NAROM 2011 Slide 1

Prof. Gunnar Stette G.Stette@iet.ntnu.no

TELEMETRY the efficient transfer of information

The functions of telemetry

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Telemetry – the collection of information from distance

Tele (Greek: far away, far off, at a distance) – can be anything from inside the body to deep space

At Andøya it means receiving information from sounding rockets travelling to the ionosphere, both from the scientific instruments and also the position and state of the rocket.

The topic will be covered more broadly, because telemetry is processing

and transport of information.

Example: Telemetry system

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Example: Telemetry from Cassini

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Cassini's 12 instruments have returned a daily stream of data from Saturn's system since arriving at Saturn in 2004

Telemetry system

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Source Channel Receiver

• parameter extraction • required resolution • encoding • source compression • formating • transmission

• tracking • demodulation • decoding • data analysis • presentation

• modulation • channel coding

Telemetry for a sounding rocket

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Telemetry system

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Source Channel Receiver

• parameter extraction • required resolution • encoding • source compression • formating • transmission

• tracking • demodulation • decoding • data analysis • presentation

• modulation • channel coding

Example: Information source

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9

Claude Shannon

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Source Coding

1log( )ii

Hp

=The information content of symbol i with probability pi:

Information source Symbols

N

i

aaaa

2

1

With probabilities

N

i

pppp

2

1

)log(1ii

iaverage pp

NH ⋅−= ∑

The average information content per symbol: (if the symbols are statistical independent)

If the symbols are NOT statistically independent, - then source compression

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A well known example

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The signal processing in an ordinary camera

Typical data volume reduction from RAW to JPEG, from 15 to 5 Mbit

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More advanced compression (1)

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More advanced compression (2)

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More advanced compression (3)

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Formatting of information

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PICTURE CODING

Scanned TV picture

625 lines Number of pixels per picture 625 x (625X4/3) = 500 000 pixels

Quantization of each pixel individually, (8+8) bit/pixel

500 000 x 16 = 8 Mbit/picture

Transmisson of 25 pictures per second:

8 Mbit/picture x 25 pictures/s = 200 Mbit/s

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Video Coding Evolution and Revolution

0

1

2

3

4

5

6

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Bit

-rat

e (M

bit

/s)

MPEG-4 part2

MPEG-2

H.264/AVC

The «RAW» format data rate is > 200 Mbit/s

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Telemetry system

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Source Channel Receiver

• parameter extraction • required resolution • encoding • source compression • formating • transmission

• tracking • demodulation • decoding • data analysis • presentation

• modulation • channel coding

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SHANNON on CHANNEL CAPACITY

C R bit/s

Forbidden region

Region for error free transmission

Erro

r pro

babi

lity

Information source

Information channel

R bit/s Channel capacity C bit/s

(2) Defined the INFORMATION CAPACITY of information channels.

bit/s )1(log2 NS

BC +⋅=The channel capacity

S is the signal power and N is the noise power in the channel.

Important parameters for information transfer are - power requirement - bandwidth requirement There is a general trade-off between power- and bandwidth efficiency

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Pt Pr

Transmission link (Physical layer)

10)(1)(1)d 4

()()( 2

0=×××××= • KG

RTG

kGP

NE

m

msatsat

b

πλ

Bit energy

Noise power density

Transmit power Transmit antenna

Distance Boltzmanns constant

Receive antenna

Receiver noise temperature

Coding gain

Data rate

Wavelength

Source A/D FEC MOD AMPL

Low noise a.

Demod. FEC D/A Sink.

Distance d

Noise

”Typical Value”

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Goldstone – 70 meter antenna

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When the source is far away and the transmit

power limited the receiver antenna must be

large.

Received power is power flux density multiplied

by the antenne effective area

ASK – Amplitude Shift Keying

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FSK - Frequency shift keying

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PSK – Phase Shift Keying

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Shannon

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TRANSMISSION PERFORMANCE

BPSK (and QPSK) is the most efficient modulation method for bit-by-bit transmission.

BPSK and QPSK

8PSK

But we are still far from SHANNON’s limit, error free at -1.6 dB

0

1 ( )2

be

EP erfN

= ⋅

BPSK QPSK

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CODING

Example: Code performance

for a particular method, BCH-codes

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Convolutional coding

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Coding gain

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Turbo codes

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Turbo coder

”Closing in on the perfect code” IEEE Spectrum March 2004

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Satellite telemetry

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OLYMPUS, ESA

Marisat

Deep Space Networks development

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Display- according to the application

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