A closed-loop transcranial electrical stimulation method, apparatus, device, and storage medium

Abstract

The application discloses a closed-loop transcranial electrical stimulation method, device, equipment and storage medium, and comprises the following steps of brain electrical signal acquisition, autoregressive model construction and prediction, phase extraction, phase difference calculation and adjustment, AM signal generation and TIS stimulation signal generation. The method can predict future brain electrical signals by using an autoregressive model, and combines a phase extraction technology to ensure that an electrical stimulation signal is synchronized with a specific phase of target brain electrical activity, the generated stimulation signal is used for nerve regulation in a TIS mode, the overlap of the stimulation signal interference frequency band and the brain electrical signal spectrum is effectively avoided, and therefore the space-time accuracy and individualized adjustment capability of nerve regulation are greatly improved. Moreover, the TIS signal can noninvasively regulate deep brain areas, and has better brain area stimulation effect. The application relates to nerve regulation technology.

Description

TECHNICAL FIELD

[0001] The present application relates to neuromodulation technology, and in particular to a closed-loop transcranial electrical stimulation system. BACKGROUND

[0002] Neuromodulation technology has made significant progress in treating neurological diseases and enhancing cognitive function. Traditional neuromodulation methods, such as transcranial electrical stimulation (tES) and transcranial magnetic stimulation (TMS), rely on pre-set stimulation parameters to affect brain activity in a fixed manner. However, this "open-loop" stimulation approach has limitations, mainly manifested in large individual differences in stimulation effects, low repeatability, and unintentional activation of non-target brain regions. These limitations hinder precise neuromodulation and limit its widespread clinical application.

[0003] Closed-loop neuromodulation technology effectively overcomes the shortcomings of traditional methods by monitoring neural activity in real time and dynamically adjusting stimulation parameters according to individual brain states. Closed-loop systems can precisely lock the activity of specific brain regions through neural feedback, thereby improving the spatial and temporal accuracy of stimulation and enhancing the specificity and effectiveness of neuromodulation. This technology has shown great potential in multiple fields, particularly in treating neurological diseases such as depression, Parkinson's disease, and epilepsy.

[0004] Among them, the technology combining closed-loop transcranial electrical stimulation (tES) with electroencephalogram (EEG) has received widespread attention. By monitoring the electrical activity of the brain in real time through EEG, the closed-loop system can precisely apply stimulation under specific brain states, thereby optimizing the treatment effect. However, a key challenge in the process of electrical stimulation is that the electric field signal interferes with EEG recording, affecting the accurate monitoring of neural activity. This interference significantly reduces the accuracy of the closed-loop control system. SUMMARY

[0005] To at least partially solve one of the technical problems existing in the prior art, the purpose of the present application is to provide a closed-loop transcranial electrical stimulation method, device, equipment and storage medium, which can reduce the interference of stimulation artifacts on EEG signals and reconstruct high-quality electroencephalogram signals.

[0006] The first technical solution adopted by the present application is:

[0007] A closed-loop transcranial electrical stimulation method, comprising the following steps:

[0008] Collecting electroencephalogram signals for a specific duration to obtain electroencephalogram data;

[0009] Using the least squares method to construct an autoregressive model to analyze the collected electroencephalogram data and give a prediction signal of the electroencephalogram; performing Hilbert transform on the prediction signal to obtain the instantaneous phase information θ p (t) of the signal;

[0010] calculating a phase sequence θ of the stimulation envelope signal based on the phase of the prediction signal and a set target phase difference Δθ b (t);

[0011] multiplying the envelope signal with a high-frequency carrier signal to obtain an AM signal, and outputting the AM signal through a pair of electrodes, so that closed-loop AM-tACS can be realized.

[0012] performing product integration and difference transformation on the generated AM signal to decompose the AM signal into two TIS stimulation signals, and outputting the two TIS signals.

[0013] According to some embodiments of the present application, the collected electroencephalogram data is band-pass filtered before being analyzed.

[0014] According to some embodiments of the present application, the prediction signal is band-pass filtered before being subjected to Hilbert transformation.

[0015] According to some embodiments of the present application, the envelope signal B(t)=sin[θ b (t)] and the carrier signal

[0016] C(t)=cos[θ c (t)].

[0017] According to some embodiments of the present application, the two TIS signals are a first TIS signal and a second TIS signal, and the first TIS signal is: the second TIS signal is:

[0018] The second technical solution adopted by the present application is:

[0019] A closed-loop transcranial electrical stimulation device for performing the closed-loop transcranial electrical stimulation method described above, comprising:

[0020] An electroencephalogram amplifier for collecting electroencephalogram signals for a certain duration to obtain electroencephalogram data;

[0021] An autoregressive model prediction module for analyzing the collected electroencephalogram data and giving a prediction signal of the electroencephalogram;

[0022] A phase extraction module for performing Hilbert transformation on the prediction signal to obtain instantaneous phase information of the signal;

[0023] A phase difference calculation and adjustment module for calculating a phase sequence of a stimulation envelope signal;

[0024] An AM signal generation module is configured to multiply the envelope signal and a high-frequency carrier signal to obtain an AM signal, and output the AM signal through a pair of electrodes to realize closed-loop AM-tACS.

[0025] A TIS stimulation signal generation module is configured to perform integration and difference transformation on the generated AM signal to decompose the AM signal into two TIS stimulation signals, and output the two TIS signals respectively.

[0026] According to some embodiments of the present application, the closed-loop transcranial electrical stimulation device further comprises a first band-pass filtering module configured to perform band-pass filtering on the collected electroencephalogram data.

[0027] According to some embodiments of the present application, the closed-loop transcranial electrical stimulation device further comprises a second band-pass filtering module configured to perform band-pass filtering on the predicted signal.

[0028] The third technical solution adopted by the present application is:

[0029] An electronic device comprises a processor and a memory, and the memory stores at least one instruction, at least one program, a code set or an instruction set, which are loaded and executed by the processor to implement the closed-loop transcranial electrical stimulation method as described above.

[0030] The fourth technical solution adopted by the present application is:

[0031] A computer-readable storage medium stores at least one instruction, at least one program, a code set or an instruction set, which are loaded and executed by a processor to implement the closed-loop transcranial electrical stimulation method as described above.

[0032] The present application has the following beneficial effects:

[0033] The present method predicts future electroencephalogram signals by using an autoregressive model, and combines a phase extraction technique to ensure that the electrical stimulation signal is synchronized with the specific phase of the target electroencephalogram activity, and the generated stimulation signal is used for neural regulation in a TIS manner, effectively avoiding the overlap of the stimulation signal interference frequency band and the electroencephalogram signal spectrum, thereby greatly improving the spatiotemporal accuracy and individualized adjustment ability of neural regulation. Moreover, the TIS signal can non-invasively regulate deep brain regions, and has better brain region stimulation effect. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following introduces the drawings of the related technical solutions in the embodiments of the present application or the prior art. It should be understood that the drawings in the following introduction are only for the convenience of clearly describing part of the embodiments of the technical solutions of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the premise that there is no creative labor.

[0035] Figure 1 is the working flow chart of the closed-loop transcranial electrical stimulation device in the embodiments of the present application.

[0036] Reference signs: 101-first TIS signal end, 102-AM signal generation module, 103-second TIS signal end, 104-carrier signal, 105-envelope signal, 106-phase sequence, 107-target phase difference, 108-phase calculation module, 109-Hilbert transform module, 201-electroencephalogram amplifier, 202-first band-pass filter module, 203-autoregressive model, 204-prediction module, 205-second band-pass filter module. DETAILED DESCRIPTION

[0037] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. For the step numbers in the following embodiments, they are only set for the convenience of description and explanation, and the order between the steps is not limited in any way, and the execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0038] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0039] In the description of the present application, the meaning of several is one or more, and the meaning of multiple is more than two, greater than, less than, more than, etc. are understood as not including the number, and above, below, etc. are understood as including the number. If the first, second, etc. are described, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of indicated technical features.

[0040] In the description of the present application, the words such as arrangement, installation, connection, etc. should be understood broadly unless otherwise explicitly limited, and the person skilled in the art can determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0041] Embodiment 1

[0042] The present embodiment provides a closed-loop transcranial electrical stimulation method, comprising the following steps:

[0043] S100. Collecting brain electrical signals for a certain duration, for example, the brain electrical signals can be F1 electrode signals, obtaining brain electrical data;

[0044] S200. Using the least square method to construct an autoregressive model (AR model), analyzing the collected brain electrical data, and giving a predicted signal of the brain electrical signals;

[0045] S300. Hilbert transforming the predicted signal to obtain the instantaneous phase information θ p (t) of the signal;

[0046] S400. Based on the phase of the predicted signal and the set target phase difference Δθ (for example, 90 degrees), calculating the phase sequence θ b (t) of the stimulation envelope signal;

[0047] S500. Multiplying the envelope signal with a high-frequency carrier signal to obtain an AM signal, and outputting the AM signal through a pair of electrodes, which can realize closed-loop AM-tACS;

[0048] S600. Integrating and difference transforming the generated AM signal to decompose it into two TIS stimulation signals, and outputting the two TIS signals respectively, which can realize precise closed-loop electrical stimulation on specific brain areas or deep brain areas.

[0049] Wherein, the AM signal is equivalent to the combination of the two TIS signals, which can be regarded as a special form of TIS (TIS two pairs of electrodes in parallel), so that the signal is output through a pair of electrodes, which can realize closed-loop AM-tACS.

[0050] Further, before analyzing the collected brain electrical data, the collected brain electrical data is first band-pass filtered. The filtering here is to eliminate the interference of electrical stimulation and polarization voltage on the EEG signal, limit the signal within the target frequency range, and remove the electrical stimulation artifact and polarization voltage.

[0051] Further, before Hilbert transforming the predicted signal, the predicted signal is first band-pass filtered. The filtering here is to extract the brain electrical activity of the target frequency band (for example, Theta rhythm), and further focus on the brain electrical signals of the target frequency band by applying a band-pass filter to the predicted brain electrical signals.

[0052] Further, the envelope signal is B(t) = sin[θ b (t)], and the carrier signal is C(t) = cos[θ c (t)]. In the subsequent integration and difference transformation of the generated AM signal, the two TIS signals are the first TIS signal and the second TIS signal, where the first TIS signal is: The second TIS signal is:

[0053] Specifically, for the collection of electroencephalogram signals, the collection duration is 2 to 4 seconds, which provides sufficient data samples for subsequent prediction analysis. The prediction signal given by the autoregressive model is at least 1 second of future electroencephalogram activity signals.

[0054] The closed-loop transcranial electrical stimulation method uses TIS technology to generate high-frequency interference signals in vivo, effectively reducing the interference of stimulation artifacts on EEG signals, and has higher spatial specificity and depth selectivity, making the regulation of target brain regions more accurate. This technology can ensure the high-quality reconstruction of EEG signals, making the monitoring of brain activity more accurate during stimulation, thereby improving the overall accuracy of the closed-loop regulation system. Moreover, TIS signals can non-invasively regulate deep brain regions, with better brain region stimulation effect.

[0055] The collected electroencephalogram signals are modeled by an autoregressive model (AR model), and future 1 second or more of electroencephalogram data is predicted. Compared with the traditional method relying on real-time signal regulation strategy, the AR model can predict the future neural state in advance, thereby providing more sufficient data support for the generation of stimulation. This prediction capability makes the regulation more accurate, reduces the delay and enhances the responsiveness of the system.

[0056] The method generates a stimulation signal that matches the target phase difference based on the instantaneous phase of the electroencephalogram signal, achieving phase-specific neural regulation. For example, the system can accurately control the stimulation phase according to the set phase difference (such as 90 degrees), so that the electrical stimulation waveform is synchronized or delayed with the electroencephalogram signal at a specific phase relationship. This phase-specific regulation can enhance the regulation effect on specific rhythms of the brain, and is particularly suitable for precise regulation of specific brain regions and frequency bands.

[0057] Embodiment 2

[0058] Referring to Figure 1 , the embodiment provides a closed-loop transcranial electrical stimulation device, comprising:

[0059] The electroencephalogram amplifier 201 is used to collect electroencephalogram signals for a specific duration to obtain electroencephalogram data;

[0060] An autoregressive model prediction module, comprising an autoregressive model 203 and a prediction module 204, is used to analyze the collected electroencephalogram data and give a prediction signal of the electroencephalogram;

[0061] A phase extraction module, comprising a phase calculation module 108 and a Hilbert transform module 109, is used to perform Hilbert transform on the prediction signal to obtain instantaneous phase information of the signal;

[0062] A phase difference calculation and adjustment module is used to adjust the envelope signal based on the target phase difference 107, and calculate the phase sequence 106 of the stimulation envelope signal;

[0063] An AM signal generation module 102 is used to multiply the adjusted envelope signal 105 with the high-frequency carrier signal 104 to obtain an AM signal, and output the AM signal through a pair of electrodes to realize closed-loop AM-tACS;

[0064] A TIS stimulation signal generation module is used to integrate and difference transform the generated AM signal to decompose it into two TIS stimulation signals, which are output through the first TIS signal end 101 and the second TIS signal end 103 respectively.

[0065] Further, the closed-loop transcranial electrical stimulation device further comprises a first band-pass filtering module 202 for band-pass filtering the collected electroencephalogram data.

[0066] Further, the closed-loop transcranial electrical stimulation device further comprises a second band-pass filtering module 205 for band-pass filtering the prediction signal.

[0067] The working process of the closed-loop transcranial electrical stimulation device is as follows:

[0068] After the electroencephalogram amplifier 201 collects and amplifies the electroencephalogram signal, it is band-pass filtered by the first band-pass filtering module 202, and then the electroencephalogram data is analyzed by the autoregressive model 203 and the prediction model 204 to give a prediction signal. The prediction signal is band-pass filtered by the second band-pass filtering module 205 and then enters the phase extraction module, which is Hilbert transformed by the Hilbert transform module 109, and the instantaneous phase information θ p (t) is calculated by the phase calculation module 108.

[0069] The envelope signal is adjusted based on the target phase difference 107 to obtain the phase sequence 106, and finally the adjusted envelope signal 105, B(t) = sin[θ b (t)], is obtained. The carrier signal 104 is introduced, which is C(t) = cos[θ c(t)] is multiplied with the carrier signal 104 and input to the AM signal generation module 102. The AM signal generation module 102 is subjected to product integration and difference transformation to obtain a first TIS signal and a second TIS signal, respectively, wherein the first TIS signal is: The second TIS signal is: The first TIS signal and the second TIS signal are input to the first TIS signal end 101 and the second TIS signal end 103, respectively, to complete signal output.

[0070] Embodiment 3

[0071] The embodiments of the present application also provide an electronic device, which comprises a processor and a memory. The memory stores at least one instruction, at least one program, a code set or an instruction set. The at least one instruction, the at least one program, the code set or the instruction set is loaded and executed by the processor to implement the closed-loop transcranial electrical stimulation method described above.

[0072] It can be understood that the memory can include a random access memory (RAM) and a read-only memory (ROM). Optionally, the memory includes a non-transitory computer-readable storage medium. The memory can be used to store instructions, programs, codes, code sets or instruction sets. The memory can include a program storage area and a data storage area, wherein the program storage area can store instructions for implementing an operating system, instructions for at least one function, instructions for implementing various method embodiments described above, etc.; and the data storage area can store data created according to the use of the server, etc.

[0073] The processor can include one or more processing cores. The processor connects various parts within the entire server by various interfaces and lines, executes various functions of the server and processes data by running or executing instructions, programs, code sets or instruction sets stored in the memory, and calling data stored in the memory. Alternatively, the processor can be implemented in at least one of a hardware form of a digital signal processing (DSP), a field-programmable gate array (FPGA), and a programmable logic array (PLA). The processor can be integrated with one or several combinations of a central processing unit (CPU) and a modem. Among them, the CPU mainly processes operating systems and application programs; the modem is used to process wireless communication. It can be understood that the above-mentioned modem can also not be integrated into the processor, but be realized by a single chip.

[0074] Since the electronic device is an electronic device corresponding to the closed-loop transcranial electrical stimulation method of the embodiments of the present application, and the principle of solving problems of the electronic device is similar to that of the method, the implementation of the electronic device can be referred to the implementation process of the above-mentioned method embodiments, and the repeated parts will not be described again.

[0075] Embodiment 4

[0076] The embodiments of the present application also provide a computer readable storage medium, wherein at least one instruction, at least one program, a code set or an instruction set are stored in the storage medium, and the at least one instruction, the at least one program, the code set or the instruction set are loaded and executed by the processor to realize the above-mentioned closed-loop transcranial electrical stimulation method.

[0077] Those skilled in the art can understand that all or part of the steps of various methods in the above embodiments can be instructed by programs to relevant hardware, and the programs can be stored in a computer readable storage medium, including Read-Only Memory (ROM), Random Access Memory (RAM), Programmable Read-only Memory (PROM), Erasable Programmable Read Only Memory (EPROM), One-time Programmable Read-Only Memory (OTPROM), Electrically-Erasable Programmable Read-Only Memory (EEPROM), Compact Disc Read-Only Memory (CD-ROM) or other optical disk storage, magnetic disk storage, magnetic tape storage, or any other medium that can be used to carry or store data which can be read by a computer.

[0078] Since the storage medium is a storage medium corresponding to the closed-loop transcranial electrical stimulation method of the embodiments of the present application, and the problem solving principle of the storage medium is similar to that of the method, the implementation of the storage medium can refer to the implementation process of the above method embodiments, and the repeated parts will not be described again.

[0079] Embodiment 5

[0080] In some possible implementation manners, various aspects of the method of the embodiments of the present application can also be implemented in the form of a program product, which includes program codes for causing a computer device to execute the steps of the closed-loop transcranial electrical stimulation method according to various exemplary embodiments of the present application described above in the specification when the program product is run on the computer device. Among them, the executable computer program code or "code" for executing various embodiments can be written in a high-level programming language such as C, C++, C#, Smalltalk, Java, JavaScript, Visual Basic, Structured Query Language (for example, Transact-SQL), Perl, or in various other programming languages.

[0081] It should be understood that various aspects of the application can be implemented in hardware, software, firmware or a combination of them. In the above embodiments, various steps or methods can be implemented in software or firmware which is stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, and in another embodiment, any of the following technologies, known in the art, or their combination, can be used: discrete logic circuitry having logic gates for implementing logic functions upon an application of data signals, application-specific integrated circuits having appropriate combinational logic gates, programmable gate arrays (PGA), field-programmable gate arrays (FPGA), and so forth.

[0082] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, a person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples, without contradiction.

[0083] The above embodiments are only for the purpose of illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the essence of the present application should be covered within the protection scope of the present application.

Claims

1. A closed-loop transcranial electrical stimulation device for performing a closed-loop transcranial electrical stimulation method, characterized in that: include: An EEG amplifier, which is used to collect EEG signals and obtain EEG data; The autoregressive model prediction module is used to analyze the collected EEG data and provide EEG prediction signals; A phase extraction module, configured to perform a Hilbert transform on the predicted signal to obtain instantaneous phase information of the signal; A phase difference calculation and adjustment module, which is used to calculate the phase sequence of the stimulus envelope signal; An AM signal generation module is configured to multiply the envelope signal with a high-frequency carrier signal to obtain an AM signal, and output the AM signal through a pair of electrodes to implement a closed-loop AM-tACS; A TIS stimulation signal generation module is used to perform product and difference transformation on the generated AM signal, decompose it into two TIS stimulation signals, and output the two TIS signals respectively; The closed-loop transcranial electrical stimulation method comprises the following steps: Collect EEG signals and obtain EEG data; The autoregressive model is constructed using the least squares method to analyze the collected EEG data and give the EEG prediction signal; the prediction signal is subjected to Hilbert transform to obtain the instantaneous phase information θ of the signal. p (t) Based on the phase of the predicted signal and the set target phase difference Δθ, the phase sequence θ of the stimulus envelope signal is calculated. b (t); multiplying the envelope signal by a high-frequency carrier signal to obtain an AM signal, and outputting the AM signal through a pair of electrodes to achieve closed-loop AM-tACS; Perform product and difference transformation on the generated AM signal to decompose it into two TIS stimulation signals, and output the two TIS signals separately; The envelope signal B(t)=sin[θ b (t)], the carrier signal C(t)=cos[θ c (t)]; The two TIS signals are the first TIS signal and the second TIS signal. The first TIS signal is: The second TIS signal is:

2. The closed-loop transcranial electrical stimulation device according to claim 1, wherein: The closed-loop transcranial electrical stimulation device further includes a first bandpass filtering module, which is used to perform bandpass filtering on the collected EEG data.

3. The closed-loop transcranial electrical stimulation device according to claim 1, wherein: The closed-loop transcranial electrical stimulation device further includes a second band-pass filtering module, which is used to perform band-pass filtering on the prediction signal.

4. An electronic device, characterized in that: The electronic device includes a processor and a memory, wherein the memory stores at least one instruction, at least one program, a code set, or an instruction set, and the at least one instruction, at least one program, the code set, or the instruction set is loaded and executed by the processor to implement a closed-loop transcranial electrical stimulation method, wherein the closed-loop transcranial electrical stimulation method includes the following steps: Collect EEG signals and obtain EEG data; The autoregressive model is constructed using the least squares method to analyze the collected EEG data and give the EEG prediction signal; the prediction signal is subjected to Hilbert transform to obtain the instantaneous phase information θ of the signal. p (t) Based on the phase of the predicted signal and the set target phase difference Δθ, the phase sequence θ of the stimulus envelope signal is calculated. b (t); multiplying the envelope signal by a high-frequency carrier signal to obtain an AM signal, and outputting the AM signal through a pair of electrodes to achieve closed-loop AM-tACS; Perform product and difference transformation on the generated AM signal to decompose it into two TIS stimulation signals, and output the two TIS signals separately; The envelope signal B(t)=sin[θ b (t)], the carrier signal C(t)=cos[θ c (t)]; The two TIS signals are the first TIS signal and the second TIS signal. The first TIS signal is: The second TIS signal is:

5. A computer-readable storage medium, characterized in that The storage medium stores at least one instruction, at least one program, a code set, or an instruction set, and the at least one instruction, the at least one program, the code set, or the instruction set is loaded and executed by the processor to implement a closed-loop transcranial electrical stimulation method, wherein the closed-loop transcranial electrical stimulation method includes the following steps: Collect EEG signals and obtain EEG data; The autoregressive model is constructed using the least squares method to analyze the collected EEG data and give the EEG prediction signal; the prediction signal is subjected to Hilbert transform to obtain the instantaneous phase information θ of the signal. p (t) Based on the phase of the predicted signal and the set target phase difference Δθ, the phase sequence θ of the stimulus envelope signal is calculated. b (t); multiplying the envelope signal by a high-frequency carrier signal to obtain an AM signal, and outputting the AM signal through a pair of electrodes to achieve closed-loop AM-tACS; Perform product and difference transformation on the generated AM signal to decompose it into two TIS stimulation signals, and output the two TIS signals separately; The envelope signal B(t)=sin[θ b (t)], the carrier signal C(t)=cos[θ c (t)]; The two TIS signals are the first TIS signal and the second TIS signal. The first TIS signal is: The second TIS signal is:

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