Channel estimation and equalization method applicable to OFDM (Orthogonal Frequency Division Multiplexing) satellite communication system

Abstract

The invention discloses a channel estimation and equalization method suitable for an OFDM satellite communication system, and relates to the technical field of satellite communication. The method comprises the following steps: firstly, calculating a frequency domain channel estimation result, then extracting a time domain channel response with the maximum energy, then calculating amplitude information and the frequency domain channel response, or calculating an average phase value after compensating time delay for a preliminary channel estimation result to obtain a phase value of a data symbol; and finally, balancing the channel according to the amplitude information and the frequency domain channel response or the phase value of the data symbol. According to the method, a channel model of satellite communication is fully considered, the channel estimation and equalization method is adaptively simplified according to channel characteristics, and the method is more practical.

Description

Technical Field

[0001] The present invention relates to the field of satellite communication technologies, and particularly to a channel estimation and equalization method applicable to an OFDM satellite communication system. Background Art

[0002] In a satellite mobile communication system, due to characteristics such as the rapid relative movement between the transmitter and the receiver, large signal attenuation, and limited signal-to-noise ratio, the signal deteriorates severely after being transmitted to the receiving end. To minimize the influence of factors such as noise on the signal as much as possible and more accurately recover the transmitted signal, it depends on the good performance of channel estimation and equalization;

[0003] In a satellite mobile communication system based on the OFDM waveform, especially in a low-earth orbit satellite communication system, the high-speed movement of the transmitter and the receiver will generate Doppler frequency shift. The OFDM system using multi-carrier transmission is very sensitive to frequency offset. The Doppler frequency shift will destroy the orthogonality between sub-carriers, generate interference between sub-carriers, and severely deteriorate the demodulation performance of the system. Therefore, it is necessary to recover the transmitted signal from the received signal through channel estimation, and the accuracy of channel estimation has an important impact on the performance of the entire communication system. Summary of the Invention

[0004] In view of this, the present invention proposes a channel estimation and equalization method applicable to an OFDM satellite communication system. This method fully considers the channel model of satellite communication, makes adaptive simplifications to the channel estimation and equalization method according to the channel characteristics, and is more practical.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A channel estimation and equalization method applicable to an OFDM satellite communication system, comprising the following steps:

[0007] Step 1, extracting the data on the pilot sub-carriers from the received frequency-domain data, and performing conjugate multiplication with the pre-generated local pilots to obtain the frequency-domain LS channel estimation result;

[0008] Step 2, transforming the frequency-domain LS channel estimation result to the time domain through IFFT to obtain the time-domain channel response;

[0009] Step 3, respectively extracting the time-domain channel response with the maximum energy corresponding to each pilot symbol;

[0010] Step 4, performing calculations according to the configuration parameters in combination with Step 3 to obtain the amplitude information A of the pilot symbol and the frequency-domain channel response H DFT (k,i);

[0011] Wherein, i represents the index of the pilot symbol in each OFDM symbol of each time slot, and k represents the sub - carrier index;

[0012] Step 5: Obtain the frequency - domain channel response H data (k,m) of the data symbol where the user is located through time - domain interpolation, where m represents the index of the data symbol in each OFDM symbol of each time slot;

[0013] Step 6: Perform channel equalization on the received frequency - domain service signal according to the calculated amplitude information A and the frequency - domain channel response H data (k,m), and finally obtain the channel equalization result

[0014] Furthermore, the specific method of step 4 is as follows:

[0015] For the pilot symbol with pilot symbol index i, record the maximum value of the time - domain channel response energy as P i,max ;

[0016] Where is the number of pilot symbols;

[0017] Record the number of sub - carriers occupied by the pilot data on each pilot symbol as Calculate the frequency - domain amplitude information A of the pilot symbol according to the above configuration parameters as:

[0018]

[0019] The frequency - domain channel response H DFT (k,i) of the frequency - domain position where the user is located on the pilot symbol is:

[0020]

[0021] Where h DFT (maxpos i ,i) = h LS (maxpos i ,i), maxpos i represents the sampling - point index corresponding to the maximum value of the time - domain channel response energy in the pilot symbol with pilot symbol index i, h LS (maxpos i ,i) represents the time - domain channel response of the pilot symbol with sampling - point index maxpos i and pilot symbol index i; j represents the imaginary number, and normpi i represents the normalized phase value of h DFT (maxpos i ,i); M represents the number of points of the FFT of the OFDM symbol.

[0022] Further, the specific manner of step 5 is as follows:

[0023] First, calculate the phase difference on each sub - carrier between two adjacent pilot symbols:

[0024]

[0025] L i is the interval between the pilot symbol with pilot symbol index i and the pilot symbol with pilot symbol index i + 1; represents the phase difference between the pilot symbol with pilot symbol index i and the pilot symbol with pilot symbol index i + 1 when the sub - carrier index is k;

[0026] Then linearly interpolate the phase value of the frequency - domain channel response on the data symbol where the user is located:

[0027]

[0028] represents the phase value of the frequency - domain channel response of the data symbol with sub - carrier index k and data symbol index m. If the data symbol with data symbol index m is before the first pilot signal, then i = 0 in this formula. If the data symbol with data symbol index m is after the last pilot signal, then If the data symbol with data symbol index m is between the first pilot signal and the last pilot signal, then the value of i is the index value of the pilot signal before the data symbol with data symbol index m and closest to the data symbol with data symbol index m; L is the distance between the data symbol with data symbol index m and the pilot symbol with pilot signal index value i;

[0029] Finally, calculate the frequency - domain channel response H data (k,m):

[0030]

[0031] Further, the specific manner of step 6 is as follows:

[0032]

[0033] where Y(k,m) represents the frequency - domain service signal received at sub - carrier index k and data symbol index m of the data symbol.

[0034] A channel estimation and equalization method applicable to OFDM satellite communication systems, including the following steps:

[0035] Step 1: Perform a correlation operation on the pilot data extracted from the received signal and the local pilot to obtain a preliminary channel estimation result;

[0036] Step 2: Transform the obtained preliminary channel estimation result to the time domain through IFFT, obtain the positions of the maximum energy values corresponding to each pilot symbol, and calculate the pilot symbol amplitude information according to the configuration parameters;

[0037] Step 3: After compensating for the time delay effect on the preliminary channel estimation result, segment it and calculate the average phase value of each segment;

[0038] Step 4: Use time-domain linear interpolation to obtain the phase values on the data symbols where the user is located;

[0039] Step 5: Perform channel equalization on the received signal according to the amplitude information and the interpolated phase values to finally obtain the channel equalization result.

[0040] Furthermore, the specific method of Step 2 is as follows:

[0041] Transform the result H LS (k, i) of the preliminary channel estimation to the time domain and denote it as h LS (n, i), where k is the subcarrier index, n is the sampling point index, i is the pilot symbol index, and is the number of pilot symbols; the energy value P(n, i) of the time-domain channel response is calculated by the following formula:

[0042]

[0043] where real() represents the real part and imag() represents the imaginary part; for the pilot symbol with pilot symbol index i, denote the maximum value of its time-domain channel response energy as P i,max ;

[0044] Further calculate the pilot symbol frequency-domain amplitude information A as:

[0045]

[0046] where, is the number of subcarriers occupied by the pilot data on each pilot symbol.

[0047] Furthermore, the specific method of Step 3 is as follows:

[0048] Step 301: Compensate for the time delay effect on the result H LS (k, i) of the preliminary channel estimation:

[0049]

[0050] where, H L ′S (k, i) represents the preliminary channel estimation result after compensating for the impact of the delay spread, where N = N FFT / 2, and N FFT is the number of FFT points for each OFDM symbol; maxpos i represents the sampling point index corresponding to the maximum value of the time-domain channel response energy among the pilot symbols with pilot symbol index i;

[0051] Step 302: Divide the H corresponding to each pilot symbol L ′ S (k, i) into P segments, and calculate the phase value normpi corresponding to the summation result after summing the H L ′ S within each segment respectively, where p is the segment index within each pilot symbol, and p = 0, 1,..., P - 1. i,p

[0052] Furthermore, the specific method of Step 4 is as follows:

[0053] Step 401: Calculate the phase difference between adjacent subcarriers of two adjacent pilot symbols:

[0054]

[0055] where M = N FFT , and in this formula, the value of p is the segment index to which the subcarrier index k belongs; L i is the interval between the pilot symbol with pilot symbol index i and the pilot symbol with pilot symbol index i + 1; represents the phase difference between the pilot symbol with pilot symbol index i and the pilot symbol with pilot symbol index i + 1 when the subcarrier index is k;

[0056] Step 402: Use time-domain linear interpolation to obtain the phase value on the data symbol where the user is located:

[0057]

[0058] where represents the phase value of the frequency-domain channel response of the data symbol with subcarrier index k and data symbol index m; if the data symbol with data symbol index m is before the first pilot signal, then i = 0 in this formula, and if the data symbol with data symbol index m is after the last pilot signal, then If the data symbol with data symbol index m is located between the first pilot signal and the last pilot signal, the value of i is the pilot signal index value before the data symbol with data symbol index m and closest to the data symbol with data symbol index m; L is the distance between the data symbol with data symbol index m and the pilot symbol with pilot signal index value i; in this formula, the value of p is the segment index to which the subcarrier index k belongs.

[0059] Furthermore, the specific manner of step 5 is as follows:

[0060] Step 501, calculate the frequency-domain channel response H data (k,m):

[0061]

[0062] Step 502, calculate the channel equalization result:

[0063]

[0064] Among them, Y(k,m) represents the frequency-domain service signal received at the data symbol with data symbol index m and subcarrier index k.

[0065] Due to the adoption of the above technical solutions, the beneficial effects of the present invention compared with the prior art are as follows:

[0066] 1. The present invention can adapt to the channel characteristics of satellite communication, has higher channel estimation accuracy and better demodulation performance in the case of large attenuation and large signal-to-noise ratio. And the present invention fully considers the channel model of satellite communication, and makes an adaptive simplification of the channel estimation and equalization method according to the channel characteristics, so that its implementation method is simpler and more practical.

[0067] 2. The present invention makes full use of the characteristic that the channel energy in the satellite communication system is concentrated on the direct path, and performs segmented estimation on the channel response phase for the problem of large Doppler caused by the rapid movement of the transmitter and receiver. This not only improves the receiving performance and makes the estimation of the transmitted signal more accurate, but also greatly reduces the calculation and implementation complexity of channel estimation. Brief Description of the Drawings

[0068] Figure 1 、 Figure 2 is the overall flowchart of a channel estimation and equalization method applicable to an OFDM satellite communication system in an embodiment of the present invention.

[0069] Figure 3 、 Figure 4 is the detailed processing flowchart of channel estimation and equalization in an embodiment of the present invention. Detailed Embodiment

[0070] The content of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0071] A channel estimation and equalization method applicable to an OFDM satellite communication system. Assume that one time slot of the OFDM system includes 12 OFDM symbols x 0 , x 1 , … x 11 , where the pilot signals are located in symbols x 2 , x 6 , x 9 , and the rest are non-pilot symbols. The system bandwidth occupies 264 RBs in the frequency domain, and each RB contains 12 subcarriers. The number of points for FFT of each OFDM symbol is N FFT = 4096. Assume that the user transmits data using a total of 128 RBs.

[0072] Specifically, it includes the following steps:

[0073] As Figure 1 , Figure 2 shown, (1) Perform a correlation operation on the pilot data Y(k, l) extracted from the received signal and the local pilot X pilot (k, l) to obtain the preliminary channel estimation result H LS (k, l):

[0074]

[0075] where k is the subcarrier index and l is the symbol where the pilot is located. In this embodiment, l = 2, 6, 9.

[0076] (2) Transform the obtained preliminary channel estimation result H LS (k, i) to the time domain through IFFT. The time-domain channel response is h LS (n, i), where n is the sample index and i is the pilot symbol index, i = 0, 1, 2. The energy value of the time-domain channel response is calculated by the following formula:

[0077]

[0078] Respectively find the maximum value P LS of the energy of the time-domain channel response h i,max (n, i) on each pilot symbol, and the corresponding maximum value position is maxpos i .

[0079] Number of pilot symbols The number of subcarriers occupied by the pilot on each pilot symbol is Further calculate the amplitude information according to the above configuration parameters:

[0080]

[0081] As shown in Figure 4 , the maximum position maxpos of the time-domain channel response energy calculated according to step (2) i compensates for the delay effect on the preliminary channel estimation result H LS (k, i), where N = N FFT / 2.

[0082] After compensating for the delay effect, the channel estimation results H L ′ S (k, i) on each pilot symbol are segmented. Assuming that each segment contains 8 RBs, the 128 RBs of the user's transmitted data are divided into 16 segments. For the H within each segment L ′ S (k, i), after summing, the phase value normpi is obtained i,p . Where p is the segmentation index within each pilot symbol, p = 0, 1,..., 15.

[0083] Specifically, the channel estimation result H L ′ S (k, i) can be segmented evenly or unevenly;

[0084] (4a) According to the maximum position maxpos obtained in step (2) i and the segmented phase value normpi obtained in step (3a) i,p , calculate the phase difference between subcarriers between two adjacent pilot symbols:

[0085]

[0086] where M = N FFT . k is the subcarrier index, and this subcarrier belongs to the p-th segment. i is the pilot symbol index, i = 0, 1, 2. L i is the interval between the (i + 1)-th and the i-th pilot symbols.

[0087] Subsequently, linearly interpolate the phase values of the frequency-domain channel response on non-pilot symbols

[0088]

[0089] where L is the interval between the m-th data symbol and the i-th pilot symbol, m = 0, 1,..., 8, i = 0, 1, 2.

[0090] (5a) The phase value of the frequency-domain channel response interpolated according to step (4a) Obtain the frequency-domain channel response H with an amplitude of 1 data (k,m), Further combine the amplitude information A calculated in step (2) to perform channel equalization on the frequency-domain received signal, and finally obtain the channel equalization result

[0091]

[0092] where Y(k,m) is the frequency-domain service signal received on the k-th subcarrier of the m-th data symbol.

[0093] (3b) In another embodiment, such as Figure 3 shown, the calculation of the frequency-domain channel response at the frequency-domain position where the user is located is based on the characteristic that the energy of the satellite communication channel is mainly concentrated on the main path. According to the time-domain channel response with the maximum energy obtained in step (2), the time-domain channel response can be approximately expressed as:

[0094]

[0095] where maxpos i is the position of the maximum value of the energy of the time-domain channel response of the i-th pilot symbol. According to the Fourier transform formula, perform an M-point Fourier transform on h DFT (n,i), where M = N FFT , to obtain the frequency-domain channel response at the frequency-domain position where the user is located on the pilot symbol:

[0096]

[0097] where normpi i is the normalized phase value of h DFT (maxpos i ,i).

[0098] (4b) Obtain the frequency-domain channel response on the symbol where the user is located through time-domain interpolation. The specific method is as follows:

[0099] First, calculate the phase difference between each subcarrier between two adjacent pilot symbols:

[0100]

[0101] where k is the subcarrier index, i is the pilot symbol index, i = 0,1,2. L i is the interval between the (i + 1)-th and the i-th pilot symbols. According to the expression of H DFT (k,i) in step (4), the phase difference between each subcarrier between two adjacent pilot symbols can be obtained as:

[0102]

[0103] Then linearly interpolate the phase values of the frequency-domain channel response on non-pilot symbols:

[0104]

[0105] where L is the interval between the m-th data symbol and the i-th pilot symbol, m = 0, 1, …, 8, and i = 0, 1, 2.

[0106] Furthermore, obtain the frequency-domain channel response according to the phase values of the frequency-domain channel response

[0107] (5b) Perform channel equalization on the received frequency-domain service signal according to the calculated amplitude information A and the frequency-domain channel response H data (k, m), and finally obtain the channel equalization result including:

[0108]

[0109] where Y(k, m) is the frequency-domain service signal received on the k-th subcarrier and the m-th data symbol.

[0110] Those skilled in the art will realize that the described embodiments are for helping readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to the described embodiments. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A channel estimation and equalization method suitable for OFDM satellite communication system, characterized in that: The following steps are involved: Step 1: extract the data on the pilot subcarrier from the received frequency domain data, and perform conjugate multiplication with the pre-generated local pilot to obtain the frequency domain LS channel estimation result; Step 2: transform the frequency domain LS channel estimation result to the time domain through IFFT to obtain the time domain channel response; Step 3, respectively extracting the time domain channel response with the maximum energy corresponding to each pilot symbol; Step 4: Calculate according to the configuration parameters combined with step 3 to obtain the amplitude information A of the pilot symbol and the frequency domain channel response H of the frequency domain position of the user on the pilot symbol. DFT (k,i); Wherein, i represents the index of the pilot symbol in the OFDM symbol of each time slot, and k represents the subcarrier index; Step 5: Obtain the frequency domain channel response H of the user's data symbol by time domain interpolation. data (k,m), where m represents the index of the data symbol in the OFDM symbol of each time slot; Step 6: Based on the calculated amplitude information A and frequency domain channel response H data (k,m) performs channel equalization on the received frequency domain service signal and finally obtains the channel equalization result 2. A channel estimation and equalization method suitable for OFDM satellite communication system according to claim 1, characterized in that: The specific method of step 4 is: For the pilot symbol with pilot symbol index i, the maximum value of its time domain channel response energy is recorded as P i,max ; in is the number of pilot symbols; The number of subcarriers occupied by pilot data on each pilot symbol is recorded as According to the above configuration parameters, the pilot symbol frequency domain amplitude information A is calculated as: The frequency domain channel response H of the user's frequency domain position on the pilot symbol DFT (k,i) is: Among them, h DFT (maxpos i ,i)=h LS (maxpos i ,i), maxpos i Indicates the sampling point index corresponding to the maximum value of the time domain channel response energy in the pilot symbol with pilot symbol index i, h LS (maxpos i ,i) indicates that the sampling point index is maxpos i , the time domain channel response of the pilot symbol with pilot symbol index i; j represents an imaginary number, normpi i Indicates h DFT (maxpos i ,i) is the normalized phase value; M represents the number of FFT points of OFDM symbol.

3. A channel estimation and equalization method suitable for OFDM satellite communication system according to claim 2, characterized in that: The specific method of step 5 is: First, calculate the phase difference on each subcarrier between two adjacent pilot symbols: L i is the interval between the pilot symbol with pilot symbol index i and the pilot symbol with pilot symbol index i+1; represents the phase difference between the pilot symbol with pilot symbol index i and the pilot symbol with pilot symbol index i+1 when the subcarrier index is k; Then linearly interpolate the phase value of the frequency domain channel response on the data symbol where the user is located: represents the phase value of the frequency domain channel response of the data symbol with subcarrier index k and data symbol index m. If the data symbol with data symbol index m is located before the first pilot signal, then i in this formula is 0. If the data symbol with data symbol index m is located after the last pilot signal, then If the data symbol with data symbol index m is located between the first pilot signal and the last pilot signal, the value of i is the pilot signal index value that is before the data symbol with data symbol index m and closest to the data symbol with data symbol index m; L is the distance between the data symbol with data symbol index m and the pilot symbol with pilot signal index i; Finally, the frequency domain channel response H on the data symbol where the user is located is calculated. data (k,m):

4. The channel estimation and equalization method applicable to OFDM satellite communication system according to claim 3, characterized in that: The specific method of step 6 is: Among them, Y(k,m) represents the frequency domain service signal received on the data symbol with data symbol index m and subcarrier index k.

5. A channel estimation and equalization method suitable for OFDM satellite communication system, characterized in that: The following steps are involved: Step 1, performing correlation operation on the pilot data extracted from the received signal and the local pilot to obtain a preliminary channel estimation result; Step 2: transform the obtained preliminary channel estimation result into the time domain through IFFT, obtain the position of the maximum energy corresponding to each pilot symbol, and calculate the pilot symbol amplitude information according to the configuration parameters; Step 3, after compensating the delay effect on the preliminary channel estimation result, divide it into segments and calculate the average phase value of each segment; Step 4, using time domain linear interpolation to obtain the phase value of the data symbol where the user is located; Step 5: Channel equalization is performed on the received signal according to the amplitude information and the interpolated phase value, and finally a channel equalization result is obtained.

6. A channel estimation and equalization method suitable for OFDM satellite communication system according to claim 5, characterized in that: The specific method of step 2 is: The result of the preliminary channel estimation H LS (k,i) is transformed to the time domain and recorded as h LS (n,i), where k is the subcarrier index, n is the sampling point index, and i is the pilot symbol index. is the number of pilot symbols; the energy value P(n,i) of the time domain channel response is calculated by the following formula: P(n,i)=[real(h LS (n,i))] 2 +[imag(h LS (n,i))] 2 ; Where real() represents the real part, imag() represents the imaginary part; for the pilot symbol with pilot symbol index i, the maximum value of its time domain channel response energy is recorded as P i,max ; The pilot symbol frequency domain amplitude information A is further calculated as: in, The number of subcarriers occupied by pilot data on each pilot symbol.

7. A channel estimation and equalization method suitable for OFDM satellite communication system according to claim 6, characterized in that: The specific method of step 3 is: Step 301: The result of the preliminary channel estimation H LS (k,i) Compensation delay impact: Among them, H L ′ S (k,i) represents the preliminary channel estimation result after compensating for the delay effect, N = N FFT / 2,N FFT The number of FFT points for each OFDM symbol; maxpos i represents the sampling point index corresponding to the maximum value of the time domain channel response energy in the pilot symbol with pilot symbol index i; Step 302: H corresponding to each pilot symbol L ′ S (k,i) is divided into P segments, and H in each segment is L ′ S (k,i) After summing, calculate the phase value normpi corresponding to the summation result i,p , p is the segment index within each pilot symbol, p = 0, 1, ..., P-1.

8. The channel estimation and equalization method applicable to OFDM satellite communication system according to claim 7, characterized in that: The specific method of step 4 is: Step 401, calculate the phase difference on each subcarrier between two adjacent pilot symbols: in, M=N FFT , in this formula, the value of p is the segment index to which the subcarrier index k belongs; L i is the interval between the pilot symbol with pilot symbol index i and the pilot symbol with pilot symbol index i+1; represents the phase difference between the pilot symbol with pilot symbol index i and the pilot symbol with pilot symbol index i+1 when the subcarrier index is k; Step 402: Use time domain linear interpolation to obtain the phase value of the data symbol where the user is located: in, represents the phase value of the frequency domain channel response of the data symbol with subcarrier index k and data symbol index m; if the data symbol with data symbol index m is located before the first pilot signal, then i=0 in this formula; if the data symbol with data symbol index m is located after the last pilot signal, then If the data symbol with data symbol index m is located between the first pilot signal and the last pilot signal, the value of i is the pilot signal index value that is before the data symbol with data symbol index m and closest to the data symbol with data symbol index m; L is the distance between the data symbol with data symbol index m and the pilot symbol with pilot signal index i; the value of p in this formula is the segment index to which the subcarrier index is k.

9. A channel estimation and equalization method suitable for OFDM satellite communication system according to claim 8, characterized in that: The specific method of step 5 is: Step 501: Calculate the frequency domain channel response H of the data symbol where the user is located data (k,m): Step 502, calculate the channel equalization result: Among them, Y(k,m) represents the frequency domain service signal received on the data symbol with data symbol index m and subcarrier index k.

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