

ded

(%)

Measured

ITU

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Cumulative distributions of measured Cumulative distributions of measured rain attenuation for Sparsholt compared rain attenuation for Sparsholt compared with the ITU-R 618v9 (predicted) model with the ITU-R 618v9 (predicted) model at 20.7 GHz with an elevation angle of at 20.7 GHz with an elevation angle of 3030..

0 5 10 15 20 2510

-3

10-2

10-1

100

101

102

Attenuation (dB)

Tim

e A

bsci

ssa

is E

xcee

ded

(%)

Measured

ITU

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Cumulative distributions of measured Cumulative distributions of measured rain attenuation for Dundee compared rain attenuation for Dundee compared with the ITU-R 618v9 (predicted) model with the ITU-R 618v9 (predicted) model at 20.7 GHz with an elevation angle of at 20.7 GHz with an elevation angle of 3030..

0 5 10 15 20 2510

-3

10-2

10-1

100

101

102

Attenuation (dB)

Tim

e A

bsci

ssa

is E

xcee

ded

(%)

Measured

ITU

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0 2 4 6 8 10 12 14 16 18 2010

-3

10-2

10-1

100

101

102

Attenuation (dB)

Tim

e A

bsci

ssa

is E

xcee

ded

(%)

20.7 GHz Chilbolton

20.7 GHz Sparsholt

20.7 GHz Dundee30 GHz Chilbolton

30 GHz Sparsholt

30 GHz Dundee

Cumulative distributions for three sites Cumulative distributions for three sites measured at 20.7 GHz and the scaled measured at 20.7 GHz and the scaled distribution at 30 GHz at 30distribution at 30 GHz at 30 elevation elevation angle.angle.

Evaluation, Results and Evaluation, Results and AnalysesAnalysesTime diversity gain, time percentage, time

delayCumulative distributions of rain attenuation at

time, t and (t+delay) are considered, based on a simple TD principle – retransmitted signals

Gain increases with increase in the delay and decreases with increase in the time percentage

Improves the fade margin per increased delayFor retransmission, the time shift per sample

15

ttTshift 21/04/23 01:26 AM

Evaluation and Analyses Evaluation and Analyses (contd.)(contd.)The pdf of the observed rain attenuation

series for a satellite to earth link is given by

16

)}({1})({ tApatAp From a model for TD by Ismail &

Watson developed for equatorial climate, a joint distribution is deduced to )}](),([min{1)]([ ttAtAptAAp T

This is the percentage time exceeded for an effective or minimal attenuation, and is described by the function )}(),(min{ ttAtAAA effT

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Effective attenuation, is the minimum of the two instantaneous attenuation values with time delay

17

Evaluation and Analyses Evaluation and Analyses (contd.)(contd.)

)}]1(),1([min{)1( sttAstAstAGTD )()1( tttAstAG TTD

TTD AtAG )(

The gain is a function of delays and time percentages

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Time diversity statistics at Chilbolton. Time diversity statistics at Chilbolton. This denotes gains achieved with outage This denotes gains achieved with outage probabilities at varying time delaysprobabilities at varying time delays

0 2 4 6 8 10 12 14 16 1810

-3

10-2

10-1

100

101

102

Gain (dB)

Tim

e A

bsci

ssa

is E

xcee

ded

(%)

1 mins

5 mins

10 mins

15 mins30 mins

45 mins

60 mins

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Time diversity statistics at Sparsholt. Time diversity statistics at Sparsholt. This denotes gains achieved with outage This denotes gains achieved with outage probabilities at varying time delaysprobabilities at varying time delays

0 2 4 6 8 10 12 1410

-3

10-2

10-1

100

101

102

Gain (dB)

Tim

e A

bsci

ssa

is E

xcee

ded

(%)

1 mins5 mins

10 mins

15 mins

30 mins

45 mins60 mins

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Time diversity statistics at Dundee. This Time diversity statistics at Dundee. This denotes gains achieved with outage denotes gains achieved with outage probabilities at varying time delaysprobabilities at varying time delays

0 2 4 6 8 10 12 1410

-3

10-2

10-1

100

101

102

Gain (dB)

Tim

e A

bsci

ssa

is E

xcee

ded

(%)

1 mins5 mins

10 mins

15 mins

30 mins

45 mins60 mins

Discussions and Discussions and ConclusionsConclusionsRelevant to communications network

operators and system designers in the UK wishing to offer improved broadband

Relevant to the UK propagation research programme

Improvement of performance for wireless communication systems involving BSS

Video-on-demand servicesElectronic data broadcasting and file

transfers

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Discussions and Discussions and ConclusionsConclusionsAccess to the internet and data baseE-commerce and re-mote teaching

access such as the Open UniversityTD as a fade mitigation scheme for

broadcast satellite systemsTD gain is a function of time delay and

the time percentagesThe study of TD gain on a single

downlink (OB Satellite to ES) and a subsequent study of a complete link, ES to Satellite to ES will lead to a complete evaluation of TD performance.

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ReferencesReferences1. Watson, P.A., Ismail, A.F., Seng, P. A., Ja, Y. Y., Kamaruddin, H.

S., Eastment, J. D. & Thurai, M., (1998), ”Investigation of Rain Fading and Possible Countermeasures on Satellite-Earth Links in Tropical climates”, URSI-F Open Symposium, Aviero, Portugal, pp.3-7.

2. Fukuchi, H, (1992), “Slant Path Attenuation Analysis at 20 GHz for Time Diversity Reception of future Satellite Broadcasting”, URSI-F Symposium Colloque, pp.6.5.1-6.5.4, Ravenscar, UK.

3. Ventouras, S., Wrench C. L. & Callaghan, S. A., (2000), “Earth-Space Propagation, Measurement and Analysis of Satellite Beacon Transmissions at Frequencies up to 50GHz, Part 2: Attenuation Statistics and Frequency Scaling of Attenuation Values”, RCRU, CLRC Chilton, UK

4. Emilio Matricciani, (2006), “Time Diversity as a Rain Attenuation Countermeasure in Satellite Links in the 10-100 GHz Frequency Bands,” Department of Electronic and Information, Milan Polytechnic, Milan.

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ReferencesReferences5. Ismail, A. F. & Watson, P. A., (2000), “Characteristics of

Fading and Fade Countermeasures on a Satellite-Earth Link Operating in an Equatorial Climate, with Reference to Broadcast Applications”, IEE Proc. Microwave, Antenna Propagation, vol.147, No.5, pp.369-373

6. Fabbro, V. and Castanet, L. (2006), “Characterisation and Modeling of Time Diversity in 20-50GHz Band,” Department of Electromagnetism and Radar, Unite of Research APR: Antenna and Radioelectric Propagations, Toulouse, France. 

7. Fukuchi, H & Nakayama, T. (2004), “Quantitative Evaluation of Time Diversity as a Novel Attenuation Mitigation Technology for Future High Speed Satellite Communication”, IEICE Trans., vol.E87-B, pp.2119-2123. 

8. “Propagation data and prediction methods required for the design of Earth-space telecommunication systems”, Recommendations ITU-R P.618-9, 2007, Geneva, Switzerland.

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Thank youQuestions Please