PRACH (Physical Random Access Channel) detection method combined with frequency offset estimation

Abstract

The invention discloses a PRACH (Physical Random Access Channel) detection method combined with frequency offset estimation, which comprises the following steps of: under the condition that frequency offset is not supplemented in a detection process, carrying out detection symbol by symbol, calculating a frequency spectrum peak value by utilizing IDF (Inverse Document Frequency) change, calculating frequency offset by utilizing the position of the frequency spectrum peak value, judging an actual peak value by utilizing the sign of the frequency offset when primary and secondary peaks exist in the detection process, and carrying out PRACH detection according to the actual peak value. Therefore, the actual TA value is determined, the PRACH detection complexity is simplified, and the detection performance is not affected.

Description

Technical Field

[0001] The invention relates to a PRACH detection method for joint frequency offset estimation, and belongs to the field of electronic communications. Background Art

[0002] Aiming at the detection method of low-orbit 5G Physical Random Access Channel (PRACH), a random access channel (PRACH) detection method with joint frequency offset estimation is proposed.

[0003] In low-orbit communication satellites, a key step in 5G communication is the successful completion of random access by the onboard base station. According to the movement of the satellite, there is a variable time offset and frequency offset in satellite-to-ground communication. The time offset and frequency offset are mainly caused by the ground terminal detecting the downlink broadcast channel, parsing the ephemeris information, calculating the relative delay and frequency offset calculated by the broadcast channel according to the orbital parameters, and sending the uplink random access signal after compensation. Although the ephemeris compensation is performed, there is still a residual time offset and frequency offset. The satellite movement has the characteristics of relatively fast activation. When the onboard detection does not compensate for the frequency offset, the residual frequency offset will cause a higher secondary peak to confuse the main peak, resulting in an error in the time offset estimation, which affects the subsequent access process and causes an error in the onboard analysis of MES3.

[0004] Reference 1: Zhang Yajing, Liu Yulin, Zhang Zhizhong. Simulation and implementation of physical random access channel signal detection in LTE-A system [J]. Computer Applications, 2018, 38(5): 1442-1446. This reference analyzes the impact of Doppler frequency shift on physical random access channel (PRACH) signal detection and proposes a preamble detection algorithm based on frequency offset correction. However, this algorithm is relatively complex to implement and has high resource consumption. It is a traditional PRACH signal detection algorithm.

[0005] Reference 2: Li Xiaowen, Xu Hu. Principles and implementation of RACH signal detection in TD-LTE system [J]. Electronic Technology Application, 2011(10):108-110. This reference uses the characteristics of ZC (Zadoff-Chu) sequence and FFT (Fast Fourier Transform), and then the cyclic correlation function to provide fast and effective random access for eBodeB, which is fast, stable and easy to implement.

[0006] Document 3: Dong Hang. RACH signal detection system and solution. Chinese invention patent, CN106792867A. This document proposes a RACH detection system and solution that mainly solves the competition for hardware resources between the two functions of frequency offset correction and RACH detection. It includes a signal preprocessing unit with a first external interface, which is used to perform frequency offset correction and downsampling processing on the baseband digital signal in the acquired PRACH channel, and send an interrupt instruction through the first external interface according to a preset transmission interval, and send the downsampled digital signal through the first external interface during the interruption period; a RACH signal detection unit with a second external interface, wherein the second external interface is connected to the first external interface, and is used to obtain the digital signal of the first external interface based on the received interrupt instruction, and perform RACH signal detection on the received digital signal.

[0007] Document 4: Qian Bin, Liu Bo, Zou Gang, Rong Yuanzheng, Gan Yonggang. Frequency offset estimation method, device, communication equipment and storage medium. Chinese invention patent, CN112887241 B. This document mainly obtains the main peak and secondary peak of the PRACH signal when the received signal has frequency offset, determines the first frequency offset according to the peak values ​​of the main peak and the secondary peak, and obtains the compensation sequence after compensating the signal. After accurately estimating and compensating the frequency offset, the delay estimation of the frequency offset estimation result can be improved, thereby expanding the scope of application.

[0008] It can be seen from the current literature on timing advance and time offset estimation that in the 5G system, the PRACH detection algorithm estimates the time offset value by first compensating the frequency offset to obtain the time offset, which is quite different from the PRACH detection algorithm based on frequency offset estimation in this article. Summary of the invention

[0009] The technical problem solved by the present invention is to propose a PRACH detection algorithm by joint frequency offset estimation, which reduces FPGA implementation resources without reducing performance. The algorithm can be used not only in low-orbit satellite systems, but also in other communication systems with burst communication characteristics.

[0010] The technical solution of the present invention is: when detecting an uplink random access channel (PRACH), in order to reduce resources without frequency offset compensation for the signal, when the frequency offset is relatively large, the primary and secondary peaks detected affect the estimation result, and the TA cannot be correctly estimated. A PRACH detection method with joint frequency offset estimation is proposed. For the uplink PRACH channel, without frequency offset compensation during the detection process, detection is performed symbol by symbol, the spectrum peak is calculated using the IDF change, the frequency offset is calculated using the spectrum peak position, and then when there are primary and secondary peaks in the detection, the positive and negative signs of the frequency offset are used to determine the actual peak value, and then the actual TA value is determined. Through PRACH detection with joint frequency offset estimation, the problem of frequency offset affecting TA calculation on burst capture when the frequency offset is not compensated at the receiving end is solved.

[0011] Specifically, the present invention proposes a PRACH detection method with joint frequency offset estimation, the steps are as follows:

[0012] (1) Calculate the frequency deviation value based on the result of peak detection;

[0013] (2) Determine the main peak position according to the sign of the frequency offset estimate and calculate the time offset TA;

[0014] Furthermore, the step (1) of calculating the frequency deviation value specifically comprises the following steps:

[0015] (1.1) The sequence received in the frequency domain is: Y i (n),i=0,1,…K;n=0,1,…K:The local sequence is: X(n),n=0,1,…K. The received sequence and the local sequence are conjugate multiplied to obtain the frequency domain product result sequence:

[0016] H i (n) = Y i (n).*conj(X(n))

[0017] (1.2) The frequency domain product result sequence is obtained and IDFT operation is performed:

[0018] h i (n) = IDFT(H i (n))

[0019] Where i represents the i-th symbol, h i represents the convolution result of the local sequence of the i-th symbol and the received sequence;

[0020] (1.3) The calculation results obtained by IDFT transformation are accumulated and summed:

[0021]

[0022] (1.4) Find the position of the maximum value in step (1.3) respectively, and then find the corresponding data in step (1.2) based on the maximum value position:

[0023] loc i =max(h_sum i,k (n))

[0024] h'(i)=h i (loc i )

[0025] (1.5) For step (1.4), h'(i) = h i (loc i ) Take the difference conjugate multiplication and cumulative sum, and then take arctan to get

[0026] fre=arctan(sum(h'(i)*conj(h'(i+1))))*N / 2 / π / fs

[0027] That is, the frequency deviation is obtained, where i=0,1…12, N is the FFT length, and fs is the sampling rate of the signal.

[0028] The step (2) determines the main peak position according to the sign of the frequency offset estimation value and calculates the time offset TA, and specifically includes the following steps:

[0029] (2.1) The received sequence is

[0030]

[0031] (2.2) Perform FFT on step (2.1), then there exists a value of size ε f The frequency domain received signal of the FFO can be expressed as

[0032]

[0033] in

[0034]

[0035] (2.3) The first item in the last row of step (2.2) represents the amplitude distortion and phase distortion of the kth subcarrier frequency component caused by FFT, and I l [k] represents the ICI of other subcarriers to the kth subcarrier. When the frequency offset increases, when calculating the frequency offset in (1.5), the secondary peak increases with the increase of the frequency offset, but the position of the secondary peak relative to the position of the main peak is related to the positive and negative sign of the frequency offset. According to (1-3) when i = 12, the maximum peak and secondary peak positions peak1, peak2 are calculated.

[0036] Find the sign of the positive or negative value in step (1.5):

[0037] Sign_bit = sign(fre)

[0038] At the same time, the magnitude of the combined frequency deviation and the positive or negative sign of the frequency deviation can be used to determine the actual peak value, and then calculate the true TA value.

[0039] The present invention has the following advantages over the prior art:

[0040] In the present invention, when detecting an uplink random access channel (PRACH), in order to reduce the resource usage without frequency offset compensation for the signal, when the frequency offset is relatively large, the detected primary and secondary peaks affect the estimation result, and the TA cannot be correctly estimated. A PRACH detection method with joint frequency offset estimation is proposed, which is different from the prior art in that:

[0041] For the uplink PRACH channel, without frequency offset compensation during the detection process, detection is performed symbol by symbol, the spectrum peak is calculated using the IDF change, and the frequency offset is calculated using the spectrum peak position. Then, when there are primary and secondary peaks in the detection, the positive and negative signs of the frequency offset are used to determine the actual peak value, and then the actual TA value is determined. The PRACH detection combined with frequency offset estimation solves the problem of frequency offset affecting TA calculation on burst capture when the receiving end does not compensate for the frequency offset. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is the NR-RACH process in the present invention;

[0043] Figure 2 It is the PRACH access detection process;

[0044] Figure 3 To add the frequency deviation main and secondary peak change diagram;

[0045] Figure 4 This is the position diagram of the main and secondary peaks when adding different symbols of frequency deviation;

[0046] Figure 5 Schematic diagram of the structure of a computer device in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0048] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0050] The specific steps of the present invention are as follows:

[0051] (1) Calculate the frequency deviation value based on the result of peak detection;

[0052] (2) Determine the main peak position according to the sign of the frequency offset estimate and calculate the time offset TA.

[0053] The step (1) of calculating the frequency deviation value specifically comprises the following steps:

[0054] (1.1) The sequence received in the frequency domain is: Y i (n),i=0,1,…K;n=0,1,…K:The local sequence is: X(n),n=0,1,…K. The received sequence and the local sequence are conjugate multiplied to obtain the frequency domain product result sequence:

[0055] H i (n) = Y i (n).*conj(X(n))

[0056] (1.2) Perform IDFT operation on the result of step (1.1):

[0057] h i (n) = IDFT(H i (n))

[0058] (1.3) The calculation results obtained by IDFT transformation are accumulated and summed:

[0059]

[0060] (1.4) Find the position of the maximum value corresponding to step (1.3), and then find the corresponding data in step (1.2) based on the maximum value position:

[0061] loc i =max(h_sum i,k (n))

[0062] h'(i)=h i (loc i )

[0063] (1.5) For step (1.4), h'(i) = h i (loc i ) Take the difference conjugate multiplication and cumulative sum, and then take arctan to get

[0064] fre=arctan(sum(h'(i)*conj(h'(i+1))))*N / 2 / π / fs

[0065] That is, the frequency deviation is obtained, where i=0,1…12, N is the FFT length, and fs is the sampling rate of the signal.

[0066] The step (2) determines the main peak position according to the sign of the frequency offset estimation value and calculates the time offset TA, and specifically includes the following steps:

[0067] (2.1) The received sequence is:

[0068]

[0069] (2.2) Perform FFT on step (2.1), then there exists a value of size ε f The frequency domain received signal of the FFO can be expressed as

[0070]

[0071] in

[0072]

[0073] (2.3) The first item in the last row of step (2.2) represents the amplitude distortion and phase distortion of the kth subcarrier frequency component caused by FFT, and I l [k] represents the ICI of other subcarriers to the kth subcarrier. When the frequency offset increases, when calculating the frequency offset in step (1.5), the secondary peak will increase with the increase of the frequency offset, but the position of the secondary peak relative to the position of the main peak is related to the positive and negative sign of the frequency offset. According to step (1.3) when i = 12, the maximum peak and secondary peak positions peak1, peak2 are calculated;

[0074] Find the sign of the positive or negative value in step (1.5):

[0075] Sign_bit = sign(fre)

[0076] At the same time, the magnitude of the combined frequency deviation and the positive or negative sign of the frequency deviation can be used to determine the actual peak value, and then calculate the true TA value.

[0077] Example:

[0078] Assume that the PRACH format is 139 and the subcarrier spacing is 60KHz

[0079] (1) Calculate the frequency deviation value based on the peak detection result:

[0080] (1.1) Based on Figure 2 The process calculates the frequency deviation estimation result

[0081] (2) Determine the main peak position according to the sign of the frequency offset estimate and calculate the time offset TA:

[0082] (2.1) Add different frequency offsets to the received sequence. Different peaks can be detected according to peak detection. The secondary peak increases as the frequency offset increases, while the main peak decreases as the frequency offset increases. Figure 3 As shown;

[0083] (2.2) Adding frequency deviations of positive and negative 30 kHz to the received sequence, the position of the secondary peak relative to the main peak is related to the sign of the added frequency deviation, as shown in Figure 4 As shown;

[0084] (3) When the primary and secondary peaks are detected, the magnitude of the frequency deviation and the positive and negative sign of the frequency deviation can be combined to determine the actual peak value, and then calculate the true TA value.

[0085] The present invention does not have any impact on performance. The method of the present invention determines the main and secondary peaks according to the frequency offset symbol, thereby omitting the frequency offset compensation function, reducing the complexity of the algorithm and the resource occupancy rate, and can solve the problem that the frequency offset affects the TA calculation on the burst capture when the receiving end does not compensate for the frequency offset.

[0086] Based on the same technical concept, the present application also provides a computer device, such as Figure 5 As shown, the computer device includes a transceiver, a processor and a memory, wherein the memory stores computer-readable instructions, and when the computer-readable instructions are executed by the processor, the processor executes the PRACH detection method for joint frequency offset estimation in the above-mentioned embodiments.

[0087] Based on the same technical concept, the present application also provides a storage medium storing computer-readable instructions. When the computer-readable instructions are executed by one or more processors, the one or more processors execute the PRACH detection method of joint frequency offset estimation described in the above-mentioned embodiments.

[0088] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present application, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium such as (ROM / RAM), and includes a number of instructions for a terminal (which can be a mobile phone, a computer, a server or a network device, etc.) to execute the methods described in each embodiment of the present application.

Claims

1. A PRACH detection method with joint frequency offset estimation, characterized in that: The method comprises the following steps: (1) Calculate the frequency deviation value based on the result of peak detection; (2) Determine the main peak position according to the sign of the frequency offset estimate and calculate the time offset TA.

2. The PRACH detection method of claim 1, wherein: The step (1) calculates the frequency deviation value according to the result of the peak detection, and specifically comprises the following steps: (1.1) The sequence received in the frequency domain is: Y i (n), i = 0, 1, ... K; n = 0, 1, ... K: The local sequence is: X(n), n=0,1,…K, conjugate multiply the received sequence and the local sequence to obtain the frequency domain product result sequence: H i (n)=Y i (n).*conj(X(n)); (1.2) Perform IDFT transformation on the frequency domain product result sequence: h i (n)=IDFT(H i (n)); Where i represents the i-th symbol, h i represents the convolution result of the local sequence of the i-th symbol and the received sequence; (1.3) The calculation results obtained by IDFT transformation are accumulated and summed: (1.4) In step (1.3), the maximum value position is obtained respectively; location i =max(h_sum i,k (n)) Find the corresponding data in step (1.2) according to the corresponding maximum value position in step (1.4): h'(i)=h i (loc i ) (1.5) Multiply and sum the difference conjugates in step (1.4), and then calculate arctan to obtain the formula: fre=arctan(sum(h'(i)*conj(h'(i+1))))*N / 2 / π / fs That is, the frequency deviation is obtained, where i=0,1…12, N is the FFT length, and fs is the sampling rate of the signal.

3. The PRACH detection method of claim 2, wherein: The step (2) determines the main peak position according to the sign of the frequency offset estimation value and calculates the time offset TA, and specifically includes the following steps: (2.1) The received sequence is expressed as: (2.2) Perform Fourier transform operation on step (2.1), and there exists a value of ε f The frequency domain received signal of the FFO can be expressed in the frequency domain as: in (2.3) The first item in the last row of step (2.2) represents the amplitude distortion and phase distortion of the kth subcarrier frequency component caused by FFT. At the same time, I in step (2.2) l [k] represents the ICI of other subcarriers to the kth subcarrier; and when the frequency offset increases, when the frequency offset is calculated in step (1.5), the secondary peak will increase with the increase of the frequency offset.

4. The PRACH detection method of claim 3, wherein: In the step (2.3), when the frequency deviation is calculated in the step (1.5), the secondary peak increases with the increase of the frequency deviation, and the position of the secondary peak relative to the position of the main peak is related to the positive or negative sign of the frequency deviation. At the same time, the actual peak value can be determined by combining the magnitude of the frequency deviation and the positive or negative sign of the frequency deviation, and then the real TA value can be calculated; The position of the secondary peak relative to the position of the main peak is related to the positive and negative sign of the frequency deviation. The specific process is as follows: the positive and negative value of the sign of step (1.5) is calculated, that is: Sign_bit=sign(fre).

5. A communication device comprising a memory and a processor, characterized in that: The memory stores a computer program, and when the processor executes the computer program, the PRACH detection method for joint frequency offset estimation according to any one of claims 1 to 4 is implemented.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the PRACH detection method of joint frequency offset estimation as described in any one of claims 1 to 4 is implemented.

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