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WP 2.2 Propagation and Diversity:

Topology and Mobility Effects on Links

Candida Spillard

Budapest, November 2004

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Topology and Mobility Effects

Basic link margins

Link outage durationsRainCloudsTunnels

Short-term variationsScintillationA channel model, for modulation and coding simulations

Polarisation

MultipathFrom terrainFrom buildings and other structures

Doppler Effects

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Basic Link Margins

From ITU-R P.618-7Frequency 28 GHz, elevation angle 30o, Location Torino

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Event Servicing: Variability of Margins

To deliver 99.99% availability,the link must tolerate:

in an average year,rain rate up to 24mm/hr

in 1999-2000,rain rate up to 40 mm/hr

(plot taken from S. Ventouras, C. L. Wrench, and S. A. Callaghan, "New thinking required to offset limitations imposed by V-band propagation," AIAA International Communications Satellite Systems Conference, 2001)

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Link outage durations and characteristics

Rain: ITU-R P.1623Power-law for short outages, log-normal for long outagesNo dependence on climatic zones: this is under review

Cloud edges (excessive scintillation)May disrupt higher-order modulation signals

Tunnels, cuttings, other structuresTunnel lengths in the UK have a log-normal distributionCuttings obstruct LOS at up to 60o elevation angleSignal gantries: knife-edge diffraction Power supply cable supports: knife-edge diffraction with predictable periodic occurrence

TreesRayleigh-like distributions of signal fading

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Scintillation

Phase

Variations areGaussian in

I and Q

Amplitude

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Amplitude variations

Standard deviations of signal amplitude variation as a function of meteorological parameters (ITU-R P.618-7)

city month time temperature Humidity% Nwet (dB)

Rome August 13:00 30 43 74.2 0.357

Rome December 13:00 13 70 47.8 0.272

Rome August 07:00 20 73 74.2 0.357

Rome December 07:00 6 85 38.1 0.240

Gibraltar August 14:30 29 60 98.4 0.434

Nicosia August 14:00 37 35 85.4 0.398

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Phase variations

Standard deviation of phase as a function of three atmospheric parameters

  Cn2 (m –2/3) L (m) (m/sec) (o)

air over sea

10-15 1000 15 2 10-3

heavy rain 10-13 3000 7 0.018

warm front 10-14 1000 5 2.6 10-3

edge of Cu cloud

10-11 100 10 0.05

BER = 2 erfc (/2) Phase difference between 2 points in constellation (eg 8o for 256QAM) Standard deviation of scintillating phase variations

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Model for short-term variations

Based on time-series generatorDeveloped by Fiebig

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Time-series generator developed by Fiebig

Time-series generator outputr(t)

Each time segment is:Almost constant (C), Monotonically decreasing (D) or Monotonically increasing (U)Attenuation at a certain instant depends only on the attenuation t seconds beforeand on the type of signal segment (C, D or U). Measured PDFs of the likelihood P(y/x) for the segments C, D and U has a Gaussian-like shape

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Typical output

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Multipath

0 5 10 15 20 25 300

0.5

1

1.5

2

2.5

3

3.5

4

frequency (GHz)

Crit

ical

hei

ght(

cm)

Rayleigh factor.

angle:45º

For specular-type reflection, roughness height must not exceed hc, where:

hc = /(8 sin )

Terrain is generally rougher than = 0.2 cm! Narrow antenna beams preclude multipath from buildings

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Depolarisation

Depolarisation exceeded for a given percentage of the time, 28 GHz, 30o elevation angle, Torino. ITU-R P.618_7, section 4.1

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Doppler Effects

dffc

fc

cff

1

/211

/211

2

2

Frequency shift effect:

Symbol timing effect:

tff

NtT

dc

cs

Nc ratio between the symbol and the carrier periods

fd(t) Doppler frequency shiftfc carrier frequency

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Effect on QPSK

Without Doppler With Doppler

(Oscilloscope traces of superpositions of all possible demodulated wave forms)

Eye patterns of QPSK signals (Trapezoidal pulse)

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Effect on GMSK

Without DopplerWith sinusoidally-varyingDoppler, fd(max) = 0.2fc,

fr = 10-4 fc, Bit Rate = 3000

Eye patterns of GPSK signals (BT = 0.5)

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Effect on GMSK

Without Doppler

Eye patterns of GPSK signals (BT = 0.25)

With sinusoidally-varyingDoppler, fd(max) = 0.2fc,

fr = 10-4 fc, Bit Rate = 3000

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Document Properties

Document Title WP2.2M054BudNov04.ppt

Document Number CAP-0231-WP22-UOY-CON-P00

Author (s) C. Spillard

Date November 2004

Participant (s) (short names) Candy

Workpackage(s) 2.2

Total number of slides (including title and this slide)

18

Security level (PUB, RES, CON)

CON

Description / Abstract

Presentation of Milestone 054 report ‘Topology and Mobility Effects’