[Sls-ngu] Slight update to pink sheets for adding CC(7, 1/2) code to TC standard

[Kazz, Greg J (313B)]

All,

Please see the new update to the pink sheets to TC Sync and Channel Coding (CCSDS 231.0-B-2) in the CWE under the following URL:

http://tinyurl.com/4k9ryfw

The file name now has the date: April 25 embedded in it.

The following new comments were incorporated:


CCSDS 231.0-B-2Pink Sheet May 2011



4.1.1.1         The convolutional decoder is a maximum-likelihood (Viterbi) decoder.
Why is this specified?  Why must it be a Viterbi decoder?

NOTES
2              … If the decoder’s correction capability is exceeded, undetected burst errors may appear …
Omit the word “burst”. - DONE

4.1.2.1                   not a sentence. - Made it into a Sentence

4.1.2.3
Change from
When suppressed-carrier modulation systems are used, Non-Return-to-Zero-Mark (NRZ-M) or Non-Return-to-Zero-Level (NRZ-L) may be used as a modulating waveform.  If the user contemplates conversion of his modulating waveform from NRZ-L to NRZ-M, such conversion should be performed on-board at the input to the convolutional encoder.  Correspondingly, the conversion on the ground from NRZ-M to NRZ-L should be performed at the output of the convolutional decoder.  This avoids unnecessary link performance loss.
To
When suppressed-carrier modulation systems are used, Non-Return-to-Zero-Mark (NRZ-M) or Non-Return-to-Zero-Level (NRZ-L) may be used as a data format.  If the user contemplates conversion of his data format from NRZ-L to NRZ-M, such conversion should be performed at the input to the convolutional encoder.  Correspondingly, the conversion at the receiving node from NRZ-M to NRZ-L should be performed at the output of the convolutional decoder.  This avoids unnecessary link performance loss.

NRZ-L, NRZ-M, Bi-phase etc are ways to represent digital data, it is a data format.  People incorrectly call it modulation, it is not.  It is also definitely not an RF modulation.  We should use proper terminology.  These things are data formats, ways to represent a digital 1 or 0, yes or no, Jim or Jane. - OK


7.2.2    ACQUISITION SEQUENCE
The Acquisition Sequence is a data structure forming a preamble which provides for initial symbol synchronization within the incoming stream of detected symbols.  The length of the Acquisition Sequence shall be selected according to the communications link performance requirements of the mission, but the preferred minimum length is 16 octets.  The length is not required to be an integral multiple of octets.  The Acquisition Sequence shall be the repeated pattern: 352E F853 hexadecimal.  (also see section 7.2.4        IDLE SEQUENCE) - Ditto for this one too




7.2.3    CLTU
The CLTU is the data structure (symbol sequence) furnished from the Synchronization and Channel Coding Sublayer, and defined in 4.2.  It contains the data symbols that are to be transmitted to the receiving end.  Each Codeblock within the CLTU, having the format specified in 3.2, shall provide at least 2 data transitions per Codeblock.  If the receiver symbol synchronization design necessitates more frequent transitions, either the CLTU as delivered to the Physical Layer must have been randomized as described in section 5, or the Physical Layer must invoke a technique (data format, phase-coherent data and subcarrier, or other) to guarantee sufficiently frequent transitions for adequate symbol synchronization.

If the original term “modulation type” refers to “bi-phase” this is not a modulation in the sense of putting a signal on a carrier so it can be transmitted.  Bi-phase is a way to represent digital data, it is a data format. - Done


7.2.4     IDLE SEQUENCE
    The bit pattern is a sequence of the repeated pattern.352E F853 hexadecimal
Add:     (also see 7.2.2  ACQUISITION SEQUENCE)
If the idle is going to be required and continuous, the section on Idle and Acquisition need to be combined or at least interconnected.

While this may be fine for Proximity-1, it may not be OK for near Earth missions since the 352E F853 pattern is used as an ASM in TM links.  From Pink sheet for TM Synch and Coding
8.6      ASM FOR EMBEDDED DATA STREAM
Figure 8-6: Embedded ASM Bit Pattern   352EF853
This can get very confusing for cases that were considered in Cx where there are two space vehicles and up and down or forward and return become interchangeable.  Command and Telemetry links may all similar AOS links.  Not sure if there is a problem, someone needs to think about it.

We need to address this possible duplicity at the meeting.


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