FTN-mCAP interference mitigation method and system based on gap index modulation

Abstract

The invention relates to the technical field of visible light communication, in particular to an FTN-mCAP interference mitigation method and system based on gap index modulation, and the method comprises the steps: employing FTN-mCAP-GIM mapping at a transmitting end, and employing a gap index mechanism to activate k sub-bands in m sub-bands; the gap activation mechanism is that adjacent sub-bands cannot be activated at the same time; performing up-sampling on the m sub-band signals, and performing subtraction on a real part and an imaginary part of each sub-band signal after up-sampling through an FTN in-phase filter and an FTN orthogonal filter to obtain a target signal of each sub-band; and the target signals of all the sub-bands are combined to generate a transmitting signal. According to the invention, excessive overlapping of different sub-bands on a frequency spectrum can be effectively avoided, inter-band interference generated by a transmitting end is reduced, better bit error rate performance can be realized, and bandwidth resources are saved.

Description

Technical Field

[0001] The present invention relates to the field of visible light communication technology, and in particular to a FTN-mCAP interference mitigation method and system based on gap index modulation. Background Art

[0002] Since the achievable capacity of actual visible light communication (VLC) systems is limited by the modulation bandwidth, various spectrum-efficient modulation techniques have been considered to improve the achievable rate of the system, including carrierless amplitude and phase (CAP) modulation and orthogonal frequency division multiplexing (OFDM) of higher-order modulation formats.

[0003] Compared with OFDM, CAP replaces the Discrete Fourier Transform (DFT) and Inverse Discrete Fourier Transform (IDFT) operations with two orthogonal digital filters, simplifying the implementation of the transceiver. In addition, CAP has a lower Peak-to-Average-Power Ratio (PAPR) than OFDM, which makes it less susceptible to LED nonlinearity. At the same time, multiple groups of orthogonal filters can also be used to implement multi-band CAP, namely mCAP, which is suitable for multi-user scenarios. In addition, Faster-Than-Nyquist (FTN) sampling is considered in mCAP, and the resulting FTN-mCAP scheme can reduce the required bandwidth through spectrum compression to achieve the same data rate. However, the bandwidth saving of FTN-mCAP is obtained at the expense of non-negligible inter-band interference (IBI).

[0004] So far, various interference mitigation schemes have been proposed for FTN-mCAP in band-limited VLC systems, which can be divided into the following two categories: (1) Receiver equalization; for example, there are several ICI suppression algorithms for FTN-mCAP schemes in the prior art, such as the joint Multiple Input Multiple Output (MIMO) equalizer, and the subcarrier component extraction with complex independent component analysis (SCE-ICA) and Toeplitz concatenated matrix with complex independent component analysis (TCMICA) algorithms. (2) Joint transceiver IBI mitigation; for example, there is a solution in the prior art that combines the corresponding encoding based on a neural network (NN) with the waveform-to-symbol decoding at the receiver. However, the above IBI mitigation schemes are usually very complex and occupy a lot of computing resources.

[0005] In existing research, the combination of CAP and index modulation as a new type of multi-carrier transmission scheme has superior bit error rate performance and higher energy efficiency, and has been widely concerned by researchers. For mCAP (Index Modulation Aided mCAP, mCAP-IM) based on index modulation, m subbands are divided into multiple sub-blocks, and the subbands in each sub-block are divided into active subbands or silent subbands; the active subbands are mapped with QAM orthogonal amplitude modulation (Quadrature Amplitude Modulation, QAM), while the silent subbands remain empty and do not transmit signals. The implicit index bit is used to compensate for the bit information loss caused by the lack of information transmission in the silent subband. At present, the existing technology has considered the combination of index modulation and non-orthogonal mCAP schemes. Specifically, the researchers proposed a subcarrier index modulation super-Nyquist CAP (Index Modulation Super-Nyquist CAP, SIM-SCAP) scheme with inter-carrier interference mitigation digital signal processing (Digital Signal Processing, DSP), which improves the spectrum efficiency by about 30% compared with the traditional scheme. However, the performance improvement of this scheme is still mainly achieved by using a high-complexity interference mitigation scheme at the receiving end.

[0006] In summary, the existing FTN-mCAP scheme uses a highly complex algorithm to alleviate inter-band interference at the receiving end, which consumes a large amount of memory and is not conducive to signal transmission. Summary of the invention

[0007] Therefore, the technical problem to be solved by the present invention is to overcome the inter-band interference problem caused by spectrum compression in the FTN-mCAP solution in the prior art.

[0008] In order to solve the above technical problems, the present invention provides a FTN-mCAP interference mitigation method based on gap index modulation, which is applied to a transmitting end and includes:

[0009] The input bits are mapped into m sub-band signals through FTN-mCAP-GIM, including:

[0010] The input bits include index bits and constellation bits;

[0011] Activate k subbands from the m subbands according to a gap index set corresponding to the index bit; the gap index set includes serial numbers of activated subbands obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent subbands cannot be activated at the same time;

[0012] Transmit the constellation bits using the activated sub-band to obtain m sub-band signals;

[0013] Upsample the m subband signals, separate the real part and the imaginary part of each subband signal after upsampling, and subtract the real part and the imaginary part of each subband signal after passing through the FTN in-phase filter and the FTN orthogonal filter respectively to obtain the target signal of each subband;

[0014] The target signals of all sub-bands are combined to generate a transmit signal so that the transmit signal is transmitted to the receiving end through the VLC channel. The received signal at the receiving end is passed through the FTN matched filter pair to obtain m received sub-band signals. The m received sub-band signals are down-sampled and demapped by FTN-mCAP-GIM to obtain output bits.

[0015] Preferably, the serial number of the activated subband is determined according to the gap activation mechanism to form an initial gap activation index set; according to the size of the index bit, the initial gap activation index set with relatively small gaps and large power attenuation is discarded, and only the initial gap activation index set sufficient to complete the gap index modulation is retained as the target gap activation index set.

[0016] Preferably, when the number of subband signals m=4 and the number of activated subbands k=2, the sequence number of the activated subbands is determined according to the gap activation mechanism to form an initial gap activation index set {1,3}{1,4}{2,4}; the size of the index bit is 1 bit, and 2 are required to complete the gap index modulation process. 1The initial gap activation index set {2,4} with relatively small gaps and large power attenuation is discarded, and the target gap activation index set is {1,3}{1,4}.

[0017] Preferably, when the number of subband signals m=6 and the number of activated subbands k=2, the sequence number of the activated subbands is determined according to the gap activation mechanism to form an initial gap activation index set {1,3}{1,4}{1,5}{1,6}{2,4}{2,5}{2,6}{3,5}{3,6}{4,6}; the size of the index bit is 3 bits, and 2 bits are required to complete the gap index modulation process. 3 The initial gap activation index set {3,5}{4,6} with relatively small gaps and large power attenuation is discarded, and the target gap activation index set is {1,3}{1,4}{1,5}{1,6}{2,4}{2,5}{2,6}{3,6}.

[0018] Preferably, when the number of subband signals m=6 and the number of activated subbands k=3, the sequence numbers of the activated subbands are determined according to the gap activation mechanism to form an initial gap activation index set {1,3,5}{1,3,6}{1,4,6}{2,4,6}; the size of the index bit is 2 bits, then the target gap activation index set is {1,3,5}{1,3,6}{1,4,6}{2,4,6}.

[0019] Preferably, the modulation mode of the constellation bits is M-QAM.

[0020] Preferably, the FTN in-phase filter and the FTN quadrature filter are both square root raised cosine filters.

[0021] Preferably, the real part and imaginary part of each sub-band signal are respectively passed through an FTN in-phase filter and an FTN orthogonal filter, and the filter pair formulas are respectively expressed as:

[0022]

[0023] in, represents the impulse response of the FTN in-phase filter corresponding to the real part of the nth subband signal, t represents time, g(t) represents the impulse response of the baseband shaping filter, f c,n represents the center frequency of the nth subband, It represents the impulse response of the FTN orthogonal filter corresponding to the imaginary part of the nth subband signal.

[0024] Preferably, the center frequency f of the nth sub-band c,n It is expressed as:

[0025]

[0026] Where B represents the signal bandwidth, m represents the total number of subbands, and β represents the spectrum compression factor.

[0027] The present invention also provides a FTN-mCAP interference mitigation system based on gap index modulation, comprising:

[0028] The transmitter is used to generate a transmission signal. The input bits are mapped into m sub-band signals through FTN-mCAP-GIM mapping, including:

[0029] The input bits include index bits and constellation bits;

[0030] Activate k subbands from the m subbands according to a gap index set corresponding to the index bit; the gap index set includes serial numbers of activated subbands obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent subbands cannot be activated at the same time;

[0031] Transmit the constellation bits using the activated sub-band to obtain m sub-band signals;

[0032] Upsample the m subband signals, separate the real part and the imaginary part of each subband signal after upsampling, and subtract the real part and the imaginary part of each subband signal after passing through the FTN in-phase filter and the FTN orthogonal filter respectively to obtain the target signal of each subband;

[0033] The target signals of all sub-bands are combined to generate a transmit signal;

[0034] VLC channel, used for transmitting transmission signals;

[0035] The receiving end is used to obtain a received signal; the received signal is passed through an FTN matched filter pair to obtain m received sub-band signals, and the m received sub-band signals are down-sampled and FTN-mCAP-GIM demapped to obtain output bits.

[0036] The above technical solution of the present invention has the following beneficial effects compared with the prior art:

[0037] The FTN-mCAP interference mitigation method based on gap index modulation described in the present invention adopts a gap activation mechanism at the transmitting end to select the activated subband, and does not activate adjacent subbands at the same time, which can effectively avoid excessive overlap of different subbands in the spectrum and reduce the inter-band interference generated by the transmitting end. Since the transmitting end adopts the gap index to reduce the interference between signals, the received signal is relatively clear, the processing process is simplified, and the calculation complexity is reduced. In addition, the algorithm complexity adopted by the present invention at the transmitting end is low, and better bit error rate performance can be achieved, more information can be transmitted under a narrow bandwidth, and bandwidth resources are saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0039] Figure 1 This is the principle block diagram of the FTN-mCAP transmitter;

[0040] Figure 2 is a schematic diagram of the emission spectrum of mCAP and FTN-mCAP, where Figure 2 (a) is a schematic diagram of the 4CAP transmission spectrum. Figure 2 (b) is a schematic diagram of the 6CAP transmission spectrum. Figure 2 (c) is a schematic diagram of the FTN-4CAP transmission spectrum. Figure 2 (d) is a schematic diagram of the FTN-6CAP transmission spectrum;

[0041] Figure 3 This is the principle block diagram of the mCAP-IM transmitter;

[0042] Figure 4 It is a principle block diagram of a FTN-mCAP interference mitigation method based on gap index modulation of the present invention;

[0043] Figure 5 is a schematic diagram of the transmission spectrum of FTN-mCAP and FTN-mCAP-GM, where Figure 5 (a) is a schematic diagram of the emission spectrum of FTN-4CAP. Figure 5 (b) is a schematic diagram of the emission spectrum of FTN-6CAP. Figure 5 (c) is a schematic diagram of the emission spectrum of FTN-4CAP-GM (1,3). Figure 5 (d) is a schematic diagram of the emission spectrum of FTN-6CAP-GM(1,6). Figure 5 (e) is a schematic diagram of the emission spectrum of FTN-4CAP-GM (1,4). Figure 5 (f) is a schematic diagram of the emission spectrum of FTN-6CAP-GM (1,3,6);

[0044] Figure 6 This is a graph showing the relationship between the experimental bit error rate and compression factor for different schemes based on FTN-4CAP;

[0045] Figure 7 is the relationship between the experimental bit error rate and the compression factor β of FTN-4CAP and FTN-4CAP-GIM when the number of activated subbands k = 2;

[0046] Figure 8is the relationship between the experimental bit error rate and the compression factor β of FTN-6CAP and FTN-6CAP-GIM when the number of activated subbands k = 2 and k = 3, where Figure 8 (a) is the relationship between the experimental bit error rate and the compression factor β when k = 2. Figure 8 (b) is a graph showing the relationship between the experimental bit error rate and the compression factor β when k=3. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0048] The present invention implements FTN transmission based on the FTN-mCAP scheme in the prior art. For the FTN-mCAP scheme, the spectrum is compressed to obtain a narrower signal bandwidth than the traditional mCAP scheme. Although the FTN-mCAP scheme has a certain tolerance to IBI, as the interference between adjacent sub-bands continues to increase, the system performance will gradually deteriorate.

[0049] Reference Figure 1 As shown in the figure, at the transmitter of the FTN-mCAP scheme, after the input bits are mapped and upsampled by M-QAM, the real and imaginary parts of the obtained signal are respectively passed through the FTN in-phase and orthogonal filters and subtracted, and finally the m sub-band signals are combined to generate the FTN-mCAP transmission signal. The real and imaginary parts of each sub-band signal are respectively passed through the FTN in-phase filter and the FTN orthogonal filter, and their impulse responses are respectively expressed as:

[0050]

[0051] in, represents the impulse response of the FTN in-phase filter corresponding to the real part of the nth subband signal, t represents time, g(t) represents the impulse response of the baseband shaping filter, f c,n represents the center frequency of the nth subband, represents the impulse response of the FTN orthogonal filter corresponding to the imaginary part of the nth subband signal; n = 1, 2, ..., m, where m represents the total number of subbands.

[0052] The center frequency f of the nth subband c,n It is expressed as:

[0053]

[0054] Where B represents the signal bandwidth, β represents the spectrum compression factor, which represents the ratio of the compressed total signal bandwidth, and takes the value of 0≤β≤1. In particular, for β=0, the minimum center frequency gap between adjacent sub-bands is equal to the sub-band bandwidth. The total bandwidth after the sub-band compression and overlap is defined as B′, and the minimum center frequency gap between adjacent sub-bands is less than the sub-band bandwidth. Therefore, the compressed bandwidth of the sub-band can be expressed as:

[0055] B′=B(1-β)

[0056] In the FTN-mCAP scheme, the receiving end implements the opposite operation of the transmitting end.

[0057] Figure 2 Figure 1 is a schematic diagram of the emission spectrum of mCAP and FTN-mCAP, where Figure 2 (a) is a schematic diagram of the 4CAP transmission spectrum. Figure 2 (b) is a schematic diagram of the 6CAP transmission spectrum. Figure 2 (c) is a schematic diagram of the FTN-4CAP transmission spectrum. Figure 2 (d) in the figure is a schematic diagram of the FTN-6CAP transmission spectrum. It can be seen that the IBI in traditional 4CAP and 6CAP can be ignored. For FTN-4CAP, the signal bandwidth is compressed from B to B′, and subband S1 and subband S4 are interfered by subbands S2 and S3 respectively, while subbands S2 and S3 are interfered by their two adjacent subbands. Similarly, for FTN-6CAP, it can be observed that subbands S1 and S6 are interfered by adjacent single subbands, while the remaining subbands are affected by adjacent interference on both sides. Overlapping subbands will have a significant impact on the bit error rate performance of the system.

[0058] In addition, in the mCAP-IM system, only some sub-bands are active and used to transmit constellation signals, resulting in low system spectrum efficiency. Figure 3 The block diagram of the mCAP-IM transmitter is shown in Figure 1. The input bits are first divided into G sub-blocks of length m by the bit separator. Each sub-block contains b bits, which are used to perform index modulation in the m sub-bands and activate k sub-bands in the m sub-bands. The activated sub-bands are used to transmit constellation symbols. The remaining sub-bands do not transmit signals, and each sub-block is processed independently. For the g-th sub-block, the b bits contained are divided into two aspects according to different functions, where b i The bit enters the index selector to determine the index bit information of the subband activation, b c The bits enter the constellation mapper to implement constellation symbol mapping of the activated subband according to the index bit information.

[0059] In order to solve the IBI existing in the prior art, the present invention provides a FTN-mCAP interference mitigation method based on gap index modulation based on the traditional FTN-mCAP architecture, which is applied to the transmitting end. Figure 4 As shown, including:

[0060] The input bits are mapped into m sub-band signals through FTN-mCAP-GIM, including:

[0061] The input bits include index bits and constellation bits;

[0062] Activate k subbands from the m subbands according to a gap index set corresponding to the index bit; the gap index set includes serial numbers of activated subbands obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent subbands cannot be activated at the same time;

[0063] Transmit the constellation bits using the activated sub-band to obtain m sub-band signals;

[0064] Upsample the m subband signals, separate the real part and the imaginary part of each subband signal after upsampling, and subtract the real part and the imaginary part of each subband signal after passing through the FTN in-phase filter and the FTN orthogonal filter respectively to obtain the target signal of each subband;

[0065] The target signals of all sub-bands are combined to generate a transmit signal so that the transmit signal is transmitted to the receiving end through the VLC channel. The received signal at the receiving end is passed through the FTN matched filter pair to obtain m received sub-band signals. The m received sub-band signals are down-sampled and demapped by FTN-mCAP-GIM to obtain output bits.

[0066] Specifically, the input bits are mapped into m sub-band signals through FTN-mCAP-GIM, and each sub-band signal is transmitted independently. The m sub-bands are regarded as a sub-block, that is, the length of the sub-block is equal to the total number of sub-bands.

[0067] Preferably, the modulation mode of the constellation bits is M-QAM. The input b bits are divided into index bits and constellation bits, denoted by b1 and b2 respectively. The b1 bit is used to determine the gap index information for activating k subbands in the m subband, and the b2 bit is used to transmit the M-QAM constellation symbol in the k activated subbands, denoted by b2=klog2(M), and the remaining subbands are in a silent state to eliminate inter-subband interference. The constellation set of the M-QAM constellation can be described as S M Indicates the specific transmission symbol. M indicates the constellation order, which can be 2, 4, 8, 16, 32, 64, etc., and must be a power of 2.

[0068] The difference between the FTN-mCAP-GIM proposed in the present invention and the traditional mCAP-IM lies in the activation mechanism. For the traditional IM, the activation mechanism can activate adjacent subbands while ensuring that each activated subband has the same probability of occurrence. For GIM, the index set of the gap activation mechanism determines the effectiveness of IBI mitigation. When designing the gap activation mechanism, it must be ensured that the activated subband must be gap activated, and adjacent subbands cannot be activated at the same time, while considering the impact of the low-pass characteristics of the actual VLC system on each subband.

[0069] In this embodiment, the scheme that satisfies the gap activation mechanism and does not transmit index information is called FTN-mCAP gap modulation, that is, FTN-mCAP-GM. For simplicity, FTN-mCAP-GM selects index sets {ξ,γ} and {ξ,γ,δ} when k=2 and 3 as FTN-mCAP-GM(ξ,γ) and FTN-mCAP-GM(ξ,γ,δ), respectively; where ξ,γ,δ all represent the indexes of the activated subbands.

[0070] Preferably, the serial number of the activated subband is determined according to the gap activation mechanism to form an initial gap activation index set; according to the size of the index bit, the initial gap activation index set with relatively small gaps and large power attenuation is discarded, and only the initial gap activation index set sufficient to complete the gap index modulation is retained as the target gap activation index set.

[0071] When the number of subband signals m=4 and the number of activated subbands k=2, the sequence number of the activated subbands is determined according to the gap activation mechanism to form an initial gap activation index set {1,3}{1,4}{2,4}; the size of the index bit is 1 bit, so only two index sets are needed to complete the gap index modulation; however, for the initial gap activation index set {2,4}, it experiences more power attenuation than {1,3}{1,4}, which is not conducive to effectively suppressing interference; the initial gap activation index set {2,4} with relatively small gaps and large power attenuation is discarded, and the target gap activation index set is {1,3}{1,4}.

[0072] When the number of subband signals m = 6 and the number of activated subbands k = 2, the sequence number of the activated subbands is determined according to the gap activation mechanism to form an initial gap activation index set {1,3}{1,4}{1,5}{1,6}{2,4}{2,5}{2,6}{3,5}{3,6}{4,6}; the size of the index bit is 3 bits, so it takes 2 to complete the gap index modulation process. 3 The initial gap activation index set {3,5}{4,6} with relatively small gaps and large power attenuation is discarded, and the target gap activation index set is {1,3}{1,4}{1,5}{1,6}{2,4}{2,5}{2,6}{3,6}.

[0073] When the number of subband signals m=6 and the number of activated subbands k=3, the sequence numbers of the activated subbands are determined according to the gap activation mechanism to form an initial gap activation index set {1,3,5}{1,3,6}{1,4,6}{2,4,6}; the size of the index bit is 2 bits, and the target gap activation index set is {1,3,5}{1,3,6}{1,4,6}{2,4,6}.

[0074] In this embodiment, the mapping table of FTN-mCAP-GIM mapping is shown in Table 1.

[0075] Table 1. Mapping table

[0076]

[0077] Therefore, when designing the mapping table for m sub-bands, two points need to be followed: (1) the activated sub-bands must be activated intermittently; and (2) the impact of the low-pass characteristics of the actual VLC system on each sub-band should be considered.

[0078] After performing the FTN-mCAP-GIM mapping, the m subbands are upsampled, and then the real and imaginary parts of the signal are separated and passed through the FTN in-phase (I) and FTN quadrature (Q) filters respectively. The pulse shaping filter used is the square-root raised cosine (SRRC) filter with a rolling factor of α. Then, the output signals of the I and Q filters of each subband are subtracted and the m subband signals are added to obtain the transmitted FTN-mCAP-GIM signal s(t). The receiving end implements the opposite operation of the transmitting end.

[0079] Preferably, the FTN in-phase filter and the FTN quadrature filter are both square-root raised cosine (SRRC) filters, and the rolling factor is α.

[0080] The real part and imaginary part of each subband signal pass through the FTN in-phase filter and FTN orthogonal filter respectively, and their impulse responses are expressed as follows:

[0081]

[0082] in, represents the impulse response of the FTN in-phase filter corresponding to the real part of the nth subband signal, t represents time, g(t) represents the impulse response of the baseband shaping filter, f c,n represents the center frequency of the nth subband, represents the impulse response of the FTN orthogonal filter corresponding to the imaginary part of the nth subband signal; n = 1, 2, ..., m, where m represents the total number of subbands.

[0083] The center frequency f of the nth subband c,n It is expressed as:

[0084]

[0085] Where B represents the signal bandwidth, β represents the spectrum compression factor, which represents the ratio of the compressed total signal bandwidth, and takes the value of 0≤β≤1. In particular, for β=0, the minimum center frequency gap between adjacent sub-bands is equal to the sub-band bandwidth. The total bandwidth after the sub-band compression and overlap is defined as B′, and the minimum center frequency gap between adjacent sub-bands is less than the sub-band bandwidth. Therefore, the compressed bandwidth of the sub-band can be expressed as B′=B(1-β).

[0086] In addition, the information bits transmitted by FTN-mCAP-GM do not include index bits. Therefore, the achievable rate in a band-limited VLC system using FTN-mCAP-GM based on M-QAM constellation can be expressed as:

[0087]

[0088] For FTN-mCAP-GIM, the transmitted information bits consist of index bits and constellation bits. Therefore, the achievable rate of FTN-mCAP-GIM with M-QAM constellation in a band-limited VLC system can be expressed as:

[0089]

[0090] Therefore, compared with FTN-mCAP-GM, FTN-mCAP-GIM can transmit more information bits and achieve a larger achievable rate.

[0091] In FTN-mCAP, adjacent subbands are overlapped to effectively utilize limited bandwidth at the expense of increasing IBI, and the increased IBI causes the system performance to gradually degrade. The present invention combines gap index modulation with FTN-mCAP to mitigate IBI. In the process of designing subband activation, gap activation needs to be performed with the purpose of alleviating IBI as much as possible, while considering the challenges faced in the actual system so that it can be applied in actual VLC scenarios.

[0092] Figure 5 Figure 1 is a schematic diagram of the transmission spectrum of FTN-mCAP and FTN-mCAP-GM, where Figure 5 (a) is a schematic diagram of the emission spectrum of FTN-4CAP. Figure 5 (b) is a schematic diagram of the emission spectrum of FTN-6CAP. Figure 5 (c) is a schematic diagram of the emission spectrum of FTN-4CAP-GM (1,3). Figure 5(d) is a schematic diagram of the emission spectrum of FTN-6CAP-GM(1,6). Figure 5 (e) is a schematic diagram of the emission spectrum of FTN-4CAP-GM (1,4). Figure 5 (f) in FIG. 1 is a schematic diagram of the transmission spectrum of FTN-6CAP-GM (1,3,6). For FTN-4CAP and FTN-6CAP, there is overlap in the subbands. For FTN-4CAP-GM (1,3), the index set {1,3} indicates that only subbands S1 and S3 transmit signals, while the remaining subbands remain silent. It can be observed that when the signal bandwidth is compressed to B′, subbands S1 and S3 do not overlap, eliminating interference between adjacent subbands. Compared with the index set {1,3}, the index set {1,4} provides enhanced interference suppression after signal bandwidth compression and allows further bandwidth compression without overlap. Similarly, for FTN-6CAP-GM (1,6), only subbands S1 and S6 transmit signals. After compression, a very large gap is maintained between the two subbands to ensure that there is no bandwidth overlap when compressed again. Compared with the index set {1,6}, the index set {1,3,6} activates three subbands for signal transmission.

[0093] Figure 6 The relationship between the experimental bit error rate and the compression factor of different schemes based on FTN-4CAP is shown in Figure 2. When the compression factor is 0.1-0.7, the bit error rate performance of FTN-4CAP cannot meet the 7% FEC coding limit BER = 3.8×10 -3 , which is due to the combined effect of the low-pass characteristics of the actual VLC system and the gradually increasing IBI in FTN-4CAP. Taking FTN-4CAP-GM(1,4) as an example, when the compression factor is in the range of 0.1-0.5, the low-pass effect of the actual system is the main influencing factor. When the compression factor is between 0.5-0.7, the reduced signal bandwidth leads to a weakened low-pass effect. However, the increased IBI leads to unrecoverable signal demodulation. Therefore, IBI becomes the dominant factor, gradually reducing the bit error rate performance of the system. Specifically, the BER performance of FTN-4CAP-GM(1,3) is better than that of FTN-4CAP-GM(2,4). Compared with other schemes, the maximum compression factor β supported by FTN-4CAP-GM(1,4) is 0.57, which means that the target data rate of 25Mbps can be achieved with a signal bandwidth of 10.75MHz, and the bandwidth saving rate is 57%. Therefore, the gap activation mechanism of FTN-4CAP-GIM includes the index sets of {1,3} and {1,4} when the number of activated subbands k=2, which is more meaningful for IBI mitigation.

[0094] Figure 7The relationship between the experimental bit error rate and the compression factor β of FTN-4CAP and FTN-4CAP-GIM when the number of activated subbands k = 2, where the rollover factors α are 0.2 and 0.5 respectively. In order to meet the BER = 3.8 × 10 -3 With a 7% FEC coding limit, FTN-4CAP and FTN-4CAP-GIM with a rollover factor α of 0.5 can achieve compression factors of 0.22 and 0.38 respectively, and the corresponding signal bandwidths required to achieve the same data rate are 19.5 and 15.5 MHz, indicating that FTN-4CAP-GIM achieves the target rate at a lower signal bandwidth, saving bandwidth resources.

[0095] Figure 8 is the relationship between the experimental bit error rate and the compression factor β of FTN-6CAP and FTN-6CAP-GIM when the number of activated subbands k = 2 and k = 3, where Figure 8 (a) is the relationship between the experimental bit error rate and the compression factor β when k = 2. Figure 8 (b) is the relationship between the experimental bit error rate and the compression factor β when k = 3. Compared with other schemes, FTN-6CAP-GIM with a rollover factor α of 0.5 can achieve the maximum compression factor when k = 2 and k = 3. Moreover, FTN-6CAP-GIM with a rollover factor α of 0.5 achieves a larger compression factor of 0.44 when k = 2. The larger compression factor indicates that FTN-6CAP-GIM requires a lower signal bandwidth.

[0096] In summary, the FTN-mCAP interference mitigation method based on gap index modulation described in the present invention adopts a gap activation mechanism at the transmitting end to select the activated subband, and does not activate adjacent subbands at the same time, which can effectively avoid excessive overlap of different signals in the spectrum and reduce the inter-band interference generated by the transmitting end. Since the transmitting end adopts the gap index to reduce the interference between signals, the received signal is relatively clear, the processing process is simplified, and the calculation complexity is reduced. In addition, the algorithm complexity adopted by the present invention at the transmitting end is low, a higher target data rate can be achieved, more information can be transmitted under a narrower bandwidth, and bandwidth resources are saved.

[0097] Based on the above-mentioned FTN-mCAP interference mitigation method based on gap index modulation, the present invention also provides a FTN-mCAP interference mitigation system based on gap index modulation, including:

[0098] The transmitter is used to generate a transmission signal. The input bits are mapped into m sub-band signals through FTN-mCAP-GIM mapping, including:

[0099] The input bits include index bits and constellation bits;

[0100] Activate k subbands from the m subbands according to a gap index set corresponding to the index bit; the gap index set includes serial numbers of activated subbands obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent subbands cannot be activated at the same time;

[0101] Transmit the constellation bits using the activated sub-band to obtain m sub-band signals;

[0102] Upsample the m subband signals, separate the real part and the imaginary part of each subband signal after upsampling, and subtract the real part and the imaginary part of each subband signal after passing through the FTN in-phase filter and the FTN orthogonal filter respectively to obtain the target signal of each subband;

[0103] The target signals of all sub-bands are combined to generate a transmit signal;

[0104] VLC channel, used for transmitting transmission signals;

[0105] The receiving end is used to obtain a received signal; the received signal is passed through an FTN matched filter pair to obtain m received sub-band signals, and the m received sub-band signals are down-sampled and FTN-mCAP-GIM demapped to obtain output bits.

[0106] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0107] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0108] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0109] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0110] Obviously, the above embodiments are merely examples for the purpose of clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A FTN-mCAP interference mitigation method based on gap index modulation, characterized in that: Applied to the transmitter, including: The input bits are mapped into m sub-band signals through FTN-mCAP-GIM, including: The input bits include index bits and constellation bits; Activate k subbands from the m subbands according to a gap index set corresponding to the index bit; the gap index set includes serial numbers of activated subbands obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent subbands cannot be activated at the same time; Transmit the constellation bits using the activated sub-band to obtain m sub-band signals; Upsample the m subband signals, separate the real part and the imaginary part of each subband signal after upsampling, and subtract the real part and the imaginary part of each subband signal after passing through the FTN in-phase filter and the FTN orthogonal filter respectively to obtain the target signal of each subband; The target signals of all sub-bands are combined to generate a transmit signal so that the transmit signal is transmitted to the receiving end through the VLC channel. The received signal at the receiving end is passed through the FTN matched filter pair to obtain m received sub-band signals. The m received sub-band signals are down-sampled and demapped by FTN-mCAP-GIM to obtain output bits.

2. The FTN-mCAP interference mitigation method based on gap index modulation according to claim 1, characterized in that: The serial number of the activated subband is determined according to the gap activation mechanism to form an initial gap activation index set; according to the size of the index bit, the initial gap activation index set with relatively small gaps and large power attenuation is discarded, and only the initial gap activation index set that is sufficient to complete the gap index modulation is retained as the target gap activation index set.

3. The FTN-mCAP interference mitigation method based on gap index modulation according to claim 2, characterized in that: When the number of subband signals m = 4 and the number of activated subbands k = 2, the sequence number of the activated subbands is determined according to the gap activation mechanism to form an initial gap activation index set {1,3}{1,4}{2,4}; the size of the index bit is 1 bit, and it takes 2 to complete the gap index modulation process. 1 The target gap activation index set is {1,3}{1,4}, which has a relatively small gap and a large power attenuation.

4. The FTN-mCAP interference mitigation method based on gap index modulation according to claim 1, characterized in that: When the number of subband signals m = 6 and the number of activated subbands k = 2, the sequence number of the activated subbands is determined according to the gap activation mechanism to form an initial gap activation index set {1,3}{1,4}{1,5}{1,6}{2,4}{2,5}{2,6}{3,5}{3,6}{4,6}; the size of the index bit is 3 bits, so it takes 2 to complete the gap index modulation process. 3 The initial gap activation index set {3,5}{4,6} with relatively small gaps and large power attenuation is discarded, and the target gap activation index set is {1,3}{1,4}{1,5}{1,6}{2,4}{2,5}{2,6}{3,6}.

5. The FTN-mCAP interference mitigation method based on gap index modulation according to claim 1, characterized in that: When the number of subband signals m=6 and the number of activated subbands k=3, the sequence numbers of the activated subbands are determined according to the gap activation mechanism to form an initial gap activation index set {1,3,5}{1,3,6}{1,4,6}{2,4,6}; the size of the index bit is 2 bits, and the target gap activation index set is {1,3,5}{1,3,6}{1,4,6}{2,4,6}.

6. The FTN-mCAP interference mitigation method based on gap index modulation according to claim 1, characterized in that: The modulation mode of the constellation bits is M-QAM.

7. The FTN-mCAP interference mitigation method based on gap index modulation according to claim 1, characterized in that: The FTN in-phase filter and the FTN quadrature filter are both square root raised cosine filters.

8. The FTN-mCAP interference mitigation method based on gap index modulation according to claim 7, characterized in that: The real part and imaginary part of each subband signal pass through the FTN in-phase filter and FTN orthogonal filter respectively. The filter pair formulas are expressed as: in, represents the impulse response of the FTN in-phase filter corresponding to the real part of the nth subband signal, t represents time, g(t) represents the impulse response of the baseband shaping filter, f c,n represents the center frequency of the nth subband, It represents the impulse response of the FTN orthogonal filter corresponding to the imaginary part of the n-th subband signal.

9. The FTN-mCAP interference mitigation method based on gap index modulation according to claim 8, characterized in that: The center frequency f of the nth subband c,n It is expressed as: Where B represents the signal bandwidth, m represents the total number of subbands, and β represents the spectrum compression factor.

10. A FTN-mCAP interference mitigation system based on gap index modulation, characterized in that: include: A transmitting end, used for generating a transmitting signal; The input bits are mapped into m sub-band signals through FTN-mCAP-GIM, including: The input bits include index bits and constellation bits; Activate k subbands from the m subbands according to a gap index set corresponding to the index bit; the gap index set includes serial numbers of activated subbands obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent subbands cannot be activated at the same time; Transmit the constellation bits using the activated sub-band to obtain m sub-band signals; Upsample the m subband signals, separate the real part and the imaginary part of each subband signal after upsampling, and subtract the real part and the imaginary part of each subband signal after passing through the FTN in-phase filter and the FTN orthogonal filter respectively to obtain the target signal of each subband; The target signals of all sub-bands are combined to generate a transmit signal; VLC channel, used for transmitting transmission signals; The receiving end is used to obtain a received signal; the received signal is passed through an FTN matched filter pair to obtain m received sub-band signals, and the m received sub-band signals are down-sampled and FTN-mCAP-GIM demapped to obtain output bits.

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