A visible light heterogeneous networking switching method based on communication blind zone dwell time

Abstract

The present invention belongs to the field of visible light communication technology, and in particular, is a visible light heterogeneous networking switching method based on the residence time of communication blind spots, comprising the following steps: Step 1, constructing an indoor visible light heterogeneous networking model: while ensuring the VLC communication coverage and lighting requirements, LED lights are arranged on the ceiling so that the lights are distributed throughout the corners of the room. Each indoor LED light source can be used as an access point for visible light communication, and its downlink data transmission speed is very fast. However, the high-speed coverage area of ​​each VLC AP is very small, and the uplink of the VLC APs is interfered with by the downlink light, making communication transmission more difficult. In order to improve the uplink access problem, a Wi-Fi AP with a wider coverage range is arranged in the middle of the room to form a heterogeneous network together with the VLC APs. The present invention adopts ACO-OFDM technology for signal processing, effectively eliminating multipath interference, and at the same time constructing a spatial bit error rate, providing corresponding data for detecting communication blind spots.

Description

Technical Field

[0001] The present invention relates to the field of visible light communication technology, and in particular to a visible light heterogeneous networking switching method based on communication blind zone residence time. Background Art

[0002] Visible light communication (VLC) offers the advantages of wide spectrum, high transmission rates, environmental friendliness, and the ability to combine lighting and communication, making it a very promising indoor communication networking method. However, due to its direct transmission characteristics, VLC cannot meet users' needs for uninterrupted mobile communication. Radio frequency (RF) communication networks enable non-line-of-sight communication, and the integration of these two technologies is a key research direction for indoor high-speed communication networks. For optoelectronic heterogeneous networks composed of VLC and RF (radio frequency communication), network handover is a key scientific issue that must be addressed.

[0003] Most of the existing heterogeneous network switching technologies are vertical switching, but not all scenarios are suitable for vertical switching. For example, the movement of indoor users between adjacent networks is more suitable for horizontal switching. Therefore, indoor visible heterogeneous network switching needs to combine horizontal switching and vertical switching to provide higher service quality. The existing visible light heterogeneous network switching technology is based on detecting the indoor visible light received signal strength (Received Signal Strength, RSS) as the switching threshold to perform horizontal or vertical switching. However, due to the complex indoor environment, there are phenomena such as wall reflection or mirror reflection, which causes multipath interference in the received signal, thereby reducing the communication quality. Currently, OFDM technology is generally used in the market to deal with multipath interference in the communication process, but because visible light communication transmits positive real signals, the problem cannot be solved by simply using OFDM technology.

[0004] The Chinese patent publication number is "CN107846714A", and the name is "A switching method and device for a visible light communication and WiFi heterogeneous system". The method includes: if entering the initial switching state, obtaining QoS parameters of all candidate networks, the QoS parameters including available bandwidth, end-to-end delay, jitter and bit error rate; based on the QoS parameters of each candidate network, normalizing and fuzzifying the QoS parameters to obtain fuzzy values ​​and weight values ​​of each parameter in the QoS parameters; based on the fuzzy values ​​and weight values, using fuzzy rules to obtain a performance evaluation value of each candidate network, and switching from the current network to a candidate network whose performance evaluation value meets preset conditions. Summary of the Invention

[0005] (1) Technical problems solved

[0006] In view of the deficiencies in the prior art, the present invention provides a visible light heterogeneous networking switching method based on the communication blind zone residence time, which solves the problems raised in the above background technology.

[0007] (2) Technical solution

[0008] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0009] A visible light heterogeneous networking switching method based on communication blind zone dwell time comprises the following steps:

[0010] Step 1: Build an indoor visible light heterogeneous networking model: To ensure VLC communication coverage and lighting requirements, LED lights are placed on the ceiling so that the light is distributed throughout the room. Each indoor LED light source can be used as a visible light communication access point. Its downlink data transmission speed is very fast, but the high-speed coverage area of ​​each VLCAP is very small, and the uplink of VLCAPs is interfered with by the downlink light, making communication transmission difficult. To improve the uplink access problem, Wi-Fi APs with wider coverage are placed in the middle of the room to form a heterogeneous network together with VLCAPs.

[0011] Step 2, establish a visible light communication system based on ACO-OFDM: Based on the indoor visible light heterogeneous networking model of step 1, the carrier modulation method is first used to modulate the communication signal in the form of a serial binary bit stream to generate a complex signal, and then the complex signal is subjected to Hermitian mapping and IFFT operations to output a real signal. Then a limiting operation is performed to intercept the negative part and convert the signal into a positive real signal to meet the transmission requirements. Finally, a cyclic prefix (CP) is inserted into the head of the real signal after limiting, followed by parallel-to-serial conversion, digital-to-analog conversion and other operations. Finally, the electrical signal is converted into an optical signal of different intensities through the LED driver and sent to the channel for transmission. The receiving end is equivalent to the inverse process of the transmitting end;

[0012] Step 3: Construct a spatial distribution model of the bit error rate. First, calculate the indoor visible light communication signal-to-noise ratio (SNR), add it to a Gaussian white noise channel, process it through ACO-OFDM, and convert the output signal into an electrical signal through the receiving end's photoelectric converter. Finally, calculate the error between the output signal and the input signal of the serial binary bit stream to obtain the bit error rate. Finally, convert the bit error rate into an indoor spatial distribution in the form of a matrix.

[0013] Step 4: Construct a random motion model and performance evaluation indicators: Based on the indoor layout design, randomly define the user's starting and ending coordinates. Then, based on the layout design in step 1, analyze three visible light communication blind area motion models: 1. Movement in the visible light coverage overlap area; 2. Movement in the visible light coverage tangent area; 3. Movement in the visible light coverage area without visible light coverage. The average network throughput and average number of handoffs are used as evaluation indicators.

[0014] Step 5: Establish a horizontal and vertical switching mechanism based on the residence time in the communication blind spot: Using the three visible light communication blind spot motion models analyzed in step 4, when a mobile user enters the communication blind spot, the corresponding horizontal switching or vertical switching is performed by calculating the residence time of the mobile user in the communication blind spot.

[0015] Furthermore, in step 1, the indoor layout is 9 LED lights distributed in a room with a length and width of 6*6 meters, and the WiFi is arranged in the center of the room, with 5 of them having a radius of LED lights with a radius of 1 meter are distributed around and in the middle of the room, 4 LED lights with a radius of 1 meter are distributed above, below, left and right of the room, and a WiFi is arranged in the middle of the room so that the signal is evenly distributed around the room.

[0016] Furthermore, in step 2, in the ACO-OFDM visible light communication system, hexadecimal QAM modulation technology is used to modulate the communication signal; Hermitian symmetric mapping is performed to ensure that when the negative part of the real signal after IFFT transformation is set to zero, the information can still be transmitted completely; a limiting operation is performed to intercept the negative part and convert the signal into a positive real signal; a cyclic prefix (CP) is inserted into the head of the real signal after limiting, and in order to eliminate system inter-symbol interference, parallel-to-serial conversion, digital-to-analog conversion and other operations are then performed. Finally, the electrical signal is converted into an optical signal of different intensities through an LED driver and sent to the channel for transmission.

[0017] Furthermore, in step 3, the signal-to-noise ratio (SNR) of the signal needs to be calculated first. The definition of SNR is the ratio of signal power to noise. The received power of the visible light signal P is R By the transmission power P T Multiply by the channel DC gain H Los It is found that in indoor VLC transmission channels, two main types of noise need to be considered: one is shot noise and the other is preamplifier noise. Both can be treated as additive white Gaussian noise. The signal-to-noise ratio is defined as the ratio of signal power to noise. Finally, the bit error rate is calculated through ACO-OFDM processing.

[0018] Furthermore, in step 4, the average network throughput and the average number of handovers are used as evaluation indicators, firstly to judge the network communication performance received by the mobile user, and secondly to judge the handover signaling cost required during the entire mobile process.

[0019] Furthermore, in step 5, the minimum standard of the bit error rate of the general communication system is 10 -4 ~10 -5 , using the bit error rate distribution constructed in step 3, when the bit error rate of the detected user is lower than this standard, it means that the moving user enters the communication blind area, let T s The dwell time from entering the communication blind area to leaving is set, and the threshold time T is set. threshold , by comparing with the threshold time size, the corresponding switching method is executed.

[0020] (3) Beneficial effects

[0021] Compared with the prior art, the present invention provides a visible light heterogeneous networking switching method based on communication blind zone dwell time, which has the following beneficial effects:

[0022] 1. ACO-OFDM technology is used for signal processing, which effectively eliminates multipath interference and constructs the spatial bit error rate, providing corresponding data for detecting communication blind spots.

[0023] 2. The random motion model is simplified, and only the bit error rate and the residence time in the communication blind area need to be considered, replacing complex factors such as motion direction, speed and time.

[0024] 3. Taking into account various types of communication instability, it is closer to real-life scenarios, and at the same time establishes a horizontal and vertical switching networking switching mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a diagram of indoor visible light communication heterogeneous networking light sources and WiFi distribution of the present invention;

[0026] Figure 2 This is a block diagram of the ACO-OFDM visible light communication system in the present invention;

[0027] Figure 3 This is a flow chart of horizontal and vertical switching based on the communication blind area dwell time of the present invention;

[0028] Figure 4 This is a comparison chart of the average number of handovers and average throughput of IVHO, DVHO, and CBD-VHO of the present invention. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] Example 1

[0031] like Figure 1-4 As shown, an embodiment of the present invention proposes a visible light heterogeneous networking switching method based on communication blind zone dwell time, including the following steps:

[0032] Step 1: Construct an indoor visible light heterogeneous networking model: Based on the size of a normal office space, design a square room with a length and width of 6 meters and a height of 3 meters, and then use two types of lamps for spatial layout. The purpose is to produce a variety of communication instability situations that exist in reality, mainly divided into visible light coverage overlapping areas, visible light coverage tangent areas, and visible light no coverage areas. The radius of the first lamp is meters, distributed in an X-shaped layout around and in the middle of the room. The radius of the second type of lamps is 1 meter, and they are distributed in a +-shaped layout on the X-axis and Y-axis of the central coordinate axis of the room. Their coordinates are (1, 1), (1, 5), (3, 3), (5, 1), (5, 5) and (1, 3), (3, 1), (3, 5), (5, 3), and their heights are all 3 meters. Then a WiFi communication is arranged in the room, its coordinates are (3, 3), and its WiFi signal is evenly distributed around the room.

[0033] Step 2: Establish an ACO-OFDM visible light communication system: Figure 2 As shown, first, the serial bit stream at the transmitting end is converted into serial-to-parallel, and the parallel signal is modulated by QAM. The output after modulation is a complex signal. Let the sampling function of the signal be s(k), and the value of its K-point DFT be S(n). From the theory, when s(k) is a real function, then S(n) will satisfy the symmetry condition, that is,

[0034] S(Kk-1)=S * (k) k=0,1,2,....K-1

[0035] Among them S * (k) is the complex conjugate of S(k), and the symmetry of the above formula is Hermitian symmetry.

[0036] Now the modulated signal is a complex signal. In order to make the IFFT transform output a real signal, the complex signal needs to be mapped to satisfy the Hermintian symmetry characteristic, and then the odd subcarriers contain information, while the even subcarriers are 0. If the mapped signal is X m ,but

[0037]

[0038] is x m The conjugate function of x m It is represented as the frequency domain data modulated onto the mth subcarrier after mapping. The IFFT operation is performed on the signal that meets the above formula. The output after the IFFT transformation operation is the OFDM real signal, which is set as X IFFT

[0039] X IFFT =F H X m

[0040]

[0041] Where F is the N×N normalized discrete Fourier transform matrix, N is the length of IFFT, and H represents the conjugate transpose of the matrix.

[0042] Perform a limiting operation on the output OFDM real signal and set X IFFT Delete the values ​​less than zero in the equation to get the unipolar real signal X clip (k)

[0043]

[0044] where n clip (k) is the clipping noise, and the frequency domain signal corresponding to the clipped signal is

[0045] X clip (k) = 1 / 2X m (n)

[0046] As the above equation shows, the useful signal on odd-numbered subcarriers has an amplitude half that of the unlimited frequency-domain signal, while the limiting noise falls on even-numbered subcarriers. Accordingly, the receiver demodulates the received signal and then adjusts the amplitude of the information on the odd bits to half to restore the original signal. This process does not damage any other useful information.

[0047] Step 3: Construct a three-dimensional bit error rate spatial distribution model: First, establish an LED using the Lambert model, and its Lambert order in is the half-power angle of the LED light. In the case of a line-of-sight link, the channel DC gain HLOS It is expressed as follows:

[0048]

[0049] In the formula, d represents the distance from the light source, T s (ψ) is the DC gain of the optical filter, g(ψ) is the gain of the concentrator, and ψ c It represents the half field of view of the receiver, A R is the photodetection area, where the light concentrator gain is expressed as follows:

[0050]

[0051] Where n is the refractive index of the optical receiving end,

[0052] The received power under LOS is:

[0053] P R =P T H LOS

[0054] Among them, P R Received optical power, P T is the transmitted optical power,

[0055] In indoor visible transmission channels, there are two main types of noise that need to be considered: one is shot noise and the other is preamplifier noise, both of which can be treated as additive white Gaussian noise.

[0056] Shot noise can be expressed as:

[0057]

[0058] Where q is the charge, P R(signal) is the signal power, P R(ISI) is the intersymbol interference power, B is the equivalent noise bandwidth, I bg is the dark current and I2 is the noise bandwidth factor.

[0059] Thermal noise can be expressed as:

[0060]

[0061] Where k is the Boltzmann constant, T is the absolute temperature, η is the fixed capacitance per unit area of ​​the photodetector. G is the open-loop voltage gain, Γ is the FET channel noise factor, and g m is the FET transconductance.

[0062] The signal-to-noise ratio can be expressed as:

[0063]

[0064] The signal-to-noise ratio is added to the Gaussian white noise channel, and the error between the output bit stream and the input bit stream is calculated to obtain the bit error rate. Finally, the bit error rate is converted into an indoor spatial distribution in the form of a matrix.

[0065] Step 4: Construct random motion model and performance evaluation index: The mobile user moves randomly from one point to another in a restricted indoor area, and the mobile user speed is modeled as V min and V max Uniform distribution between, where V min is the minimum speed; V max is the maximum speed. During mobility, handovers are primarily performed in three communication blind spots: overlapping visible light coverage areas, tangent visible light coverage areas, and areas without visible light coverage. We use average network throughput as a performance indicator of network communication quality, and the average number of handovers as the signaling cost incurred during handovers.

[0066] Average throughput A th It can be expressed as

[0067]

[0068] where O(i,r) is the throughput during the i-th network connection in the r-th iteration, T i (r) is the duration of the i-th network period in the r-th iteration, T d (r) is the switching delay of the ith switching in the rth iteration, N r is the total number of iterations.

[0069] The average number of switching times can be expressed as:

[0070]

[0071] Among them A HO is the average number of switching times for the switching scheme, N HO is the number of switches in iteration R.

[0072] Step 5: Establish a horizontal and vertical switching mechanism based on the residence time of the communication blind area: According to step 4, three communication blind area motion models are analyzed, and T s T is the dwell time from entering the communication blind area to leaving the area, threshold is the threshold time. Considering that the network switching delay time will change in real time, T threshold Corresponding adaptation should also be carried out. The specific flow chart is as follows Figure 3 As shown, let T res The time limit for maintaining uninterrupted response time for the user's thought flow, T maxis the maximum waiting time for a short interruption in the VLC channel. To ensure normal communication when moving in a communication blind area, the threshold time T threshold Follow [T res ,T max ] interval is randomly distributed. When the user enters the communication blind area, the time starts. When T s Less than T threshold When T s Greater than T threshold When the VLC channel is disconnected, vertical switching will not affect user communication. In order to reduce the signaling cost caused by switching, no further switching will be performed after vertical switching until the movement process is completed.

[0073] Example 2

[0074] A visible light heterogeneous networking switching method based on communication blind zone dwell time, the method specifically comprising the following steps:

[0075] Step 1: Construct an indoor visible light heterogeneous networking model: Use two types of lamps to The light sources with a radius of 1 meter are arranged in an X-shaped layout, and the light sources with a radius of 1 meter are arranged in a +-shaped layout. Finally, the indoor visible light distribution is simulated by a program on Matlab;

[0076] Step 2: Establish an ACO-OFDM visible light communication system: First, perform QAM modulation on the bit stream to output a complex signal, and then map it to satisfy the Hermintian symmetry property. Assume that the mapped signal is X m ,but

[0077]

[0078] is x m The conjugate function of x m It is represented as the frequency domain data modulated onto the mth subcarrier after mapping. Then after the IFFT operation, the output is the OFDM real signal, which is set as X IFFT

[0079]

[0080] Where F is the N×N normalized discrete Fourier transform matrix, N is the length of IFFT, and H represents the conjugate transpose of the matrix.

[0081] Then perform a limiting operation on the output OFDM real signal, and set X IFFT Delete the values ​​less than zero in the equation to get the unipolar real signal X clip (k)

[0082]

[0083] where n clip (k) is the clipping noise, and the frequency domain signal corresponding to the clipped signal is

[0084] X clip (k) = 1 / 2X m (n)

[0085] Correspondingly, the receiving end demodulates the received signal and then adjusts the information amplitude on the odd bits to half to restore it to the original signal.

[0086] Step 3: Construct a three-dimensional bit error rate spatial distribution model: First, calculate the channel DC gain H under the line-of-sight link condition. LOS It is expressed as follows:

[0087]

[0088] in is the half-power angle of the LED lamp. Based on the two visible light lamp layouts in step 1, 30 degrees and 45 degrees respectively. In the formula, d represents the distance from the light source, T s (ψ) is the DC gain of the optical filter, g(ψ) is the gain of the concentrator, and ψ c It represents the half field of view of the receiver, A R is the photoelectric detection area. Then calculate the received power under LOS as:

[0089] P R =P T H LOS

[0090] Among them, P R The received optical power is in the range of [-10, -4]dBm, P T is the transmitted optical power, set the value to 18W, and then calculate the shot noise and preamplifier noise.

[0091] Shot noise can be expressed as:

[0092]

[0093] Where q is the charge, P R(signal) is the signal power, P R(ISI) is the intersymbol interference power, B is the equivalent noise bandwidth, I bg is the dark current and I2 is the noise bandwidth factor.

[0094] Thermal noise can be expressed as:

[0095]

[0096] Where k is the Boltzmann constant, T is the absolute temperature, η is the fixed capacitance per unit area of ​​the photodetector, G is the open-loop voltage gain, Γ is the FET channel noise factor, and g m is the FET transconductance.

[0097] The signal-to-noise ratio can be expressed as:

[0098]

[0099] The SNR obtained by simulation is in the range of [13,19]dB. The signal-to-noise ratio is added to the Gaussian white noise channel. The error between the output bit stream and the input bit stream is calculated by outputting the bit stream to obtain the bit error rate (BER). Finally, the bit error rate is converted into an indoor spatial distribution in the form of a matrix. The distribution range of the value is [0.15,10 -6 ].

[0100] Step 4: Construct random motion model and performance evaluation index: First, define the mobile user speed V so that the speed V ranges from [0.3, 0.7] ms. -1 Distribution. Establish the average network throughput as a performance indicator of network communication quality.

[0101] Average throughput A th It can be expressed as

[0102]

[0103] where O(i,r) is the throughput during the i-th network connection in the r-th iteration, T i (r) is the duration of the i-th network period in the r-th iteration, T d (r) is the switching delay of the ith switching in the rth iteration, N r is the total number of iterations.

[0104] The average number of switching times can be expressed as:

[0105]

[0106] Among them A HO is the average number of switching times for the switching scheme, N HO is the number of switches in iteration R.

[0107] Step 5: Establish a horizontal and vertical collaborative switching mechanism based on the dwell time in the communication blind area:

[0108] Assume T s T is the dwell time from entering the communication blind area to leaving the area, threshold is the threshold time, and the threshold time Tthreshold Follow [T res ,T max ] interval, where T res =1s,T max =2s. When T s <T threshold When T s >T threshold To avoid channel interruption in VLC communication blind spots, vertical switching is performed. To avoid excessive switching, no horizontal switching is performed after vertical switching.

[0109] By comparing the traditional Immediate Vertical Handover (IVHO) and Dwell Vertical Handover (DVHO) algorithms with the proposed method, the feasibility and superiority of the proposed method are further verified. Figure 4 As shown,

[0110] It can be seen that the method proposed in the present invention has higher average throughput and fewer average handover times than IVHO and DVHO.

[0111] In summary, the present invention aims to solve the problems of indoor visible light multipath interference and monotonous networking switching methods, and designs a horizontal and vertical switching algorithm based on the residence time of communication blind spots. At the same time, the use of ACO-OFDM technology not only eliminates the multipath interference caused by the complex indoor environment to a large extent, but also improves the average network throughput through its networking switching algorithm, reduces the number of switching times, and reduces the signaling cost generated when performing switching.

[0112] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A visible light heterogeneous networking switching method based on communication blind zone dwell time, characterized by: The steps include: Step 1: Build an indoor visible light heterogeneous networking model: To ensure VLC communication coverage and lighting requirements, LED lights are placed on the ceiling so that the light is distributed throughout the room. Each indoor LED light source can be used as a visible light communication access point. Its downlink data transmission speed is very fast, but the high-speed coverage area of ​​each VLCAP is very small, and the uplink of VLCAPs is interfered with by the downlink light, making communication transmission difficult. To improve the uplink access problem, Wi-Fi APs with wider coverage are placed in the middle of the room to form a heterogeneous network together with VLCAPs. Step 2: Establish an ACO-OFDM-based visible light communication system: Based on the indoor visible light heterogeneous networking model in step 1, the carrier modulation method is first used to modulate the communication signal in the form of a serial binary bit stream to generate a complex signal. The complex signal is then subjected to Hermitian mapping and IFFT operations to output a real signal. The limiting operation is then performed to intercept the negative part and convert the signal into a positive real signal to meet the transmission requirements. Finally, a cyclic prefix (CP) is inserted into the head of the real signal after limiting. Then, parallel-to-serial conversion and digital-to-analog conversion are performed. Finally, the electrical signal is converted into an optical signal of different intensities through an LED driver and sent to the channel for transmission. The receiving end is equivalent to the inverse process of the transmitting end. Step 3: Construct a spatial distribution model of the bit error rate. First, calculate the indoor visible light communication signal-to-noise ratio (SNR), add it to a Gaussian white noise channel, process it through ACO-OFDM, and convert the output signal into an electrical signal through the receiving end's photoelectric converter. Finally, calculate the error between the output signal and the input signal of the serial binary bit stream to obtain the bit error rate. Finally, convert the bit error rate into an indoor spatial distribution in the form of a matrix. Step 4: Construct a random motion model and performance evaluation indicators: Based on the indoor layout design, randomly define the user's starting and ending coordinates. Then, based on the layout design in step 1, analyze three visible light communication blind area motion models:

1. Movement in the visible light coverage overlap area; 2. Movement in the visible light coverage tangent area; 3. Movement in the visible light coverage area without visible light coverage. The average network throughput and average number of handoffs are used as evaluation indicators. Step 5: Establish a horizontal and vertical switching mechanism based on the residence time in the communication blind spot: Using the three visible light communication blind spot motion models analyzed in step 4, when a mobile user enters the communication blind spot, the corresponding horizontal switching or vertical switching is performed by calculating the residence time of the mobile user in the communication blind spot.

2. The visible light heterogeneous networking switching method based on communication blind zone dwell time according to claim 1 is characterized by: In step 1, the indoor layout is 9 LED lights distributed in a room with a length and width of 6*6 meters, and the WiFi is arranged in the center of the room, with 5 of them having a radius of LED lights with a radius of 1 meter are distributed around and in the middle of the room, 4 LED lights with a radius of 1 meter are distributed above, below, left and right of the room, and a WiFi is arranged in the middle of the room so that the signal is evenly distributed around the room.

3. The visible light heterogeneous networking switching method based on communication blind zone dwell time according to claim 1 is characterized by: In step 2, in the ACO-OFDM visible light communication system, hexadecimal QAM modulation technology is used to modulate the communication signal; Hermitian symmetric mapping is performed to ensure that when the negative part of the real signal after IFFT transformation is set to zero, the information can still be transmitted completely; a limiting operation is performed to intercept the negative part and convert the signal into a positive real signal; a cyclic prefix (CP) is inserted into the head of the real signal after limiting, and in order to eliminate system inter-symbol interference, parallel-to-serial conversion, digital-to-analog conversion and other operations are then performed. Finally, the electrical signal is converted into an optical signal of different intensities by an LED driver and sent to the channel for transmission.

4. The visible light heterogeneous networking switching method based on communication blind zone dwell time according to claim 1 is characterized by: In step 3, the signal-to-noise ratio (SNR) of the signal must be calculated first. The definition of SNR is the ratio of signal power to noise. The received power of the visible light signal P is R By the transmission power P T Multiply by the channel DC gain H Los It is found that in indoor VLC transmission channels, two main types of noise need to be considered: one is shot noise and the other is preamplifier noise. Both can be treated as additive white Gaussian noise. The signal-to-noise ratio is defined as the ratio of signal power to noise. Finally, the bit error rate is calculated through ACO-OFDM processing.

5. The visible light heterogeneous networking switching method based on communication blind zone dwell time according to claim 1, characterized in that: In step 4, the average network throughput and the average number of handovers are used as evaluation indicators, firstly to determine the network communication performance received by the mobile user, and secondly to determine the handover signaling cost required during the entire mobile process.

6. The visible light heterogeneous networking switching method based on communication blind zone dwell time according to claim 1, characterized in that: In step 5, the minimum standard of the bit error rate of the general communication system is 10 -4 ~10 -5 , using the bit error rate distribution constructed in step 3, when the bit error rate of the detected user is lower than this standard, it means that the moving user enters the communication blind area, let T s The dwell time from entering the communication blind area to leaving is set, and the threshold time T is set. threshold , by comparing with the threshold time size, the corresponding switching method is executed.

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