Underwater wireless optical communication system based on index modulation technique and multi-band CAP technique

Abstract

The application relates to the field of underwater wireless optical communication and discloses an underwater wireless optical communication system based on index modulation technology and a multi-band CAP technology, which comprises an optical transmitting module, an optical receiving module, a transmitting end signal processing module and a receiving end signal processing module. The transmitting end signal processing module carries out sub-band multi-mode ordering mapping and multi-band CAP modulation on original data, the receiving end signal processing module carries out multi-band CAP demodulation, multi-channel DFE equalization and signal-to-noise ratio weight-assisted multi-mode demapping on digital signals, and the original data is recovered. Compared with a traditional method, the mapping relationship between data and the ordering mode of a multi-constellation pattern is established, more index bit information can be transmitted, the error code rate can be reduced through the multi-channel DFE equalization and the weight-assisted demapping scheme, and the system performance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underwater wireless optical communication, and in particular to an underwater wireless optical communication system based on index modulation technology and multi-band CAP technology. BACKGROUND

[0002] In recent years, with the development of ocean exploration and monitoring technology, the demand for high-speed underwater wireless communication has increased dramatically. Underwater wireless optical communication (UWOC) in the blue-green spectrum range has the characteristics of low cost and high speed, and is expected to become a complementary means of underwater wireless communication. How to improve the achievable transmission rate in the bandwidth-limited UWOC system is an important problem that needs to be solved.

[0003] Currently, the commonly used spectrum-efficient modulation schemes in the UWOC system are orthogonal frequency division multiplexing (OFDM) and discrete multi-tone (DMT) modulation, but their high peak-to-average power ratio (PAPR) limits their application in UWOC. The carrierless amplitude phase (CAP) modulation has been widely proven to be a promising technology for practical visible light communication (VLC) systems due to its high spectral efficiency and low PAPR. Index modulation (IM) consumes little or no power by embedding resource activation state information in certain dimensions, achieving a trade-off between spectral efficiency (SE) and energy efficiency (EE). The combination of index modulation technology and CAP modulation technology can further improve the spectral efficiency and improve the performance of the communication system. The present application proposes a sub-band multi-mode sorting carrierless amplitude phase (SMMP-CAP) modulation technology. This technology uses a set of constellation of multiple modes to map signals in different frequency bands, and uses the sorting of these distinguishable modes to transmit additional information bits. Compared with the traditional combination of index modulation and CAP technology, this technology can transmit more index information. In addition, considering that the uneven channel has different signal-to-noise ratios (SNRs) in different frequency bands, a signal-to-noise ratio weight-assisted multi-mode demapping (SNR-WD) demodulator is proposed to improve the demodulation effect. Finally, considering the characteristics of the SNR-WD simultaneously demodulating multiple signals in parallel, a multi-channel decision feedback equalizer (MC-DFE) is proposed to equalize the received signal. The present application designs a complete set of modulation, demodulation and equalization schemes, effectively improving the performance of long-distance high-speed UWOC systems. SUMMARY

[0004] The purpose of the present application is to provide a digital signal processing technology that combines index modulation technology and multi-band CAP technology to effectively increase the communication rate of the system, improve the transmission performance, and reduce the bit error rate, in view of the low bandwidth characteristics of existing long-distance underwater wireless optical communication systems.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is:

[0006] An underwater wireless optical communication system based on index modulation technology and multi-band CAP technology, comprising: an optical transmitting module, an optical receiving module, a transmitting end signal processing module, and a receiving end signal processing module.

[0007] The optical transmitting module converts a digital signal into an optical signal and sends it to the optical receiving module; the optical receiving module converts the received optical signal into a digital signal; the transmitting end signal processing module sends the digital signal obtained after processing the original data to the optical transmitting module; the receiving end signal processing module processes the received digital signal to recover the original data; the transmitting end signal processing module is connected to the optical transmitting module; and the optical receiving module is connected to the receiving end signal processing module.

[0008] Further, the optical transmitting module comprises a signal generator, a power amplifier, an adjustable electric attenuator, a T-type biasing device, a direct current power module, a laser, and a collimating lens; wherein the signal generator, the power amplifier, the adjustable electric attenuator, the T-type biasing device, and the laser are connected in sequence, the T-type biasing device is provided with a biasing current by the direct current power module, and the transmitting end of the laser is arranged opposite to the collimating lens.

[0009] Further, the optical receiving module comprises a Fresnel lens, a photomultiplier tube, and a mixed signal oscilloscope; the Fresnel lens is arranged in front of the photomultiplier tube and used to converge the divergent light spots after long-distance transmission onto the detection surface of the photomultiplier tube; the photomultiplier tube is used to convert the optical signal into an electrical signal, the output of which is connected to the mixed signal oscilloscope through a cable; and the mixed signal oscilloscope is used to collect signals for subsequent processing by the receiving end signal processing module.

[0010] Further, the transmitting end signal processing module comprises a sub-band multi-mode ordering mapping module and a multi-band CAP modulation module.

[0011] The sub-band multi-mode ordering mapping module designs different constellation mapping sets, establishes a corresponding mapping relationship between the ordering of the constellation set and the information bits, and completes the symbol mapping of the data bits to the constellation points.

[0012] The multi-band CAP modulation module designs a pair of orthogonal Hilbert filters and completes the modulation of the multi-band CAP signal.

[0013] Further, the receiving end signal processing module comprises a multi-band CAP demodulation module, a multi-channel DFE equalization module, and a weight-assisted multi-mode demapping module.

[0014] The multi-band CAP demodulation module designs a matching filter, filters the down-sampled received signal, and completes the separation of the signals in each frequency band.

[0015] The multi-channel DFE equalization module is parallelly connected with multiple DFE equalizers, and all the decision modules in the multiple DFE equalizers are replaced with a weight-assisted multi-mode demapping module to complete equalization of the multiple signals.

[0016] The weight-assisted multi-mode demapping module calculates a signal-to-noise ratio weighted and corrected minimum Euclidean distance matrix, selects corresponding values from each row in the corrected minimum Euclidean distance matrix according to an ordering mode of a constellation mapping set, adds the values to obtain a sum, determines the constellation ordering mode corresponding to the group of symbols according to the minimum sum, and completes demodulation of the ordering information and subsequent demodulation of the mapped symbols in the constellation.

[0017] The application designs multiple mode constellation sets to map signals in different frequency bands on the basis of combination of the conventional index modulation and CAP modulation technology, and uses ordering of the distinguishable modes to transmit more additional information bits; considering that the signal-to-noise ratios of the symbols in different frequency bands are different, a signal-to-noise ratio weight-assisted multi-mode demapping scheme is proposed to improve the demodulation effect; finally, a multi-channel decision feedback equalizer is proposed to equalize the received signals. The application designs a complete set of modulation, demodulation and equalization schemes, and has a good application prospect in the long-distance underwater wireless optical communication system. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a structure schematic diagram of the underwater wireless optical communication system based on the index modulation technology and the multi-band CAP technology.

[0019] Figure 2 It is an algorithm flowchart of the transceiver end of the underwater wireless optical communication system based on the index modulation technology and the multi-band CAP technology.

[0020] Figure 3 It is a 4-constellation mapping relationship diagram designed for the sub-band multi-mode ordering mapping module.

[0021] Figure 4 It is a 4-constellation ordering and index information mapping relationship diagram designed for the sub-band multi-mode ordering mapping module.

[0022] Figure 5 It is a structure schematic diagram of the multi-channel DFE equalizer.

[0023] Figure 6 It is a relationship between the communication rate and the bit error rate of the underwater wireless optical communication system based on the index modulation technology and the multi-band CAP technology when transmitting 90 meters in a swimming pool. DETAILED DESCRIPTION

[0024] The specific embodiments of the application will be described in detail below with reference to the accompanying drawings;

[0025] As Figure 1As shown, the underwater wireless optical communication system based on index modulation technology and multi-band CAP technology comprises a transmitting end signal processing module, a signal generator, a power amplifier, an adjustable electric attenuator, a T-type biasing device, a direct current power supply, a laser, a collimating lens, a transmitting end watertight cabin, a mirror, a Fresnel lens, a photomultiplier tube, a receiving end watertight cabin, a mixed signal oscilloscope and a receiving end signal processing module.

[0026] The transmitting end signal processing module generates a digital signal after processing original data, and loads the digital signal into the signal generator through a USB data line. The electrical signal generated by the signal generator is amplified by the power amplifier, and the signal power is adjusted by the adjustable electric attenuator. The direct current power supply module provides a direct current bias to make the laser work in a linear range. The T-type biasing device is used to superimpose a direct current bias on the signal. The output signal of the T-type biasing device is used to drive the laser after being transmitted through a cable. The collimating lens is used to adjust the exit angle of the laser. The laser and the collimating lens are installed in the transmitting end watertight cabin.

[0027] The optical signal enters the water, is reflected by the mirror once and reaches the receiving end. The Fresnel lens is used to converge the energy of the light spot to the photomultiplier tube. The photomultiplier tube converts the optical signal into an electrical signal and transmits the electrical signal to the mixed signal oscilloscope. The mixed signal oscilloscope samples the electrical signal and imports the sampled signal into the receiving end signal processing module. The receiving end signal processing module processes the sampled signal to restore the original data.

[0028] As shown in the transmitting end signal processing module, Figure 2 the transmitting end signal processing module comprises a sub-band multi-mode ordering mapping module and a multi-band CAP modulation module, which respectively map and modulate the data to be transmitted.

[0029] The sub-band multi-mode ordering mapping module designs four sets of constellation mapping sets. As shown in the four sets of constellation mapping sets, Figure 3 there are 24 ordering modes, and 16 of them are selected to transmit 4-bit index information, to establish a corresponding relationship between the ordering mode and the information bits. The specific corresponding relationship is shown in the four sets of constellation mapping sets. Figure 4 Each set of constellation mapping set internally contains four constellation mapping points, which can transmit 2-bit information. The sub-band multi-mode ordering mapping module completes the symbol mapping of data bits to constellation points according to these mapping relationships.

[0030] The multi-band CAP modulation module designs four sets of orthogonal Hilbert filter pairs. The up-sampled symbols are convolved with the corresponding orthogonal Hilbert filter pairs to complete the modulation of the multi-band CAP signal.

[0031] As shown in the receiving end signal processing module, Figure 2As shown, including multi-band CAP demodulation module, multi-channel DFE equalization module and weight-assisted multi-mode demapping module, respectively, band separation, equalization and mapping of the received data are performed;

[0032] The multi-band CAP demodulation module designs four groups of matched filters corresponding to the orthogonal Hilbert filters at the transmitting end, and performs convolution on the down-sampled received signal to separate four groups of signals;

[0033] The multi-channel DFE equalization module connects four decision feedback equalizers in parallel, wherein the tap number of the feedforward equalizer is 51, and the tap number of the feedback equalizer is 25. Figure 5 As shown, the equalization of the multi-channel signal is completed;

[0034] The weight-assisted multi-mode demapping module first estimates the signal-to-noise ratio of the signals in the four frequency bands, and then calculates the minimum Euclidean distance between the symbols in the four frequency bands and the four constellation mapping sets in a symbol period. × A 4x4 minimum Euclidean distance matrix is constructed, each row of the matrix is multiplied by the signal-to-noise ratio coefficient of the corresponding frequency band to obtain a corrected minimum Euclidean distance matrix, each row of the matrix represents the corresponding frequency band, and each column represents the corresponding constellation mapping set.

[0035] Figure 6 In order to transmit the error code rate of the signal corresponding to different rates after 90 meters in the swimming pool, it can be seen from the figure that the method proposed in the application can achieve a communication rate of 560Mbps, which is 20Mbps higher than the traditional multi-band CAP modulation scheme, and the error code rate performance is also better than the traditional scheme when the rate is low;

[0036] Finally, it should be noted that the above enumeration is only a specific embodiment of the present application. Obviously, the present application is not limited to the above embodiments, but can have many variations. All variations that can be directly derived or inferred from the content disclosed in the present application by those of ordinary skill in the art should be considered as falling within the scope of protection of the present application.

[0037] Although the specific embodiments of the present application have been described in detail above, the present application is not limited to the above embodiments, but can have various changes within the knowledge of those skilled in the art without departing from the purpose of the present application, and modifications or variations without creative labor are still within the scope of protection of the present application.

Claims

1. An underwater wireless optical communication system based on indexed modulation technology and multi-band CAP technology, characterized in that, include: Optical transmitting module, optical receiving module, transmitting end signal processing module, receiving end signal processing module; The optical transmitting module converts digital signals into optical signals and sends them to the optical receiving module; The optical receiving module converts the received optical signal into a digital signal; the transmitting signal processing module sends the digital signal obtained after processing the original data to the optical transmitting module; the receiving signal processing module processes the received digital signal to recover the original data; the transmitting signal processing module and the optical transmitting module are connected; the optical receiving module and the receiving signal processing module are connected. The transmitter signal processing module includes a sub-band multi-mode sorting and mapping module and a multi-band CAP modulation module. The sub-band multi-mode sorting mapping module first designs N different constellation mapping sets based on the number of sub-bands N. Each constellation mapping set can transmit b m Each bit of information; the number of bits that can be transmitted in its full permutation is determined based on the number N of the constellation mapping set. Establish a mapping relationship between the sorting method of constellation sets and information bits, where A represents the permutation symbol in mathematical terms. This represents the number of possible permutations of N elements selected from N distinct elements and arranged in order; the data to be transmitted is divided into groups, each group containing b bits. t =b s +N×b m Based on the first b in each set of data s Each bit of data determines the constellation mapping set used sequentially for each sub-band, and the subsequent N×b... m Each bit of data is sequentially mapped to N constellation sets to complete the sub-band multi-mode sorting mapping; The multi-band CAP modulation module designs N pairs of orthogonal Hilbert filters based on the number of sub-bands N, and their expression is: Where g(t) is the root-raised cosine filter, f c,n It is the center frequency of the nth sub-band; after upsampling the symbols that have completed the sub-band multimode sorting mapping, the real and imaginary parts are convolved with the orthogonal Hilbert filter pair and then added to complete the multi-band CAP modulation; The receiver signal processing module includes a multi-band CAP demodulation module, a multi-channel DFE equalization module, and a weight-assisted multi-mode demapping module. The multi-band CAP demodulation module is designed with N sets of matched filters corresponding to the orthogonal Hilbert filter pairs of the transmitter to filter the downsampled received signal and complete the separation of signals in each frequency band. The weighted multimode demapping module sequentially calculates the minimum Euclidean distance of the signal in each separated frequency band within the N sets of constellation mappings, constructing an N... × The minimum Euclidean distance matrix of N: Where, r i C represents the symbol in the i-th frequency band. k Let s represent the set of mappings for the kth constellation. j The mapping points are defined; weights are designed based on the estimated signal-to-noise ratio of each frequency band, and the minimum Euclidean distance matrix is ​​corrected. The corrected minimum Euclidean distance matrix is ​​as follows: Where snr represents the signal-to-noise ratio, f1(snr), f2(snr), ..., f N (snr) represents the correction coefficients related to the signal-to-noise ratio of the signal in frequency band 1, frequency band 2, ..., frequency band N, respectively; Finally, based on the sorting method of the constellation mapping set, select the corresponding values ​​from each row of the corrected minimum Euclidean distance matrix and sum them; since there are a total of sorting methods for the constellation set... One, so we can get The sum of each element is determined by the constellation sorting method corresponding to the smallest sum. This method yields the index bit data represented by the sorting and enables the demodulation of subsequent constellation mapping symbols. The multi-channel DFE equalization module connects N decision feedback equalizers in parallel according to the number of sub-bands, and replaces N decision modules with one weighted multi-mode demapping module as described above, thereby completing the equalization of multiple signals.

2. The underwater wireless optical communication system based on index modulation technology and multi-band CAP technology according to claim 1, characterized in that, The optical emission module includes a signal generator, a power amplifier, an adjustable electrical attenuator, a T-type bias, a DC power supply module, a laser, and a collimating lens. The signal generator, power amplifier, adjustable electrical attenuator, T-type bias, and laser are connected in sequence. The T-type bias is provided with a DC bias signal by the DC power supply module. The emitting end of the laser is arranged opposite to the collimating lens.

3. The underwater wireless optical communication system based on index modulation technology and multi-band CAP technology according to claim 1, characterized in that, The optical receiving module includes a Fresnel lens, a photomultiplier tube, and a mixed-signal oscilloscope. The Fresnel lens is placed in front of the photomultiplier tube to focus the diverging light spot after long-distance transmission onto the detection surface of the photomultiplier tube. The photomultiplier tube is used to convert the optical signal into an electrical signal, and its output end is connected to the mixed-signal oscilloscope via a cable. The mixed-signal oscilloscope is used to collect signals for subsequent signal processing by the receiving end signal processing module.

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