I/Q Shift Compensation In Oqpsk Mode; Ccitt V.35 De-Scrambler; Bem: 4D-8Psk-Tcm-Dvb-S Reed Solomon Decoding; Introduction - Safran CORTEX Series User Manual

3.3.5

I/Q Shift Compensation in OQPSK Mode

In OQPSK mode, I and Q symbols are ideally shifted by half symbol.
BER degradation is expected if the I-to-Q phase offset is not exactly half symbol.
OQPSK co-timing compensation can be automatically and precisely performed by the DEAF using the LMS algorithm.
The impulse response of the digital filter is indeed able to adapt to the co-timing error.
3.3.6

CCITT V.35 De-scrambler

The Cortex HDR supports the V.35 descrambler.
In the demodulation channel, this descrambler is implemented after the Viterbi decoder and the
differential decoder if used and before the frame synchronizer.
The V.35 descrambler is basically a 20-stages shift register with XORED specific outputs. In addition, a
specific operation is used inside the process to guarantee an output transition once every 32 bits for
long sequences of 0 or 1.
Two standards are implemented inside the Cortex HDR:
 the CCITT V.35 standard
 the INTELSAT V.35 standard
The descrambler can be enabled or disabled by set-up (from the Cortex HDR GUI or by TCP/IP remote
control). The selection of the standard is done also by set-up.
3.3.7

BEM: 4D-8PSK-TCM-DVB-S Reed Solomon Decoding

This mode is compatible with the CCSDS REPORT ON BANDWIDTH-EFFICIENT MODULATIONS
(CCSDS 413.0-G-1, GREEN BOOK, 31 March 2003) with completion for updating ECSS RF &
Modulation standard ECSS E-50-05A and ECSS Telemetry channel coding ECSS E-50-01 draft 0.5
This modulation is compatible with the PLEIADES satellites.
3.3.7.1

Introduction

The L-dimensional MPSK-TCM (LD-MPSK-TCM) belongs to a family of modulations first introduced by
G. Ungerboeck and improved by S. Pietrobon with the introduction of the multidimensional techniques.
The MPSK-TCM are based on MPSK modulations with the use of convolutional coding to introduce
"authorized sequences" between signal points linked by the trellis of the code. Note that single
constellation MPSK modulations may also be referred to as "bi-dimensional" in reference to the
representation of the MPSK constellation points in a signal space defined by orthogonal I and Q
vectors.
In any case, the application of this procedure to several parallel constellations of the same size is
referred to as L-dimensional TCM, denoted LD-MPSK-TCM (with L > 1 and M = 8). The trellis is
constructed to maximize the minimum Euclidian distance between different paths originating and
merging to the same state. The construction of the optimum trellis code and partitioning for the M
points in the constellation is based on heuristic rules proposed in G. Ungerboeck. "Channel Coding with
Multilevel/Phase Signals", IEEE Transactions on Information Theory, vol. IT-28, no. 1, pp.55-67,
January 1982 and S. Pietrobon et al. "Trellis-Coded Multidimensional Phase Modulation", IEEE
Transaction on Information Theory, vol. 36, no. 1, pp.63-89, January 1990.
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