Safran CORTEX CRT Quantum - 8 PSK-TCM Coder

COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
Ref. DTU 100042
Is.Rev. 5.17
Date: Dec.
03, 2021Sept. 30, 2021
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Page 65
3.3.6.3.2. 4D-8PSK-TCM Coder
The 4D-8PSK Trellis-Coded Modulator consists of a serial to parallel converter, a differential coder, a trellis
encoder (convolutional coder), a constellation mapper and an 8PSK modulator (see Figure 19).
Note that in this figure, wi (with index i = 1, … , m) represent the uncoded bits and xj (with index j = 0, … , m) are
the coded bits. The trellis encoder is based on a 64 state systematic convolutional coder and can be considered
as the inner code if an outer block code is introduced. Carrier phase ambiguity is resolved by the use of a
differential coder located prior to the trellis encoder. Spectral efficiencies of 2, 2.25, 2.5, and 2.75 bits/channel-
symbol are achieved with four possible architectures of the constellation mapper. The output switch addresses
successively one of the four symbols ( Z(0) – Z(3) ) from the constellation mapper to the 8PSK modulator (which
is in fact a QPSK modulator for the 2 first efficiencies values).
The present standard is based on the use of a 4D-8PSK-TCM characterized by the following parameters:
 Size of the constellation: M = 8 phase states (8PSK)
 Number of signal set constituents: L = 4 (shown as Z(0) … Z(3) in Figure 19)
 Number of states for the trellis encoder: 64
 Rate of the convolutional coder used for the construction of the trellis: R = ¾
 Rate of the modulation: Rm = m/(m+1) selectable to 8/9, 9/10, 10/11, or 11/12
 Efficiency of the modulation:
 Reff = 2 bits per channel-symbol (for Rm = 8/9)
 Reff = 2.25 bits per channel-symbol (for Rm = 9/10)
 Reff = 2.5 bits per channel-symbol (for Rm = 10/11)
 Reff = 2.75 bits per channel-symbol (for Rm = 11/12)
In fact, the serial to parallel conversion is a byte (8 bits) to symbol (8 to 11 bits) conversion that will be described
later.