Communication method for designing conduction integrated anti-interference signal based on pilot frequency

Abstract

The invention relates to the fields of communication and navigation integration, pilot frequency design, interference resistance, delay Doppler and the like, in particular to a pilot frequency design conduction integrated anti-interference signal communication method. Specifically, the traditional pilot frequency design scheme can realize interference resistance, but is not favorable for realizing conduction integration. According to the method for resisting the five-point comb interference based on the superposed pilot frequency design, the signal pilot frequency and the data symbol are superposed, a guard interval is not set, and therefore no loss exists on the communication symbol. Theoretical derivation and simulation experiments both verify the effectiveness of the scheme.

Description

Technical Field

[0001] The present invention relates to the fields of communication and navigation integration, pilot design, anti-interference, delayed Doppler, and in particular to a communication method for anti-interference signals based on pilot design integrated communication and navigation. Background Art

[0002] At present, my country has established a space-time benchmark guarantee capability with the BeiDou-3 global satellite navigation system as the core. However, satellite signals have shortcomings such as weak signal strength, poor penetration, and susceptibility to interference. Navigation positioning and timing (PNT) services in complex electromagnetic environments and urban valleys still have shortcomings. Considering the advantages of wide coverage, strong stability, and high popularity of communication networks, supplementing, backing up, and enhancing satellite navigation systems based on communication networks can effectively meet the needs of the coordinated development of satellites and communication networks, and provide wider coverage, higher accuracy, and more robust space-time services. With the development and iteration of communication and navigation positioning technologies, the coupling relationship between the two is not only satisfied at the system level, but also rises to the integrated design at the signal level. To achieve efficient and flexible integration of communication and navigation, efficient and compatible signal design is the foundation, and "elastic scaling on demand and autonomous adaptation to the environment" is the goal.

[0003] In recent years, orthogonal frequency division multiple access (ODFM) signals have been widely used in the signal design of integrated communication and navigation systems due to their high spectrum efficiency, strong anti-multipath effect and anti-interference capabilities. However, for OFDM systems, narrowband interference is a form of interference that seriously affects communication and navigation performance. On the one hand, since narrowband interference only occupies a small bandwidth, it appears as a local peak or protrusion of the spectrum in the frequency domain. This limits the frequency domain resources of the OFDM system because the number of subcarriers in the system is limited and needs to be reasonably allocated to various data transmission tasks and navigation parameter estimation tasks. The narrow spectrum occupancy of narrowband interference makes it more difficult to suppress in the OFDM system. On the other hand, the center frequency of narrowband interference is usually not completely matched with the subcarrier frequency in the OFDM system, and there is a certain frequency offset, which will lead to serious spectrum leakage, so that the interference signal actually affects a wider frequency range. Compared with the OFDM signal system, the OTFS signal has two main anti-interference performance advantages in terms of time-frequency scalability and low additional complexity overhead of the system.

[0004] The pilot design of traditional OTFS signal is usually as follows: Figure 2 As shown in , a pilot symbol is placed on a single delay-Doppler grid point, and several guard intervals without data symbols are placed around it. Figure 2As shown in (b), the main function of the guard interval is to separate the point spread function after the channel acts on the pilot symbol from the data symbol, so as to avoid mutual interference between the pilot symbol and the data symbol. The above pilot design scheme can eliminate the interference between the data symbol and the pilot symbol and avoid affecting the communication bit error rate, but it is not conducive to achieving communication and pilot integration.

[0005] In order to further reduce the impact of interference on the performance of the integrated communication and navigation system, the method proposed in the present invention is based on the OTFS modulation technology of orthogonal time-frequency space, performs data modulation in the delay-Doppler domain and expands it in the entire time-frequency domain, so as to achieve high-reliability and high-speed data transmission under the time-frequency dual-selective channel, and achieve good resistance to Doppler frequency shift and delay spread performance. Summary of the invention

[0006] The present invention proposes a communication method for integrated communication and navigation anti-interference signals based on pilot design, by superimposing the pilot and data symbols without a protection interval, thereby causing no loss in terms of communication symbol throughput and achieving better communication and navigation integration performance.

[0007] The technical solution adopted by the present invention is:

[0008] A communication method for integrated anti-interference signals based on pilot design includes the following processes:

[0009] (1) At the transmitting end, the pilot symbols and data symbols are superimposed without a guard interval, and the superimposed symbol matrix is ​​subjected to ISFFT and converted to the delay-Doppler domain;

[0010] (2) Transmitting the converted symbol data through OTFS modulation;

[0011] (3) At the receiving end, the transmitted symbol data, including the superimposed pilot symbols and data symbols, is first received, and then demodulated and SFFT is performed to restore the pilot symbols and data symbols from the time-frequency domain to the delay-Doppler domain;

[0012] (4) Using the sequential interference cancellation method, the pilot symbol is reconstructed by using the high energy of the pilot symbol to eliminate the interference between the pilot symbol and the data symbol;

[0013] (5) After the interference is eliminated, the received symbol data is equalized and detected to restore the original data.

[0014] Furthermore, the specific process of OTFS modulation in step (2) is as follows:

[0015] The converted symbol data is remapped, that is, (Mq)×(Nq) data symbols are first generated in the delay-Doppler domain, and then the ISFFT of the (Mq, Nq) points is calculated, and finally the time-frequency resources are rearranged; where M is the number of subcarriers, N is the number of time domain symbols, and q is the number of interfered sampling points.

[0016] Furthermore, the specific processing process of step (3) is as follows:

[0017] At the receiving end, the transmitted symbol data, including the superimposed pilot symbols and data symbols, is received, and the Wigner transform is performed to estimate the time-frequency distribution of the signal. The time-frequency distribution information is then used to eliminate interference, and demodulation and SFFT are performed to restore the pilot symbols and data symbols from the time-frequency domain to the delay-Doppler domain.

[0018] Furthermore, the specific processing process of step (4) is: using the strength effect of the signal to perform sequential interference elimination, so that the energy of the pilot symbol is much larger than the energy of a single data symbol, so that it can be accurately reconstructed and cancelled, eliminating the interference between the pilot symbol and the data symbol, and then demodulating the corresponding data symbol. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a block diagram of the OTFS transceiver in active interference avoidance mode.

[0020] Figure 2 This is a diagram of the traditional OTFS pilot design.

[0021] Figure 3 It is a design scheme diagram of the superimposed OTFS pilot designed by the present invention.

[0022] Figure 4 OTFS interference cancellation superimposed pilot pattern.

[0023] Figure 5 Interference cancellation superposition process flow chart.

[0024] Figure 6 Superimposed pilot design implements anti-interference execution flow chart.

[0025] Figure 7 It is the Wigner-Ville time-frequency distribution diagram of five-point comb interference.

[0026] Figure 8 It is the bit error rate performance diagram of OTFS and OFDM signals against five-point comb interference.

[0027] Fig. 9 It is the signal-to-interference-noise ratio performance diagram of OTFS and OFDM signals against five-point comb interference. DETAILED DESCRIPTION

[0028] The present invention will be further explained below in conjunction with the accompanying drawings.

[0029] like Figure 6 As shown, a communication method for integrated anti-interference signals based on pilot design includes the following processes:

[0030] At the transmitting end, the pilot symbols and data symbols are superimposed instead of isolating them, eliminating the guard interval in the traditional pilot design; then the superimposed symbol matrix is ​​subjected to ISFFT and converted to the delay-Doppler domain; the pilot and data symbols are transmitted together through OTFS modulation, utilizing time-frequency resources to achieve better anti-interference performance.

[0031] At the receiving end, the transmitted symbol data is first received, including the superimposed pilot and data symbols, and the Wigner transform is performed to estimate the time-frequency distribution of the signal. Then, the time-frequency distribution information is used to eliminate interference, and demodulation and SFFT are performed to restore the pilot symbols and data symbols from the time-frequency domain to the delay-Doppler domain. Then, sequential interference elimination is performed using the strength effect of the signal, so that the energy of the pilot symbol is much larger than the energy of a single data symbol, so that it can be accurately reconstructed and canceled, eliminating the interference between the pilot symbol and the data symbol. After the interference is eliminated, the received symbols are equalized and detected to restore the original data.

[0032] Specifically, the size of the guard interval in the traditional pilot design depends on the maximum delay and maximum Doppler in the channel, which corresponds to the range of distance measurement and speed measurement. Therefore, if the navigation range of distance measurement and speed measurement is as large as possible, the guard interval is also enlarged accordingly, resulting in serious communication rate loss. To this end, inspired by the superposition coding and sequential interference elimination in non-orthogonal multiple access, the present invention designs the following Figure 3 The superimposed pilot is shown to resist five-point comb interference.

[0033] like Figure 4 As shown, the pilot is directly superimposed on the entire OTFS symbol frame, so the OTFS transmission signal can be expressed as:

[0034]

[0035] Define the pilot energy as E p =|x p | 2 =σ 2 p , the data energy is Since the pilot signal is directly superimposed on the signal, the interference to the receiving end signal will be greatly increased compared to the embedded pilot pattern. The signal related to the pilot signal in the received signal is regarded as the useful signal, and the other signals are regarded as interference signals. Figure 4 The signal in the box area, i.e. the channel estimation area, can be expressed as:

[0036]

[0037] Among them, represents the interference introduced by the data symbol, that is:

[0038]

[0039] Due to the existence of interference terms, it is impossible to directly obtain the channel parameters based on the set threshold value, so an iterative estimation method is used here to estimate the channel.

[0040] Specifically, if Figure 5 As shown in the figure, first, as with the embedded pilot channel estimation, a threshold is set and a decision is made to obtain rough channel parameters. Then, based on the obtained channel parameters and the received signal, the SPA algorithm is used to perform preliminary signal detection. Then, the detected transmission data and the estimated channel parameters are combined to eliminate the interference in the transmission signal, and a fine channel estimation algorithm is performed. Since the interference is eliminated, the threshold value in the fine channel estimation link also changes accordingly. Finally, the algorithm iterates between channel estimation and signal detection until the optimal results of both are output simultaneously.

[0041] In short, the pilot of the present invention is superimposed on the data symbol, and no protection interval is set, so that no loss is caused in terms of communication symbol throughput. However, at the receiving end, the pilot will spread to a large number of data symbols, causing interference between the pilot and the data. In non-orthogonal multiple access technology, a powerful method to deal with this interference is to use the strength effect of the signal to perform sequential interference elimination. Specifically, the energy of the pilot symbol is made much larger than the energy of a single data symbol, so that it can be accurately reconstructed and canceled, and then the corresponding data symbol is demodulated. In this signal system, the performance trade-off between communication and navigation is reflected in the energy allocation of the pilot: the more energy allocated to the pilot, the easier it is to distinguish and reconstruct it from the data symbol; but under the total energy constraint, the energy that the data symbol can carry is reduced, resulting in a loss of signal-to-noise ratio, thereby reducing the effective communication rate.

[0042] For the OTFS integrated communication and navigation signal system proposed in the present invention, the data symbols need to be remapped to achieve active interference avoidance, and the navigation ranging and speed measurement also need to be adjusted accordingly, which is analyzed in detail below.

[0043] First, the (M, N)-point symplectic finite Fourier transform (SFFT) expression from the time-frequency domain to the delay-Doppler domain is written as follows:

[0044]

[0045] Assume that in the previous data frame, a certain subcarrier i and a certain time sampling point j are found to be seriously interfered, and it is hoped to avoid them. The SFFT after closing the corresponding time-frequency resources can be expressed as

[0046]

[0047] If the subcarriers and sampling points are rearranged, i=N-1 and j=M-1 (this rearrangement is denoted as f(n,m)). At this time, the relationship between the time-frequency domain and the delay-Doppler domain is the SFFT of (M-1,N-1) points. Therefore, when performing data modulation, (M-1)×(N-1) data symbols can be generated in the delay-Doppler domain first, and then the ISFFT of (M-1,N-1) points is calculated, and finally the time-frequency resource rearrangement operation f(n,m) is performed. During demodulation, the corresponding inverse transform is performed in the opposite order. For the general case where there are p interfered subcarriers and q interfered sampling points, the above process is as follows: Figure 1 shown.

[0048] After active interference avoidance is performed according to the above process, the remaining interference can be further eliminated to improve the communication performance. Compared with the completely passive interference elimination mode, the active interference avoidance mode has a smaller signal-to-noise ratio loss, but it also causes additional communication throughput loss because the time-frequency resource blocks with severe interference are closed and cannot be used for communication. When the output signal-to-noise ratio of passive interference elimination is low, it may cause the bit error rate to be too high and normal communication cannot be achieved. At this time, it is suitable to use the active interference avoidance mode, exchanging a certain rate loss for communication reliability.

[0049] The simulation parameters common to all simulation scenarios are shown in the following table.

[0050] Simulation parameters Parameter Value Modulation 4QAM Subcarrier number M 2048 Number of time domain symbols N 32 Signal-to-noise ratio (per symbol) 10dB Subcarrier spacing 40kHz Total bandwidth 81.92MHz Symbol duration 25us <![CDATA[Carrier frequency f c > 5GHz speed 20m / s distance 100m Delay grid interval 12.2ns Doppler interval 1.25kHz

[0051] Next, a specific discussion is given on the impact of comb interference on the communication and navigation performance of the anti-interference signal studied in the present invention.

[0052] In terms of communication performance, the present invention verifies the ability of the proposed adaptive anti-interference signal design to resist five-point comb interference. Comb interference is a typical narrowband interference form, which is composed of multiple single-frequency interference points. The comb interference frequency point is located at 5GHz+[-31.3021,-15.3021,0.6979,16.6979,32.6979]MHz, and its expression is:

[0053]

[0054] In the formula, f i is the i-th interference frequency, f c is the center frequency.

[0055] The corresponding Wigner-Ville time-frequency distribution is as follows Figure 7 shown.

[0056] From the color of the spectrum in the figure, it can be seen that the heights of the peaks are not the same. This is because the interference frequency is not aligned with the subcarrier frequency center, and spectrum leakage occurs, causing the interference power to spread to the entire frequency band. In this case, if the corresponding subcarrier is only turned off in the frequency domain (whether active or passive), the interference cannot be completely eliminated. When the signal-to-noise ratio is low (such as -30dB), the residual interference will still drown out the signal, so the aforementioned residual interference elimination method is particularly important.

[0057] Figure 8 The bit error rate performance of OTFS and OFDM signals against five-point comb interference is shown. It can be seen that OFDM signals have weak resistance to five-point comb interference, and OTFS has significantly stronger anti-interference ability. It is worth noting that OFDM signals cannot significantly improve their anti-interference performance in active interference avoidance mode. This further shows that after the subcarrier is turned off, the residual interference is still very strong. The OTFS signal has a significantly higher resistance to residual interference than OFDM because it spreads the interference energy evenly throughout the time-frequency domain. After turning on active interference avoidance, the bit error rate of the OTFS signal can be further reduced due to the avoidance of signal energy loss caused by passive interference elimination.

[0058] Figure 8 The equivalent output signal-to-interference-noise ratio of OTFS and OFDM signals under five-point comb interference is shown in Figure 2. For the 4QAM modulation method considered in this section, the equivalent output signal-to-interference-noise ratio is defined as:

[0059] SINR eff =2(erfc -1 (2·BER) 2 (7)

[0060] Fig. 9 The decoding signal-to-noise ratio threshold is 4096 code length and 0.5 code rate of Polar code when the bit error rate is less than 10 -5 The minimum signal-to-noise ratio required when the signal-to-interference ratio is 0.0447 dB. As can be seen from the figure, the OTFS signal can be successfully decoded when the signal-to-interference ratio is higher than -60 dB, while the OFDM signal cannot be successfully decoded when the signal-to-interference ratio is -20 dB. Compared with the two, the interference elimination gain of the OTFS signal exceeds 40 dB, achieving good anti-interference.

[0061] Therefore, no matter in passive or active interference avoidance mode, interference can be effectively eliminated based on accurate time-frequency distribution estimation.

Claims

1. A communication method for integrated anti-interference signals based on pilot design, characterized in that: The process includes: (1) At the transmitting end, the pilot symbols and data symbols are superimposed without a guard interval, and the superimposed symbol matrix is ​​subjected to ISFFT and converted to the delay-Doppler domain; (2) Transmitting the converted symbol data through OTFS modulation; (3) At the receiving end, the transmitted symbol data, including the superimposed pilot symbols and data symbols, is first received, and then demodulated and SFFT is performed to restore the pilot symbols and data symbols from the time-frequency domain to the delay-Doppler domain; (4) Using the sequential interference cancellation method, the pilot symbol is reconstructed by using the high energy of the pilot symbol to eliminate the interference between the pilot symbol and the data symbol; (5) After the interference is eliminated, the received symbol data is equalized and detected to restore the original data.

2. According to claim 1, a communication method for integrated anti-interference signal based on pilot design is characterized in that: The specific process of OTFS modulation in step (2) is as follows: The converted symbol data is remapped, that is, (Mq)×(Nq) data symbols are first generated in the delay-Doppler domain, and then the ISFFT of the (Mq, Nq) points is calculated, and finally the time-frequency resources are rearranged; where M is the number of subcarriers, N is the number of time domain symbols, and q is the number of interfered sampling points.

3. According to claim 1, a communication method for integrated anti-interference signal based on pilot design is characterized in that: The specific processing process of step (3) is as follows: At the receiving end, the transmitted symbol data, including the superimposed pilot symbols and data symbols, is received, and the Wigner transform is performed to estimate the time-frequency distribution of the signal. The time-frequency distribution information is then used to eliminate interference, and demodulation and SFFT are performed to restore the pilot symbols and data symbols from the time-frequency domain to the delay-Doppler domain.

4. The communication method of the anti-interference signal based on pilot design integrated communication and guidance according to claim 1 is characterized in that: The specific processing process of step (4) is: using the strength effect of the signal to perform sequential interference elimination, so that the energy of the pilot symbol is much larger than the energy of a single data symbol, so that it can be accurately reconstructed and cancelled, eliminating the interference between the pilot symbol and the data symbol, and then demodulating the corresponding data symbol.

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