Rate-adaptive short-wave OTFS communication and detection integrated transmission method

Abstract

The invention relates to a short-wave communication technology, in particular to a rate-adaptive short-wave OTFS communication and detection integrated transmission method, which comprises the following steps of: modulating a signal by adopting an OTFS method, introducing a guard interval setting scheme to carry out rate-adaptive transmission, and transmitting by using different adaptive schemes in different channel environments. Meanwhile, delay-Doppler domain channel detection is carried out by using a single pilot frequency communication method so as to realize channel estimation and channel equalization; according to the invention, rate adaptive adjustment can be carried out on the change of a short-wave channel environment so as to realize high transmission connectivity rate.

Description

Technical Field

[0001] The present invention relates to shortwave communication technology, and particularly to a shortwave OTFS communication and detection integrated transmission method with rate adaptability. Background Art

[0002] Shortwave communication is a long-distance communication method that can reach thousands of kilometers. It mainly propagates through the reflection of the sky wave by the ionosphere and actually operates at 1.5 - 30 MHz. Shortwave communication has the characteristics of low cost, flexibility, and difficulty in being destroyed, which makes it an effective complement to satellite communication and is widely used in military communication, emergency communication, aviation, and navigation and other fields.

[0003] The shortwave channel changes with the ionosphere, and the complexity and variability of ionospheric activities result in the shortwave channel being random and time-varying. Specifically, first, the change in the height and reflection characteristics of the ionosphere will cause phase fluctuations in multipath propagation, which in turn leads to the occurrence of Doppler frequency shift. Second, there are changes in the noise level during the propagation in the ionosphere. There is atmospheric noise that varies with the season in atmospheric discharges, and there are also radio interference and industrial interference noises generated by human interference. At the same time, as a typical multipath doubly selective dispersive channel, the shortwave channel's time delay and Doppler spread will cause frequency selectivity and time selectivity. The above reasons lead to the characteristic of rapid time variation of the shortwave channel, and thus the problem of low channel utilization rate occurs.

[0004] In the development process of shortwave communication, a large number of scholars have conducted research at different depths. Some people proposed to use MFSK and OFDM in shortwave communication. This communication method has achieved certain results through diversity processing domain technology, but it does not adopt an adaptive processing method and cannot change the communication rate in response to sudden changes in the channel environment. Some research scholars proposed an adaptive modulation communication method, using different allocation algorithms to simulate bit allocation and power allocation under the condition of a multipath Rayleigh fading channel. However, when the shortwave channel condition is relatively poor, the OFDM system still cannot guarantee a low bit error rate. The literature "TiM: Fine-Grained Rate Adaptation in WLANs" proposed a three-dimensional modulation scheme with an additional time domain, Time-line Modulation (TIM), which adds a time domain to the two-dimensional (amplitude-phase) domain of the existing modulation scheme to fill the matching gap between limited modulation types and continuously changing channel conditions. However, this method is mainly applied to high-speed communication systems and is not suitable for shortwave systems with low-speed propagation. The literature "Research on a Rate Adaptive Waveform Design" designed a deleted redundant convolutional code burst waveform to achieve the effect of rate adaptation based on a combined coding method. To overcome the influence of Doppler spread on shortwave communication and reduce the sensitivity of shortwave radios to the Doppler effect, the literature "Research on the Application of OTFS Waveform in Shortwave Communication" first applied the OTFS waveform to shortwave communication, using block minimum mean square error (Block-MMSE) equalization in the time-frequency domain to achieve the same performance as the DD domain MMSE equalization method, reducing the implementation complexity of the system and reflecting the characteristics and advantages of the OTFS waveform in the shortwave channel. However, it does not consider the rate adaptation problem under different shortwave channel environments. To sum up, although the existing technologies have achieved great technical effects, there are still problems such as low connectivity rate in shortwave communication and inability to adaptively adjust the rate according to changes in the shortwave channel environment; especially under poor shortwave communication conditions, to achieve good channel utilization, the sender needs to select the highest transmission rate supported by the current channel and continuously change the rate matching to adapt to the changing link conditions. Summary of the Invention

[0005] To solve the above problems, the present invention provides a rate-adaptive shortwave OTFS communication and detection integrated transmission method, including the following steps:

[0006] S1. Map the signal to be transmitted to the delay-Doppler domain to obtain the DD domain transmitted signal matrix;

[0007] S2. Place pilots at the center of the DD domain transmitted signal matrix and set a pilot protection band around the center; set a protection band around each data symbol according to the guard interval setting scheme;

[0008] S3. Perform the inverse symplectic Fourier transform on the signal matrix sent to the DD domain to obtain the time-frequency domain signal block, and then perform the Heisenberg transform on the time-frequency domain signal block to obtain the time-domain signal, and transmit the time-domain signal through the short-wave channel;

[0009] S4. The receiving end performs the Wigner transform and the symplectic Fourier transform on the received time-domain signal to obtain the DD domain received signal matrix;

[0010] S5. Obtain a set of pilot symbol matrices and multiple sets of data symbol matrices according to the symbol arrangement of the DD domain received signal matrix;

[0011] S6. Screen the pilot symbol matrix, only keep the 6 signals with the largest amplitudes in the pilot symbol matrix and set the other positions to 0 to obtain the retention matrix;

[0012] S7. Calculate the soft information matrix according to the conjugate matrix of the retention matrix and the data symbol matrix; each soft information in the soft information matrix corresponds to a data symbol;

[0013] S8. Extract the real part symbol and the imaginary part symbol of each data symbol in the soft information matrix, and judge and restore the original data symbol according to the positive and negative conditions of the two types of symbols;

[0014] S9. Perform channel detection according to the pilot symbols in the DD domain received signal matrix, obtain a new guard interval setting scheme, and send the new guard interval setting scheme to the sending end for update.

[0015] Further, step S2 specifically includes:

[0016] Expand outward with the pilot as the center, extend m symbols in the up and down directions of the time delay axis respectively, and extend n symbols in the left and right directions of the Doppler axis respectively to form a pilot protection band; set the symbols other than the pilot position in the pilot protection band to 0;

[0017] Determine the guard interval radii a and b according to the channel detection results; for each data symbol, expand outward with its position as the center, extend a symbols in the up and down directions of the time delay axis respectively, and extend b symbols in the left and right directions of the Doppler axis respectively to form a protection band; set the symbols other than the data symbol position in the protection band to 0.

[0018] Further, obtaining the pilot symbol matrix and the data symbol matrix according to the symbol arrangement of the DD domain received signal matrix includes:

[0019] In the DD domain received signal matrix, with the position of the pilot as the center, extend a symbols in the up and down directions of the time delay axis respectively, and extend b symbols in the left and right directions of the Doppler axis respectively to obtain a set of pilot symbol matrices;

[0020] For each data symbol in the DD-domain received signal matrix, centered on its position, extend a symbols in the up and down directions of the time delay axis and b symbols in the left and right directions of the Doppler axis to obtain a set of data symbol matrices.

[0021] Further, step S7 specifically includes

[0022] For each set of data symbol matrices, multiply it by the conjugate matrix of the reserved matrix to obtain a dot product matrix, and sum up all the elements in the dot product matrix to obtain a soft information;

[0023] Combine the soft information corresponding to all data symbol matrices to obtain a soft information matrix.

[0024] Further, step S8 for judging and restoring each data symbol according to the positive and negative situations of the two types of symbols includes

[0025] If the real part symbol is positive and the imaginary part symbol is positive, the data symbol is restored to 00;

[0026] If the real part symbol is positive and the imaginary part symbol is negative, the data symbol is restored to 10;

[0027] If the real part symbol is negative and the imaginary part symbol is positive, the data symbol is restored to 11;

[0028] If the real part symbol is negative and the imaginary part symbol is negative, the data symbol is restored to 01.

[0029] Further, step S9 specifically includes:

[0030] Calculate the data average value average1 at the position of the pilot on the time delay axis in the DD-domain received signal matrix;

[0031] Centered on the pilot position in the DD-domain received signal matrix, for each extension of one position on the time delay axis, judge whether the data average value at this time delay axis position is less than average1 / 4. If so, record the vertical distance between this time delay axis position and the time delay axis position where the pilot is located, and use this vertical distance as the time delay axis extension distance, and stop extending outward;

[0032] Calculate the data average value average2 at the position of the pilot on the Doppler axis in the DD-domain received signal matrix;

[0033] Centered on the pilot position in the DD-domain received signal matrix, for each extension of one position on the Doppler axis, judge whether the data average value at this Doppler axis position is less than average2 / 4. If so, record the vertical distance between this Doppler axis position and the Doppler axis position where the pilot is located, and use this vertical distance as the Doppler axis extension distance;

[0034] Let the guard interval radius \(a\) be the extension distance on the time delay axis, and the guard interval radius \(b\) be the extension distance on the Doppler axis; in the new guard interval setting scheme, each data symbol is centered at its position, and extends \(a\) empty symbols in the up and down directions of the time delay axis, and \(b\) empty symbols in the left and right directions of the Doppler axis respectively.

[0035] Advantages of the present invention:

[0036] The present invention proposes a rate adaptation method, which mainly includes setting a guard band for each data symbol, and the range of the guard band can be adjusted in real time according to the channel detection result. This method can better utilize the discrete energy of the short-wave channel for reception when a guard band is provided.

[0037] The present invention can perform rate adaptation adjustment on the changes in the short-wave channel environment, improve the connection rate of short-wave communication, and further improve the utilization rate of the short-wave channel. Experiments prove that the present invention can increase the transmission connection rate to 90% in short-wave communication. Description of the drawings

[0038] Figure 1 It is the application scenario diagram of the short-wave OTFS of the present invention;

[0039] Figure 2 It is the transmission framework diagram of the short-wave OTFS of the present invention;

[0040] Figure 3 It is the data symbol distribution diagram of the present invention;

[0041] Figure 4 It is the symbol distribution diagram of one frame of the present invention;

[0042] Figure 5 It is the method flow diagram of the present invention;

[0043] Figure 6 It is the comparison diagram of the transmission connection rate of the present invention. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] The present invention provides a rate-adaptive short-wave OTFS integrated communication and detection transmission method, and builds as Figure 2The short-wave OTFS transmission framework shown in the figure. This framework includes a transmitter, a short-wave channel, and a receiver. The transmitter includes a modulation module and a guard interval setting module, and the receiver includes a demodulation module and a channel information detection module. The present invention can be applied to, for example, Figure 1 The natural disaster emergency communication scenario shown in the figure, where the base station, satellite, and mobile emergency communication vehicle can act as both the transmitter and the receiver. Bilateral communication is carried out between the base station and the mobile emergency communication vehicle based on short-wave communication, and a satellite-assisted transmission guard interval setting scheme is adopted.

[0046] Such as Figure 5 As shown in the figure, the specific scheme includes:

[0047] S1. Map the signal to be transmitted to the delay-Doppler domain to obtain the DD-domain transmission signal matrix.

[0048] S2. Place pilots at the center of the DD-domain transmission signal matrix and set pilot guard bands around the center.

[0049] Specifically, pilots are placed at the center of the DD-domain transmission signal matrix, which are used at the receiver to detect the Doppler effect and multipath delay effect of the channel and for subsequent equalization and compensation operations.

[0050] Specifically, the present invention designs a guard interval setting module. By the guard interval setting module, guard bands are set for each data symbol between the DD-domain transmission signal matrices. The guard band means that there are empty symbols between the symbols, which can also be interpreted as for a data symbol, centered on its position, a empty symbols are extended in the up and down directions of the delay axis respectively, and b empty symbols are extended in the left and right directions of the Doppler axis respectively. a and b are the guard interval radii, and empty symbols are filled in the remaining positions. The empty symbol is set to 0. The specific setting process of the guard interval includes: the transmitter determines the guard interval radii a and b according to the guard interval setting scheme returned by the channel detection result of the receiver. Each data symbol in the DD-domain transmission signal matrix sets corresponding empty symbols according to the guard interval radius. For example, when the guard interval radii a = b = 4, the setting distribution is as Figure 3 Shown in the figure.

[0051] In an embodiment, the symbol distribution of a set frame is as Figure 4 Shown in the figure, where the red ones are pilots and the black ones are data symbols. There are empty symbols between the pilots and the data symbols, indicating that the empty symbols between them exist as pilot guard bands.

[0052] The size range of the pilot guard band is fixed, while the range of the guard band set for the data symbol needs to be adjusted in real time according to the channel detection result.

[0053] S3. Perform an inverse symplectic Fourier transform on the DD-domain transmitted signal matrix to obtain a time-frequency domain signal block, then perform a Heisenberg transform on the time-frequency domain signal block to obtain a time-domain signal, and transmit the time-domain signal through a shortwave channel.

[0054] S4. The receiving end performs a Wigner transform and a symplectic Fourier transform on the received time-domain signal to obtain a DD-domain received signal matrix.

[0055] S5. Obtain a set of pilot symbol matrices and multiple sets of data symbol matrices according to the symbol arrangement of the DD-domain received signal matrix.

[0056] Specifically, according to the symbol arrangement of the DD-domain received signal matrix, determine the current guard interval radii a and b, and then obtain the pilot symbol matrix and the data symbol matrix, including:

[0057] In the DD-domain received signal matrix, with the position of the pilot as the center, extend a symbols in the up and down directions of the time delay axis and b symbols in the left and right directions of the Doppler axis to obtain a set of pilot symbol matrices;

[0058] For each data symbol in the DD-domain received signal matrix, with its position as the center, extend a symbols in the up and down directions of the time delay axis and b symbols in the left and right directions of the Doppler axis to obtain a set of data symbol matrices.

[0059] S6. Screen the pilot symbol matrix, only keep the 6 signals with the largest amplitudes in the pilot symbol matrix, and set the other positions to 0 to obtain a retained matrix. S7. Calculate a soft information matrix based on the conjugate matrix of the retained matrix and the data symbol matrix; the soft information matrix. The size range of the soft information matrix is determined by the data symbols in the DD-domain received signal matrix.

[0060] Specifically, step S7 specifically includes

[0061] For each set of data symbol matrices, multiply it point by point with the conjugate matrix of the retained matrix to obtain a point multiplication matrix, and sum up all the elements in the point multiplication matrix to obtain a soft information;

[0062] Combine the soft information corresponding to all data symbol matrices to obtain a soft information matrix.

[0063] S8. Extract the real part symbol and the imaginary part symbol of each data symbol in the soft information matrix, and perform judgment and restoration according to the positive and negative situations of the two types of symbols.

[0064] Specifically, step S8 performs judgment and restoration on each data symbol according to the positive and negative situations of the two types of symbols, including

[0065] If the real part symbol is positive and the imaginary part symbol is positive, the data symbol is restored to 00;

[0066] If the sign of the real part is positive and the sign of the imaginary part is negative, the data symbol is restored to 10;

[0067] If the sign of the real part is negative and the sign of the imaginary part is positive, the data symbol is restored to 11;

[0068] If the sign of the real part is negative and the sign of the imaginary part is negative, the data symbol is restored to 01.

[0069] S9. Perform channel detection based on the pilot symbols in the received signal matrix in the DD domain to obtain a new protection interval setting scheme, and send the new protection interval setting scheme to the transmitter for updating.

[0070] Specifically, the present invention designs a channel information detection module to adjust the protection interval radius according to the change of the short-wave channel with the channel detection result.

[0071] Step S9 specifically includes:

[0072] Calculate the data average value average1 at the time delay axis position where the pilot is located in the received signal matrix in the DD domain; that is, based on the received signal matrix in the DD domain, the average value of all data on the axis corresponding to the time delay coordinate where the pilot is located;

[0073] Taking the pilot position in the received signal matrix in the DD domain as the center, every time it extends one time delay axis position outward, it is judged whether the data average value at this time delay axis position is less than average1 / 4. If so, record the vertical distance between this time delay axis position and the time delay axis position where the pilot is located, that is, the distance between the two axes, and use this vertical distance as the time delay axis extension distance, and stop extending outward;

[0074] Calculate the data average value average2 at the Doppler axis position where the pilot is located in the received signal matrix in the DD domain;

[0075] Taking the pilot position in the received signal matrix in the DD domain as the center, every time it extends one Doppler axis position outward, it is judged whether the data average value at this Doppler axis position is less than average2 / 4. If so, record the vertical distance between this Doppler axis position and the Doppler axis position where the pilot is located, and use this vertical distance as the Doppler axis extension distance;

[0076] Let the protection interval radius a be the time delay axis extension distance, and the protection interval radius b be the Doppler axis extension distance; in the new protection interval setting scheme, each data symbol extends a blank symbol in the up and down directions of the time delay axis and b blank symbols in the left and right directions of the Doppler axis with its position as the center.

[0077] For example, when the time delay spread distance is 4 units and the Doppler spread distance is 2 units, the (4, 2) guard interval setting scheme is selected. In the present invention, the principle for selecting the guard interval radius is to make the obtained Doppler frequency shift and multipath time delay duration consistent.

[0078] In order to verify the feasibility of the method of the present invention in shortwave communication, the existing iturHF shortwave channel in MATLAB is used to conduct simulation tests on the shortwave OTFS transmission scheme based on rate adaptation and the shortwave OFDM transmission scheme. The simulation parameters are shown in Table 1. Each segment is subjected to 1,000 simulation tests, and the channel is changed after 10,000 times to verify the rationality of the adaptive scheme. The channel SNR used in the simulation is -5 dB, 0 dB, 5 dB, and a total of 3 segments of simulations are conducted.

[0079] Table 1 System simulation parameters

[0080]

[0081] In Figure 6 , the simulation channels are the iturHFMD, iturHFMM, and iturHFMQ channels in sequence. When the bit error rate per frame reaches 10 -2 or less, the transmission connection is successful. It can be seen from the figure that as the signal-to-noise ratio decreases, the transmission connection rate of the OTFS rate adaptation scheme is slightly affected, and the decrease is not significant. However, the OFDM scheme is more affected. As the signal-to-noise ratio decreases, the connection rate decreases. This is because the OFDM does not use the rate adaptation scheme (that is, adaptively changing the guard interval radius according to the channel change), so it cannot improve the channel utilization rate, resulting in a greater impact on the transmission connection rate by the change of SNR. Similarly, as the shortwave channel environment gradually improves to the iturHFMQ channel, the transmission connection rate of the OTFS rate adaptation scheme is slightly affected, but the change is not significant. Even when the channel environment is poor, it can maintain a high transmission connection rate. However, for the OFDM scheme, it can only reach a 90% transmission connection rate at a signal-to-noise ratio of 5 dB and in the iturHFMQ channel with the best channel environment. But when the channel environment changes, its transmission connection rate drops sharply, still due to the fact that the OFDM scheme does not use the rate adaptation method.

[0082] In the present invention, unless otherwise clearly specified and defined, terms such as "installation", "setting", "connection", "fixation", "rotation", etc. shall be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. It can be the communication inside two components or the interaction relationship between two components. Unless otherwise clearly defined, for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0083] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A rate-adaptive shortwave OTFS integrated transmission method, characterized in that: The following steps are involved: S1. Map the signal to be transmitted to the delay-Doppler domain to obtain the DD domain transmit signal matrix; S2. Place a pilot signal in the center of the DD domain signal matrix, and set a pilot guard band around the center; set a guard band around each data symbol according to the guard interval setting scheme; S3. Perform an inverse symplectic Fourier transform on the DD domain transmission signal matrix to obtain a time-frequency domain signal block, then perform a Heisenberg transform on the time-frequency domain signal block to obtain a time domain signal, and transmit the time domain signal through a shortwave channel; S4. The receiving end performs Wigner transform and symplectic Fourier transform on the received time domain signal to obtain a DD domain received signal matrix; S5. Obtain a set of pilot symbol matrices and multiple sets of data symbol matrices according to the symbol arrangement of the received signal matrix in the DD domain; S6. Filter the pilot symbol matrix, retain only the 6 signals with the largest amplitude in the pilot symbol matrix, and set the other positions to 0 to obtain a retained matrix; S7. Calculate a soft information matrix based on the conjugate matrix of the retained matrix and the data symbol matrix; each soft information in the soft information matrix corresponds to a data symbol; S8. Extract the real and imaginary symbols of each data symbol in the soft information matrix, and restore the original data symbol according to the positive and negative conditions of the two types of symbols; S9. Perform channel detection according to the pilot symbols in the DD domain received signal matrix to obtain a new guard interval setting scheme, and send the new guard interval setting scheme to the transmitting end for updating.

2. A rate-adaptive shortwave OTFS integrated transmission method according to claim 1, characterized in that: Step S2 specifically includes: Expand outward from the pilot as the center, extend m symbols in the up and down directions of the delay axis, and extend n symbols in the left and right directions of the Doppler axis, to form a pilot protection band; except for the pilot position, the rest of the symbols in the pilot protection band are set to 0; The guard interval radii a and b are determined based on the channel detection results. For each data symbol, the guard interval radii a and b are expanded outward from its position as the center, extending a symbols in the upper and lower directions of the delay axis and b symbols in the left and right directions of the Doppler axis to form a guard band. The symbols in the guard band except the data symbol position are set to 0.

3. The rate-adaptive shortwave OTFS integrated transmission method according to claim 1 is characterized in that: Obtaining a pilot symbol matrix and a data symbol matrix according to the symbol arrangement of the DD domain received signal matrix includes: In the DD domain received signal matrix, with the pilot position as the center, a symbols are extended in the up and down directions of the delay axis, and b symbols are extended in the left and right directions of the Doppler axis, to obtain a set of pilot symbol matrices; For each data symbol in the DD domain received signal matrix, with its location as the center, a symbols are extended in the up and down directions of the delay axis, and b symbols are extended in the left and right directions of the Doppler axis, to obtain a set of data symbol matrices.

4. The rate-adaptive shortwave OTFS integrated transmission method according to claim 1, characterized in that: Step S7 specifically includes: For each set of data symbol matrix, multiply it with the conjugate matrix of the retained matrix to obtain a dot product matrix, and sum up all elements in the dot product matrix to obtain a soft information; The soft information corresponding to all data symbol matrices is combined to obtain a soft information matrix.

5. The rate-adaptive shortwave OTFS integrated transmission method according to claim 1, characterized in that: Step S8 determines and restores each data symbol according to the positive and negative conditions of the two types of symbols. If the real part sign is positive and the imaginary part sign is positive, the data sign is restored to 00; If the real part sign is positive and the imaginary part sign is negative, the data sign is restored to 10; If the real part sign is negative and the imaginary part sign is positive, the data sign is restored to 11; If the sign of the real part is negative and the sign of the imaginary part is negative, the data sign is restored to 01.

6. A rate-adaptive shortwave OTFS integrated transmission method according to claim 1, characterized in that: Step S9 specifically includes: Calculate the data average value average1 at the delay axis position where the pilot signal is located in the DD domain receiving signal matrix; Taking the pilot position in the DD domain receiving signal matrix as the center, each time a delay axis position is extended outward, it is determined whether the data average value at the delay axis position is less than average1 / 4. If so, the vertical distance between the delay axis position and the delay axis position where the pilot is located is recorded, and the vertical distance is used as the delay axis extension distance, and the extension is stopped; Calculate the data average value average2 at the Doppler axis position where the pilot signal is located in the DD domain received signal matrix; Taking the pilot position in the DD domain received signal matrix as the center, each time a Doppler axis position is extended outward, it is determined whether the data average value at the Doppler axis position is less than average2 / 4. If so, the vertical distance between the Doppler axis position and the Doppler axis position where the pilot is located is recorded, and the vertical distance is used as the Doppler axis extension distance; Let the guard interval radius a be the delay axis extension distance, and the guard interval radius b be the Doppler axis extension distance.

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