A Prach detection method in NR 5G

Abstract

The present invention discloses a Prach detection method in NR 5G, which relates to the field of communication technologies and includes: calculating a frequency-domain product by conjugate multiplication according to a root sequence locally generated by a base station and frequency-domain data of a Prach; subjecting the frequency-domain product to IFFT to obtain a time-domain correlation value; calculating an average antenna power based on the time-domain correlation value; setting a determination threshold, and screening effective antennas according to the average antenna power and the determination threshold; combining the effective antennas to obtain a combined power delay profile; calculating a detection threshold according to the power delay profile; and performing a preamble detection decision based on the detection threshold. The present invention calculates the average antenna power, can screen effective antennas based on the average antenna power and the determination threshold, eliminates invalid antennas, only combines the effective antennas, and performs Prach detection, thereby reducing the probability of random access false detection.

Description

Technical Field

[0001] The present invention relates to the field of communication technologies, and in particular, to a Prach detection method in NR 5G. Background Art

[0002] In NR-5G, the UE performs downlink synchronization by receiving the SSB sent by the base station, and then obtains the time-frequency resource information of Prach through the information of SIB1, and initiates random access. The base station extracts the Prach time-frequency resource on the slot where Prach may be sent (Prach Occasion slot), and then performs Prach demodulation. If the preamble is decoded, it means that the msg1 of the UE is received, and then operations such as RAR (Random Access Response) will be sent through msg2.

[0003] For the demodulation of Prach, the base station, as the receiver, generates a set of base sequences locally. The Prach sequence sent by the UE can be expressed as (3GPP protocol 38.211 6.3.3.1):

[0004] x u,v (n) = x u ((n + C v ) mod L RA )

[0005]

[0006] where u represents the root sequence number, L RA is the length of the Prach sequence (839 for the long format sequence and 139 for the short format), C v is the cyclic shift value, e represents the exponent exp, and n ranges from 0 to L RA -1;

[0007]

[0008] where n ranges from 0 to L RA -1, and m ranges from 0 to L RA -1;

[0009] The Prach sequence is generated from the root sequence, where the root sequence is

[0010]

[0011] where u represents the root sequence number, L RA is the length of the Prach sequence (839 for the long format sequence and 139 for the short format), and i ranges from 0 to L RA -1;

[0012] where both the UE and the base station know C v and the root sequence number u, Prach length L RA and other information. Since the Prach sequence has strong autocorrelation characteristics, the base station performs a frequency-domain conjugate multiplication operation on the data on the extracted Prach slot with the root sequence, converts it to the time domain through IFFT to obtain the time-domain correlation value, finds the time-domain correlation peak, and determines whether there is a Prach signal of the UE currently and determines the preamble Id through a decision threshold. The decision threshold is related to the format of Prach, the repetition times of the Prach sequence, and the number of antennas of the base station receiver. Currently, the frequency-domain processing process of the base station for detecting the preamble is as Figure 1 shown. When the number of base station receiving antennas is greater than 1, the antenna combining mode is adopted for the detection of Prach. Since the detection threshold is related to the number of antennas, the detection threshold is different in different receiving antenna cases. If there is no UE sending a Prach signal at this time, due to external interference or interference inside the RRU, the noise power of the receiving antennas is inconsistent, and the power difference between the antennas is large. If antenna combining detection is performed at this time, there may be a false detection of Prach.

[0013] A patent of Huawei Technologies Co., Ltd., with the publication number CN111328088A, provides a PRACH detection method. The method includes: sequentially detecting the frequency-domain data of each beam in at least two groups of beams; obtaining the frequency-domain data corresponding to the Prach from the frequency-domain data of the currently detected beam; determining the time-domain correlation peak of the Prach according to the frequency-domain data corresponding to the Prach; determining a first peak value according to the time-domain correlation peak of the Prach; the first peak value is the highest peak value among the time-domain correlation peaks of the Prach; when the first peak value is greater than or equal to a first threshold, sending a random access response message to the user equipment, and the random access response message is used for the user equipment to establish a connection with the base station. Its detection method is that when the first peak value of each beam in at least two groups of beams is less than the first threshold, and the first peak values of at least two beams in at least two groups of beams are greater than or equal to a second threshold, performing non-coherent combination on the time-domain correlation peaks of at least two beams whose first peak values are greater than or equal to the second threshold; determining a second peak value according to the non-coherently combined time-domain correlation peaks; the second peak value is the highest peak value among the non-coherently combined time-domain correlation peaks; when the second peak value is greater than or equal to the first threshold, sending the random access response message to the user equipment, and the random access response message is used for the user equipment to establish a connection with the base station. This method is a detection method for detecting the preamble, but it does not describe the relationship between the threshold and the beam, and whether the first threshold and the second threshold are fixed values or updated values calculated through the beam. If there is only noise at this time and the interference of each beam varies greatly, false detection may occur.

[0014] The patent of Datang Mobile Communications Equipment Co., Ltd., with the publication number CN109842945A, describes a method for completing Prach detection using FPGA. The purpose is to use time-division multiplexing of FPGA detection resources. In a low-density wide-coverage scenario, a high Ncs (Number of cyclic shift) value can be used to increase the detection time-delay redundancy and improve the detection success rate. In a hot-spot high-capacity small-coverage scenario, a low Ncs value can be used to shorten the detection duration of the PRACH preamble sequence and increase the number of random access users. It can effectively reduce the consumption of FPGA resources in the detection of the PRACH preamble sequence and effectively ensure the random access user capacity and detection success rate. However, it does not consider the Prach false detection problem caused by different inter-antenna interferences. Summary of the Invention

[0015] The present invention aims to provide a Prach detection method in NR5G, which can reduce the probability of false detection of PRACH in the base station.

[0016] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0017] The present invention provides a Prach detection method in NR5G, including the following steps:

[0018] S1. Calculate the frequency-domain product according to the root sequence generated locally at the base station and the PRACH frequency-domain data;

[0019] S2. Perform IFFT on the frequency-domain product to obtain the time-domain correlation value;

[0020] S3. Calculate the average antenna power based on the time-domain correlation value;

[0021] S4. Set a decision threshold, and screen the effective antennas according to the average antenna power and the decision threshold;

[0022] S5. Combine the effective antennas to obtain the combined power delay spectrum;

[0023] S6. Calculate the detection threshold according to the power delay spectrum;

[0024] S7. Perform Preamble detection decision based on the detection threshold.

[0025] The technical effect of this technical solution is that the average antenna power is calculated. Based on the average antenna power and the decision threshold, the effective antennas can be screened, the invalid antennas are eliminated, only the effective antennas are combined, and Prach detection is performed, reducing the probability of random access false detection.

[0026] In a preferred embodiment of the present invention, in step S1, after the base station receiving antenna receives the PRACH time-domain data, according to the high-layer resource configuration, the CP is removed from the PRACH time-domain data, FFT is performed, and demapping is carried out to extract the PRACH frequency-domain data therefrom.

[0027] The technical effect of this technical solution is that the Prach frequency-domain data is extracted from the Prach time-domain data, and the amount of Prach frequency-domain data is much less than that of Prach time-domain data, which is more conducive to the demodulation of the Preamble Id.

[0028] In a preferred embodiment of the present invention, in step S3, the calculation formula of the antenna average power is as follows:

[0029]

[0030] Where, P u (r) is the antenna average power, r is the antenna index, c u (n,r) is the time-domain correlation value, where r is the antenna index, n represents the index of the time-domain correlation value, and Nifft represents the number of points of the IFFT.

[0031] The technical effect of this technical solution is that the time-domain correlation is completed by IFFT, which simplifies the complexity of the correlation operation.

[0032] In a preferred embodiment of the present invention, in step S4, the method for screening valid antennas is specifically as follows:

[0033] Find the maximum antenna average power among the antenna average powers of each antenna;

[0034] Calculate the difference between the maximum antenna average power and the antenna average powers of other antennas, and determine the corresponding antennas with the difference less than the determination threshold as valid antennas.

[0035] The technical effect of this technical solution is that valid antennas can be quickly screened for subsequent antenna combination, reducing the false detection probability of Prach.

[0036] In a preferred embodiment of the present invention, the determination threshold is 6dB.

[0037] The technical effect of this technical solution is that according to the relationship between the Thr threshold factor and the number of antennas, through simulation, it is obtained that if the power between antennas is greater than 6dB, the Prach false detection probability is greater than 0. Therefore, this determination threshold can well meet the condition of reducing false detection.

[0038] In a preferred embodiment of the present invention, in step S5, the calculation formula of the power delay profile is as follows:

[0039]

[0040] Among them, P 0,u (n) is the power delay profile, and Nant is the number of effective antennas.

[0041] The technical effect of this technical solution is: removing the antennas with abnormal power and only using the antennas with similar power to obtain the power delay profile, thereby reducing the false detection rate of Prach.

[0042] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specifically provides embodiments of the present invention and, in conjunction with the accompanying drawings, makes a detailed description as follows. Description of the Drawings

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0044] Figure 1 is the Prach detection flowchart in the prior art;

[0045] Figure 2 is the Prach detection flowchart of the present invention. Detailed Embodiments

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will, in conjunction with the drawings in the embodiments of the present invention, clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, 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.

[0047] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0048] Embodiment

[0049] Please refer to Figure 2 , this embodiment provides a Prach detection method in NR 5G, specifically as follows:

[0050] 1) Calculate the time-domain correlation value.

[0051] From the Fourier transform, it can be seen that the time-domain correlation can be obtained by multiplying the product obtained by multiplying in the frequency domain, and the time-domain correlation result can be obtained by performing a frequency-domain to time-domain transformation on the product result.

[0052] Therefore, first perform a conjugate multiplication operation on the PRACH frequency-domain data of each antenna and the root sequence generated locally at the base station to obtain the frequency-domain product C u (k,r);

[0053] C u (k,r) = conj(Y(k,r)) · X u (k)

[0054] where conj() represents taking the conjugate, the PRACH frequency-domain data is denoted as Y(k,r), which is obtained by removing the CP, performing FFT, and demapping on the PRACH time-domain data according to the high-layer resource configuration. The PRACH time-domain data is the signal data received by the base station receiving antenna.

[0055] The root sequence generated locally at the base station is denoted as X u (k), which is generated locally according to the high-layer resource configuration and is used to detect the Preamble Id, where k = 0.., Lra - 1, and Lra is the length of the sequence, which is 839 for format 0. r is the antenna index, and the value range is 0.., AntLen - 1, and AntLen can be 1 or 2 or 4 or 8, depending on the antenna configuration of the base station.

[0056] After that, perform IFFT on the frequency-domain product C u (k,r) result to obtain the time-domain correlation value c u (n,r);

[0057] c u (n,r) = IFFT(C u (k,r)) · sqrt(N ifft )

[0058] where N ifft is the number of points of the IFFT. If this value is greater than Lra, only zero-padding is required before the transformation. r is the antenna index, and the effective antenna will be reselected later for antenna data merging. Sqrt() represents the square root operation.

[0059] 2) Obtain the antenna average power P u (r) by taking the mean of the squares of the time-domain correlation values of each antenna.

[0060]

[0061] 3) Find the maximum antenna average power in P u (r) and denote it as P max, record the clue index r0 of that day, and then calculate the difference between the maximum antenna average power and the average power of other antennas:

[0062] P diff (r) = P max -P u (r)

[0063] If the difference P diff (r) is less than or equal to the determination threshold, the antenna corresponding to the antenna average power P u (r) is an effective and available antenna, that is, it can be used for antenna combination detection of PRACH. Record the antenna index, count the number of finally selected antennas. If 1 antenna is effective, the number of effective antennas is set to 1. If 2 antennas or 3 antennas are effective, the number of effective antennas is set to 2. If 4 antennas or more are effective, the number of effective antennas is set to 4. If the difference P diff (r) is greater than the determination threshold, then eliminate the combination qualification of the antenna corresponding to the antenna average power P u (r).

[0064] 4) Calculate the combined power delay profile:

[0065]

[0066] Among them, Nant is the number of effective antennas, and the value of r here should exclude the unavailable antennas.

[0067] 5) Calculate the detection thresholds. There are two thresholds in total, namely Thr u，A and Thr u，B .

[0068] First, calculate:

[0069] Thr u，A = Thr·P u，avg

[0070]

[0071] Among them, Thr is the threshold factor, which can be obtained by chi-square distribution. This value is jointly obtained by the number of antennas and the Repeat number of PRACH, and can be read by pre-calculating and storing in a table. The Thr factor table is as follows:

[0072] Threshold Table for Different Formats

[0073]

[0074] Then, based on the threshold Thr u，A , calculate Preamble PowerPu，signal ;

[0075]

[0076] where N u，s is P 0，u (n) greater than Thr u，A in number.

[0077] 6) Set Thr u，B = P u，signal If P 0，u (n) > Thr u，B then a Preamble is detected in the detection window.

[0078] From the threshold factor values in the above table, it can be found that assuming the Prach configuration is Format0, the threshold factor for the receiver with 1 antenna is 17.5320, the threshold factor for the receiver with 2 antennas is 11.7240, and the threshold factor for the receiver with 4 antennas is 8.5440. Assume that the current base station receiver has 2 antennas, but the noise power received by each antenna is inconsistent (there is interference outside the rru radio frequency unit). If antenna screening is not performed, and the threshold factor corresponding to the 2-antenna threshold factor 11.7240 is selected, then the value of the first threshold Thr u,A will be reduced, resulting in false detection.

[0079] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A Prach detection method in NR 5G, characterized in that, It includes the following steps: S1. Calculate the frequency-domain product according to the root sequence generated locally by the base station and the PRACH frequency-domain data; S2. Perform IFFT on the frequency-domain product to obtain the time-domain correlation value; S3. Calculate the average antenna power based on the time-domain correlation value; S4. Set a determination threshold, and screen for effective antennas according to the average antenna power and the determination threshold; S5. Combine the effective antennas to obtain the combined power delay profile; S6. Calculate the detection threshold according to the power delay profile; S7. Perform Preamble detection decision based on the detection threshold; In step S3, the calculation formula for the average antenna power is as follows: Among them, P u (r) is the average power of the antenna, r is the antenna index, c u (n, r) is the time-domain correlation value, n represents the index of the time-domain correlation value, N ifft represents the number of points of the IFFT; In step S4, the method for screening effective antennas is specifically as follows: Find the maximum average antenna power among the average antenna powers of each antenna; Calculate the difference between the maximum average antenna power and the average antenna powers of other antennas, and determine the corresponding antennas with the difference less than the determination threshold as effective antennas.

2. The method according to claim 1, characterized in that, In step S1, after the base station receiving antenna receives the PRACH time-domain data, according to the high-layer resource configuration, perform CP removal, FFT, and demapping on the PRACH time-domain data, and extract the PRACH frequency-domain data therefrom.

3. The method according to claim 1, characterized in that, The determination threshold is 6 dB.

4. The method according to claim 3, characterized in that, In step S5, the calculation formula for the power delay profile is as follows: Among them, P 0,u (n) is the power delay profile, and Nant is the number of effective antennas.

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