Adaptive filter based echo channel estimation method

Abstract

This invention discloses an echo channel estimation method based on adaptive filtering, belonging to the field of wireless communication. First, channel estimation of the mixed signal is performed using pilot signals. Then, a correlation algorithm is used to estimate the impulse response of the echo channel to obtain an estimated value of the echo channel. Next, the estimated echo channel value is used to calculate the echo signal and perform channel estimation of the near-end transmitted signal. This value is then subtracted from the first channel estimate to obtain a second estimate of the channel through which the near-end signal passes. Finally, a partial estimate of the near-end signal is calculated using the pilot signals and the second estimate, and this value is subtracted from the received signal to obtain an estimated value of the echo signal, which is then fed into an adaptive filter to update the filter coefficients. This invention fully utilizes pilot channel estimation in OFDM signals and combines it with adaptive filtering to achieve effective echo channel estimation in two-talk scenarios, reducing the bit error rate under echo interference.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to an echo channel estimation method based on adaptive filtering. Background Technology

[0002] With the widespread adoption of fifth-generation (5G) wireless communication networks and the increasing maturity of technology and hardware, more optimization algorithms have been proposed to improve communication reliability and quality. Echo interference refers to the phenomenon where a transmitted signal from a distant end returns to the distant end after passing through a specific Rayleigh fading channel. At this point, the echo signal from the distant end overlaps with the transmitted signal from the near end, interfering with the distant end's reception and recovery of the near-end signal. Echo interference in communication systems has always been a difficult type of interference to handle, and it cannot be completely eliminated through channel estimation. Currently, effective methods to reduce interference include beamforming, which reduces sidelobe power by transmitting directional beams, thus reducing the number of signal reflections and scatterings. Ideally, the transmitting and receiving ends should form a direct path.

[0003] The same problem arises in acoustics, especially during voice calls. When the near end is in a closed space, the speech from the far end is reflected by the closed space, re-recorded into the microphone, and then sent back to the far end. Acoustic echo cancellation uses an adaptive filter to eliminate this interference. In addition, most acoustic adaptive echo cancellation models adopt a double talk detection (DTD) scheme, which is implemented as follows: the number of signals in the channel is determined by the double talk detector at the far end. If both ends are sending data simultaneously, the coefficient update of the adaptive filter is stopped or slowed down. If only the far end is sending data, the coefficient update of the adaptive filter is performed. After that, it is assumed that the echo channel does not change during double talk.

[0004] Echo cancellation in wireless communication can also be implemented using adaptive filtering. Simulations show that when only the far-end signal is transmitted, adaptive filtering can be directly used to estimate the echo channel. However, in two-talk scenarios, the coefficients of the adaptive filter cannot converge. To implement adaptive filtering in the field of wireless communication, we can imitate acoustic echo cancellation by using two-talk detection to control the updating of filter coefficients. However, unlike echo cancellation in voice calls, the two parties in a voice call speak simultaneously with a low probability. Therefore, the voice channel can be regarded as a half-duplex channel in most cases, which is suitable for detection using a two-talk detector, and sufficient time is allowed for the adaptive filter to update its coefficients. In contrast, the transmission and reception of signals in a wireless channel are random, and the channel can be regarded as a full-duplex channel. If adaptive filtering can only be performed in single-talk scenarios, the filter coefficients may not converge completely. In addition, the channel coefficients of the wireless channel itself will also fluctuate to some extent. Therefore, adaptive filtering in wireless channels needs to be real-time, that is, it is desirable to achieve adaptive filtering simultaneously in two-talk scenarios. Summary of the Invention

[0005] This invention provides an echo channel estimation method based on adaptive filtering, which combines an adaptive filter with OFDM (Orthogonal Frequency Division Multiplexing) signals to achieve echo channel estimation based on adaptive filtering for interference cancellation in two-talk scenarios, thus solving the problem of echo interference in traditional wireless channels.

[0006] This invention provides an echo channel estimation method based on adaptive filtering, comprising the following steps:

[0007] The pilot signal of the near-end signal is used to perform the first channel estimation of the mixed signal to obtain the first estimated value of the near-end channel. The mixed signal is a mixture of the far-end signal after passing through the echo channel and the near-end signal after passing through the near-end channel.

[0008] A coarse estimate of the echo channel is obtained by estimating the impulse response of the echo channel using a relevant algorithm. The coarse estimate of the echo channel is then convolved with the far-end signal to calculate the estimated value of the echo signal. A second channel estimation is performed on the calculated estimated value of the echo signal using the pilot of the near-end signal to obtain the second estimated value of the near-end channel. The second estimated value of the near-end channel is then subtracted from the first estimated value of the near-end channel to obtain the estimated value of the near-end signal passing through the near-end channel.

[0009] The estimated value of the near-end signal via the near-end channel is convolved with the pilot signal of the near-end signal to obtain the received signal estimate of the pilot portion of the near-end signal. The received signal estimate of the pilot portion of the near-end signal is subtracted from the mixed signal to obtain the estimated value of the far-end signal at the corresponding near-end signal pilot position via the echo channel. This value is then fed into an adaptive filter to update the filter coefficients. The estimated value of the echo channel is obtained based on the updated coefficients.

[0010] In one embodiment of the present invention, the far-end signal and the near-end signal are OFDM signals, and before performing the first channel estimation of the mixed signal using the pilot of the near-end signal, the method further includes:

[0011] Remove the cyclic prefix from the OFDM signal.

[0012] In one embodiment of the present invention, when performing calculations and first and second channel estimations using the correlation algorithm, only the estimated value with a length equal to the OFDM symbol cyclic prefix length is taken, and the portion greater than the cyclic prefix length is defaulted to 0.

[0013] In one embodiment of the present invention, the impulse response of the echo channel is:

[0014]

[0015] Where L is the length of the echo channel, n is the time axis offset of the impulse response, and a i This represents the value of the impulse response at offset i.

[0016] In one embodiment of the present invention, the first channel estimation of the mixed signal is performed using the pilot signal of the near-end signal to obtain a first estimated value of the near-end channel, including:

[0017] The mixed signal y(n) is composed as follows:

[0018]

[0019] Where x(n) is the far-end signal, u(n) is the near-end signal, and h echo (n) represents the impulse response of the echo channel, h u (n) represents the channel of the near-end signal, and v(n) represents Gaussian white noise;

[0020] Transforming the mixed signal to the frequency domain yields:

[0021] Y(k)=X(k)·H echo (k)+U(k)·H u (k)+V(k)

[0022]

[0023] The process involves estimating the pilot channel of the near-end signal, and the first estimated value of the near-end channel is:

[0024]

[0025] In one embodiment of the present invention, a coarse estimate of the echo channel is obtained by estimating the impulse response of the echo channel using a correlation algorithm, including:

[0026] The echo signal of the remote signal is:

[0027]

[0028] The correlation algorithm involves correlating the echo signal with the far-end signal:

[0029]

[0030] Where, x h * (n) represents the echo signal of the far-end signal, a i * Let x be the value of the impulse response at offset i. * (n) represents the far-end signal, k is the time offset between the echo signal and the far-end signal, and R xx (k) is the autocorrelation function of the far-end signal, var * This represents the conjugate transpose, where var is any variable, and if R... xx (k)=Cδ(k), then:

[0031]

[0032] The cross-correlation function between the far-end signal and the near-end signal is 0. The mixed signal y(n) is cross-correlated with the far-end signal x(n), and then divided by the value of the far-end signal at offset 0, and the conjugate is taken to obtain a rough estimate of the echo channel.

[0033]

[0034] In one embodiment of the invention, the second estimate of the near-end channel is derived from a coarse estimate of the echo channel. and the first estimate of the near-end channel This yields a rough estimate of the echo channel. Perform an FFT transform to the frequency domain to obtain Combined with the first estimate of the near-end channel The estimated value H′ of the near-end signal through the near-end channel is obtained.u (k):

[0035]

[0036] in, This refers to the secondary channel estimation process.

[0037] In one embodiment of the present invention, the estimated value of the far-end echo signal is:

[0038]

[0039] X(k)·H echo (k) is the estimated value of the far-end echo signal, and V is the frequency response value of Gaussian white noise;

[0040] The estimated value of the far-end echo signal is input into the far-end adaptive filter to obtain the estimated value of the echo channel.

[0041] The echo channel estimation method based on adaptive filtering in this invention combines adaptive filtering with OFDM channel estimation, fully utilizing the advantages of both techniques. Channel estimation and correlation are used to estimate the near-end channel and echo channel, reducing estimation errors; adaptive filtering further improves the accuracy of the estimation. Thus, adaptive filtering is implemented in a two-talk scenario, improving the effectiveness and real-time performance of the wireless communication system.

[0042] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0043] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0044] Figure 1 A flowchart of an echo channel estimation method based on adaptive filtering according to an embodiment of the present invention;

[0045] Figure 2 An execution framework diagram of an echo channel estimation method based on adaptive filtering provided according to an embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram of simulation results provided according to an embodiment of the present invention. Detailed Implementation

[0047] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0048] Figure 1 This is a flowchart of an echo channel estimation method based on adaptive filtering according to an embodiment of the present invention.

[0049] like Figure 1 As shown, the echo channel estimation method based on adaptive filtering includes the following steps:

[0050] In step S101, the pilot signal of the near-end signal is used to perform the first channel estimation of the mixed signal to obtain the first estimated value of the near-end channel. The mixed signal is a mixture of the far-end signal passing through the echo channel and the near-end signal passing through the near-end channel.

[0051] In this invention, the far-end signal and the near-end signal refer to OFDM signals. The echo channel and the near-end signal channel are Rayleigh channels with different channel impulse responses. The pilot is the DMRS in the OFDM signal, which is generated using the GOLD sequence to ensure that the signal has good autocorrelation characteristics in the correlation calculation. The adaptive filtering adopts the NLMS algorithm, which uses iterative calculation to make the signal obtained after convolving the far-end signal with the filter coefficients approximate the estimated value of the echo signal.

[0052] The length of the echo channel is L, and the impulse response of the echo channel is... Where L is the length of the echo channel, n is the time axis offset of the impulse response, and a i This represents the value of the impulse response at offset i.

[0053] The mixed signal y(n) is constructed as follows:

[0054]

[0055] Where x(n) is the far-end signal, u(n) is the near-end signal, and h echo (n) represents the impulse response of the echo channel, h u (n) represents the channel of the near-end signal, and v(n) represents Gaussian white noise.

[0056] The mixed signal is transformed to the frequency domain using FFT to obtain:

[0057] Y(k)=X(k)·H echo (k)+U(k)·H u (k)+V(k)

[0058]

[0059] The process involves estimating the pilot channel of the near-end signal. The first estimated value of the near-end channel is:

[0060]

[0061] The first channel estimate is a rough estimate of the near-end signal.

[0062] In step S102, the impulse response of the echo channel is estimated using a correlation algorithm to obtain a coarse estimate of the echo channel. The coarse estimate of the echo channel is convolved with the far-end signal to calculate the estimate of the echo signal. The calculated echo signal estimate is then used to perform a second channel estimation using the pilot signal of the near-end signal to obtain a second estimate of the near-end channel. The second estimate of the near-end channel is then subtracted from the first estimate of the near-end channel to obtain the estimate of the near-end signal passing through the near-end channel.

[0063] Dual-channel estimation only requires strict synchronization of the near-end signal, and the phase difference between the echo signal and the near-end signal can be calculated by correlation.

[0064] Optionally, in one embodiment of the present invention, when performing dual channel estimation, in order to avoid the influence of ISI and ICI on channel estimation, the cyclic prefix of the OFDM signal is removed first.

[0065] When performing related calculations and dual channel estimation, only the estimated value with a length equal to the OFDM symbol cyclic prefix length is taken, and the part greater than the cyclic prefix length is defaulted to 0.

[0066] In one embodiment of the present invention, a coarse estimate of the echo channel is obtained by estimating the impulse response of the echo channel using a correlation algorithm, including:

[0067] The echo signal of the far-end signal is:

[0068]

[0069] The relevant algorithm involves correlating the echo signal with the far-end signal:

[0070]

[0071] Where, x h * (n) represents the echo signal of the far-end signal, a i * Let x be the value of the impulse response at offset i. * (n) represents the far-end signal, k is the time offset between the echo signal and the far-end signal, and R xx (k) is the autocorrelation function of the far-end signal, var* This represents the conjugate transpose, where var is any variable, and if R... xx (k)=Cδ(k), then:

[0072]

[0073] The cross-correlation function between the far-end and near-end signals is 0. The mixed signal y(n) is cross-correlated with the far-end signal x(n), and then divided by the value of the far-end signal at offset 0, with the conjugate obtained, yielding a rough estimate of the echo channel.

[0074]

[0075] The second estimate of the near-end channel is derived from the coarse estimate of the echo channel. and the first estimate of the near-end channel This yields a rough estimate of the echo channel. Perform an FFT transform to the frequency domain to obtain Combined with the first estimate of the near-end channel The estimated value H of the near-end signal through the near-end channel is obtained. u ′(k):

[0076]

[0077] in, This is a secondary channel estimation process.

[0078] In step S103, the estimated value of the near-end signal via the near-end channel is convolved with the pilot of the near-end signal to obtain the estimated value of the received signal of the pilot part of the near-end signal. The estimated value of the received signal of the pilot part of the near-end signal is subtracted from the mixed signal to obtain the estimated value of the far-end signal via the echo channel at the corresponding near-end signal pilot position. This value is then sent to the adaptive filter to update the filter coefficients. The estimated value of the echo channel is obtained based on the updated coefficients.

[0079] In one embodiment of the present invention, the estimated value of the far-end echo signal is:

[0080]

[0081] X(k)·H echo (k) is the estimated value of the far-end echo signal, and V is the frequency response value of Gaussian white noise;

[0082] The estimated value of the far-end echo signal is input into the far-end adaptive filter to obtain the estimated value of the echo channel.

[0083] like Figure 2As shown, in an embodiment of the present invention, the mixed signal and the far-end transmitted signal are first correlated to obtain a coarse estimate of the echo channel. Then, the near-end signal pilot channel is estimated from the mixed signal to obtain a coarse estimate of the near-end signal channel. Next, the coarse estimate of the echo channel is convolved with the far-end signal to generate an estimate of the echo signal, and this estimate is used for near-end signal pilot estimation. The coarse estimate of the near-end signal channel obtained in the previous step is subtracted from the pilot estimate to obtain a further estimate of the near-end signal channel. Finally, the near-end signal pilot is convolved with the further estimate of the near-end signal channel to obtain an estimate of the near-end signal pilot portion. This estimate is subtracted from the position of the pilot in the mixed signal to obtain an estimate of the echo signal. This value is then fed into an adaptive filter to update the filter coefficients. The updated coefficients are the further estimate of the echo channel.

[0084] The invention will be further explained below with reference to signal examples.

[0085] The system uses a 5G OFDM signal with a subcarrier spacing of 30kHz. The duration of the radio frame is 10ms. Each radio frame has 10 subframes. Each subframe is divided into two time slots. Each time slot is divided into 14 OFDM symbols. The FFT points are 4096. 16QAM modulation is used and the signal-to-noise ratio is 30dB.

[0086] The far-end signal passes through the echo channel, and the near-end signal passes through the near-end channel. The two signals are superimposed to form a mixed signal.

[0087]

[0088] At the remote receiver, the first channel estimation is performed on the mixed signal:

[0089] Y(k)=X(k)·H echo (k)+U(k)H u (k)+V(k)

[0090]

[0091] The channel estimate for the near-end signal is:

[0092]

[0093] This estimate contains interference from echo signals, so it can only be used as a rough estimate of the near-end channel.

[0094] In the correlation calculation, the mixed signal and the remote transmitted signal are cross-correlated. The calculation result including the remote echo is as follows:

[0095]

[0096] Among them, R xx (k) represents the autocorrelation function of the far-end signal. Furthermore, in this embodiment, the autocorrelation function of the signal satisfies R... xx (k)=C·δ(k), then we can further derive:

[0097]

[0098] Furthermore, the cross-correlation function between the far-end signal and the near-end signal is always 0. Therefore, by performing a cross-correlation calculation on the mixed signal y(n) and the far-end signal x(n), and then dividing by the value of the far-end signal at offset 0 and taking the conjugate, a rough estimate of the echo channel can be obtained.

[0099]

[0100] A more efficient estimate of the near-end channel can be obtained from and It is concluded that... Perform an FFT transform to the frequency domain to obtain A more efficient estimate of the near-end channel, H′, is obtained. u (k):

[0101]

[0102] in This is a secondary channel estimation process.

[0103] According to Y(k)=X(k)·H echo (k)+U(k)H u (k)+V(k), the estimated value of the far-end echo signal is:

[0104]

[0105] The above results are fed into an adaptive filter, and the estimated value of the echo channel is calculated through continuous iterative updates.

[0106] like Figure 3 The figure shows the MATLAB simulation results of the embodiment, where the horizontal axis represents the number of iterations and the vertical axis represents the absolute error between the estimated and actual echo channel values. After about 50 OFDM symbols, the error function basically converges.

[0107] The echo channel estimation method based on adaptive filtering proposed in this invention includes dual channel estimation, correlation calculation, and adaptive filtering. The signal transmitted from the far end is mixed with the transmitted signal from the near end via an echo channel. At the far end, the echo channel is estimated. First, pilot signals are used to estimate the channel of the mixed signal. Then, a correlation algorithm is used to estimate the impulse response of the echo channel to obtain an estimated value of the echo channel. Next, the estimated value of the echo channel is used to calculate the echo signal and to estimate the channel of the near-end transmitted signal. This estimated value is then subtracted from the first channel estimate to obtain a secondary estimate of the channel traversed by the near-end signal. Finally, the pilot signals and the secondary estimate are used to calculate a partial estimate of the near-end signal, which is then subtracted from the received signal to obtain an estimated value of the echo signal, which is then fed into an adaptive filter to update the filter coefficients. This invention fully utilizes pilot channel estimation in OFDM signals and combines it with adaptive filtering to achieve effective echo channel estimation in dual-talk scenarios, reducing the bit error rate under echo interference.

[0108] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0109] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0110] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or N executable instructions for implementing custom logic functions or processes, and the scope of preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

Claims

1. An echo channel estimation method based on adaptive filtering, characterized in that, Includes the following steps: The pilot signal of the near-end signal is used to perform the first channel estimation of the mixed signal to obtain the first estimated value of the near-end channel. The mixed signal is a mixture of the far-end signal after passing through the echo channel and the near-end signal after passing through the near-end channel. A coarse estimate of the echo channel is obtained by estimating the impulse response of the echo channel using a relevant algorithm. The coarse estimate of the echo channel is then convolved with the far-end signal to calculate the estimated value of the echo signal. A second channel estimation is performed on the calculated estimated value of the echo signal using the pilot of the near-end signal to obtain the second estimated value of the near-end channel. The second estimated value of the near-end channel is then subtracted from the first estimated value of the near-end channel to obtain the estimated value of the near-end signal passing through the near-end channel. The estimated value of the near-end signal via the near-end channel is convolved with the pilot signal of the near-end signal to obtain the received signal estimate of the pilot portion of the near-end signal. The received signal estimate of the pilot portion of the near-end signal is subtracted from the mixed signal to obtain the estimated value of the far-end signal at the corresponding near-end signal pilot position via the echo channel. This value is then fed into an adaptive filter to update the filter coefficients. The estimated value of the echo channel is obtained based on the updated coefficients.

2. The method according to claim 1, characterized in that, The far-end signal and the near-end signal are OFDM signals. Before performing the first channel estimation of the mixed signal using the pilot of the near-end signal, the method further includes: Remove the cyclic prefix from the OFDM signal.

3. The method according to claim 2, characterized in that, When using the aforementioned algorithm for calculation and the first and second channel estimations, only the estimated value with a length equal to the OFDM symbol cyclic prefix length is taken, and the part greater than the cyclic prefix length is defaulted to 0.

4. The method according to claim 1, characterized in that, The impulse response of the echo channel is: in, The length of the echo channel, This represents the time axis offset of the impulse response. For the impulse response at the offset The value at that location.

5. The method according to claim 4, characterized in that, The first channel estimation of the mixed signal is performed using the pilot signals of the near-end signal, resulting in the first estimate of the near-end channel, including: The mixed signal The composition is as follows: in, For remote signals, For near-end signals, The impulse response of the echo channel. This refers to the channel impulse response experienced by the near-end signal. It is Gaussian white noise; Transforming the mixed signal to the frequency domain yields: The process involves estimating the pilot channel of the near-end signal, and the first estimated value of the near-end channel is: 。 6. The method according to claim 5, characterized in that, A coarse estimate of the echo channel is obtained by estimating the impulse response of the echo channel using a correlation algorithm, including: The echo signal of the remote signal is: The correlation algorithm involves correlating the echo signal with the far-end signal: in, The echo signal of the distant signal. For the impulse response at the offset The value at that location, Let k be the echo signal from the far end, and k be the time offset between the echo signal and the far end signal. The autocorrelation function of the far-end signal is given. This indicates the conjugate transpose. Let be any variable, if ,but: The cross-correlation function between the far-end signal and the near-end signal is 0, and the mixed signal... With the remote signal Perform cross-correlation calculations, then divide the result by the value of the far-end signal at offset 0 and take its conjugate to obtain a rough estimate of the echo channel: 。 7. The method according to claim 6, characterized in that, The second estimate of the near-end channel is derived from the coarse estimate of the echo channel. and the first estimate of the near-end channel This yields a rough estimate of the echo channel. Perform an FFT transform to the frequency domain to obtain Combined with the first estimate of the near-end channel The estimated value of the near-end signal through the near-end channel is obtained. : in, This refers to the secondary channel estimation process.

8. The method according to claim 7, characterized in that, The estimated value of the far-end echo signal is: in, This is an estimate of the far-end echo signal. The frequency response value of Gaussian white noise; The estimated value of the far-end echo signal is input into the far-end adaptive filter to obtain the estimated value of the echo channel.

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