Fast time-varying Doppler estimation and compensation method and system in underwater acoustic communication

Abstract

The invention provides an underwater acoustic communication fast time-varying Doppler estimation and compensation method and system, and the method comprises the steps: a transmitting end of underwater acoustic communication transmits an OFDM signal frame, and each OFDM symbol in the OFDM signal frame is preset with subcarrier bit information fixed for Doppler estimation as detection information; a receiving end receives an OFDM signal frame, Doppler estimation bit information preset in each OFDM symbol is utilized, Doppler frequency offset meeting the optimal significance of error bit information is searched within a certain range according to a set frequency offset interval, and then estimation and compensation are carried out; taking the optimal bit error information of the current OFDM symbol as a search index, and taking the corresponding Doppler frequency offset as a current Doppler frequency offset value; and gradually executing the operation on each OFDM symbol until the estimation compensation process is completed. According to the method, after Doppler estimation is corrected, the bit error rate of underwater acoustic OFDM communication is remarkably reduced, and the system performance is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater acoustic communication and signal processing, and in particular relates to an underwater acoustic communication fast time-varying Doppler estimation and compensation method and system. Background Art

[0002] Compared with wireless communication, the poor transmission characteristics of underwater acoustic channels pose a great challenge to high-performance underwater acoustic communication. The performance of underwater acoustic communication systems is usually severely limited by environmental background noise, multipath effects, and Doppler effects. Compared with radio communication, the Doppler factor in underwater acoustic communication is several orders of magnitude higher, and usually a small relative motion will produce a Doppler effect that cannot be ignored.

[0003] The Doppler effect can cause compression or stretching of the received signal in the time domain, resulting in the accumulation of symbol synchronization errors, which seriously deteriorates the demodulation performance of the receiver. Especially for high-data-rate mobile underwater communication scenarios, one of the factors that restricts the practical application of OFDM underwater acoustic communication using multi-carrier modulation is that it is extremely sensitive to Doppler. The influence of the Doppler effect not only causes the frequency offset of the subcarriers in the OFDM signal and destroys the orthogonality between the subcarriers, but also causes the amplitude of the output signal of each subcarrier to decrease, reducing the signal-to-noise ratio of the received signal. Therefore, Doppler estimation and compensation are an indispensable part of underwater acoustic OFDM communication research.

[0004] Domestic and foreign scholars have conducted a lot of research and exploration on Doppler estimation and compensation. Sharif BS et al. proposed a block Doppler estimation algorithm, Zakharov YV et al. proposed a mutual ambiguity function Doppler estimation algorithm, Li B, Tong F et al. proposed a quasi-gradient cross-correlation Doppler estimation algorithm, and Li B, Zheng S et al. proposed a bit error rate search Doppler estimation algorithm. These methods assume that the Doppler effect experienced by the entire signal frame is constant (corresponding to the uniform motion of the receiving and transmitting ends), and have achieved better Doppler estimation performance under this relatively ideal situation.

[0005] However, when there is variable speed motion between the receiving and transmitting ends of underwater acoustic communication, the estimation performance of the Doppler estimation algorithm proposed for the constant Doppler effect is often greatly reduced. Considering that time-varying Doppler is more suitable for underwater mobile platform underwater acoustic communication scenarios, the estimation of time-varying Doppler frequency deviation has become a research hotspot.

[0006] In view of this, it is very meaningful to propose a method and system for estimating and compensating fast time-varying Doppler in underwater acoustic communication. Summary of the invention

[0007] When there is variable speed motion between the receiving and transmitting ends of underwater acoustic communication, the estimation performance of the Doppler estimation algorithm proposed above for the constant Doppler effect is often greatly reduced. The present invention aims at underwater mobile platform underwater acoustic communication scenarios, and provides an underwater acoustic communication fast time-varying Doppler estimation and compensation method and system based on the OFDM symbol-by-OFDM symbol minimum bit error information criterion, which can effectively solve the problem of decreased underwater acoustic communication performance when there is variable speed motion between the receiving and transmitting ends in underwater mobile platform underwater acoustic communication.

[0008] In a first aspect, the present invention proposes a method for estimating and compensating fast time-varying Doppler in underwater acoustic communication, the method comprising the following steps:

[0009] In response to a transmitting end of underwater acoustic communication sending an OFDM signal frame, each OFDM symbol in the OFDM signal frame is pre-set with subcarrier bit information fixed for Doppler estimation as detection information;

[0010] The receiving end receives the OFDM signal frame, and uses the Doppler estimation bit information pre-set in each OFDM symbol to search for the Doppler frequency offset that satisfies the optimal meaning of the error bit information within a certain range according to the set frequency offset interval, and then estimates and compensates, and saves the corresponding demodulated Doppler estimation bit information and data transmission bit information;

[0011] Taking the optimal bit error information of the current OFDM symbol as the search index, taking the corresponding Doppler frequency offset as the Doppler frequency offset value of the current OFDM symbol, and saving the demodulated data transmission bit information corresponding to the Doppler frequency offset; and

[0012] Repeat the above steps, and gradually perform the above operations on each OFDM symbol until the estimation and compensation process of the entire OFDM signal frame is completed, and all the data transmission bit information is saved, so as to obtain the optimal demodulated data transmission bit information.

[0013] Preferably, it also includes: constructing a cost function from the perspective of time-frequency difference OFDM modulation and demodulation, and using the Doppler tolerance of the time-frequency difference OFDM modulation and demodulation system itself to suppress the influence of residual Doppler, without setting a high-density two-dimensional Doppler frequency offset-delay search grid.

[0014] Further preferably, the method further includes: determining the Doppler frequency offset of the optimal meaning of the bit error information by constructing the cost function; the cost function of the fast time-varying Doppler estimation and compensation algorithm based on the optimal bit error information can be expressed as: Where i represents the i-th OFDM symbol; ξ represents the Doppler frequency deviation; x s,i represents the local bit information sequence used for Doppler estimation in the i-th OFDM symbol; xt,i (ξ) represents the bit information sequence for Doppler estimation that is demodulated and recovered in the i-th OFDM symbol.

[0015] Further preferably, the Doppler in the optimal sense of the bit error information of the current OFDM symbol can be expressed as: Among them, [ξ b ,ξ e ] indicates the preset Doppler frequency deviation search range.

[0016] Preferably, the format of the OFDM signal frame to be sent includes: using a linear frequency sweep signal with a length of 22.7 ms as a synchronization signal of the transmission signal, and a blank signal thereafter as a protection interval.

[0017] Further preferably, it also includes: the two LFM signals before and after the OFDM data frame are used as block Doppler estimation, and the OFDM data frame is used as mutual ambiguity function Doppler estimation, quasi-gradient cross-correlation Doppler estimation and the Doppler estimation and compensation.

[0018] Further preferably, it also includes: when executing the Doppler estimation and compensation algorithm, the 201-bit information carried by each OFDM symbol in the OFDM data frame is used as the Doppler estimation of the current OFDM symbol, and the 67-bit information is used as data information transmission.

[0019] In a second aspect, an embodiment of the present invention further provides a system for estimating and compensating fast time-varying Doppler in underwater acoustic communication, comprising:

[0020] A transmitting end module, configured to send an OFDM signal frame, wherein each OFDM symbol in the OFDM signal frame is pre-set with subcarrier bit information fixed for Doppler estimation as detection information;

[0021] A receiving end module is configured to receive the OFDM signal frame, and use the Doppler estimation bit information pre-set in each OFDM symbol to search for the Doppler frequency offset that satisfies the optimal meaning of the error bit information within a certain range according to the set frequency offset interval, and then estimate and compensate, and save the corresponding demodulated Doppler estimation bit information and data transmission bit information;

[0022] The receiving end module is also configured to use the optimal bit error information of the current OFDM symbol as a search index, determine the corresponding Doppler frequency deviation as the Doppler frequency deviation value of the current OFDM symbol, and save the demodulated data transmission bit information corresponding to the Doppler frequency deviation; and repeatedly perform the above operations until the estimation and compensation process of the entire OFDM signal frame is completed, and save all the data transmission bit information, so as to obtain the optimal demodulated data transmission bit information.

[0023] Further preferably, it also includes: the receiving end module constructs a cost function from the perspective of time-frequency difference OFDM modulation and demodulation, and uses the Doppler tolerance of the time-frequency difference OFDM modulation and demodulation system itself to suppress the influence of residual Doppler, without setting a high-density two-dimensional Doppler frequency deviation-delay search grid.

[0024] Compared with the prior art, the beneficial results of the present invention are:

[0025] The present invention starts from the purpose of underwater information transmission through underwater acoustic communication, defines the Doppler frequency deviation value corresponding to the optimal bit error information on each OFDM symbol, thereby realizing Doppler estimation and compensation for each OFDM symbol in the entire OFDM signal frame; after the Doppler estimation is corrected, the bit error rate of underwater acoustic OFDM communication is significantly reduced, and the system performance is greatly improved; compared with the block Doppler estimation method, the mutual ambiguity function Doppler estimation method and the quasi-gradient cross-correlation Doppler estimation method, the fast time-varying Doppler estimation and compensation algorithm proposed by the present invention is more suitable for the scenario where there is variable speed motion at the receiving end and the transmitting end. Therefore, after the corresponding Doppler estimation and compensation, the underwater acoustic OFDM communication of this embodiment obtains the optimal bit error rate performance, and the system performance is significantly improved. The present invention constructs a cost function from the perspective of time-frequency differential OFDM modulation and demodulation, and utilizes the Doppler tolerance of the communication system itself to suppress the influence of residual Doppler. Therefore, there is no need to set a high-density two-dimensional Doppler frequency deviation-delay search grid, which greatly reduces the completion complexity of the method proposed in the present invention, thereby having the characteristics of simple algorithm implementation and convenient system implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated into and constitute a part of this specification. The accompanying drawings illustrate the embodiments and are used together with the description to explain the principles of the present invention. It will be easy to recognize other embodiments and many expected advantages of the present embodiment because they become better understood by reference to the following detailed description. The elements of the accompanying drawings are not necessarily to scale with each other. The same reference numerals refer to corresponding similar parts.

[0027] Figure 1 A schematic diagram of a flow chart of a method for estimating and compensating a fast time-varying Doppler in underwater acoustic communication according to an embodiment of the present invention;

[0028] Figure 2 A block diagram of an implementation method of an underwater acoustic communication fast time-varying Doppler estimation and compensation method according to an embodiment of the present invention;

[0029] Figure 3 A schematic diagram of a transmission signal frame format in a method for estimating and compensating for fast time-varying Doppler in underwater acoustic communication according to an embodiment of the present invention;

[0030] Figure 4 A schematic diagram of simulating Doppler frequency deviation in a method for estimating and compensating fast time-varying Doppler in underwater acoustic communication according to an embodiment of the present invention;

[0031] Figure 5 A comparison diagram of bit error rates of four Doppler estimation and compensation methods in the underwater acoustic communication fast time-varying Doppler estimation and compensation method according to an embodiment of the present invention;

[0032] Figure 6 It is a schematic diagram of a fast time-varying Doppler estimation and compensation system for underwater acoustic communication according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It is also necessary to explain that, for ease of description, only the parts related to the relevant invention are shown in the accompanying drawings.

[0034] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] The present invention belongs to the field of underwater acoustic communication and signal processing technology. The research focus of this field is to solve the problem of Doppler frequency shift caused by relative motion during signal transmission in an underwater environment. The Doppler effect is particularly significant in underwater acoustic communication, because underwater vehicles or communication platforms such as buoys are often in a dynamically changing environment, and their relative motion will cause changes in signal frequency, thereby affecting the communication quality.

[0036] In underwater acoustic communication systems, the purpose of Doppler estimation and compensation algorithms is to accurately estimate the Doppler frequency shift of the signal and perform corresponding compensation to ensure the effectiveness and robustness of underwater information transmission in mobile scenarios.

[0037] Compared with wireless communication, the poor transmission characteristics of underwater acoustic channels pose a great challenge to high-performance underwater acoustic communication. The performance of underwater acoustic communication systems is usually severely limited by environmental background noise, multipath effects, and Doppler effects. Since the propagation speed of sound waves in the ocean medium is very slow, about 1500m / s, and the speed of underwater mobile platforms is generally between 1.5m / s and 15m / s, the Doppler factor generated is about 1×10 -3 Up to 1×10 -2 Compared with radio communication, the Doppler factor in underwater acoustic communication is several orders of magnitude higher, and usually a small relative motion will produce a Doppler effect that cannot be ignored.

[0038] The specific process of the fast time-varying Doppler estimation and compensation method in underwater acoustic communication proposed by the present invention is described as follows:

[0039] In a first aspect, an embodiment of the present invention discloses a method for estimating and compensating fast time-varying Doppler in underwater acoustic communication, such as Figure 1 As shown, the method comprises the following steps:

[0040] S1, in response to the transmitting end of the underwater acoustic communication sending an OFDM signal frame, each OFDM symbol in the OFDM signal frame is pre-set with fixed subcarrier bit information for Doppler estimation as detection information;

[0041] S2, the receiving end receives the OFDM signal frame, and uses the Doppler estimation bit information pre-set in each OFDM symbol to search for the Doppler frequency offset that satisfies the optimal meaning of the error bit information within a certain range according to the set frequency offset interval, and then estimates and compensates, and saves the corresponding demodulated Doppler estimation bit information and data transmission bit information;

[0042] S3, taking the optimal bit error information of the current OFDM symbol as the search index, taking the corresponding Doppler frequency offset as the Doppler frequency offset value of the current OFDM symbol, and saving the demodulated data transmission bit information corresponding to the Doppler frequency offset; and

[0043] S4. Repeat the above steps, and gradually perform the above operations on each OFDM symbol until the estimation and compensation process of the entire OFDM signal frame is completed, and all the data transmission bit information is saved, so as to obtain the optimal demodulated data transmission bit information.

[0044] Specifically, when the receiving and transmitting ends of underwater acoustic communication have variable speed motion, the estimation performance of the Doppler estimation algorithm proposed above for the constant Doppler effect is often greatly reduced. Considering that time-varying Doppler is more in line with underwater mobile platform underwater acoustic communication scenarios, the estimation of time-varying Doppler frequency deviation has become a research hotspot. Aiming at underwater mobile platform underwater acoustic communication scenarios, the present invention proposes a method for estimating and compensating fast time-varying Doppler in underwater acoustic communication based on the OFDM symbol-by-OFDM symbol minimum bit error information criterion, which can effectively solve the problem of decreased performance of underwater acoustic communication when the receiving and transmitting ends of underwater mobile platform underwater acoustic communication have variable speed motion.

[0045] Considering that the purpose of underwater acoustic communication is to transmit underwater information, the present invention starts from the perspective of underwater information transmission implementation, defines the Doppler frequency deviation that best corresponds to the bit error information used for Doppler estimation subcarrier demodulation in the current OFDM symbol as the optimal bit error information Doppler on each OFDM symbol, and accordingly proposes a fast time-varying Doppler estimation and compensation method in underwater acoustic communication of the present invention, thereby realizing Doppler estimation and compensation for each OFDM symbol in the entire OFDM signal frame, and the specific implementation steps are as follows:

[0046] Step 1: The underwater acoustic communication transmitter sends an OFDM signal frame. In each OFDM symbol in the OFDM signal frame, subcarrier bit information used for Doppler estimation is preset as detection information;

[0047] Step 2: The receiving end receives the OFDM signal frame, and uses the Doppler estimation bit information pre-set in each OFDM symbol to perform Doppler search estimation and compensation in the optimal sense of error bit information within a certain range at the set frequency offset search interval, and saves the corresponding demodulated Doppler estimation bit information and data transmission bit information;

[0048] Step 3: Taking the optimal bit error information of the current OFDM symbol as the search index, the corresponding Doppler frequency offset is the Doppler frequency offset value of the current OFDM symbol obtained by the method proposed in the present invention, and saving the demodulated data transmission bit information corresponding to the Doppler frequency offset;

[0049] Step 4: Repeat steps 1-3, that is, perform the above process by OFDM symbol by OFDM symbol until the estimation and compensation process of the entire OFDM signal frame is completed, and all data transmission bit information is saved, which is regarded as obtaining the optimal demodulated data transmission bit information.

[0050] Furthermore, the fast time-varying Doppler estimation and compensation method proposed in the present invention constructs a cost function from the perspective of completing time-frequency differential OFDM modulation and demodulation, and uses its own Doppler tolerance to suppress the influence of residual Doppler. Therefore, there is no need to set up a high-density two-dimensional Doppler frequency deviation-delay search grid, which effectively reduces the computational complexity of the method proposed in the present invention.

[0051] The cost function of the fast time-varying Doppler estimation and compensation algorithm based on optimal bit error information proposed in the embodiment of the present invention can be expressed as:

[0052]

[0053] Where i represents the i-th OFDM symbol; ξ represents the Doppler frequency deviation; x s,i represents the local bit information sequence used for Doppler estimation in the i-th OFDM symbol; x t,i(ξ) represents the bit information sequence for Doppler estimation that is demodulated and recovered in the i-th OFDM symbol.

[0054] In summary, the Doppler in the optimal sense of the current OFDM symbol bit error information proposed in the embodiment of the present invention can be expressed as:

[0055]

[0056] In the formula, [ξ b ,ξ e ] indicates the preset Doppler frequency deviation search range.

[0057] It can be seen from formula (2) that, considering that the purpose of underwater acoustic communication is to transmit underwater information, the Doppler search estimation algorithm proposed in the optimal sense of the current OFDM symbol bit error information can realize fast time-varying Doppler estimation and compensation for each OFDM symbol, that is, to realize real-time tracking estimation and compensation of the Doppler effect, thereby adapting to the scenario where there is variable speed motion at the receiving and transmitting ends of underwater acoustic communication.

[0058] Furthermore, the fast time-varying Doppler estimation and compensation method according to the embodiment of the present invention is implemented as follows: Figure 2 shown. Figure 2 Wherein Δξ represents the frequency offset search interval used in searching for bit error information in the fast time-varying Doppler estimation and compensation method provided in the embodiment of the present invention.

[0059] Since the present invention constructs the cost function from the perspective of time-frequency differential OFDM modulation and demodulation, and utilizes the Doppler tolerance of the communication system itself to suppress the influence of residual Doppler, there is no need to set up a high-density two-dimensional Doppler frequency deviation-delay search grid, which greatly reduces the completion complexity of the method proposed in the present invention, thereby having the characteristics of simple algorithm implementation and convenient system implementation.

[0060] Specifically, the signal frame format transmitted by the embodiment of the present invention is as follows: Figure 3 As shown. A linear frequency sweep signal with a length of 22.7ms is used as the synchronization signal of the transmitted signal, and the blank signal thereafter is used as the protection interval. The two LFM signals before and after the OFDM data frame are used as block Doppler estimation, and the OFDM data frame is used as mutual ambiguity function Doppler estimation, quasi-gradient cross-correlation Doppler estimation and Doppler estimation of the method proposed in the present invention. In particular, when executing the Doppler estimation and compensation algorithm proposed in the present invention, the 201-bit information carried by each OFDM symbol in the OFDM data frame is used as the Doppler estimation of the current OFDM symbol, and the 67-bit information is used for data information transmission.

[0061] In this embodiment, in order to simulate the scenario where the underwater acoustic communication receiving end and the transmitting end have variable speed motion, different Doppler frequency offsets are introduced into the 30 OFDM symbols in the OFDM data frame by artificial resampling, such as Figure 4 As shown. Doppler estimation is performed by using the block Doppler estimation method, the mutual ambiguity function Doppler estimation method, the quasi-gradient cross-correlation Doppler estimation method and the Doppler estimation method proposed in the embodiment of the present invention, and then the received signal is resampled and compensated according to the estimated Doppler frequency offset. Under different signal-to-noise ratio conditions, Doppler estimation and compensation are performed on the OFDM signal when there is variable speed motion at the underwater acoustic communication transceiver. The bit error rate results are shown in the figure below. Figure 5 shown.

[0062] from Figure 5 It can be seen that after the Doppler estimation correction is performed by the Doppler estimation and compensation algorithm proposed in the embodiment of the present invention, the bit error rate of underwater acoustic OFDM communication is significantly reduced, and the system performance is greatly improved. Compared with the block Doppler estimation method, the mutual ambiguity function Doppler estimation method and the quasi-gradient cross-correlation Doppler estimation method, the fast time-varying Doppler estimation and compensation algorithm proposed in the embodiment of the present invention is more suitable for the scenario where the receiving end and the transmitting end have variable speed motion. Therefore, after the corresponding Doppler estimation and compensation, the underwater acoustic OFDM communication of this embodiment obtains the optimal bit error rate performance, and the system performance is significantly improved.

[0063] The embodiment of the present invention is aimed at the common underwater acoustic communication scenario when the receiving end and the transmitting end are in variable speed motion, and proposes an underwater acoustic communication fast time-varying Doppler estimation and compensation algorithm. The core innovation of the present invention is: starting from the purpose of underwater information transmission by underwater acoustic communication, the Doppler frequency deviation value corresponding to the optimal bit error information is defined on each OFDM symbol, so as to realize Doppler estimation and compensation for each OFDM symbol in the entire OFDM signal frame.

[0064] Specifically, by setting fixed subcarrier bit information for Doppler estimation on each OFDM symbol at the transmitting end, the receiving end uses the pre-set Doppler estimation bit information to perform Doppler search in the sense of optimal error bit information at the set frequency offset search interval, and uses the optimal error bit information for Doppler estimation subcarrier demodulation in the current OFDM symbol as the search index, completing the optimal Doppler frequency offset estimation of the current OFDM symbol while realizing the optimal data information subcarrier bit information demodulation of the current OFDM symbol. By performing the above process one by one OFDM symbol, the fast time-varying Doppler estimation and compensation process is completed from the perspective of optimal error bit information, thereby obtaining the optimal demodulation result.

[0065] Compared with the existing underwater acoustic communication Doppler estimation and compensation algorithms, the fast time-varying Doppler estimation and compensation algorithm proposed in the present invention has two outstanding features:

[0066] First, by defining the Doppler frequency deviation value corresponding to the optimal bit error information on each OFDM symbol, the traditional signal-level Doppler estimation is transformed into the search problem of the subcarrier demodulation bit error information of the current OFDM symbol Doppler estimation from the perspective of the optimal bit error information, thus solving the mismatch problem between signal-level Doppler estimation and bit-level demodulation.

[0067] Secondly, through the search, estimation and compensation of OFDM symbols one by one, the Doppler estimation and compensation in the fast time-varying underwater acoustic channel are completed, solving the problem of variable speed motion during information transmission between the underwater acoustic communication receiver and transmitter.

[0068] Further references Figure 6 As an implementation of the methods shown in the above figures, the present application provides an embodiment of a system, which is similar to Figure 1 Corresponding to the method embodiment shown, the system can be specifically applied to various electronic devices.

[0069] In a second aspect, an embodiment of the present invention further discloses a system for estimating and compensating fast time-varying Doppler in underwater acoustic communication, such as Figure 6 As shown, it includes: a transmitting end module 61 and a receiving end module 62.

[0070] The transmitting end module 61 is configured to send an OFDM signal frame, and each OFDM symbol in the OFDM signal frame is pre-set with subcarrier bit information fixed for Doppler estimation as detection information;

[0071] The receiving end module 62 is configured to receive the OFDM signal frame, and use the Doppler estimation bit information pre-set in each OFDM symbol to search for the Doppler frequency offset that satisfies the optimal meaning of the error bit information within a certain range according to the set frequency offset interval, and then estimate and compensate, and save the corresponding demodulated Doppler estimation bit information and data transmission bit information;

[0072] The receiving end module 62 is also configured to use the optimal bit error information of the current OFDM symbol as a search index, determine the corresponding Doppler frequency deviation as the Doppler frequency deviation value of the current OFDM symbol, and save the demodulated data transmission bit information corresponding to this Doppler frequency deviation; and repeatedly perform the above operations until the estimation and compensation process of the entire OFDM signal frame is completed, and save all the data transmission bit information, so as to obtain the optimal demodulated data transmission bit information.

[0073] In a preferred embodiment, the receiving end module 62 constructs a cost function from the perspective of time-frequency differential OFDM modulation and demodulation, and utilizes the Doppler tolerance of the time-frequency differential OFDM modulation and demodulation system itself to suppress the influence of residual Doppler, without setting a high-density two-dimensional Doppler frequency offset-delay search grid.

[0074] The functions of the above modules correspond to the methods and will not be repeated here.

[0075] The present invention starts from the purpose of underwater information transmission through underwater acoustic communication, defines the Doppler frequency deviation value corresponding to the optimal bit error information on each OFDM symbol, thereby realizing Doppler estimation and compensation for each OFDM symbol in the entire OFDM signal frame; after the corresponding Doppler estimation and correction of the present invention, the bit error rate of underwater acoustic OFDM communication is significantly reduced, and the system performance is greatly improved; compared with the block Doppler estimation method, the mutual ambiguity function Doppler estimation method and the quasi-gradient cross-correlation Doppler estimation method, the fast time-varying Doppler estimation and compensation algorithm proposed by the present invention is more suitable for the scenario where there is variable speed motion at the receiving end and the transmitting end. Therefore, after the corresponding Doppler estimation and compensation, the underwater acoustic OFDM communication of this embodiment obtains the optimal bit error rate performance, and the system performance is significantly improved.

[0076] The present invention constructs a cost function from the perspective of time-frequency differential OFDM modulation and demodulation, and utilizes the Doppler tolerance of the communication system itself to suppress the influence of residual Doppler. Therefore, there is no need to set a high-density two-dimensional Doppler frequency deviation-delay search grid, which greatly reduces the completion complexity of the method proposed in the present invention, thereby having the characteristics of simple algorithm implementation and convenient system implementation.

[0077] The above description is only a preferred embodiment of the present invention and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present invention is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above inventive concept. For example, the above features are replaced with the technical features with similar functions disclosed in the present invention (but not limited to) to form a technical solution.

Claims

1. A method for estimating and compensating fast time-varying Doppler in underwater acoustic communication, characterized in that: The method comprises the following steps: In response to a transmitting end of underwater acoustic communication sending an OFDM signal frame, each OFDM symbol in the OFDM signal frame is pre-set with subcarrier bit information fixed for Doppler estimation as detection information; The receiving end receives the OFDM signal frame, and uses the Doppler estimation bit information pre-set in each OFDM symbol to search for the Doppler frequency offset that satisfies the optimal meaning of the error bit information within a certain range according to the set frequency offset interval, and then estimates and compensates, and saves the corresponding demodulated Doppler estimation bit information and data transmission bit information; Taking the optimal bit error information of the current OFDM symbol as the search index, taking the corresponding Doppler frequency offset as the Doppler frequency offset value of the current OFDM symbol, and saving the demodulated data transmission bit information corresponding to the Doppler frequency offset; as well as Repeat the above steps, and gradually perform the above operations on each OFDM symbol until the estimation and compensation process of the entire OFDM signal frame is completed, and all the data transmission bit information is saved, so as to obtain the optimal demodulated data transmission bit information.

2. The method for estimating and compensating fast time-varying Doppler in underwater acoustic communication according to claim 1, characterized in that: Also includes: The cost function is constructed from the perspective of time-frequency difference OFDM modulation and demodulation, and the Doppler tolerance of the time-frequency difference OFDM modulation and demodulation system itself is used to suppress the influence of residual Doppler, without setting a high-density two-dimensional Doppler frequency offset-delay search grid.

3. The method for estimating and compensating fast time-varying Doppler in underwater acoustic communication according to claim 2, characterized in that: Also includes: Determining the Doppler frequency deviation with the best meaning of the bit error information by constructing the cost function; The cost function of the fast time-varying Doppler estimation and compensation algorithm based on optimal bit error information can be expressed as: Where i represents the i-th OFDM symbol; ξ represents the Doppler frequency deviation; x s,i represents the local bit information sequence used for Doppler estimation in the i-th OFDM symbol; x t,i (ξ) represents the bit information sequence for Doppler estimation that is demodulated and recovered in the i-th OFDM symbol.

4. The method for estimating and compensating fast time-varying Doppler in underwater acoustic communication according to claim 3, characterized in that: The Doppler of the optimal sense of the bit error information of the current OFDM symbol can be expressed as: Among them, [ξ b ,ξ e ] indicates the preset Doppler frequency deviation search range.

5. The method for estimating and compensating fast time-varying Doppler in underwater acoustic communication according to claim 1, characterized in that: The format of the OFDM signal frame to be sent includes: using a linear frequency sweep signal with a length of 22.7 ms as a synchronization signal of the transmission signal, and a blank signal thereafter as a protection interval.

6. The method for estimating and compensating fast time-varying Doppler in underwater acoustic communication according to claim 5, characterized in that: Also includes: The two LFM signals before and after the OFDM data frame are used as block Doppler estimation, and the OFDM data frame is used as mutual ambiguity function Doppler estimation, quasi-gradient cross-correlation Doppler estimation, and the Doppler estimation and compensation.

7. The method for estimating and compensating fast time-varying Doppler in underwater acoustic communication according to claim 6, characterized in that: Also includes: When executing the Doppler estimation and compensation algorithm, the 201-bit information carried by each OFDM symbol in the OFDM data frame is used as the Doppler estimation of the current OFDM symbol, and the 67-bit information is used for data information transmission.

8. A fast time-varying Doppler estimation and compensation system for underwater acoustic communication, characterized in that: include: A transmitting end module, configured to send an OFDM signal frame, wherein each OFDM symbol in the OFDM signal frame is pre-set with subcarrier bit information fixed for Doppler estimation as detection information; A receiving end module is configured to receive the OFDM signal frame, and use the Doppler estimation bit information pre-set in each OFDM symbol to search for the Doppler frequency offset that satisfies the optimal meaning of the error bit information within a certain range according to the set frequency offset interval, and then estimate and compensate, and save the corresponding demodulated Doppler estimation bit information and data transmission bit information; The receiving end module is also configured to use the optimal bit error information of the current OFDM symbol as a search index, determine the corresponding Doppler frequency deviation as the Doppler frequency deviation value of the current OFDM symbol, and save the demodulated data transmission bit information corresponding to the Doppler frequency deviation; and repeatedly perform the above operations until the estimation and compensation process of the entire OFDM signal frame is completed, and save all the data transmission bit information, so as to obtain the optimal demodulated data transmission bit information.

9. The underwater acoustic communication fast time-varying Doppler estimation and compensation system according to claim 8, characterized in that: Also includes: The receiving end module constructs a cost function from the perspective of time-frequency difference OFDM modulation and demodulation, and uses the Doppler tolerance of the time-frequency difference OFDM modulation and demodulation system itself to suppress the influence of residual Doppler, without setting a high-density two-dimensional Doppler frequency offset-delay search grid.

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