A low-orbit satellite wideband Doppler simulation and compensation method based on OFDM system

Abstract

The present invention relates to the field of wireless communication technology, and in particular to a low-orbit satellite broadband Doppler simulation and compensation method based on an OFDM system, which includes two processes: simulation and compensation, and the compensation includes time domain compensation and frequency domain compensation. The broadband Doppler simulation method provided by the present invention can generate a wireless signal that is more in line with a real satellite-to-ground communication scenario, and a 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, and basically does not require modification of the original ground cellular network terminal receiving solution, and can obtain better demodulation performance at a low development cost.

Description

Technical Field

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

[0002] 5G-Advanced communication technology has developed rapidly in the past two years, with satellite communication technology being a research hotspot. The primary goal of this research is to use it as an extension of 5G NR, enabling 5G terminals to maintain access to 5G networks in areas difficult to reach by traditional terrestrial base stations, such as uninhabited and underdeveloped regions. Compared to high-orbit satellites, low-orbit satellites offer shorter transmission latency and lower transmit power, reducing the design cost and complexity of base stations and terminals. Therefore, low-orbit satellite communication technology is a key research direction within 5G-Advanced.

[0003] Due to the high speed of low-orbit satellites, the signals they transmit to the ground inevitably experience significant Doppler shift. Over time, the Doppler shift decreases as the satellite moves toward the ground terminal, reaching zero when it reaches the terminal. Then, as the satellite gradually moves away from the ground terminal, the Doppler shift gradually increases. According to the 3GPP protocol, the maximum Doppler shift caused by a low-orbit satellite at an altitude of 600 km at a 20 GHz carrier frequency can reach 480 kHz, which is unacceptable for current 5G communications based on OFDM systems. Furthermore, 5G-A imposes higher throughput requirements than 5G. High throughput inevitably requires large bandwidth for data transmission. Different subcarriers in a large-bandwidth signal will be affected by varying degrees of Doppler shift, resulting in inter-subcarrier interference and deteriorating 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 wireless signals that are 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 low development cost.

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

[0007] A method for simulating and compensating broadband Doppler of a low-orbit satellite 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, namely frequency points N, cyclic prefix length N cp And the number of continuously transmitted OFDM symbols L; 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 shift value Δf at each frequency point based on the configured Doppler parameters norm (k):

[0010]

[0011] Step 3: Copy the N×L resource grid N times and fill it with 0, then fill the L transmission data at the same frequency point with different symbols into N N×L resource grids in sequence 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 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 multiple symbols at the same frequency point, 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 Doppler shifted 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 velocity 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;

[0030] Step 103: Calculate the normalized Doppler 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 velocity 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;

[0046] Step 204: Calculate the normalized Doppler 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 analog signals of low-orbit satellites affected by broadband Doppler based on the OFDM system, which is more consistent with wireless signals in actual environments and is helpful for simulation analysis during system design.

[0052] 2. The time-domain wideband Doppler compensation scheme proposed in this invention can accurately compensate for the influence of wideband Doppler, maximize the signal quality and demodulation performance of ground terminals, 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 requires little computation and basically does not require modification of the original ground cellular network terminal reception 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 reception and demodulation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a flow chart of the low-orbit satellite broadband Doppler signal simulation method of the present invention.

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

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

[0057] Figure 4 This is the constellation diagram of the signal reception affected by Doppler under the 256QAM modulation mode of the present invention.

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

[0059] Figure 6 This is the 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 with reference to the accompanying drawings and specific embodiments. The following examples will help those skilled in the art further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that those skilled in the art may make several changes and modifications without departing from the scope of the present invention. These all fall within the scope of protection 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] Example 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, namely frequency points N, cyclic prefix length N cp And the number of continuously transmitted OFDM symbols L; 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 shift value Δf at each frequency point based on 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 an N*L resource grid and sent in the time domain signal generated by IFFT. To add wideband Doppler effects, a single resource grid mapping is required. The N×L resource grid is copied N times and filled with 0s. Then, L transmission data with different symbols at the same frequency (same k value but different L) are sequentially filled into N N×L resource grids to 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 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 multiple symbols at the same frequency point, 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 Doppler shifted 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 figure shows the receiving constellation diagram for four symbols of data transmitted using 256QAM modulation at a 20GHz carrier frequency and a median Doppler of 360kHz. As can be seen from the figure, Doppler significantly affects high-bandwidth, high-order modulated signals in the high-frequency band. Starting from the second symbol, the receiving constellation diagram undergoes significant rotation and diffusion. Failure to consider wideband Doppler when designing a ground terminal's receiving solution will inevitably affect reception performance. The wideband Doppler signal simulation method proposed in this application can be used to assist in the design of ground terminal receiving solutions, making the simulation design more realistic.

[0078] Example 2, as Figure 2 As shown in Figure 2, the specific process of time domain compensation includes:

[0079] Step 1: Convert the received length to 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 from the six-digit orbital ephemeris information received by the terminal.

[0085] Step 3: Calculate the normalized Doppler shift Δf at each frequency point based on 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 receiving constellation diagram of the 4-symbol data after time domain Doppler compensation under the conditions of 20GHz carrier frequency and 360kHz 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] Example 3, as Figure 3As shown in Figure 2, the specific process of frequency domain compensation includes:

[0094] Step 1: Convert the received length to 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 velocity 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 for each frequency point based on 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 receiving constellation diagram of the 4-symbol data after frequency domain Doppler compensation under the conditions of 20GHz carrier frequency and 360kHz 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 impact on demodulation. Because the signal demodulation in the original 5G terrestrial cellular communication system includes steps 1 and 2 of Example 3, this solution can avoid major modifications to the original 5G reception solution and reduce development time and cost.

Claims

1. A method for simulating and compensating low-orbit satellite wideband Doppler 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, namely frequency points N, cyclic prefix length N cp And the number of continuously transmitted OFDM symbols L; 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 shift value Δf at each frequency point based on the configured Doppler parameters norm (k): Step 3: Copy the N×L resource grid N times and fill it with 0, then fill the L transmission data at the same frequency point with different symbols into N N×L resource grids in sequence 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 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 multiple symbols at the same frequency point, 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 Doppler shifted 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 OFDM-based low-orbit satellite broadband Doppler simulation and compensation method 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 velocity 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; Step 103: Calculate the normalized Doppler 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 an OFDM system according to claim 1, wherein: 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 velocity 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; Step 204: Calculate the normalized Doppler 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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