Method for extending available bandwidth of band-limited VLC system

Abstract

The present invention relates to the field of visible light communication technology, and specifically discloses a method for expanding the available bandwidth of a band-limited VLC system, the method comprising the steps of: at the transmitting end, evenly dividing N subcarriers into G subblocks, each subblock containing n subcarriers, and the number of activated subcarriers in each subblock being k; allocating input information bits to the G subblocks, wherein the information bits in each subblock are jointly mapped in number and constellation through a joint mapping table; interleaving the G mapped subblocks, and then integrating them to obtain an OFDM block. The present invention determines the number of activated subcarriers in each subblock and the constellations they carry through a joint mapping table, and interleaves subcarriers between the mapped subblocks, so that the activated subcarriers are distributed in a low-frequency region, reducing the power attenuation suffered by the activated subcarriers, thereby greatly expanding the available bandwidth of the band-limited VLC system.

Description

Technical Field

[0001] The present invention relates to the technical field of visible light communication, and in particular to a method for extending the available bandwidth of a band-limited VLC system. Background Art

[0002] With the rapid development of mobile Internet, the number of mobile users and smart devices continues to increase, and the mobile data traffic generated shows an explosive growth trend. In order to effectively support the growing mobile data traffic and meet the communication needs of future 6G networks, visible light communication (VLC) with huge spectrum resources has become an indispensable key enabling technology in the future wireless communication field. Although VLC has inherent advantages such as rich spectrum resources and no need for authorization, the available modulation bandwidth of the VLC system based on commercial LED / LD light sources is relatively limited, which seriously limits the transmission capacity of the actual VLC system.

[0003] The existing capacity improvement technologies of band-limited VLC systems are mainly divided into two categories. One is to use equalization technology to expand the available bandwidth of the system, and the other is to improve the spectrum efficiency of the system under the premise of a given modulation bandwidth. Equalization is performed in digital or analog form at the transmitting or receiving end, which can effectively expand the available bandwidth of the system. However, the existing equalization technology is usually achieved at the expense of the signal-to-noise ratio of the low-frequency frequency components or the computational complexity of the system. In terms of improving spectrum efficiency, orthogonal frequency division multiplexing (OFDM) technology with high spectrum efficiency has been widely used and developed in the field of VLC. Recently, based on OFDM, OFDM subcarrier index modulation (OFDM-SIM) technology has become a research hotspot due to its better bit error rate (BER) performance. In OFDM-SIM, the index of the activated subcarrier in each subblock is used as an additional information carrying unit, so that higher spectrum efficiency can be obtained. However, in OFDM-SIM, all subcarriers may be selected to transmit constellation symbols, so they will be affected by the low-pass frequency response of the band-limited VLC system, resulting in poor overall bit error performance of the high-frequency subblock. In addition, OFDM subcarrier number modulation (OFDM-SNM) technology uses the number of activated subcarriers in a subblock as an additional information-carrying unit, and each subblock transmits both the number information and the constellation information carried on the activated subcarriers. Similarly, OFDM-SNM will also be affected by the low-pass frequency response of the band-limited VLC system, resulting in poor overall bit error performance of the high-frequency subblock. Summary of the invention

[0004] The invention provides a method for extending the available bandwidth of a band-limited VLC system, and solves the technical problem of how to extend the available bandwidth of the band-limited VLC system.

[0005] In order to solve the above technical problems, the present invention provides a method for extending the available bandwidth of a band-limited VLC system, the key of which is that it comprises the steps of:

[0006] S1. At the transmitting end, N subcarriers are evenly divided into G subblocks, each subblock contains n subcarriers, and the number of activated subcarriers in each subblock is k;

[0007] S2. Distribute the input information bits to the G sub-blocks, wherein the information bits in each sub-block are jointly mapped in number and constellation through a joint mapping table. After mapping, the number of bits of information bits transmitted by each sub-block is:

[0008]

[0009] Where M is the transmitted constellation order, Indicates rounding down;

[0010] S3, interleaving is performed between the G mapped sub-blocks, and then integrated to obtain an OFDM block;

[0011] S4, performing inverse fast Fourier transform and parallel-to-serial conversion on the OFDM block to generate a serial signal and send it to a receiving end;

[0012] S5. At the receiving end, the inverse operation of steps S2 to S4 is performed to obtain output information bits.

[0013] Furthermore, in step S3:

[0014] The G sub-blocks after joint mapping are expressed as:

[0015]

[0016] Among them, the superscript T represents transposition, and the g-th sub-block X g It is expressed as:

[0017] X g =[A g,1 ,A g,2 ,A g,k ,…0] T ,

[0018] Among them, [A g,1 ,A g,2 ,A g,k ,…0] indicates activating k subcarriers from the lowest frequency to the high frequency, A g,l Indicates the constellation point of the lth activated subcarrier of the subblock, g = 1, 2, ..., G, l = 1, 2 ..., k;

[0019] The signal after inter-block interleaving is expressed as:

[0020] X′=[X 0,0 ,X 1,0 ,…,X G-1,0 ,…,X0,n-1 ,X 1,n-1 ,…,X G-1,n-1 ] T .

[0021] Furthermore, the specific process of inter-block interleaving is to rearrange the subcarriers of the G sub-blocks in the following order:

[0022] The first activated subcarrier of the 1st subblock, the first activated subcarrier of the second subblock until the first activated subcarrier of the Gth subblock, the second activated subcarrier of the first subblock, the second activated subcarrier of the second subblock until the second activated subcarrier of the Gth subblock, until the kth activated subcarrier of the first subblock, the kth activated subcarrier of the second subblock until the kth activated subcarrier of the Gth subblock, then the first inactivated subcarrier of the first subblock, the first inactivated subcarrier of the second subblock until the first inactivated subcarrier of the Gth subblock, until the last inactivated subcarrier of the first subblock, the last inactivated subcarrier of the second subblock until the last inactivated subcarrier of the Gth subblock, and finally obtain X′.

[0023] Furthermore, in step S2, the joint mapping table is constructed using the following steps:

[0024] S21. Determine the number of activated subcarriers k and the constellation order M according to the relationship between the number of activated subcarriers and the constellation order;

[0025] S22, when the number of activated subcarriers is 0, 1, 2 ..., k respectively, determine the corresponding relationship between the subblock data carrying constellation information and the information bit, and form a joint mapping table, wherein:

[0026] When the number of activated subcarriers is 0, the subblock data carrying constellation information is all zero, and the corresponding information bits are also all 0, which can correspond to 1 type of information bit;

[0027] When the number of activated subcarriers is 1, the first subcarrier is activated to carry M types of constellation information. There are M subblock data in total, which can correspond to M types of information bits.

[0028] And so on;

[0029] When the number of activated subcarriers is k, the first k subcarriers are activated to carry M k There are M constellation information k Seed block data, corresponding to M k information bits;

[0030] Before Seed block data creation and 2 b The mapping relationship of the information bits is obtained to obtain a joint mapping table.

[0031] Furthermore, the step S5 specifically includes the steps of:

[0032] The step S5 specifically comprises the following steps:

[0033] S51, receiving a serial signal sent by a transmitting end and sequentially performing serial-to-parallel conversion, fast Fourier transform, and frequency domain equalization;

[0034] S52, performing OFDM segmentation on the signal after frequency domain equalization to obtain G segmentation sub-blocks;

[0035] S53, deinterleave the G divided sub-blocks to obtain G deinterleaved sub-blocks;

[0036] S54, jointly demap the number and constellation of the G deinterleaving sub-blocks to obtain G information bits;

[0037] S55. Integrate the G information bits to obtain output information bits.

[0038] Furthermore, in the step S52, the OFDM segmentation is specifically: every n subcarriers in the frequency domain equalized signal are connected in parallel to form a subblock, and a total of G subblocks are obtained.

[0039] Further, in the step S53, the deinterleaving is specifically:

[0040] Position restoration is performed according to the interleaving position exchange rule in step S3.

[0041] Furthermore, the step S54 specifically includes the steps of:

[0042] S541, restore the data of each sub-block according to the following formula:

[0043]

[0044] in, represents the data of the g-th sub-block recovered, Y g and H g are the signal and channel matrix received by the g-th sub-block after deinterleaving, respectively. The subscript F indicates the F-norm of the vector.

[0045] S542, according to and the joint mapping table to obtain corresponding information bits.

[0046] The method for expanding the available bandwidth of a band-limited VLC system provided by the present invention determines the number of activated subcarriers in each subblock and the constellations they carry through a joint mapping table, and interleaves subcarriers between the mapped subblocks, so that the activated subcarriers are distributed in a low-frequency area, reducing the power attenuation of the subcarriers, thereby greatly expanding the available bandwidth of the band-limited VLC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a flow chart of a method for extending available bandwidth of a band-limited VLC system provided in Embodiment 1 of the present invention;

[0048] Figure 2 1 is an example diagram of the inter-subcarrier block interleaving principle provided by Embodiment 1 of the present invention, wherein:

[0049] Figure 2 (a) is the spectrum of the transmitting end when there is no interleaving;

[0050] Figure 2 (b) is the spectrum of the transmitting end when there is interleaving;

[0051] Figure 2 (c) is the spectrum at the receiving end when there is no interleaving;

[0052] Figure 2 (d) is the spectrum at the receiving end when interleaving is enabled. DETAILED DESCRIPTION

[0053] The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0054] Example 1

[0055] In order to significantly expand the available bandwidth of a band-limited VLC system, an embodiment of the present invention provides a method for expanding the available bandwidth of a band-limited VLC system, such as Figure 1 As shown in the flowchart, the method specifically comprises the steps of:

[0056] S1. At the transmitting end, N subcarriers are evenly divided into G subblocks, each subblock contains n subcarriers, and the number of activated subcarriers in each subblock is k;

[0057] S2. Divide the input information bits into G sub-blocks, wherein the information bits in each sub-block are jointly mapped in number and constellation through a joint mapping table. After mapping, the number of information bits transmitted by each sub-block is:

[0058]

[0059] Where M is the transmitted constellation order, Indicates rounding down;

[0060] Therefore, the spectral efficiency of the system is expressed as:

[0061]

[0062] S3, interleaving is performed between the G mapped sub-blocks, and then integrated to obtain an OFDM block;

[0063] S4, performing inverse fast Fourier transform and parallel-to-serial conversion on the OFDM block to generate a serial signal and send it to a receiving end;

[0064] S5. At the receiving end, the inverse operation of steps S2 to S4 is performed to obtain output information bits.

[0065] The step S5 specifically includes the following steps:

[0066] S51, receiving a serial signal sent by a transmitting end and sequentially performing serial-to-parallel conversion, fast Fourier transform, and frequency domain equalization;

[0067] S52, performing OFDM segmentation on the signal after frequency domain equalization to obtain G segmentation sub-blocks;

[0068] S53, deinterleave the G divided sub-blocks to obtain G deinterleaved sub-blocks;

[0069] S54, jointly demap the number and constellation of the G deinterleaving sub-blocks to obtain G information bits;

[0070] S55. Integrate the G information bits to obtain output information bits.

[0071] Specifically, in step S2, the joint mapping table is constructed using the following steps:

[0072] S21. Determine the number of activated subcarriers k and the constellation order M according to the relationship between the number of activated subcarriers and the constellation order (if the number of activated subcarriers is small, the constellation order needs to be set to a larger value; similarly, if the number of activated subcarriers is large, the constellation order can be lower);

[0073] S22, when the number of activated subcarriers is 0, 1, 2 ..., k respectively, determine the corresponding relationship between the subblock data carrying constellation information and the information bit, and form a joint mapping table, wherein:

[0074] When the number of activated subcarriers is 0, the subblock data carrying constellation information is all zero, and the corresponding information bits are also all 0, which can correspond to 1 type of information bit;

[0075] When the number of activated subcarriers is 1, the first subcarrier is activated to carry M types of constellation information. There are M subblock data in total, which can correspond to M types of information bits.

[0076] And so on;

[0077] When the number of activated subcarriers is k, the first k subcarriers are activated to carry M k There are M constellation information k Seed block data, corresponding to M k information bits;

[0078] Before Seed block data creation and 2 b The mapping relationship of the information bits is obtained to obtain a joint mapping table.

[0079] Table 1 is a joint mapping table when the number of subcarriers in a subblock is n=4, the numbers of activated subcarriers are k1=0, k2=1, k3=2, and the constellation order is M=4.

[0080] Table 1

[0081]

[0082] It can be seen that when the information bits are different, the number of activated subcarriers and the constellation information carried on the activated subcarriers will change. According to formula (2), at this time, the spectrum efficiency SE = 1 = bit / s / Hz. When the number of activated subcarriers remains unchanged and the constellation order increases, the spectrum efficiency will increase accordingly; similarly, if the constellation order remains unchanged and the number of activated subcarriers increases, the spectrum efficiency will also increase accordingly. However, a constellation order that is too large will lead to poor system error performance, and an increase in the number of activated subcarriers will weaken the advantage of interleaving between subblocks, making it impossible to reduce the impact of the system's low-pass frequency response. The purpose of mapping table design is to seek a balance between the number of activated subcarriers and the constellation order to obtain the best system performance. After simulation comparison, when the number of subcarriers in a subblock is n = 4, choosing k1 = 0, k2 = 1, and k3 = 2 is the best solution.

[0083] In step S3, the G sub-blocks after joint mapping are expressed as:

[0084]

[0085] Among them, the superscript T represents transposition, and the g-th sub-block X g It is expressed as:

[0086] X g =[A g,1 ,A g,2 ,A g,k ,…0] T==========================(4)

[0087] Among them, [A g,1 ,A g,2 ,A g,k ,…0] indicates activating k subcarriers from the lowest frequency to the high frequency, A g,l Indicates that the sub-block (i.e., the g-th sub-block X g ) The constellation point of the lth activated subcarrier, g = 1, 2, ..., G, l = 1, 2 ..., k;

[0088] The signal after inter-block interleaving is expressed as:

[0089] X′=[X 0,0 ,X 1,0 ,…,X G-1,0 ,…,X 0,n-1 ,X 1,n-1 ,…,X G-1,n-1 ] T = = = = = (5)

[0090] X 0,0 ,X 1,0 ,…,X G-1,0 ,…,X 0,n-1 ,X 1,n-1 ,…,X G-1,n-1 Represents G×n=N subcarriers arranged in sequence from low frequency to high frequency after interleaving.

[0091] The specific process of inter-block interleaving is to rearrange the subcarriers of the G sub-blocks in the following order:

[0092] The first activated subcarrier of the 1st subblock, the first activated subcarrier of the second subblock until the first activated subcarrier of the Gth subblock, the second activated subcarrier of the first subblock, the second activated subcarrier of the second subblock until the second activated subcarrier of the Gth subblock, until the kth activated subcarrier of the first subblock, the kth activated subcarrier of the second subblock until the kth activated subcarrier of the Gth subblock, then the first inactivated subcarrier of the first subblock, the first inactivated subcarrier of the second subblock until the first inactivated subcarrier of the Gth subblock, until the last inactivated subcarrier of the first subblock, the last inactivated subcarrier of the second subblock until the last inactivated subcarrier of the Gth subblock, and finally obtain X′.

[0093] Figure 2 The example shown shows the principle of interleaving between subcarrier blocks, and the figure shows the subcarrier distribution of four adjacent subcarriers. Each subcarrier block contains n=4 subcarriers, and the number of activated subcarriers is k=2. Figure 2(a) is the spectrum of the transmitting end when there is no interleaving. Because subcarrier selection is performed within the block, the activated subcarriers in each subblock are distributed in a relatively low-frequency area within the block. Figure 2 (b) is the spectrum of the transmitter when inter-block interleaving is applied. It can be seen that when intra-block subcarrier selection and inter-block subcarrier interleaving are applied simultaneously, the activated subcarriers are distributed in the low-frequency area of ​​the entire frequency band. Figure 2 (c) is the spectrum of the receiving end without interleaving. In this case, the activated subcarriers are distributed in the entire frequency band, and the subcarriers distributed in the high-frequency area are greatly attenuated in power. Figure 2 (d) is the spectrum of the receiving end when interleaving is performed. Obviously, the activated subcarriers are distributed in the low-frequency area of ​​the entire frequency band, and the overall power attenuation is small, so the available bandwidth can be effectively expanded.

[0094] At the receiving end, for step S52, OFDM segmentation is performed on the signal after frequency domain equalization, specifically: every n subcarriers in the signal after frequency domain equalization are connected in parallel to form a subblock, and a total of G subblocks are obtained.

[0095] In step S53, the G divided sub-blocks are de-interleaved, specifically, the positions are restored according to the interleaving position exchange rule of step S3.

[0096] For step S54, the number and constellation joint demapping is performed on the G deinterleaved sub-blocks, which specifically includes the steps of:

[0097] S541, restore the data of each sub-block according to the following formula:

[0098]

[0099] in, Represents the data of the g-th sub-block recovered, Y g and H g are the signal and channel matrix received by the g-th sub-block after deinterleaving, respectively. The subscript F indicates the F-norm of the vector.

[0100] S542, according to and the joint mapping table to obtain corresponding information bits.

[0101] In summary, the method for expanding the available bandwidth of a band-limited VLC system provided in an embodiment of the present invention determines the number of activated subcarriers and the constellations they carry in each sub-block through a joint mapping table, and interleaves subcarriers between the mapped sub-blocks, so that the activated subcarriers are distributed in the low-frequency region, reducing the power attenuation of the subcarriers, thereby greatly expanding the available bandwidth of the band-limited VLC system.

[0102] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for extending the available bandwidth of a band-limited VLC system, characterized in that: VLC refers to visible light communication, and the method comprises the steps of: S1. At the transmitting end, N subcarriers are evenly divided into G subblocks, each subblock contains n subcarriers, and the number of activated subcarriers in each subblock is k; S2. Distribute the input information bits to the G sub-blocks, wherein the information bits in each sub-block are jointly mapped in number and constellation through a joint mapping table. After mapping, the number of bits of information bits transmitted by each sub-block is: Where M is the transmitted constellation order, Indicates rounding down; S3, inter-block interleaving is performed between the G mapped sub-blocks, and then integrated to obtain an OFDM block; the specific process of inter-block interleaving is to rearrange the subcarriers of the G sub-blocks in the following order: The first activated subcarrier of the 1st subblock, the first activated subcarrier of the second subblock until the first activated subcarrier of the Gth subblock, the second activated subcarrier of the first subblock, the second activated subcarrier of the second subblock until the second activated subcarrier of the Gth subblock, until the kth activated subcarrier of the first subblock, the kth activated subcarrier of the second subblock until the kth activated subcarrier of the Gth subblock, then the first inactivated subcarrier of the first subblock, the first inactivated subcarrier of the second subblock until the first inactivated subcarrier of the Gth subblock, until the last inactivated subcarrier of the first subblock, the last inactivated subcarrier of the second subblock until the last inactivated subcarrier of the Gth subblock, and finally obtain X′; S4, performing inverse fast Fourier transform and parallel-to-serial conversion on the OFDM block to generate a serial signal and send it to a receiving end; S5, taking the inverse operation opposite to steps S2 to S4 at the receiving end to obtain output information bits; The step S5 specifically comprises the following steps: S51, receiving a serial signal sent by a transmitting end and sequentially performing serial-to-parallel conversion, fast Fourier transform, and frequency domain equalization; S52, performing OFDM segmentation on the signal after frequency domain equalization to obtain G segmentation sub-blocks; S53, deinterleave the G divided sub-blocks to obtain G deinterleaved sub-blocks; S54, jointly demap the number and constellation of the G deinterleaving sub-blocks to obtain G information bits; S55. Integrate the G information bits to obtain output information bits.

2. The method for extending the available bandwidth of a band-limited VLC system according to claim 1, characterized in that: In step S3: The G sub-blocks after joint mapping are expressed as: Among them, the superscript T represents transposition, and the g-th sub-block X g It is expressed as: X g =[A g,1 ,A g,2 ,A g,k ,…0] T , Among them, [A g,1 ,A g,2 ,A g,k ,…0] indicates activating k subcarriers from the lowest frequency to the high frequency, A g,l Indicates the constellation point of the lth activated subcarrier of the subblock, g = 1, 2, ..., G, l = 1, 2 ..., k; The signal after inter-block interleaving is expressed as: X′=[X 0,0 ,X 1,0 ,…,X G-1,0 ,…,X 0,n-1 ,X 1,n-1 ,…,X G-1,n-1 ] T 。 3. The method for extending the available bandwidth of a band-limited VLC system according to claim 1, characterized in that: In step S2, the joint mapping table is constructed using the following steps: S21. Determine the number of activated subcarriers k and the constellation order M according to the relationship between the number of activated subcarriers and the constellation order; S22. When the number of activated subcarriers is 0, 1, 2, ..., k respectively, the corresponding relationship between the sub-block data carrying constellation information and the information bit is determined to form a joint mapping table, where: When the number of activated subcarriers is 0, the subblock data carrying constellation information is all zero, and the corresponding information bits are also all 0, which can correspond to 1 type of information bit; When the number of activated subcarriers is 1, the first subcarrier is activated to carry M types of constellation information. There are M subblock data in total, which can correspond to M types of information bits. And so on; When the number of activated subcarriers is k, the first k subcarriers are activated to carry M k There are M constellation information k Seed block data, corresponding to M k information bits; Before Seed block data creation and 2 b The mapping relationship of the information bits is obtained to obtain a joint mapping table.

4. The method for extending the available bandwidth of a band-limited VLC system according to claim 1, characterized in that: In the step S52, the OFDM segmentation is specifically: every n subcarriers in the frequency domain equalized signal are connected in parallel to form a subblock, and a total of G subblocks are obtained.

5. The method for extending the available bandwidth of a band-limited VLC system according to claim 4, characterized in that: In the step S53, the deinterleaving is specifically as follows: Position restoration is performed according to the interleaving position exchange rule in step S3.

6. The method for extending the available bandwidth of a band-limited VLC system according to claim 5, characterized in that: The step S54 specifically includes the following steps: S541, restore the data of each sub-block according to the following formula: in, represents the data of the g-th sub-block recovered, Y g and H g are the signal and channel matrix received by the g-th sub-block after deinterleaving, respectively. The subscript F indicates the F-norm of the vector. S542, according to and the joint mapping table to obtain corresponding information bits.

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