[Sls-rfm] [Sls-slp] Table form of Prox-1 Phy Layer

[Thomas Jedrey]

Matthew,

A symbol to symbol to symbol variation was included.  

Your comments on the decision to use a non-integer divisor are correct in
that it was a program decision to use this.  Unfortunately this is not a
negotiable point since this form of the radio will be providing network
support at Mars for the next 20 years or so.  So any design expecting
support from the NASA Mars network assets will have to be compatible with
these specifications - regardless of whether they are included in the prox-1
specification or not.

Thomas C. Jedrey
Supervisor, Wireless Communications Group
Jet Propulsion Laboratory
Phone: 818-354-5187
Fax: 818-354-6825


-----Original Message-----
From: Matthew Cosby [mailto:MCosby at space.qinetiq.com] 
Sent: Thursday, March 24, 2005 8:26 AM
To: sls-slp at mailman.ccsds.org
Cc: David.J.Bell at jpl.nasa.gov; Eric.Schwartzbaum at jpl.nasa.gov;
Thomas.C.Jedrey at jpl.nasa.gov; Dennis Lee; Charles.D.Edwards at jpl.nasa.gov;
SJKynaston at space.qinetiq.com; adstanton at keltik.co.uk;
adstanton at space.qinetiq.com
Subject: [Sls-rfm] [Sls-slp] Table form of Prox-1 Phy Layer

Greg,

here are the BNSC responses to the new pink sheets...

See you in Athens.

Matt.

We would like to voice our concerns regarding this new pink sheets for the 
data rate stability for Proximity-1. These concerns have been developed in 
consultation with engineers at QinetiQ (Steve Kynaston, Dai Stanton and 
myself) who have been responsible for several baseband and RF CCSDS 
systems, including 2 implementations of Proximity 1.

We can't accept a change to a recommendation just because a single 
implementation cannot meet the current specification. The reason why 
Electra could not meet this requirement is due to a design decision not 
because the specification is too stringent. Making this type of change has 
serious knock-on interoperability issues.

The correct cause of action would be for the Electra implementers to issue 
a waiver, to their customers, indicating that they don't meet the current 
Proximity-1 specification. We should not accommodate in the recommendation 
a symbol-to-symbol timing deviation that could lead to, at best, large 
implementation losses in the bit synchroniser and, at worst, a total 
inability of a bit synchroniser to track the incoming data.

We believe that the modifications made to the recommendation at the Autumn 
2004 meeting have severely compromised interoperability between orbiters 
and landers (both extant and planned) by not specifying a symbol-to-symbol 
frequency deviation. The current form of words and, to a greater extent, 
the statements in the pink sheets allow for pathologically behaved baseband 
implementations which would be impossible to decode. (E.g. a waveform which 
had a symbol 99 bit periods long followed by 99 symbols squeezed into a 
single period). We do not believe that it is prudent to issue a 
recommendation which does not provide enough rigor to guarantee 
orbiter/lander interoperability at the bit synchronisation level.



------------------------------------------------
Matthew Cosby
Digital & Embedded Technology,
Space Department,
Arthur C Clarke Building,
QinetiQ Ltd,
Cody Technology Park,
Farnborough,
Hants, UK.
GU14 0LX.

Tel:            +44 (0)1252 396313
Pager:  +44 (0)7659 130547
------------------------------------------------
e-mail  : MCosby at space.QinetiQ.com
WWW : http://www.QinetiQ.com
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