Low-orbit satellite broadband Doppler simulation and compensation method based on OFDM (Orthogonal Frequency Division Multiplexing) system

Abstract

The invention relates to the technical field of wireless communication, in particular to a low-orbit satellite broadband Doppler simulation and compensation method based on an OFDM (Orthogonal Frequency Division Multiplexing) system, which comprises a simulation process and a compensation process, and the compensation comprises time domain compensation and frequency domain compensation. According to the broadband Doppler simulation method provided by the invention, the wireless signal more conforming to a real satellite-ground communication scene can be generated, and a ground terminal receiver which performs simulation design based on the analog signal can obtain better performance. The broadband Doppler time domain compensation method provided by the invention is suitable for high-throughput, large-bandwidth and high-order modulation scenes, and can accurately compensate the interference of Doppler frequency shift and improve the demodulation performance. The broadband Doppler frequency domain compensation method provided by the invention is suitable for low-delay, small-bandwidth and low-order modulation scenes, an original ground cellular network terminal receiving scheme does not need to be modified basically, and better demodulation performance can be obtained under the condition of low development cost.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless communications, and in particular to a low-orbit satellite broadband Doppler simulation and compensation method based on an OFDM system. Background Art

[0002] In the past two years, 5G-Advanded communication technology has developed rapidly, and satellite communication technology is a research hotspot. The main purpose of the research is to use it as an extension of 5G NR so that 5G terminal devices can still access the 5G network in areas that are difficult to cover with traditional ground base stations (such as uninhabited areas, underdeveloped areas, etc.). Compared with high-orbit satellites, low-orbit satellites have short transmission delays and low transmission power, which can reduce the design cost and complexity of base stations and terminals. Therefore, low-orbit satellite communication technology is a key research direction in 5G-A.

[0003] Due to the high speed of low-orbit satellites, the signals transmitted to the ground must have a large Doppler shift. As time goes by, the Doppler gradually decreases when the satellite moves toward the top of the ground terminal. When it reaches the top of the terminal, the Doppler is 0. Then the satellite will gradually move away from the ground terminal, and the Doppler will gradually increase. According to the 3GPP agreement, the maximum Doppler shift caused by the movement of a low-orbit satellite 600km above the ground at a carrier frequency of 20GHz can reach 480kHz, which is intolerable for the current 5G communication based on the OFDM system. Moreover, 5G-A has higher requirements on throughput than 5G. High throughput inevitably requires the use of large bandwidth to transmit data. Different subcarriers on large bandwidth signals will be affected by different degrees of Doppler shift, which will cause interference between subcarriers and deteriorate communication quality.

[0004] General satellite Doppler simulation technology does not take into account the impact of broadband Doppler, and there is no corresponding broadband Doppler compensation solution, which will lead to problems such as high bit error rate and poor communication quality of broadband low-orbit satellite signals. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a low-orbit satellite broadband Doppler simulation and compensation method based on the OFDM system. The broadband Doppler simulation method provided by the present invention can generate a wireless signal that is more in line with the actual satellite-to-ground communication scenario, and the ground terminal receiver designed based on the simulation signal can obtain better performance. The broadband Doppler time domain compensation method provided by the present invention is suitable for high-throughput, large bandwidth and high-order modulation scenarios, and can accurately compensate for the interference of Doppler frequency shift and improve demodulation performance. The broadband Doppler frequency domain compensation method provided by the present invention is suitable for low-latency, small bandwidth and low-order modulation scenarios. There is basically no need to modify the original ground cellular network terminal receiving solution, and better demodulation performance can be obtained at a development cost.

[0006] The technical solution adopted by the present invention is:

[0007] A low-orbit satellite broadband Doppler simulation and compensation method based on an OFDM system comprises the following steps:

[0008] Step 1: Configure Doppler parameters, including carrier frequency f c , median Doppler frequency shift value Δf c , subcarrier spacing Δf, system sampling rate f s , FFT points, i.e. frequency points N, cyclic prefix length N cp and the number of continuously transmitted OFDM symbols L; and at the same time, generate L*N groups of transmission data X according to the number of OFDM symbols L and the number of frequency points N l (k),k=0,1,…,N-1; l=0,1,…,L;

[0009] Step 2: Calculate the normalized Doppler frequency shift value Δf at each frequency point according to the configured Doppler parameters norm (k):

[0010]

[0011] Step 3: Copy the N×L resource grid into N copies and fill them with 0, then fill the L transmission data with different symbols at the same frequency into N N×L resource grids in turn to obtain the transmission data X' after mapping a single resource grid. l,j (k):

[0012] j represents the jth resource grid;

[0013] Step 4: Perform IFFT transformation on the transmitted data after resource grid mapping to transform it into time domain data x l,j (n):

[0014]

[0015] Step 5: Add a cyclic prefix to the N×L group of time domain data with a length of N, that is, add the last N of the original time domain data with a length of N. cp The data of length is copied and spliced ​​to the beginning of the time domain data, forming a length of N+N cp Data

[0016]

[0017] Step 6: Splice the time domain signals of the same frequency point with multiple symbols, that is, splice the time domain signals of the same frequency point into a group of length L*(N+N cp ) of the time domain signal xj (m),m=0,1,…,L*(N+N cp )-1;

[0018] Step 7: The length of different frequency points is L*(N+N cp )'s time domain signal is added with Doppler frequency shift to obtain x' j (m):

[0019]

[0020] Step 8: Accumulate the time domain signals of different frequency points into a set of time domain signals x'(m) and send them:

[0021]

[0022] Step 9: The receiving end receives the time domain signal y(m), and then performs time domain compensation and frequency domain compensation to obtain compensated data.

[0023] Furthermore, the specific process of time domain compensation in step 9 includes:

[0024] Step 101: The received length is L*(N+N cp ) is segmented into L symbols of time domain data, and the cyclic prefix is ​​removed:

[0025] y l (n) = y(l*N+(l+1)*N cp +n)

[0026] y l =[y l (0),y l (1),…,y l (N-1)];

[0027] Step 102: Calculate the median Doppler delta f c

[0028]

[0029] Among them, f c represents the carrier frequency, Δv represents the relative speed between the low-orbit satellite and the ground terminal, cosθ represents the angle between the satellite-ground relative speed vector and the satellite-ground line, and c represents the speed of light;

[0030] Step 103: Calculate the normalized Doppler frequency shift Δf of each frequency point according to the configuration parameters norm (k):

[0031]

[0032] Step 104: Calculate the time domain Doppler compensation matrix B of each symbol:

[0033] β=(l+1)·N cp +l·N

[0034]

[0035] Step 105: Perform Doppler compensation on the time domain signal of each symbol to obtain compensated time domain data

[0036]

[0037] Furthermore, the specific process of frequency domain compensation in step 9 includes:

[0038] Step 201: The received length is L*(N+N cp ) is segmented into L symbols of time domain data, and the cyclic prefix is ​​removed:

[0039] y l (n) = y(l*N+(l+1)*N cp +n)

[0040] y l =[y l (0),y l (1),…,y l (N-1)];

[0041] Step 202: Perform FFT on the time domain data of each symbol to obtain the frequency domain data affected by wideband Doppler: Y l (k)

[0042]

[0043] Step 203: Calculate the median Doppler Δf c :

[0044]

[0045] Among them, f c represents the carrier frequency, Δv represents the relative speed between the low-orbit satellite and the ground terminal, cosθ represents the angle between the satellite-ground relative speed vector and the satellite-ground line, and c represents the speed of light;

[0046] Step 204: Calculate the normalized Doppler frequency shift Δf of each frequency point according to the configuration parameters norm (k):

[0047]

[0048] Step 205: Perform Doppler compensation on the frequency domain data of each symbol to obtain compensated frequency domain data

[0049]

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] 1. The present invention can generate a simulated signal of a low-orbit satellite affected by broadband Doppler based on an OFDM system, which is more consistent with the wireless signal in an actual environment and is helpful for simulation analysis during system design.

[0052] 2. The time-domain wideband Doppler compensation scheme proposed in the present invention can accurately compensate for the influence of wideband Doppler, maximize the signal quality and demodulation performance of the ground terminal, and is suitable for high-throughput, large-bandwidth and high-order modulation scenarios.

[0053] 3. The frequency domain broadband Doppler compensation scheme proposed in the present invention has small computational complexity and basically does not require modification of the original ground cellular network terminal receiving scheme. It can roughly compensate for the impact of broadband Doppler and restore the quality of the ground terminal receiving signal to a receivable level. It is suitable for low-latency, small-bandwidth, and low-order modulation scenarios that do not require high receiving and demodulation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The present invention is a flow chart of the method for simulating broadband Doppler signals of low-orbit satellites.

[0055] Figure 2 The present invention is a flow chart of the time domain compensation method for broadband Doppler signals of low-orbit satellites.

[0056] Figure 3 The present invention is a flow chart of the frequency domain compensation method for broadband Doppler signals of low-orbit satellites.

[0057] Figure 4 This is a constellation diagram for receiving signals affected by Doppler under the 256QAM modulation mode of the present invention.

[0058] Figure 5 This is a constellation diagram for receiving signals affected by Doppler in the time domain compensation under the 256QAM modulation mode of the present invention.

[0059] Figure 6 This is a receiving constellation diagram for frequency domain compensation of Doppler-affected signals under the 256QAM modulation mode of the present invention. DETAILED DESCRIPTION

[0060] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0061] A low-orbit satellite broadband Doppler simulation and compensation method based on an OFDM system includes two processes: simulation and compensation.

[0062] Embodiment 1, as Figure 1 As shown, the simulation process includes the following steps:

[0063] Step 1: Configure Doppler parameters, including carrier frequency f c , median Doppler frequency shift value Δf c , subcarrier spacing Δf, system sampling rate f s , FFT points, i.e. frequency points N, cyclic prefix length N cp and the number of continuously transmitted OFDM symbols L; and at the same time, generate L*N groups of transmission data X according to the number of OFDM symbols L and the number of frequency points N l (k), k=0,1,…,N-1; l=0,1,…,L.

[0064] Step 2: Calculate the normalized Doppler frequency shift value Δf at each frequency point according to the configured Doppler parameters norm (k):

[0065]

[0066] Step 3: Send data X l (k) Perform single resource grid mapping. The original transmission data X l (k) is mapped to the N*L resource grid and sent in the time domain signal generated by IFFT. In order to add the wideband Doppler effect, a single resource grid mapping is required. Copy the N×L resource grid N times and fill it with 0, then fill the L transmission data of different symbols at the same frequency point (same k value but different L) into N N×L resource grids in turn, and obtain the transmission data X' after single resource grid mapping l,j (k):

[0067] j represents the jth resource grid.

[0068] Step 4: Perform IFFT transformation on the transmitted data after resource grid mapping to transform it into time domain data x l,j (n):

[0069]

[0070] Step 5: Add a cyclic prefix to the N×L group of time domain data with a length of N, that is, add the last N of the original time domain data with a length of N. cp The data of length is copied and spliced ​​to the beginning of the time domain data, forming a length of N+N cp Data

[0071]

[0072] Step 6: Splice the time domain signals of the same frequency point with multiple symbols, that is, splice the time domain signals of the same frequency point into a group of length L*(N+N cp ) of the time domain signal x j (m),m=0,1,…,L*(N+N cp )-1.

[0073] Step 7: The length of different frequency points is L*(N+N cp )'s time domain signal is added with Doppler frequency shift to obtain x' j (m):

[0074]

[0075] Step 8: Accumulate the time domain signals of different frequency points into a set of time domain signals x'(m) and send them:

[0076]

[0077] The embodiment of the present invention generates an analog signal affected by wideband Doppler through the above process. Figure 4 The receiving constellation diagram of 4 symbols of the data sent using 256QAM modulation mode at a carrier frequency of 20GHz and a median Doppler of 360kHz is shown. As can be seen from the figure, Doppler has a great impact on high-frequency band, large-bandwidth, high-order modulation signals. The receiving constellation diagram starting from the second symbol has undergone a large rotation and diffusion. If the wideband Doppler is not considered when designing the receiving scheme of the ground terminal, it will inevitably affect the receiving performance. The wideband Doppler signal simulation method proposed in this application can be used to assist in the design of the receiving scheme of the ground terminal, making the simulation design closer to the actual scenario.

[0078] Embodiment 2, as Figure 2 As shown in FIG. 1 , the specific process of time domain compensation includes:

[0079] Step 1: The received length is L*(N+N cp ) is segmented into L symbols of time domain data, and the cyclic prefix is ​​removed:

[0080] yl (n) = y(l*N+(l+1)*N cp +n)

[0081] y l =[y l (0),y l (1),…,y l (N-1)].

[0082] Step 2: Calculate the median Doppler Δf c

[0083]

[0084] Among them, f c represents the carrier frequency, Δv represents the relative speed between the low-orbit satellite and the ground terminal, cosθ represents the angle between the satellite-ground relative speed vector and the satellite-ground line, and c represents the speed of light; the relative speed and angle here are generally deduced through the six-digit orbital ephemeris information received by the terminal.

[0085] Step 3: Calculate the normalized Doppler shift Δf of each frequency point according to the configuration parameters norm (k):

[0086]

[0087] Step 4: Calculate the time domain Doppler compensation matrix B for each symbol:

[0088] β=(l+1)·N cp +l·N

[0089]

[0090] Step 5: Perform Doppler compensation on the time domain signal of each symbol to obtain the compensated time domain data

[0091]

[0092] The embodiment of the present invention performs time domain compensation on the time domain signal affected by wideband Doppler through the above process. Figure 5 The figure shows the received constellation diagram of the 4-symbol data after time domain Doppler compensation under the conditions of 20 GHz carrier frequency and 360 kHz median Doppler when the data is sent using 256QAM modulation. Figure 4 In comparison, the rotation and diffusion of the receiving constellation diagram caused by broadband Doppler have been almost perfectly compensated, which will greatly improve the communication quality between ground terminals and low-orbit satellites in large bandwidth scenarios.

[0093] Embodiment three, as Figure 3As shown in FIG. 1 , the specific process of frequency domain compensation includes:

[0094] Step 1: The received length is L*(N+N cp ) is segmented into L symbols of time domain data, and the cyclic prefix is ​​removed:

[0095] y l (n) = y(l*N+(l+1)*N cp +n)

[0096] y l =[y l (0),y l (1),…,y l (N-1)].

[0097] Step 2: Perform FFT on the time domain data of each symbol to obtain the frequency domain data affected by wideband Doppler: Y l (k)

[0098]

[0099] Step 3: Calculate the median Doppler Δf c :

[0100]

[0101] Among them, f c represents the carrier frequency, Δv represents the relative speed between the low-orbit satellite and the ground terminal, cosθ represents the angle between the satellite-ground relative velocity vector and the satellite-ground line, and c represents the speed of light.

[0102] Step 4: Calculate the normalized Doppler shift Δf of each frequency point according to the configuration parameters norm (k):

[0103]

[0104] Step 5: Perform Doppler compensation on the frequency domain data of each symbol to obtain the compensated frequency domain data

[0105]

[0106] The embodiment of the present invention performs frequency domain compensation on the time domain signal affected by wideband Doppler through the above process. Figure 6 The figure shows the received constellation diagram of the 4-symbol data after frequency domain Doppler compensation under the conditions of 20 GHz carrier frequency and 360 kHz median Doppler when the data is sent using 256QAM modulation. Figure 4In comparison, the rotation and diffusion of the receiving constellation diagram caused by wideband Doppler are basically compensated, and the remaining constellation point diffusion caused by ICI has little effect on demodulation. Because the signal demodulation in the original 5G terrestrial cellular communication system includes steps 1 and 2 of embodiment 3, this solution can avoid major modifications to the original 5G receiving solution and reduce development time and cost.

Claims

1. A low-orbit satellite broadband Doppler simulation and compensation method based on OFDM system, characterized in that: The following steps are involved: Step 1: Configure Doppler parameters, including carrier frequency f c , median Doppler frequency shift value Δf c , subcarrier spacing Δf, system sampling rate f s , FFT points, i.e. frequency points N, cyclic prefix length N cp and the number of continuously transmitted OFDM symbols L; and at the same time, generate L*N groups of transmission data X according to the number of OFDM symbols L and the number of frequency points N l (k),k=0,1,…,N-1; l=0,1,…,L; Step 2: Calculate the normalized Doppler frequency shift value Δf at each frequency point according to the configured Doppler parameters norm (k): Step 3: Copy the N×L resource grid into N copies and fill them with 0, then fill the L transmission data with different symbols at the same frequency into N N×L resource grids in turn to obtain the transmission data X' after mapping a single resource grid. l,j (k): j represents the jth resource grid; Step 4: Perform IFFT transformation on the transmitted data after resource grid mapping to transform it into time domain data x l,j (n): Step 5: Add a cyclic prefix to the N×L group of time domain data with a length of N, that is, add the last N of the original time domain data with a length of N. cp The data of length is copied and spliced ​​to the beginning of the time domain data, forming a length of N+N cp Data Step 6: Splice the time domain signals of the same frequency point with multiple symbols, that is, splice the time domain signals of the same frequency point into a group of length L*(N+N cp ) of the time domain signal x j (m),m=0,1,…,L*(N+N cp )-1; Step 7: The length of different frequency points is L*(N+N cp )'s time domain signal is added with Doppler frequency shift to obtain x' j (m): Step 8: Accumulate the time domain signals of different frequency points into a set of time domain signals x'(m) and send them: Step 9: The receiving end receives the time domain signal y(m), and then performs time domain compensation and frequency domain compensation to obtain compensated data.

2. The method for simulating and compensating low-orbit satellite wideband Doppler based on OFDM system according to claim 1, characterized in that: The specific process of time domain compensation in step 9 includes: Step 101: The received length is L*(N+N cp ) is segmented into L symbols of time domain data, and the cyclic prefix is ​​removed: y l (n)=y(l*N+(l+1)*N cp +n) and l =[and l (0),and l (1),…,and l (N-1)]; Step 102: Calculate the median Doppler Δf c Among them, f c represents the carrier frequency, Δv represents the relative speed between the low-orbit satellite and the ground terminal, cosθ represents the angle between the satellite-ground relative speed vector and the satellite-ground line, and c represents the speed of light; Step 103: Calculate the normalized Doppler frequency shift Δf of each frequency point according to the configuration parameters norm (k): Step 104: Calculate the time domain Doppler compensation matrix B of each symbol: β=(l+1)·N cp +l·N Step 105: Perform Doppler compensation on the time domain signal of each symbol to obtain compensated time domain data 3. The method for simulating and compensating low-orbit satellite wideband Doppler based on OFDM system according to claim 1, characterized in that: The specific process of frequency domain compensation in step 9 includes: Step 201: The received length is L*(N+N cp ) is segmented into L symbols of time domain data, and the cyclic prefix is ​​removed: y l (n)=y(l*N+(l+1)*n cp +n) and l =[and l (0),and l (1),…,and l (N-1)]; Step 202: Perform FFT on the time domain data of each symbol to obtain the frequency domain data affected by wideband Doppler: Y l (k) Step 203: Calculate the median Doppler Δf c : Among them, f c represents the carrier frequency, Δv represents the relative speed between the low-orbit satellite and the ground terminal, cosθ represents the angle between the satellite-ground relative speed vector and the satellite-ground line, and c represents the speed of light; Step 204: Calculate the normalized Doppler frequency shift Δf of each frequency point according to the configuration parameters norm (k): Step 205: Perform Doppler compensation on the frequency domain data of each symbol to obtain compensated frequency domain data

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