Method for enhancing uplink coverage in 5G mobile communication system

Abstract

The present invention discloses an uplink coverage enhancement method in a 5G mobile communication system, mainly solving the problem that the uplink coverage distance in the prior art is insufficient, resulting in the interruption of communication transmission. The solution is as follows: configure the working frequency band available for the terminal; perform link budget to obtain the maximum allowable path loss; send a detection signal in the high-frequency band, detect the signal-to-noise ratio and received power information, and calculate the proportion of the tap energy of the direct path in the total energy of all paths and the path loss; the base station selects the uplink data transmission frequency band according to the initial detection result and timely feedbacks the selection result to the user; track the uplink coverage status under high-frequency band communication; when the initial detection time interval reaches a cycle, the user sends a detection signal again, the base station selects the uplink data transmission frequency band according to the detection status and feedbacks it to the user, and the user timely performs frequency band switching. The present invention enhances the uplink coverage and improves the performance of 5G uplink data transmission, and can be used for wireless communication.

Description

Technical Field

[0001] The present invention belongs to the field of mobile communications, and particularly relates to a coverage enhancement method, which can be used for the 5G uplink to improve its data transmission performance. Background Art

[0002] 5G has the advantages of high speed, low latency, and ultra-large connection. Compared with 4G, it not only improves the user's network experience and brings higher transmission rates to mobile terminals, but also meets the application requirements of future Internet of Everything and endows everything with the ability of online connection. The 5G new radio, also known as 5G NR, adopts a brand-new air interface design based on orthogonal frequency division multiplexing (OFDM), which is a very important core technology in the 5G mobile communication system.

[0003] 5G NR base stations generally adopt large-scale antenna arrays. The increase in the number of antennas provides more multiplexing gain and diversity gain for the propagation channel, enabling the system to have better performance in terms of downlink data rate, link reliability, and coverage. However, the terminal volume limits the number of antennas, and the antenna gain cannot be obtained by using large-scale multiple-input multiple-output (MIMO) technology, resulting in limited 5G uplink coverage, as Figure 2 shown. In the uplink direction, that is, on the path from the terminal to the base station for sending data, the transmit power limitation of the terminal restricts the 5G uplink coverage. In addition, combined with the differences in the time division duplex (TDD) uplink and downlink time slot ratios, etc., the uplink and downlink coverage gap is further enlarged, restricting the advantages of 5G in practical applications.

[0004] 5G NR supports frequency bands below 6 GHz and millimeter wave bands. The limited uplink coverage makes users unable to use the high-speed data services of high-frequency downlink after exceeding the uplink coverage area, restricting the advantages of high-frequency downlink large bandwidth. Currently, most of the 5G network frequency bands are high-frequency bands with rich bandwidth resources, but they have relatively high path loss and penetration loss, and the uplink coverage is relatively weak. Due to the uplink coverage disadvantage of the medium and high-frequency bands, the high-frequency coverage is weaker than the low-frequency coverage, so there will be a situation where the high-frequency coverage is discontinuous, which makes users unable to continuously use the high-speed data services of high-frequency. When users move out of the high-frequency coverage area, the data rate drops due to the data service falling back to the low-frequency, resulting in a poor user experience and poor robustness.

[0005] For 4G, usually the downlink traffic is more than the uplink traffic. However, in the 5G era, many target applications such as video live streaming will generate uplink traffic of the same magnitude as the downlink. Such services require continuous high-quality uplink coverage and sufficient robustness. Therefore, it is necessary to continuously improve the uplink performance of the high-frequency network and overcome the bottleneck. Therefore, the uplink enhancement technology is one of the key focus directions of the 5G commercial network. Therefore, specific algorithms and solutions must be designed for the 5G uplink to improve coverage. If low-frequency band resources are introduced for uplink transmission, the cooperation of high- and low-frequency carriers helps to improve uplink coverage.

[0006] The patent document with the application number 202011296498.2 discloses an uplink coverage improvement method, device, storage medium, and terminal device. Although this patent has been improved from the perspective of signaling configuration, it still cannot achieve coverage when the distance increases, and due to insufficient uplink coverage distance, it wastes the downlink coverage range, affects the uplink transmission robustness, and causes communication transmission interruptions. Summary of the Invention

[0007] The purpose of the present invention is to propose an uplink coverage enhancement method in a 5G mobile communication system to enhance the uplink coverage of 5G NR, improve the robustness of uplink coverage, and ensure that communication transmission does not interrupt, aiming at the deficiencies of the above-mentioned existing technologies.

[0008] The technical solution to achieve the purpose of the present invention is: Through link budget, combined with the newly designed tap energy ratio calculation method based on IDFT transformation and the communication frequency band switching method, timely frequency band mode switching is performed according to the identified channel conditions, thereby enhancing the uplink coverage of 5G NR. It includes the following steps:

[0009] 1) In addition to the original high-frequency band, an additional uplink in the low-frequency band is configured to ensure downlink coverage using the original high-frequency band, and ensure uplink coverage using the two frequency bands of the original high-frequency band and the newly configured low-frequency band.

[0010] 2) Perform link budget on the communication uplink in different scenarios to obtain the maximum allowable path loss PL when meeting the system performance requirements.

[0011] 3) Detect the channel conditions in the high-frequency band, calculate the path loss L1, the ratio p1 of the tap energy of the direct path to the total energy of all paths, and the signal-to-noise ratio SINR1.

[0012] 4) Set the path loss switching threshold LH, the ratio switching threshold p0 of the tap energy of the direct path to the total energy of all paths, and the signal-to-noise ratio switching threshold SINR0 according to the current channel condition and communication environment. The base station comprehensively selects the current data transmission frequency band based on multiple indicators such as the ratio p1 of the tap energy of the direct path to the total energy of all paths, the detected path loss L1, and the signal-to-noise ratio SINR1, combined with the current service requirements, and feeds back the selection result to the user. The user performs frequency band switching according to the received feedback result;

[0013] 5) When communicating in the high frequency band, send a detection signal to monitor the uplink coverage condition, and the user performs frequency band switching according to the monitoring result;

[0014] 6) When the time interval of the detection signal transmission reaches a cycle, the user sends a detection signal again in the high frequency band. The base station calculates the path loss L4 in the current frequency band, the ratio p4 of the tap energy of the direct path of the high frequency channel to the total energy of all paths, and the signal-to-interference-plus-noise ratio SINR4 of the detection signal using the currently received detection signal;

[0015] 7) For the currently data-transmitting frequency band, the base station selects different frequency bands based on the calculation results in 6) and feeds them back to the user for frequency band switching to achieve uplink coverage and ensure the normal progress of uplink communication:

[0016] 7a) For the currently data-transmitting frequency band using the high frequency band: If L4 is greater than the threshold LH, or p4 is less than the switching threshold p0, or SINR4 is less than the switching threshold SINR0, then the base station will select the low frequency band and feed back the selection result to the user, and the user switches the transmission frequency band to the low frequency band to enhance the uplink coverage stability; otherwise, the base station will select the high frequency band and feed back the selection result to the user, maintaining the high frequency band transmission unchanged;

[0017] 7b) For the currently data-transmitting frequency band using the low frequency band: If L4 is less than the threshold LH, and p4 is greater than the switching threshold p0, and SINR4 is greater than the switching threshold SINR0, then the base station will select the high frequency band and feed back the selection result to the user, and the user switches the transmission frequency band to the high frequency band; otherwise, the base station will select the low frequency band and feed back the selection result to the user, and the user maintains the low frequency band transmission unchanged to enhance the uplink coverage stability.

[0018] The present invention has the following advantages compared with the prior art:

[0019] First, the present invention combines link budget and channel detection to detect the signal coverage of the uplink in real time. When the communication quality deteriorates, it will switch to a lower frequency band in time to continue communication, overcoming the problem that long-distance communication is prone to disconnection during 5G uplink transmission in the high frequency band, and enhancing the 5G uplink coverage.

[0020] Second, based on the obtained power attenuation and the energy distribution of the channel, and combined with the results of the link budget, the present invention determines the coverage situation in real time through multiple indicators, overcomes the inaccuracy of judging only based on simple variables such as SINR, enhances the robustness of 5G uplink coverage, and ensures the stability of communication transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall implementation process of the present invention;

[0022] Figure 2 It is a schematic diagram of the 5G NR system used in the present invention;

[0023] Figure 3 It is a block diagram of the implementation for calculating the proportion of the direct path tap energy in the total energy of all paths in the present invention;

[0024] Figure 4 It is a sub-flowchart of the working mode switching in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] The implementation of this example is based on Figure 2 A point-to-point wireless communication dual-band integrated system shown in the figure. The system includes a user terminal and a base station, and is applicable to a variety of communication scenarios and provides uninterrupted data transmission. However, the uplink coverage range in the figure is smaller than the downlink coverage range, resulting in waste of the downlink coverage range and also affecting the uplink transmission robustness.

[0027] Referring to Figure 1 , the implementation steps of this example in the dual-band integrated system are as follows:

[0028] Step 1, configure the uplink frequency band.

[0029] In addition to the original high-frequency band, an additional uplink in the low-frequency band is configured to obtain two frequency bands, namely the high-frequency band + the low-frequency band. The original high-frequency band is used to ensure downlink coverage, and the newly configured high-frequency band + the low-frequency band are used together to ensure uplink coverage.

[0030] Step 2, perform link budget to obtain the maximum allowable path loss of the high-frequency band and the low-frequency band.

[0031] The specific implementation method of this step is as follows:

[0032] Predict the uplink coverage when communicating in the high frequency band, and the prediction is as follows:

[0033] Predict the uplink coverage when communicating in the high frequency band, and obtain the maximum allowable path loss LH of the high frequency band:

[0034]

[0035] where; h BS is the base station height; h UT is the terminal height, with a value of 1.5 meters; fc is the center frequency; h is the building height; W is the street width; in the rural scenario, h takes 3m and W takes 3m; in the urban scenario, h takes 30m and W takes 10m.

[0036] Step 3: Conduct channel sounding in the high frequency band.

[0037] 3.1) The user sends a sounding reference signal SRS in the high frequency band, detects the millimeter wave channel power and noise power, and calculates the signal-to-interference-plus-noise ratio SINR1;

[0038]

[0039] where, P S is the signal power, and N1 is the noise power;

[0040] 3.2) The base station calculates the path loss L1 in the high frequency band according to the transmission power and the detected received power:

[0041] L1 = P T - P R ,

[0042] where P T represents the transmission power, and P R represents the received power;

[0043] 3.3) The base station performs an IDFT transform on the received sounding reference signal, transforms the channel into multiple paths, calculates the tap energy distribution matrix V k of the high frequency band channel by shaping the normalized energy on the taps, obtains the coordinated tap energy distribution, and obtains the proportion p1 of the tap energy of the direct path in the total energy of all paths:

[0044] Existing methods for calculating channel energy information include the method based on likelihood ratio test, the method based on machine learning theory for analysis, and the channel identification method based on fuzzy association analysis. The present invention adopts but is not limited to the channel identification method based on IDFT, obtains multiple paths through IDFT transform, and obtains the channel condition by comparing the energy ratio of the direct path.

[0045] Refer to Figure 3, the specific implementation of this step is as follows:

[0046] 3.3.1) Establish the channel as follows;

[0047]

[0048] where h u,s,n (t) is the channel impulse response, P n,m is the power of ray m in cluster n. For a pair of antenna elements of the base station and user k, namely u and s, c u,s,n,m represents the coefficient calculated from the field pattern and the initial random phase, d s represents the position of antenna element s, d u represents the position of antenna element u, λ is the wavelength, and are the unit vectors of the departure angle and arrival angle respectively, v n,m represents the Doppler frequency component;

[0049] 3.3.2) Represent the 2D distance between the base station and a user as d 2D , and calculate the probability P L of the line-of-sight (LOS) channel:

[0050]

[0051] where h UT is the height of the user;

[0052] 3.3.3) Calculate the received signal vector:

[0053] Assume that K users simultaneously use sounding reference signals (SRS) to access M subcarriers. Represent the SRS sequence vector S k of user k as:

[0054]

[0055] where, represents the basic sequence allocated to the base station (BS), α k = 2πn k / 8 represents the cyclic shift, n k is a constant, and n k ∈ {0, 1, 2, 3, 4, 5, 6, 7};

[0056] Suppose the pilot symbol transmitted on any m-th subcarrier, and the power of the symbol satisfies Represent the subcarrier channel in the frequency domain on antenna i as the channel matrix The diagonal elements of this channel matrix are equal to Obtain the received signal vector Y (i) :

[0057]

[0058] where n (i) is the additive white Gaussian noise vector with zero mean and power , and is the signal at the m-th tap;

[0059] 3.3.4) Multiply Y (i) by to obtain the initial least squares (LS) channel estimation result:

[0060]

[0061] where is the Hermitian complex conjugate transform of S k ;

[0062] 3.3.5) Calculate the tap energy distribution of user k on antenna i:

[0063] Perform the inverse Fourier IDFT transform on the channel estimation result in 5e) as follows to obtain the time-domain channel

[0064]

[0065] Express the time-domain channel in the following matrix form:

[0066]

[0067] where represents the m-th channel tap received by the base station BS in the time domain, and the basic components of are expressed as:

[0068]

[0069] where is the signal at the m-th tap, and is the noise at the m-th tap;

[0070] 3.3.6) Add the window to the time-domain channel after the IDFT transform in 5f) to obtain the denoised channel vector

[0071]

[0072]

[0073]

[0074] Among them, M k equals min(n j.k M / 8, L cp ), where n j.k is the minimum value of |n j - n k |, and L cp is the normalized equivalent CP length, is the noise cancellation threshold, and is the signal at the m-th tap;

[0075] 3.3.7) Normalize the energy at each tap to obtain the normalized energy matrix

[0076]

[0077] Among them, is the result after energy normalization of the m-th tap;

[0078] 3.3.8) Select the tap with the strongest energy and shape the normalized energy at this tap into a matrix V k that contains the conditional characteristics of the channel power distribution, to obtain the tap energy p z of the direct path after normalization and the total energy p m of all taps after normalization:

[0079]

[0080]

[0081] 3.3.9) According to the result of 3.3.8), calculate the proportion p1 of the tap energy of the direct path in the total energy of all paths:

[0082]

[0083] Step 4. The base station comprehensively selects the current data transmission frequency band according to multiple indicators such as the proportion of the tap energy of the direct path in the total energy of all paths, the detection signal power, and the signal-to-noise ratio, combined with the current service requirements, and feeds back the selection result to the user.

[0084] 4.1) Let the path loss, the proportion of the tap energy of the direct path in the total energy of all paths, and the frequency band switching thresholds corresponding to the signal-to-noise ratio detected be: LH, p0, SINR0;

[0085] 4.2) The base station compares the three indicators of path loss, the proportion of the tap energy of the direct path in the total energy of all paths, and the signal-to-noise ratio with the set thresholds:

[0086] If L1 is less than the path loss handover threshold LH, p1 is greater than the tap energy ratio threshold p0 of the direct path, and SINR1 is greater than the signal-to-noise ratio handover threshold SINR0, the base station will select the high frequency band and feedback the selection result to the user. The user will still select the high frequency band as the data transmission band and execute step 5;

[0087] If L1 is greater than the path loss handover threshold LH, or p1 is less than the tap energy ratio threshold p0 of the direct path, or SINR1 is less than the signal-to-noise ratio handover threshold SINR0, the base station will select the low frequency band and feedback the selection result to the user. The user will then switch to the low frequency band for data uplink transmission to enhance the uplink coverage stability and execute step 6.

[0088] Step 5: Track the uplink coverage status under high frequency band communication.

[0089] 5.1) The base station calculates the path loss L2 and the signal-to-interference-plus-noise ratio SINR2 under the current high frequency band using the reference signal received in the high frequency band:

[0090] The calculation formula for this step is the same as that in step 3:

[0091] 5.2) Before the time interval from the previous detection signal reaches one cycle, compare L2 and SINR2 with the handover threshold;

[0092] If L2 is greater than LH or SINR2 is less than SINR0, the base station will select the low frequency band and feedback the selection result to the user. The user will then switch to the low frequency band for data transmission to ensure uplink coverage and return to step 4;

[0093] Otherwise, the base station will feedback the selection result "high frequency band" to the user, and the user will maintain the low frequency band transmission unchanged and return to step 4.

[0094] Step 6: The user sends a detection signal again.

[0095] 6.1) After the time interval for sending the detection signal reaches one cycle, the user sends a detection signal again in the millimeter wave band. The base station calculates the ratio p4 of the tap energy of the direct path to the total energy of all paths using the currently received detection signal. The calculation process is the same as that in 3.3.1)-3.3.8) in step 1;

[0096] 6.2) The base station calculates the power attenuation L4 and the signal-to-interference-plus-noise ratio SINR4 of the detection signal based on the received detection signal and executes step 7;

[0097] Step 7: Monitor the uplink coverage situation.

[0098] Refer to Figure 4 , the base station analyzes the information fed back by the current data transmission band and feedbacks the selection result to the user, and the user performs a data transmission band switch:

[0099] If data transmission is currently carried out in the low-frequency band, when L4 is less than the threshold LH, p4 is greater than the tap energy ratio switching threshold p0, and SINR4 is greater than the signal-to-noise ratio switching threshold SINR0, the base station will select the high-frequency band and feedback the selection result to the user, and the user will switch the transmission band to the high-frequency band and return to step 5; otherwise, the base station will select the low-frequency band and feedback the selection result to the user, and the user will maintain the low-frequency band transmission unchanged to ensure uplink coverage and return to step 6.

[0100] If data transmission is currently carried out in the high-frequency band, when L4 is greater than the path loss switching threshold LH, or p4 is less than the tap energy ratio switching threshold p0, or SINR4 is less than the signal-to-noise ratio switching threshold SINR0, the base station will select the low-frequency band and feedback the selection result to the user, and the user will switch the transmission band to the low-frequency band to ensure uplink coverage and return to step 6; otherwise, the base station will select the high-frequency band and feedback the selection result to the user, and the user will maintain the high-frequency band transmission unchanged and return to step 5.

[0101] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for enhancing uplink coverage in a 5G mobile communication system, characterized in that, It includes the following: 1) An additional uplink in the low-frequency band is configured outside the original high-frequency band to utilize the original high-frequency band to ensure downlink coverage and use the two frequency bands of the original high-frequency band and the newly configured low-frequency band to ensure uplink coverage; 2) Perform link budget for the communication uplink in different scenarios to obtain the maximum allowable path loss LH when meeting the system performance requirements; 3) Detect the channel condition in the high-frequency band and calculate the path loss L1, the proportion p1 of the tap energy of the direct path in the total energy of all paths, and the signal-to-noise ratio SINR1; 4) Set the path loss switching threshold LH, the proportion switching threshold p0 of the tap energy of the direct path in the total energy of all paths, and the signal-to-noise ratio switching threshold SINR0 according to the current channel condition and communication environment; The base station comprehensively selects the current data transmission frequency band based on multiple indicators such as the proportion p1 of the tap energy of the direct path in the total energy of all paths, the detected path loss L1, and the signal-to-noise ratio SINR1, combined with the current service requirements, and feeds the selection result back to the user. The user performs frequency band switching according to the received feedback result; 5) When communicating in the high-frequency band, send a detection signal to monitor the uplink coverage condition, and the user performs frequency band switching according to the monitoring result; 6) When the time interval of the detection signal transmission reaches a cycle, the user sends a detection signal in the high-frequency band again. The base station calculates the path loss L4 in the current frequency band, the proportion p4 of the tap energy of the direct path of the high-frequency channel in the total energy of all paths, and the signal-to-interference-plus-noise ratio SINR4 of the detection signal using the currently received detection signal; 7) For the frequency band currently performing data transmission, the base station selects different frequency bands based on the calculation results in 6) and feeds them back to the user for frequency band switching to achieve uplink coverage and ensure the normal progress of uplink communication: 7a) For the frequency band currently using the high-frequency band for data transmission: If L4 is greater than the threshold LH, or p4 is less than the switching threshold p0, or SINR4 is less than the switching threshold SINR0, the base station will select the low-frequency band and feed the selection result back to the user, and the user switches the transmission frequency band to the low-frequency band to enhance the uplink coverage stability; Otherwise, the base station will select the high-frequency band and feed the selection result back to the user, maintaining the high-frequency band transmission unchanged; 7b) For the frequency band currently using the low-frequency band for data transmission: If L4 is less than the threshold LH, and p4 is greater than the switching threshold p0, and SINR4 is greater than the switching threshold SINR0, the base station will select the high-frequency band and feed the selection result back to the user, and the user switches the transmission frequency band to the high-frequency band; Otherwise, the base station will select the low-frequency band and feed the selection result back to the user, and the user maintains the low-frequency band transmission unchanged to enhance the stability of the uplink coverage.

2. The method according to claim 1, characterized in that In 2), performing link budget for the communication uplink in different scenarios is to predict the uplink coverage situation when communicating in the high-frequency band based on the base station height, the terminal height, the center frequency, the building height, and the scenario channel width. The formula is as follows: Wherein; h BS is the base station height, h UT is the terminal height, fc is the center frequency, h is the building height, W is the scene width, and LH is the maximum allowable path loss.

3. The method according to claim 1, characterized in that, In 3), calculating the path loss L1 is implemented as follows: L1 = P T -P R , Among which P T represents the transmit power, and P R represents the receive power.

4. The method according to claim 1, characterized in that In 3), calculating the signal-to-noise ratio SINR1, the formula is as follows: where P S is the signal power and N1 is the noise power.

5. The method according to claim 1, wherein In step 3), calculate the proportion p1 of the tap energy of the direct path in the total energy of all paths, and the implementation is as follows: 5a) The user sends a sounding reference signal SRS in the high frequency band; 5b) Establish the channel as follows; where h u,s,n (t) is the channel impulse response, P n,m is the power of ray m in cluster n, for a pair of antenna elements of the base station and user k, namely u and s, c u,s,n,m represents the coefficient calculated from the field pattern and the initial random phase, d s represents the position of antenna element s, d u represents the position of antenna element u, λ is the wavelength, and are the unit vectors of the departure angle and the arrival angle respectively, v n,m represents the Doppler frequency component; 5c) Represent the planar 2D distance between a base station and a user as d 2D , and calculate the probability P of the line-of-sight (LOS) channel L : where h UT is the height of the user; 5d) Calculate the received signal vector: Assume that K users simultaneously use SRS to access M subcarriers, and denote the SRS sequence vector S of user k as: k as follows: Among them, represents the basic sequence allocated to the BS, and α k = 2πn k / 8 represents the cyclic shift, and n k is a constant, and n k ∈ {0, 1, 2, 3, 4, 5, 6, 7}; Assume that the pilot symbol transmitted on any m-th subcarrier, and the power of the symbol satisfies Express the subcarrier channel in the frequency domain on antenna i as a channel matrix This channel matrix The diagonal elements of which are equal to Obtain the received signal vector Y (i) : where n (i) is an additive white Gaussian noise vector with power , and is the signal on the m-th tap; 5e) Multiply Y (i) by to obtain the initial least squares (LS) channel estimation result: Among them, is the Hermitian complex conjugate transformation of S k ; 5f) Calculate the tap energy distribution of user k on antenna i: The inverse Fourier IDFT transform is performed on the estimation result of the channel in 5e) as follows to obtain the time-domain channel The time-domain channel is expressed in the following matrix form: Among them, represents the m-th channel tap received by the base station BS in the time domain, The basic components of are expressed as: wherein is the signal on the m-th tap, is the noise on the m-th tap; 5g) The time-domain channel after IDFT transformation in 5f) Add a window Obtain the denoised channel vector Among them, M k equals min(n j.k M / 8, L cp ), where n j.k is the minimum value of |n j - n k |, and L cp is the normalized equivalent CP length, is the noise cancellation threshold, is the signal at the m-th tap; 5h) Normalize the energy on each tap to obtain a normalized energy matrix Among them, is the result after energy normalization of the m-th tap; 5i) Take the tap with the strongest energy and shape the normalized energy on this tap into a matrix V that contains the conditional characteristics of the channel power distribution k , obtaining the tap energy p of the direct path after normalization z and the total energy p of all taps after normalization m , calculate the proportion p1 of the tap energy of the direct path in the total energy of all paths: Among them, 6. The method according to claim 1, characterized in that, In step 5), the user performs frequency band switching according to the received feedback result. That is, compare the path loss L1, the proportion p1 of the tap energy of the direct path in the total energy of all paths, and the signal-to-interference-plus-noise ratio SINR1 within the receive bandwidth of the millimeter wave band system when the sounding signal is first sent, with the set thresholds respectively: If L1 is less than the path loss switching threshold LH, p1 is greater than the proportion switching threshold p0, and SINR1 is greater than the signal-to-noise ratio threshold SINR0 are all satisfied, the base station will select the high frequency band and feedback the selection result to the user, and the user still selects the high frequency band as the data transmission frequency band; If L1 is greater than the path loss switching threshold LH, or p1 is less than the proportion switching threshold p0, or SINR1 is less than the signal-to-noise ratio threshold SINR0, the base station will select the low frequency band and feedback the selection result to the user, and the user switches to the low frequency band for data uplink transmission to enhance the uplink coverage stability.

7. The method according to claim 1, characterized in that, In step 5), monitor the uplink coverage status when communicating in the high frequency band, and the implementation is as follows: 7a) The base station uses the reference signal received in the high frequency band to calculate the path loss L2 and the signal-to-interference-plus-noise ratio SINR2 under the current high frequency band; 7b) Before the time interval from the previous sounding signal has reached one period, compare L2 and SINR2 with the switching threshold: If L2 is greater than the path loss switching threshold LH or SINR2 is less than the signal-to-noise ratio switching threshold SINR0, the base station will select the low frequency band and feedback the selection result to the user, and the user switches to the low frequency band for data transmission to ensure the uplink coverage; Otherwise, the base station will select the high frequency band and feedback the selection result to the user, and the user maintains the high frequency band transmission unchanged.

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