CN115603888B

CN115603888B - A method for estimating intra-symbol delay of wireless communication system and recovering signal

Info

Publication number: CN115603888B
Application number: CN202211200705.9A
Authority: CN
Inventors: 刘垚圻; 周德恒; 石晶林; 李磊; 董孟雪; 董淮成; 李民; 石瑾凌; 付垠凯
Original assignee: Institute of Computing Technology of CAS
Current assignee: Institute of Computing Technology of CAS
Priority date: 2021-09-29
Filing date: 2022-09-29
Publication date: 2025-03-21
Anticipated expiration: 2042-09-29
Also published as: CN115603888A

Abstract

The present invention provides a method for estimating intra-symbol delay of a signal in a wireless communication system, the method comprising: step 1: preprocessing baseband information to obtain a modulated signal after orthogonal amplitude modulation; step 2: performing delay estimation based on an IQ sequence of the modulated signal, wherein the delay is a ratio of an offset ε within a time T of interest to T. Based on the embodiments of the present invention, the intra-symbol delay can be accurately estimated.

Description

Method for estimating time delay in signal symbol of wireless communication system and recovering signal

Technical Field

The present invention relates to the field of wireless communications technologies, and in particular, to a method for estimating time delay in a symbol and recovering a signal.

Background

In a wireless communication system, a complete communication process is performed between a transmitting end and a receiving end of communication. The method comprises the steps of firstly, a transmitting end carries out baseband modulation on original information to be transmitted so as to achieve the aim of transmitting as much information as possible by using a bandwidth as small as possible, pulse shaping is transmitted, delay, frequency offset, phase shift and the like of signals are caused in a channel due to noise and the like, a receiving end eliminates intersymbol interference through matched filtering, then carries out channel estimation (such as delay estimation, frequency estimation, phase estimation and the like) and compensation (such as timing correction, frequency correction, phase correction and the like), and recovers baseband information after demodulation. During communication, symbol delay problems, also known as timing offsets, are caused by local clock offsets, relative motion between the transmitting and receiving ends.

In some communication systems, in order to increase the signal-to-noise ratio of the sampled signal, the signal is up-sampled, i.e. interpolated, and then decimated by digital means to equalize the final sampling rate to the symbol rate. After up-sampling, there are several more interpolated symbols between the original adjacent symbols, and when the time delay is greater than the number of interpolated symbols between the original adjacent two symbols, an off-symbol time delay will be generated, otherwise called an intra-symbol time delay.

In the existing intra-symbol delay estimation method, under the burst scene of low signal-to-noise ratio and high frequency offset phase shift, the obtained estimation value has larger error, which can cause that the signal cannot be correctly demodulated and even can cause communication interruption, especially when burst signals are transmitted, the traditional method has larger limitation and cannot meet the communication requirement, because the burst signals have short time, strong burst performance and low signal-to-noise ratio. For example, in a data-aided based system, the most typical of the conventional approach is the Schmidl scheme, which uses two repeated training sequences to complete the estimation and compensation of the timing offset, but the timing estimation error of this scheme is large due to the influence of the system itself (e.g., the influence of OFDM cyclic prefix, etc.). In addition, the signal recovery rule adopted by the conventional algorithm is usually mechanically compensated according to the estimated time delay, and is difficult to cope with the situation that the time delay estimation is inaccurate due to various factors such as noise.

Therefore, the prior art needs to be improved, the time delay in the symbol is accurately estimated, so that the link performance is improved, and the demodulation signal is rapidly and accurately obtained.

Disclosure of Invention

The present invention aims to overcome the above-mentioned drawbacks of the prior art and provide an estimation method for effectively estimating the intra-symbol delay and a corresponding signal recovery method.

According to a first aspect of the present invention, there is provided a method for estimating delay in a signal symbol of a wireless communication system, comprising the steps of 1 preprocessing baseband information to obtain a quadrature amplitude modulated signal, and 2 estimating delay based on an IQ sequence of the modulated signal, wherein the delay is a ratio of an offset in a time period of interest to the time period.

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

In one embodiment, the step 2 further includes multiplying the I-path sequence and the Q-path sequence by a sine sequence and a cosine sequence, respectively, performing low-pass filtering and squaring operation, adding and averaging the real part sequences and the imaginary part sequences of the obtained I-path sequence and the obtained Q-path sequence, respectively, and performing arctangent operation on the obtained average value.

In one embodiment, the time delay is

Wherein, T is the current time, T is the total time of interest, and T _s is the symbol period.

In one embodiment, the time delay is

Wherein, T is the current time, T is the total time of interest, T _s is the symbol period, L is the number of symbols used to calculate the delay, and N is the number of upsamples.

According to a second aspect of the present invention there is provided a signal recovery method based on a delay estimate of the aforementioned method, the method comprising compensating for its real and imaginary parts, respectively, based on a received signal in complex form and the delay estimate.

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

In one embodiment, the method further comprises recovering the ambient signal based on the amplitude of the signal.

According to a third aspect of the present invention, there is provided a computer readable storage medium having stored therein one or more computer programs which when executed are adapted to carry out the aforementioned delay estimation method and/or signal recovery method.

According to a fourth aspect of the present invention there is provided a computing system comprising storage means and a processor, the storage means for storing one or more computer programs which when executed by the processor are adapted to carry out the aforementioned delay estimation method and/or signal recovery method.

Compared with the prior art, the method has the advantages that a new technical thought and a new technical scheme are provided for estimating the time delay in the symbol and recovering the signal, the time delay in the symbol can be accurately estimated, the method has a good effect on the signal recovery under the condition of high signal-to-noise ratio, and the method can obtain accurate time delay estimation and recover the original signal under the burst scene of low signal-to-noise ratio and high frequency offset phase shift.

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. It is evident that the drawings in the following description are only some embodiments of the present invention and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art. In the drawings:

fig. 1 shows a block diagram of a timing error estimation algorithm based on the use of two signal sequences, I and Q.

Detailed Description

In the whole communication process, symbol time delay is generated due to the fact that clocks of a sending end and a receiving end are inconsistent, frequency offset is generated by relative movement of the sending end and the receiving end, and a method of interpolating and re-extracting signals is adopted to obtain a higher signal to noise ratio, so that intra-symbol time delay is generated. Without a good method for estimating the intra-symbol delay, the signal may not be properly demodulated, or even cannot be communicated. The inventor finds that the problem can be solved by processing and calculating the signal through the IQ sequence to accurately estimate the symbol delay through researching an estimation algorithm of the intra-symbol delay, and the method has good practicability. The solution idea is quite different from the technical idea of solving according to the peak value of the correlation function and the like in the prior art, and belongs to a new technical idea and technical scheme.

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

1. Baseband information preprocessing

After the baseband information is transmitted by the antenna, the effective information is influenced by factors such as additive Gaussian white noise, doppler effect, different sources of local oscillators of transceivers and the like in a channel, and noise, time delay and frequency offset are introduced. Let the baseband binary information sequence be p (k), and the filter be represented as h (k) digitally, the modulated information sequence be s (k). H (k). The expression of the modulated information sequence after the channel can be obtained:

Wherein A is the amplitude of the signal, s (k) is the k symbol of the modulation sequence, namely data modulation information, epsilon is the offset of the timing point between the signal sending end and the receiving end, namely errors caused by time delay, inaccurate timing of the receiving end and other factors, delta f is the frequency offset of the sequence, theta is an unknown initial phase, T _s is a symbol period, the duration from the k symbol to the k+1st symbol of the modulation sequence is the duration from the k symbol to the k+1st symbol of the modulation sequence, and n is zero mean and additive Gaussian white noise with variance sigma ².

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

r(k)=a(k)·h(k-ε)+n(k) (2)

To facilitate an understanding of the delay estimation of the present invention, NT sequences in a mobile communication system are described herein as examples. The time delay estimation is carried out on the NT Burst signal, namely the estimation of the time delay bit number in one symbol is carried out on the Burst signal with time delay, so as to complete signal recovery. After the terminal samples and matched filters the signal, the delay estimation in one symbol is performed. Taking the case of four-fold up-sampling, i.e. 4 points are inserted between two adjacent points of the original signal, the number of bits of the delay may be {0,1,2,3}, and if eight-fold up-sampling, the possible values are {0,1,2,3,4,5,6,7}.

2. IQ sequence based delay estimation

Fig. 1 shows a block diagram of a timing error estimation algorithm by a receiving end using two signal sequences of I and Q simultaneously. The I and Q signal sequences herein are quadrature amplitude modulations in a wireless communication system, with the I path representing the real part of a complex sequence signal and the Q path representing the imaginary part of the complex sequence signal. As shown in fig. 1, the I-path sequence is multiplied by a sine sequence and a cosine sequence, the Q-path sequence is also multiplied by a sine sequence and a cosine sequence, and then low-pass filtering is performed, then squaring operation is performed, the real part sequences obtained by the I-path sequence sample and the Q-path sequence sample are added and averaged with the obtained imaginary part sequences, and finally arctan operation is performed to calculate the symbol time delay.

Where the input signal is shown in equation (2), k=t/T, where T is the current time and T is the total time of interest. The signal is first multiplied by an exponent e ^jπk, then passed through a low pass filter l (k) with a cut-off bandwidth of α/2T, where 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) to obtain

N ₁ (k) is the complex conjugate of n (k). f (k) is the baseband frequency band conversion of the inverse fourier transform of the low-pass filter, expressed as follows:

Wherein:

n₁(k)＝[n(k)e^jπk]*l(k) (8)

According to an embodiment of the invention, the delay phi is defined as the ratio of the offset epsilon to T over the time of interest T. Further, according to an embodiment of the present invention, the time delay, that is, the normalized offset of the time delay information, may be calculated by solving for the desired angle by using the nature of the complex number. Further, the time delay may be expressed as:

Wherein,

According to another embodiment of the present invention, the time delay may also be calculated by simplifying the following:

where L represents the number of symbols used to calculate the delay and N is the number of upsamples.

By means of the delay estimation, an integer part t _e and a fractional part u ₀ of the delay can be obtained. According to one embodiment of the invention, further adjustments to the value of u ₀ are required to obtain u. Further, considering that u ₀ is usually N pi+u, the value of u can be obtained by removing N pi. For example, if u ₀ is substantially within the range of-pi/2, or 0, then u ₀ needs to be adjusted to the same range of values, e.g., 0, to obtain u.

3. Recovery of signals

The inventor finds that the signal recovery rule in the prior art is usually to mechanically compensate according to the estimated time delay, and is difficult to cope with the situation that the time delay estimation is inaccurate due to various factors such as noise. Meanwhile, the signal recovery rule in the prior art is not generally considered as a fraction of the time delay. In view of the above, the present invention provides a method for signal recovery. The method is based on complex signals received by a receiving end, and the method can recover the original signals more accurately by respectively carrying out corresponding compensation and recovery on the real part and the imaginary part, and further improves the accuracy of signal recovery by comprehensively considering the decimal part of time delay and/or the amplitude of surrounding signals in signal recovery.

Let the signal received by the receiver be:

r(n)=r_I(n)+j·r_Q(n),n=1,2,...,L (11)

Let the sequence after the completion of delay estimation and signal recovery be expressed as:

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

the rule of signal recovery according to an embodiment of the invention is described herein with 4-fold upsampling only as an example:

where n=n/4, the same applies:

by respectively compensating and recovering the real part and the imaginary part in the signal recovery and comprehensively considering the decimal part of the time delay and/or the amplitude of the surrounding signal, the good effect of recovering the signal under the high signal-to-noise ratio can be realized.

Further, according to another embodiment of the present invention, considering that when the signal-to-noise ratio is low, the noise is correspondingly superimposed by using the downsampling algorithm of the continuous data points, and the variance of the noise is increased, the information of which the signal strength is highest and is recovered as the signal delay can be directly extracted from the continuous data points. Taking 4 times up sampling as an example, the point with the highest signal intensity is directly extracted from four points, and the first point in every four points is extracted to serve as information for signal delay recovery, so that the accuracy of signal recovery when the signal-to-noise ratio is low is ensured, 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 the embodiments according to the present invention are described and illustrated above by taking 4-fold upsampling as an example, it is not meant that the implementation of the technical solution of the present invention will be limited by a specific upsampling multiple. Furthermore, although the steps are described above in a particular order, it is not meant to necessarily be performed in the particular order described above, and in fact, some of the steps may be performed concurrently or even in a modified order as long as the desired functionality is achieved.

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

The computer readable storage medium may be a tangible device that retains and stores instructions for use by an instruction execution device. The computer readable storage medium may include, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium include a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a Static Random Access Memory (SRAM), a portable compact disc read-only memory (CD-ROM), a Digital Versatile Disc (DVD), a memory stick, a floppy disk, a mechanical encoding device, punch cards or intra-groove protrusion structures such as those having instructions stored thereon, and any suitable combination of the foregoing.

The previous description is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Moreover, all or a portion of any aspect and/or embodiment may be used with all or a portion of any other aspect and/or embodiment, unless otherwise indicated. Thus, the present disclosure is not 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

1. A method for estimating intra-symbol delay of a signal in a wireless communication system, comprising the following steps:

Step 1: pre-process the baseband information to obtain a modulated signal after orthogonal amplitude modulation;

Step 2: Perform delay estimation based on the IQ sequence of the modulated signal, where the delay is the ratio of the offset in the time period of interest to the time period, wherein the I-channel sequence and the Q-channel sequence are multiplied by the sine sequence and the cosine sequence, respectively, and low-pass filtering and square operations are performed; the real part sequence and the imaginary part sequence of the obtained I and Q sequences are added and averaged, respectively; and an inverse tangent operation is performed on the obtained average value.

2. The method according to claim 1 is characterized in that the delay is a normalized offset of the delay information.

3. The method according to claim 1, characterized in that the time delay is

in, k=t/T, t is the current moment, T is the total time of interest, _Ts is the symbol period, u(k) is the real part of the modulated signal, and v(k) is the imaginary part of the modulated signal.

4. The method according to claim 1, characterized in that the time delay is

in, k=t/T, t is the current moment, T is the total time of interest, _Ts is the symbol period, L is the number of symbols used to calculate the delay, N is the number of upsampling, u(k) is the real part of the modulated signal, and v(k) is the imaginary part of the modulated signal.

5. A signal recovery method based on the delay estimation of one of claims 1 to 4, characterized in that the method comprises: based on the received complex signal and the delay estimation, respectively compensating for its real part and imaginary part.

6. The method according to claim 5, characterized in that the method comprises: recovering the signal based on the fractional part of the delay estimate.

7. The method according to claim 6, further comprising: restoring the signal based on the amplitude of surrounding signals.

8. A computer-readable storage medium, storing one or more computer programs, wherein the computer programs are used to implement the method according to any one of claims 1 to 7 when executed.

9. A computing system, comprising a storage device and a processor, wherein the storage device is used to store one or more computer programs, and when the computer programs are executed by the processor, they are used to implement the method of any one of claims 1 to 7.