Terahertz and low-frequency cooperative communication sensing integrated beam management method

Abstract

The invention provides a terahertz and low-frequency cooperative communication sensing integrated beam management method, which realizes positioning and user tracking by using a communication sensing integrated technology ISAC, further assists terahertz beam alignment, and realizes high-efficiency seamless beam switching in terahertz cells, between terahertz cells and between terahertz-low frequency bands. According to the method, firstly, low-frequency coarse sensing user position detection is utilized, and on the premise that the user position is determined through coarse sensing, fine scanning, user speed estimation and switching type decision determination are carried out in a specific area only through high frequency, so that the overhead can be remarkably reduced, and meanwhile, the accuracy and effectiveness of beam switching are ensured. The problems that high overhead is caused by frequent signaling transmission and information updating is not perceived in time and effective switching cannot be achieved due to insufficient signaling transmission are solved. According to the invention, a synchronization signal block SSB period is further designed, and the measurable speed requirement, the beam alignment capability requirement and the coverage range requirement can be met at the same time.

Description

Technical Field

[0001] The present invention relates to wireless communication technology, and in particular to a beam management technology suitable for a wireless mobile network where terahertz and Sub-6 GHz frequency bands coexist. Background Art

[0002] The future 6G network is designed to support new applications such as smart transportation and low-altitude economy, which require high data transmission rates and precise perception. Existing frequency bands are difficult to support huge data throughput and perception positioning accuracy, thus driving wireless communications to higher undeveloped frequency bands. The terahertz band with ultra-wideband is regarded as a key technology to achieve Tera-bps data transmission rate and millimeter-level perception resolution, but terahertz communication faces serious path loss and direct path LoS (Line-of-Sight) occlusion challenges, limiting network coverage. Current communication standards allow multiple frequency bands to coexist, namely dual-connectivity DC technology. DC allows users to connect to two different frequency bands at the same time, such as terahertz and Sub-6GHz bands. Sub-6GHz band is low frequency relative to terahertz. Compared with independent terahertz communication, DC provides a stable Sub-6 GHz link to improve network coverage, but the coexistence network of terahertz and low frequency has the following technical problems:

[0003] 1) In order to compensate for the terahertz path loss, the transceiver usually uses the power gain provided by the highly directional beam. However, the extremely narrow beam brings challenges to the beam management of mobile users, including frequent beam switching and severe beam misalignment effects, which leads to extremely high switching overhead and limits the effective data throughput of the terahertz network.

[0004] 2) Terahertz narrow beam alignment requires frequent control signaling transmission, which is very costly. Moreover, in high-density, high-mobility networks, extremely narrow beam alignment requires high precision, which can easily lead to beam misalignment, thereby reducing link stability. A design solution is needed to assist terahertz beam alignment and ensure seamless switching of users in the network.

[0005] 3) It is necessary to develop a dual-band switching solution for terahertz and low frequency based on the current communication standards and frame structure, and collaborate with the ISAC with integrated communication perception in the terahertz band to minimize the switching time for mobile users. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a mobile user beam management method for a terahertz and low frequency coexistence network, which utilizes dual-band cooperative communication perception integration technology to achieve stronger beam alignment and lower overhead beam switching.

[0007] The technical solution adopted by the present invention to solve the above technical problems is a beam management method integrating terahertz and low-frequency cooperative communication perception, comprising the following steps:

[0008] S1. Set the performance requirements of the terahertz ISAC network for communication and sensing services;

[0009] S2. Extract current network parameters, signal parameters and frame structure parameters;

[0010] S3. Calculate the average beam misalignment probability and the average beam switching overhead as a function of the user speed and the synchronization signal block SSB (Synchronization Signal Block) period according to the performance requirements of the terahertz ISAC network, the current network parameters, the signal parameters and the frame structure parameters;

[0011] S4. Obtain a feasible SSB period that meets the performance requirements of the terahertz ISAC network based on the average beam misalignment probability function and the average beam switching overhead function;

[0012] S5. Mobile user random access and data transmission phase:

[0013] User location detection steps: The Sub-6GHz macro base station sends synchronization signal blocks SSB according to the feasible SSB period to continuously monitor and locate the base station location information and user location information in the network. The base station location information and user location information are transmitted to the nearest terahertz base station through the backhaul link;

[0014] User random access step: the nearest terahertz base station sends a preset number of synchronization signal blocks SSB to the mobile user according to the feasible SSB period, the mobile user receives and measures the SSB, selects the SSB with the largest power and reports the SSB information to the nearest terahertz base station, and the nearest terahertz base station configures a beam for the user according to the SSB information reported by the mobile user and establishes a communication link;

[0015] Data transmission steps: The nearest terahertz base station uses the reference signal to continuously estimate the user speed and predict the user trajectory. When it is predicted that beam switching is required, it enters step S6; by sensing the obstacle position and predicting beam switching, the terahertz beam alignment capability is improved, and by predicting the user movement trajectory, the required beam switching is predicted, thereby reducing the control signaling overhead;

[0016] S6. Beam switching based on ISAC perception assistance: The nearest terahertz base station obtains candidate beam information based on the received SSB. One SSB represents the corresponding candidate beam and determines whether the candidate beam is blocked. If not, the nearest terahertz base station estimates the speed of the mobile user and the coverage distance of the current beam, triggers the terahertz same-station beam switching, and determines that the switched terahertz beam accesses the nearest terahertz base station; if so, determines whether the next nearest terahertz base station is available. When the next nearest terahertz base station is available, triggers the terahertz same-frequency cell switching, and determines that the switched terahertz beam accesses the next nearest terahertz base station; when the next nearest terahertz base station is not available, triggers the low-frequency band switching, and selects the low-frequency beam to access the Sub-6GHz macro base station.

[0017] The present invention utilizes the integrated sensing and communication technology ISAC (Integrated Sensing and Communication) to achieve positioning and user tracking, and then assists in terahertz beam alignment to achieve efficient seamless beam switching within a terahertz cell, between terahertz cells, and between terahertz and low-frequency bands. Conventional ISAC assistance only utilizes a single frequency band. There is insufficient accuracy for low frequencies, and for high frequencies, there are problems of high signal processing complexity and high signaling overhead. The present invention innovatively proposes to utilize low-frequency coarse sensing of user position detection. The size of the user is at the m level, and coarse-precision detection is sufficient, using sub-6GHz signals.

[0018] On the premise that the user's position is determined by coarse perception, terahertz is only used to perform precise scanning and accurate speed estimation in a specific area. Using THz signals to estimate user speed and determine switching type decisions can significantly reduce overhead while ensuring the accuracy and effectiveness of beam switching.

[0019] Specifically, the specific steps of terahertz co-station beam switching are as follows: the nearest terahertz base station divides the estimated coverage distance of the current beam by the time length of the feasible SSB cycle to obtain a speed threshold, and determines whether the estimated speed of the mobile user is less than or equal to the speed threshold. If so, the nearest terahertz base station transmits a preset number of SSBs according to the SSB cycle; if not, the nearest terahertz base station immediately transmits a preset number of SSBs; the mobile user receives and measures the SSB, selects the SSB with the largest power and reports the SSB information to the nearest terahertz base station; the nearest terahertz base station configures a beam for the user according to the SSB information reported by the mobile user, and completes the beam switching.

[0020] The specific steps of terahertz co-frequency cell switching are as follows: the nearest terahertz base station notifies the next nearest terahertz base station through the backhaul link to immediately transmit an SSB burst set, which represents all beams of the next nearest terahertz base station; the mobile user receives and measures the SSB burst set, selects the SSB with the largest power and reports the SSB information to the next nearest terahertz base station; the next nearest terahertz base station configures a beam for the user according to the SSB information reported by the mobile user, executes cell switching, completes the initial access to the next nearest terahertz base station, and completes the beam switching.

[0021] The specific steps of low-frequency band switching are as follows: the nearest terahertz base station notifies the Sub-6GHz macro base station through the backhaul link to immediately transmit an SSB burst set; the SSB burst set represents all beams of the Sub-6GHz macro base station, and the mobile user receives and measures the SSB burst set, selects the SSB with the highest power and reports the SSB information to the Sub-6GHz macro base station; the Sub-6GHz macro base station configures a beam for the user based on the SSB information reported by the mobile user, executes frequency band switching to complete the initial access to the Sub-6GHz macro base station, and completes the beam switching.

[0022] On this basis, the frame structure design of ISAC balances the high overhead caused by frequent signaling transmission and the problem of untimely perception information and ineffective switching caused by insufficient signaling transmission. The present invention designs a terahertz and low-frequency collaborative ISAC scheme and a beam management signaling cycle, namely the synchronization signal block SSB cycle, and finds the most suitable SSB cycle, which can simultaneously meet the requirements of measurable speed, beam alignment capability and coverage range.

[0023] The beneficial effects of the present invention are:

[0024] (1) In order to improve the terahertz narrow beam alignment performance and reduce the alignment overhead, the present invention provides a beam switching solution for terahertz and low frequency collaboration based on ISAC. The present invention can effectively reduce the beam misalignment probability and beam switching signaling overhead in the network, and is compatible with the existing 5G protocol.

[0025] (2) The present invention is an ISAC-based communication network, and designs an SSB cycle that can simultaneously meet the requirements of beam misalignment threshold, user speed and data load efficiency. The improved ISAC frame structure is compatible with the current air interface standard frame structure.

[0026] (3) The beam switching solution provided by the present invention is compatible with the current wireless communication network air interface. The proposed SSB period design is highly compatible with the current 5G frame structure and only makes minor adjustments to the current parameter set, which has high practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1This is a flow chart of the sensing resource allocation solution of the present invention.

[0028] Figure 2 A flow chart of a feasible SSB cycle design of the present invention.

[0029] Figure 3 The present invention is a flowchart of random access and data transmission of mobile users based on ISAC.

[0030] Figure 4 This is a flow chart of the terahertz and low frequency collaborative ISAC sensing auxiliary beam switching of the present invention.

[0031] Figure 5 This is the curve of network beam misalignment probability change under different numbers of beams.

[0032] Figure 6 This is the curve of network beam switching overhead change under different numbers of beams.

[0033] Figure 7 for the feasible SSB periods at different maximum user speeds. DETAILED DESCRIPTION

[0034] The present invention is applicable to wireless mobile networks where terahertz and Sub-6GHz frequency bands coexist, and the network can use the sensing function to provide assistance for beam alignment. The present invention provides a beam switching solution for terahertz and low-frequency collaboration based on ISAC for such networks. At the same time, the present invention provides a beam switching signaling cycle that simultaneously meets the requirements of beam misalignment threshold, user speed and data load efficiency.

[0035] The present invention is implemented in a network consisting of multiple randomly distributed terahertz base stations and Sub-6GHz base stations, where the terahertz base stations and Sub-6GHz base stations are independently distributed and linked by backhaul. There are multiple users moving in random directions in the network, accessing the nearest available base station based on the criterion of maximizing received power. In addition to communication nodes, the present invention also considers the problem of obstacles blocking communication signals, and considers all base stations and users in the network except communication nodes as potential obstacles to the typical communication node.

[0036] The present invention is described in detail below with reference to the accompanying drawings and simulation examples, and the practicability of the present invention is demonstrated.

[0037] The present invention is applicable to wireless mobile networks where terahertz and Sub-6GHz frequency bands coexist. The network can use the sensing function to provide assistance for beam alignment, thereby improving the probability of beam alignment and reducing the overhead of beam alignment. The present invention provides a beam switching solution for terahertz and low-frequency collaboration based on ISAC for such networks, and provides a signaling transmission cycle design that simultaneously meets the requirements of beam misalignment threshold, user speed and data load efficiency. Specifically, the present invention considers a network composed of multiple randomly distributed terahertz base stations and Sub-6GHz base stations, wherein the terahertz base stations and Sub-6GHz base stations are independently distributed and linked by backhaul. There are multiple users in the network that move in random directions, accessing the nearest available base station based on the criterion of maximizing received power. In addition to communication nodes, the present invention also considers the problem of obstacles blocking communication signals, and considers all base stations and users in the network except communication nodes as potential blockers of the typical communication node. The time-frequency signal structure proposed in the present invention is based on the orthogonal frequency division multiplexing (OFDM) frame structure and parameter set design of the current 5G communication system, has high practicality, and can be integrated into the existing system. Figure 1 As shown, the specific implementation scheme of the beam switching scheme proposed in the present invention is as follows:

[0038] Step S1: Set the performance requirements of the terahertz ISAC network for communication and perception services, and obtain the following three performance parameters: 1) Beam misalignment probability threshold 2) Maximum user speed v Q ; 3) Data load efficiency β Q .

[0039] Step S2 extracts network parameters, signal parameters and frame structure parameters, including the density of nodes in the network, the density of terahertz base stations, Sub-6GHz macro base stations, and the density of mobile users, respectively. T ,λ M ,λ U ; 2) Number of beams, number of beams of terahertz base station The number of beams used by the Sub-6GHz base station The beam widths are θ T ,θ M ; 3) Base station radius r B The signal parameters include 1) Terahertz frequency band: center frequency Total bandwidth RS Bandwidth RS duration 2) Sub-6GHz signal parameters: center frequency Total bandwidth Frame structure parameters include 1) frame length T F; 2) SSB duration: terahertz frequency band Sub-6GHz frequency band 3)SSB burst set size: terahertz frequency band Sub-6GHz frequency band

[0040] Step S3: Calculate the average beam misalignment probability and beam switching overhead. First, according to the maximum user speed v Q , calculate the average beam misalignment probability About user speed v and SSB period τ T The function is as follows

[0041]

[0042] in λ=λ T +λ M +λ U , function Next, calculate the average beam switching cost T SW About User Speed ​​and SSB Period τ T The function is as follows

[0043]

[0044] in represents the ceiling function,

[0045] Step S4 specifically includes the following sub-steps: Figure 2 As shown, the details are as follows:

[0046] Step S410: Set the beam misalignment threshold Substitute S3 to obtain the average beam misalignment probability as a function of the SSB period Solve the function of the maximum user speed with respect to the SSB period as follows

[0047]

[0048] Step S420: Use one-dimensional linear search to obtain the SSB cycle that supports the required speed, recorded as set A

[0049] A={τ T |v max (τ T )≥v Q}

[0050] Step S430: Set the maximum user speed v QSubstitute the average beam switching cost function to solve for the data payload efficiency β Q and the SSB period function β D (τ T ), as follows

[0051]

[0052] Step S440: Use one-dimensional linear search to obtain the SSB period that satisfies the data load efficiency, recorded as set B

[0053] B = {τ T |β D (τ T )≥β Q}

[0054] Step S450: Take the maximum value in the intersection of sets A and B as the SSB period, and configure the frame structure.

[0055]

[0056] Step S5 specifically includes the following sub-steps: Figure 3 As shown, the details are as follows:

[0057] Step S510: User location detection. The Sub-6GHz macro base station MBS performs the following operations according to the period τ T The SSB burst set is transmitted, and the SSB burst set includes all the macro base station beam directions. Based on the sensing information, the macro base station performs coarse precision positioning of the base station and user positions in the network, and transmits it to the nearest TBS through the backhaul connection, which is recorded as TBS1.

[0058] Step S520: User random access. TBS1 periodically transmits SSB burst sets to mobile users. The SSB burst sets include all TBS base station beam directions. The user receives SSB and measures the power, and reports the beam information corresponding to the SSB with the highest power to TBS1. TBS1 configures the beam to serve the user and establishes a communication link.

[0059] Step S530: Data transmission. TBS1 uses the reference signal in the data frame to perform fine-precision sensing, continuously estimate the user speed, predict the trajectory, and predict the required beam switching type.

[0060] S6. Same-site beam switching, same-frequency cell switching and low-frequency band switching based on ISAC perception assistance.

[0061] 1) First, based on the acquired perception information, TBS1 selects the switching type and the corresponding command transmission according to different situations. If the candidate beam of TBS1 is not blocked, the terahertz co-station beam switching is triggered, that is, when the high frequency is available (i.e. not blocked), the high frequency transmission is used first. Specifically, TBS1 estimates the speed of the mobile user MT and the coverage distance d of the current beam b .like Then TBS1 immediately transmits 4 synchronization signal blocks SSB, representing the corresponding 4 candidate beams, to facilitate the MT end to perform beam switching measurement and candidate beam selection.

[0062] 2) If the candidate beam of TBS1 is blocked and the next closest base station TBS2 is available, the terahertz same-frequency cell switching is triggered. Specifically, TBS1 notifies the next closest base station TBS2 to immediately transmit an SSB burst set through the backhaul link. The SSB burst set represents all beams of TBS2, which is convenient for the MT to perform measurements and access new cells.

[0063] 3) If the next closest base station TBS2 is not available, the low frequency band switching is triggered. TBS1 notifies the MBS to immediately transmit an SSB burst set through the backhaul link. The SSB burst set represents all beams of the MBS and is used by the user end to perform candidate beam measurement and frequency band switching.

[0064] like Figure 4 As shown, the details are as follows:

[0065] Step S610: MBS transmits base station location information and user location information to TBS1. TBS1 determines whether the candidate beam is blocked. If not, it proceeds to step S620 to trigger terahertz co-station beam switching; if yes, it proceeds to step S640.

[0066] Step S620: TBS1 estimates the speed of MT and the coverage distance d of the current beam b .

[0067] Step S630: TBS1 determines whether the user receives the preset SSB burst set at the current speed. Specifically, it can be divided into the following sub-steps:

[0068] Sub-step S631: If That is, if yes, TBS1 transmits 4 candidate SSBs according to the preset SSB period, represents the corresponding candidate beams, and proceeds to sub-step S633.

[0069] Sub-step S632: If That is, if the answer is no, TBS1 immediately transmits the candidate SSB and proceeds to sub-step S633.

[0070] d bRefers to the current beam coverage distance, τ T Refers to the current transmission period. The user needs to select and report a candidate beam before disconnection, that is, it is necessary to receive τ within the coverage distance of the current beam. T SSB is sent periodically. If the speed is greater than d b / τ T That is to say, within the coverage area, it is possible that an SSB is not received, and the selection and reporting of the candidate beam cannot be completed. When the user leaves the current beam coverage, a disconnection will occur, that is, the beam is misaligned.

[0071] Sub-step S633: The user receives and measures the SSB, selects the SSB with the highest power and reports its information. TBS1 configures a beam for the user based on the information and completes beam switching.

[0072] Step S640: TBS1 determines whether base station TBS2 is available. Specifically, it can be divided into the following sub-steps:

[0073] Sub-step S641: If the next closest base station TBS2 is available, trigger the terahertz same-frequency cell switching. Specifically, TBS1 notifies the next closest base station TBS2 through the backhaul link to immediately transmit an SSB burst set. The SSB burst set represents all beams of TBS2. The user measures the SSB burst set, initiates random access with the new base station, performs cell switching, and completes beam switching.

[0074] Sub-step S642: If the next closest base station TBS2 is unavailable, trigger low frequency band switching. Specifically, TBS1 notifies MBS via the backhaul link to immediately transmit an SSB burst set. The SSB burst set represents all beams of the MBS. The user measures the SSB burst set and initiates random access with the low frequency base station, performs band switching, and completes beam switching.

[0075] The present invention will further illustrate the effectiveness of the proposed ISAC-based terahertz and low-frequency collaborative beam switching scheme and the trend of the optimal SSB period changing with system parameters. By comparing the beam misalignment probability and beam switching overhead of a system that does not adopt the scheme of the present invention, it is proved that the scheme provided by the present invention can provide significant performance gains.

[0076] Figure 5 The curve of network beam misalignment probability under different numbers of beams is shown in Figure 2. In typical urban scenarios, the terahertz and low-frequency collaborative ISAC scheme can reduce the average beam misalignment probability by 34.1%. In typical high-speed scenarios, the proposed scheme can reduce the beam misalignment probability by 42.9%.

[0077] Figure 6The curve of network beam switching overhead changes under different numbers of beams. In typical urban scenarios, the terahertz and low-frequency collaborative ISAC solution can reduce the average beam switching overhead by 41.9%. In typical high-speed scenarios, the proposed solution can reduce the beam switching overhead by 46.1%. And the proposed solution shows greater advantages when using large-scale narrow beams.

[0078] Figure 7 is the feasible SSB period at different maximum user speeds. The beam alignment probability threshold is The data load efficiency requirement is It is represented by a gray strip. When the maximum user speed v Q =250km / h, a shorter SSB cycle is required, about 15-25 milliseconds. Q =120km / h, a longer SSB cycle is required, about 45-65 milliseconds.

[0079] In summary, the present invention provides a beam switching scheme for terahertz and low frequency collaboration based on ISAC and an SSB period that simultaneously meets the requirements of beam misalignment threshold, user speed and data load efficiency for wireless mobile networks where terahertz and Sub-6GHz frequency bands coexist. The scheme proposed in the present invention significantly reduces the beam misalignment probability and beam switching overhead of the network, and the designed SSB period is compatible with the current 5G standard parameter set, with high compatibility and high practicality.

Claims

1. A beam management method integrating terahertz and low-frequency cooperative communication perception, characterized in that: The steps include: S1. Set the performance requirements of the terahertz ISAC network for communication and sensing services; S2. Extract current network parameters, signal parameters and frame structure parameters; S3. Calculate the average beam misalignment probability and the average beam switching overhead as a function of the user speed and the synchronization signal block SSB period according to the performance requirements of the terahertz ISAC network, the current network parameters, the signal parameters and the frame structure parameters; S4. Obtain a feasible SSB period that meets the performance requirements of the terahertz ISAC network based on the average beam misalignment probability function and the average beam switching overhead function; S5. Mobile user random access and data transmission phase: User location detection steps: The Sub-6GHz macro base station sends synchronization signal blocks SSB according to the feasible SSB period to continuously monitor and locate the base station location information and user location information in the network. The base station location information and user location information are transmitted to the nearest terahertz base station through the backhaul link; User random access step: the nearest terahertz base station sends a preset number of synchronization signal blocks SSB to the mobile user according to the feasible SSB period, the mobile user receives and measures the SSB, selects the SSB with the largest power and reports the SSB information to the nearest terahertz base station, and the nearest terahertz base station configures a beam for the user according to the SSB information reported by the mobile user and establishes a communication link; Data transmission step: The nearest terahertz base station uses the reference signal to continuously estimate the user speed and predict the user trajectory, and enters step S6 when it is predicted that beam switching is required; S6. Beam switching based on ISAC perception assistance: The nearest terahertz base station determines the candidate beam based on the SSB measurement information reported by the user, one SSB corresponds to one candidate beam, and determines whether the candidate beam is blocked. If not, the nearest terahertz base station estimates the speed of the mobile user and the coverage distance of the current beam, triggers the terahertz same-station beam switching, and determines that the switched terahertz beam accesses the nearest terahertz base station; if so, it determines whether the next nearest terahertz base station is available. When the next nearest terahertz base station is available, it triggers the terahertz same-frequency cell switching, and determines that the switched terahertz beam accesses the next nearest terahertz base station; when the next nearest terahertz base station is not available, it triggers the low-frequency band switching, and selects the low-frequency beam to access the Sub-6GHz macro base station.

2. The method according to claim 1, characterized in that: The specific steps of terahertz co-station beam switching are as follows: the nearest terahertz base station divides the estimated coverage distance of the current beam by the time length of the feasible SSB cycle to obtain a speed threshold, and determines whether the estimated speed value of the mobile user is less than or equal to the speed threshold. If so, the nearest terahertz base station transmits a preset number of SSBs according to the SSB cycle; if not, the nearest terahertz base station immediately transmits a preset number of SSBs; the mobile user receives and measures the SSB, selects the SSB with the largest power, and reports the SSB information to the nearest terahertz base station; The nearest terahertz base station configures the beam for the user based on the SSB information reported by the mobile user and completes the beam switching.

3. The method according to claim 1, characterized in that: The specific steps of terahertz intra-frequency cell switching are as follows: The nearest terahertz base station notifies the next nearest terahertz base station through the backhaul link to immediately transmit an SSB burst set, which represents all beams of the next nearest terahertz base station; the mobile user receives and measures the SSB burst set, selects the SSB with the largest power and reports the SSB information to the next nearest terahertz base station; the next nearest terahertz base station configures a beam for the user according to the SSB information reported by the mobile user, performs cell switching, completes the initial access to the next nearest terahertz base station, and completes the beam switching.

4. The method according to claim 1, characterized in that: The specific steps of low-frequency band switching are as follows: the nearest terahertz base station notifies the Sub-6GHz macro base station through the backhaul link to immediately transmit an SSB burst set; the SSB burst set represents all beams of the Sub-6GHz macro base station, and the mobile user receives and measures the SSB burst set, selects the SSB with the largest power and reports the SSB information to the Sub-6GHz macro base station. The Sub-6GHz macro base station configures a beam for the user based on the SSB information reported by the mobile user, executes frequency band switching, completes the initial access to the Sub-6GHz macro base station, and completes the beam switching.

5. The method according to claim 1, characterized in that: The performance requirements of terahertz ISAC networks include the beam misalignment probability threshold Maximum user rate v Q and data payload efficiency β Q .

6. The method according to claim 5, characterized in that Current network parameters include: the density of terahertz base stations λ T 、Sub-6GHz Acer's density λ M and the density of mobile users λ U , the number of beams used by the terahertz base station and beam width θ T 、Number of beams used by Sub-6GHz base stations and beam width θ M ; Base station radius r B ; Signal parameters include the center frequency of the terahertz signal Total bandwidth Reference signal bandwidth and duration The center frequency of Sub-6GHz signal and total bandwidth The frame structure parameters include frame length T F , the duration of the synchronization signal block SSB in the terahertz frequency band The duration of the synchronization signal block SSB in the Sub-6GHz band SSB burst set size in the terahertz band and SSB burst set size for Sub-6GHz band 7. The method according to claim 6, characterized in that: Average beam misalignment probability The rate is related to the user speed v and the SSB period τ T The function is: Among them, c is the speed of light, and the intermediate quantity Total density λ=λ T +λ M +λ U , the intermediate amount Intermediate function x is the independent variable; Average beam switching overhead T SW About user speed v and SSB period τ T The function is: in, Represents the ceiling function, function r is the independent variable.

8. The method according to claim 7, characterized in that: The specific method of obtaining a feasible SSB period that meets the performance requirements of the terahertz ISAC network based on the average beam misalignment probability function and the average beam switching cost function is: Beam Misalignment Threshold Average beam misalignment probability Function, get the maximum user speed v max About SSB period τ T Function: Use one-dimensional linear search to obtain the maximum user speed v max Required SSB cycle τ T , recorded as set A: A={τ T |v max (t T )≥v Q }; Set the user speed threshold v Q Average beam switching cost function T SW , we get the data load efficiency β D About SSB period τ T Function: The SSB period τ that meets the data load efficiency requirements is obtained by one-dimensional linear search. T , recorded as set B: B={τ T |b D (t T )≥β Q }; Take the maximum value in the intersection of sets A and B as the final SSB period τ T :

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