A signal processing method and device under multipath effect

Abstract

The present invention discloses a signal processing method and device under multipath effect, which relates to the field of signal processing technology, including: a wireless signal receiving end performs coherent demodulation on a received signal to obtain i baseband signals and q baseband signals; the data in the i baseband signals and the q baseband signals are simultaneously correlated with a local chirp sequence to obtain an i-path sequence and a q-path sequence; the i-path sequence and the q-path sequence are assembled into a first complex correlation peak sequence; wherein the first complex correlation peak sequence includes a certain frame structure length; the points in the certain frame structure length are grouped and accumulated to obtain a second complex correlation peak sequence; multiple module values ​​of the second complex correlation peak sequence are calculated; the size of each module value is compared to find the maximum correlation peak corresponding to the maximum module value; the sequence number corresponding to the maximum correlation peak is determined to obtain a high-precision timestamp of the signal. The method can also realize high-precision time extraction in a multipath environment, and the amount of calculation is relatively small, and it is easy to realize fast and accurate signal processing.

Description

Technical Field

[0001] The present invention relates to the technical field of signal processing, and in particular to a method and device for processing signals under multipath effects. Background Art

[0002] In the wireless communication channel, in addition to direct waves and ground reflected waves, there are also scattered waves caused by various obstacles during the propagation of radio waves, resulting in multipath effect. Multipath effect refers to the rapid attenuation of the amplitude of wireless signals after a short distance of propagation, so that the large-scale impact can be ignored. This attenuation is caused by the interference of the signals that arrive at the receiver along two or more paths with a small time difference. These waves are called multipath waves. The receiver antenna synthesizes them into a signal with sharply changing amplitude and phase. The degree of change depends on the strength of the multipath waves, the relative propagation time and the bandwidth of the propagation signal.

[0003] The multipath effect will cause the component fields to arrive at the wireless signal receiving end at different times, and the superposition of their respective phases will cause interference, causing the original signal to be distorted or errors to occur.

[0004] In the case of multipath, the traditional method of multiplying by the maximum coefficient of the equalizer cannot completely concentrate the energy of the iq part of the multipath signal in the i part, and it is impossible to perform time extraction by discarding the q part of the multipath signal. Therefore, the method of multiplying by the maximum coefficient of the equalizer is not applicable to the multipath situation. Summary of the invention

[0005] In order to solve the technical problem in the prior art that, in the case of multipath, it is impossible to perform time extraction on a signal by multiplying by the maximum coefficient of an equalizer, the present invention provides a signal processing method and device under the multipath effect.

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

[0007] The first aspect of the present application provides a signal processing method under multipath effect, comprising:

[0008] The wireless signal receiving end performs coherent demodulation on the received signal to obtain i baseband signals and q baseband signals;

[0009] Correlate the data in the i-part baseband signal and the q-part baseband signal with the local chirp sequence to obtain an i-way sequence and a q-way sequence;

[0010] Assembling the i-way sequence and the q-way sequence into a first complex correlation peak sequence; wherein the first complex correlation peak sequence includes a certain frame structure length;

[0011] The points in the certain frame structure length are grouped and accumulated to obtain a second complex correlation peak sequence;

[0012] calculating a plurality of modulus values ​​of the second complex correlation peak sequence;

[0013] Compare the sizes of each modulus value and find the maximum correlation peak corresponding to the maximum modulus value;

[0014] Determine the sequence number corresponding to the maximum correlation peak and obtain a high-precision timestamp of the signal.

[0015] Preferably, determining the sequence number corresponding to the maximum correlation peak and obtaining a high-precision timestamp of the signal includes:

[0016] Perform multi-rate interpolation on the maximum correlation peak to detect whether there is a peak on the left side of the maximum correlation peak. If there is no peak on the left side of the maximum correlation peak, determine the sequence number corresponding to the maximum correlation peak to obtain a high-precision timestamp of the signal.

[0017] Preferably, determining the sequence number corresponding to the maximum correlation peak and obtaining a high-precision timestamp of the signal includes:

[0018] Perform multi-rate interpolation on the maximum correlation peak to detect whether there is a peak on the left side of the maximum correlation peak. If there is a peak on the left side of the maximum correlation peak, determine whether the peak on the left side of the maximum correlation peak is greater than or equal to a preset threshold. If the peak on the left side of the maximum correlation peak is greater than or equal to the preset threshold, the time corresponding to the peak on the left side of the maximum correlation peak is the high-precision timestamp of the signal.

[0019] Preferably, the process in which the wireless signal receiving end performs coherent demodulation on the received signal to obtain i baseband signals and q baseband signals includes:

[0020] The i-part link of the wireless signal receiving end multiplies the received radio frequency signal with the in-phase component of the local carrier signal to obtain a first mixed signal, and the q-part link of the receiver multiplies the received radio frequency signal with the orthogonal component of the local carrier signal to obtain a second mixed signal;

[0021] The first mixed signal is input into i low-pass filters to obtain i baseband signals, and the second mixed signal is input into q low-pass filters to obtain q baseband signals.

[0022] A second aspect of the present application provides a signal processing device under multipath effects, including a transmitter and a receiver, and also includes the above-mentioned signal processing method under multipath effects.

[0023] The beneficial effects of the present invention are: i baseband signals and q baseband signals are correlated with a local chirp sequence to generate a first complex correlation peak sequence, a certain frame structure length in the first complex correlation peak sequence is grouped and accumulated to form multiple correlation peaks, and then the maximum correlation peak is determined by calculating the modulus value of each correlation peak to obtain a high-precision timestamp of the signal, thereby realizing high-precision time extraction even in a multipath environment, and the amount of calculation is relatively small, and it is easy to realize fast and accurate signal processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of a method according to Embodiment 1 of the present invention.

[0025] Figure 2 It is a schematic diagram of the signal frame structure in the first embodiment of the present invention. DETAILED DESCRIPTION

[0026] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0027] Embodiment 1: In a complex indoor environment, the signal transmitted by the transmitting end is blocked by obstacles, and after reflection and refraction, multiple paths are formed to reach the wireless signal receiving end. The signal actually received by the wireless signal receiving end is the superposition of multiple paths, which is the multipath effect.

[0028] In the specific implementation process, the transmitter sends a modulated electromagnetic wave signal, that is, a real signal, and the signal on the receiving antenna is also a real number, but the signal is usually processed by means of complex numbers. First, the transmitter signal is modeled, and the complex baseband signal emitted by the transmitter is assumed to be:

[0029] (1)

[0030] in, is the expression of the complex baseband signal of the transmitter, is the expression of the transmitter i-channel signal, is the expression of the q-channel signal of the transmitter, and j is the imaginary unit.

[0031] The complex baseband signal is usually modulated by i and q paths. Specifically, the i path and the q path are multiplied by and , and then add them together, the expression of the RF signal is:

[0032] (2)

[0033] in is the expression of the transmitter's RF signal, represents the transmitter's carrier angular frequency, is the initial phase of the transmitter carrier.

[0034] The RF signal will pass through the channel, and the channel has three effects on the RF signal. The first is the amplitude change effect. Assume that the amplitude of the signal will attenuate to the original times, is a real number greater than 0; the second is the phase shift effect. Assume that the phase of the signal is shifted ; The third is the delay effect. Assuming the delay time is In general, these three effects of the channel are equivalent to an impulse response of , the impulse response is (t) After convolution, the signal received by the receiver is obtained. In this way, the signal expression after the channel effect is:

[0035] (3)

[0036] in, is the signal expression of the transmitter's RF signal after being acted upon by the channel, is the attenuation factor of the RF signal amplitude, is the delay time.

[0037] It can be seen that the i and q parts of the received signal are still orthogonal, that is, the phase difference between the carrier signals of the i and q parts is 90 degrees. It can also be seen that the delay effect will also cause the phase of the carrier signal to change. In actual operation, the effects of the two can be combined together.

[0038] The receiver performs coherent demodulation on the received iq signals. Multiply , q part multiplied by , and then through low-pass filtering, the amplitude and phase information of the original signal can be effectively restored, and the baseband signal of part i is:

[0039]

[0040] The baseband signal of the q part is:

[0041]

[0042] If this is the season is the complex number received, and the expression of the complex signal received by the receiver is:

[0043]

[0044] The above formula proves that after the transmitted iq-channel complex baseband signal is coherently demodulated by the receiver, the complex sequence constructed by the iq-channel data is equal to the delayed complex baseband signal multiplied by the complex rotation factor composed of four angles.

[0045] From formula (5) and formula (6), it can be seen that the baseband signal received by the receiver's iq path only has a phase angle of 90 degrees different from the carrier signal. It can also be seen that the signal received by the receiver contains the channel attenuation effect and phase shift, that is, ,at the same time The effect of time delay is included.

[0046] When there are multiple paths, suppose there are k paths in total, and the transfer function of each path is:

[0047] (7)

[0048] When multipath is considered, the signal received by the receiver is expressed as:

[0049]

[0050] In the above formula, , which means that the phase angle change of the signal caused by phase shift and delay of the kth path is taken into consideration. The above formula shows that the phase angle generated by each path to the receiver is composed of three terms, among which and represent the phase angles of the transmitter and the receiver, which are the same in all paths, and Items, each path is not the same.

[0051] In order to simplify the analysis, we analyze it with two paths and assume that , , , so the real part of the received two-path signal is:

[0052] (9)

[0053] The imaginary part is:

[0054] (10)

[0055] Due to arctan It is changing all the time, which means that when there are two paths, the iq path signal received by the receiver is not the signal of the same expression multiplied by two constant constants. Similarly, when the number of paths is more, this property is even less valid.

[0056] Therefore, in the case of multipath, if the traditional method of multiplying by the maximum coefficient of the equalizer is used to extract a high-precision timestamp, the following will occur:

[0057] Assuming that the amplitude of the second path is 1 / 10 of the first path, according to formula (8), the expression of the signal received by the receiver is:

[0058] (11)

[0059] Since the power of the first path is much greater than the power of the second path, the tap coefficient of the equalizer is basically equal to , which can make the power of the first path concentrated in the i part, but cannot make the energy of the second path also concentrated in the i part. In this way, after discarding the q part, we get The real signal expression of is:

[0060] (12)

[0061] In the above formula, only when When it is an integer multiple of 360 degrees, can be equal to 1, the second path can store the complete energy in the i part, and the energy in the q part can be equal to 0; and as long as When it is not equal to an integer multiple of 360 degrees, are all less than 1, and the energy corresponding to the q part is not equal to 0. Therefore, the traditional method of extracting a high-precision timestamp by multiplying by the maximum coefficient of the equalizer is not applicable to the multipath situation.

[0062] In order to solve the technical problem that the traditional method of multiplying the maximum coefficient of the equalizer is not applicable to the multipath situation, this embodiment provides a signal processing method under the multipath effect, such as Figure 1 As shown, the following steps are included:

[0063] Step 1: The wireless signal receiving end performs coherent demodulation on the received signal to obtain i baseband signals and q baseband signals.

[0064] It should be noted that in modern communication systems, the traditional filtering method is to convert the time domain signal into the frequency domain signal through Fourier transform. However, in this embodiment, the transmitter and the receiver are both handheld terminals. In the specific application process, considering the high computational complexity of Fourier transform, the fast Fourier transform (FFT) is used. For devices with limited resources such as handheld terminals, this high computational complexity will significantly increase the burden on the processor, resulting in a decrease in processing speed and affecting real-time performance.

[0065] In order to solve the above problem, in a specific implementation process, the i-part link of the wireless signal receiving end multiplies the received RF signal with the in-phase component of the local carrier signal to obtain a first mixed signal, and the q-part link of the receiver multiplies the received RF signal with the orthogonal component of the local carrier signal to obtain a second mixed signal; for example, as shown in formula (4), the first mixed signal is input into the i-part low-pass filter to obtain the i-part baseband signal; for example, as shown in formula (5), the second mixed signal is input into the q-part low-pass filter to obtain the q-part baseband signal.

[0066] By using the mixing and low-pass filtering methods at the wireless signal receiving end, this solution not only effectively solves the high computational complexity problem brought by Fourier transform, but also significantly improves the processing speed and real-time performance of the system, simplifies the hardware design, and reduces the workload of the processor and power consumption due to the reduction in calculation amount, making it suitable for devices with limited resources such as handheld terminals.

[0067] Step 2: Correlate the data in the i-part baseband signal and the q-part baseband signal with the local chirp sequence to obtain an i-way sequence and a q-way sequence.

[0068] It should be noted that the Chirp signal is a signal whose frequency changes linearly with time, and has good autocorrelation and cross-correlation. When the Chirp signal is processed by a matched filter, the originally scattered energy can be concentrated through pulse compression technology to form a peak. Specifically, when the Chirp signal encounters a multipath effect, the signal on each path will produce a peak, but since the direct path signal strength is the largest, its peak will also be the highest. By detecting this highest peak, the actual high-precision timestamp of the signal from the transmitter to the wireless signal receiver can be determined. This is because the highest peak represents the time delay of the shortest path from the transmission to the reception of the signal, which is the best estimate of the actual high-precision timestamp of the signal.

[0069] Therefore, in a multipath environment, the delay estimate corresponding to the strongest path of the Chirp signal processed by the matched filter can be used as an accurate estimate of the actual high-precision timestamp of the signal.

[0070] Step 3: assemble the i-way sequence and the q-way sequence into a first complex correlation peak sequence; wherein the first complex correlation peak sequence includes a certain frame structure length.

[0071] Among them, referring to formula (4), formula (5) and formula (6), the data of the i-th baseband signal can be assumed to be , the data in the q-part baseband signal is , the two correlated sequences are assembled into a complex first correlation peak sequence, .

[0072] Step 4: Group and accumulate the points in the certain frame structure length to obtain a second complex correlation peak sequence.

[0073] like Figure 2 As shown, in the structure of the information frame, one chirp has 80 bits. In this embodiment, 10 chirps are selected, and a certain frame structure length contains 10 chirps with a total of 800 points. Each 80 points are divided into a group, and then 10 groups are added together to obtain a complex correlation peak sequence of 80 points. .

[0074] Step 5, calculating multiple modulus values ​​of the second complex correlation peak sequence.

[0075] Step 6, compare the sizes of each modulus value and find the maximum correlation peak corresponding to the maximum modulus value.

[0076] For example, it is calculated that the maximum modulus of the 80 complex correlation peaks appears near N=40, that is, the modulus of the 40th correlation peak is the largest, that is, there is the following relationship:

[0077] Established.

[0078] It should be noted that the modulus of the complex correlation peak sequence represents the amplitude of the complex signal. Among the 80 complex correlation peaks, the maximum modulus refers to the maximum value among all moduli. The N corresponding to this maximum value is the position where the maximum modulus appears. The maximum modulus is the maximum peak value among the 80 complex correlation peaks.

[0079] Step 7: Determine the sequence number corresponding to the maximum correlation peak and obtain a high-precision timestamp of the signal.

[0080] Among them, the modulus of the 40th correlation peak is the largest, and the corresponding time is the high-precision timestamp of the signal. The high-precision timestamp refers to the nanosecond level time.

[0081] Considering that there may be an earlier path before the maximum correlation peak, in a possible implementation manner, determining the sequence number corresponding to the maximum correlation peak and obtaining a high-precision timestamp of the signal includes:

[0082] Perform multi-rate interpolation on the maximum correlation peak to detect whether there is a peak on the left side of the maximum correlation peak. If there is no peak on the left side of the maximum correlation peak, determine the sequence number corresponding to the maximum correlation peak and obtain a high-precision timestamp of the signal. If there is a peak on the left side of the maximum correlation peak, determine whether the peak on the left side of the maximum correlation peak is greater than or equal to the preset threshold. If the peak on the left side of the maximum correlation peak is greater than or equal to the preset threshold, the time corresponding to the peak on the left side of the maximum correlation peak is the high-precision timestamp of the signal. Only when the peak is greater than or equal to the preset threshold can it be considered a reliable signal. This helps to improve the reliability and accuracy of time measurement.

[0083] For example, considering that there may be an earlier path before the maximum correlation peak, the maximum correlation peak is interpolated 90 times, and 45 points are inserted on the left and right of the maximum correlation peak to consider whether there are multiple peaks in these 45 points. If there are two peaks, and the peak that appears in front is greater than or equal to the preset threshold, the moment of the path that arrives first can be considered as the moment corresponding to the high-precision timestamp. If there are no two peaks, the time corresponding to the maximum correlation peak is determined as the high-precision timestamp of the signal. Through multiple interpolation and peak detection, nanosecond-level time measurement can be achieved, greatly improving the accuracy of time measurement.

[0084] Embodiment 2 provides a signal processing device under multipath effect, including a transmitter and a receiver, and also includes a signal processing method under multipath effect described in Embodiment 1.

[0085] It should be noted that during the signal transmission stage of the transmitter, the Chirp Spread Spectrum (CSS) technology is used to expand the signal bandwidth to 80MHz. This can improve the signal's time resolution, enhance anti-interference capabilities, and improve detection performance.

[0086] In the signal receiving stage of the receiver: the received signal is coherently demodulated: the signal received by the receiver is coherently demodulated to separate the i-part baseband signal and the q-part baseband signal. The i-part baseband signal is correlated with the local Chirp sequence to obtain the i-way sequence. The q-part baseband signal is correlated with the local Chirp sequence to obtain the q-way sequence. The i-way sequence and the q-way sequence are assembled into a first complex correlation peak sequence, which contains a certain frame structure length. The points in a certain frame structure length are grouped and accumulated to obtain a second complex correlation peak sequence. Multiple modulus values ​​of the second complex correlation peak sequence are calculated. Compare the size of the modulus value and find the maximum correlation peak corresponding to the maximum modulus value: Determine the sequence number corresponding to the maximum correlation peak, that is, obtain a high-precision timestamp of the signal.

[0087] In summary, by using the mixing and low-pass filtering methods at the receiver and transmitter, combined with the autocorrelation and cross-correlation of the Chirp signal, this scheme not only effectively solves the high computational complexity problem brought by Fourier transform, but also significantly improves the processing speed and real-time performance of the system, simplifies the hardware design, and reduces power consumption, which is particularly suitable for devices with limited resources such as handheld terminals. In addition, this method performs well in dealing with multipath effects, can achieve high-precision time measurement, and has broad application prospects. In particular, through multiple interpolation and peak detection, nanosecond time measurement is achieved, which greatly improves the accuracy and reliability of time measurement.

[0088] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A signal processing method under multipath effect, characterized in that: Includes the following: The wireless signal receiving end performs coherent demodulation on the received signal to obtain i baseband signals and q baseband signals; The process of the wireless signal receiving end coherently demodulating the received signal to obtain i baseband signals and q baseband signals includes: The i-part link of the wireless signal receiving end multiplies the received radio frequency signal with the in-phase component of the local carrier signal to obtain a first mixed signal, and the q-part link of the receiver multiplies the received radio frequency signal with the orthogonal component of the local carrier signal to obtain a second mixed signal; Input the first mixed signal into the i-part low-pass filter to obtain the i-part baseband signal, and input the second mixed signal into the q-part low-pass filter to obtain the q-part baseband signal; The baseband signal of part i is: ； The baseband signal of the q part is: ； Correlate the data in the i-part baseband signal and the q-part baseband signal with the local chirp sequence to obtain an i-way sequence and a q-way sequence; Assembling the i-way sequence and the q-way sequence into a first complex correlation peak sequence; wherein the first complex correlation peak sequence includes a certain frame structure length; The points in the certain frame structure length are grouped and accumulated to obtain a second complex correlation peak sequence; calculating a plurality of modulus values ​​of the second complex correlation peak sequence; Compare the sizes of each modulus value and find the maximum correlation peak corresponding to the maximum modulus value; Determine the sequence number corresponding to the maximum correlation peak and obtain a high-precision timestamp of the signal.

2. A method for processing signals under multipath effects according to claim 1, characterized in that: Determine the sequence number corresponding to the maximum correlation peak and obtain the high-precision timestamp of the signal including: Perform multi-rate interpolation on the maximum correlation peak to detect whether there is a peak on the left side of the maximum correlation peak. If there is no peak on the left side of the maximum correlation peak, determine the sequence number corresponding to the maximum correlation peak to obtain a high-precision timestamp of the signal.

3. A method for processing signals under multipath effects according to claim 2, characterized in that: Determine the sequence number corresponding to the maximum correlation peak and obtain the high-precision timestamp of the signal including: Perform multi-rate interpolation on the maximum correlation peak to detect whether there is a peak on the left side of the maximum correlation peak. If there is a peak on the left side of the maximum correlation peak, determine whether the peak on the left side of the maximum correlation peak is greater than or equal to a preset threshold. If the peak on the left side of the maximum correlation peak is greater than or equal to the preset threshold, the time corresponding to the peak on the left side of the maximum correlation peak is the high-precision timestamp of the signal.

4. A signal processing device under multipath effect, comprising a transmitter and a receiver, characterized in that: A signal processing method under multipath effect as described in any one of claims 1 to 3 is adopted.

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