CN115296739B - SCMA assisted quick decoding method and system for visible light communication - Google Patents
SCMA assisted quick decoding method and system for visible light communication Download PDFInfo
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Abstract
The invention provides a quick decoding method and a quick decoding system for SCMA assisted visible light communication, wherein the method comprises the following steps: the sending end carries out codebook mapping on the bit signal according to a pre-constructed specific codebook to obtain a complex signal; modulating the complex signal to convert the complex signal into a positive real signal; the receiving end demodulates the received positive real number signal, and splits the horizontal dimension of the complex number received signal according to the number of the resource blocks, so as to obtain all possible bit information of each resource block according to the splitting result; and calculating all corresponding possible superposed signals, judging all the superposed signals based on the minimum Euclidean distance criterion to obtain target superposed signals, and performing parallel decoding on each resource block according to the target superposed signals to obtain signals transmitted by each user. The SCMA assisted rapid decoding method for visible light communication provided by the invention has the advantages of low complexity and good error rate performance.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a quick decoding method and system for SCMA (sparse code multiple access) assisted visible light communication.
Background
In recent years, visible Light Communication (VLC) has gradually become a traditional Radio Frequency (RF) Communication-based alternative due to advantages of free spectrum, no electromagnetic interference, easy deployment using existing lighting infrastructure, and high level of security, especially in indoor scene applications.
Meanwhile, non-Orthogonal Multiple Access (NOMA) has been a key technology for implementing a massive Machine Type Communication (mtc) system, and has been receiving more and more research attention in the past years. The main concept behind NOMA is to serve multiple users on the same resource element (frequency or time slot) using different CodeBooks (CBs) or power levels, and furthermore, more and more researchers choose to use SCMA technology in visible light communication systems to achieve the significance of everything interconnection.
However, in the 6G era with ultra-large scale connection and high-speed communication, the high-speed transmission thereof is one of the key technologies of visible light communication, so that the visible light communication becomes one of the 6G technologies, and the SCMA assisted visible light communication will face the difficulty of how to further increase the transmission speed of visible light communication under the condition that the bandwidth of the LED is limited, that is, the difficulty of how to decode quickly and efficiently when the modulation order is larger. The problem of high power consumption of a receiving end is caused by the fact that the SCMA assisted visible light communication is inevitably high in detection complexity at the receiving end, and the problem is more prominent when high-speed communication is oriented.
Aiming at the problem of high complexity caused by detection of an MPA decoding algorithm at a VLC-SCMA receiving end, people provide a plurality of improved MPA algorithms, such as an MPA algorithm based on a log domain, an MPA decoding algorithm based on a serial mode, an MPA decoding algorithm based on partial code words and other algorithms for reducing the MPA decoding complexity, and can find that the algorithms are only slightly improved on the basis of the original MPA decoding algorithm and do not provide a new decoding strategy different from the MPA. Meanwhile, researchers also propose that successive interference cancellation technology is utilized in an SCMA system to reduce the decoding complexity of the SCMA system, however, the drawback of the successive interference cancellation technology is not negligible, firstly, compared with the traditional SIC receiver, the SIC receiver adopted in NOMA is more complex and requires stronger signal processing capability; secondly, it can be known from the above process that the best receiving effect is determined according to the user sequence of the signal power rows, and in the actual process, the power of the user is constantly changed, which requires the SIC receiver to constantly sequence the user power; thirdly, as can be seen from the SIC structure diagram, each stage of processing will generate a certain time delay, and the generated time delay is very large in the actual multi-stage processing process.
Therefore, how to design a detection method aiming at low complexity of high-speed communication without losing decoding accuracy is a major problem currently faced.
Disclosure of Invention
Based on this, the present invention provides a fast decoding method and system for SCMA assisted visible light communication, which aims to solve the problem that the existing decoding algorithm cannot achieve both low complexity and good detection performance, and meanwhile, the present invention has good applicability for VLC-SCMA system detection with larger overload rate and higher order.
According to the fast decoding method for SCMA assisted visible light communication provided by the invention, the method comprises the following steps:
a sending end acquires bit signals of a plurality of users, and performs codebook mapping on the bit signals according to a pre-constructed specific codebook so as to perform signal superposition on the bit signals to obtain a complex signal;
carrying out ACO-OFDM modulation on the complex signal to convert the complex signal into a positive real signal, carrying out channel gain on the positive real signal and transmitting the positive real signal to a receiving end;
the receiving end carries out ACO-OFDM demodulation on the received positive real number signal so as to convert the positive real number signal into a complex number receiving signal, and carries out transverse dimension splitting on the complex number receiving signal according to the number of resource blocks so as to obtain all bit information possibly existing in each resource block according to splitting results;
and calculating all corresponding possible superposed signals according to all bit information possibly existing on each resource block, judging all the superposed signals based on a minimum Euclidean distance criterion so as to obtain target superposed signals corresponding to the minimum Euclidean distance according to a judgment result, and performing parallel decoding on each resource block according to the target superposed signals so as to obtain signals transmitted by each user.
Further, the step of acquiring bit signals of multiple users by the transmitting end, and performing codebook mapping on the bit signals according to a pre-constructed specific codebook to perform signal superposition on the bit signals to obtain a complex signal includes:
acquiring an overload rate target value according to the requirement of an actual application scene, and setting the corresponding size of a codebook, the maximum bearing quantity of users, the number of resource blocks and the number of overloaded users of each resource block according to the overload rate target value;
defining a mother constellation structure in the specific codebook as a row matrix, wherein the row matrix comprises two characters with mutually opposite numbers, and setting the number of the characters in the row matrix according to the size of the codebook;
and performing rotation operation and power distribution on the mother constellation structure according to the number of overloaded users of each resource block to construct and obtain a factor matrix corresponding to each resource block.
Further, the step of performing ACO-OFDM demodulation on the received positive real signal by the receiving end to convert the positive real signal into a complex received signal includes:
receiving the positive real signal according to the following formula:
Y=HX+n
wherein Y represents a received signal, X represents a positive real signal, H represents a visible light channel gain, and n represents gaussian noise;
and the receiving end carries out ACO-OFDM demodulation on the received signal so as to convert the positive real number signal into a complex number receiving signal.
Further, the step of splitting the plurality of received signals in the horizontal dimension according to the number of resource blocks to obtain all bit information that may exist in each resource block according to the splitting result includes:
splitting the plural received signals bit by bit according to the specific codebook, and performing codebook mapping on bit information obtained after splitting to convert the plural received signals into single-bit information;
acquiring a user index occupying each resource block according to the factor matrix so as to obtain all user numbers occupied on each resource block;
and listing all possible combinations of bit sequences of the users occupying each resource block according to all the user numbers occupied on each resource block and all the obtained single-bit information.
Further, the step of calculating all possible superposed signals according to all bit information that may exist on each resource block, and determining all the superposed signals based on the minimum euclidean distance criterion to obtain a target superposed signal corresponding to the minimum euclidean distance according to the determination result, and performing parallel decoding on each resource block according to the target superposed signal to obtain a signal transmitted by each user includes:
respectively calculating superposed code words corresponding to the bit sequences one by one according to the combination of all the bit sequences possibly existing in each user, wherein each bit sequence and the superposed code word corresponding to the bit sequence have a unique interpretable principle;
and calculating Euclidean distances between each superposed code word and the complex received signals according to the superposed code words possibly existing in each resource block and the complex received signals, and screening out a minimum Euclidean distance from all the obtained Euclidean distances so as to lock a target superposed code word corresponding to the minimum Euclidean distance.
Further, the step of calculating all possible superposed signals according to all bit information that may exist on each resource block, and determining all the superposed signals based on the minimum euclidean distance criterion to obtain a target superposed signal corresponding to the minimum euclidean distance according to the determination result, and performing parallel decoding on each resource block according to the target superposed signal to obtain a signal transmitted by each user further includes:
and acquiring a target bit sequence corresponding to the target superposition code word based on the unique interpretable principle, and decoding the target bit sequence corresponding to each resource block in parallel according to decoders respectively preset on each resource block.
Further, the step of calculating the euclidean distances between each kind of superimposed codeword and the complex received signals according to the superimposed codewords that may exist in each resource block and the complex received signals includes:
calculating the Euclidean distance according to the following formula:
wherein | represents solving Euclidean distance, min represents retrieving the minimum value of all Euclidean distances, y k And representing the kth dimension signal in the complex number receiving signals, s (j) representing the superposition code word mapped corresponding to the jth group of bit sequences, and m representing the position of the decoded target superposition code word for retrieving the target superposition code word.
Further, the step of obtaining the user index occupying each resource block according to the factor matrix to obtain all the user numbers occupied on each resource block includes:
indexing is performed according to the following formula:
wherein, U (:, k) is the user number occupied on the resource block k, find represents the find matlab function, and F represents the factor matrix.
Further, a k-dimension signal of the complex received signals is obtained according to the following formula:
y k =Hx k +n
wherein x is k Superimposed signal, y, representing df users on the kth resource block k A k-dimensional signal representing a complex received signal, df representing the number of users on a k-th resource block, H representing a visible light channel gain, and n representing GaussNoise.
According to the embodiment of the invention, the SCMA assisted rapid decoding system for visible light communication comprises a transmitting end and a receiving end, wherein:
the transmitting end comprises:
the codebook mapping module is used for acquiring bit signals of a plurality of users and performing codebook mapping on the bit signals according to a pre-constructed specific codebook so as to perform signal superposition on the bit signals to obtain complex signals;
the signal modulation module is used for carrying out ACO-OFDM modulation on the complex signal so as to convert the complex signal into a positive real signal, carrying out channel gain on the positive real signal and transmitting the positive real signal to a receiving end;
the receiving end includes:
the signal demodulation module is used for carrying out ACO-OFDM demodulation on the received positive real number signal so as to convert the positive real number signal into a complex number receiving signal, carrying out transverse dimension splitting on the complex number receiving signal according to the number of the resource blocks and obtaining all bit information possibly existing in each resource block according to a splitting result;
and the parallel decoding module is used for calculating all corresponding possible superposed signals according to all bit information possibly existing on each resource block, judging all the superposed signals based on the minimum Euclidean distance criterion so as to obtain target superposed signals corresponding to the minimum Euclidean distance according to the judgment result, and decoding each resource block in parallel according to the target superposed signals so as to obtain signals transmitted by each user.
Compared with the prior art: the signal of the transmitting terminal is split through a specific codebook structure, the signal and the code word of the transmitting terminal are split and recombined according to the characteristic that the codebook is splittable, and the sequence and the superposed signal after the code word recombination are set to be unique and interpretable, so that the decoding of the received signal is completed, and the method has the advantages of low complexity and good error rate performance. The method specifically comprises the following steps: the method comprises the steps that a sending end firstly carries out codebook mapping on bit signals of a plurality of users through a completely new specific codebook, so that the bit signals are superposed to obtain complex signals, then the complex signals are respectively subjected to modulation conversion and channel gain, then positive real number signals with signal gain completed are sent to a receiving end, the receiving end correspondingly demodulates the received positive real number signals, then the complex received signals obtained after demodulation are subjected to transverse dimension splitting to obtain all possible bit information of each resource block, then all possible superposed signals are calculated according to all the bit information, then all the possible superposed signals are judged based on a minimum Euclidean distance criterion to obtain target superposed signals, and then each resource block is parallelly decoded according to the target superposed signals, so that the signals sent by each user are decoded, the whole decoding process is simple, and meanwhile, the method has good applicability to VLC-SCMA system detection with larger overload rate and higher order.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
Fig. 1 is a flowchart of a fast decoding method for SCMA assisted visible light communication according to a first embodiment of the present invention;
fig. 2 is a flowchart of a second embodiment of a fast decoding method for SCMA assisted visible light communication according to the present invention;
FIG. 3 is a codebook splitting mapping parser in a second embodiment of the present invention;
FIG. 4 is a graph showing the comparison of the bit error rate performance of the same codebook at 150% in the second embodiment of the present invention;
fig. 5 is a schematic structural diagram of a SCMA assisted fast decoding system for visible light communication according to a third embodiment of the present invention.
The following detailed description will further illustrate the invention in conjunction with the above-described figures.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Several embodiments of the invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
Referring to fig. 1, a flowchart of a SCMA assisted fast decoding method for visible light communication according to a first embodiment of the present invention is shown, the method includes steps S01 to S04, wherein:
step S01: a sending end acquires bit signals of a plurality of users, and performs codebook mapping on the bit signals according to a pre-constructed specific codebook so as to perform signal superposition on the bit signals to obtain complex signals;
it should be noted that the specific codebook is pre-stored in the sending end and the receiving end before signal transmission, and when the sending end acquires the bit signals of each user, the bit signals are mapped through the specific codebook, so that a plurality of bit signals are superposed to obtain the complex signal, which includes two parts, namely a real number signal and an imaginary number signal.
Step S02: carrying out ACO-OFDM modulation on the complex signal to convert the complex signal into a positive real signal, carrying out channel gain on the positive real signal and transmitting the positive real signal to a receiving end;
it is to be understood that in this step, the channel gain generally refers to the direct gain to the visible light channel.
Step S03: the receiving end carries out ACO-OFDM demodulation on the received positive real number signal so as to convert the positive real number signal into a complex number receiving signal, and carries out transverse dimension splitting on the complex number receiving signal according to the number of the resource blocks so as to obtain all bit information possibly existing in each resource block according to a splitting result;
specifically, the positive real signal is received according to the following formula:
Y=HX+n
wherein, Y represents a received signal, X represents a positive real number signal, H represents a visible light channel gain, and n represents Gaussian noise;
and the receiving end carries out ACO-OFDM demodulation on the received signal so as to convert the positive real number signal into a complex number receiving signal.
Further, in order to reduce the complexity of the decoding algorithm, the obtained complex received signals need to be split in the horizontal dimension according to the number of resource blocks, and then decoding is performed according to each resource block dimension, which needs to be described that each resource block dimension corresponds to a plurality of possible bit information.
Step S04: and calculating all corresponding possible superposed signals according to all bit information possibly existing on each resource block, judging all the superposed signals based on a minimum Euclidean distance criterion so as to obtain target superposed signals corresponding to the minimum Euclidean distance according to a judgment result, and performing parallel decoding on each resource block according to the target superposed signals so as to obtain signals transmitted by each user.
It can be understood that, in order to lock the bit information corresponding to each resource block, first, the superposed signal on the resource block needs to be calculated according to all the bit information that may exist, and the superposed signal is a transmission signal occupying all users on the resource block, and then the superposed signal is subjected to minimum euclidean distance determination, so as to obtain a target superposed signal corresponding to the minimum euclidean distance, it should be noted that each resource block has multiple possible bit information, and therefore, multiple superposed signals are calculated corresponding to each resource block, and then the target superposed signal that matches the resource block is locked, and then the corresponding target bit information is found according to the target superposed signal, so as to decode the target bit information corresponding to all the resource blocks in parallel, and further obtain the signal transmitted by each user, and then complete the whole decoding operation, the complexity of the whole decoding process is low, and the error rate is low.
In summary, according to the SCMA assisted fast decoding method for visible light communication, the signal at the transmitting end is split through a specific codebook structure, the signal and the codeword at the transmitting end are split and recombined according to the characteristic that the codebook is split, and the sequence and the superposed signal after the codeword recombination are set to be unique and translatable, so as to complete decoding of the received signal, and the method has the advantages of low complexity and good error rate performance. The method comprises the following specific steps: the method comprises the steps that a sending end firstly carries out codebook mapping on bit signals of a plurality of users through a completely new specific codebook, so that the bit signals are superposed to obtain complex signals, then the complex signals are respectively subjected to modulation conversion and channel gain, then positive real number signals with signal gain completed are sent to a receiving end, the receiving end correspondingly demodulates the received positive real number signals, then the complex received signals obtained after demodulation are subjected to transverse dimension splitting to obtain all possible bit information of each resource block, then all possible superposed signals are calculated according to all the bit information, then all the possible superposed signals are judged based on a minimum Euclidean distance criterion to obtain target superposed signals, and then each resource block is parallelly decoded according to the target superposed signals, so that the signals sent by each user are decoded, the whole decoding process is simple, and meanwhile, the method has good applicability to VLC-SCMA system detection with larger overload rate and higher order.
Referring to fig. 2, a flowchart of a SCMA assisted fast decoding method for visible light communication according to a second embodiment of the present invention is shown, the method includes steps S101 to S108, wherein:
step S101: a sending end acquires bit signals of a plurality of users, and performs codebook mapping on the bit signals according to a pre-constructed specific codebook so as to perform signal superposition on the bit signals to obtain complex signals;
it should be noted that, in this embodiment, the step of constructing the specific codebook specifically includes:
acquiring an overload rate target value according to the requirement of an actual application scene, and setting the corresponding size of a codebook, the maximum bearing quantity of users, the number of resource blocks and the number of overloaded users of each resource block according to the overload rate target value;
defining a mother constellation structure in the specific codebook as a row matrix, wherein the row matrix comprises two characters which are opposite numbers, and setting the number of the characters in the row matrix according to the size of the codebook, specifically, the number of each character is the arithmetic square root of the size of the codebook;
and performing rotation operation and power distribution on the mother constellation structure according to the number of the overloaded users of each resource block to construct and obtain a factor matrix corresponding to each resource block, wherein the rotation operation times are the same as the number of users borne by each resource block.
By way of example and not limitation, taking M =4, j =6, k =4, df =3 as an example, the mother constellation structure is designed as follows:
wherein A represents character, and then the rotation operation and power distribution are carried out to the mother constellation, wherein the rotation operation is the mother constellation multiplied by e α And α = j φ i π, where it represents the jth column of the factor matrix, φ i The rotation angle of the ith user occupying the resource block is shown, because each resource block occupies 3 users, the rotation needs to be carried out for three times, power needs to be further distributed for the 3 users, because the power of each resource block is the same as MJ/K, wherein M represents the size of a codebook, J represents the maximum user bearing quantity of all resource blocks, K represents the quantity of the resource blocks, and E represents the quantity of the resource blocks i Expressed as the power allocated to the ith user, then on one resource block, E i The sum of MJ/K, finally obtaining the one-dimensional constellation of the 3 users, and further setting the non-zero element in the factor matrix as C i ，C i That is, a one-dimensional constellation of user i is represented, and the obtained factor matrix F is as follows:
step S102: carrying out ACO-OFDM modulation on the complex signal to convert the complex signal into a positive real signal, carrying out channel gain on the positive real signal and transmitting the positive real signal to a receiving end;
and the receiving end carries out ACO-OFDM demodulation on the received signal so as to convert the positive real number signal into a complex number receiving signal.
Step S103: splitting the plural received signals bit by bit according to the specific codebook, and performing codebook mapping on bit information obtained after splitting to convert the plural received signals into single-bit information;
firstly, splitting a codebook, taking a 4 × 6 system as an example, as shown in fig. 3, for a codebook splitting mapping analysis chart in this embodiment, in general, a 2-bit signal sent by a user is mapped into a K-dimensional vector, two-bit information of each user can be further split bit by bit according to a specific codebook, a K-dimensional vector corresponding to the two-bit information can also be further split, and the split signal and a mapping codeword can be mapped bit by bit, that is, mapping of multi-bit information is converted into mapping of single-bit information.
Step S104: acquiring a user index occupying each resource block according to the factor matrix so as to obtain all user numbers occupied on each resource block;
specifically, the indexing is performed according to the following formula:
wherein, U (: k) is the user number occupied on the resource block k, find represents the find matlab function, and F represents the factor matrix.
Step S105: listing all possible combinations of bit sequences of each user occupying each resource block according to all user numbers occupied on each resource block and all obtained single bit information;
by way of example and not limitation, a user codebook structure under 4 spectrum resource blocks shared by 6 users is given to facilitate explanation of specific operations, and each user codebook structure is as follows:
wherein, CB 1 、CB 2 、CB 3 、CB 4 、CB 5 And CB 6 Each represents a codebook structure of 6 users, and a, B, and C each represent a character.
Suppose that 6 users transmit signals as follows:
further, splitting the two-bit information transmitted by each user and the code word mapped by the two-bit information, namely mapping the single-bit information into a four-dimensional code word occupying one resource block, namely splitting the two-bit information of the users on 2 resource blocks for separate transmission, wherein for the resource block 1, the overloaded user is 2,3 and 5, the code word corresponding to the user 2 when the transmission signal is 0 on the resource block 1 is A, and the code word corresponding to the user 2 when the transmission signal is 1 is-A;
further, all possible combinations of df users transmitting binary bit signals occupying each resource are listed;
for example: the possible bit sequences of users 2,3,5 are (0, 0), (0, 1), (0, 1, 0) \ 8230; \ 8230;, respectively.
Step S106: respectively calculating superposed code words corresponding to the bit sequences one by one according to the combination of all the bit sequences possibly existing in each user, wherein each bit sequence and the superposed code word corresponding to the bit sequence have a unique translatable principle;
for M =4,k =4,j =6, each user has only 2 different codewords per resource block, so there may be 2 superimposed codewords 3 In such a way that the number of possible superposed code words is 2 df And (4) seed preparation.
By way of example and not limitation, if for one of the groups of bit sequences, the sequence is (0, 0), s (1) = a + B + C, where s (1) represents 000 corresponding superposition codewords, a represents a codeword mapped when user 2 transmits 0, B represents a codeword mapped when user 3 transmits 0, C represents a codeword mapped when user 5 transmits 0, and all superposition codewords s (j) uniquely correspond to the bit sequence, for example: s (1) uniquely corresponds to the bit sequence (0, 0).
The method is characterized in that a user-specific codebook is used for increasing the difference between code words in signals transmitted by each user, namely the difference of each superposed signal is increased, for example, s (i) (0, 0) = A + B + C ≠ s (j) (0, 1) = A + B-C is very definite, namely two superposed signals which are very close to each other do not appear in the same sequence, a reliable basis is provided for the unique interpretable characteristic of the superposed code words, simultaneously, signals subjected to noise interference surround the superposed signals due to distortion but are not too far away, and further, the method adopts a minimum Euclidean distance criterion, selects to judge the signals according to the close distance, namely y k When the distance of-s (i) is minimum, the target superposition signal can be distinguished, and s (i) represents the target superposition code word.
The method has the advantages that the difference of signals transmitted by each user is increased by constructing the specific codebook, the characteristics that the bit signals transmitted by a plurality of users can be split are provided, the split signals and the split codebook are mapped, the unique translatable criterion is set, further, the receiving end splits the received complex signals according to the unique translatable criterion and the resource blocks are decoded, and the effect of reducing the complexity is achieved.
Step S107: calculating Euclidean distances between each superposed code word and the complex received signals according to the superposed code words possibly existing in each resource block and the complex received signals, and screening out a minimum Euclidean distance from all the obtained Euclidean distances so as to lock a target superposed code word corresponding to the minimum Euclidean distance according to the minimum Euclidean distance;
specifically, the euclidean distance is calculated according to the following formula:
wherein | represents solving Euclidean distance, min represents retrieving all Euclidean distancesMinimum value of (1), y k And representing the kth dimension signal in the complex number receiving signals, s (j) representing the superposition code word mapped corresponding to the jth group of bit sequences, and m representing the position of the decoded target superposition code word for retrieving the target superposition code word.
Further, a k-dimension signal of the complex received signals is obtained according to the following formula:
y k =Hx k +n
wherein x is k Superimposed signal, y, representing df users on the kth resource block k A k-th dimension signal representing a complex number of received signals, df representing the number of users on the k-th resource block, H representing a visible light channel gain, and n representing gaussian noise.
Step S108: and acquiring a target bit sequence corresponding to the target superposition code word based on the unique translatable principle, and decoding the target bit sequence corresponding to each resource block in parallel according to decoders respectively preset on each resource block.
It should be noted that, each resource block is provided with a decoder, and in the actual decoding process, the K-dimensional complex signal at the receiving end is split into K dimensions, and K decoders capable of decoding in parallel are designed to decode the received signal, so that the method has the advantages of low complexity and good error rate performance, and further solves the problem of overhigh decoding complexity in the prior art.
Please refer to table 1 below, which shows the complexity of the conventional decoding algorithm and the present invention in various operations, wherein dv represents the column weight of the factor matrix, K represents the number of resource blocks, M represents the size of the codebook, and N represents the number of iterations, where MPA and LOG-MPA represent the message passing algorithm and the LOG-domain-based MPA algorithm, respectively, and it is obvious from table 1 that the number of operations of MPA and LOG-MPA is much greater than that of the present invention algorithm, and meanwhile, as the overload factor increases, the complexity level index increases, and the complexity comparison result is: MPA > LOG-MPA > the present invention.
TABLE 1
Please refer to fig. 4, which is a comparison diagram of bit error rate performance of the detection algorithm implemented by using MPA detection and the detection algorithm implemented in the present embodiment under 150% of conditions in the same codebook, where "MPA" and "the present invention" correspond to a bit error rate performance curve of the same codebook, and Eb/N0 represents a bit signal to noise ratio, so it is obvious from fig. 4 that the bit error rate performance of MPA detection and the detection algorithm implemented in the present embodiment is similar, but the complexity of the detection process in the present embodiment is much smaller than that of the MPA algorithm, so that the detection algorithm provided in the present embodiment is beneficial to detection of a VLC-SCMA system with a larger overload rate and a higher order.
In summary, according to the SCMA assisted fast decoding method for visible light communication, the signal at the transmitting end is split through a specific codebook structure, the signal and the codeword at the transmitting end are split and recombined according to the characteristic that the codebook is split, and the sequence and the superposed signal after the codeword recombination are set to be unique and translatable, so as to complete decoding of the received signal, and the method has the advantages of low complexity and good error rate performance. The method specifically comprises the following steps: the method comprises the steps that a sending end firstly carries out codebook mapping on bit signals of a plurality of users through a completely new specific codebook, so that the bit signals are superposed to obtain complex signals, then the complex signals are respectively subjected to modulation conversion and channel gain, then positive real number signals with signal gain completed are sent to a receiving end, the receiving end correspondingly demodulates the received positive real number signals, then the complex received signals obtained after demodulation are subjected to transverse dimension splitting to obtain all possible bit information of each resource block, then all possible superposed signals are calculated according to all the bit information, then all the possible superposed signals are judged based on a minimum Euclidean distance criterion to obtain target superposed signals, and then each resource block is parallelly decoded according to the target superposed signals, so that the signals sent by each user are decoded, the whole decoding process is simple, and meanwhile, the method has good applicability to VLC-SCMA system detection with larger overload rate and higher order.
Referring to fig. 5, a schematic structural diagram of a SCMA assisted fast decoding system for visible light communication according to a third embodiment of the present invention is shown, where the system includes:
the transmitting end comprises:
a codebook mapping module 10, configured to obtain bit signals of multiple users, and perform codebook mapping on the bit signals according to a pre-constructed specific codebook, so as to perform signal superposition on the bit signals, so as to obtain a complex signal;
the signal modulation module 20 is configured to perform ACO-OFDM modulation on the complex signal to convert the complex signal into a positive real signal, and perform channel gain on the positive real signal and transmit the positive real signal to a receiving end;
the receiving end includes:
the signal demodulation module 30 is configured to demodulate a received positive real number signal to convert the positive real number signal into a complex number received signal, and split the complex number received signal in a transverse dimension according to the number of resource blocks to obtain all bit information that may exist in each resource block according to a splitting result;
receiving the positive real signal according to the following equation:
Y=HX+n
wherein, Y represents a received signal, X represents a positive real number signal, H represents a visible light channel gain, and n represents Gaussian noise;
and the receiving end carries out ACO-OFDM demodulation on the received signal so as to convert the positive real number signal into a complex number receiving signal.
Further, the signal demodulation module 30 further includes:
the signal splitting unit is used for carrying out bit-by-bit splitting on the complex received signals according to the specific codebook and carrying out codebook mapping on bit information obtained after splitting so as to convert the complex received signals into single bit information;
the index calculation unit is used for acquiring the user index occupying each resource block according to the factor matrix so as to obtain all user numbers occupied on each resource block;
indexing is performed according to the following formula:
wherein, U (: k) is the user number occupied on the resource block k, find represents the find matlab function, and F represents the factor matrix.
And the permutation and combination unit is used for listing all possible combinations of bit sequences of each user occupying each resource block according to all user numbers occupied on each resource block and all the obtained single bit information.
The parallel decoding module 40 is configured to calculate all possible superposed signals according to all bit information that may exist on each resource block, determine all the superposed signals based on a minimum euclidean distance criterion, obtain a target superposed signal corresponding to the minimum euclidean distance according to a determination result, and perform parallel decoding on each resource block according to the target superposed signal to obtain a signal transmitted by each user.
Further, the parallel decoding module 40 further includes:
a superposition code word calculation unit, configured to calculate superposition code words corresponding to the bit sequences one to one according to combinations of all bit sequences that may exist in each user, where each bit sequence and the superposition code word corresponding to the bit sequence have a unique interpretable principle;
the Euclidean distance calculating unit is used for calculating the Euclidean distance between each superposed code word and the complex received signals according to the superposed code words possibly existing in each resource block and the complex received signals, and screening out the minimum Euclidean distance from all the obtained Euclidean distances so as to lock the target superposed code word corresponding to the minimum Euclidean distance;
calculating the Euclidean distance according to the following formula:
wherein | - | represents solving Euclidean distance, min tableSearching for the minimum value, y, of all Euclidean distances k And representing the kth dimension signal in the complex number receiving signals, s (j) representing the superposition code word mapped corresponding to the jth group of bit sequences, and m representing the position of the decoded target superposition code word for retrieving the target superposition code word.
And the decoding execution unit is used for acquiring the target bit sequence corresponding to the target superposition code word based on the unique translatable principle and decoding the target bit sequence corresponding to each resource block in parallel according to the decoder preset on each resource block.
Further, in some optional embodiments of the present invention, the system further comprises:
the overload rate acquisition module is used for acquiring an overload rate target value according to the requirement of an actual application scene and setting the corresponding size of a codebook, the maximum bearing quantity of users, the number of resource blocks and the number of overload users of each resource block according to the overload rate target value;
a primary constellation constructing module, configured to define a primary constellation structure in the specific codebook as a row matrix, where the row matrix includes two characters that are opposite to each other, and the number of the characters in the row matrix is set according to the size of the codebook;
and the factor matrix construction module is used for performing rotation operation and power distribution on the mother constellation structure according to the number of the overloaded users of each resource block so as to construct and obtain a factor matrix corresponding to each resource block.
Further, in some optional embodiments of the present invention, the system further comprises:
a received signal processing module, configured to obtain a kth-dimension signal in the complex received signals according to the following formula:
y k =Hx k +n
wherein x is k Superimposed signal, y, representing df users on the kth resource block k A k-th dimension signal representing a complex number of received signals, df representing the number of users on the k-th resource block, H representing a visible light channel gain, and n representing gaussian noise.
In summary, according to the SCMA assisted fast decoding method for visible light communication, the signal at the transmitting end is split through a specific codebook structure, the signal and the codeword at the transmitting end are split and recombined according to the characteristic that the codebook is split, and the sequence and the superposed signal after the codeword recombination are set to be unique and translatable, so as to complete decoding of the received signal, and the method has the advantages of low complexity and good error rate performance. The method specifically comprises the following steps: the method comprises the steps that a sending end firstly carries out codebook mapping on bit signals of a plurality of users through a completely new specific codebook, so that the bit signals are superposed to obtain complex signals, then the complex signals are respectively subjected to modulation conversion and channel gain, then positive real number signals with signal gain completed are sent to a receiving end, the receiving end correspondingly demodulates the received positive real number signals, then the complex received signals obtained after demodulation are subjected to transverse dimension splitting to obtain all possible bit information of each resource block, then all possible superposed signals are calculated according to all the bit information, then all the possible superposed signals are judged based on a minimum Euclidean distance criterion to obtain target superposed signals, and then each resource block is parallelly decoded according to the target superposed signals, so that the signals sent by each user are decoded, the whole decoding process is simple, and meanwhile, the method has good applicability to VLC-SCMA system detection with larger overload rate and higher order.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.
Claims (8)
1. A fast decoding method for SCMA assisted visible light communication, the method comprising:
the method comprises the steps that a sending end obtains bit signals of a plurality of users, codebook mapping is carried out on the bit signals according to a pre-constructed specific codebook, signal superposition is carried out on the bit signals, and a complex signal is obtained, wherein the construction of the specific codebook comprises the following steps:
acquiring an overload rate target value according to the requirement of an actual application scene, and setting the corresponding size of a codebook, the maximum bearing quantity of users, the number of resource blocks and the number of overloaded users of each resource block according to the overload rate target value;
defining a mother constellation structure in the specific codebook as a row matrix, wherein the row matrix comprises two characters with mutually opposite numbers, and setting the number of the characters in the row matrix according to the size of the codebook;
performing rotation operation and power distribution on the mother constellation structure according to the number of overloaded users of each resource block to construct and obtain a factor matrix corresponding to each resource block;
carrying out ACO-OFDM modulation on the complex signal to convert the complex signal into a positive real number signal, carrying out channel gain on the positive real number signal and transmitting the positive real number signal to a receiving end;
the method comprises the following steps that the receiving end carries out ACO-OFDM demodulation on a received positive real number signal so as to convert the positive real number signal into a complex number receiving signal, and carries out transverse dimension splitting on the complex number receiving signal according to the number of resource blocks so as to obtain all bit information existing in each resource block according to a splitting result, and specifically comprises the following steps:
splitting the plural received signals bit by bit according to the specific codebook, and performing codebook mapping on bit information obtained after splitting to convert the plural received signals into single-bit information;
acquiring a user index occupying each resource block according to the factor matrix so as to obtain all user numbers occupied on each resource block;
listing all combinations of bit sequences existing in each user occupying each resource block according to all user numbers occupied on each resource block and all obtained single bit information;
and calculating all corresponding superposed signals according to all bit information existing on each resource block, judging all the superposed signals based on a minimum Euclidean distance criterion, acquiring a target superposed signal corresponding to the minimum Euclidean distance according to a judgment result, and performing parallel decoding on each resource block according to the target superposed signal to obtain a signal transmitted by each user.
2. The method as claimed in claim 1, wherein the step of performing ACO-OFDM demodulation on the positive real signal received by the receiving end to convert the positive real signal into a complex received signal comprises:
receiving the positive real signal according to the following equation:
Y=HX+n
wherein, Y represents a received signal, X represents a positive real number signal, H represents a visible light channel gain, and n represents Gaussian noise;
and the receiving end carries out ACO-OFDM demodulation on the received signal so as to convert the positive real number signal into a complex number receiving signal.
3. The SCMA-assisted fast decoding method for visible light communication according to claim 2, wherein the step of calculating all corresponding superimposed signals according to all bit information existing on each resource block, and deciding all the superimposed signals based on the minimum Euclidean distance criterion to obtain the target superimposed signal corresponding to the minimum Euclidean distance according to the decision result, and decoding each resource block in parallel according to the target superimposed signal to obtain the signal transmitted by each user comprises:
respectively calculating superposed code words corresponding to the bit sequences one by one according to the combination of all the bit sequences existing in each user, wherein each bit sequence and the superposed code word corresponding to the bit sequence have a unique translatable principle;
and calculating Euclidean distances between each superposed code word and the complex received signals according to the superposed code word existing in each resource block and the complex received signals, and screening out a minimum Euclidean distance from all the obtained Euclidean distances so as to lock a target superposed code word corresponding to the minimum Euclidean distance.
4. The SCMA-assisted fast decoding method for visible light communication according to claim 3, wherein the step of calculating all corresponding superimposed signals according to all bit information existing on each resource block, and deciding all the superimposed signals based on the minimum Euclidean distance criterion to obtain the target superimposed signal corresponding to the minimum Euclidean distance according to the decision result, and decoding each resource block in parallel according to the target superimposed signal to obtain the signal transmitted by each user further comprises:
and acquiring a target bit sequence corresponding to the target superposition code word based on the unique translatable principle, and decoding the target bit sequence corresponding to each resource block in parallel according to decoders respectively preset on each resource block.
5. The SCMA-assisted fast decoding method of visible light communication according to claim 4, wherein the step of calculating Euclidean distances between each kind of superimposed codewords and the complex received signals according to the superimposed codewords existing in each resource block and the complex received signals, and selecting a minimum Euclidean distance from all the obtained Euclidean distances, so as to lock a target superimposed codeword corresponding to the minimum Euclidean distance comprises:
calculating the Euclidean distance according to the following formula:
wherein | represents solving Euclidean distance, min represents retrieving the minimum value of all Euclidean distances, y k And the k-dimension signal in the complex received signal is represented, s (j) represents a superposition code word mapped correspondingly to the j-th group of bit sequences, and m represents the position of the decoded target superposition code word and is used for retrieving the target superposition code word.
6. The SCMA-assisted fast decoding method of claim 5, wherein the step of obtaining the index of the user occupying each resource block according to the factor matrix to obtain all the numbers of the users occupied on each resource block comprises:
indexing is performed according to the following formula:
wherein, U (: k) is the user number occupied on the resource block k, find represents the find matlab function, and F represents the factor matrix.
7. The SCMA-assisted fast decoding method of visible light communication according to claim 6, wherein the k-dimension signal of the complex received signals is obtained according to the following formula:
y k =Hx k +n
wherein x is k Represents the superimposed signal of df users on the k-th resource block, y k A k-th dimension signal representing a complex received signal, df representing the number of users on the k-th resource block, H representing a visible light channel gain, and n representing gaussian noise.
8. The utility model provides a quick decoding system of SCMA supplementary visible light communication which characterized in that, the system includes transmitting end and receiving end, wherein:
the transmitting end comprises:
a codebook mapping module, configured to obtain bit signals of multiple users, and perform codebook mapping on the bit signals according to a pre-constructed specific codebook to perform signal superposition on the bit signals to obtain complex signals, where constructing the specific codebook includes:
the overload rate acquisition module is used for acquiring an overload rate target value according to the requirement of an actual application scene, and setting the corresponding size of a codebook, the maximum bearing quantity of users, the number of resource blocks and the number of overload users of each resource block according to the overload rate target value;
a primary constellation constructing module, configured to define a primary constellation structure in the specific codebook as a row matrix, where the row matrix includes two characters with opposite numbers, and the number of the characters in the row matrix is set according to the size of the codebook;
the factor matrix construction module is used for performing rotation operation and power distribution on the mother constellation structure according to the number of overloaded users of each resource block so as to construct and obtain a factor matrix corresponding to each resource block;
the signal modulation module is used for carrying out ACO-OFDM modulation on the complex signal so as to convert the complex signal into a positive real signal, carrying out channel gain on the positive real signal and transmitting the positive real signal to a receiving end;
the receiving end includes:
the signal demodulation module is configured to perform ACO-OFDM demodulation on a received positive real signal to convert the positive real signal into a complex received signal, and split the complex received signal in a transverse dimension according to the number of resource blocks to obtain all bit information existing in each resource block according to a splitting result, and specifically includes:
the signal splitting unit is used for carrying out bit-by-bit splitting on the complex received signals according to the specific codebook and carrying out codebook mapping on bit information obtained after splitting so as to convert the complex received signals into single bit information;
the index calculation unit is used for acquiring the user index occupying each resource block according to the factor matrix so as to obtain all user numbers occupied on each resource block;
the permutation and combination unit is used for listing all combinations of bit sequences existing in each user occupying each resource block according to all user numbers occupied on each resource block and all obtained single bit information;
and the parallel decoding module is used for calculating all corresponding superposed signals according to all bit information existing on each resource block, judging all the superposed signals based on the minimum Euclidean distance criterion so as to obtain target superposed signals corresponding to the minimum Euclidean distance according to the judgment result, and performing parallel decoding on each resource block according to the target superposed signals so as to obtain the signals transmitted by each user.
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