NON-UNIFORM CONSTELLATIONS

Abstract

A method for generating a non-uniform constellation is provided. The method comprises the step of performing a first process, the first process comprising the steps of: obtaining a first constellation defined by one or more parameter values; and generating a second constellation based on the first constellation using a second process. The second process comprises the steps of: obtaining a set of candidate constellations, wherein the set of candidate constellations comprises the first constellation and one or more modified constellations, wherein each modified constellation is obtained by modifying the parameter values defining the first constellation; determining the performance of each candidate constellation according to a predetermined performance measure; selecting the candidate constellation having the best performance as the second constellation.

Claims

1-4. (canceled)

5. A receiving method comprising: demodulating a signal received from a transmitting apparatus to generate values; deinterleaving the values; and decoding the deinterleaved values based on a low density parity check (LDPC) code, a code rate of the LDPC code being 11/15, wherein the signal is demodulated based on position vectors for 16-quadrature amplitude modulation (QAM), and wherein the position vectors are represented as below: TABLE-US-00014 0.9342 + 0.9847i 0.9866 + 0.2903i 0.2716 + 0.9325i 0.2901 + 0.2695i

6. The method as claimed in claim 5, wherein the position vectors comprise the represented position vectors in one quadrant and position vectors in remaining quadrants, and wherein the position vectors in the remaining quadrants are obtained by indicating each represented position vector a as a*, a*, and a, respectively, * indicating complex conjugation.

7. A transmitting method comprising: interleaving a codeword comprising input bits and parity bits; demultiplexing bits of the interleaved codeword to generate cells; mapping the cells to constellation points for 16-quadrature amplitude modulation (QAM) using position vectors; and transmitting a signal which is generated based on the constellation points, wherein the parity bits are generated by encoding the input bits based on a low density parity check (LDPC) code, a code rate of the LDPC code being 11/15, and wherein the position vectors are represented as below: TABLE-US-00015 0.9342 + 0.9847i 0.9866 + 0.2903i 0.2716 + 0.9325i 0.2901 + 0.2695i

8. The method as claimed in claim 7, wherein the position vectors comprise the represented position vectors in one quadrant and position vectors in remaining quadrants, and wherein the position vectors in the remaining quadrants are obtained by indicating each represented position vector a as a*, a*, and a, respectively, * indicating complex conjugation.

Description

DESCRIPTION OF DRAWINGS

[0066] The above and other aspects, and features and advantages of certain exemplary embodiments and aspects of the present invention will be more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:

[0067] FIG. 1 is a schematic diagram of a first algorithm according to an embodiment of the present invention;

[0068] FIG. 2 is a flowchart illustrating the steps of the first algorithm;

[0069] FIG. 3 illustrates the convergence of C_last with respect to one of the parameters as the first algorithm of FIGS. 1 and 2 is performed;

[0070] FIG. 4 illustrates a second algorithm according to an embodiment of the present invention for determining an optimal constellation at a given SNR value S in an AWGN channel;

[0071] FIG. 5 illustrates the convergence of the constellation C_best as the second algorithm of FIG. 4 is performed;

[0072] FIG. 6 illustrates a third algorithm according to an embodiment of the present invention for determining the optimal constellation at a given SNR value S in a Rician fading channel for a desired Rician factor K_rice;

[0073] FIG. 7 illustrates a fourth algorithm according to an embodiment of the present invention for determining the optimal constellation at a given SNR value S in a Rayleigh fading channel;

[0074] FIG. 8 illustrates a fifth algorithm according to an embodiment of the present invention for determining an optimal constellation;

[0075] FIG. 9 illustrates a process for obtaining an optimal constellation for a specific system;

[0076] FIG. 10 illustrates an exemplary BER versus SNR plot for 64-QAM using a Low-Density Parity-Check, LDPC, coding rate (CR) of 2/3 from DVB-T2 in an AWGN channel;

[0077] FIG. 11 illustrates a sixth algorithm according to an embodiment of the present invention for determining an optimal constellation;

[0078] FIG. 12 further illustrates the sixth algorithm illustrated in FIG. 11;

[0079] FIG. 13a illustrates a uniform constellation (64-QAM), FIG. 13b illustrates a non-uniform constellation (64-QAM) characterised by 3 parameters, and FIG. 13c illustrates a non-uniform constellation (64-QAM) characterised by 16 parameters;

[0080] FIG. 14a illustrates a set of BER curves obtained using a non-uniform 16-QAM constellation using respective code rates of 6/15, 7/15, 8/15, 9/15, 10/15, 11/15, 12/15 and 13/15, and a set of BER curves obtained using a corresponding uniform 16-QAM constellation using the same code rates;

[0081] FIG. 14b is a table indicating, for various code rates, the SNR values at the waterfall zone for the uniform and non-uniform constellations used to obtain the BER curves illustrated in FIG. 14a, and the resulting SNR gain;

[0082] FIGS. 15a-17b illustrate BER curves and tables, similar to those illustrated in FIGS. 14a and 14b, for 64-QAM, 256-QAM and 1024-QAM;

[0083] FIGS. 18-25 illustrate exemplary non-uniform 16-QAM constellations obtained by applying the algorithms illustrated in FIGS. 1-12, using code rates of 6/15, 7/15, 8/15, 9/15, 10/15, 11/15, 12/15 and 13/15, respectively;

[0084] FIGS. 26-33 illustrate exemplary non-uniform 64-QAM constellations obtained by applying the algorithms illustrated in FIGS. 1-12, using code rates of 6/15, 7/15, 8/15, 9/15, 10/15, 11/15, 12/15 and 13/15, respectively;

[0085] FIGS. 34-41 illustrate exemplary non-uniform 256-QAM constellations obtained by applying the algorithms illustrated in FIGS. 1-12, using code rates of 6/15, 7/15, 8/15, 9/15, 11/15, 12/15 and 13/15, respectively;

[0086] FIGS. 42-49 illustrate exemplary non-uniform 1024-QAM constellations obtained by applying the algorithms illustrated in FIGS. 1-12, using code rates of 6/15, 7/15, 8/15, 9/15, 11/15, 12/15 and 13/15, respectively;

[0087] FIG. 50 illustrates a process for obtaining the waterfall SNR for a certain channel type according to certain exemplary embodiments;

[0088] FIG. 51 schematically illustrates a process for obtaining a weighted performance measure function for an input constellation based on different transmission scenarios according to certain exemplary embodiments;

[0089] FIG. 52 illustrates a process for obtaining an optimum constellation according to certain exemplary embodiments;

[0090] FIGS. 53a and 53b illustrate alternative schemes for generating a candidate constellation from a previous constellation according to certain exemplary embodiments;

[0091] FIG. 54 illustrates a technique for reducing complexity in certain exemplary embodiments;

[0092] FIG. 55 illustrates an apparatus for implementing an algorithm according to an exemplary embodiment; and

the Annexes to the Description illustrate results obtained from various embodiments of the present invention.

MODE FOR INVENTION

[0093] The following description of exemplary embodiments of the present invention, with reference to the accompanying drawings, is provided to assist in a comprehensive understanding of the present invention, as defined by the claims. The description includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention.

[0094] The same or similar components may be designated by the same or similar reference numerals, although they may be illustrated in different drawings.

[0095] Detailed descriptions of techniques, structures, constructions, functions or processes known in the art may be omitted for clarity and conciseness, and to avoid obscuring the subject matter of the present invention.

[0096] The terms and words used herein are not limited to the bibliographical or standard meanings, but, are merely used by the inventors to enable a clear and consistent understanding of the invention.

[0097] Throughout the description and claims of this specification, the words comprise, contain and include, and variations thereof, for example comprising, containing and including, means including but not limited to, and is not intended to (and does not) exclude other features, elements, components, integers, steps, processes, functions, characteristics, and the like.

[0098] Throughout the description and claims of this specification, the singular form, for example a, an and the, encompasses the plural unless the context otherwise requires. For example, reference to an object includes reference to one or more of such objects.

[0099] Throughout the description and claims of this specification, language in the general form of X for Y (where Y is some action, process, function, activity or step and X is some means for carrying out that action, process, function, activity or step) encompasses means X adapted, configured or arranged specifically, but not necessarily exclusively, to do Y.

[0100] Features, elements, components, integers, steps, processes, functions, characteristics, and the like, described in conjunction with a particular aspect, embodiment, example or claim of the present invention are to be understood to be applicable to any other aspect, embodiment, example or claim described herein unless incompatible therewith.

[0101] Embodiments of the present invention may be implemented in the form of any suitable method, system and/or apparatus for use in digital broadcasting, for example in the form of a mobile/portable terminal (e.g. mobile telephone), hand-held device, personal computer, digital television and/or digital radio broadcast transmitter and/or receiver apparatus, set-top-box, etc. Any such system and/or apparatus may be compatible with any suitable existing or future digital broadcast system and/or standard, for example one or more of the digital broadcasting systems and/or standards referred to herein.

[0102] A non-uniform constellation according to embodiments of the present invention may be generated or obtained using any suitable method or algorithm comprising steps for generating or obtaining such a non-uniform constellation. A non-uniform constellation according to embodiments of the present invention may be generated or obtained by any suitably arranged apparatus or system comprising means for generating or obtaining such a non-uniform constellation. The methods or algorithms described herein may be implemented in any suitably arranged apparatus or system comprising means for carrying out the method or algorithm steps.

[0103] Certain embodiments of the present invention provide an algorithm for obtaining a non-uniform constellation. A non-uniform constellation obtained in certain embodiments of the present invention may provide a higher capacity than an equivalent uniform constellation (e.g. a uniform constellation of the same order). Certain embodiments of the present invention may obtain an optimised non-uniform constellation using an algorithm with relatively low complexity and relatively high computational efficiency. For example, an algorithm in certain embodiments of the present invention may obtain an optimised non-uniform constellation much faster that an algorithm using a brute force method that searches all (or a high proportion of) possible candidate constellations. Certain embodiments of the present invention provide an algorithm for obtaining optimised non-uniform constellations suitable for very high-order constellation (e.g. comprising more than 1024 constellation points).

[0104] Various embodiments are described below in which Non-Uniform (NU) Quadrature Amplitude Modulation (QAM) constellations are obtained. However, the skilled person will appreciate that the present invention is not limited to QAM constellations, but may be applied to other types of constellation.

[0105] As mentioned above, a constellation may be characterised by a number of parameters, for example specifying the spacings between constellation points, or specifying the position of each positive real level (the complete constellations may be obtained from these parameters because the constellations are the same for real and imaginary axis and the same for positive and negative values). In order to obtain an optimum constellation, a brute force approach may be taken in which combinations of values for each of the parameters are searched with a certain step size up to a certain maximum value. Each combination of values for each parameter corresponds to a distinct constellation. The constellation having the best performance is selected.

[0106] However, in certain embodiments, the number of parameters may be reduced by imposing one or more certain geometric and/or symmetry constraints on the constellations. For example, a first constraint may be that the constellations are symmetric among the four quadrants of the constellation. In addition, the constellations may be constrained in that the constellation points are arranged in a QAM type lattice in which, within each quadrant, (i) constellation points are arranged in horizontal and vertical lines, (ii) the number of horizontal lines is the same as the number of vertical lines, (iii) the same number of constellation points are arranged in each horizontal line, and (iv) the same number of constellation points are arranged in each vertical line. In another example, the constellation may be constrained to be a circular constellation (e.g. a constellation having circular symmetry). Furthermore, constellations having the same relative arrangement, differing only in size, may be regarded as equivalent. In this, case one of the parameters may be set to a fixed value. The skilled person will appreciate that the present invention is not limited to the above examples, and that one or more additional or alternative constraints may be used.

[0107] In certain embodiments, a NU-QAM constellation may comprise a constellation conforming to one or more geometric and/or symmetry constraints, for example one or more, or all, of the above constrains, or a rotation and/or scaling thereof. An NU N-QAM constellation may comprise a NU-QAM constellation comprising N constellation points.

[0108] By applying the constraints described above, the number of parameters may be reduced, for example to 1, 3, 7, 15, 31 and 63 parameters for constellations comprising 16, 64, 256, 1024, 4096 and 16384 constellation points, respectively. The number of parameters in a reduced set of parameters may be denoted by b. For example b=1 for 16-QAM (in which there are 16 positions that are symmetric on the real/imaginary and positive/negative axes). Thus there are only 2 points to define. Since the total power of the constellation is typically normalized to one then fixing one parameter will fix the other. Thus b=1 for square 16QAM.

[0109] In certain embodiments of the present invention, combinations of values for each of the b parameter are searched with a step size d up to a maximum value A. Thus, the number of search iterations is equal to (A/d).sup.b.

[0110] A first exemplary algorithm according to certain embodiments of the present invention for obtaining an optimum non-uniform constellation for a given SNR will now be described. The algorithm uses an iterative scheme to gradually modify an initial constellation until the constellation converges. For example, the initial constellation may be a uniform constellation, the constellation may be modified by changing the values of the parameters between iterations, and convergence occurs when the values of all the parameters change by less than a threshold amount between iterations. An optimum constellation may be defined as the constellation having the best performance according to any suitable measure. For example, the measure may comprise CM capacity or BICM capacity. In the following example a NU 64-QAM constellation is obtained, in which the (reduced) number of variable parameters, b, is equal to 3.

[0111] FIG. 1 is a schematic diagram of the first algorithm and FIG. 2 is a flowchart illustrating the steps of the first algorithm. In the algorithm, the following variables are used. The parameter C_last denotes a particular constellation, corresponding to a particular set of values of the b parameters. The parameter C_last is initialised with a certain initial constellation, for example a uniform constellation. The parameter SNR denotes a Signal-to-Noise Ratio. The SNR parameter is set to a desired value equal to the SNR for which an optimum constellation is desired. The parameter C_best denotes a constellation that maximises performance, for example maximises the CM capacity or BICM capacity, for a given SNR. The parameter d denotes a first step size used in the algorithm. The parameter d (or Step) is initialised to a suitable value that may be determined theoretically and/or experimentally. The parameter Min_Step denotes a minimum allowed value for d, and is set to a fixed value.

[0112] In a first step 201, C_last is initialised to an input constellation. In a next step 203, step d is initialised to a value Ini_step. In a next step 205, a set of candidate constellations is obtained. The set of candidate constellations comprise the constellation C_last and one or more modified constellations, where each modified constellation is obtained by modifying one or more of the parameter values defining C_last using any suitable scheme. In the illustrated example, the set of candidate constellations are created based on C_last and step size d, denoted by function CreateSet(C_Last, d). For example, for each constellation point, three derived constellations are generated [C_last, C_last+d, C_lastd]. Specifically, a set of constellations is derived such that the values of the b parameters in C_last are each set to one of n new values varying around the current parameter value. For example, three new values (n=3) may be used, comprising (i) the current parameter value, (ii) a value d greater than the current parameter value, and (iii) a value d less than the current parameter value. For example, if there are two constellation levels to be defined then the number of combinations to be tested are 33 (corresponding to three positions for each level). All combinations of the new parameter values are used to generate the set of constellation. Thus, the set of constellations comprises a total of n.sup.b constellations. Although three new values for each parameter are used in the embodiment described above, any suitable number of new values may be used in other embodiment. The set of new values may include the old value, or may not include the old value.

[0113] In certain embodiments, three values of each level are chosen so that the total number of possibilities to be tested is 3.sup.b where b is the number of levels (parameters) to be optimised. In the case of very high-order constellations, for example above 1K, 3.sup.b may be very high. In this case, all the levels may be fixed except one, for which three possibilities are tested, C_last, C_last+d and C_lastd until convergence is achieved. The same operation may then be repeated for the other levels. The cost of this operation is multiplicative and not exponential (for example, if it is supposed that each level converges in one iteration then the cost will be 3*b instead 3.sup.b.)

[0114] In a next step 207, the performance of each constellation in the set of derived (candidate) constellations is calculated or determined using any suitable performance measure (e.g. capacity). In a next step 209 the candidate constellation having the best performance (e.g. the candidate constellation that maximises the capacity) is assigned to C_best. In a next step 211, it is determined whether C_best differs from C_last by more than a threshold amount. For example, in the illustrated example, the threshold amount is equal to zero, so that it is determined whether C_best=C_last. That is, it is determined whether there is any difference between constellation C_best and constellation C_last (e.g. within a certain resolution). The difference may comprise any suitable measure of difference, for example including a difference based on geometry (e.g. differences in the locations of the constellation points of the constellations) and/or a performance measure (e.g. a difference in a certain performance measure between the constellations). If it is determined in step 211 that C_bestC_last, then in a next step 213, C_last takes the value C_best (i.e. so that the value of C_Last in the next iteration is equal to the value of C_Best in the current iteration) and the method returns to step 205 in which a set of candidate constellations are created based on C_last and step, CreateSet(C_Last, d). On the other hand, if it is determined in step 211 that C_best=C_Last, then, in a next step 215, C_last takes the value C_best and the method moves to a next step 217.

[0115] In step 217, it is determined whether d<Min_Step. If it is determined in step 217 that dMin_Step then the method moves to a next step 219 in which the step size d is reduced. For example, d is divided by a certain factor (e.g. 2). Following step 219, the method returns to step 205 in which a set of candidate constellations are created based on C_last and step, CreateSet(C_Last, d). On the other hand, If it is determined in step 217 that d<Min_Step then the value of C_best is saved and the algorithm ends.

[0116] FIG. 3 illustrates the convergence of C_last with respect to one of the parameters as the first algorithm of FIGS. 1 and 2 is performed. Initially, the value of the parameter converges to a certain value. When the value of the parameter has converged within a certain resolution, the step size d is reduced and the value of the parameter converges further, until the step size d has reached the minimum step size.

[0117] In the example shown in FIG. 3, for each iteration, three new parameter values are tried, as represented by the vertical columns of circles. The best new parameter for each iteration is indicated in FIG. 3 as a filled circle. The best parameter value in one iteration is used as the new parameter value for the next iteration. Thus, in the example illustrated in FIG. 3, in which three new parameter values are tried (comprising the current parameter and parameters an amount d above and below the current parameter), the filled circle of one iteration corresponds to the middle of the three circles arranged in a column for the next iteration.

[0118] In certain embodiments, Steps 217 and 219 of the algorithm illustrated in FIG. 2 may be omitted so that steps 205, 207, 209, 211, 213 and 215 are performed using the initial step size. In this case, when it is determined in Step 215 that C_best=C_last, the step size is not reduced, but rather the value of C_best is saved and the algorithm ends. By omitting Steps 217 and 219, the algorithm may potentially complete more quickly. However, in this case the output constellation C_best may differ from the true optimum constellation more than the output constellation C_best obtained in the algorithm illustrated in FIG. 2 where the step size d is decreased. This may be seen in FIG. 3, where it can be seen that the best parameter value in the final iteration lies closer to the optimal value (indicated by the horizontal line) than the best parameter value at the stage of convergence with the initial step size.

[0119] The first algorithm described above determines the optimum constellation based on a certain performance measure (e.g. capacity). In the following, various algorithms for determining an optimum constellation for a defined transmission system defined by a set of one or more system parameter values, where the constellation is optimised for a certain desired value of a system parameter (e.g. a certain SNR value or certain Ricean factor). In these embodiments, a system parameter value is set to an initial value (e.g. a relatively high value) and an optimum constellation is generated using an algorithm described above (e.g. the algorithm illustrated in FIG. 2), wherein the performance measure is based on a defined transmission system having the set system parameter value. The system parameter value is then reset to a modified value (e.g. by reducing the value by a certain step size) and the algorithm is re-run. The other system parameter values may remain fixed. This process is repeated until the system parameter value reaches a certain desired value.

[0120] For example, FIG. 4 illustrates a second algorithm for determining the optimal constellation at a given SNR value S in an AWGN channel. In a first step 401, the algorithm is initialised by setting a SNR parameter to a high value N, where N is large. For example, the initial SNR value may be set to a SNR value above which a non-uniform constellation provides no better performance than an equivalent uniform constellation. This value may be determined, for example, theoretically and/or experimentally. In step 401, the parameter C_last is also initialised to a certain constellation, for example a uniform constellation.

[0121] In a next step 403 the first algorithm described above is run using the initialised constellation C_last as the input constellation and using the initialised SNR ratio. By applying the first algorithm, the constellation C_last will converge to an optimal constellation C_best for the specific input value of SNR. The output of step 403 is C_best obtained using the first algorithm. In a next step 405 the SNR value is reduced by a certain amount, for example one unit or step size. In step 405, C_last takes the value of C_best (i.e. so that the value of C_Last in the next iteration is equal to the value of C_Best in the current iteration). In a next step 407 it is determined whether SNR<S. If it is determined in step 407 that SNRS then the method returns to step 403, in which the first algorithm is run with the new values of C_last and SNR. On the other hand, if it is determined in step 407 that SNR<S, then the value of C_best is saved and the algorithm ends. By applying the second algorithm, the resulting constellation C_best is the optimal constellation for the desired SNR value S.

[0122] FIG. 5 illustrates the convergence of the constellation C_best as the second algorithm of FIG. 4 is performed. Each of the three curves represents the variation in the value of a respective one of the three variable parameters. The solid constant line represents the fixed value of a fixed parameter. As shown in FIG. 5, at the start of the second algorithm, starting from the right-hand side of FIG. 5, the SNR value is high and the constellation is a uniform constellation, as defined by the values of the parameters on the right-hand side of FIG. 5, labelled Initial condition. At each iteration, the optimal constellation is obtained for the specific SNR value (indicated in FIG. 5 by the markers). The SNR is then reduced and the optimal constellation is obtained for the new SNR (this process being indicated for one of the parameters by the stepped line in FIG. 5). As shown in FIG. 5, the values of the parameters corresponding to the optimal constellation vary smoothly with varying SNR values. The iterations are repeated until the SNR value reaches the desired SNR value S.

[0123] By running the second algorithm illustrated in FIG. 4, an optimal constellation is derived from each of a set of SNR values. These constellations may be stored in association with the corresponding SNR values, for example in a look-up table.

[0124] FIG. 6 illustrates a third algorithm for determining the optimal constellation at a given SNR value S in a Rician fading channel for a desired Rician factor K_rice. The Rician channel is given by:

[00001]$\sqrt{\frac{K}{K+1}}+\sqrt{\frac{1}{K+1}}h$

[0125] where K is the Rician factor and h is Rayleigh distributed (centred and normalised). Initially, the third algorithm applies the second algorithm described above to obtain the optimal constellation C_best at a SNR value S for an AWGN channel, C_best(AWGN). In a first step 601, parameter C_last is initialised to C_best(AWGN). In step 601 the Rician factor K is initialised to a high value, which may be determined theoretically and/or experimentally. For example, K may be initialised to a value K_rice+N, where N is large.

[0126] In a next step 603, the first algorithm described above is run using the initialised constellation C_last as the input constellation and using the initialised Rician factor K to obtain an optimal constellation C_best. In a next step 605, the Rician factor K is reduced by a certain amount, for example by one unit. In step 605, C_last takes the value of C_best (i.e. so that the value of C_Last in the next iteration is equal to the value of C_Best in the current iteration). In a next step 607 it is determined whether K<K_rice. If it is determined in step 607 that KK_rice then the method returns to step 603, in which the first algorithm is run with the new values of C_last and K. On the other hand, if it is determined in step 607 that K<K_rice, then the value of C_best is saved and the algorithm ends. By applying the second algorithm, the resulting constellation C_best is the optimal constellation for the desired Rician factor K_rice.

[0127] FIG. 7 illustrates a fourth algorithm for determining the optimal constellation at a given SNR value S in a Rayleigh fading channel. A Rayleigh fading channel is a special case of Rician fading with the Rician factor K=0. Accordingly, the fourth algorithm is the same as the third algorithm described above, except that K_rice is set to zero.

[0128] Table 1 below compares the number of capacity calculation function calls for obtaining optimal constellations for various constellation sizes (16-QAM, 64-QAM and 256-QAM) using an exhaustive search, a restricted exhaustive search and an algorithm according to an embodiment of the present invention. The values in Table 1 are based on a step size d of and maximum value for the parameters of 10. Table 1 also indicates the factor difference between using a restricted exhaustive search and a search using an algorithm according to an embodiment of the present invention. As can be seen, the algorithm according to an embodiment of the present invention is significantly more efficient, for example by a factor of 1.1510.sup.10 for 256-QAM.

TABLE-US-00001 TABLE 1 Restricted Algorithm Gain Exhaustive exhaustive according to the versus search search present invention restricted 16QAM 800 800 21 38 64QAM 5.1e9 1.9e8 1701 117577 256QAM 2.1e21 2.5e15 216513 1.15e10

[0129] In Table 1, the difference between exhaustive search and restrictive exhaustive search is the following. It is assumed in the following that there are 4 levels (parameters) between 0 and 10. In the exhaustive search each of the 4 parameters is searched over the whole range [0-10] with a certain granularity. In the case of restricted exhaustive search, the range in which each level will fall is fixed. For example level1 (first parameter) will be in the range [0-2.5] level2 in the range [2.5-5], level3 in the range [5-7.5], level4 in the range [7.5-10]. By doing so, the number of possibilities is reduced.

[0130] FIG. 8 illustrates a fifth algorithm for determining an optimal constellation. This algorithm corresponds closely to the algorithm illustrated in FIG. 2, but is modified to increase overall efficiency. This algorithm comprises an inner loop that comprises steps (steps 803-819) corresponding to steps 203-219 of FIG. 2. However, step 805 for creating a set of candidate constellations is modified from the corresponding step 205 of FIG. 2. Specifically, in the algorithm of FIG. 8, rather than modify each of the b parameters and trying all combinations of the new parameters as in the algorithm of FIG. 2, only one parameter is modified at a time. For example, within one iteration of the inner loop 803-819, only one parameter (parameter i) is modified to produce a set of candidate constellation. The capacities of these constellations are calculated and the best constellation selected, as in FIG. 2.

[0131] In the algorithm of FIG. 8, the value of i is varied from 1 to b using an outer loop (steps 821-825). The algorithm of FIG. 8 is initialised in step 801, corresponding to step 201 of FIG. 2. It can be seen that, by using the algorithm of FIG. 8, rather than the algorithm of FIG. 2, the total number of candidate constellation tried (i.e. the total number of capacity calculations) is significantly reduced. However, in simulations, the optimal constellation obtained using the algorithm of FIG. 8 is very close to the optimal constellation obtained using the algorithm of FIG. 2, which in turn is very close to the true optimal constellation obtained using an exhaustive search. The improvement in computational efficiency using algorithms according to embodiments of the present invention, including the algorithms described above, when compared to an exhaustive search, increases as the constellation order increases.

[0132] As with the algorithm illustrated in FIG. 2, in certain embodiments, Steps 817 and 819 of the algorithm illustrated in FIG. 8 may be omitted.

[0133] Using the techniques described above, optimal constellations may be obtained for particular parameters, for example SNR, Rician factor etc. These optimum constellations are obtained independently of any particular system implementation, for example independent of a particular coding scheme. In the following, various embodiments are described for obtaining an optimal constellation for a specific transmission system.

[0134] A transmission system may comprise a number of processes which may affect the optimal constellation, for example FEC encoding, bit interleaving, demultiplexing bits to cells, mapping cells to constellations, cell interleaving, constellation rotation, I/Q component interleaving, inter-frame convolution and inter-frame block interleaving, and MISO precoding. A QAM mapper is used in the Bit Interleaved Coded Modulation (BICM) chain to map bits to symbols. The QAM mapper may use a uniform constellation to map bits to cells (for example as done in DVB-T2). However, an increase in capacity may be achieved by using a fixed non-uniform constellation. A non-fixed non-uniform constellation (e.g. QAM) may be used to further increase capacity. The BICM capacity depends on the bit to cell mapping used. Optimisations are desirable in the LDPC design, the QAM mapping and the mapping of bits to cells.

[0135] In certain techniques, different constellations are generated using a certain step size. The Bit Error Rate (BER), the Block Error Rate and/or the Packet Error Rate corresponding to the constellations are obtained and the best constellation is selected based on one or more of the aforementioned error rates.

[0136] In certain embodiments of the present invention, the process illustrated in FIG. 9 may be carried out to obtain an optimal constellation for a specific system. In a first step 901, a uniform constellation (e.g. uniform QAM) is selected. In a next step 903, BER values for the selected uniform constellation are obtained over a range of SNR values (e.g. using simulation or by obtaining the BER values theoretically or experimentally). These values may be obtained based on a specific system, for example using a particular coding scheme (e.g. LDPC code with a certain parity check matrix) with a certain coding rate and a certain bit interleaver and cell interleaver. FIG. 10 illustrates an exemplary plot for 64-QAM using an LDPC coding rate (CR) of 2/3 from DVB-T2 in an AWGN channel.

[0137] In a next step 905, the SNR at which the BER falls below a threshold value (e.g. 0.001) is determined. The threshold value may be selected such that the resulting SNR falls within a waterfall zone of the BER curve (i.e. the zone at which the BER falls relatively rapidly with increasing SNR). The determined SNR value may be denoted S and referred to as a waterfall SNR.

[0138] In a next step, the optimal constellation may be obtained for the SNR value S determined in step 905.

[0139] For example, in some embodiments, in step 907a, the optimal constellation may be selected from the optimal constellations obtained when performing the algorithms described above in relation to FIGS. 1-8 (and stored in a look-up table). Specifically, the optimal constellation previously determined for the SNR value S may be retrieved from the look-up table.

[0140] Alternatively, an iterative process may be performed to obtain an optimal (non-uniform) constellation, as follows. Specifically, following step 905, the method moves to step 907b in which the algorithms described above in relation to FIGS. 1-8 are used to obtain an optimal constellation for the SNR value S (or for a value close to S). Following step 907b, the method returns to step 903, in which BER values are obtained over a range of SNR. In this iteration, the BER values are obtained for the optimal constellation obtained in step 907b (rather than for the initial uniform constellation as in the first iteration). In a similar manner as previously described, the SNR value at which the BER falls below a threshold value (using the new set of BER values for the optimal constellation) is determined in step 905, and a new optimal constellation for the newly determined SNR value is obtain in step 907b. The previously described steps 903, 905, 907 may be repeated a certain number of time (for example a predetermined number of times). Alternatively, the algorithm may terminate when the waterfall SNR stops decreasing between iterations, and instead starts increasing.

[0141] FIGS. 11 and 12 illustrate a sixth algorithm for determining an optimal constellation. This algorithm corresponds closely to the algorithm illustrated in FIG. 8, but is modified to improve performance. In particular, this algorithm introduces the concept of a direction of convergence of a parameter value. For example, within the inner loop of the algorithm, the direction is initialised to 0. When creating a set of candidate constellations, the candidate set depends on the direction parameter. When the best constellation is selected in step 1109, the direction of convergence of the value of parameter i is obtained. For example, if the parameter value is converging upwards then the direction parameter may be set to +1, if the parameter is converging downwards then the direction parameter may be set to 1, and if the parameter does not change then the direction parameter may be set to 0. As illustrated in FIG. 12, the number of candidate constellations may be reduced when the parameter value is converging upwards or downwards.

[0142] In an exemplary embodiment marked Example 1 of FIG. 12, in a first iteration all the 3 points are computed, and the upper one is the best one. In a second iteration only the top one is computed, and the upper is the best one. In a third iteration only the one is computed, the middle is the best one. Instead of 9 points, we needed only 5.

[0143] Further, in an exemplary embodiment marked Example 2 of FIG. 12, in a first iteration all the 9 points are computed, and the bottom one is the best one. In a second iteration only the 3 bottom ones is computed, and the corner is the best one. In a third iteration only the 5 borders are computed, and the middle is the best one. Instead of 9*3=27 points, we needed only 9+3+5=17.

[0144] As described above, an optimum constellation may be obtained for a particular system implementation, and/or for certain system parameter values. For example, an optimum constellation (e.g. a constellation that optimises the BICM capacity) may be obtained for a certain propagation channel type (e.g. AWGN, Rayleigh or Typical Urban, TU6, channel) and for a certain SNR. However, in some cases, data may be transmitted in different scenarios. For example, data may be transmitted through different types of channels and may be received with different SNRs. Furthermore, it may be desirable or required that a data transmission system uses the same constellation, regardless of the scenario (e.g. channel type or SNR), for example in order to reduce system complexity. In some cases, a transmission system may use a certain constellation for many different scenarios (e.g. channel types and SNRs).

[0145] FIGS. 50-53 illustrate an algorithm for obtaining a constellation that is optimised (e.g. achieves the best capacity) with respect to two or more different scenarios (e.g. different channel types and/or SNR values). The algorithm comprises a number of different parts. First, the waterfall SNR for each channel type (e.g. propagation channel type) is obtained using an algorithm similar to the algorithm illustrated in FIG. 9. A weighted performance measure function (e.g. weighted capacity) for an input constellation is defined, based on different scenarios (e.g. different channel types and SNR values). Then, an algorithm similar to the algorithms illustrated in FIG. 2, 8 or 11 is applied to determine an optimum constellation, where the performance measure used is based on the weighted performance measure.

[0146] FIG. 50 illustrates a process for obtaining the waterfall SNR for each channel type. Each channel type is treated separately in order to obtain its waterfall SNR. In particular, the process illustrated in FIG. 50 is repeated for each channel type to obtain a respective waterfall SNR for that channel type. The process illustrated in FIG. 50 operates in substantially the same manner as the algorithm illustrated in FIG. 9, and therefore a detailed description will be omitted for conciseness. However, rather than outputting an optimal constellation, as in the algorithm illustrated in FIG. 9, the process illustrated in FIG. 50 instead outputs the waterfall SNR determined in the final iteration of the process. The process illustrated in FIG. 50 (including BER simulation and capacity optimisation steps) is performed based on a certain channel type, and the output waterfall SNR is determined as the waterfall SNR associated with that channel type.

[0147] FIG. 51 schematically illustrates a process for obtaining a weighted performance measure function for an input constellation based on different transmission scenarios. In this example, the weighted performance measure is a weighted capacity, and the different scenarios comprise different channel types and associated waterfall SNR values. As illustrated in FIG. 51, a candidate constellation is provided as an input. For each channel type and associated waterfall SNR, the BICM capacity for the input constellation based on the channel type and waterfall SNR is obtained. Each obtained BICM capacity is then multiplied by a respective weight and the weighted BICM capacities are added together to obtain an output weighted average BICM capacity. The weights may be selected according to any suitable criteria. For example, a relatively common or important channel type may be associated with a relatively large weight.

[0148] FIG. 52 illustrates a process for obtaining an optimum constellation. The process illustrated in FIG. 52 operates in substantially the same manner as the algorithm illustrated in FIG. 2, 8 or 11, and therefore a detailed description will be omitted for conciseness. However, when determining the performance of a candidate performance in the process illustrated in FIG. 52, the performance is determined based on the weighted performance measure described above in relation to FIG. 51.

[0149] In the process illustrated in FIG. 52, in some situation, a certain constellation may achieve the best performance with respect to the weighted performance measure, even though the performance of that constellation with respect to the BICM capacity based on an individual channel and SNR may be relatively low. In certain embodiments, to ensure that a constellation obtained using the algorithm is able to achieve at least a certain level of performance for one or more, or all, transmission scenarios, an additional criterion may be applied when testing each candidate constellation to obtain the constellation C_best. Specifically, any candidate constellation that does not achieve at least a threshold performance with respect to one or more certain individual scenarios, or all scenarios, is ignored and cannot be selected as C_best, even if that constellation achieves the best performance with respect to the weighted performance measure.

[0150] In the process illustrated in FIG. 52, the set of candidate constellations may be derived using any suitable method, for example the method described above in relation to FIG. 9 based on a step size d. FIGS. 53a and 53b illustrate alternative schemes for generating a candidate constellation from a previous constellation, C_last, that may be used in certain embodiments. In FIGS. 53a and 53b, the open circles represent the constellation points of a previous constellation, C_last. For each constellation point of the previous constellation, a respective set of N modified constellation points are defined, indicated in FIGS. 53a and 53b as filled circles. Each set of modified constellation points forms a pattern of constellation points located relatively close to the respective constellation point of the previous constellation.

[0151] For example, as illustrated in FIG. 53a, each set of modified constellation points may form a square or rectangular lattice of N=8 constellation points surrounding a respective constellation point of the previous constellation. The lattice spacing is equal to d. Alternatively, as illustrated in FIG. 53b, each set of modified constellation points may form a ring of N=8 constellation points surrounding a respective constellation point of the previous constellation. The radius of the ring is equal to d.

[0152] A candidate constellation may be obtained by selecting, for each constellation point in the previous constellation, either the constellation point of the previous constellation itself or one of the constellation points of a respective set of modified constellation points.

[0153] In the examples described above, a weighted performance measure is defined based on different transmission scenarios. For example, in the case illustrated in FIG. 51, each transmission scenario comprises a different channel type and an associated waterfall SNR value. Accordingly, a constellation optimised for a range of channel types and associated SNR values may be obtained. In an alternative embodiment, an optimal constellation may be obtained for different transmission scenarios, in the case where each transmission scenario comprises the same channel type, but involves different SNR values (e.g. a set of SNR values S1, S1+d, S1+2d, S1+3d, . . . , S2, where d is a step size). That is, an optimal constellation may be obtained for a fixed channel type that is intended to be used over a range of SNR values. In this case, the algorithm described above in relation to FIGS. 50-53 may be used, except that when determining the weighted performance measure as illustrated in FIG. 51, instead of determining individual BICM capacities based on respective channel types and associated waterfall SNR values, the individual BICM capacities are determined based on the fixed channel type and respective SNR values S1, S1+d, S1+2d, S1+3d, . . . , S2.

[0154] In the algorithms described above, a technique may be applied to reduce the overall complexity. In particular, when a set of candidate constellations is generated and the performance of the candidate constellations are tested, those candidate constellations that have been previously tested (i.e. in one or more previous iteration) are not re-tested. That is, in a current iteration, only those candidate constellations that have not been tested in previous iterations are tested.

[0155] For example, as described above, a first set of candidate constellations, A, is generated in an iteration, and the best performing candidate constellation, a (aA), is selected from this set. In the next iteration, a second set of candidate constellations, B, is generated based on the previously selected constellation a (aB). In this next iteration, the best performing candidate constellation b (bB) from set B needs to be determined.

[0156] Typically, there will be at least some overlap between the two sets of candidate constellations A and B, such that one or more candidate constellations belong to both sets A and B (i.e. AB), including constellation a. Since it is known that constellation a has the best performance of all the constellations in set A, then it is also known that constellation a has the best performance of all the constellations belonging to the overlap between sets A and B (i.e. AB).

[0157] Accordingly, when testing the constellations in set B to determine the best performing constellation, b, it is not necessary to re-test those constellations belonging to the overlap between sets A and B (i.e. it is not necessary to re-test those constellations in the set A.Math.B). Instead, rather than testing all constellations in set B, only those constellations belonging to the smaller set of constellations B*, comprising constellations belonging to set B but excluding any constellations that also belong to set A (i.e. B*=B\A) are tested. Then, the best performing constellation from the set formed from the union of B* and the previous best performing constellation, a (i.e. the best performing constellation from the set B*a) is selected as the best performing constellation, b, of set B.

[0158] An example of the above principle in relation to the example shown in FIG. 53a is illustrated in FIG. 54. In the example of FIG. 54, at iteration i, it was found that the constellation point indicated as a black circle is the best performing. At iteration i+1, there is no need to test the common subset (including the white circles and the black circle), because it was already tested before and gave an inferior performance. That is, at iteration i+1, only the dark grey circles need to be tested. Accordingly, in the illustrated example, a reduction in complexity of 44% (=4/9) is achieved.

[0159] FIG. 55 illustrates an apparatus for implementing an algorithm according to an exemplary embodiment, for example one or more of the embodiments described above. The apparatus is configured for generating a non-uniform constellation. The apparatus comprises a block for performing a first process. The block for performing the first process comprises: a block for obtaining a first constellation defined by one or more parameter values; and a block for generating a second constellation based on the first constellation using a second process. The block for generating the second constellation based on the first constellation using the second process comprises: a block for obtaining a set of candidate constellations, wherein the set of candidate constellations comprises the first constellation and one or more modified constellations, wherein each modified constellation is obtained by modifying the parameter values defining the first constellation; a block for determining the performance of each candidate constellation according to a predetermined performance measure; and a block for selecting the candidate constellation having the best performance as the second constellation. The block for performing the first process further comprises a block for determining a difference between the first constellation and the second constellation; and a block for, if the second constellation differs from the first constellation by more than a threshold amount, causing the block for performing the first process to repeat the first process using the second constellation generated in the current iteration of the first process as the first constellation in the next iteration.

[0160] The skilled person will appreciate that the functions of any two or more blocks illustrated in FIG. 55 may be performed by a single block, and that the functions of any block illustrated in FIG. 55 may be performed by two or more blocks. A block may be implemented in any suitable form, for example hardware, software, firmware, or any suitable combination of hardware, software and firmware.

[0161] A constellation obtained by a method according to exemplary embodiments of the present invention may be used in a digital broadcasting system to transmit data from a transmitter side to a receiver side. In certain exemplary embodiments, the system comprises a transmitter arranged to obtain data (e.g. a data stream), perform any required encoding and/or other processing of the data, modulate a signal using the data according to a modulation scheme corresponding to the constellation, and transmit the modulated signal. The system further comprises a receiver configured to receive a modulated signal, demodulate the signal according to a demodulation scheme corresponding to the constellation (or a similar or corresponding constellation), and perform any necessary decoding and/or other processing to recover the original data. Certain embodiments may comprise a transmitter side apparatus only, a receiver side apparatus only, or a system comprising both a transmitter side apparatus and a receiver side apparatus.

[0162] FIG. 13a illustrates a uniform constellation (64-QAM), FIG. 13b illustrates a non-uniform constellation (64-QAM) characterised by 3 parameters, and FIG. 13c illustrates a non-uniform constellation (64-QAM) characterised by 16 parameters. As illustrated in FIG. 13c, in some embodiments, the constellation points are not constrained to lie on a square lattice.

[0163] The number of parameters depends on the number of constraints, as can be seen by comparing the non-uniform constellations illustrated in FIGS. 13b and 13c.

[0164] The Annexes to this description include various tables comprising data obtained using certain embodiments of the present invention. Annex 1a covers square constellations and Annex 2a covers non-square constellations. Each Annex covers four constellation sizes, 16, 64, 256 and 1024.

[0165] The first column in each table is the optimal SNR for which the values are optimal. In the case of the tables indicated NU-QAM (square), the tables contain the optimal normalized levels/parameters (L1, L2, L3 . . . ). There are different numbers of levels for each order of constellation.

[0166] In the case of the tables indicated NUC (non-square), the tables contain the raw point values (a1, a2, a3 . . . ) in the first quadrant (the other 3 quadrants can be derived by symmetry). The values in these tables are complex (A+Bi) since the constellation is two dimensional.

[0167] The Annexes to the Figures illustrate results obtained from various embodiments of the present invention.

[0168] Various results obtained by applying the algorithms described above will now be described. For example, results obtained for NU-QAM constellations of different sizes (specifically NU 16-QAM, NU 64-QAM, NU 256-QAM and NU 1024-QAM), and using different code rates (specifically 6/15, 7/15, 8/15, 9/15, 10/15, 11/15, 12/15 and 13/15), are described. These results show that non-uniform constellations provide a significant gain over corresponding uniform constellations. The values of the set of constellation points for various exemplary constellations obtained by applying the algorithms described above are also described.

[0169] FIG. 14a illustrates a set of BER curves obtained using a NU 16-QAM constellation, NUC, using respective code rates, CRs (specifically the code rates mentioned above), and a set of BER curves obtained using a corresponding (uniform) 16-QAM constellation using the same code rates. The solid curves are the BER curves for the NU 16-QAM constellation and the dotted curves are the BER curves for the corresponding uniform 16-QAM constellation. FIG. 14a also indicates the SNR gain (at the waterfall, WF, zone) obtained using the NU 16-QAM constellation with respect to the corresponding 16-QAM constellation for each code rate.

[0170] FIG. 14b is a table indicating, for each code rate, the SNR values at the waterfall zone (e.g. the waterfall SNR values) for the uniform and non-uniform constellations used to obtain the BER curves illustrated in FIG. 14a, and the resulting SNR gain (obtained as a difference between the SNR values). As indicated, a SNR gain of up to 0.3 dB (e.g. for code rates of 8/15 and 9/15) may be obtained.

[0171] FIGS. 15a and 15b illustrate a set of BER curves and SNR gain values, similar to FIGS. 14a and 14b, using a NU 64-QAM constellation and a corresponding (uniform) 64-QAM constellation, and using the code rates mentioned above.

[0172] FIGS. 16a and 16b illustrate a set of BER curves and SNR gain values, similar to FIGS. 14a and 14b, using a NU 256-QAM constellation and a corresponding (uniform) 256-QAM constellation, and using the code rates mentioned above.

[0173] FIGS. 17a and 17b illustrate a set of BER curves and SNR gain values, similar to FIGS. 14a and 14b, using a NU 1024-QAM constellation and a corresponding (uniform) 1024-QAM constellation, and using the code rates mentioned above.

[0174] FIG. 18 illustrates an exemplary NU 16-QAM constellation obtained by applying the algorithms described above using a code rate of 6/15. The positions of the individual constellation points are indicated in the constellation diagram on the right-hand side of FIG. 18. The values of the constellation points of the top-right quadrant are indicated on the lefthand side of FIG. 18. The values of the constellation points of the other quadrants may be deduced by symmetry. In particular, for each constellation point A in the top-right quadrant, there is a corresponding constellation point in each of the three other quadrants (bottom-right, bottom-left and top-left), given, respectively, by A*, A* and A, where * denotes complex conjugation.

[0175] FIGS. 19-25 illustrate exemplary NU 16-QAM constellations obtained by applying the algorithms described above using code rates of 7/15, 8/15, 9/15, 10/15, 11/15, 12/15 and 13/15, respectively. As with FIG. 18, the complete set of constellation points are indicated in the constellation diagram on the right-hand side of the Figures, and the values of the constellation points of the top-right quadrant are indicated on the left-hand side of the Figures. As with FIG. 18, the values of the constellation points in the other three quadrants may be similarly deduced by symmetry.

[0176] In alternative embodiments, the constellations illustrated in FIGS. 18-25 may comprise constellation points given in Tables 2-6 in Annex 7.

[0177] FIGS. 26-33 illustrate exemplary NU 64-QAM constellations obtained by applying the algorithms described above using code rates of 6/15, 7/15, 8/15, 9/15, 10/15, 11/15, 12/15 and 13/15, respectively. As with FIG. 18, the complete set of constellation points are indicated in the constellation diagram on the right-hand side of the Figures, and the values of the constellation points of the top-right quadrant are indicated on the left-hand side of the Figures. As with FIG. 18, the values of the constellation points in the other three quadrants may be similarly deduced by symmetry.

[0178] In alternative embodiments, the constellations illustrated in FIGS. 26-33 may comprise constellation points given in Tables 7-11 in Annex 7.

[0179] FIGS. 34-41 illustrate exemplary NU 256-QAM constellations obtained by applying the algorithms described above using code rates of 6/15, 7/15, 8/15, 9/15, 10/15, 11/15, 12/15 and 13/15, respectively. As with FIG. 18, the complete set of constellation points are indicated in the constellation diagram on the right-hand side of the Figures, and the values of the constellation points of the top-right quadrant are indicated on the left-hand side of the Figures. As with FIG. 18, the values of the constellation points in the other three quadrants may be similarly deduced by symmetry.

[0180] In alternative embodiments, the constellations illustrated in FIGS. 34-41 may comprise constellation points given in Tables 12-16 in Annex 7.

[0181] FIGS. 42-49 illustrate exemplary NU 1024-QAM constellations obtained by applying the algorithms described above using code rates of 6/15, 7/15, 8/15, 9/15, 10/15, 11/15, 12/15 and 13/15, respectively. As with FIG. 18, the complete set of constellation points are indicated in the constellation diagram on the right-hand side of the Figures. The values of the constellation points of the top-right quadrant are indicated on the left-hand side of the Figures. In FIGS. 42-49, in contrast to FIGS. 18-41, rather than giving the values of the constellation points explicitly, a set of levels of the constellation point are given instead, from which the actual values of the constellation points may be deduced. Specifically, given a set of m levels A=[A.sub.1, A.sub.2, . . . , A.sub.m], a set of m.sup.2 constellation point values C+Dj may be deduced, wherein C and D each comprise a value selected from the set, A, of levels. The complete set of constellation points in the top-right quadrant is obtained by considering all possible pairs of values C and D. As with FIG. 18, the values of the constellation points in the other three quadrants may be similarly deduced by symmetry.

[0182] In alternative embodiments, the constellations illustrated in FIGS. 42-49 may comprise constellation points given in Tables 17-21 in Annex 7.

[0183] The skilled person will appreciate that, in certain embodiments, the constellations indicated in FIGS. 18-49 may be rotated and/or scaled (where the scaling factor applied to the real and imaginary axis may be the same or different) and/or have any other transformation applied thereto. The constellations indicated in FIGS. 18-49 may be regarded as constellations, which indicate the relative positions of the constellation points, and from which other constellations may be derived through rotation and/or scaling and/or any other suitable transformation.

[0184] Tables 2-6 in Annex 7 indicate the values of the constellation points of exemplary normalised NU 16-QAM constellations obtained by applying the algorithms described above using coding rates of 5/15, 7/15, 9/15, 11/15, and 13/15, and fora single SNR value.

[0185] Tables 7-11 in Annex 7 indicate the values of the constellation points of exemplary normalised NU 64-QAM constellations obtained by applying the algorithms described above using coding rates of 5/15, 7/15, 9/15, 11/15, and 13/15, and for one SNR, in a similar manner to Tables 2-6.

[0186] Tables 12-16 in Annex 7 indicate the values of the constellation points of exemplary normalised NU 256-QAM constellations obtained by applying the algorithms described above using coding rates of 5/15, 7/15, 9/15, 11/15, and 13/15, and for one SNR, in a similar manner to Tables 2-11.

[0187] Tables 17-21 in Annex 7 indicate the values of the constellation points of exemplary normalised NU 1024-QAM constellations obtained by applying the algorithms described above using coding rates of 5/15, 7/15, 9/15, 11/15 and 13/15, and for one SNR. In tables 17-21, in contrast to Tables 2-16, rather than giving the values of the constellation points explicitly, a set of levels of the constellation point are given instead, from which the actual values of the constellation points may be deduced, as described above.

[0188] The skilled person will appreciate that the present invention is not limited to the specific constellations indicated in FIGS. 18-49 and Tables 2-22. For example, in certain embodiments, constellations of different orders and/or constellation comprising different arrangements or relative positions of constellation points may be used. In some embodiments, a constellation similar to one of the constellations indicated in FIGS. 18-49 and/or Tables 2-22 may be used. For example, a constellation having constellation point values differing by no more than a certain threshold amount (or tolerance or error) from the values indicated in FIGS. 18-49 and/or Tables 2-22 may be used. The threshold amount may be expressed, for example, as a relative amount (e.g. 0.1%, 1%, 5% etc.), as an absolute amount (e.g. 0.001, 0.01, 0.1 etc.), or in any other suitable way. In certain embodiments, a constellation point may be rounded using any suitable rounding operator. For example, a constellation point given by A1=0.775121+0.254211 j may be rounded to A2=0.775+0.254j. The non-rounded or the rounded value may be stored in a table.

[0189] In certain exemplary embodiments, the transmitter and the receiver may use constellations that are not exactly the same. For example, the transmitter and the receiver may user respective constellations in which one or more constellation points differ by no more than a certain threshold amount. For example, the receiver may use a constellation comprising one or more rounded constellation points (e.g. A2) to de-map the constellation value, while the transmitter may use a constellation comprising the non-rounded constellation points (e.g. A1).

[0190] Annexes 1b and 2b include alternative data to the data included in Annexes 1a and 2a. Annex 1b covers square constellations and Annex 2b covers non-square constellations. Each Annex covers four constellation sizes, 16, 64, 256 and 1024. The tables in Annex 2b contain the 2D constellation points for a range of SNR values. Different labelling (i.e. mappings between bits and constellation points) can be used. For each constellation, there exist (log 2(points)2)!*2{circumflex over ()}(log 2(points)2) possible labellings that lead to an optimal capacity value. The Annex 2b tables only show one possible, exemplary, labelling. However, the skilled person can reorder the points of a given constellation/SNR, obtaining a different labelling but maintaining the same performance.

[0191] The Annexes to this description include various LDPC parity bit accumulator tables that may be used in certain embodiments of the present invention. Specifically, Annex 3 contains parity bit accumulator tables used to generate the Parity Check Matrix for each coding rate. A table is provided for each LDPC length, specifically 64 k or 16 k. For example, tables in Annex 3 were used in obtaining the results illustrated in FIGS. 14-49. When applying the algorithms described above, the waterfall zone and waterfall SNR depends on the LDPC matrix used. In the tables of Annex 3, each row represents one of the Quasi-Cyclic Low-Density Parity-Check, QC LDPC, columns generators.

[0192] Annex 4 indicates the values of the constellation points of further exemplary 16-QAM, 64-QAM, 256-QAM and 1024-QAM constellations obtained by applying an algorithm according to an exemplary embodiment of the present invention, for example one or more of the algorithms described above, using coding rates of 7/15, 9/15, 11/15 and 13/15. The 16-QAM, 64-QAM and 256-QAM constellations are NUC constellations, where constellation points are given for the first quadrant only. The constellation points for the other three quadrants may be deduced by symmetry, as described above in relation to FIGS. 18-41. The 1024-QAM constellation is an NU-QAM (rectangular) constellation, where the constellation points are defined by a set of levels, as described above in relation to FIGS. 42-49.

[0193] Annex 5 indicates the values of the constellation points of further exemplary 16-QAM, 64-QAM and 256-QAM constellations obtained by applying an algorithm according to an exemplary embodiment of the present invention, for example one or more of the algorithms described above. In certain exemplary embodiments, these constellations may be used for coding rates of 3/10 or below.

[0194] Annex 6 indicates the values of the constellation points of further exemplary 16-QAM, 64-QAM, 256-QAM and 1024-QAM constellations obtained by applying an algorithm according to an exemplary embodiment of the present invention, for example one or more of the algorithms described above, using coding rates of 5/15 (for 64-QAM and 256-QAM only), 7/15, 9/15, 11/15 and 13/15. The 16-QAM, 64-QAM, 256-QAM constellations, and the second 1024-QAM constellation, are NUC constellations, where constellation points are given for the first quadrant only. The constellation points for the other three quadrants may be deduced by symmetry, as described above in relation to FIGS. 18-41. The first 1024-QAM constellation is an NU-QAM (rectangular) constellation, where the constellation points are defined by a set of levels, as described above in relation to FIGS. 42-49.

[0195] In cases where the constellations are indicated in terms of a set of levels, the actual constellation points may be constructed from the indicated levels. For example, Annex 6 gives a 1K-QAM (1 dimension) constellation in terms of a set of levels. Table 22 in Annex 8 gives the values of the constellation points in the first quadrant for the 1K-QAM (1 dimension) constellation, which may be constructed from the set of levels given in Annex 6. The constellation points for the other three quadrants may be deduced by symmetry. One example of the construction of a set of constellation points from a set of levels is given in Annex 9.

[0196] The constellation points coordinates included in the present disclosure may be rounded off to the nearest whole number at any decimal point. For example, a constellation point coordinate may be rounded off in the fifth decimal place after the decimal point.

[0197] It will be appreciated that embodiments of the present invention can be realized in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage, for example a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape or the like.

[0198] It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement certain embodiments of the present invention. Accordingly, certain embodiments provide a program comprising code for implementing a method, apparatus or system as claimed in any one of the claims of this specification, and a machine-readable storage storing such a program. Still further, such programs may be conveyed electronically via any medium, for example a communication signal carried over a wired or wireless connection, and embodiments suitably encompass the same.

[0199] While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention, as defined by the appended claims.

TABLE-US-00002 Lengthy table referenced here US20230421427A1-20231228-T00001 Please refer to the end of the specification for access instructions.

TABLE-US-00003 Lengthy table referenced here US20230421427A1-20231228-T00002 Please refer to the end of the specification for access instructions.

TABLE-US-00004 Lengthy table referenced here US20230421427A1-20231228-T00003 Please refer to the end of the specification for access instructions.

TABLE-US-00005 Lengthy table referenced here US20230421427A1-20231228-T00004 Please refer to the end of the specification for access instructions.

TABLE-US-00006 Lengthy table referenced here US20230421427A1-20231228-T00005 Please refer to the end of the specification for access instructions.

TABLE-US-00007 Lengthy table referenced here US20230421427A1-20231228-T00006 Please refer to the end of the specification for access instructions.

TABLE-US-00008 Lengthy table referenced here US20230421427A1-20231228-T00007 Please refer to the end of the specification for access instructions.

TABLE-US-00009 Lengthy table referenced here US20230421427A1-20231228-T00008 Please refer to the end of the specification for access instructions.

TABLE-US-00010 Lengthy table referenced here US20230421427A1-20231228-T00009 Please refer to the end of the specification for access instructions.

Annex to the DescriptionAnnex 9

[0200] In certain exemplary embodiments, a two-dimensional constellation may be constructed from a set of one-dimensional levels according to the method described below. The specific example described below is based on the table for the CR 13/15, 1K constellation given in Annex 6, which is reproduced below.

[0201] The vector of levels may be denoted A={a.sub.i}, i=0, 1, 2, . . . , L1.

[0202] In a first step, the vector A is normalized to obtain a normalised vector using the following formula:

[00002]$\stackrel{\_}{A}=\frac{A}{\sqrt{\frac{2}{L}{.Math.}_i{a}_i^2}}$

where L is the number of levels (i.e. the dimensionality of A).

[0203] In this example, the resulting normalised vector is indicated below.

[0204] In a next step, the full constellation is generated as comprising all the possibilities of combinations of real and imaginary parts equal to one of the entries (i.e. components) of , In certain exemplary embodiments, a gray mapping may be used.

[0205] In this example, the resulting constellation points of the first quadrant are indicated below.

Annex to the DescriptionAnnex 9

[0206] In certain exemplary embodiments, a two-dimensional constellation may be constructed from a set of one-dimensional levels according to the method described below. The specific example described below is based on the table for the CR 13/15, 1K constellation given in Annex 6, which is reproduced below.

TABLE-US-00011 CR 13/15 1 2.975413 4.997551 7.018692 9.102872 11.22209 13.42392 15.69921 18.09371 20.61366 23.2898 26.15568 29.23992 32.59361 36.30895 40.58404

[0207] The vector of levels may be denoted A={a.sub.i}, i=0, 1, 2, . . . , L1.

[0208] In a first step, the vector A is normalized to obtain a normalised vector using the following formula:

[00003]$\stackrel{\_}{A}=\frac{A}{\sqrt{\frac{2}{L}{.Math.}_i{a}_i^2}}$

where L is the number of levels (i.e. the dimensionality of A).

[0209] In this example, the resulting normalised vector is indicated below.

TABLE-US-00012 CR 13/15 0.0325 0.0967 0.1623 0.228 0.2957 0.3645 0.4361 0.51 0.5878 0.6696 0.7566 0.8497 0.9498 1.0588 1.1795 1.3184

[0210] In a next step, the full constellation is generated as comprising all the possibilities of combinations of reap and imaginary parts equal to one of the entries (i.e. components) of . In certain exemplary embodiments, a gray mapping may be used.

[0211] In this example, the resulting constellation points of the first quadrant are indicated below.

TABLE-US-00013 Label (int.) Contellation 0 1.3184 + 1.3184i 1 1.3184 + 1.1795i 2 1.1795 + 1.3184i 3 1.1795 + 1.1795i 4 1.3184 + 0.9498i 5 1.3184 + 1.0588i 6 1.1795 + 0.9498i 7 1.1795 + 1.0588i 8 0.9498 + 1.3184i 9 0.9498 + 1.1795i 10 1.0588 + 1.3184i 11 1.0588 + 1.1795i 12 0.9498 + 0.9498i 13 0.9498 + 1.0588i 14 1.0588 + 0.9498i 15 1.0588 + 1.0588i 16 1.3184 + 0.5878i 17 1.3184 + 0.6696i 18 1.1795 + 0.5878i 19 1.1795 + 0.6696i 20 1.3184 + 0.8497i 21 1.3184 + 0.7566i 22 1.1795 + 0.8497i 23 1.1795 + 0.7566i 24 0.9498 + 0.5878i 25 0.9498 + 0.6696i 26 1.0588 + 0.5878i 27 1.0588 + 0.6696i 28 0.9498 + 0.8497i 29 0.9498 + 0.7566i 30 1.0588 + 0.8497i 31 1.0588 + 0.7566i 33 0.5878 + 1.1795i 34 0.6696 + 1.3184i 35 0.6696 + 1.1795i 36 0.5878 + 0.9498i 37 0.5878 + 1.0588i 38 0.6696 + 0.9498i 39 0.6696 + 1.0588i 40 0.8497 + 1.3184i 41 0.8497 + 1.1795i 42 0.7566 + 1.3184i 43 0.7566 + 1.1795i 44 0.8497 + 0.9498i 45 0.8497 + 1.0588i 46 0.7566 + 0.9498i 47 0.7566 + 1.0588i 48 0.5878 + 0.5878i 49 0.5878 + 0.6696i 50 0.6696 + 0.5878i 51 0.6696 + 0.6696i 52 0.5878 + 0.8497i 53 0.5878 + 0.7566i 54 0.6696 + 0.8497i 55 0.6696 + 0.7566i 56 0.8497 + 0.5878i 57 0.8497 + 0.6696i 58 0.7566 + 0.5878i 59 0.7566 + 0.6696i 60 0.8497 + 0.8497i 61 0.8497 + 0.7566i 62 0.7566 + 0.8497i 63 0.7566 + 0.7566i 64 1.3184 + 0.0325i 65 1.3184 + 0.0967i 66 1.1795 + 0.0325i 67 1.1795 + 0.0967i 68 1.3184 + 0.2280i 69 1.3184 + 0.1623i 70 1.1795 + 0.2280i 71 1.1795 + 0.1623i 72 0.9498 + 0.0325i 73 0.9498 + 0.0967i 74 1.0588 + 0.0325i 75 1.0588 + 0.0967i 76 0.9498 + 0.2280i 77 0.9498 + 0.1623i 78 1.0588 + 0.2280i 79 1.0588 + 0.1623i 80 1.3184 + 0.5100i 81 1.3184 + 0.4361i 82 1.1795 + 0.5100i 83 1.1795 + 0.4361i 84 1.3184 + 0.2957i 85 1.3184 + 0.3645i 86 1.1795 + 0.2957i 87 1.1795 + 0.3645i 88 0.9498 + 0.5100i 89 0.9498 + 0.4361i 90 1.0588 + 0.5100i 91 1.0588 + 0.4361i 92 0.9498 + 0.2957i 93 0.9498 + 0.3645i 94 1.0588 + 0.2957i 95 1.0588 + 0.3645i 96 0.5878 + 0.0325i 97 0.5878 + 0.0967i 98 0.6696 + 0.0325i 99 0.6696 + 0.0967i 100 0.5878 + 0.2280i 101 0.5878 + 0.1623i 102 0.6696 + 0.2280i 103 0.6696 + 0.1623i 104 0.8497 + 0.0325i 105 0.8497 + 0.0967i 106 0.7566 + 0.0325i 107 0.7566 + 0.0967i 108 0.8497 + 0.2280i 109 0.8497 + 0.1623i 110 0.7566 + 0.2280i 111 0.7566 + 0.1623i 112 0.5878 + 0.5100i 113 0.5878 + 0.4361i 114 0.6696 + 0.5100i 115 0.6696 + 0.4361i 116 0.5878 + 0.2957i 117 0.5878 + 0.3645i 118 0.6696 + 0.2957i 119 0.6696 + 0.3645i 120 0.8497 + 0.5100i 121 0.8497 + 0.4361i 122 0.7566 + 0.5100i 123 0.7566 + 0.4361i 124 0.8497 + 0.2957i 125 0.8497 + 0.3645i 126 0.7566 + 0.2957i 127 0.7566 + 0.3645i 128 0.0325 + 1.3184i 129 0.0325 + 1.1795i 130 0.0697 + 1.3184i 131 0.0967 + 1.1795i 132 0.0325 + 0.9498i 133 0.0325 + 1.0588i 134 0.0967 + 0.9498i 135 0.0967 + 1.0588i 136 0.2880 + 1.3184i 137 0.2280 + 1.1795i 138 0.1623 + 1.3184i 139 0.1623 + 1.1795i 140 0.2280 + 0.9498i 141 0.2280 + 1.0588i 142 0.1623 + 0.9498i 143 0.1623 + 1.0588i 144 0.0325 + 0.5878i 145 0.0325 + 0.6696i 146 0.0967 + 0.5878i 147 0.0967 + 0.6696i 148 0.0325 + 0.8497i 149 0.0325 + 0.7566i 150 0.0967 + 0.8497i 151 0.0967 + 0.7566i 152 0.2280 + 0.5878i 153 0.2280 + 0.6696i 154 0.1623 + 0.5878i 155 0.1623 + 0.6696i 156 0.2280 + 0.8497i 157 0.2280 + 0.7566i 158 0.1623 + 0.8497i 159 0.1623 + 0.7566i 160 0.5100 + 1.3184i 161 0.5100 + 1.1795i 162 0.4361 + 1.3184i 163 0.4361 + 1.1795i 164 0.5100 + 0.9498i 165 0.5100 + 1.0588i 166 0.4361 + 0.9498i 167 0.4361 + 1.0588i 168 0.2957 + 1.3184i 169 0.2957 + 1.1795i 170 0.3645 + 1.3184i 171 0.3645 + 1.1795i 172 0.2957 + 0.9498i 173 0.2957 + 1.0588i 174 0.3645 + 0.9498i 175 0.3645 + 1.0588i 176 0.5100 + 0.5878i 177 0.5100 + 0.6696i 178 0.4361 + 0.5878i 179 0.4361 + 0.6696i 180 0.5100 + 0.8497i 181 0.5100 + 0.7566i 182 0.4361 + 0.8497i 183 0.4361 + 0.7566i 184 0.2957 + 0.5878i 185 0.2957 + 0.6696i 186 0.3645 + 0.5878i 187 0.3645 + 0.6696i 188 0.2957 + 0.8497i 189 0.2957 + 0.7566i 190 0.3645 + 0.8497i 191 0.3645 + 0.7566i 192 0.0325 + 0.0325i 193 0.0325 + 0.0967i 194 0.0967 + 0.0325i 195 0.0967 + 0.0967i 196 0.0325 + 0.2280i 197 0.0325 + 0.1623i 198 0.0967 + 0.2280i 199 0.0967 + 0.1623i 200 0.2280 + 0.0325i 201 0.2280 + 0.0967i 202 0.1623 + 0.0325i 203 0.1623 + 0.0967i 204 0.2280 + 0.2280i 205 0.2280 + 0.1623i 206 0.1623 + 0.2280i 207 0.1623 + 0.1623i 208 0.0325 + 0.5100i 209 0.0325 + 0.4361i 210 0.0967 + 0.5100i 211 0.0967 + 0.4361i 212 0.0325 + 0.2957i 213 0.0325 + 0.3645i 214 0.0967 + 0.2957i 215 0.0967 + 0.3645i 216 0.2280 + 0.5100i 217 0.2280 + 0.4361i 218 0.1623 + 0.5100i 219 0.1623 + 0.4361i 220 0.2280 + 0.2957i 221 0.2280 + 0.3645i 222 0.1623 + 0.2957i 223 0.1623 + 0.3645i 224 0.5100 + 0.0325i 225 0.5100 + 0.0967i 226 0.4361 + 0.0325i 227 0.4361 + 0.0967i 228 0.5100 + 0.2280i 229 0.5100 + 0.1623i 230 0.4361 + 0.2280i 231 0.4361 + 0.1623i 232 0.2957 + 0.0325i 233 0.2957 + 0.0967i 234 0.3645 + 0.0325i 235 0.3645 + 0.0967i 236 0.2957 + 0.2280i 237 0.2957 + 0.1623i 238 0.3645 + 0.2280i 239 0.3645 + 0.1623i 240 0.5100 + 0.5100i 241 0.5100 + 0.4361i 242 0.4361 + 0.5100i 243 0.4361 + 0.4361i 244 0.5100 + 0.2957i 245 0.5100 + 0.3645i 246 0.4361 + 0.2957i 247 0.4361 + 0.3645i 248 0.2957 + 0.5100i 249 0.2957 + 0.4361i 250 0.3645 + 0.5100i 251 0.3645 + 0.4361i 252 0.2957 + 0.2957i 253 0.2957 + 0.3645i 254 0.3645 + 0.2957i 255 0.3645 + 0.3645i 256 1.3184 1.3184i

TABLE-US-LTS-00001 LENGTHY TABLES The patent application contains a lengthy table section. A copy of the table is available in electronic form from the USPTO web site (). An electronic copy of the table will also be available from the USPTO upon request and payment of the fee set forth in 37 CFR 1.19(b)(3).