Introduction - Safran CORTEX CRT Quantum User Manual

3.3.6.3.1. 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.
With 4D-8PSK-TCM, the combination of convolutional coding, multiphase modulation and multidimensional
techniques offers a substantial power gain together with bandwidth conservation or reduction, in comparison to
their separate utilization as it is done frequently with binary or quaternary modulations (i.e., sequential
implementation of convolutional coding). The result is an improvement of the performances in terms of BER
versus signal to noise ratio for the same or better bandwidth efficiency, compared with the uncoded (or even
convolutionally coded) OQPSK or QPSK modulations.
The performances of 4D-8PSK-TCM scheme can be substantially improved when concatenated with Reed
Solomon (R-S).
© Safran Data Systems
COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
Figure 32: CRT Performance versus CCSDS Simulations
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