TCM scheme with fractional bit rates, framing signals and conste

Details TCM scheme with fractional bit rates, framing signals and conste TCM scheme with fractional bit rates, framing signals and conste

1993-12-01

1996-02-20

Chin, Stephen

Pulse or digital communications

Systems using alternating or pulsating current

Plural channels for transmission of a single pulse train

375261, 375298, H04L 512, H04L 2302

Patent

active

054935865

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to data transmission in which a sequence of symbols, viz. signals of selectable phase and amplitude are selected from a range of discrete phase/amplitude combinations.
2. Description of the Prior Art
Examples of prior systems capable of transmitting fractional bits/baud and/or for modulation shaping a sequence of symbols of selectable amplitude and phase so as to control average power of transmitted signals are described, for example, in U.S. Pat. No. 5,214,672--Eyuboglu et al and U.S. Pat. No. 5,150,381--Forney, Jr., et al.
Prior art techniques have included quadrature amplitude modulation (QAM) where groups of q bits are assembled and one or more bit in each group is coded (e.g. by a convolutional or block code) to produce an augmented group having at least q+1 bits. For each such augmented group, a symbol is selected for transmission from a signal point constellation having more than 2.sup.q points using a variable mapping controlled by generating, for each augmented group, power signals representing the signal power corresponding to each of a plurality of alternative mappings of the group. Such power signals are decoded by a Viterbi decoder to determine a mapping for that group that substantially minimizes the time averaged power of the transmitted signals.


BRIEF SUMMARY OF THE INVENTION

In one exemplary embodiment of the invention, such a system is improved by making the number of bits q per group repetitively variable and then choosing, according to the value of q, the signal constellation and mapping associated therewith so that the power signals are generated by and in response to a signal ts indicative of the value of q and to stored information defining the mappings to produce power signals corresponding to the mappings associated with the chosen constellation.
In one embodiment having enhanced frame synchronicity features, the constellation may include a plurality of subgroups of points with a first variable mapping being used for a symbol at a predetermined position within each transmitted frame and a second variable mapping is used for the remaining symbols in each frame. The first variable mapping permits selection of a symbol from a subgroup having a larger mean power than the remaining subgroups and the second mapping not permitting selection of a symbol from that subgroup having larger mean power.
Alternatively for enhanced frame synchronicity, at a predetermined position within each frame, whenever a symbol from one predetermined group is selected for that position, a symbol from an additional subgroup is actually transmitted instead.
This invention provides a QAM technique for use wherein the number of bits per symbol is a rational non-integer greater than unity when expressed as a ratio B/A of two integers having no common factor, A not being a power of two and each group of B bits is transmitted by means of A-d symbols where d is an integer less than A and greater than or equal to one, each chosen from a first symbol point constellation and d symbols each chosen from a second, larger signal point constellation.
The invention in its various aspects is further defined in the claims.


BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a block diagram of one form of coding apparatus according to the invention;
FIG. 2 is a timing diagram for the apparatus of FIG. 1;
FIGS. 3 and 4 are phase diagrams showing respectively a 16-point and 32-point signal constellation;
FIG. 5 is a phase diagram showing division of a 64-point constellation into regions;
FIG. 6 is a block diagram illustrating the principles of shaping;
FIGS. 7 and 8 are trellis diagrams illustrating the principles of shaping;
FIG. 9 is a block diagram of a shaping unit for use with the apparatus of FIG. 1;
FIG. 10 is a phase diagram showing division of a 128-point constellation into regions;
FIG. 11 is a phase di

REFERENCES:
patent: 4713817 (1987-12-01), Wei
patent: 4837766 (1989-06-01), Yoshida
patent: 5150381 (1992-09-01), Forney, Jr. et al.
patent: 5214672 (1993-05-01), Eyuboglu et al.
Calderbank et al, "Nonequiprobable Signaling on the Gaussian Channel", IEEE Transactions on Information Theory 36 (1990) Jul., No. 4, New York, US, pp. 726-740.
Forney, Jr., "Multidimensional Constellations--Part I: Introduction, Figures of Merit, and Generalized Cross Constellations", IEEE Jornal on Selected Areas in Communication, vol. SAC-7, No. 6, Aug. 1989, New York US, pp. 877-892.
Forney, "Multidimensional Constellations--Part II: Voronoi Constellations", IEEE Journal on Selected Areas in Communication, vol. SAC-7, No. 6, Aug. 1989, New York US, pp. 941-958.
Forney, Jr., "Trellis Shaping" IEEE Transactions on Information Theory, vol. 38, No. 2, Mar. 1992, pp. 281-300.

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