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Proposal to P1A P1B Increasing allowed frame
lengths and interleaving depths for AOS TM
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Summary

• Background
• Targeted applications e.g. Pleiades-HR
• Rationale for changes
• Impacts w.r.t. blue books
• Conclusion

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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, E8)
  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

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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)

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Background (cnt d)

• Rationale for theses limitations
• loss of power efficiency was considered small
  (for low rate systems) between I 5 and I8 or
  16 for  Conv(7,1/2)RS(223,255)  over BPSK
• approx. 0,4 dB loss (Eb/N0) _at_ FER 10-8 (between
  I5 and I8)
• 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 ?

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Background (cnt d)

• 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, E8) 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

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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 lt 10-10 to 10-12 due to
  compression

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Targeted applications e.g. PLEIADES-HR

• 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

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Targeted applications e.g. PLEIADES-HR

• 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 _at_ 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)

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Targeted applications e.g. PLEIADES-HR

• 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.

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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

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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 _at_ 8 Hz max
• Frame rate 5 kHz _at_ I16, 16 kHz _at_ I5

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Rationale for changes (ctn d)

• Vast oversampling of ancillary data
• frame sync rate much higher than needed
• between I5 and I16 represents a net capacity
  loss of 7.5 Mbps
• as a reference SPOT5 TM proprietary format has
  an overhead of 0.52

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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 _at_ 2 bits/symbol
• MTCM 8-PSK _at_ 2.5 bits/symbol (PLEIADES-HR)
• 2 performance levels in terms of BER
• 10-10
• 10-12
• simulations were feasible down to BER10-9
  (typ.)
• extrapolations were done for lower BER

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Rationale for changes (ctn d)

• 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 _at_ 2b/symbol
• 0.32 dB _at_ 2.5 b/symbol

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Rationale for changes (ctn d)

• 1st case MTCM 8-PSK _at_ 2 bits/symbol

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Rationale for changes (ctn d)

• 2nd case MTCM 8-PSK _at_ 2.5 bits/symbol

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Rationale for changes (ctn d)

• I 8 gives a 1 dB gain _at_ 10-12 over I 5 for
  8-PSK 2.5 b/s/Hz
• I 16 gives a 0.4 dB gain _at_ 10-12 over I 8 for
  8-PSK 2.5 b/s/Hz
• very significant gain for power constrained
  spacecraft transmiting at 600 Mbps

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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).

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Conclusion

• 2nd solution (add I8 16) is our preferred
  solution
• I16 provides near optimal performance in terms
  of power
• improves significantly the suitability of CCSDS
  AOS and TM channel coding to high rate /
  powerbandwidth constrained systems
• changes to existing books are minor but impact on
  existing AOS infrastructure is to be assessed