CN103166903B  The soft solution preprocess method of constellation mapping and soft solution method  Google Patents
The soft solution preprocess method of constellation mapping and soft solution method Download PDFInfo
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 CN103166903B CN103166903B CN201310088740.0A CN201310088740A CN103166903B CN 103166903 B CN103166903 B CN 103166903B CN 201310088740 A CN201310088740 A CN 201310088740A CN 103166903 B CN103166903 B CN 103166903B
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Abstract
Description
Technical field
The present invention relates to the digital information communications field, particularly relate to a kind of soft solution preprocess method of constellation mapping and soft solution method.
Background technology
The soft solution method of constellation mapping the most frequently used at present comprises the following steps:
Step 1: receive information symbol;
Step 2: according to each constellation point in bit each in information symbol and signal space, ask for loglikelihood ratio by formula (2), this method is called MaxLogMAP algorithm;
Loglikelihood ratio LLR(LogLikelihood Ratio) be usually used in the Soft Inform ation of each bit in expressing information symbol;
For certain bit b, its loglikelihood ratio is defined as:
The symbology of the loglikelihood ratio the obtained court verdict of this bit, the absolute value of the value of loglikelihood ratio is the confidence level of this result, then completes soft demapping after obtaining loglikelihood ratio.
Such as, in additive white Gaussian noise AWGN (Additive White Gaussian Noise) channel model, mapping exponent number is that namely M comprises in the planisphere of M constellation point:
Wherein G _{i}for the channel fading of ith information symbol obtained before demapping estimates (i.e. channel condition information); For ith receiving symbol yi; represent that a kth bit is the set of the constellation symbols (i.e. constellation point) of 1, represent that a kth bit is the set of the constellation symbols of 0.
From the foregoing, the loglikelihood ratio of each bit in information symbol is asked for according to MaxLogMAP method, then need the computing of O (M) subaddition, O (M) secondary multiplying and O (MlogM) secondary compare operation, therefore known for map in planisphere exponent number M value larger time, amount of calculation is large, thus the system resource consumed is many, hardwired cost is large.
Summary of the invention
(1) technical problem that will solve
The present invention aims to provide a kind of loglikelihood calculations amount, computing time and minimizing system resource of reducing and takies, reduces the soft solution preprocess method of the constellation mapping of hardware implementation cost and soft solution method.
(2) technical scheme
For solving the problem, the soft solution preprocess method of constellation mapping of the present invention comprises the following steps:
According to adopted constellation mapping, the signal space including M constellation point is divided into N number of region;
Build table B, in table B, record the constellation point set S for loglikelihood calculations in the i of region _{i}; I is the integer being not more than N;
Wherein,
Described S _{i}comprise constellation point subset and constellation point subset
Described comprise kth bit and be 0 and the constellation point nearest with preset in the i of region;
Described comprise kth bit and be 1 and the constellation point nearest with preset in the i of region;
Described k is for being not more than log _{2}the positive integer of M.
Further, in the soft solution preprocess method of described constellation mapping, according to constellation mapping, Region dividing and performance requirement, one or more preset is set in the i of region.
Further, described constellation point set S _{i}interior constellation point is calculated by Monte Carlo EGS4 method or greedy algorithm and asks for.
Further, described table B is stored in random access storage device, readonly memory or combinational logic circuit.
For solving the problem, the soft solution method of constellation mapping of the present invention, for after the preliminary treatment that the soft solution preprocess method of abovementioned constellation mapping carries out, comprises the following steps:
Receive information symbol, the region i belonging to determination information symbol;
Region i from table B belonging to obtaining information symbol is used for the constellation point set S of loglikelihood calculations _{i}, and press presetting method to information symbol and S _{i}in constellation point carry out loglikelihood calculations.
Preferably, described presetting method is for passing through formula
Wherein, LLR is loglikelihood ratio; b _{k}for a kth bit of information symbol, and k is for being not more than log _{2}the positive integer of M.
Preferably, by region that hard decision method determination information symbol belongs to.
Preferably, also comprise and utilize channel condition information to be normalized described information symbol receiving after information symbol with before the region judged belonging to described information symbol, thus obtain normalization information symbol.
(3) beneficial effect of the present invention
By repeatedly studying and verifying in the soft solution preocess of discovery constellation mapping, be usually located at the information symbol of close positions in signal space, when carrying out the loglikelihood calculations of each bit, tagmeme same with it be 0 or 1 the nearest point of constellation point middle distance concentrate on some specific position of signal space, and in traditional MaxLogMAP method, when the loglikelihood ratio computing carrying out each bit in information symbol, what do not add screening carries out computing with all constellation point;
The soft solution preprocess method of constellation mapping of the present invention is then utilize abovementioned rule, abovementioned special point is screened, and the soft solution method of constellation mapping of the present invention, it is then the computing that the result utilizing the soft solution preprocess method of constellation mapping of the present invention to solve carries out loglikelihood ratio, thus greatly reduce operand, decrease taking of system resource, reduce hardwired cost, especially for mapping the large constellation mapping of exponent number, soft solution effect is especially obvious.
Accompanying drawing explanation
Fig. 1 is the signal space schematic diagram described in the embodiment of the present invention one;
The soft solution method flow diagram that Fig. 2 is the constellation mapping described in second embodiment of the invention;
Fig. 3 is the signal space schematic diagram described in fourth embodiment of the invention;
Fig. 4 is the schematic diagram after the signal space described in Fig. 3 is divided into multiple region;
Fig. 5 is soft solution method and traditional MaxLogMAP method performance comparison figure under awgn channel of constellation mapping described in fourth embodiment of the invention;
Fig. 6 is soft solution method and traditional MaxLogMAP method performance comparison figure under i.i.d.Rayleigh channel of constellation mapping described in fourth embodiment of the invention.
Embodiment
Below in conjunction with Figure of description and embodiment to the soft solution preprocess method of constellation mapping of the present invention to be described further.
Embodiment one:
As shown in Figure 1, the soft solution preprocess method of the present embodiment constellation mapping comprises the following steps:
According to adopted constellation mapping, the signal space including 16 constellation point is divided into 4 regions; Each region all distinguishes with different shades, and the digitized representation of each regional center numbering in region, wherein comprises 4 constellation point in each region; Each information symbol comprises 4 bits;
Build table B; The constellation point set S for loglikelihood calculations in the i of region is recorded in table B _{i}; I be not more than 4 integer and i be 1,2,3 or 4; Concrete region 1 as shown in Figure 1, region 2, region 3 and region 4;
Wherein,
Described S _{i}comprise constellation point subset and constellation point subset
Described contain kth bit be 0 and with preset in the i of regionthe nearest constellation point of some p;
Described contain kth bit be 1 and with preset in the i of regionthe nearest constellation point of some p;
Described k is for being not more than log _{2}the positive integer of M, can be less than or equal to 4;
Build table B; The constellation point set of each region for loglikelihood calculations is recorded in table B;
As in region 1, when preset is one and is the central point in region 1, constellation point set includes the constellation point subset that highorder first bit is 0 and highorder first bit is the constellation point subset of 1 therefore in computational process, information symbol only needs to be that 4 constellation point of 0 and 2 constellation point of highorder first bit 1 carry out computing with highorder first bit, relative to traditional MaxLogMAP method and highorder first bit be 08 constellation point and highorder first bit be 18 constellation point carry out computing, save operand, reduce the consumption of system resource, hardware implementation cost is lower.
And in traditional MaxLogMAP method, there is no the soft solution preprocessing process of constellation mapping, wherein computing each time included M/2 and information symbol with tagmeme be 0 or be 1 constellation point calculate; And the soft solution preprocess method of the present embodiment constellation mapping, first confirmed the nearest point that may occur in followup loglikelihood calculations by preliminary treatment, not only reduce the multiplication between information symbol and constellation point and add operation; Also reduce comparison operation, be applied in effect of optimization in the soft solution preocess of the constellation mapping of highorder especially obvious.
In concrete implementation process, described preset is one or more according to the requirement of constellation mapping, Region dividing and performance, is distributed in the diverse location of region i; Required precision is higher, and the value of preset should be more.As in region 1, when preset comprises center and two marginal points in region 1, and described marginal point one is positioned at the central point of the edge line had a common boundary with region 2, a central point being positioned at the edge line had a common boundary with region 3; Then described constellation point set includes the constellation point subset that highorder first bit is 0 and highorder first bit is the constellation point subset of 1
As from the foregoing, the number of preset and position are all related to the composition of constellation point subset, be related to the accuracy etc. of final operation result equally, therefore in concrete implementation process, the position of preset and number decide according to Region dividing, constellation mapping and performance requirement again, when the number of preset is 1, be usually chosen for the center of constellation point in region.
In concrete implementation process, the division in region should according to different types of constellation mapping, divide the required precision of solving result and the size of operand, and the region divided is unsuitable excessive.
Embodiment two:
On the basis of a upper embodiment, provide at the soft solution preprocess method of the present embodiment constellation mapping the method that two kinds are asked for constellation point set,
Described constellation point set S _{i}interior constellation point is asked for by Monte Carlo EGS4 method or greedy algorithm computing method.
Method one: Monte Carlo EGS4 method is asked for:
Based on statistics and probability, through checking repeatedly, the described constellation point set obtained;
Method two: greedy algorithm is asked for:
A: the point in definition information mark signal space to the distance of region i,
B: then calculate and n is the nth bit of information symbol, and n is for being not more than log _{2}arrive a little the distance of region i in M (the mapping exponent number that M is planisphere), get several the shortest conducts be expressed as ith region, u is expressed as u bit of the information symbol of reception; W is 0 or 1; Wherein, the constellation point in signal space can have different definition modes to the distance of region i.Especially, when having in the i of region and only have a constellation point, can using the Euclidean distance to this point as the distance to region i.
In the present embodiment, provide in particular two kinds and obtain regional for solving the method for information symbol each bit loglikelihood ratio, have and realize advantage simply and easily.
Comprehensive abovementioned known, described constellation point concentrates the constellation point number of subsets comprised to be at most 2*log _{2}m.
At the soft solution preprocess method of the present embodiment constellation mapping, provide the method for optimizing that two kinds solve constellation point set, above two kinds of equal technology maturations of method, apply easy, thus the soft solution preprocess method of constellation mapping described in the present embodiment have use simply, feature easily.
Particularly, described table B is stored in random access storage device, readonly memory or combinational logic circuit.The number of the constellation point that described constellation point is concentrated is different from the difference of the region at place, the mode of constellation mapping and implementation, usually all much smaller than the mapping exponent number M of constellation mapping.
Below in conjunction with Figure of description and embodiment to the soft solution method of constellation mapping of the present invention to be described further.
First embodiment:
The soft solution method of the present embodiment constellation mapping, after the preliminary treatment that the soft solution preprocess method being applied to abovementioned constellation mapping carries out, comprises the following steps particularly:
Receive information symbol, the region i belonging to determination information symbol;
Region i from table B belonging to obtaining information symbol is used for the constellation point set S of loglikelihood calculations _{i}, and press presetting method to information symbol and S _{i}in constellation point carry out loglikelihood calculations.
In the soft solution method of the present embodiment constellation mapping, owing to being obtained the table B for loglikelihood calculations by the soft solution preprocess method of the constellation mapping as described in embodiment one or embodiment two, and the number of the constellation point recorded in table B, the number of the constellation point of carrying out loglikelihood calculations is needed much smaller than MaxLogMAP method, thus decrease amount of calculation, decrease taking of system resource simultaneously, reduce hardwired cost.The particularly constellation mapping of highorder, the bit number that information symbol carries is many, and constellation point in information space is also many, but concentrate on some specific position with the nearest point of arbitrfary point in the i of region, when adopting traditional MaxLogMAP method to go to calculate, carry out the calculating that much obviously can not be conducive to final result, and screened out these useless points by pretreated method in the present embodiment, thus reach the object reducing amount of calculation.
As the improvement further of the present embodiment, the soft solution method of the present embodiment constellation mapping gives the method for solving of the loglikelihood ratio of each bit in information symbol further, and concrete passes through following formula
Described presetting method is for passing through formula
Calculate the loglikelihood ratio of each bit in described information symbol;
Wherein, LLR is loglikelihood ratio; b _{k}for a kth bit of information symbol, and k is for being not more than log _{2}the positive integer of M.
As the constellation mapping on 16 rank, then each information symbol in signal space and constellation point form (as 0000,1111 etc.) by 4 bits.The constellation mapping on 256 rank, then each information symbol in signal space and star chart o'clock are by 8 bits compositions (as 00010010 etc.).
By abovementioned formula, when soft solution constellation mapping, there is directly easy advantage, the soft solution method of constellation mapping described in the present embodiment is adopted to ask for solving of the loglikelihood ratio of each bit of information symbol convenient, fast, operand is little, it is few that system takies resource, realizes cost low in concrete hardware implementing process.
Second embodiment:
As shown in Figure 2, the soft solution method of the present embodiment constellation mapping comprises the following steps:
The pretreatment step of the soft solution preprocess method realization of the constellation mapping as described in embodiment one or embodiment two;
Step S1: receive information symbol;
Step S2: utilize the information symbol of channel condition information to described reception to be normalized, thus obtain normalization information symbol.When the state of channel changes, usually need to be normalized the information symbol received according to the decay behavior of signal, thus obtain equal strong and weak information symbol so that followup process;
Step S3: judge the region i belonging to described information symbol;
Step S4: obtaining information symbol area i is used for the constellation point set of loglikelihood calculations from table B, and by presetting method, loglikelihood calculations is carried out to the constellation point that information symbol and constellation point are concentrated.
The multiple advantages such as adopt the soft solution method of the constellation mapping described in the present embodiment, the loglikelihood ratio solving each bit of information symbol obtains final soft solution result, and have amount of calculation few, system resource is few, and operation time is few.
3rd embodiment:
The soft solution method of the present embodiment constellation mapping comprises the following steps:
Step S1: receive information symbol, judgement judges the region belonging to described information symbol; In concrete implementation process, hard decision (namely comparing with the Region dividing border) region belonging to determination information symbol can be adopted; Much more no longer hard decision is the decision method being applied to decoding of technology maturation, to repeat at this;
Step S2: the region from table B belonging to obtaining information symbol is used for the constellation point set of loglikelihood calculations, and by presetting method, loglikelihood calculations is carried out to the constellation point that information symbol and constellation point are concentrated;
Wherein, show B to be obtained by the soft solution preprocess method of constellation mapping; The soft solution preprocess method of described constellation mapping comprises the following steps again:
The signal space including M constellation point is divided into N number of region according to adopted constellation mapping by S0.1;
S0.2 builds table B; The constellation point set S for loglikelihood calculations in the i of region is recorded in table B _{i}; I is the integer being not more than N;
Preferred hard decision in the present embodiment, adopt the decision method of this technology maturation, ensure that the realizability of judgement on the one hand, ensure that the simple and efficient property of realization simultaneously, adopt the table B generated in preprocessing process to carry out solving of followup loglikelihood ratio, operand is little, and result acquisition time is short simultaneously, system resource is few, and hardware implementation cost is low.
4th embodiment:
As shown in figures 3 to 6, the soft solution method of the present embodiment constellation mapping, the environment applied is, constellation mapping is the GrayAPSK(AmplitudePhase Shift Keying on 256 rank) GrayAmplitude phase shift keying; Chnnel coding adopts LDPC codethe low density parity check code Low Density Parity Check Code in DVBS2 standard; LDPC decoding algorithm adopts modified minsum algorithm, and maximum iteration time is 50 times; Transmission channel is AWGN (Additive White Gaussian Noise) channel or i.i.d.Rayleigh channelindependent Rayleigh channel;
Wherein, shown signal space annular signal space as shown in Figure 3;
First, the pretreated of the constellation mapping of carrying out arrives table B, and concrete operation is as follows:
According to adopted constellation mapping, the signal space including 256 constellation point is divided into 256 regions, the signal space after division as shown in Figure 4;
Build table B; The constellation point set S for loglikelihood calculations in the i of region is recorded in table B _{i}; I be not more than 256 integer;
Wherein,
Described S _{i}comprise constellation point subset and constellation point subset
Described contain kth bit and be 0 and the constellation point nearest with preset in the i of region;
Described contain kth bit and be 1 and the constellation point nearest with preset in the i of region; Wherein described preset is the point of constellation point position in each region in the present embodiment;
Described k is for being not more than log _{2}the positive integer of M
Receive information symbol and channel condition information;
Utilize channel condition information to be normalized information symbol, obtain the normalization information symbol after processing;
Judging the region belonging to normalization information symbol;
Region from table B belonging to obtaining information symbol is used for the constellation point set of loglikelihood calculations, and carries out loglikelihood calculations by presetting method to the constellation point that information symbol and constellation point are concentrated.
What the soft solution method of the constellation mapping described in the present embodiment was applied in the arithmetic speed of MaxLogMAP method in the communication being provided with abovementioned parameter with traditional and operand is compared as follows table:
In addition, the performance of the soft solution method of the constellation mapping described in the present embodiment is also very little relative to the difference of traditional MaxLogMAP method on error rate of system, concrete as shown in Fig. 5Fig. 6:
Fig. 5 is when transmission channel is awgn channel (Additive White Gaussian Noise) channel, the soft solution method of constellation mapping described in the present embodiment and the comparison diagram of MaxLogMAP method.
Fig. 6 is when transmission channel is i.i.d.Rayleigh channelduring independent Rayleigh channel, and the soft solution method of constellation mapping described in the present embodiment and the comparison diagram of MaxLogMAP method.
Comprehensive abovementioned known, the soft solution method of the constellation mapping described in the present embodiment, under the condition almost not having performance loss, greatly reducing the operand of the loglikelihood ratio of each bit of information symbol, especially in the constellation mapping of highorder is as the constellation mapping on 256 rank, effect is especially obvious, thus decrease the system resource taken when adjudicating in soft solution preocess, also reduce hardwired cost.
Above execution mode is only for illustration of the present invention; and be not limitation of the present invention; the those of ordinary skill of relevant technical field; without departing from the spirit and scope of the present invention; can also make a variety of changes and modification; therefore all equivalent technical schemes also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.
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