WO2014153732A1

WO2014153732A1 - Channel estimating and equalizing method and apparatus for ultrasonic communication

Info

Publication number: WO2014153732A1
Application number: PCT/CN2013/073256
Authority: WO
Inventors: 孟剑强; 刘明刚; 张江红
Original assignee: 北京印声科技有限公司
Priority date: 2013-03-27
Filing date: 2013-03-27
Publication date: 2014-10-02
Also published as: CN105052101A; HK1211396A1

Abstract

Disclosed is a channel estimating and equalizing method for ultrasonic communication, comprising: in response to reception of an ultrasonic signal, estimating a channel response; equalizing the ultrasonic signal based on the estimated channel response by using a linear equalizer; and adjusting a coefficient of the linear equalizer according to a change of the channel response. Further disclosed is a corresponding channel estimating and equalizing apparatus for ultrasonic communication.

Description

Channel estimation and equalization method and device for ultrasonic communication

The present invention relates to channel estimation and equalization techniques, and in particular to a channel estimation and equalization method and apparatus for ultrasonic communication.

In the case of communication using an ultrasonic signal, since the ultrasonic signal is transmitted in space, especially in a confined space, there is a large multipath superposition or interference, and the signal changes greatly. Therefore, in order to improve the accuracy of decoding, reduce inter-code crosstalk, multipath effects, etc., it is necessary to estimate and equalize the ultrasonic channel.

Channel estimation and equalization techniques have been extensively studied in wireless communication, and proposed, for example, channel estimation techniques based on least mean square (LMS), channel estimation techniques based on least squares (LS), and recursive least squares (RLS). Channel estimation techniques, channel estimation techniques based on maximum likelihood sequence detection (MLSE), equalization techniques based on maximum a posteriori probability (MAP), etc. However, the channel estimation and equalization techniques used in wireless communications are highly complex and computationally intensive.

In addition, in the existing signal equalization techniques, it is generally assumed that the channel response obtained by channel estimation is constant in one frame, but in fact the channel response is time-varying, and therefore, the existing signal equalization technique cannot Track changes in the channel. Summary of the invention

The present invention has been made in view of the above technical problems, and an object thereof is to provide a channel estimation and equalization method and apparatus for ultrasonic communication, which can reduce multipath effect and inter-code crosstalk of an ultrasonic signal during transmission, and is remarkable Reduce the amount of calculations and track changes in the channel.

According to an aspect of the present invention, a channel estimation and equalization method for ultrasonic communication is provided, comprising: estimating a channel response in response to receiving an ultrasonic signal; and using the linear equalizer to the ultrasonic signal based on the estimated channel response Performing equalization; and according to the channel The coefficient of the linear equalizer is adjusted by the change in response.

According to another aspect of the present invention, a channel estimation and equalization apparatus for ultrasonic communication is provided, comprising: a channel estimator configured to estimate a channel response in response to receiving an ultrasonic signal; a linear equalizer configured And equalizing the ultrasonic signal based on the estimated channel response; and an adjuster configured to adjust a coefficient of the linear equalizer according to the change in the channel response. DRAWINGS

1 is a schematic flow chart of a channel estimation and equalization method for ultrasonic communication according to an embodiment of the present invention;

Figure 2 is a schematic flow chart showing an example of adjusting coefficients of a linear equalizer in the method of the embodiment shown in Figure 1;

Figure 3 is a schematic flow chart showing another example of adjusting the coefficients of the linear equalizer in the method of the embodiment shown in Figure 1;

4 is a schematic block diagram of a channel estimation and equalization apparatus for ultrasonic communication, in accordance with one embodiment of the present invention. detailed description

The above and other objects, features and advantages of the present invention will become more apparent from

1 shows a schematic flow chart of a channel estimation and equalization method for ultrasonic communication in accordance with one embodiment of the present invention. The present embodiment will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, in step S110, the channel response of the ultrasonic channel is estimated in response to receiving the ultrasonic signal. In the present embodiment, the ultrasonic signal may use a frequency in the range of 20 kHz to 22 kHz, and may take the form of a frame. Each frame of the ultrasonic signal may include a header and a data portion. The header uses a pseudo-random code (PN) sequence, for example, a PN code sequence of code length 31 is used. Next, the ultrasonic signal is frequency modulated for transmission. For example, the frequencies used for frequency modulation can be 20.5 kHz and 21.5 kHz, respectively. After receiving the ultrasonic signal, it can be adapted The processing, including channel compensation, extracting frequency domain signals, signal filtering and normalization, synchronization processing, etc., obtains a synchronized frequency domain signal of the ultrasonic signal. Channel estimation is performed on the ultrasonic channel based on the obtained synchronized frequency domain signal.

First, the initial channel response of the ultrasonic channel can be calculated using the synchronous frequency domain signal of the ultrasonic signal (hereinafter referred to as "ultrasonic signal" for convenience of explanation). In one example, the initial channel response can be calculated using an existing channel estimation method. For example, the initial channel response of the ultrasound channel can be expressed as h={/3⁄4, h _h hc-i ^ The length of the initial channel response h is C, and the coefficients are calculated as K = E{y _n r _n _ _k }l E{r _n r _n ) , where k=0, 1, . . . , C-1, r _n represents a sequence of PN codes with a value of {-1, 1 }, and y _n represents the received ultrasound at time n The difference in amplitude obtained after the signal is subjected to Fast Fourier Transform (FFT) at two transmission frequencies, and EW represents the mean. Next, a minimum mean square (LMS) based adaptive estimation is performed on the calculated initial channel response to obtain a channel response of the ultrasonic channel. Specifically, in the LMS-based adaptive estimation, the initial channel response h is estimated in the time domain using the PN code sequence in the header of each frame of the ultrasonic signal, and the channel at the beginning of the data portion of the frame is obtained. response. In the above LMS-based adaptive estimation, the step size can be set to 0.005.

After the channel response of the ultrasonic channel is obtained, the ultrasonic signal is equalized using a linear equalizer based on the estimated channel response in step S120. In this embodiment, the linear equalizer can adaptively equalize the signal based on the minimum mean square error (MMSE). In one example, assuming that the length of the linear equalizer is / = / _{1 +} / _{2 +} 1, where A, / ₂ represent the forward filter length and the backward filter length, respectively, then the output of the linear equalizer is „= ( y _n - + ), where c „ denotes the coefficient vector of the linear equalizer at time n, represents the channel response matrix, consists of the channel response / z, represents the a priori information vector, and s denotes the constant coefficient vector.

Since the coefficient vector of the linear equalizer needs to be calculated at each sampling instant, and the channel response of the ultrasonic channel changes with time, in order to reduce the amount of calculation, the coefficient vector of the linear equalizer can be adjusted according to the change of the channel response. The adjustment method of the coefficient of the linear equalizer will be specifically described below with reference to Figs. 2 and 3.

Fig. 2 shows a schematic flow chart showing an example of the adjustment of the coefficients of the linear equalizer. As shown in FIG. 2, in step S210, the line is calculated according to the channel response at the current sampling time. The coefficient of the sex equalizer at the current sampling instant. In one example, the current sampling instant is set to the start time n ₁ of the data portion of the frame of the ultrasonic signal _(> such that, by the above-described step S110, the channel response of the current sampling instant is obtained / ^. Then, using the above signal The adaptive equalization method can obtain the coefficient vector c of the linear equalizer at the current sampling moment. Next, in step S220, the channel response of the current sampling moment and the amount of change of the channel response at the subsequent sampling moment are calculated. The amount of change can reflect the change of the channel. In the above example, the subsequent sampling instant is the next moment ( m+i ) of the current sampling instant. Similarly, the channel at time (I +1 ) can be obtained by the above step siio Response / In one example, the absolute value of the change in channel response. Of course, it will be readily apparent to one of ordinary skill in the art that other variations can be made in the amount of change in channel response. Then, in step S230, the comparison is in step S220 calculates the amount of change and the predetermined channel change threshold. If the comparison result indicates that the amount of change is large The channel change threshold is then, in step S240, the coefficient of the linear equalizer at the subsequent sampling instant is calculated using the adaptive equalization method of the signal described above, and the channel response of the subsequent sampling instant is set to the channel response of the current sampling instant. In the above example, at this point, the current sampling time becomes

(m+i), and the channel response of the current sampling instant becomes /, and the coefficient vector of the linear equalizer becomes _c „ ₊₁ . If the comparison result of step S230 indicates that the amount of change is smaller than the channel change threshold, then in step S250, The coefficient of the linear equalizer at the current sampling instant. In the above example, the coefficient vector of the linear equalizer remains unchanged. Then, for the next sampling instant (+2) of the current sampling instant (+1), repeat the above change. The quantity calculation step S220 and the comparison step S230 are performed until one frame of the ultrasonic signal ends.

Fig. 3 shows a schematic 3⁄4⁄2 diagram illustrating another example of the adjustment of the coefficients of the linear equalizer. In the present example, steps S310 to S340 are the same as steps S210 to S240 in Fig. 2, except for the processing when the amount of change is smaller than the channel change threshold.

In the present example, if the amount of change is less than the channel change threshold, then the coefficient of the linear equalizer at the current sampling instant is updated using a minimum mean square (LMS) based adaptive estimate in step S350 to track subtle changes in the channel. In this LMS adaptive estimation, the step size is set to 0.005. Next, in step S360, determining, according to the updated coefficient of the linear equalizer, The first threshold of the number ^. Due to the inherent specificity of the linear equalizer, when there are more coefficients close to zero in its coefficient vector, it will bring more noise to the output. Therefore, some coefficients need to be forced to zero. The first threshold may be determined based on the relative magnitude of the coefficients of the linear equalizer. In one embodiment, the first threshold may be determined to be 0.1 of the absolute value of the maximum of the updated coefficients of the linear equalizer. It will be readily apparent to one of ordinary skill in the art that the first threshold can also be defined in other ways. Then, in step S370, the updated respective coefficients of the linear equalizer are compared with the first threshold. In one example, the absolute value of each coefficient can be compared to a first threshold. Then, in step S380, the updated coefficient of, for example, the linear equalizer whose absolute value is smaller than the first threshold is set to zero. In addition, the step size of the LMS estimation used in updating the coefficients of the linear equalizer may be adjusted according to the ratio of the number of zeroing coefficients to the number of all coefficients. When the zeroing coefficient is larger, the step size is adjusted larger.

As can be seen from the above description, the method of the present embodiment can adaptively perform channel estimation and equalization, reduce multipath effects and inter-code crosstalk caused by transmission of ultrasonic signals in space, and can adjust linear equalizer according to channel changes. The coefficients are such that the channel changes are quickly tracked so that channel estimation and equalization can accommodate channel variations. Further, the method of this embodiment has the advantage of a small amount of calculation.

Under the same inventive concept, Fig. 4 shows a schematic block diagram of a channel estimation and equalization apparatus 400 for ultrasonic communication in accordance with one embodiment of the present invention. The present embodiment will be described in detail below with reference to the accompanying drawings, wherein the description of the same portions as those of the previous embodiment will be appropriately omitted.

As shown in FIG. 4, the channel estimation and equalization apparatus 400 of the present embodiment includes: a channel estimator 401 configured to estimate a channel response of an ultrasonic channel in response to receiving an ultrasonic signal; a linear equalizer 402 configured to be based on The estimated channel response, equalizing the ultrasonic signal; and an adjuster 403 configured to adjust the coefficients of the linear equalizer 402 based on changes in the channel response.

The received ultrasonic signal is subjected to appropriate processing to obtain a synchronized frequency domain signal of the ultrasonic signal, and is supplied to the apparatus 400 of the present embodiment. In the device 400, the channel estimator 401 pairs the ultrasonic wave according to the synchronous frequency domain signal of the ultrasonic signal (hereinafter referred to as "ultrasonic signal":) The channel performs channel estimation to obtain the channel response of the ultrasonic channel. In one example, channel response calculation module 4011 in channel estimator 401 calculates the initial channel response of the ultrasound channel using the ultrasound signal. As previously discussed, channel response calculation module 4011 can estimate the channel response using existing channel estimation methods. Next, the adaptive estimation module 4012 performs a least mean square based adaptive estimation on the obtained initial channel response to obtain a channel response of the ultrasonic channel.

The channel response is then provided to a linear equalizer 402 to equalize the ultrasonic signals. The coefficients of linear equalizer 402 can be adjusted by regulator 403 based on changes in channel response. In one example, linear equalizer 402 can equalize the ultrasonic signals using existing adaptive equalization methods.

In the adjuster 403, the coefficient calculation module 4031 calculates the coefficient of the linear equalizer 402 at the current sampling instant based on the channel response of the current sampling instant obtained by the channel estimator 401. The delta calculation module 4032 can then calculate the amount of change in the channel response at the current sampling instant and the channel response at the subsequent sampling instant. The channel response at the subsequent sampling instant is obtained by the channel estimator 401. In one example, the amount of change in the channel response is defined as the absolute value of the difference between the channel response at the current sampling instant and the channel response at the subsequent sampling instant. The first comparison module 4033 then compares the calculated amount of change to a predetermined channel change threshold. If the amount of change is greater than the channel change threshold, the coefficient calculation module 4031 calculates the coefficient of the sampling instant at which the linear equalizer 402 is based on the obtained channel response of the subsequent sampling instant. In addition, the channel response of the sampling time of ^ is set to the channel response at the current sampling time. If the amount of change is less than the channel change threshold, coefficient calculation module 4031 maintains the coefficients of linear equalizer 402 at the current sampling instant. At each sampling instant, the operations of the delta calculation module 4032 and the first comparison module 4033 can be repeatedly executed until one frame of the ultrasonic signal ends.

In another example, the adjuster 403 can further include a coefficient update module 4034, a threshold determination module 4035, a second comparison module 4036, and a zeroing module 4037. The coefficient update module 4034 may update the coefficients of the linear equalizer 402 at the current sampling instant using the least mean square based adaptive estimation when the amount of change obtained by the delta calculation module 4033 is less than the channel change threshold. Threshold determination module 4035 then determines a first threshold for zeroing the coefficient based on the updated coefficients of linear equalizer 402. In one embodiment, the first threshold can be determined to be linear The absolute value of the maximum of the updated coefficients of the scale 402 is 0.1. Then, the second comparison module 4036 compares the updated respective coefficients of the linear equalizer 402 with the first threshold, and sets the updated coefficients of the linear equalizer 402 that are less than the first threshold to zero by the zeroing module 4037. In one embodiment, the second comparison module 4036 compares the absolute values of the coefficients of the linear equalizer 402 with a first threshold and sets the coefficients of the linear equalizer 402 whose absolute value is less than the first threshold by the zeroing module 4037. Zero.

It should be noted that the channel estimation and equalization apparatus 400 for ultrasonic communication of the present embodiment is operationally capable of realizing the channel estimation and equalization method for ultrasonic communication of the embodiment shown in Figs.

Furthermore, the channel estimation and equalization apparatus 400 for ultrasonic communication of the above embodiment may be included in the mobile terminal to perform channel estimation and equalization on the ultrasonic signals mixed in the audio signal.

The methods of the above disclosed embodiments can be implemented in software, hardware, or a combination of software and hardware. The hardware part can be implemented using dedicated logic. For example, the apparatus for providing enhanced audio data streams and its various components in the above embodiments may be comprised of semiconductors such as very large scale integrated circuits or gate arrays, such as logic chips, transistors, etc., or such as field programmable gate arrays, programmable logic The hardware circuit implementation of the programmable hardware device such as a device can also be implemented by software executed by various types of processors, or by a combination of the above hardware circuits and software. The software portion can be stored in memory and executed by a suitable instruction execution system, such as a microprocessor, personal computer (PC) or mainframe.

Although the channel estimation and equalization method and apparatus for ultrasonic communication of the present invention have been described in detail above by way of exemplary embodiments, the above embodiments are not exhaustive, and those skilled in the art may have the spirit and scope of the present invention. Various changes and modifications are implemented within. Therefore, the invention is not limited to the embodiments, and the scope of the invention is limited only by the appended claims.

Claims

Rights request

A channel estimation and equalization method for ultrasonic communication, comprising:

Estimating a channel response of the ultrasonic channel in response to receiving the ultrasonic signal;

The ultrasonic signal is equalized using a linear equalizer based on the estimated channel response; wherein the coefficients of the linear equalizer are adjusted according to changes in the channel response.

The method according to claim 1, wherein the adjusting of the coefficient of the linear equalizer according to the change of the channel response comprises:

Calculating a coefficient of the linear equalizer at the current sampling time according to a channel response at a current sampling moment;

Calculating a channel response of the current sampling instant and a variation of a channel response at a subsequent sampling instant;

Comparing the amount of change with a predetermined channel change threshold;

If the amount of change is greater than the channel change threshold, calculating a coefficient of the linear equalizer at the subsequent sampling moment, the channel response of the sampling moment of the ^ is the channel response of the current sampling moment;

Maintaining a coefficient of the linear equalizer at the current sampling instant if the amount of change is less than the channel change threshold;

The above-described variation calculation step and comparison step are repeated.

The method according to claim 2, wherein the adjusting the coefficients of the linear equalizer according to the change of the channel response further comprises:

If the amount of change is less than the channel change threshold, updating the coefficient of the linear equalizer at the current sampling instant using a least mean square based adaptive estimate;

Determining a first threshold for the coefficient based on the updated coefficients of the linear equalizer; comparing the updated respective coefficients of the linear equalizer with the first threshold;

The updated coefficients of the linear equalizer that are less than the first threshold are set to zero.

The method according to claim 3, wherein the first threshold is determined to be 0.1 of an absolute value of a maximum value of updated coefficients of the linear equalizer;

Comparing the updated respective coefficients of the linear equalizer with the first threshold includes: The absolute values of the respective coefficients are related to the first threshold.

The method according to claim 1, wherein estimating a channel response of the ultrasonic channel in response to receiving the ultrasonic signal comprises:

Calculating an initial channel response of the ultrasonic channel using the ultrasonic signal; and performing a least mean square based adaptive estimation on the initial channel response to obtain the channel response.

6. A channel estimation and equalization apparatus for ultrasonic communication, comprising:

a channel estimator configured to estimate a channel response of the ultrasonic channel in response to receiving the ultrasonic signal;

a linear equalizer configured to equalize the ultrasonic signal based on the estimated channel response;

An adjuster configured to adjust a coefficient of the linear equalizer based on a change in the channel response.

The device according to claim 6, wherein the adjuster comprises:

a coefficient calculation module configured to calculate a coefficient of the linear equalizer at the current sampling instant according to a channel response at a current sampling instant;

a change amount calculation module configured to calculate a channel response of the current sampling instant and a change amount of a channel response at a subsequent sampling instant;

a first comparison module configured to compare the amount of change with a predetermined channel change threshold; wherein the coefficient calculation module is further configured to calculate the linear equalization if the amount of change is greater than the channel change threshold a coefficient of the subsequent sampling instant, a channel response of the subsequent sampling instant becomes a channel response of the current sampling instant, and maintaining the linear equalizer if the amount of change is less than the channel change threshold a coefficient at the current sampling instant;

The operations of the change amount calculation module and the first comparison module are repeatedly performed.

The device according to claim 6, wherein the tamper further comprises:

a coefficient update module configured to update the linear equalizer at the current sample using a minimum mean square based adaptive estimate if the amount of change is less than the channel change threshold Coefficient of time

a threshold determination module configured to determine a first threshold for the coefficient based on the updated coefficients of the linear equalizer;

a second comparison module configured to compare the updated respective coefficients of the linear equalizer with the first threshold;

A zeroing module is configured to set an updated coefficient of the linear equalizer that is less than the first threshold to zero.

9. The apparatus of claim 8, wherein the threshold determination module is further configured to determine 0.1 of an absolute value of a maximum of the updated coefficients of the linear equalizer as the first threshold;

The second comparison module is further configured to compare an absolute value of the respective coefficients with the first threshold.

10. The apparatus of claim 6, wherein the channel estimator comprises: a channel response calculation module configured to calculate an initial channel response of the ultrasound channel using the ultrasonic signal;

An adaptive estimation module configured to perform a minimum mean square based adaptive estimation of the initial channel response to obtain the channel response.