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

Abstract

The present application relates to the technical field of visible light communication, in particular to a FTN-mCAP interference mitigation method and system based on gap index modulation, comprising: using FTN-mCAP-GIM mapping at the transmitting end, using a gap index mechanism to activate k subbands in m subbands; the gap activation mechanism is that adjacent subbands cannot be activated at the same time; the m subband signals are up-sampled, the real part and the imaginary part of each subband signal after up-sampling are subtracted after passing through FTN in-phase filters and FTN quadrature filters respectively, and the target signal of each subband is obtained; the target signals of all subbands are combined to generate a transmitting signal. The present application can effectively avoid excessive overlap of different subbands in the frequency spectrum, reduce the inter-band interference generated at the transmitting end, achieve better bit error rate performance, and save bandwidth resources.

Description

TECHNICAL FIELD

[0001] The present application 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. BACKGROUND

[0002] The achievable capacity of practical visible light communication (VLC) systems is limited by the modulation bandwidth. Various spectrum-efficient modulation techniques are considered to improve the achievable rate of the system, including carrierless amplitude and phase (CAP) modulation and high-order modulation format orthogonal frequency division multiplexing (OFDM).

[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 sets of orthogonal filters can be used to implement multi-band CAP, i.e. 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 by spectrum compression to achieve the same data rate. However, the bandwidth saving of FTN-mCAP is obtained at the cost 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 inter-carrier interference mitigation algorithms for FTN-mCAP schemes in the prior art, such as joint Multiple Input Multiple Output (MIMO) equalizer, and 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 a neural network (NN) based corresponding encoding with a waveform-to-symbol decoding at the receiver. However, the above IBI mitigation schemes usually have high complexity and consume more computing resources.

[0005] In existing research, the combination of CAP and index modulation as a new type of multicarrier transmission scheme has superior bit error rate performance and higher energy efficiency, and has been widely concerned by researchers. For mCAP based on index modulation (Index Modulation Aided mCAP, mCAP-IM), m subbands are divided into multiple subblocks, and the subbands in each subblock are divided into active subbands or silent subbands; the active subbands are mapped by QAM (Quadrature Amplitude Modulation) modulation, while the silent subbands remain empty and do not transmit signals. The implicit index bits are used to compensate for the loss of bit information caused by not transmitting information in the silent subbands. At present, the prior art has considered the combination of index modulation and non-orthogonal mCAP schemes. Specifically, researchers have 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 spectral efficiency by about 30% compared with the traditional scheme. However, the performance improvement of this scheme is still mainly achieved by using high complexity interference mitigation schemes at the receiver.

[0006] In summary, the existing FTN-mCAP scheme uses an algorithm with high complexity to mitigate inter-band interference at the receiving end, consumes a large amount of memory and is not conducive to signal transmission. SUMMARY

[0007] To this end, the technical problem to be solved by the present application is to overcome the inter-band interference problem caused by spectrum compression in the FTN-mCAP scheme in the prior art.

[0008] To solve the above technical problems, the present application provides an FTN-mCAP interference mitigation method based on gap index modulation, applied to a transmitting end, comprising:

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

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

[0011] According to the gap index set corresponding to the index bits, k sub-bands are activated in the m sub-bands; the gap index set includes the serial numbers of the activated sub-bands obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent sub-bands cannot be activated at the same time;

[0012] The constellation bits are transmitted using the activated sub-bands to obtain m sub-band signals;

[0013] The m sub-band signals are up-sampled, and the real part and the imaginary part of each sub-band signal after up-sampling are separated, and each sub-band signal is subtracted after passing through an FTN in-phase filter and an FTN quadrature filter, respectively, to obtain a target signal of each sub-band;

[0014] All target signals of the sub-bands are combined to generate a transmitting signal, so that the transmitting signal is transmitted to a receiving end through a VLC channel, and the receiving signal of the receiving end is obtained through an FTN matched filter to obtain m receiving sub-band signals, and the m receiving sub-band signals are down-sampled and FTN-mCAP-GIM demapped to obtain output bits.

[0015] Preferably, the serial numbers of the activated sub-bands are determined according to the gap activation mechanism to form an initial gap activation index set; according to the size of the index bits, 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 reserved as a target gap activation index set.

[0016] Preferably, when the number of sub-band signals m = 4 and the number of activated sub-bands k = 2, the serial numbers of the activated sub-bands are 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 bits is 1 bit, and 2 1An index set, discarding the initial gap activation index set {3, 5} {4, 6} which has relatively small gaps and large power attenuation, the target gap activation index set is {1, 3} {1, 4} {1, 5} {1, 6} {2, 4} {2, 5} {2, 6} {3, 6}.

[0017] Preferably, the number of sub-band signals m = 6, the number of activated sub-bands k = 2, the sequence number of the activated sub-band is determined according to the gap activation mechanism, and the initial gap activation index set is {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 the gap index modulation process needs 2 3 An index set, discarding the initial gap activation index set {3, 5} {4, 6} which has relatively small gaps and large power attenuation, 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, the number of sub-band signals m = 6, the number of activated sub-bands k = 3, the sequence number of the activated sub-band is determined according to the gap activation mechanism, and the initial gap activation index set is {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}.

[0019] Preferably, the modulation mode of the constellation bit 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 the imaginary part of each sub-band signal pass through the FTN in-phase filter and the FTN quadrature filter respectively, and the filter is represented as:

[0022]

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

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

[0025]

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

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

[0028] The transmitting end is used for generating a transmitting signal; input bits are mapped into m subband signals through FTN-mCAP-GIM, and the m subband signals comprise:

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

[0030] According to a gap index set corresponding to the index bits, k subbands are activated in the m subbands; the gap index set comprises serial numbers of activated subbands obtained according to a gap activation mechanism; and the gap activation mechanism is that adjacent subbands cannot be activated simultaneously.

[0031] The constellation bits are transmitted by using the activated subbands to obtain the m subband signals;

[0032] The m subband signals are up-sampled, and the real part and the imaginary part of each subband signal after up-sampling are separated; the real part and the imaginary part of each subband signal are subtracted after passing through FTN in-phase filters and FTN quadrature filters respectively to obtain a target signal of each subband.

[0033] The target signals of all subbands are combined to generate a transmitting signal.

[0034] The VLC channel is used for transmitting the transmitting signal.

[0035] The receiving end is used for acquiring a receiving signal; the receiving signal is subjected to FTN matched filtering to obtain m receiving subband signals; and the m receiving subband signals are subjected to down-sampling and FTN-mCAP-GIM demapping to obtain output bits.

[0036] Compared with the prior art, the above technical scheme of the application has the following beneficial effects:

[0037] The FTN-mCAP interference mitigation method based on gap index modulation has the following beneficial effects: the gap activation mechanism is used in the transmitting end to select activated subbands, adjacent subbands are not activated simultaneously, the excessive overlap of different subbands in the frequency spectrum can be effectively avoided, and the inter-band interference generated in the transmitting end is reduced; the interference between signals is reduced in the transmitting end, the receiving signal is relatively clear, the processing process is simplified, and the calculation complexity is reduced; the algorithm complexity is low in the transmitting end, the better bit error rate performance can be realized, more information can be transmitted in a relatively narrow bandwidth, and the bandwidth resource is saved. BRIEF DESCRIPTION OF DRAWINGS

[0038] For the purpose of making the content of the present application more easily understood, the present application is further described in detail below according to specific embodiments of the present application and in conjunction with the accompanying drawings, in which:

[0039] Figure 1 is a schematic diagram of the FTN-mCAP transmitter;

[0040] Figure 2 is a schematic diagram of the mCAP and FTN-mCAP transmission spectrum, wherein Figure 2 (a) in FIG. 1 is a schematic diagram of the 4CAP transmission spectrum, Figure 2 (b) in FIG. 1 is a schematic diagram of the 6CAP transmission spectrum, Figure 2 (c) in FIG. 1 is a schematic diagram of the FTN-4CAP transmission spectrum, Figure 2 (d) in FIG. 1 is a schematic diagram of the FTN-6CAP transmission spectrum;

[0041] Figure 3 is a schematic diagram of the mCAP-IM transmitter;

[0042] Figure 4 is a schematic diagram of the FTN-mCAP interference mitigation method based on gap index modulation according to the present application;

[0043] Figure 5 is a schematic diagram of the FTN-mCAP and FTN-mCAP-GM transmission spectrum, wherein Figure 5 (a) in FIG. 2 is a schematic diagram of the FTN-4CAP transmission spectrum, Figure 5 (b) in FIG. 2 is a schematic diagram of the FTN-6CAP transmission spectrum, Figure 5 (c) in FIG. 2 is a schematic diagram of the FTN-4CAP-GM(1,3) transmission spectrum, Figure 5 (d) in FIG. 2 is a schematic diagram of the FTN-6CAP-GM(1,6) transmission spectrum, Figure 5 (e) in FIG. 2 is a schematic diagram of the FTN-4CAP-GM(1,4) transmission spectrum, Figure 5 (f) in FIG. 2 is a schematic diagram of the FTN-6CAP-GM(1,3,6) transmission spectrum;

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

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

[0046] Figure 8This is a graph showing the relationship between the experimental bit error rate and compression factor β for FTN-6CAP and FTN-6CAP-GIM when the number of activation subbands k=2 and k=3. Figure 8 (a) in the figure is the relationship between the experimental bit error rate and the compression factor β when k=2. Figure 8 (b) in the figure is the relationship between the experimental bit error rate and the compression factor β when k=3. Detailed Implementation

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

[0048] This invention implements FTN transmission based on the existing FTN-mCAP scheme. The FTN-mCAP scheme achieves a narrower signal bandwidth than the traditional mCAP scheme by compressing the spectrum. Although the FTN-mCAP scheme has some tolerance for IBI (Inter-band Interference), system performance will gradually deteriorate as interference between adjacent subbands increases.

[0049] Reference Figure 1 As shown, at the transmitter of the FTN-mCAP scheme, after the input bits undergo M-QAM mapping and upsampling, the real and imaginary parts of the resulting signal are passed through FTN in-phase and quadrature filters respectively and subtracted. The resulting m sub-band signals are then combined to generate the FTN-mCAP transmit signal. The real and imaginary parts of each sub-band signal are passed through an FTN in-phase filter and an FTN quadrature filter respectively, and their impulse responses are expressed as follows:

[0050]

[0051] in, Let f(t) represent the impulse response of the FTN in-phase filter corresponding to the real part of the nth subband signal, where t represents time, g(t) represents the impulse response of the baseband shaping filter, and f(t) represents the impulse response of the baseband shaping filter. c,n This represents the center frequency of the nth sub-band. Let n represent the impulse response of the FTN quadrature 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 sub-band c,n Represented as:

[0053]

[0054] where B denotes the signal bandwidth, β denotes the spectral compression factor, and denotes the ratio of the compressed total signal bandwidth, with 0≤β≤1. In particular, for β=0, the minimum center frequency gap between adjacent subbands is equal to the subband bandwidth. The total bandwidth after compressing and overlapping the subbands is defined as B', and the minimum center frequency gap between adjacent subbands is less than the subband bandwidth. Therefore, the compressed bandwidth of the subbands can be expressed as:

[0055] B' = B(1 - β)

[0056] In the FTN-mCAP scheme, the receiver performs the inverse operation of the transmitter.

[0057] Figure 2 Figures showing the mCAP and FTN-mCAP transmission spectra, where Figure 2 (a) is a schematic diagram of a 4CAP transmission spectrum, Figure 2 (b) is a schematic diagram of a 6CAP transmission spectrum, Figure 2 (c) is a schematic diagram of an FTN-4CAP transmission spectrum, Figure 2 (d) is a schematic diagram of an FTN-6CAP transmission spectrum. As can be seen, the IBI in the conventional 4CAP and 6CAP can be ignored. For the FTN-4CAP, the signal bandwidth is compressed from B to B', and the subbands S1 and S4 are interfered by the subbands S2 and S3, respectively, while the subbands S2 and S3 are interfered by their two adjacent subbands. Similarly, for the FTN-6CAP, it can be observed that the subbands S1 and S6 are interfered by the adjacent single subband, while the remaining subbands are interfered by the adjacent two sides. The overlapping subbands have a great impact on the bit error rate performance of the system.

[0058] In addition, in the mCAP-IM system, only part of the subbands are in an active state and are used to transmit constellation signals, and the system spectral efficiency is low. Figure 3 Fig. 1 is a schematic diagram of the principle of the mCAP-IM transmitter. The input bits are first separated into G subblocks of length m by a bit separator, each of which contains b bits and is used to perform index modulation in m subbands, activate k subbands in m subbands, and transmit constellation symbols using the activated subbands. The remaining subbands do not transmit signals, and each subblock is processed independently. For the gthsubblock, the b bits contained therein are divided into two aspects according to different functions, where b i bits enter an index selector to determine the index bit information of the subband activation, and b c bits enter a constellation mapper to implement constellation symbol mapping of the activated subbands according to the index bit information.

[0059] In order to solve the IBI in the prior art, the application provides an FTN-mCAP interference mitigation method based on gap index modulation, applied to a transmitting end, and a principle block diagram thereof is shown in Figure 4 The input bit is mapped into m subband signals through FTN-mCAP-GIM, and the m subband signals comprise:

[0060] The input bit is mapped into m subband signals through FTN-mCAP-GIM, and the m subband signals comprise:

[0061] The input bit comprises index bits and constellation bits.

[0062] According to a gap index set corresponding to the index bits, k subbands are activated in the m subbands; the gap index set comprises serial numbers of the activated subbands obtained according to a gap activation mechanism; and the gap activation mechanism is that adjacent subbands cannot be activated simultaneously.

[0063] The constellation bits are transmitted by using the activated subbands, and m subband signals are obtained.

[0064] The m subband signals are up-sampled, and the real part and the imaginary part of each subband signal after up-sampling are separated; the real part and the imaginary part of each subband signal are subtracted after passing through FTN in-phase filters and FTN quadrature filters respectively, and a target signal of each subband is obtained.

[0065] The target signals of all the subbands are combined to generate a transmitting signal, so that the transmitting signal is transmitted to a receiving end through a VLC channel; the receiving signal of the receiving end is obtained by passing through an FTN matched filter to obtain m receiving subband signals; and the m receiving subband signals are up-sampled and demapped by FTN-mCAP-GIM to obtain output bits.

[0066] Specifically, the input bit is mapped into m subband signals through FTN-mCAP-GIM, and each subband signal is independently transmitted. The m subbands are regarded as a subblock, and the length of the subblock is equal to the total number of the subbands.

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

[0068] The FTN-mCAP-GIM and the conventional mCAP-IM differ in the activation mechanism. For the conventional IM, the activation mechanism is to activate adjacent subbands while ensuring that each activated subband has the same occurrence probability. For the GIM, the index set of the gap activation mechanism determines the effectiveness of the IBI mitigation. In designing the gap activation mechanism, it must be ensured that the activated subbands must be activated by the gap, and adjacent subbands cannot be activated at the same time, while considering the influence of the low-pass characteristic of the actual VLC system on each subband.

[0069] The scheme of the FTN-mCAP-GIM and the conventional mCAP-IM differ in the activation mechanism. For the conventional IM, the activation mechanism is to activate adjacent subbands while ensuring that each activated subband has the same occurrence probability. For the GIM, the index set of the gap activation mechanism determines the effectiveness of the IBI mitigation. In designing the gap activation mechanism, it must be ensured that the activated subbands must be activated by the gap, and adjacent subbands cannot be activated at the same time, while considering the influence of the low-pass characteristic of the actual VLC system on each subband.

[0070] Preferably, the order of the activated subbands 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 reserved 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 order 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 has experienced more power attenuation than {1, 3} {1, 4}, which is not conducive to effectively suppressing interference; therefore, 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 order 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 2 3 index sets are needed to complete the gap index modulation process, 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] The number of subband signals m = 6, the number of activated subbands k = 3, the serial number of the activated subbands is determined according to the gap activation mechanism, and the initial gap activation index set is {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 subbands, two points need to be followed: (1) the activated subband must be activated by the gap; (2) the influence of the low-pass characteristic of the actual VLC system on each subband is considered.

[0078] After performing the FTN-mCAP-GIM mapping, the m subbands are upsampled, and then the real part and the imaginary part 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 a square-root raised-cosine (SRRC) filter with a roll-off 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 performs the reverse 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 with a roll-off factor of α.

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

[0081]

[0082] wherein, 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, and f c,n represents the center frequency of the nth subband, represents the impulse response of the FTN quadrature filter corresponding to the imaginary part of the nth subband signal; n = 1, 2, …, m, wherein m represents the total number of subbands.

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

[0084]

[0085] where B denotes the signal bandwidth, β denotes the spectral compression factor, and denotes the ratio of the compressed total signal bandwidth, and β is in the range of 0≤β≤1. In particular, for β=0, the minimum center frequency gap between adjacent subbands is equal to the subband bandwidth. The total bandwidth after the compression and overlap of the subbands is defined as B', and the minimum center frequency gap between adjacent subbands is less than the subband bandwidth. Therefore, the compressed bandwidth of the subband can be represented as B'=B(1-β).

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

[0087]

[0088] For FTN-mCAP-GIM, the transmitted information bits are composed of index bits and constellation bits. Therefore, the achievable rate of FTN-mCAP-GIM with M-QAM constellation in the band-limited VLC system can be represented 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 the limited bandwidth at the cost of IBI, and the increased IBI gradually degrades the system performance. The present application combines gap index modulation with FTN-mCAP to mitigate IBI. In the design of subband activation, gap activation is needed to alleviate IBI as much as possible, while considering the challenges faced in actual systems, so that it can be applied in actual VLC scenarios.

[0092] Figure 5 Spectrum diagram of FTN-mCAP and FTN-mCAP-GM, wherein Figure 5 (a) in FIG. 1 is a spectrum diagram of FTN-4CAP, Figure 5 (b) in FIG. 1 is a spectrum diagram of FTN-6CAP, Figure 5 (c) in FIG. 1 is a spectrum diagram of FTN-4CAP-GM(1, 3), Figure 5(d) is a transmission spectrum diagram of FTN-6CAP-GM (1, 6) in FIG. 1, Figure 5 (e) is a transmission spectrum diagram of FTN-4CAP-GM (1, 4) in FIG. 1, Figure 5 (f) is a transmission spectrum diagram of FTN-6CAP-GM (1, 3, 6) in FIG. 1. For FTN-4CAP and FTN-6CAP, there is an overlap of subbands. For FTN-4CAP-GM (1, 3), the index set {1, 3} means 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 compression of bandwidth without producing 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, which can ensure that there is no overlap in bandwidth when further compression is performed. Compared with the index set {1, 6}, the index set {1, 3, 6} activates three subbands for signal transmission.

[0093] Figure 6 FIG. 6 is a graph of the experimental bit error rate versus compression factor for different schemes based on FTN-4CAP. When the compression factor is 0.1-0.7, the bit error rate performance of FTN-4CAP cannot meet the 7% FEC encoding limit BER = 3.8 x 10 -3 This is due to the combined effect of the low-pass characteristic 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. While the compression factor is between 0.5-0.7, the reduced signal bandwidth leads to a weakening of the low-pass effect. However, the increased IBI will cause 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 in the case of a signal bandwidth of 10.75 MHz, a target data rate of 25 Mbps can be achieved, with a bandwidth saving rate of 57%. Therefore, the gap activation mechanism of FTN-4CAP-GIM includes the index sets {1, 3} and {1, 4} when the number of activated subbands k = 2, and it is more meaningful for IBI mitigation.

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

[0095] Figure 8 Figures showing the relationship between the experimental BER and the compression factor β of FTN-6CAP and FTN-6CAP-GIM when the number of activated subbands k = 2 and k = 3, wherein Figure 8 (a) in Figure 7 is a figure showing the relationship between the experimental BER and the compression factor β when k = 2, Figure 8 (b) in Figure 7 is a figure showing the relationship between the experimental BER and the compression factor β when k = 3. Compared with other schemes, FTN-6CAP-GIM with a roll-off factor α of 0.5 can achieve the maximum compression factor when k = 2 and k = 3. Moreover, FTN-6CAP-GIM with a roll-off factor α of 0.5 can achieve a larger compression factor of 0.44 when k = 2, and a 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 provided by the present application can effectively avoid excessive overlap of different signals in the frequency spectrum by using a gap activation mechanism to select activated subbands at the transmitting end and activating adjacent subbands at different times, thereby reducing the inter-band interference generated at the transmitting end. Since the gap index is used at the transmitting end to reduce the interference between signals, the received signal is relatively clear, the processing process is simplified, and the computational complexity is reduced. Moreover, the algorithm used at the transmitting end has low complexity, can achieve a high target data rate, and can transmit more information at a narrower bandwidth, thereby saving bandwidth resources.

[0097] Based on the FTN-mCAP interference mitigation method based on gap index modulation described above, the present application further provides an FTN-mCAP interference mitigation system based on gap index modulation, which comprises:

[0098] a transmitting end configured to generate a transmitting signal; input bits are mapped to m subband signals by FTN-mCAP-GIM, including:

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

[0100] According to the gap index set corresponding to the index bit, k subbands are activated in m subbands; the gap index set includes the serial number of the activated subband obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent subbands cannot be activated at the same time;

[0101] The constellation bits are transmitted by using the activated subbands to obtain m subband signals;

[0102] The m subband signals are up-sampled, and the real part and the imaginary part of each subband signal after up-sampling are separated, and the real part and the imaginary part of each subband signal are subtracted after passing through FTN in-phase filters and FTN quadrature filters respectively to obtain a target signal of each subband;

[0103] The target signals of all subbands are combined to generate a transmission signal;

[0104] A VLC channel is used to transmit the transmission signal;

[0105] A receiving end is used to obtain a receiving signal; the receiving signal passes through an FTN matched filter to obtain m receiving subband signals, and the m receiving subband signals pass through down-sampling and FTN-mCAP-GIM demapping to obtain output bits.

[0106] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can adopt a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt a computer program product in the form of one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program codes.

[0107] The present application is described with reference to flowcharts and / or block diagrams according to the method, device (system), and computer program product of the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to produce a machine, so that the instructions executed by the computer or other programmable data processing devices produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one or more flows and / or blocks Figure 1 The functions specified in one or more flows and / or blocks

[0108] These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the flow Figure 1 of the flow or flows and / or blocks Figure 1 of the block or blocks specified in the flow.

[0109] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the flow Figure 1 of the flow or flows and / or blocks Figure 1 of the block or blocks specified in the flow.

[0110] Obviously, the above-described embodiments are only examples and are not intended to limit the present application. Other variations and modifications can be made based on the above description and illustrations, and the present application is not limited to the embodiments described above. The scope of the present application is defined by the appended claims rather than the embodiments described above.

Claims

1. A FTN-mCAP interference mitigation method based on gap index modulation, characterized in that, Applied to a transmitting end, comprising: The input bits are mapped into m sub-band signals through FTN-mCAP-GIM mapping, comprising: The input bits include index bits and constellation bits; According to a gap index set corresponding to the index bits, k sub-bands are activated in the m sub-bands; the gap index set includes serial numbers of activated sub-bands obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent sub-bands cannot be activated at the same time; The constellation bits are transmitted by using the activated sub-bands to obtain m sub-band signals; The m sub-band signals are up-sampled, and the real part and the imaginary part of each sub-band signal after up-sampling are separated, and the real part and the imaginary part of each sub-band signal are subtracted after passing through an FTN in-phase filter and an FTN quadrature filter respectively to obtain a target signal of each sub-band; All target signals of the sub-bands are combined to generate a transmitting signal, so that the transmitting signal is transmitted to a receiving end through a VLC channel, and the receiving signal of the receiving end is obtained through an FTN matched filter to obtain m receiving sub-band signals, and the m receiving sub-band signals are down-sampled and FTN-mCAP-GIM demapped 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 numbers of the activated sub-bands are determined according to the gap activation mechanism to form an initial gap activation index set; according to the size of the index bits, 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 gap index modulation is reserved as a 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 numbers of activated subbands are determined according to the gap activation mechanism to form an initial gap activation index set {1, 3} {1, 4} {2, 4}; the size of index bits is 1 bit, and therefore 2 1 An index set, and the initial gap activation index set {2, 4} with relatively small gaps and large power attenuation is discarded, so that the target gap activation index set is {1, 3} {1, 4}.

4. The FTN-mCAP interference mitigation method based on gap index modulation of claim 1, wherein, The number of subband signals m=6, the number of activated subbands k=2, the sequence number of activated subbands is determined according to the gap activation mechanism, and the 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} is constituted; the size of the index bit is 3 bits, and the gap index modulation process needs 2 3 The index set, the initial gap activation index set {3, 5} {4, 6} is discarded because the gap is relatively small and the power attenuation is relatively large, 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 of claim 1, wherein, When the number of sub-band signals m is 6 and the number of activated sub-bands k is 3, the serial numbers of the activated sub-bands 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}; and the size of the index bits is 2 bits, so 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 of claim 1, wherein, The modulation mode of the constellation bits is M-QAM.

7. The FTN-mCAP interference mitigation method based on gap index modulation of claim 1, wherein, 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, wherein, The formula of the FTN in-phase filter and the FTN quadrature filter is respectively represented as: wherein, denotes the impulse response of the FTN in-phase filter corresponding to the real part of the nth subband signal, t denotes time, g(t) denotes the impulse response of the baseband shaping filter, f c,n denotes the center frequency of the nth subband, denotes the impulse response of the FTN quadrature filter corresponding to the imaginary part of the nth subband signal.

9. The FTN-mCAP interference mitigation method based on gap index modulation according to claim 8, wherein, The center frequency f of the nth sub-band c,n is represented as: Wherein, B represents a signal bandwidth, m represents a total number of sub-bands, and β represents a spectrum compression factor.

10. A FTN-mCAP interference mitigation system based on gap index modulation, characterized in that, Comprising: A transmitting end for generating a transmitting signal; The input bits are mapped into m sub-band signals through FTN-mCAP-GIM mapping, comprising: The input bits include index bits and constellation bits; According to a gap index set corresponding to the index bits, k sub-bands are activated in the m sub-bands; the gap index set includes serial numbers of activated sub-bands obtained according to a gap activation mechanism; the gap activation mechanism is that adjacent sub-bands cannot be activated at the same time; The constellation bits are transmitted by using the activated sub-bands to obtain m sub-band signals; The m sub-band signals are up-sampled, and the real part and the imaginary part of each sub-band signal after up-sampling are separated, and the real part and the imaginary part of each sub-band signal are subtracted after passing through an FTN in-phase filter and an FTN quadrature filter respectively to obtain a target signal of each sub-band; All target signals of the sub-bands are combined to generate a transmitting signal; A VLC channel for transmitting the transmitting signal; The receiving end is used for acquiring a receiving signal; the receiving signal is subjected to FTN matched filtering to obtain m receiving sub-band signals; the m receiving sub-band signals are subjected to downsampling and FTN-mCAP-GIM demapping to obtain output bits.

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