On 3/25/22 7:45 AM, Azelio Boriani wrote:
From the paper "PRESENT STATE OF LONG DISTANCE TIME TRANSFER VIA
SATELLITES WITH APPLICATION OF THE MITREX - MODEM", Hartl specifies
that "The PN-code is a truncated maximum length sequence of period
10.000, instead of the 16.383 chips". In the Xilinx application note
XAPP052, we can find that the taps for an MLS of 14 bits should be
14,5,3,1. In the paper "GEOSTATIONARY SATELLITE POSITION DETERMINATION
FOR COMMON-VIEW TWO-WAY TIME TRANSFER MEASUREMENTS" there is an
introduction that suggests the MITREX 2500 modem has a variable
pseudorandom noise sequence. Maybe the modem was built in different
versions wrt the PN sequence generation.
There's a fair number of of maximal sequences of length 2^14-1 . And
it's possible that they chose a non-maximal sequence that had "better"
properties. Maximal sequences will have a run of N ones and (N-1) zeros,
for instance, which might not have enough transitions per unit time to
let the receiver get a good lock. Or they picked a "good" 10kbit
sequence in the middle of a maximal sequence.
It could also be a composite code (the XOR of multiple PN sequences) -
none of the papers seems to say anything about tap configurations.
I'd suggest seeing if you could find an email address for Professor
Hartl - He'd be 94 now. I think he retired from Univ Stuttgart in 1990.
At 2 Mchip/second, you could pretty easily build a MITREX type modem today.
On Fri, Mar 25, 2022 at 2:37 PM <jeanmichel.fri...@femto-st.fr> wrote:
Dear community,
I am trying to find historical documents describing the pseudo random sequences
used
in the SATRE Two-Way Satellite Time and Frequency Transfer (TWSTFT) modem.
K. Imamura & F. Takahashi (Two Way Time Transfer Via a Geostationnary Satellite,
J. of the Comm. Research Lab., 39(1), March 1992) describe the code structure
(14-bit long pseudo random sequence truncated to 10000 bit length) but the
generator polynomial coefficients are not given. I have not been able to find
this
information in Timetech's SATRE manual nor in the publicly available literature.
This paper cites "P. Hartl, A modem for microwave time and ranging experiments
via telecommunication satellites, MITREX2500 Manual, Jan 1989" which I am unable
to locate.
Would anyone have such a document, or at least could tell me whether the
generator
polynomials are described there? Alternatively, does anyone have a description
of these
14-bit polynomial generators?
Thanks, Jean-Michel
--
JM Friedt, FEMTO-ST Time & Frequency, 26 rue de l'Epitaphe, 25000 Besancon,
France
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