CN112104587A - 64QAM signal soft demodulation simplified algorithm - Google Patents
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0045—Arrangements at the receiver end
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
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- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/38—Demodulator circuits; Receiver circuits
Abstract
The invention provides a 64QAM signal soft demodulation simplification algorithm, which is combined with a 64QAM constellation mapping chart to obtain an LLR (log likelihood ratio) of a Q path of a first bit of a symbol; only Q paths are calculated when LLRs of the first three bits of the 64QAM modulation symbol are calculated, and only I paths are calculated when LLRs of the last three bits are calculated. When calculating the LLR of the 64QAM modulation symbol, the method only needs to carry out addition and subtraction and logical judgment operations without addition operation, greatly reduces the operation amount, has certain advantages in the aspect of saving operation resources, has very small performance loss and has higher practical value.
Description
Technical Field
The invention belongs to the field of wireless communication and digital signal processing, and particularly relates to a soft demodulation simplified algorithm design of a high-order modulation signal.
Background
In the present day with the development of multimedia communication, under the condition that the transmission bandwidth is limited and the transmission power is constant, how to improve the spectrum utilization rate in a high-rate transmission system is a hot point of research in the field of modern wireless communication. The high-order quadrature amplitude modulation (mQAM) with the characteristic of high spectrum utilization rate can relieve the current situation of shortage of spectrum resources and realize the high-efficiency transmission of multimedia integrated services. Therefore, the mQAM modulation technology has been widely applied to the fields of digital television networks for high-speed data transmission, satellite communication, VDSL, digital microwave systems, and the like, and the TDS-OFDM terrestrial digital television broadcasting standard in China also adopts a 64QAM modulation mode.
The communication system adopting 64QAM modulation will certainly have a great improvement in spectrum utilization, but under the same transmission power, the high-order modulation mode will increase the error rate of the system during demodulation. In order to reduce the error rate of a system and ensure the availability of the system, the system adopts an advanced error correction code technology, and soft information decoding with higher coding gain is generally adopted for error correction codes such as Turbo codes, convolutional codes, LDPC codes and the like, so that a soft decision technology is required to be adopted to replace the traditional hard decision output during demodulation, and the method has important significance for the research of a 64QAM signal soft demodulation algorithm.
Soft demodulation of 64QAM signals typically takes log-likelihood ratios (LLRs) as the soft information output of the demodulator. Let the coordinates of the transmitted symbol A in the constellation diagram be (A)I,AQ) The received signal after passing through the AWGN channel is r ═ a + w ═ rI+jrQWherein r isI＝aI+wI，rQ＝aQ+wQA is the original signal and w is the variance σ2When the homodromous component and the orthogonal component can be regarded as random variables independent of each other, the LLR function is defined as:
the calculation of the above formula is complicated, and according to log sigma in the classical algorithmiri≈maxilogriBy substituting the above formula into
Completion calculationAnd (4) optimizing the method.
Although the existing classic algorithm for soft demodulation of 64QAM signals has better performance, the following defects still exist:
1. all constellation points still need to be searched for soft decision information operation of each bit of 64QAM symbols, so that the overall operation amount is still large, and high requirements on hardware resources are met in the implementation.
2. The soft decision information operation has a large amount of multiplication operation, the operation amount is large and complex, the hardware multiplier has higher requirements, and the algorithm is not easy to realize.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a soft demodulation simplified algorithm aiming at 64QAM signals, simplifies and improves the traditional 64QAM soft demodulation classical algorithm, and provides a method for further reducing the overall operation amount by combining the characteristics of a constellation distribution structure of the 64QAM signals. Compared with a 64QAM soft demodulation classical algorithm, the method can greatly reduce the operation amount of the demodulator under the condition of ensuring that the system performance loss is extremely low.
The technical scheme adopted by the invention for solving the technical problem comprises the following steps: the LLR calculation formula of the Q path for obtaining the first bit of the symbol by combining the 64QAM constellation mapping chart is
Wherein r isQThe orthogonal component of the received signal after the original signal a passes through an AWGN channel; only Q paths are calculated when LLRs of the first three bits of the 64QAM modulation symbol are calculated, and only I paths are calculated when LLRs of the last three bits are calculated.
In the LLR calculation, let x1＝min{(rQ+7a),(rQ+5a),(rQ+3a),(rQ+a)}，
x0＝min{(rQ-7a),(rQ-5a),(rQ-3a),(rQ-a)}，
Then there is LLR ═ x1-x0)(x1+x0) Simplifying the calculation to LLR ≈ x1-x0) Only the symbols on the coordinate axes need to be considered in calculationThe distance of the projection from the constellation point projection.
The LLR calculation adopts logic judgment to replace the calculation of solving the minimum value, the whole space is divided into a plurality of judgment domains by taking the position of each constellation point as the center and the perpendicular bisector of the connecting line of adjacent constellation points as the boundary according to the Euclidean space distribution of a 64QAM constellation, and the corresponding logic judgment condition is obtained according to the distribution of the value of each bit in the constellation diagram, thereby completing the soft-decision demodulation of the symbol.
The invention has the beneficial effects that: when calculating the LLR of the 64QAM modulation symbol, only addition and subtraction and logical judgment operations are needed, and addition operation is not needed, so that the operation amount is greatly reduced, certain advantages are realized in the aspect of saving operation resources, and meanwhile, the performance loss is very small, and the practical value is higher.
Drawings
Fig. 1 is a flow chart of the 64QAM modulation soft demodulation algorithm of the present invention.
Fig. 2 is a 64QAM modulation constellation distribution diagram.
FIG. 3 is a 64QAM modulation constellation decision domain division diagram of the present invention
FIG. 4 is a graph showing the comparison of the performance of the 64QAM modulation soft demodulation algorithm and the classic soft demodulation algorithm cascaded 3/4LDPC code.
Detailed Description
The present invention will be further described with reference to the following drawings and examples, which include, but are not limited to, the following examples.
The technical scheme and steps adopted by the embodiment of the invention comprise:
1. according to the simplified algorithm formula, the calculation formula of the LLR of the Q path of the first bit of the symbol obtained by combining the 64QAM constellation map is as follows:
let x1＝min{(rQ+7a),(rQ+5a),(rQ+3a),(rQ+a)}，x0＝min{(rQ-7a),(rQ-5a),(rQ-3a),(rQA) } thenLLR＝(x1-x0)(x1+x0). Wherein (x)1-x0) The sign of LLR is determined, (x)1+x0) Is an amplification factor and has small influence on the judgment result. The calculation can be simplified to LLR ≈ (x)1-x0) And the calculation only needs to consider the distance between the projection of the symbol on the coordinate axis and the projection of the constellation point.
2. According to the 64QAM constellation mapping chart, the change of the first three bits of the symbol is only related to the value of the Q path, and the change of the last three bits is only related to the value of the I path, so that only the Q path needs to be calculated when the LLRs of the first three bits of the 64QAM modulation symbol are calculated, and only the I path needs to be calculated when the LLRs of the last three bits are calculated. The improved simplified algorithm formula of the LLR for obtaining the first bit to the sixth bit of the 64QAM modulation symbol is as follows:
LLR(r1)＝min{(rQ+7a),(rQ+5a),(rQ+3a),(rQ+a)}-min{(rQ-7a),(rQ-5a),(rQ-3a),(rQ-a)}
LLR(r2)＝min{(rQ+3a),(rQ+a),(rQ-a),(rQ-3a)}-min{(rQ-7a),(rQ-5a),(rQ+5a),(rQ+7a)}
LLR(r3)＝min{(rQ+5a),(rQ+3a),(rQ-3a),(rQ-5a)}-min{(rQ-7a),(rQ-a),(rQ+a),(rQ+7a)}
LLR(r4)＝min{(rI+7a),(rI+5a),(rI+3a),(rI+a)}-min{(rI-7a),(rI-5a),(rI-3a),(rI-a)}
LLR(r5)＝min{(rI+3a),(rI+a),(rI-a),(rI-3a)}-min{(rI-7a),(rI-5a),(rI+5a),(rI+7a)}
LLR(r6)＝min{(rI+5a),(rI+3a),(rI-3a),(rI-5a)}-min{(rI-7a),(rI-a),(rI+a),(rI+7a)}
wherein r isQModulating the quadrature component of the symbol for 64QAM, where rIThe in-phase component of the symbol is modulated by 64 QAM.
3. And the calculation of solving the minimum value is replaced by logic judgment, so that the operation amount can be further reduced, and the hardware realization of the module is easy. According to the Euclidean spatial distribution of 64QAM constellations, the whole space is divided into a plurality of judgment domains by combining the vector corresponding to each constellation. Since the first three bits change only with respect to the Q-way value and the last three bits change only with respect to the I-way value in the 64QAM constellation mapping. The LLR calculation formula for the first bit of the symbol is:
then LLR (r)1)＝x1,1-x1,0Wherein r isQThe quadrature component of the 64QAM modulation symbol.
The LLR calculation formula of the second bit can be obtained in the same way:
obtaining LLR (r)2)＝x2,1-x2,0。
LLR calculation formula of the third bit:
obtaining LLR (r)3)＝x3,1-x3,0。
LLR calculation formula of the fourth bit:
then LLR (r)4)＝x4,1-x4,0Wherein r isIThe in-phase component of the symbol is modulated by 64 QAM.
LLR calculation formula of the fifth bit:
obtaining LLR (r)5)＝x5,1-x5,0。
LLR calculation formula of the sixth bit:
obtaining LLR (r)6)＝x6,1-x6,0And completing soft demodulation of 64QAM symbols.
When the algorithm of the invention is used for calculating the LLR of the 64QAM modulation symbol, only addition and subtraction and logical judgment operation are needed, multiplication operation is not needed, and the operation amount is greatly reduced. The operations required to compute the LLR for each bit include: and 6 logical judgments and 3 additions are performed at most, so that the total operation amount of each symbol is 6 × 6-36 logical judgments and 3 × 6-18 additions, the operation resources and the operation amount are optimized, and the method is suitable for hardware implementation.
Table 1 soft demodulation algorithm calculated quantity comparison
The method has the advantages that the performance of the algorithm is very close to that of the classical algorithm, the operation amount is greatly reduced, and the method has higher practical value.
Claims (3)
1. A simplified algorithm for soft demodulation of 64QAM signals, comprising the steps of: the LLR calculation formula of the Q path for the first bit of the symbol obtained by combining the 64QAM constellation map is:
wherein r isQThe orthogonal component of the received signal after the original signal a passes through an AWGN channel; only Q paths are calculated when LLRs of the first three bits of the 64QAM modulation symbol are calculated, and only I paths are calculated when LLRs of the last three bits are calculated.
2. The simplified algorithm for soft demodulation of a 64QAM signal according to claim 1, wherein: in the LLR calculation, let x1＝min{(rQ+7a),(rQ+5a),(rQ+3a),(rQ+a)}，
x0＝min{(rQ-7a),(rQ-5a),(rQ-3a),(rQ-a)}，
Then there is LLR ═ x1-x0)(x1+x0) Simplifying the calculation to LLR ≈ x1-x0) And the calculation only needs to consider the distance between the projection of the symbol on the coordinate axis and the projection of the constellation point.
3. The simplified algorithm for soft demodulation of a 64QAM signal according to claim 1, wherein: the LLR calculation adopts logic judgment to replace the calculation of solving the minimum value, the whole space is divided into a plurality of judgment domains by taking the position of each constellation point as the center and the perpendicular bisector of the connecting line of adjacent constellation points as the boundary according to the Euclidean space distribution of a 64QAM constellation, and the corresponding logic judgment condition is obtained according to the distribution of the value of each bit in the constellation diagram, thereby completing the soft-decision demodulation of the symbol.
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| CN114285524A (en) * | 2021-12-24 | 2022-04-05 | 北京中科晶上科技股份有限公司 | LLR vector quantization calculation method, device and communication system |
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| CN114285524A (en) * | 2021-12-24 | 2022-04-05 | 北京中科晶上科技股份有限公司 | LLR vector quantization calculation method, device and communication system |
| CN114285524B (en) * | 2021-12-24 | 2024-01-23 | 北京中科晶上科技股份有限公司 | LLR vector quantization calculation method, device and communication system |
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