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

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

Technical Field

[0001] The present invention relates to the technical field of wireless communications, and in particular to a method for estimating intra-symbol delay and signal recovery. Background Art

[0002] In wireless communication systems, the communication process between the transmitter and the receiver is complete. First, the transmitter performs baseband modulation on the original information to be transmitted in order to transmit as much information as possible with the smallest possible bandwidth, and sends it out in pulse forming; due to noise and other reasons in the channel, it will cause signal delay, frequency deviation and phase shift, etc.; the receiver eliminates inter-symbol 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 restores the baseband information after demodulation. In the communication process, due to local clock offset and the relative motion between the transmitter and the receiver, symbol delay problem, also known as timing offset, occurs.

[0003] In some communication systems, in order to improve the signal-to-noise ratio of the sampled signal, the signal is upsampled, that is, interpolated, and then the signal is extracted using digital methods to make the final sampling rate equal to the symbol rate. After upsampling, there are several interpolated symbols between the original adjacent symbols. When the delay is greater than the number of interpolated symbols between the original two adjacent symbols, it will generate symbol delay, otherwise it is called symbol delay.

[0004] The existing intra-symbol delay estimation method has a large error in the estimated value in the burst scenario with low signal-to-noise ratio and high-frequency 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, traditional methods have great limitations and cannot meet communication requirements. This is because the burst signal is short in time, strong in burstiness, and has a 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, the influence of OFDM cyclic prefix, etc.), the timing estimation error of this scheme is large. In addition, the signal recovery rules used by conventional algorithms often mechanically compensate according to the estimated delay, which is difficult to deal with the situation where the delay estimation is inaccurate due to various factors such as noise.

[0005] Therefore, it is necessary to improve the existing technology and accurately estimate the intra-symbol delay, thereby improving link performance and demodulating signals quickly and accurately. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and provide an estimation method for effectively estimating intra-symbol delay and a corresponding signal recovery method.

[0007] According to a first aspect of the present invention, there is provided a method for estimating intra-symbol delay of a signal in a wireless communication system, comprising the following steps: Step 1: preprocessing baseband information to obtain a modulated signal after orthogonal amplitude modulation; Step 2: estimating delay based on an IQ sequence of the modulated signal, wherein the delay is a ratio of an offset within a time period of interest to a time period.

[0008] In one embodiment, the delay is a normalized offset of the delay information.

[0009] In one embodiment, step 2 further includes: multiplying the I-path sequence and the Q-path sequence by the sine sequence and the cosine sequence respectively, performing low-pass filtering and squaring operations; adding and averaging the real part sequences and the imaginary part sequences of the obtained I and Q-path sequences respectively; and performing an inverse tangent operation on the obtained average values.

[0010] In one embodiment, the delay is

[0011]

[0012] in, t is the current moment, T is the total time of attention, T s is the symbol period.

[0013] In one embodiment, the delay is

[0014]

[0015] in, t is the current moment, T is the total time of attention, T s is the symbol period, L is the number of symbols used to calculate the delay, and N is the number of up-sampled symbols.

[0016] According to a second aspect of the present invention, a signal recovery method based on the delay estimation of the aforementioned method is provided, the method comprising: compensating its real part and imaginary part respectively based on a received complex signal and the delay estimation.

[0017] In one embodiment, the method includes recovering the signal based on a fractional portion of the delay estimate.

[0018] In one embodiment, the method further comprises: restoring the signal based on the amplitude of the surrounding signal.

[0019] According to a third aspect of the present invention, there is provided a computer-readable storage medium storing one or more computer programs, wherein the computer programs are used to implement the aforementioned delay estimation method and / or signal recovery method when executed.

[0020] According to a fourth aspect of the present invention, there is provided a computing system comprising a storage device and a processor, wherein the storage device is used to store one or more computer programs, and the computer programs are used to implement the aforementioned delay estimation method and / or signal recovery method when executed by the processor.

[0021] Compared with the prior art, the advantages of the present invention are: providing a new technical idea and technical solution to estimate the intra-symbol delay and perform signal recovery; being able to accurately estimate the intra-symbol delay; having a good effect on signal recovery under a high signal-to-noise ratio; and being able to obtain accurate delay estimation and restore the original signal in a burst scenario with a low signal-to-noise ratio and a high-frequency phase shift. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings herein are incorporated into and constitute a part of the specification, showing embodiments consistent with the present invention, and together with the specification, are used to explain the principles of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0023] Figure 1 A block diagram of a timing error estimation algorithm based on the use of I and Q signal sequences is shown. DETAILED DESCRIPTION

[0024] During the entire communication process, due to practical problems such as inconsistent clocks between the transmitter and the receiver, and frequency deviation caused by the relative movement of the transmitter and the receiver, symbol delays are generated. In order to obtain a higher signal-to-noise ratio, the signal is interpolated and then extracted, resulting in intra-symbol delays. If there is no better method for estimating the intra-symbol delay, the signal cannot be demodulated correctly, and even communication cannot be achieved. After studying the estimation algorithm for the intra-symbol delay, the inventors found that the problem can be solved by processing and calculating the signal through the IQ sequence to accurately estimate the symbol delay, and it has good feasibility. This solution is completely different from the technical idea of ​​solving the problem based on the peak value of the correlation function in the prior art, and it is a new technical idea and technical solution.

[0025] For ease of understanding, the embodiments according to the present invention will be described below respectively according to baseband information preprocessing, delay estimation based on IQ sequences, and signal recovery.

[0026] 1. Baseband information preprocessing

[0027] 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 transceiver local oscillator, and its effective information introduces noise, delay, and frequency deviation. Let the baseband binary information sequence be p(k), and the filter be digitally represented as h(k), then the modulated information sequence is s(k)·h(k). The expression of the modulated information sequence after passing through the channel can be obtained:

[0028]

[0029] Where A is the amplitude of the signal, s(k) is the kth symbol of the modulation sequence, i.e., the data modulation information, ε is the offset of the timing point between the signal transmitter and the receiver, i.e., the error caused by factors such as delay and inaccurate timing at the receiver, Δf is the frequency deviation 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 zero mean and variance σ 2 Additive white Gaussian noise.

[0030] 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 the frequency offset phase shift can be regarded as one. The signal at this time contains three parts, namely, comprehensive information a(k), time delay and noise, which can be expressed by the following formula:

[0031] r(k)=a(k)·h(k-ε)+n(k) (2)

[0032] In order to facilitate the understanding of the delay estimation of the present invention, the NT sequence in the mobile communication system is used as an example for explanation. The delay estimation of the NT Burst signal is to estimate the number of delay bits within a symbol of the burst signal with delay to complete signal recovery. After the terminal samples and matches the signal, it estimates the delay within a symbol. Taking four-fold upsampling as an example, that is, inserting four points between two adjacent points of the original signal, the number of delay bits may be {0, 1, 2, 3}; if it is eight-fold upsampling, the possible values ​​are {0, 1, 2, 3, 4, 5, 6, 7}.

[0033] 2. Delay estimation based on IQ sequence

[0034] Figure 1 The block diagram of the timing error estimation algorithm using both I and Q signal sequences at the receiving end is given. The I and Q signal sequences here are orthogonal amplitude modulation in wireless communication systems. 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. Figure 1As shown, the I-path sequence is multiplied by a sine sequence and a cosine sequence, and the Q-path sequence is also multiplied by a sine sequence and a cosine sequence, respectively, and then low-pass filtered and then squared. The real sequence and the imaginary sequence obtained from the I and Q sequence samples are added and averaged, and finally an inverse tangent (arctan) operation is performed to calculate the symbol delay.

[0035] 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 the exponent e jπk , and then passes through a low-pass filter l(k). The cutoff bandwidth of the low-pass filter is α / 2T. At this time, the signal can be expressed as:

[0036] y(k)=u(k)+jv(k)=[r(k)e jπk ]*l(k) (3)

[0037] where u(k) and v(k) are the real and imaginary parts of y(k), respectively.

[0038] Substituting equation (2) into equation (3), we get

[0039]

[0040] n1(k) is the complex conjugate of n(k). f(k) is the baseband frequency conversion of the inverse Fourier transform of the low-pass filter, expressed as follows:

[0041]

[0042] in:

[0043]

[0044]

[0045] n1(k)=[n(k)e jπk ]*l(k) (8)

[0046] According to an embodiment of the present invention, the delay φ is defined as the ratio of the offset ε within the time T of interest to T. Further, according to an embodiment of the present invention, the delay can be calculated by using the properties of complex numbers by finding the expected angle, which is the normalized offset of the delay information. Furthermore, the delay can be expressed as:

[0047]

[0048] in,

[0049] According to another embodiment of the present invention, the delay can also be calculated by simplifying the following method:

[0050]

[0051] Where L is the number of symbols used to calculate the delay, and N is the number of upsampling.

[0052] Through delay estimation, the integer part of the delay t can be obtained e and the fractional part u0. According to one embodiment of the present invention, it is necessary to further adjust the value of u0 to obtain u. Further, considering that the value of u0 is usually Nπ+u, the value of u can be obtained by removing Nπ. For example, if the value of u0 is basically around -π / 2, π / 2 or 0, it is necessary to adjust u0 to the same value range, such as around 0, to obtain u.

[0053] 3. Signal recovery

[0054] After research, the inventors found that the signal recovery rules in the prior art often mechanically compensate according to the estimated delay, which is difficult to deal with the situation where the delay estimation is inaccurate due to various factors such as noise. At the same time, the signal recovery rules in the prior art usually do not take into account the fractional part of the delay. In response to the above problems, the present invention provides a signal recovery method. The method is based on the complex signal received by the receiving end, and performs signal recovery by respectively compensating and restoring the real part and the imaginary part, so that the original signal can be recovered more accurately; by comprehensively considering the fractional part of the delay and / or the amplitude of the surrounding signal in the signal recovery, the accuracy of signal recovery is further improved.

[0055] Assume that the signal received by the receiver is:

[0056] r(n)=r I (n)+j·r Q (n),n=1,2,...,L (11)

[0057] Assume that the sequence after delay estimation is completed and signal recovery is expressed as:

[0058] R(N)=R I (N)+j·R Q (N),N=1,2,...,L / 4 (12)

[0059] Here, only 4 times upsampling is taken as an example to describe the signal recovery rule according to the embodiment of the present invention:

[0060]

[0061] Where N = n / 4, similarly we can get:

[0062]

[0063] By compensating and restoring the real part and the imaginary part respectively in signal recovery and comprehensively considering the fractional part of the time delay and / or the amplitude of the surrounding signal, a good effect of signal recovery at a high signal-to-noise ratio can be achieved.

[0064] Further, according to another embodiment of the present invention, considering that when the signal-to-noise ratio is low, the noise is also superimposed accordingly by using the downsampling algorithm of continuous data points, thereby increasing the variance of the noise, the point with the highest signal strength can be directly extracted from the continuous data points as the information for signal delay recovery. Taking 4x 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, thereby ensuring the accuracy of signal recovery when the signal-to-noise ratio is low and reducing the complexity of the calculation. The specific expression is shown in the following formula.

[0065] R′(N)=r(4N),N=1,2,...,L / 4 (15)

[0066] 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 above describes each step in a specific order, it does not mean that each step must be performed in the above specific order. In fact, some of these steps can be executed concurrently or even in a different order, as long as the required functions can be achieved.

[0067] The present invention may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present invention.

[0068] Computer readable storage medium can be a tangible device that holds and stores instructions used by an instruction execution device. Computer readable storage medium can include, for example, but is not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (non-exhaustive list) of computer readable storage medium include: a portable computer disk, 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 disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, for example, a punch card or a protruding structure in a groove on which instructions are stored, and any suitable combination thereof.

[0069] To enable any person of ordinary skill in the art to implement or use the present disclosure, the above description is centered around the present disclosure. It is obvious to those of ordinary skill in the art that various modifications are made to the present disclosure, and the general principles defined herein may also be applied to other variations without departing from the spirit or scope of the present disclosure. In addition, unless otherwise stated, all or part of any aspect and / or embodiment may be used together with all or part of any other aspect and / or embodiment. Therefore, the present disclosure is not limited to the examples and designs described herein, but is consistent with the broadest range of 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, characterized in that The delay is a normalized offset of the delay information.

3. The method according to claim 1, characterized in that The delay is in, k = t / T, t is the current moment, T is the total time of attention, T s 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 delay is in, k = t / T, t is the current moment, T is the total time of attention, T s is the symbol period, L is the number of symbols used to calculate the delay, N is the number of up-sampling, 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 any one of claims 1 to 4, characterized in that: The method comprises: compensating the real part and the imaginary part respectively based on the received signal in complex form and the delay estimate.

6. The method according to claim 5, characterized in that The method includes recovering the signal based on a fractional portion of the delay estimate.

7. The method according to claim 6, characterized in that The method further includes 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 according to any one of claims 1 to 7.

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