TCM scheme with fractional bit rates, framing signals and constellation shaping

A method of transmitting data using quadrature amplitude modulation, said method comprising the steps of:

• assembling groups of q bits,
• coding one or more of the bits of each said group by a convolutional or block code to produce an augmented group having at least q+1 bits,
• selecting for each said augmented group a symbol for transmission from a signal point constellation having more than 2.sup.q points by using a variable mapping, the mapping being 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, and decoding the power signals by a Viterbi decoder to determine a mapping for that group which substantially minimizes the time averaged power of the transmitted symbols,
• the constellation including a plurality of subgroups of points, in which the transmission has a framing structure, and
• using a first variable mapping for a symbol at a predetermined position within each frame of the framing structure and a second variable mapping for the remaining symbols in that frame,
• the first variable mapping permitting 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.

A method of transmitting data using quadrature amplitude modulation, said method comprising the steps of:

• assembling groups of q bits,
• coding one or more of the bits of each group by a convolutional or block code to produce an augmented group having at least q+1 bits,
• selecting for each said augmented group a symbol for transmission from a signal point constellation having more than 2.sup.q points by using a variable mapping, the mapping being 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, and decoding the power signals by a Viterbi decoder to determine a mapping for that group which substantially minimizes the time averaged power of transmitted symbols,
• the constellation including a plurality of subgroups of points,
• the symbol transmission having a framing structure,
• the constellation having additional signal points forming an additional subgroup not included in said mapping, and
• at a predetermined position within each frame of the framing structure, whenever one predetermined group is selected for that position, a signal from the additional subgroup is transmitted in lieu thereof.

An apparatus for transmitting data using a quadrature amplitude modulation, said apparatus comprising:

• (a) means for assembling successive groups of q bits;
• (b) means for coding one or more bits of each group by a convolutional or block code to produce an augmented group having at least q+1 bits;
• (c) means for selecting for each said augmented group a symbol for transmission from a signal point constellation having more than 2.sup.q points using a variable mapping,
• (d) means to generate, for each augmented group, power signals representing the signal power corresponding to each of a plurality of alternative mappings of the group;
• (e) means for receiving said power signals and, in dependence on the power signals for a plurality of groups, to determine mappings therefor which substantially minimize the time averaged power of the groups;
• (f) switching means for determining a framing structure for the transmission and for selecting groups having different numbers q of bits, and different signal constellations and mappings associated therewith, to control the power signal generating means (d) to produce power signals corresponding to the selected respective mappings and constellations.

An apparatus for transmitting data using a quadrature amplitude modulation, said apparatus comprising:

• (a) means for assembling successive groups of q bits;
• (b) means for coding one or more bits of each group by a convolutional or block code to produce an augmented group having at least q+1 bits;
• (c) means for selecting for each said augmented group a symbol for transmission from a signal point constellation having more than 2.sup.q points using a variable mapping;
• (d) means to generate, for each augmented group, power signals representing the signal power corresponding to each of a plurality of alternative mappings of the group;
• (e) means for receiving said power signals and, in dependence on the power signals for a plurality of groups, to determine mappings therefor which substantially minimize the time averaged power of the groups;
• (f) switching means for determining a framing structure for the transmission and for selecting a first variable mapping to be employed for a symbol, chosen from a constellation comprising a plurality of subgroups of points, at a predetermined position within each frame of the framing structure and a second variable mapping to be employed for other symbols chosen from the constellation, the first variable mapping permitting 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, to control the power signal generating means (d) to produce power signals corresponding to the selected mappings.

An apparatus for transmitting data using quadrature amplitude modulation, said apparatus comprising:

• (i) means for assembling groups of q bits and coding one or more of the bits of each said group by a convolutional code to produce an augmented group having at least q+1 bits;
• (ii) means for selecting for each said augmented group a symbol for transmission from a signal point constellation having more than 2.sup.q points using a variable mapping, the mappings being 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, and decoding the power signals by a Viterbi decoder to determine a mapping for that group which substantially minimizes the time averaged power of transmitted symbols;
• (iii) switchable means for operating said apparatus at any one of a plurality of data rates;
• (iv) means for generating signals selected from a signal point constellation of a nested set of signal constellations, each larger constellation having twice as many points as, and including all points of, the next smaller constellation;
• (v) each constellation including a first, second and third subgroups of points, the mappings associated with each constellation having a fixed mapping between bits of the group other than said one or more bits and the points of a subgroup, those bits serving to select one candidate point within each subgroup and a variable mapping between the other bits of the augmented group and the subgroups, those bits serving to select one subgroup and one of the candidate points;
• (vi) in any constellation, the average power of the first subgroup being less than that of the other subgroups, the average power of the second subgroup being less than of the third and that of the third being less than that of any further subgroup;
• (vii) the said fixed mapping in each subgroup being such that:
• if the points in the second subgroup are ordered in ascending order of the powers of the points having the same mapping in the first subgroup then the powers of those points are in descending order;
• if the points in the third subgroup power are also ordered in ascending order of the powers of the points having the same mapping in the first subgroup then the powers of those points are in ascending order;
• and if the points in a fourth subgroup (if used) also are ordered in ascending order of the powers of the points having the same mapping in the first subgroup then their powers are in ascending order;
• (viii) the first subgroup of points of each larger constellation having all the points of the first and second subgroups of points of the next smaller constellation and its second subgroup including all the points of the third subgroup of the next smaller constellation;
• (ix) the mapping pertaining to each signal subgroup of a larger constellation which contains two subgroups of a smaller constellation and the mapping pertaining to the latter two subgroups being related in that:
• the mapping of the fixedly mapped bits in the smaller subgroups is unchanged in the larger subgroup;
• the mapping of an additional bit required for the larger constellation is such that, in the first subgroup, a first and second value of that bit causes selection of, respectively, points belonging to first and second subgroup of the smaller constellation and, in the second subgroup, the said first and second values of that bit cause selection of, respectively, points belonging to the fourth and third subgroup of the smaller constellation.