A FBMC-OQAM passband underwater acoustic communication system realizing peak-to-average ratio suppression

Abstract

The present application discloses an FBMC‑OQAM passband underwater acoustic communication system for realizing peak-to-average ratio suppression, and relates to the field of FBMC‑OQAM passband underwater acoustic communication systems. The system adds a compression and expansion processing module to a transmitting link, and adds a de-spreading processing module to a receiving link. The Laplace distribution function is used to fit the signal amplitude according to the data characteristics of the passband transmission signal, and then the expression of the peak-to-average ratio of the passband transmission signal after compression and expansion is constructed in combination with the function of the compression and expansion function. Then, the compression and expansion function with known compression and expansion parameters can be used so that the compression and expansion processing module compresses and expands the passband transmission signal according to the compression and expansion function to obtain a compressed passband transmission signal with a smaller peak-to-average ratio, and then sends it, and performs inverse processing and de-spreading at the receiving end. The system can realize FBMC‑OQAM peak-to-average ratio suppression, which is beneficial to improving the transmission distance.

Description

Technical Field

[0001] The present application relates to the field of FBMC-OQAM passband underwater acoustic communication systems, and in particular to a FBMC-OQAM passband underwater acoustic communication system that achieves peak-to-average ratio suppression. Background Art

[0002] At present, the passband underwater acoustic communication system based on FBMC-OQAM (Filter Bank-Based MultiCarrier / OffsetQuadrature Amplitude Modulation) waveform is mainly used to realize shallow water underwater acoustic communication. The system schematic diagram is shown in the figure. Figure 1 As shown, the FBMC-OQAM passband underwater acoustic communication system includes a transmitting link, an underwater acoustic channel and a receiving link. In the transmitting link, the code stream to be transmitted (generally a binary bit stream) is subjected to QAM modulation and OQAM preprocessing, and then enters the synthesis filter group, and forms a baseband transmission signal after parallel-to-serial conversion. Thereafter, a time domain passband transmission signal is generated after a transmitting end preprocessing including upsampling and up-conversion. The transmitting link sends the time domain passband transmission signal to the receiving link through the underwater acoustic channel. The time domain passband transmission signal reaches the passband receiving link after being distorted by the underwater acoustic channel. Since the underwater non-uniform Doppler frequency shift has a great influence on the system performance, in the receiving link, the time domain receiving signal is usually first resampled and preprocessed to compensate for part of the non-uniform Doppler frequency shift. Thereafter, the receiving link performs the inverse process of the transmitting end on the time domain receiving signal, that is, after serial-to-parallel conversion, analysis filter group, OQAM post-processing and QAM demodulation, the receiving code stream is finally obtained. The synthesis filter group and the analysis filter group are both obtained by prototype filter modulation.

[0003] The passband underwater acoustic communication system based on FBMC-OQAM waveform adopts prototype filter combined with offset quadrature amplitude modulation technology. Subcarrier-by-subcarrier filtering makes it have extremely low sidelobes, thus obtaining better anti-carrier frequency deviation characteristics. In addition, the use of offset quadrature amplitude modulation makes it unnecessary to use cyclic prefix to resist channel multipath interference, thereby improving the bandwidth utilization.

[0004] However, since the FBMC-OQAM waveform is generated by the superposition of multiple subcarriers, the FBMC-OQAM waveform has a natural high peak-to-average ratio characteristic. In fact, due to its own special data frame structure, the FBMC-OQAM waveform faces a more severe peak-to-average ratio challenge. The full name of the peak-to-average ratio is the Peak to Average Power Ratio (PAPR). The peak-to-average ratio is a measurement parameter of the waveform. For shallow water horizontal communication scenarios, in the case of a large peak-to-average ratio, due to the limitation of the power amplifier on the peak power, the overall average power of the time domain passband transmission signal will be too small, affecting the transmission distance of the FBMC-OQAM underwater acoustic communication system. Summary of the invention

[0005] In view of the above problems and technical requirements, this application proposes a FBMC-OQAM passband underwater acoustic communication system that realizes peak-to-average ratio suppression. The technical solution of this application is as follows:

[0006] A FBMC-OQAM passband underwater acoustic communication system for realizing peak-to-average ratio suppression, the FBMC-OQAM passband underwater acoustic communication system comprising a transmitting link, an underwater acoustic channel and a receiving link, the transmitting link comprising a passband signal generating module and a companding processing module, the receiving link comprising a despreading processing module and a receiving signal parsing module;

[0007] The passband signal generation module is used to generate the code stream to be sent to generate the passband transmission signal s p (t d ), the compression and expansion processing module is used to compress the passband transmission signal s according to the compression and expansion function p (t d ) is compressed and expanded, and the compressed and expanded passband transmission signal is sent to the receiving link through the underwater acoustic channel. Passband transmit signal after compression and expansion The peak-to-average ratio is lower than the passband transmission signal s p (t d ) peak-to-average ratio, t d represents a discrete time index,

[0008] The despreading processing module is used to process the original received signal y(t d ) to perform decompression and expansion processing to obtain the received signal after decompression and expansion The received signal analysis module is used to analyze the received signal after despreading. Parse to obtain the received code stream;

[0009] The method for determining the companding function used by the companding processing module and the despreading function used by the despreading processing module includes:

[0010] Using the Laplace distribution function to fit the passband transmission signal sp (t d ), the signal amplitude f(s) in a single data frame, the location parameter μ of the Laplace distribution function used is 0, and the scale parameter λ is based on the passband transmission signal s p (t d )'s average power To determine, s is a complex parameter;

[0011] According to the function form of the compression and expansion function, the signal amplitude f(s) in a single data frame is combined to construct the compressed and expanded passband transmission signal Peak-to-average ratio The expression of peak-to-average ratio The expression of includes the unknown compression parameters in the compression function;

[0012] In satisfying Under the condition of , the value of the compression parameter in the compression function is determined to obtain the compression function used by the compression processing module, and the inverse transformation process of the compression function is taken to obtain the despreading function used by the despreading processing module, PAPR (s p (t d )) is the passband transmit signal s p (t d ) of the peak-to-average ratio.

[0013] Its further technical solution is that the compression and expansion processing module is The compression and expansion function of the passband transmission signal s p (t d ) after linear asymmetric compression and expansion, the compression and expansion parameters in the compression and expansion function include the compression and expansion ratio coefficient C and the power threshold D, A M is the passband transmit signal s p (t d )'s maximum power.

[0014] A further technical solution is that the compression and expansion processing module is also used to send the time index set θ to the receiving link through the underwater acoustic channel. 1 (D) and the time index set θ 2 (D), time index set θ 1 (D) is to transmit the signal s in the passband p (t d ) is determined when linear asymmetric compression and expansion is performed to satisfy 0<|s p (t d )|≤D, the time index set θ 2 (D) is to transmit the signal s in the passband p (t d ) is determined when performing linear asymmetric compression and expansion to satisfy D<|s p (t d )|≤AM A collection of discrete-time indices of ;

[0015] The despreading processing module is also used to obtain the time index set θ through the underwater acoustic channel 1 (D) and the time index set θ 2 (D) and in accordance with The despreading function of the original received signal y(t d ) performs linear asymmetric decompression and expansion processing.

[0016] Its further technical solution is to construct a passband transmission signal after compression and expansion Peak-to-average ratio The expressions include:

[0017] According to the function form of the compression and expansion function, the signal amplitude f(s) in a single data frame is combined to construct the compressed and expanded passband transmission signal The average power The expression for average power The expression for contains unknown compression parameters;

[0018] Construct the passband transmission signal after compression and expansion according to the function form of the compression and expansion function Maximum power

[0019] Construct the passband transmission signal after compression and expansion Peak-to-average ratio

[0020] A further technical solution is to use the Laplace distribution function to fit the passband transmission signal s p (t d ) in a single data frame According to the function form of the compression and expansion function, the signal amplitude f(s) in a single data frame is combined to construct the compressed and expanded passband transmission signal The average power The expression is:

[0021]

[0022] A further technical solution is to use the Laplace distribution function to fit the passband transmission signal s p (t d ), the scale parameter of the Laplace distribution function used satisfies The passband transmission signal after compression and expansion is obtained The average power The expression is:

[0023]

[0024] A further technical solution is that the method for determining the compression function used by the compression processing module and the de-spreading function used by the de-spreading processing module further includes:

[0025] Based on the passband transmit signal s p (t d ) and the passband transmit signal after compression and expansion All normalized features are determined Sure The conditions are It is established and expressed as:

[0026]

[0027] A further technical solution is that determining the value of the compression parameter in the compression function includes:

[0028] Determine satisfaction The coefficient value range of the compression and expansion ratio coefficient C and the threshold value range of the power threshold D under the conditions;

[0029] Within the coefficient value range and the threshold value range, select the passband transmission signal after compression and expansion. The combination of the compression and expansion ratio coefficient C and the power threshold D with the lowest peak-to-average ratio.

[0030] A further technical solution is that the combination of values ​​for determining the compression and expansion ratio coefficient C and the power threshold D also includes:

[0031] Selecting the value of the compression and expansion ratio coefficient C within the coefficient value range so that the system bit error rate of the FBMC-OQAM passband underwater acoustic communication system reaches the bit error rate requirement;

[0032] Based on the determined value of the compression and expansion ratio coefficient C, the threshold value range is updated, and the passband transmission signal after compression and expansion is selected within the updated threshold value range. The value of the power threshold D with the lowest peak-to-average ratio.

[0033] A further technical solution is that the method for determining the compression function used by the compression processing module and the de-spreading function used by the de-spreading processing module further includes:

[0034] A variety of different distribution functions are used to fit the amplitude of each FBMC-OQAM waveform. The distribution functions used are consistent with the amplitude trend of the FBMC-OQAM data frame modulation method, which has a large amplitude in the middle and small amplitudes on both sides.

[0035] Amplitude fitting is performed on a plurality of different FBMC-OQAM waveforms having different numbers of symbol blocks in a single data frame, respectively, and the number of symbol blocks in a single data frame of all FBMC-OQAM waveforms does not exceed a quantity threshold;

[0036] The amplitude fitting results of all FBMC-OQAM waveforms are comprehensively analyzed to determine the Laplace distribution function with the best amplitude fitting effect to fit the passband transmission signal s p (t d ) is the signal amplitude f(s) within a single data frame.

[0037] The beneficial technical effects of this application are:

[0038] The present application discloses an FBMC-OQAM passband underwater acoustic communication system for realizing peak-to-average ratio suppression. The system uses the Laplace distribution function to fit the amplitude according to the data characteristics of low energy of symbols on both sides and high energy of symbols in the middle superimposed part caused by the modulation mode of FBMC-OQAM, and then constructs an expression of the peak-to-average ratio of the passband transmission signal after compression and expansion in combination with the function form of the compression and expansion function. Finally, based on the characteristic that the peak-to-average ratio of the passband transmission signal after compression and expansion is less than the peak-to-average ratio of the passband transmission signal, the value of the compression and expansion parameter in the compression and expansion function can be optimally determined. After the passband transmission signal is compressed and expanded according to the determined compression and expansion function, FBMC-OQAM peak-to-average ratio suppression can be realized, which is beneficial to improving the transmission distance of the FBMC-OQAM passband underwater acoustic communication system.

[0039] In addition, when determining the value of the compression and expansion parameter, not only the suppression of the peak-to-average ratio is considered, but also the impact of the compression and expansion parameter on the bit error rate performance is considered. Ultimately, the compression and expansion parameter that achieves the lowest peak-to-average ratio while ensuring the bit error rate performance is selected. This allows the peak-to-average ratio to be suppressed while avoiding the degradation of the bit error rate performance caused by the compression and expansion processing, thereby ensuring system performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is the system structure diagram of the existing traditional FBMC-OQAM passband underwater acoustic communication system.

[0041] Figure 2 It is a system structure diagram of the FBMC-OQAM passband underwater acoustic communication system of the present application.

[0042] Figure 3 It is a flow chart of a method for determining compression and expansion parameters in one embodiment of the present application.

[0043] Figure 4 It is a schematic diagram of the FBMC-OQAM interleaved superposition data frame modulation method.

[0044] Figure 5: are the amplitude distribution diagram of the FBMC-OQAM signal and the amplitude curves fitted using the Laplace distribution function and the Gaussian distribution function respectively.

[0045] Figure 6 The graph is a surface diagram of the peak-to-average ratio of the passband transmission signal after compression and expansion under different combinations of compression and expansion ratio coefficients and power thresholds within the coefficient value range and the threshold value range when CCDF=0.1 in an example.

[0046] Figure 7 It is a surface diagram of the peak-to-average ratio of the passband transmission signal after compression and expansion at different power thresholds and different CCDF levels when the compression and expansion ratio is 0.7.

[0047] Figure 8 The present invention is a comparison chart of peak-to-average ratio suppression CCDF curves of an original passband transmission signal, a passband transmission signal compressed and expanded using a comparative example method, and a passband transmission signal compressed and expanded using the method of the present application in an example.

[0048] Fig. 9 The present invention is a comparison chart of bit error rate curves of an original passband transmission signal, a passband transmission signal compressed and expanded using a comparative example method, and a passband transmission signal compressed and expanded using the method of the present application in an example. DETAILED DESCRIPTION

[0049] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0050] This application discloses a FBMC-OQAM passband underwater acoustic communication system that achieves peak-to-average ratio suppression. Please refer to Figure 2 The system structure shown in FIG. 1 is a FBMC-OQAM passband underwater acoustic communication system, which includes a transmitting link, an underwater acoustic channel, and a receiving link. However, both the transmitting link and the receiving link are relatively Figure 1 There are improvements to the conventional structure shown, including:

[0051] The transmission link of the present application includes a passband signal generation module and a compression and expansion processing module. The passband signal generation module can adopt the structure of the transmission link in the existing FBMC-OQAM passband underwater acoustic communication system, such as based on Figure 1 The typical structure shown in the figure is that the passband signal generation module includes a QAM modulation unit, an OQAM preprocessing unit, a synthesis filter bank unit, a parallel-to-serial conversion unit, and a transmitter preprocessing unit. This application will not introduce this part in detail, and it will be collectively referred to as the passband signal generation module. The passband signal generation module is used to generate a code stream to be transmitted to generate a passband transmission signal s p (t d ), in the traditional structure, the passband transmission signal s generated by the passband signal generation modulep (t d ) is directly sent to the receiving link through the underwater acoustic channel. However, in the present application, a compression and expansion processing module is also added to the transmitting link, and the passband transmission signal s generated by the passband signal generation module p (t d ) is first sent to the compression and expansion processing module, which processes the passband transmission signal s according to the compression and expansion function. p (t d ) is compressed and expanded to obtain the passband transmission signal after compression and expansion Then the compressed and expanded passband transmission signal is sent to the receiving link through the underwater acoustic channel. Passband transmit signal after compression and expansion The peak-to-average ratio is lower than the passband transmission signal s p (t d ), thereby achieving peak-to-average ratio suppression, which is beneficial to improving the transmission distance of the FBMC-OQAM passband underwater acoustic communication system. d Represents a discrete time index.

[0052] The corresponding receiving link of the present application includes a despreading processing module and a receiving signal analysis module. The receiving signal analysis module can adopt the structure of the receiving link in the existing FBMC-OQAM passband underwater acoustic communication system, such as based on Figure 1 In the conventional structure, the received signal analysis module directly analyzes the original received signal y(t d ) is parsed to obtain the received code stream. However, the present application adds a despreading processing module in the receiving link. The despreading processing module firstly processes the original received signal y(t d ) to perform decompression and expansion processing to obtain the received signal after decompression and expansion The received signal analysis module then analyzes the despread received signal. Parse to get the received code stream.

[0053] Compared with the traditional structure, the FBMC-OQAM passband underwater acoustic communication system of the present application adds a compression and expansion processing module and a decompression processing module. The compression and expansion processing operation implemented by the compression and expansion processing module is the core of achieving peak-to-average ratio suppression to increase the transmission distance, and the decompression and expansion processing implemented by the decompression and expansion processing module can be regarded as the inverse process of the compression and expansion processing implemented by the compression and expansion processing module. Therefore, the method of determining the compression and expansion function used by the compression and expansion processing module is first introduced, please refer to Figure 3 The method flow chart shown:

[0054] First, the passband transmit signal s p (t d) is used to analyze the signal characteristics. FBMC-OQAM adopts interleaved superposition data frame modulation. The schematic diagram of interleaved superposition modulation is shown in Figure 4 As shown, a single data frame includes multiple symbol blocks, each of which includes a real part and an imaginary part. Starting from the first symbol block of the data frame, the real part and the imaginary part of each symbol block are interleaved and superimposed in sequence, for example Figure 4 In the embodiment, the second information bit of the real part of the first symbol block is superimposed and modulated with the first information bit of the imaginary part of the first symbol block, the third information bit of the real part of the first symbol block is superimposed and modulated with the second information bit of the imaginary part of the first symbol block and the first information bit of the real part of the second symbol block, and so on.

[0055] Based on this data frame modulation method, it can be found that the amplitude distribution of FBMC-OQAM has an obvious amplitude trend of large amplitude in the middle and small amplitude on both sides. Based on this amplitude trend, the function form of the compression function can be determined first. The function form of the compression function matches the amplitude distribution trend of FBMC-OQAM. In one embodiment, the function form of the compression function constructed by using a linear asymmetric compression processing method is:

[0056]

[0057] Among them, A M is the passband transmit signal s p (t d ) The compression parameters in the compression function include the compression ratio coefficient C and the power threshold D. The values ​​of these two compression parameters directly affect the effect of the compression function, so it is very critical to determine the values ​​of these two compression parameters.

[0058] The signal gain G of the FBMC-OQAM passband underwater acoustic communication system of the present application after compression and expansion transformation C It can be expressed as:

[0059]

[0060] Where PAPR(sp(td)) is the passband transmit signal s before compression and expansion. p (t d ) and represents the passband transmission signal s p (t d )’s average power.

[0061] is the passband transmit signal after compression and expansion The peak-to-average ratio of is the passband transmit signal after compression and expansion The maximum power can be expressed as Indicates the passband transmit signal after compression and expansion The average power of the passband transmitted signal after compression and expansion is related to the compression and expansion parameters.

[0062] Therefore, the ratio of the peak-to-average ratio before and after compression and expansion can be expressed as:

[0063]

[0064] The compression and expansion processing module uses the compression and expansion function to passband transmit signal s p (t d ) The core of compression and expansion is to make the passband transmission signal s p (t d ) becomes smaller after compression and expansion, so as long as equation (3) is greater than 1, So as to achieve the effect of peak-to-average ratio suppression. Therefore, it is necessary to construct a passband transmission signal after compression and expansion. Peak-to-average ratio The expression of is used to select the compression and expansion parameters that meet the conditions.

[0065] To construct the peak-to-average ratio To find the expression of the passband transmission signal s p (t d ) is used to fit the signal amplitude in a single data frame. When fitting, a suitable distribution function needs to be selected. The selected distribution function needs to conform to the amplitude trend of the FBMC-OQAM data frame modulation mode, which has a large amplitude in the middle and small amplitudes on both sides. However, there are many distribution functions that conform to this amplitude trend. For example, the common Laplace distribution function and Gaussian distribution function both conform to this amplitude trend. Selecting a distribution function based on experience cannot achieve a good fitting effect.

[0066] Therefore, in one embodiment, a plurality of different distribution functions are first used to perform amplitude fitting on each FBMC-OQAM waveform. The distribution function used here conforms to the amplitude trend of the FBMC-OQAM data frame modulation method, which has a large amplitude in the middle and small amplitudes on both sides. The number of symbol blocks contained in a single data frame in the FBMC-OQAM waveform does not exceed the quantity threshold. This is because in the actual communication signal design, the excessively long frame symbol will undoubtedly suffer from severe channel time-varying and noise during the transmission process. Therefore, in order to reduce the influence of interference and channel time-varying, the number of symbol blocks in a single data frame is generally set to be less than a preset quantity threshold, and the quantity threshold is typically 100.

[0067] For example, in one example, a single data frame contains 100 symbol blocks of FBMC-OQAM waveform as shown below: Figure 5 As shown in (a) in Figure 5 As can be seen from (a), when a single data frame contains 100 symbol blocks, the minimum amplitude value appears very efficiently. In this case, the results of amplitude fitting using the more commonly used Laplace distribution function and Gaussian distribution function are shown in Figure 1. Figure 5 As shown in (b), compared with Figure 5 (b) It can be seen that the fitting effect of using the Laplace distribution function is better. Figure 5 In (b), the blue curve represents the original amplitude curve, the yellow curve represents the amplitude curve fitted by the Laplace distribution function, and the red curve represents the amplitude curve fitted by the Gaussian distribution function.

[0068] The above amplitude fitting is performed on multiple different FBMC-OQAM waveforms containing different numbers of symbol blocks in a single data frame, and the number of symbol blocks contained in a single data frame in all FBMC-OQAM waveforms does not exceed the number threshold. The FBMC-OQAM waveforms with the number of symbol blocks less than the number threshold basically present Figure 5 The characteristics of (a), and basically the fitting effect of using Laplace distribution function is better.

[0069] Finally, the amplitude fitting results of all FBMC-OQAM waveforms can be integrated to determine the Laplace distribution function with the best amplitude modulation effect to fit the passband transmission signal s p (t d ) is the signal amplitude f(s) within a single data frame.

[0070] According to the above analysis of the amplitude distribution characteristics of FBMC-OQAM, when the number of symbol blocks contained in a single data frame does not exceed the number threshold, the efficiency of the amplitude minimum is very high. Therefore, the Laplace distribution function with position parameter μ = 0 is used to fit the passband transmission signal s p (t d ), and the scale parameter λ of the Laplace distribution function depends on the passband transmission signal s p (t d )'s average power Determine, s is a complex parameter. Therefore, the Laplace distribution function is used to fit the passband transmission signal s p (t d ) is expressed as:

[0071]

[0072] Then, according to the function form of the compression function and the signal amplitude f(s) in a single data frame, the compressed passband transmission signal can be constructed. Peak-to-average ratio The peak-to-average ratio constructed The expression for includes the unknown companding parameters in the companding function. As mentioned above, the peak-to-average ratio and Therefore, this step focuses on constructing the passband transmission signal after compression and expansion according to the function form of the compression and expansion function combined with the signal amplitude f(s) in a single data frame The average power The peak-to-average ratio can be constructed by Similarly, the average power is constructed The expression for contains unknown companding parameters.

[0073] According to the function form of the compression function of formula (1), the average power The expression is:

[0074]

[0075] Substituting the fitting expression of the signal amplitude in a single data frame of equation (4) into equation (5) can further obtain:

[0076]

[0077] By simplifying formula (6), we can further obtain:

[0078]

[0079] In one embodiment, according to the passband transmission signal s p (t d )'s average power When setting the scale parameter λ of the Laplace distribution function, let Therefore, there is Substituting it into equation (7) we can further obtain the average power including the compression and expansion parameters: The expression is:

[0080]

[0081] Formula (8) and Substituting into equation (3), we can get the solution that satisfies The value of the compression parameter of the condition.

[0082] In one embodiment, the signal is generally normalized before and after the compression and expansion process, that is, the passband transmission signal s p (t d ) and the passband transmit signal after compression and expansion All are normalized, based on which we can directly determine Therefore, we can further simplify formula (3) to determine It can be guaranteed The condition is established, and then the following inequality can be obtained through formula (8):

[0083]

[0084] Therefore, as long as formula (9) is satisfied, The condition is established, so the value of the corresponding compression and expansion parameter can be determined.

[0085] Whether the complete form of equation (3) or the simplified form of equation (9) is used to solve, When the conditions are met, generally only the coefficient value range of the compression and expansion ratio coefficient C and the threshold value range of the power threshold D can be determined, but the specific values ​​of these two compression and expansion parameters cannot be obtained. The compression and expansion ratio coefficient C and the power threshold D will affect the passband transmission signal after compression and expansion. The peak-to-average ratio of the two compression and expansion parameters exists in a certain coupling relationship.

[0086] Therefore, the compression and expansion ratio coefficient C is optimized according to the predetermined step within the coefficient value range, and the power threshold D is optimized according to the predetermined step within the threshold value range, so as to finally obtain the passband transmission signal after compression and expansion. The combination of the compression and expansion ratio coefficient C and the power threshold D with the lowest peak-to-average ratio.

[0087] In one example, in satisfying Under the conditions, it can be determined that the coefficient value range is [0.3, 0.5] and the threshold value range is [0.5, 0.7]. The compression ratio coefficient C is optimized in steps of 0.01 within the coefficient value range, and the power threshold D is optimized in steps of 0.01 within the threshold value range. When the CCDF (Complementary Cumulative Distribution Function) level is 0.1, the peak-to-average ratio under different value combinations of the compression ratio coefficient C and the power threshold D is obtained. Surfaces such as Figure 6 As shown. Figure 6 It can be seen from the example that the entire peak-to-average ratio plane will have a lower peak-to-average ratio when the power threshold D and the compression and expansion ratio coefficient C are small. When the power threshold D is small, the compression and expansion ratio coefficient C has a greater impact on the peak-to-average ratio. In addition, as the power threshold D or the compression ratio C increases, the peak-to-average ratio In this example, it can be determined that the passband transmission signal after compression and expansion is The compression and expansion coefficient C with the lowest peak-to-average ratio is 0.54, and the power threshold D is 0.3.

[0088] However, it can be found that the increase of the compression and expansion ratio coefficient C will cause the loss of the overall bit error rate performance of the system. At the same time, with the increase of the compression and expansion ratio coefficient C, the value of the power threshold D required to achieve the minimum bit error rate also increases, and the increase of the power threshold D will also reduce the overall bit error rate performance of the system. Therefore, in another embodiment, in order to avoid the problem of bit error rate performance degradation caused by adding compression and expansion processing, it is not directly selected in the whole domain so that the passband transmission signal after compression and expansion is Instead of choosing the compression ratio coefficient C and power threshold D with the lowest peak-to-average ratio, the bit error rate performance will be given priority. Since the change of power threshold D has a relatively small impact on the system bit error rate performance, the value of the compression ratio coefficient C that makes the system bit error rate of the FBMC-OQAM passband underwater acoustic communication system meet the bit error rate requirement is first selected within the coefficient value range. Then, based on the determined value of the compression ratio coefficient C, the value that satisfies The power threshold D value range of the condition is updated to update the threshold value range, and then the passband transmission signal after compression and expansion is selected within the updated threshold value range. The value of the power threshold D with the lowest peak-to-average ratio.

[0089] In the above example, the compression and expansion coefficient C is not directly determined to be 0.54, but the compression and expansion coefficient C is first determined to be 0.7 when the system bit error rate reaches the bit error rate requirement. Then, the threshold value range is updated to [0.3, 0.6] in combination with equation (3) or equation (9). The optimization is performed in steps of 0.01 after the updated threshold value range [0.3, 0.6]. On the basis of the compression and expansion coefficient C being 0.7, when CCDF is at different levels, the peak-to-average ratio of the power threshold D at different values ​​is The surface diagram of Figure 7 As shown by Figure 7 It can be seen that under different CCDFs, the value of the power threshold D with the lowest peak-to-average ratio is basically unchanged at 0.49, so the final value of the power threshold D is determined to be 0.49. On the basis of ensuring the system bit error rate, the final value is determined to make the passband transmission signal after compression and expansion The compression and expansion coefficient C with the lowest peak-to-average ratio is 0.7, and the power threshold D is 0.49.

[0090] The compression function used by the compression processing module has been determined by the above method, and then the despreading function used by the despreading processing module is obtained by taking the inverse transformation process of the compression function. Based on the function form of the compression function of formula (1), the despreading function can be determined as:

[0091]

[0092] The despreading processing module processes the original received signal y(t d ) performs linear asymmetric decompression and expansion processing. Among them, the time index set θ 1 (D) is to transmit the signal s in the passband p (t d ) is determined when linear asymmetric compression and expansion is performed to satisfy 0<|s p (t d )|≤D, the time index set θ 2 (D) is to transmit the signal s in the passband p (t d ) is determined when performing linear asymmetric compression and expansion to satisfy D<|s p (t d )|≤A M A collection of discrete-time indices.

[0093] Time index set θ 1 (D) and the time index set θ 2 (D) The compression and expansion processing module sends the compressed and expanded passband transmission signal to the receiving link through the underwater acoustic channel. Time index set θ 1 (D) and the time index set θ 2 (D) The packets are sent to the receiving link via the underwater acoustic channel.

[0094] Passband transmit signal after compression and expansion The original received signal y(t d ) can be expressed as ω(t d ) represents additive ambient noise, Q(t d ) represents the quantization environmental noise. It is worth noting that if the word length of the D / A converter is long enough, the impact of the quantization environmental noise can be ignored. In addition, the environmental noise of the receiving link after despreading can be expressed as The two noise terms and They are:

[0095]

[0096]

[0097] Among them, σ N represents the variance of additive ambient noise, σ Q Represents the variance of the quantization environment noise.

[0098] The same time index set θ received by the despreading processing module 1 (D) and the time index set θ 2 (D) is also affected by noise, but the noise does not change the time index set θ 1 The position of the discrete time index in (D) will therefore not affect the addressing of the discrete time index by the despreading processing module.

[0099] In order to prove the effectiveness of the present application, the present application also designs a comparative example to compare the effect of the present application method. The comparative example uses a Gaussian distribution function to fit the passband transmission signal s p (t d ), the subsequent steps can adopt the same steps of the present application. The peak-to-average ratio suppression CCDF curves when the original passband transmission signal is used, after the passband transmission signal is compressed and expanded using the comparative method (recorded as G-LNST), and after the passband transmission signal is compressed and expanded using the method of the present application (recorded as L-LNST) are as follows: Figure 8 As shown. Figure 8 It can be clearly seen that in terms of peak-to-average ratio suppression effect, under various conditions of the number of symbol blocks in a single frame, the compression and expansion processing method of the present application has a very obvious performance advantage. -3 At the horizontal level, the compression and expansion processing method of the present application can bring at least about 5dB performance advantage compared with the comparative method. Therefore, from the perspective of practical application, the compression and expansion processing method of the present application is undoubtedly a very reasonable solution.

[0100] In the case of using the original passband transmission signal, after companding the passband transmission signal using the comparative method (referred to as G-LNST), and after companding the passband transmission signal using the method of the present application (referred to as L-LNST), the bit error rate curves when the number of symbol blocks in a single data frame is different are as follows: Fig. 9 As shown, through Fig. 9 It can be seen that when a single data frame contains different numbers of symbol blocks, the compression and expansion processing method of the present application is superior to the comparative method in terms of bit error rate performance loss.

[0101] The above is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A FBMC-OQAM passband underwater acoustic communication system for peak-to-average ratio suppression, characterized in that: The FBMC-OQAM passband underwater acoustic communication system includes a transmitting link, an underwater acoustic channel and a receiving link, wherein the transmitting link includes a passband signal generating module and a companding processing module, and the receiving link includes a despreading processing module and a received signal parsing module; The passband signal generation module is used to generate the code stream to be sent to generate the passband transmission signal s p (t d ), the compression and expansion processing module is used to compress the passband transmission signal s according to the compression and expansion function p (t d ) is compressed and expanded, and the compressed and expanded passband transmission signal is sent to the receiving link through the underwater acoustic channel. Passband transmit signal after compression and expansion The peak-to-average ratio is lower than the passband transmission signal s p (t d ) peak-to-average ratio, t d represents a discrete time index; The compression and expansion processing module is based on The compression and expansion function of the passband transmission signal s p (t d ) after linear asymmetric compression and expansion, the compression and expansion parameters in the compression and expansion function include the compression and expansion ratio coefficient C and the power threshold D, A M is the passband transmit signal s p (t d )'s maximum power; The despreading processing module is used to process the original received signal y(t d ) to perform decompression and expansion processing to obtain the received signal after decompression and expansion The received signal analysis module is used to analyze the received signal after despreading. Parse to obtain the received code stream; The method for determining the companding function used by the companding processing module and the despreading function used by the despreading processing module includes: Using the Laplace distribution function to fit the passband transmission signal s p (t d ), the signal amplitude f(s) in a single data frame, the location parameter μ of the Laplace distribution function used is 0, and the scale parameter λ is based on the passband transmission signal s p (t d )'s average power To determine, s is a complex parameter; According to the function form of the compression and expansion function, the signal amplitude f(s) in a single data frame is combined to construct the compressed and expanded passband transmission signal Peak-to-average ratio The expression of peak-to-average ratio The expression of includes the unknown compression parameters in the compression function; among them, PAPR (s p (t d )) is the passband transmit signal s before compression and expansion p (t d ) and represents the passband transmission signal s p (t d )’s average power; Constructing the passband transmit signal after compression and expansion Peak-to-average ratio The expressions include: According to the function form of the compression function and the signal amplitude f(s) in a single data frame, the compressed passband transmission signal is constructed. The average power The expression for average power The expression for contains unknown compression parameters; Construct the passband transmission signal after compression and expansion according to the function form of the compression and expansion function Maximum power Construct the passband transmission signal after compression and expansion Peak-to-average ratio Using the Laplace distribution function to fit the passband transmission signal s p (t d ) in a single data frame According to the function form of the compression function and the signal amplitude f(s) in a single data frame, the compressed passband transmission signal is constructed. The average power The expression is: In using the Laplace distribution function to fit the passband transmission signal s p (t d ), the scale parameter of the Laplace distribution function used satisfies The passband transmission signal after compression and expansion is obtained The average power The expression is: In satisfying Under the condition of , the value of the compression parameter in the compression function is determined to obtain the compression function used by the compression processing module, and the inverse transformation process of the compression function is taken to obtain the despreading function used by the despreading processing module, PAPR (s p (t d )) is the passband transmit signal s p (t d ) of the peak-to-average ratio.

2. The FBMC-OQAM passband underwater acoustic communication system according to claim 1, characterized in that: The compression and expansion processing module is also used to send a time index set θ1(D) and a time index set θ2(D) to the receiving link through the underwater acoustic channel. The time index set θ1(D) is a set of time indexes for the passband transmission signal s p (t d ) is determined when linear asymmetric compression and expansion is performed to satisfy 0<|s p (t d )|≤D, the time index set θ2(D) is the set of discrete time indices for the passband transmitted signal s p (t d ) is determined when linear asymmetric compression and expansion is performed to satisfy D<|s p (t d )|≤A M A collection of discrete-time indices of ; The despreading processing module is also used to obtain the time index set θ1(D) and the time index set θ2(D) through the underwater acoustic channel, and The despreading function of the original received signal y(t d ) performs linear asymmetric decompression and expansion processing.

3. The FBMC-OQAM passband underwater acoustic communication system according to claim 2, characterized in that: The method for determining the companding function used by the companding processing module and the despreading function used by the despreading processing module also includes: Based on the passband transmit signal s p (t d ) and the passband transmit signal after compression and expansion All normalized features are determined Sure The conditions are It is established and expressed as:

4. The FBMC-OQAM passband underwater acoustic communication system according to claim 1, characterized in that: The values ​​of the compression parameters in the compression function are determined as follows: Determine satisfaction The coefficient value range of the compression and expansion ratio coefficient C and the threshold value range of the power threshold D under the conditions; Within the coefficient value range and the threshold value range, select the passband transmission signal after compression and expansion. The combination of the compression and expansion ratio coefficient C and the power threshold D with the lowest peak-to-average ratio.

5. The FBMC-OQAM passband underwater acoustic communication system according to claim 4, characterized in that: The combination of values ​​for determining the compression and expansion ratio coefficient C and the power threshold D also includes: Selecting the value of the compression and expansion ratio coefficient C within the coefficient value range so that the system bit error rate of the FBMC-OQAM passband underwater acoustic communication system reaches the bit error rate requirement; Based on the determined value of the compression and expansion ratio coefficient C, the threshold value range is updated, and the passband transmission signal after compression and expansion is selected within the updated threshold value range. The value of the power threshold D with the lowest peak-to-average ratio.

6. The FBMC-OQAM passband underwater acoustic communication system according to claim 1, characterized in that: The method for determining the companding function used by the companding processing module and the despreading function used by the despreading processing module also includes: A variety of different distribution functions are used to fit the amplitude of each FBMC-OQAM waveform. The distribution functions used are consistent with the amplitude trend of the FBMC-OQAM data frame modulation method, which has a large amplitude in the middle and small amplitudes on both sides. Amplitude fitting is performed on a plurality of different FBMC-OQAM waveforms having different numbers of symbol blocks in a single data frame, respectively, and the number of symbol blocks in a single data frame of all FBMC-OQAM waveforms does not exceed a quantity threshold; The amplitude fitting results of all FBMC-OQAM waveforms are comprehensively analyzed to determine the Laplace distribution function with the best amplitude fitting effect to fit the passband transmission signal s p (t d ) is the signal amplitude f(s) within a single data frame.

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