CN115603888A - A method for estimating intra-symbol time delay of wireless communication system signals and recovering signals - Google Patents

Abstract

The invention provides an estimation method for time delay in a signal symbol of a wireless communication system, which comprises the following steps: step 1: preprocessing baseband information to obtain a modulated signal after quadrature amplitude modulation; step 2: and performing time delay estimation based on the IQ sequence of the modulated signal, wherein the time delay is the ratio of the offset epsilon to T in the concerned time T. Based on the embodiment of the invention, the time delay in the symbol can be accurately estimated.

Description

A Method for Estimation and Signal Recovery of Signal Intra-symbol Delay in Wireless Communication System

technical field

The invention relates to the technical field of wireless communication, in particular to a method for estimating and signal recovery of time delay within a symbol.

Background technique

In a wireless communication system, there is a complete communication process between the sending end and the receiving end of the communication. First of all, the sending end performs baseband modulation on the original information to be transmitted to achieve the purpose of transmitting as much information as possible with the smallest possible bandwidth, and sends it out by pulse shaping; in the channel, due to noise and other reasons, the signal delay and frequency deviation will be caused and phase shift, etc.; the receiving end eliminates intersymbol interference through matched filtering, and then performs channel estimation (such as delay estimation, frequency estimation, and phase estimation, etc.), compensation (such as timing correction, frequency correction, and phase correction, etc.), and after solution Restore the baseband information after tuning. During the communication process, due to the local clock offset and the relative movement between the sending end and the receiving end, the problem of symbol delay is caused, which is also called timing offset.

In some communication systems, in order to improve the signal-to-noise ratio of the sampled signal, the signal is up-sampled, that is, interpolated, and then digitally extracted to make the final sampling rate equal to the symbol rate. After upsampling, there are several interpolated symbols between the original adjacent symbols, and when the delay is greater than the number of interpolated symbols between the original two adjacent symbols, an out-of-symbol delay will be generated, and vice versa It is called intra-symbol delay.

The existing intra-symbol delay estimation method has a large error in the estimated value obtained in the burst scene of low signal-to-noise ratio and high-frequency offset phase shift, which will cause the signal to be unable to be demodulated correctly, and may even cause communication interruption, especially When transmitting burst signals, the traditional method has great limitations and cannot meet the communication requirements. This is due to the short duration of the burst signal, strong burstiness, and low signal-to-noise ratio. For example, in a data-assisted system, the most representative conventional method is the Schmidl scheme, which uses two repeated training sequences to complete the estimation and compensation of timing offset, but due to the influence of the system itself (for example, OFDM cyclic prefix impact, etc.), the timing estimation error of this scheme is relatively large. In addition, the signal recovery rules adopted by conventional algorithms are often mechanically compensated according to the estimated time delay, which is difficult to deal with the inaccurate time delay estimation caused by various factors such as noise.

Therefore, it is necessary to improve the existing technology to accurately estimate the time delay within the symbol, thereby improving link performance and demodulating signals quickly and accurately.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects in the prior art, and provide an estimation method for effectively estimating intra-symbol time delay and a corresponding signal restoration method.

According to the first aspect of the present invention, there is provided a method for estimating the intra-symbol delay of a wireless communication system signal, comprising the following steps: Step 1: Preprocessing the baseband information to obtain the modulated signal after quadrature amplitude modulation signal; Step 2: Estimate the time delay based on the IQ sequence of the modulated signal, and the time delay is the ratio of the offset in the time period concerned to the time period.

In one embodiment, the delay is a normalized offset of delay information.

In one embodiment, the step 2 further includes: multiplying the I-way sequence and the Q-way sequence by the sine sequence and the cosine sequence respectively, performing low-pass filtering and square operation; The sequence and the obtained imaginary part sequence are respectively added and averaged; and the arctangent operation is performed on the obtained average value.

In one embodiment, the delay is

t是当前时刻，T为关注的总时间，T_s为符号周期。in,

t is the current moment, T is the total time of attention, and T _s is the symbol period.

In one embodiment, the delay is

t是当前时刻，T为关注的总时间，T_s为符号周期，L表示用来计算时延的符号的个数,N为上采样的个数。in,

t is the current moment, T is the total time of attention, T _s is the symbol period, L represents the number of symbols used to calculate the delay, and N is the number of upsampling.

According to the second aspect of the present invention, there is provided a signal recovery method based on the time delay estimation of the aforementioned method, the method includes: based on the received signal in complex form and the time delay estimation, the real part and the imaginary part respectively department to compensate.

In one embodiment, the method comprises: recovering said signal based on said fractional portion of said delay estimate.

In one embodiment, the method further comprises recovering the signal based on the magnitude of surrounding signals.

According to a third aspect of the present invention, there is provided a computer-readable storage medium, in which one or more computer programs are stored, and the computer programs are used to implement the aforementioned time delay estimation method and/or signal recovery when executed method.

According to a fourth aspect of the present invention, there is provided a computing system, comprising a storage device and a processor, the storage device is used to store one or more computer programs, the computer programs are executed by the processor using In order to implement the aforementioned time delay estimation method and/or signal recovery method.

Compared with the prior art, the present invention has the advantages of: providing a new technical idea and technical solution to estimate the time delay within the symbol and perform signal recovery; it can accurately estimate the time delay within the symbol; The comparison has a good effect on signal recovery; it can obtain accurate time delay estimation and restore the original signal in burst scenarios with low signal-to-noise ratio and high-frequency phase shift.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description serve to explain the principles of the invention. Apparently, the drawings in the following description are only some embodiments of the present invention, and those skilled in the art can obtain other drawings according to these drawings without creative efforts. In the attached picture:

FIG. 1 shows a block diagram of an algorithm for timing error estimation based on two signal sequences of I and Q.

detailed description

During the entire communication process, due to practical problems such as clock inconsistency between the sending end and the receiving end, and frequency offset caused by relative motion between the sending end and the receiving end, symbol delays are generated. In order to obtain a higher signal-to-noise ratio, internal The method of inserting and extracting again results in an intra-symbol delay. If there is no better estimation method for the time delay within a symbol, the signal cannot be demodulated correctly, and even communication cannot be performed. After studying the estimation algorithm of the time delay within the symbol, the inventor found that the problem can be solved by processing and calculating the signal through the IQ sequence to accurately estimate the time delay of the symbol, and it has good practicability. This solution idea is completely different from the prior art that solves the problem based on the peak value of the correlation function, etc., and belongs to a new technical idea and technical solution.

For ease of understanding, the embodiments according to the present invention will be described below according to baseband information preprocessing, time delay estimation based on IQ sequence, and signal recovery.

1. Baseband information preprocessing

After the baseband information is transmitted through the antenna, it is affected by factors such as additive white Gaussian noise in the channel, the Doppler effect, and different sources of the local oscillator of the transceiver, and its effective information introduces noise, time delay, and frequency offset. Let the baseband binary information sequence be p(k), express the digital filter as h(k), then the modulated information sequence is s(k)·h(k). The expression after the modulated information sequence passes through the channel can be obtained:

Among them, A is the amplitude of the signal, s(k) is the kth symbol of the modulation sequence, that is, the data modulation information, ε is the offset of the timing point between the signal sending end and the receiving end, that is, due to time delay and receiving Δf is the frequency offset of the sequence, θ is the unknown initial phase, and T _s is the symbol period, which is the duration between the kth symbol and the k+1th symbol of the modulation sequence, n is additive Gaussian white noise with zero mean and variance ^σ2 .

The signal obtained at this time contains baseband information, time delay, frequency offset phase shift and noise. According to the embodiment of the present invention, the baseband information and frequency offset phase shift can be regarded as one. The signal at this time contains three parts, and the comprehensive information a (k), time delay and noise, expressed by the following formula:

r(k)=a(k) h(k-ε)+n(k) (2)

In order to facilitate the understanding of the time delay estimation in the present invention, the NT sequence in the mobile communication system is taken as an example for description. To estimate the time delay of the NT Burst signal is to estimate the number of time delay bits in one symbol for the time-delayed burst signal, so as to complete the signal recovery. After the terminal performs sampling and matched filtering on the signal, it performs time delay estimation within one symbol. Take quadruple upsampling as an example, that is, insert 4 points between two adjacent points of the original signal, so the number of bits of delay may be {0, 1, 2, 3}; if it is eight times upsampling, then Possible values are {0, 1, 2, 3, 4, 5, 6, 7}.

2. Delay estimation based on IQ sequence

Figure 1 shows a block diagram of a timing error estimation algorithm using both I and Q signal sequences at the receiving end. The I and Q signal sequences here are quadrature amplitude modulation in the wireless communication system, the I path represents the real part of a complex sequence signal, and the Q path represents the imaginary part of the complex sequence signal. As shown in Figure 1, the I-way sequence is multiplied by the sine sequence and the cosine sequence respectively, and the Q-way sequence is also multiplied by the sine sequence and the cosine sequence respectively, and then undergoes low-pass filtering, followed by a square operation. The samples of the I and Q two-way sequences The obtained real part sequence and the obtained imaginary part sequence are respectively added and averaged, and finally the arc tangent (arctan) operation is performed to calculate the symbol time delay.

The input signal is shown in formula (2), k=t/T, where t is the current moment, and T is the total time of attention. The signal is multiplied by the exponent e ^jπk first, and then passes through the low-pass filter l(k). The cut-off bandwidth of the low-pass filter is α/2T. At this time, the signal can be expressed as:

y(k)=u(k)+jv(k)=[r(k)e ^jπk ]*l(k) (3)

where u(k) and v(k) are the real and imaginary parts of y(k), respectively.

Substituting formula (2) into formula (3), we get

n ₁ (k) is a complex conjugate number of n(k). f(k) is the baseband frequency band conversion of the inverse Fourier transform of the low-pass filter, and the expression is as follows:

in:

n ₁ (k)=[n(k)e ^jπk ]*l(k) (8)

According to an embodiment of the present invention, the time delay φ is defined as the ratio of the offset ε to T within the time T of interest. Further, according to the embodiment of the present invention, the property of complex numbers can be used to calculate the time delay by calculating the expected angle, which is the normalized offset of the time delay information. Furthermore, the time delay can be expressed as:

in,

According to another embodiment of the present invention, the delay can also be calculated in the following way:

Among them, L represents the number of symbols used to calculate the time delay, and N is the number of upsampling.

Through time delay estimation, the integer part t _e and fractional part u ₀ of the time delay can be obtained. According to an embodiment of the present invention, the value of u ₀ needs to be further adjusted to obtain u. Further, considering that the value of u ₀ is usually Nπ+u, the value of u can be obtained by removing Nπ. For example, if the value of u ₀ is basically around -π/2, π/2 or 0, it is necessary to adjust u ₀ to the same value range, such as near 0, to obtain u.

3. Signal recovery

The inventors have found through research that the signal recovery rules in the prior art are often compensated mechanically according to the estimated time delay, and it is difficult to cope with the inaccurate time delay estimation caused by various factors such as noise. At the same time, the signal recovery rules in the prior art usually do not consider the fractional part of the time delay. In view of the above problems, the present invention provides a signal recovery method. This method is based on the complex signal received by the receiving end, and recovers the signal by compensating and recovering the real part and the imaginary part respectively, so that the original signal can be recovered more accurately; The fractional portion of the time delay and/or the magnitude of the surrounding signal further improves the accuracy of signal recovery.

Let the signal received by the receiver be:

r(n)=r _I (n)+j·r _Q (n),n=1,2,...,L (11)

The sequence after the time delay estimation is completed and the signal is recovered is expressed as:

R(N)＝R _I (N)+j·R _Q (N), N＝1,2,...,L/4 (12)

Here, only 4 times upsampling is used as an example to describe the rules of signal restoration according to the embodiment of the present invention:

In the formula, N=n/4, similarly, it can be obtained:

In the signal recovery, the real part and the imaginary part are respectively compensated and restored, and the fractional part of the time delay and/or the amplitude of the surrounding signal are comprehensively considered, so that a good effect on signal recovery under high signal-to-noise ratio can be achieved .

Further, according to another embodiment of the present invention, considering that when the signal-to-noise ratio is low, the down-sampling algorithm of continuous data points makes the noise superimposed accordingly, which increases the variance of the noise, and can be directly obtained from the continuous data Among the points, the one with the highest signal strength is extracted as the information for signal delay recovery. Taking 4 times upsampling as an example, the point with the highest signal strength is directly extracted from the four points, and the first point of every four points is extracted as the information for signal delay recovery, so as to ensure that the signal-to-noise ratio is low The accuracy of time signal recovery is reduced, and the complexity of calculation is reduced. The specific expression is shown in the following formula.

R'(N)=r(4N),N=1,2,...,L/4 (15)

It should be noted that, although 4 times upsampling is used as an example to describe and illustrate the embodiment according to the present invention, it does not mean that the implementation of the technical solution of the present invention will be limited by a specific upsampling multiple. In addition, although the various steps are described above in a specific order, it does not mean that the various steps must be performed in the above specific order. In fact, some of these steps can be performed concurrently, or even change the order, as long as the required function.

The present invention can be a system, method and/or computer program product. A computer program product may include a computer readable storage medium having computer readable program instructions thereon for causing a processor to implement various aspects of the present invention.

A computer readable storage medium may be a tangible device that holds and stores instructions for use by an instruction execution device. A computer readable storage medium may include, for example, but is not limited to, electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), or flash memory), static random access memory (SRAM), compact disc read only memory (CD-ROM), digital versatile disc (DVD), memory stick, floppy disk, mechanically encoded device, such as a printer with instructions stored thereon A hole card or a raised structure in a groove, and any suitable combination of the above.

To enable any person of ordinary skill in the art to implement or use the present disclosure, the above descriptions have been made around the present disclosure. Various modifications to the present disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other modifications without departing from the spirit or scope of the present disclosure. Furthermore, all or a portion of any aspect and/or embodiment may be utilized with all or a portion of any other aspect and/or embodiment, unless stated otherwise. Thus, the disclosure is not intended to be limited to the examples and designs described herein, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Claims (10)

1. A method for estimating time delay in a wireless communication system signal symbol, comprising the following steps: Step 1: Preprocessing the baseband information to obtain the modulated signal after quadrature amplitude modulation; Step 2: Estimate time delay based on the IQ sequence of the modulated signal, where the time delay is the ratio of the offset in the concerned time period to the time period. 2. The method according to claim 1, wherein the time delay is a normalized offset of time delay information. 3. The method according to claim 1, characterized in that, said step 2 further comprises: multiplying the I-way sequence and the Q-way sequence by a sine sequence and a cosine sequence respectively, and performing low-pass filtering and square operation; The real part sequence and the obtained imaginary part sequence of the I and Q two-way sequences are respectively added and averaged; and an arctangent operation is performed on the obtained average value. 4. The method according to claim 1, wherein the time delay is

in,

k=t/T, t is the current moment, T is the total time of attention, and T _s is the symbol period. 5. The method according to claim 1, wherein the time delay is

in,

k=t/T, t is the current moment, T is the total time concerned, T _s is the symbol period, L represents the number of symbols used to calculate the delay, and N is the number of upsampling. 6. A signal recovery method based on the time delay estimation according to one of claims 1 to 5, characterized in that, the method comprises: based on the received signal in complex form and the time delay estimation, the real part and The imaginary part is compensated. 7. The method according to claim 6, characterized in that the method comprises: recovering the signal based on the fractional part of the time delay estimate. 8. The method according to claim 7, further comprising: restoring the signal based on the magnitude of surrounding signals. 9. A computer-readable storage medium storing one or more computer programs therein, the computer programs being used to implement the method according to any one of claims 1 to 8 when executed. 10. A computing system comprising a storage device and a processor, the storage device being used to store one or more computer programs for implementing any of claims 1 to 8 when executed by the processor one of the methods described.

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