OFDM (Orthogonal Frequency Division Multiplexing) channel estimation method in high dynamic environment

Abstract

The invention belongs to the field of wireless communication, and particularly relates to an OFDM (Orthogonal Frequency Division Multiplexing) channel estimation method in a high-dynamic environment. The method comprises the steps of 1, receiving N paths of signals; 2, calculating the signal-to-noise ratio of each path of signal; step 3, carrying out noise reduction processing on the pilot frequency in each path of signal; 4, calculating the channel response of the data block in each path of signal; 5, calculating the diversity coefficient of each path of signal; step 6, carrying out equalization processing on each path of signal according to the diversity coefficient; and step 7, combining the N paths of signals after equalization processing into one path of signals.

Description

Technical Field

[0001] The invention belongs to the field of wireless communications, and in particular relates to an OFDM channel estimation method in a high dynamic environment. Background Art

[0002] In a high dynamic environment, the transmitter and receiver have a high relative movement speed, resulting in severe time selective fading. Combined with the frequency selective fading caused by the multipath effect, the two combine to generate a severe dual-selective channel, affecting the reliable reception of the signal.

[0003] OFDM technology uses a multi-carrier parallel transmission method and has good anti-multipath capability. However, OFDM systems are greatly affected by frequency. In a high dynamic environment, the signal will produce frequency domain distortion, which will have a great impact on the channel estimation results and thus affect the overall performance of the communication system.

[0004] With the increasing demand for communication in highly dynamic environments, how to quickly and accurately track and estimate channels is an urgent problem to be solved.

[0005] Channel estimation is one of the key technologies of OFDM system. Commonly used channel estimation methods include least squares (LS) and minimum mean square error (MMSE). Among them, the least squares method is widely used in communication systems due to its simple structure and easy implementation.

[0006] In a high-dynamic environment, the multipath effect and the large Doppler phase caused by the high-speed movement of the transmitter and receiver produce a fast-varying dual-selection channel. Traditional channel estimation methods perform poorly, which seriously affects the performance of the communication system. With the rapid development of high-dynamic aircraft, how to quickly and accurately track and estimate the channel has become an urgent problem to be solved. Summary of the invention

[0007] Purpose of the invention: The present invention provides an OFDM channel estimation method in a high dynamic environment, constructs a frame structure for quickly tracking channel changes, adopts multi-path signal diversity transmission, optimizes the channel estimation result by data interpolation at the receiving end, improves the receiving signal-to-noise ratio by noise reduction, diversity combining and other methods, and improves the real-time and accuracy of the channel estimation result.

[0008] The technical solution of the present invention:

[0009] An OFDM channel estimation method in a high dynamic environment, the steps are as follows:

[0010] Step 1: Receive N signals;

[0011] Step 2: Calculate the signal-to-noise ratio of each signal;

[0012] Step 3: Perform noise reduction processing on the pilot signal in each signal;

[0013] Step 4: Calculate the channel response of the data block in each signal;

[0014] Step 5: Calculate the diversity coefficient of each signal;

[0015] Step 6: Equalize each signal according to the diversity coefficient;

[0016] Step 7: Combine the N equalized signals into one signal.

[0017] Furthermore, in step 1, the N-channel signal generation method is as follows:

[0018] Perform M1-point IFFT transformation on the original data to complete OFDM modulation and obtain the original OFDM data symbols;

[0019] The original OFDM data symbol is δ i Bit cyclic shift is performed to obtain OFDM data symbols;

[0020] The single OFDM data symbol X corresponding to the i-th transmitting antenna i (k) can be expressed as:

[0021]

[0022] Among them, S(k) is the original OFDM data symbol, N is the number of transmitting antennas, δ i is the number of shift points, δ i is a random integer between 1 and M1;

[0023] The ZC sequence is used to generate a pilot signal of length M2. The relationship between M1 and M2 satisfies:

[0024] q is an integer

[0025] Perform M2-point IFFT transformation on the pilot to complete OFDM modulation;

[0026] According to the pilot and OFDM data symbols, a data block of length M1+M2 is formed. Each data frame contains D data blocks, and a pilot is added after the last data block.

[0027] The data frame is transmitted in N ways.

[0028] Furthermore, in step 2, the signal-to-noise ratio calculation process of each signal is as follows:

[0029] Taking the j-th signal as an example, calculate the time domain response of the channel at the pilot in the r-th data block of the j-th signal;

[0030] Find the maximum path power Pow in the channel time domain response at the pilot in the rth data block of the jth signal jrmax ;

[0031] According to Pow jrmax Set the noise threshold σ corresponding to the pilot in the rth data block of the jth signal jr and search threshold τ jr ;

[0032] According to the noise threshold σ of the pilot in the rth data block of the jth signal jr and search threshold τ jr Calculate the noise power Noise_avg of the pilot in the rth data block of the jth signal jr Sum signal power Signal_avg jr ;

[0033] According to the noise power Noise_avg of the pilot in the rth data block of the jth signal jr Sum signal power Signal_avg jr Calculate the signal-to-noise ratio (SNR) of the pilot signal in the rth data block of the jth signal. jr .

[0034] Furthermore, in step 3, the noise threshold σ jr as follows:

[0035]

[0036] Search threshold τ jr as follows:

[0037]

[0038] Furthermore, in step 4, during the noise reduction process, the pilot time domain response below the noise threshold σ jr The data of is set to zero, and the time domain impulse response of the pilot noise reduction in the rth data block of the jth signal is obtained, which is recorded as:

[0039] hestd jr (n) = [hestd jr (0),hestd jr (1),...,hestd jr (M2-1)]

[0040] Wherein, M2 is the pilot length.

[0041] Further, in step 5, the frequency domain channel response Hestd_data of the OFDM data symbol in the rth data block of the jth signal jr :

[0042]

[0043] Among them, Hestd jrstart is the pilot channel response in the rth data block of the jth signal, Hestd jrend is the pilot channel response of the r+1th data block of the jth signal, and the value range of α and β is 0~1.

[0044] Further, in step 6, the diversity coefficient coeff of the OFDM data symbol in the rth data block of the jth signal is jr The calculation formula is as follows:

[0045]

[0046] in, is the maximum value of the pilot signal-to-noise ratio in the rth data block among the 1 to N signals,

[0047]

[0048] Furthermore, the OFDM data symbol in the rth data block of the jth signal after equalization is The calculation formula is as follows:

[0049]

[0050] Among them, R jr (k) is the OFDM data symbol in the rth data block of the jth signal, Hes_data jr (k) is the frequency domain channel response of the OFDM data symbol in the rth data block of the jth signal, coeff jr is the diversity coefficient of the OFDM data symbol in the rth data block of the jth signal, Noise_avg jr is the noise power of the pilot in the rth data block of the jth signal, and M1 is the OFDM data symbol length.

[0051] Further, in step eight, the OFDM data symbol after the combination in the rth data block of the 1-N signals The expression is as follows:

[0052]

[0053] Where M1 is the OFDM data symbol length, is the OFDM data symbol in the rth data block of the jth signal.

[0054] Beneficial effects of the present invention:

[0055] 1. The data generation method at the transmitting end is based on the characteristics of the wireless channel in a highly dynamic environment. A data frame structure that can track channel changes in real time and quickly is designed. Multi-channel diversity transmission is used to increase the complexity and randomness of the data, providing diversity gain for the receiving end signal.

[0056] 2. The receiving end channel estimation method based on maximum ratio selection adds a time domain noise reduction processing module on the basis of LS channel estimation, and extracts the signal with the highest signal-to-noise ratio through diversity combining, which improves the accuracy of channel estimation and enhances the communication performance of OFDM system in high dynamic environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is the system structure to which the present invention is directed, and describes the interaction capabilities between various components.

[0058] Figure 2 It is the overall design concept of the present invention, describing the functional position of each component of the present invention.

[0059] Figure 3 It is the overall design of logical mapping management and describes the content of logical mapping management. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] The present invention provides an OFDM channel estimation method in a high dynamic environment, which adopts multi-path signals for diversity reception and transmission, performs cyclic delay diversity processing on the transmitting end signal, introduces phase difference, increases the complexity and randomness of data, improves the receiving signal-to-noise ratio through data noise reduction and diversity combining at the receiving end, and improves the real-time and accuracy of the channel estimation result.

[0062] The process is as follows:

[0063] Transmitter data generation

[0064] The data generated by the transmitter is as follows Figure 1 shown.

[0065] 1. First, perform M1 point IFFT transformation on the original data, complete OFDM modulation, and perform δ1~δ N After bit cyclic delay, OFDM data symbols are obtained, and then a pilot with a length of M2 is generated using a ZC sequence. The pilot generation method is:

[0066]

[0067] Where M2 is the sequence length and p is an arbitrary integer.

[0068] The relationship between M1 and M2 satisfies:

[0069] q is a positive integer

[0070] 2. According to the pilot and OFDM data symbols, the data blocks are formed. Each data frame contains D data blocks, and a pilot is added after the last data block to form a complete data frame for N-way transmission; the receiving end channel estimation method based on maximum ratio selection

[0071] The receiving end channel estimation method based on maximum ratio selection is as follows Figure 2 shown.

[0072] 1. The receiving end channel estimation method based on maximum ratio selection consists of signal-to-noise ratio estimation, time domain noise reduction and channel estimation, and diversity combining based on maximum ratio selection.

[0073] a) Signal-to-Noise Ratio Estimation

[0074] First, the noise power and signal power of the pilot in the rth data block of the jth signal are estimated.

[0075] When estimating the noise power, first estimate the time domain response of the channel at the pilot: hest jr (n).

[0076] The frequency domain signal P of the pilot in the rth data block of the jth signal jr (k) can be expressed as:

[0077] P jr (k) = [P jr (0),P jr (1),...P jr (M1-1)]

[0078] Wherein, M2 is the frequency domain pilot length.

[0079] The local pilot sequence can be expressed as:

[0080] P local (k) = [P local (0),P local (1),…P local (M2-1)]

[0081] Let the local pilot take the conjugate and then jr(k) Point multiplication, perform M2-point IFFT on the result of the point multiplication to obtain the time domain response hest of the channel at the pilot in the r-th data block of the j-th signal jr (n):

[0082] hest jr (n) = IFFT(P jr (k)·conj(P local (k))),k=0,1,...,M2-1

[0083] Then find the power Pow of the maximum path in the pilot time domain response jrmax :

[0084]

[0085] According to Pow jrmax Set the noise threshold σ jr and search threshold τ jr , and calculate the signal power and noise power. The noise threshold σ r satisfy:

[0086]

[0087] Search threshold τ jr satisfy:

[0088]

[0089] Noise power Noise_avg of the pilot in the rth data block of the jth signal jr is the pilot time domain response hest jr (n) satisfies hest jr (n) < σ1 and the first L data:

[0090]

[0091] Among them, n0 is to satisfy hest jr (n)<σ jr The sequence number corresponding to the first data of the condition, L is the total number of noise data that need to be calculated.

[0092] Signal power of the pilot signal in the rth data block of the jth signal Signal_avg j is the pilot time domain response hest j (n) satisfies hest j (n)>σ jr All data and:

[0093]

[0094] Among them, nm for hest jr (n) satisfies hest jr (n m )<τ jr data, M0 is the data that meets the condition hest jr (n)>τ jr The total amount of data.

[0095] The signal-to-noise ratio (SNR) of the pilot signal in the rth data block of the jth signal jr The calculation formula is:

[0096]

[0097] b) Time domain noise reduction and channel estimation

[0098] The noise threshold σ calculated according to b) jr , perform noise reduction on the channel response at the pilot in the rth data block of the jth signal, and convert the pilot time domain response hest jr (n) is below the noise threshold σ jr The data of is set to zero, and the channel impulse response after noise reduction at the pilot in the rth data block of the jth signal is obtained, which is recorded as:

[0099] hestd jr (n) = [hestd jr (0),hestd jr (1),…,hestd jr (M2-1)]

[0100] The time domain channel response after noise reduction at the pilot in the rth data block of the jth signal is hestd jr (n) Perform FFT transformation at M2 points to obtain the frequency domain channel response at the pilot in the rth data block of the jth signal:

[0101] Hestd jr (k) = FFT(hestd jr (n)),k=0,1,...,M2-1

[0102] Finally, according to Figure 3 The data frame structure shown in the figure uses the interpolation method to calculate the channel response Hestd_data at the OFDM data symbol in the rth data block of the jth signal. jr (n):

[0103]

[0104] Among them, Hestd jrstart is the channel response of the pilot in the rth data block of the jth signal, Hestd jrendis the channel response of the pilot in the r+1th data block of the jth signal, the value range of α and β is 0~1, q is the ratio of M1 to M2, M1 is the data length, and M2 is the pilot length.

[0105] c) Diversity combining based on maximum ratio selection

[0106] Before diversity combining, the signal with the largest pilot signal-to-noise ratio of the rth data block among the 1 to N signals is found through the estimated signal-to-noise ratio in b).

[0107]

[0108] Then calculate the diversity coefficient coeff of the OFDM data symbol in the rth data block of the jth signal jr :

[0109]

[0110] Combined with the diversity coefficient, the OFDM data symbols in the rth data block of the jth signal are equalized, and the jth signal obtained after equalization is The following formula is used for calculation:

[0111]

[0112] Among them, R jr (k) is the OFDM data symbol in the rth data block of the jth signal, Hes_data jr (k) is the frequency domain channel response of the OFDM data symbol in the rth data block of the jth signal, coeff jr is the diversity coefficient of the OFDM data symbol in the rth data block of the jth signal, Noise_avg jr is the noise power of the pilot in the rth data block of the jth signal, and M1 is the OFDM data symbol length.

[0113] Finally, the OFDM data symbols after equalization processing in the rth data block of the 1-N signal are combined into one data, and the OFDM data symbol after the rth data block is obtained.

[0114]

[0115] Among them, M1 is the OFDM data symbol length, and N is the number of receiving antennas.

[0116] The above is only a specific embodiment of the present invention, and the present invention is described in detail. The unexplained part is a conventional technology. However, the protection scope of the present invention is not limited to this. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An OFDM channel estimation method in a high dynamic environment, characterized by: Here are the steps: Step 1: Receive N signals; Step 2: Calculate the signal-to-noise ratio of each signal; Step 3: Perform noise reduction processing on the pilot tone in each signal; Step 4: Calculate the channel response of the data block in each signal; Step 5: Calculate the diversity coefficient of each signal; Step 6: Equalize each signal according to the diversity coefficient; Step 7: Combine the N equalized signals into one signal.

2. The method according to claim 1, characterized in that: In step 1, the N-channel signal generation method is as follows: Perform M1-point IFFT transformation on the original data to complete OFDM modulation and obtain the original OFDM data symbols; The original OFDM data symbol is δ i Bit cyclic shift is performed to obtain OFDM data symbols; The single OFDM data symbol X corresponding to the i-th transmitting antenna i (k) can be expressed as: X i (k)=S(k)e -j2πδik / M ,i=1,2,...N,k=1,2,...,M1 Among them, S(k) is the original OFDM data symbol, N is the number of transmitting antennas, δ i is the number of shift points, δ i is a random integer between 1 and M1; The ZC sequence is used to generate a pilot signal of length M2. The relationship between M1 and M2 satisfies: q is an integer Perform M2-point IFFT transformation on the pilot to complete OFDM modulation; According to the pilot and OFDM data symbols, a data block of length M1+M2 is formed. Each data frame contains D data blocks, and a pilot is added after the last data block. The data frame is transmitted in N ways.

3. The method according to claim 2, characterized in that: In step 2, the signal-to-noise ratio calculation process of each signal is as follows: Taking the j-th signal as an example, calculate the time domain response of the channel at the pilot in the r-th data block of the j-th signal; Find the maximum path power Pow in the channel time domain response at the pilot in the rth data block of the jth signal jrmax ; According to Pow jrmax Set the noise threshold σ corresponding to the pilot in the rth data block of the jth signal jr and search threshold τ jr ; According to the noise threshold σ of the pilot in the rth data block of the jth signal jr and search threshold τ jr Calculate the noise power Noise_avg of the pilot in the rth data block of the jth signal jr Sum signal power Signal_avg jr ; According to the noise power Noise_avg of the pilot in the rth data block of the jth signal jr Sum signal power Signal_avg jr Calculate the signal-to-noise ratio (SNR) of the pilot signal in the rth data block of the jth signal. jr .

4. The method according to claim 3, characterized in that: In step 3, the noise threshold σ jr as follows: Search threshold τ jr as follows:

5. The method according to claim 4, characterized in that: In step 4, during the noise reduction process, the pilot time domain response below the noise threshold σ jr The data of is set to zero, and the time domain impulse response of the pilot noise reduction in the rth data block of the jth signal is obtained, which is recorded as: <h2 style=";text-align:left;direction:ltr">last<h2 style=";text-align:left;direction:ltr"> jr <h2 style=";text-align:left;direction:ltr"> (n)=[hestd<h2 style=";text-align:left;direction:ltr"> jr <h2 style=";text-align:left;direction:ltr"> (0),hestd<h2 style=";text-align:left;direction:ltr"> jr <h2 style=";text-align:left;direction:ltr"> (1),...,hestd<h2 style=";text-align:left;direction:ltr"> jr <h2 style=";text-align:left;direction:ltr"> (M2-1)] Wherein, M2 is the pilot length.

6. The method according to claim 5, characterized in that: In step 5, the frequency domain channel response Hestd_data of the OFDM data symbol in the rth data block of the jth signal jr : Among them, Hestd jrstart is the pilot channel response in the rth data block of the jth signal, Hestd jrend is the pilot channel response of the r+1th data block of the jth signal, and the value range of α and β is 0~1.

7. The method according to claim 6, characterized in that: In step 6, the diversity coefficient coeff of the OFDM data symbol in the rth data block of the jth signal is jr The calculation formula is as follows: in, is the maximum value of the pilot signal-to-noise ratio in the rth data block among the 1 to N signals, 8. The method according to claim 7, characterized in that: OFDM data symbol in the rth data block of the jth signal after equalization The calculation formula is as follows: Among them, R jr (k) is the OFDM data symbol in the rth data block of the jth signal, Hes_data jr (k) is the frequency domain channel response of the OFDM data symbol in the rth data block of the jth signal, coeff jr is the diversity coefficient of the OFDM data symbol in the rth data block of the jth signal, Noise_avg jr is the noise power of the pilot in the rth data block of the jth signal, and M1 is the OFDM data symbol length.

9. The method according to claim 8, characterized in that: In step 8, the OFDM data symbol in the rth data block of the 1-N signals is combined The expression is as follows: Where M1 is the OFDM data symbol length, is the OFDM data symbol in the rth data block of the jth signal.

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