CN115603888A - Method for estimating time delay in signal symbol of wireless communication system and recovering signal - Google Patents
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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
Technical Field
The invention relates to the technical field of wireless communication, in particular to a method for estimating time delay in symbols and recovering signals.
Background
In a wireless communication system, a complete communication process is performed between a transmitting end and a receiving end of communication. Firstly, a sending end carries out baseband modulation on original information to be transmitted so as to achieve the purpose of transmitting information as much as possible by using a small amount of bandwidth, and the information is sent out by pulse forming; due to noise and the like in a channel, time delay, frequency offset, phase shift and the like of a signal can be caused; the receiving end eliminates the intersymbol interference through matched filtering, then performs channel estimation (such as time delay estimation, frequency estimation, phase estimation and the like), compensation (such as timing correction, frequency correction, phase correction and the like), and recovers the baseband information after demodulation. During communication, symbol delay problem, also called timing offset, is caused by local clock offset and relative motion between the transmitting end and the receiving end.
In some communication systems, to increase the signal-to-noise ratio of the sampled signal, the signal is up-sampled, i.e., interpolated, and then digitally decimated to equalize the final sampling rate to the symbol rate. After upsampling, several interpolated symbols are added between the original adjacent symbols, and when the time delay is greater than the number of interpolated symbols between the original two adjacent symbols, an out-of-symbol time delay is generated, otherwise, the time delay is called an in-symbol time delay.
In the existing intra-symbol delay estimation method, under a burst scene of low signal-to-noise ratio and high frequency offset phase shift, an obtained estimation value has a large error, which can cause that a signal cannot be correctly demodulated and even communication interruption is possible. For example, in a data-aided system, the conventional method is most representative of the Schmidl scheme, which uses two repeated training sequences to perform estimation and compensation of 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 compensated mechanically according to the estimated delay, and it is difficult to deal with the situation that the delay estimation is inaccurate due to various factors such as noise.
Therefore, there is a need for an improvement in the prior art to accurately estimate the time delay in a symbol, thereby improving the link performance and rapidly and accurately demodulating a signal.
Disclosure of Invention
It is an object of the present invention to overcome the above-mentioned drawbacks of the prior art and to provide an estimation method for effectively estimating the delay in a symbol and a corresponding signal recovery method.
According to a first aspect of the present invention, there is provided a method for estimating time delay in a signal symbol of a wireless communication system, comprising the steps of: 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 to the time period in the concerned time period.
In one embodiment, the delay is a normalized offset of the delay information.
In one embodiment, the step 2 further comprises: multiplying the I path sequence and the Q path sequence by a sine sequence and a cosine sequence respectively, and performing low-pass filtering and square operation; adding and averaging the real part sequences and the imaginary part sequences of the obtained I and Q two-path sequences respectively; and performing arc tangent 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, 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 L represents the number of symbols used to calculate the delay, and N is the number of upsamples, for a symbol period.
According to a second aspect of the present invention, there is provided a signal recovery method based on the delay estimation of the foregoing method, the method comprising: the real and imaginary parts of the received complex-form signal are compensated separately on the basis of the delay estimate.
In one embodiment, the method comprises: recovering the signal based on the fractional portion of the delay estimate.
In one embodiment, the method further comprises: the signal is recovered based on the amplitude of the surrounding signal.
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, which when executed, are adapted to implement 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 a storage means for storing one or more computer programs which, when executed by the processor, are adapted to implement the aforementioned delay estimation method and/or signal recovery method.
Compared with the prior art, the invention has the advantages that: a new technical idea and a 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 signal recovery effect is good under the condition of high signal-to-noise ratio; accurate time delay estimation can be obtained and original signals can be recovered under the burst scene of low signal-to-noise ratio and high frequency offset phase shift.
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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 obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. 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, because the transmitting end and the receiving end have practical problems of clock inconsistency, frequency deviation generated by relative motion of the transmitting end and the receiving end and the like, symbol time delay is generated, and in order to obtain a higher signal-to-noise ratio, a method of interpolating and then extracting is adopted for signals, so that time delay in symbols is generated. Without a good estimation method for the time delay in the symbol, the signal cannot be demodulated correctly, and even cannot be communicated. The inventor finds that the problem can be solved by processing and calculating signals through IQ sequences to accurately estimate the symbol delay through the research on an estimation algorithm of the delay in the symbol, 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 a technical scheme.
For ease of understanding, embodiments according to the present invention will be described below in terms of baseband information preprocessing, delay estimation based on IQ sequences, and signal recovery, respectively.
1. Baseband information preprocessing
After the baseband information is transmitted by an antenna, the effective information is influenced by factors such as channel additive white gaussian noise, doppler effect, different sources of local oscillators of a transceiver and the like, and noise, time delay and frequency offset are introduced into the effective information. Let the baseband binary information sequence be p (k), and the filter be digitized as h (k), the modulated information sequence is s (k) · h (k). An expression of the modulated information sequence after passing through the channel can be obtained:
wherein, A is the amplitude of the signal, s (k) is the kth symbol of the modulation sequence, i.e. data modulation information, epsilon is the offset of the timing point between the signal sending end and the receiving end, i.e. the error is brought by the time delay and the receiving end timing inaccuracy, Δ f is the frequency offset of the sequence, θ is the unknown initial phase, T (k) is the unknown initial phase s Is a symbol period which is the time length from the k symbol to the k +1 symbol of the modulation sequence, and n is a zero mean value and a variance sigma 2 White additive gaussian noise.
The signal obtained at this time contains baseband information, time delay, frequency offset phase shift and noise, and according to the embodiment of the present 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, i.e., the comprehensive information a (k), the time delay and the noise, which are expressed by the following formula:
r(k)＝a(k)·h(k-ε)+n(k) (2)
to facilitate understanding of the delay estimation of the present invention, the NT sequence in the mobile communication system is taken as an example for explanation. The delay estimation is carried out on the NT Burst signal, namely the estimation of the delay digit in one symbol is carried out on the Burst signal with the delay so as to complete the signal recovery. After the terminal samples and matches the filter to the signal, it estimates the delay in one symbol. Taking four times up-sampling as an example, that is, 4 points are inserted between two adjacent points of the original signal, so the number of bits of the time delay may be {0,1,2,3}; if it is eight times upsampled, then the possible value is {0,1,2,3,4,5,6,7}.
2. Delay estimation based on IQ sequence
Fig. 1 shows a block diagram of a timing error estimation algorithm performed by a receiving end by using two signal sequences of I and Q simultaneously. Here, the I and Q signal sequences are quadrature amplitude modulation in a 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 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, low-pass filtering is performed, square operation is performed, the real part sequence and the imaginary part sequence obtained from the I-path sequence sample and the Q-path sequence sample are added and averaged, and finally arctan (arctan) operation is performed to calculate the symbol delay.
Where the input signal is as 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 And 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 the formula (2) into the formula (3) to obtain
n 1 (k) Is the complex conjugate of n (k). f (k) is the baseband band transform of the low pass filter inverse fourier transform, expressed as follows:
wherein:
n 1 (k)＝[n(k)e jπk ]*l(k) (8)
according to an embodiment of the invention, the time delay is defined as the ratio of the offset epsilon to T over the time of interest T. Further, according to the embodiment of the present invention, the time delay can be calculated by finding a desired angle by using the property of complex numbers, which is a normalized offset of the time delay information. Further, the time delay can be expressed as:
wherein,
according to another embodiment of the present invention, the time delay can also be calculated simply by:
where L represents the number of symbols used to calculate the delay and N is the number of upsamples.
By time delay estimation, the integral part t of the time delay can be obtained e And fractional part u 0 . According to one embodiment of the present invention, u needs to be paired 0 Further adjusting the value of (a) to obtain u. Further, consider u 0 The value of (b) is usually N pi + u, and the value of u can be obtained by removing N pi. For example, if u 0 Is substantially in the range of-pi/2, pi/2 or 0, u is required to be reduced 0 Adjusted to be the sameWithin a value range, such as around 0, u is obtained.
3. Recovery of signals
The inventor has found through research that the signal recovery rule in the prior art often mechanically compensates according to the estimated time delay, and it is difficult to deal with the situation that the time delay estimation is inaccurate due to various factors such as noise. Also, the signal recovery rules of the prior art are not generally considered to be the fractional part of the delay. In view of the above problems, the present invention provides a method for signal recovery. The method carries out signal reply by respectively carrying out corresponding compensation and recovery on a real part and an imaginary part based on a complex signal received by a receiving end, thereby more accurately recovering an original signal; the accuracy of signal recovery is further improved by comprehensively considering the fractional part of the time delay and/or the amplitude of the surrounding signal in the 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 finished and the signal is restored is represented 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 here only with 4 times upsampling as an example:
where N = N/4, the same applies:
by respectively and correspondingly 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 also superimposed correspondingly by using a down-sampling algorithm of consecutive data points, so as to increase the variance of the noise, the information with the highest signal strength among the consecutive data points can be directly extracted as the signal delay recovery information. Taking 4 times of 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 of 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 embodiment according to the present invention is described and illustrated above by taking 4 times upsampling as an example, it is not meant that the implementation of the technical solution of the present invention is limited by a specific upsampling multiple. Moreover, although the steps are described above in a particular order, it is not meant that the steps must be performed in the particular order described, and indeed, some of the steps may be performed concurrently, even in varying orders, so 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 therewith for causing a processor to implement various 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 memory device, a magnetic memory device, an optical memory device, an electromagnetic memory device, a semiconductor memory device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: 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 coding device, such as punch cards or in-groove projection structures 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 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 within a signal symbol of a wireless communication system, comprising the steps of:
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 in the concerned time period to the time period.
2. The method of claim 1, wherein the time delay is a normalized offset of the time delay information.
3. The method of claim 1, wherein the step 2 further comprises: multiplying the I path sequence and the Q path sequence by a sine sequence and a cosine sequence respectively, and performing low-pass filtering and square operation; adding and averaging the real part sequences and the imaginary part sequences of the obtained I and Q two paths of sequences respectively; and performing arc tangent operation on the obtained average value.
4. The method of claim 1, wherein the time delay is
Wherein,
k = T/T, T being the current time, T being the total time of interest, T s Is the symbol period.
5. The method of claim 1, wherein the time delay is
Wherein,
k = T/T, T being the current time, T being the total time of interest, T s L represents the number of symbols used to calculate the delay, and N is the number of upsamples, for a symbol period.
6. A method for signal recovery based on the delay estimation of one of claims 1 to 5, characterized in that the method comprises: the real and imaginary parts of the received complex-form signal are compensated separately on the basis of the delay estimate.
7. The method according to claim 6, characterized in that the method comprises: recovering the signal based on the fractional portion of the delay estimate.
8. The method of claim 7, further comprising: the signal is recovered based on the amplitude of the surrounding signal.
9. A computer readable storage medium, in which one or more computer programs are stored which, when executed, are for implementing the method of any one of claims 1 to 8.
10. 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 for implementing the method of any one of claims 1 to 8.
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