ccsds p1a/b meeting - frascati - nov 8, 2001 - gilles moury, guy lesthievent - 1 proposal to p1a...

CCSDS P1A/B Meeting - Frascati - Nov 8, 2001 - Gilles Moury, Guy Lesthievent - 1

Proposal to P1A & P1B

Increasing allowed frame lengthsand

interleaving depths for AOS TM


Summary

Background

Targeted applications : e.g. Pleiades-HR

Rationale for changes

Impacts w.r.t. blue books

Conclusion


Background

Present limitations w.r.t. frame length & interleaving :

AOS blue book limits VCDU length to 5 x 223 = 1115 octets when RS is used not consistent with new RS option (239, 255, E=8) introduced in TM

channel coding blue book frame length limitations should be removed from AOS in the

« Yamada » restructured edition

TM channel coding blue book (June 2001) limits transfert frame (VCDU) length to :

1115 octets (RS(223,255)), 1195 octets (RS(239,255)) when RS is used interleaving depths for RS , I = 1, … , 5


Background (cnt ’d)

Packet TM blue book max frame length of 2048 octets (max capability of 11-bit FHP)

ESA TM channel coding & Packet TM standards allows interleaving depths for RS , I = 1, 2, 3, 4, 5 & 8 max frame length : 2040 octets (both for coded & uncoded cases)



Rationale for theses limitations loss of power efficiency was considered small (for low rate

systems) between I = 5 and [I=8 or 16] for « Conv(7,1/2)+RS(223,255) » over BPSK

approx. 0,4 dB loss (Eb/N0) @ FER = 10-8 (between I=5 and I=8)

provide acceptable frame sync rate for low to medium data rate mission : few kbps to few Mbps

limit the number of packets being lost whenever a frame is lost : optimization in terms of FER ?

limit the complexity of the RS encoder ?



New channel coding options and modulation schemes are being introduced in CCSDS blue books to cover the needs of « bandwidth limited & high rate » earth orbiting missions

RS (239, 255, E=8) code punctured convolutional code (7,1/2) with punctured rates : 2/3, 3/4, 5/6,

7/8 (as per DVB-S standard) Multidimentional Treillis Coded Modulation (MTCM) 8-PSK

modulation scheme

Example of such « bandwidth limited & high rate » missions PLEIADES-HR


Targeted applications : e.g. PLEIADES-HR

High resolution earth observation satellites :

Mission parameters : sun synchronous orbit : 500 - 800 km resolution (optical) : 0.6 to 2.5 m radiometric precision : 8 to 12 bits/pixel swath : 15 to 60 km instrument data rates : 128 Mbits/s to 2 Gbits/s image compression - Compression Ratio : 3 to 6 :

compressed rate per instrument : 50 Mbits/s to 500 Mbits/s BER requirement : BER < 10-10 to 10-12 due to compression



Constraints : minisats or small sats :

severely mass & power limited

Payload TM at X-band : 375 MHz in total band limited

Transmission data rates needed : 128 Mbits/s to 600 Mb/s depending on : nb of ground stations, on-board mass memory capacity

Rate can be splitted into up to 4 channels : 150 Mb/s max per channel

standard P/L TM I/F would be a plus for interoperability and standardisation of equipment in multimission X-band recieving stations



PLEIADES-HR payload TM characteristics 0.65 m resolution, 20 km swath

620 Mb/s of user data rate to ground at X-band 4 carriers : 155 Mb/s user data rate each MTCM 8-PSK modulation @ 2.5 bits/symbol (compliant with future

CCSDS recommendation) RS (238,254) used as outer code, interleave depth : 5, 8 or 16 ?

required BER of 10-12

due to image compression

compressed image data formated as CCSDS source packets each packet contains 8 compressed lines (for a portion of swath)



packets inserted in AOS frames AOS selected because of high rates (24-bit frame counter) Insert zone of transfer frame used to carry 12 bytes of ancillary data

interest on this project to develop generic equipment with interfaces based on non-proprietary standards

equipments : image compression unit, mass memory, modulator standard I/F :

CCSDS image lossy compression (algorithm & source format) ? CCSDS source packet AOS VCDU, AOS CVCDU and CADU CCSDS 8-PSK RF interface.


Rationale for changes

2 penalties identified for PLEIADES-HR w.r.t. CCSDS compatibility

transfer frame format overhead due to limited allowed frame length

loss of power efficiency on the link due to limited allowed interleaving depth for RS outer code


Rationale for changes (ctn ’d)

Frame format overhead overhead

VCDU frame header : 6 octets M-PDU header : 2 octets Insert : 12 octets

ancillary data sampled @ 8 Hz max Frame rate : 5 kHz @ I=16, 16 kHz @ I=5

Interleavingdepth I

VCDU data fieldlength (octets)

Frame formatoverhead

5 1170 1.71 %

8 1884 1.06 %

16 3788 0.53 %



Vast oversampling of ancillary data

frame sync rate much higher than needed

between I=5 and I=16 represents a net capacity loss of 7.5 Mbps

as a reference SPOT5 TM proprietary format has an overhead of : 0.52%


Rationale for changes (ctn ’d) Loss of power efficiency

comparison of BER (and FER) performance for various interleave depth of the RS(238, 254) outer code

I = 5, I = 8, I = 16 and infinite interleave

2 modulation schemes taken as reference MTCM 8-PSK @ 2 bits/symbol MTCM 8-PSK @ 2.5 bits/symbol (PLEIADES-HR)

2 performance levels in terms of BER : 10-10

10-12

simulations were feasible down to BER=10-9 (typ.) extrapolations were done for lower BER



Simulations were cross-verified by experiment on modulator breadboard : for I = 16 only implementation losses (FI 720 MHz w.r.t. simus) were

substracted 0.2 dB @ 2b/symbol 0.32 dB @ 2.5 b/symbol


BER of MTCM 2b/symbol concatenated with RS(254,238) = f(Eb/No in dB) with interlace size as parameter

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

4,3 4,5 4,7 4,9 5,1 5,3 5,5 5,7 5,9 6,1 6,3

I = 1

I = 2

I = 5

I = 7

I = 8

I = 16

I = 16 (mes)

I = infini


BER of MTCM 2.5b/sym concatenated with RS(254,238) = f(Eb/No in dB) with interlace size as parameter

1,0E-10

1,0E-9

1,0E-8

1,0E-7

1,0E-6

1,0E-5

1,0E-4

1,0E-3

1,0E-2

1,0E-1

5,80 6,00 6,20 6,40 6,60 6,80 7,00 7,20 7,40

I = 1

I = 5

I = 7

I = 8

I = 16

I = 16 (mes)

I = infini



1st case : MTCM 8-PSK @ 2 bits/symbol

Eb/N0 (dB)Interleavedepth I

BER = 10-10 BER = 10-12

5 + 0.55 + 0.70

8 + 0.28 + 0.36

16 + 0.06 + 0.10

Infinite ref ref



2nd case : MTCM 8-PSK @ 2.5 bits/symbol

Eb/N0 (dB)Interleavedepth I

BER = 10-10 BER = 10-12

5 + 1.10 + 1.51

8 + 0.37 + 0.54

16 + 0.11 + 0.12

Infinite ref ref



I = 8 gives a 1 dB gain @ 10-12 over I = 5 for 8-PSK 2.5 b/s/Hz

I= 16 gives a 0.4 dB gain @ 10-12 over I = 8 for 8-PSK 2.5 b/s/Hz

very significant gain for power constrained spacecraft transmiting at 600 Mbps


Proposed changes to existing Blue Books

1st solution : add I = 8 as a valid interleaving depth for RS impacts TM channel coding blue book impacts AOS blue book if frame length constraints left in that

book frame length constraints will be removed anyway from that book in

the restructured version

2nd solution : add I = 8 and I = 16 as valid interleaving depths for RS impacts TM channel coding blue book impacts AOS blue book

need to use one of the 5 spare bits of the M-PDU header to have a 12-bit First Header Pointer (minor change).


Conclusion

2nd solution (add I=8 & 16) is our preferred solution

I=16 provides near optimal performance in terms of power

improves significantly the suitability of CCSDS AOS and TM channel coding to high rate / power&bandwidth constrained systems

changes to existing books are minor but impact on existing AOS infrastructure is to be assessed

ccsds p1a/b meeting - frascati - nov 8, 2001 - gilles moury, guy lesthievent - 1 proposal to p1a...

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