Visible light communication system based on distributed passive front end and low-power-consumption transmission method

Abstract

The invention discloses a visible light communication system based on a distributed passive front end and a low-power-consumption transmission method, and relates to the technical field of visible light communication, the visible light communication system comprises an access point AP and a user side, and the access point AP and the user side carry out indoor communication through an uplink and a downlink. The access point AP comprises a first laser, a first photodiode, a side light-emitting optical fiber and a scintillation optical fiber, the user side comprises a second laser and a second photodiode, and the side light-emitting optical fiber is used for receiving a first optical signal emitted by the first laser and then emitting the first optical signal from the side. The second photodiode receives a first optical signal transmitted through a free space channel and then realizes downlink communication, and the scintillation fiber is used for receiving a second optical signal transmitted through the free space channel and emitted by a second laser. And enabling the first photodiode to realize uplink communication after receiving the second optical signal. The complexity of a visible light communication system can be reduced.

Description

Technical Field

[0001] The present application relates to the field of visible light communication technology, and in particular to a visible light communication system based on a distributed passive front end and a low-power transmission method. Background Art

[0002] For IoT applications, the topology of the visible light communication (VLC) system should be simple enough and the cost of components should be low. A typical VLC network includes multiple front-end access points, each of which consists of a light-emitting diode (LED) and a photodiode (PD). The corresponding photoelectric conversion and electro-optical conversion are completed at the front end, and the electrical signal is sent back to the residential gateway. In order to reduce the complexity of the VLC network, the concept of passive optical front end is proposed. In the indoor communication system based on passive optical front end, plastic optical fiber is used as a feeder on the ceiling of the room. For the downlink, the light generated by the residential gateway is emitted by the plastic optical fiber (POF) end for data transmission. For the uplink, the light collected by the lens is propagated through the POF to the photodiode at the residential gateway. However, this system requires a pair of POFs and a collimating lens in each optical front end. Considering that multiple optical front ends are required for indoor coverage, this optical front end-based system still has great complexity in practical applications.

[0003] The above contents are only used to assist in understanding the technical solution of the present application and do not constitute an admission that the above contents are prior art. Summary of the invention

[0004] The main purpose of the present application is to provide a visible light communication system based on a distributed passive front end and a low-power transmission method, aiming to solve the technical problem that the visible light communication system based on a passive optical front end still has great complexity in practical applications.

[0005] To achieve the above-mentioned purpose, the present application proposes a visible light communication system based on a distributed passive front-end, the visible light communication system comprising an access point AP and a user terminal, the access point AP and the user terminal perform indoor communication through an uplink and a downlink, the access point AP comprises a first laser, a first photodiode, a side-emitting optical fiber and a flashing optical fiber, the user terminal comprises a second laser and a second photodiode, the side-emitting optical fiber is used to receive a first optical signal emitted by the first laser and then emit it sideways, so that the second photodiode realizes downlink communication after receiving the first optical signal transmitted through a free space channel, and the flashing optical fiber is used to receive a second optical signal emitted by a second laser transmitted through a free space channel, so that the first photodiode realizes uplink communication after receiving the second optical signal.

[0006] In one embodiment, the side-emitting optical fiber includes a plurality of first optical fiber segments connected in sequence, and any one of the first optical fiber segments is configured as a side-emitting optical fiber transmitter.

[0007] In one embodiment, the scintillation optical fiber includes a plurality of second optical fiber segments connected in sequence, and any one of the second optical fiber segments is configured as a scintillation receiver.

[0008] In one embodiment, the emission wavelengths of the first laser and the second laser are different.

[0009] To achieve the above object, the present application also proposes a low-power transmission method, which is applied to the visible light communication system as described in the above claims, and the method comprises:

[0010] Determine the minimum received optical power according to the expected bit error rate;

[0011] Calculate the overall channel attenuation of uplink and downlink based on user location information and fiber transmission distance;

[0012] According to the minimum received optical power and the overall channel attenuation of the uplink and downlink, the minimum transmit power of the uplink and downlink when the expected bit error rate is met is determined, so as to dynamically adjust the visible light communication system based on the minimum transmit power.

[0013] In one embodiment, the step of determining the minimum received optical power according to the expected bit error rate includes:

[0014] Determine a signal-to-noise ratio according to the expected bit error rate and a Gaussian error function;

[0015] Determine the shot noise variance based on the background light noise power;

[0016] Determine the amplifier noise variance based on the amplifier noise density and the amplifier bandwidth;

[0017] determining a total noise variance based on the shot noise variance and the amplifier noise variance;

[0018] The minimum received optical power is determined according to the photodiode response rate, the total noise variance and the signal-to-noise ratio.

[0019] In one embodiment, the step of calculating the overall channel attenuation of the uplink and downlink according to the user location information and the optical fiber transmission distance includes:

[0020] Determine the location information of the side-emitting optical fiber transmitter, the location information of the flashing optical fiber receiver, and the uplink and downlink optical fiber transmission losses according to the optical fiber transmission distance;

[0021] Determine uplink and downlink free space channel gains according to the user location information, the location information of the side-emitting optical fiber transmitter, the location information of the scintillation optical fiber receiver, and a visible light free space channel model;

[0022] The uplink and downlink overall channel attenuation is determined according to the uplink and downlink optical fiber transmission losses and the uplink and downlink free space channel gains.

[0023] In one embodiment, the step of determining the location information of the side-emitting optical fiber transmitter, the location information of the flashing optical fiber receiver, and the uplink and downlink optical fiber transmission losses according to the optical fiber transmission distance comprises:

[0024] Determine the transmission length of the second optical signal of the uplink in the visible light communication system in the scintillation optical fiber according to the optical fiber transmission distance;

[0025] Determining uplink transmission loss according to the transmission length, transmission ratio, attenuation coefficient and correction factor;

[0026] Determining the fiber radius of the side-emitting optical fiber in the downlink of the visible light communication system;

[0027] The downlink transmission loss is determined according to the optical fiber radius, the scattering coefficient and the correction factor.

[0028] In one embodiment, the step of determining the uplink and downlink free space channel gains according to the user location information, the location information of the side-emitting optical fiber transmitter, the location information of the scintillation optical fiber receiver, and the visible light free space channel model comprises:

[0029] Determine a first link distance between a second laser at a user end of the visible light communication system and a scintillation optical fiber receiver of the visible light communication system according to the user location information and the location information of the scintillation optical fiber receiver;

[0030] Determine the receiver field of view angle, the first radiation intensity, the receiver effective detection area and the divergence angle of the second laser, wherein the first radiation intensity is determined according to the Lambertian emission order and the light source half-power intensity angle, and the receiver effective detection area is determined according to the scintillation fiber radius, the first link distance and the second laser divergence angle;

[0031] An uplink free space channel gain is determined according to the first link distance, the receiver field of view angle, the radiation intensity, the receiver effective detection area, and the divergence angle of the second laser.

[0032] In one embodiment, the step of determining the uplink and downlink free space channel gains according to the user location information, the location information of the side-emitting optical fiber transmitter, the location information of the scintillation optical fiber receiver, and the visible light free space channel model comprises:

[0033] Determine a second link distance between the side-emitting optical fiber transmitter and a second photodiode in the user terminal according to the user location information and the location information of the side-emitting optical fiber transmitter;

[0034] Determine a second photodiode field of view angle, a second radiation intensity, and an effective detection area of ​​the second photodiode, wherein the second radiation intensity is determined according to an initial luminous flux of a transmitter, a scattering coefficient of a side-emitting optical fiber, and a radius of the side-emitting optical fiber, and the effective detection area of ​​the second photodiode is determined according to a refractive index of an optical concentrator and an area of ​​a detector;

[0035] A downlink free space channel gain is determined according to the second link distance, the second photodiode field of view, the second radiation intensity, and the second photodiode effective detection area.

[0036] One or more technical solutions proposed in this application have at least the following technical effects:

[0037] The present application proposes a visible light communication system based on a distributed passive front end and a low-power transmission method, the visible light communication system includes an access point AP and a user end, the access point AP and the user end perform indoor communication through an uplink and a downlink, the access point AP includes a first laser, a first photodiode, a side-emitting optical fiber and a flashing optical fiber, the user end includes a second laser and a second photodiode, the side-emitting optical fiber is used to receive a first optical signal emitted by the first laser and then emit it sideways, so that the second photodiode realizes downlink communication after receiving the first optical signal transmitted through a free space channel, and the flashing optical fiber is used to receive a second laser transmitted through a free space channel. The second optical signal emitted enables the first photodiode to achieve uplink communication after receiving the second optical signal, which solves the technical problem that the visible light communication system based on the passive optical front end still has great complexity in practical applications. Compared with the prior art, the uplink and downlink of the present application adopt two different new special plastic optical fibers for signal transmission, wherein the downlink adopts side-emitting optical fiber, and the emitted optical signal can be emitted from the side of the optical fiber, thereby increasing the coverage area of ​​the visible light communication, and the uplink adopts flashing optical fiber, which can increase the input fiber light intensity, thereby improving the received optical power, and the visible light communication system does not need to use a lens for optical focusing, thereby effectively reducing the complexity of the visible light communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0040] Figure 1 This is a structural block diagram of a visible light communication system based on a distributed passive front end of this application;

[0041] Figure 2 This is a specific structural block diagram of the visible light communication system based on the distributed passive front end of this application;

[0042] Figure 3 A brief flowchart of the low-power transmission method provided in Embodiment 2 of the present application;

[0043] Figure 4 A schematic diagram of a specific process of the low-power transmission method provided in Embodiment 2 of the present application;

[0044] Figure 5 A simulation diagram of the minimum transmission power of the uplink in the low-power transmission method provided in Embodiment 2 of the present application;

[0045] Figure 6 This is a simulation diagram of the minimum transmission power of the downlink in the low-power transmission method provided in Example 2 of the present application.

[0046] Reference numerals:

[0047] 10 - access point AP; 20 - user end; 101 - first laser; 102 - first photodiode; 103 - side-emitting optical fiber; 104 - flashing optical fiber; 201 - second laser; 202 - second photodiode.

[0048] The purpose, features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0049] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0050] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0051] An embodiment of the present application provides a visible light communication system based on a distributed passive front end.

[0052] Reference Figure 1 In an embodiment of the present invention, the visible light communication system includes an access point AP10 and a user terminal 20. The access point AP10 and the user terminal 20 perform indoor communication through an uplink and a downlink. The access point AP10 includes a first laser 101, a first photodiode 102, a side-emitting optical fiber 103, and a scintillation optical fiber 104. The user terminal 20 includes a second laser 201 and a second photodiode 202. The side-emitting optical fiber 103 is used to receive a first optical signal emitted by the first laser 101 and then emit it sideways, so that the second photodiode 202 receives the first optical signal transmitted through a free space channel to achieve downlink communication. The scintillation optical fiber 104 is used to receive a second optical signal emitted by the second laser 201 transmitted through a free space channel, so that the first photodiode 102 achieves uplink communication after receiving the second optical signal.

[0053] It should be noted that if Figure 2As shown in the figure, the visible light system based on the distributed passive front end uses only two special POFs (Plastic Optical Fibers, POF) for indoor communication. The modulated user transmitted electrical signal in the uplink is converted into an optical signal after intensity modulation, and is transmitted through the free space channel and received by the side of the scintillation fiber (SF). In the SF, after the optical signal is transmitted for a certain distance, the photodiode (PD) located at the end face of the optical fiber performs direct signal detection; in the downlink, the intensity modulation / direct detection method is also used. The optical signal emitted by the transmitter at the access point (Access Point) is transmitted for a certain distance through the side-emitting fiber (SEF) and then emitted from the side of the optical fiber. After the optical signal is transmitted through the free space channel, the optical signal is received and detected by the end user on the ground.

[0054] It should be noted that both plastic optical fibers are arranged on the ceiling with the same length as the room, while the PD for detecting optical signals in the uplink and the laser for transmitting optical signals in the downlink are both located in the side walls.

[0055] In a feasible implementation manner, the side-emitting optical fiber 103 includes a plurality of first optical fiber segments connected in sequence, and any one of the first optical fiber segments is configured as a side-emitting optical fiber transmitter.

[0056] It should be noted that in the downlink, the side-emitting optical fiber 103 can be segmented into fixed lengths (such as 5 cm), and each optical fiber segment will be regarded as a transmitter, thereby increasing the communication coverage area.

[0057] In a feasible implementation manner, the scintillation optical fiber 104 includes a plurality of second optical fiber segments connected in sequence, and any one of the second optical fiber segments is configured as a scintillation optical fiber receiver.

[0058] It should be noted that, in the uplink, the scintillation optical fiber 104 can be segmented into fixed lengths (eg, 5 cm), and each optical fiber segment will be regarded as a receiver, thereby improving the information transmission rate and the communication coverage area.

[0059] In a feasible implementation manner, the emission wavelengths of the first laser 101 and the second laser 201 are different.

[0060] It should be noted that in order to avoid mutual interference between the uplink and downlink, the transmitters in the uplink and downlink use lasers of different wavelengths to transmit signals. For the uplink, in order to reduce the geometric loss in light propagation, the divergence angle of the uplink transmitter (i.e., the second laser 201 in the uplink) is limited to 1 degree. For simplicity, we also assume that the uplink transmitter only transmits signals to the ceiling and the light beams on the receiving plane do not overlap. In this case, SF can be regarded as several receiving segments, and each SF segment only receives the LOS signal emitted by the nearest transmitter; for the downlink, in order to reduce the influence of ambient light, the field of view of the downlink receiver (i.e., the second photodiode 202 in the downlink) is limited to 1 degree, and only a part of the SEF can be seen, while the other parts of the SEF outside the field of view are ignored.

[0061] The present embodiment provides a visible light communication system based on a distributed passive front end, wherein the visible light communication system includes an access point AP10 and a user terminal 10, wherein the access point AP10 and the user terminal 10 perform indoor communication via an uplink and a downlink, wherein the access point AP10 includes a first laser 101, a first photodiode 102, a side-emitting optical fiber 103, and a flashing optical fiber 104, wherein the user terminal 10 includes a second laser 201 and a second photodiode 202, wherein the side-emitting optical fiber 103 is used to receive a first optical signal emitted by the first laser 101 and then emit it sideways, so that the second photodiode 202 realizes downlink communication after receiving the first optical signal transmitted via a free space channel, and the flashing optical fiber 104 is used to receive a second optical signal transmitted via a free space channel. 1, so that the first photodiode 102 realizes uplink communication after receiving the second optical signal, which solves the technical problem that the visible light communication system based on the optical front end still has great complexity in practical applications. Compared with the prior art, the uplink and downlink of the present application adopt two different new special plastic optical fibers for signal transmission, wherein the downlink adopts the side-emitting optical fiber 103, and the emitted optical signal can be emitted from the side of the optical fiber, thereby increasing the coverage area of ​​the visible light communication, and the uplink adopts the flashing optical fiber 104, which can increase the input fiber light intensity, thereby improving the received optical power, and the visible light communication system does not need to use a lens for optical focusing, which effectively reduces the complexity of the visible light communication system, and has the advantages of large communication coverage, simple structure, low cost, flexible construction and convenient maintenance.

[0062] Based on this, the embodiment of the present application also provides a low-power transmission method, referring to Figure 3 , Figure 3 This is a flowchart of the first embodiment of the low power transmission method of the present application.

[0063] In this embodiment, the low power transmission method is applied to a visible light communication system, and the low power transmission method includes steps S10 to S30:

[0064] Step S10, determining the minimum received optical power according to the expected bit error rate;

[0065] It should be noted that the expected bit error rate may be determined by the BER (Bit Error Rate, BER) requirement of the user, and the minimum received optical power may be estimated by combining the expected bit error rate and the noise power.

[0066] In a feasible implementation manner, the step of determining the minimum received optical power according to the expected bit error rate includes: determining the signal-to-noise ratio according to the expected bit error rate and the Gaussian error function; determining the shot noise variance according to the background light noise power; determining the amplifier noise variance according to the amplifier noise density and the amplifier bandwidth; determining the total noise variance according to the shot noise variance and the amplifier noise variance; and determining the minimum received optical power according to the photodiode response rate, the total noise variance and the signal-to-noise ratio.

[0067] In a specific implementation, the minimum received optical power can be estimated based on the user BER requirement and the noise power. The minimum received optical power can be calculated by combining the signal-to-noise ratio and the noise power, where the signal-to-noise ratio can be estimated by the bit error rate. The relationship between BER and signal-to-noise ratio SNR can be expressed as:

[0068]

[0069] Where Q(·) represents the Gaussian error function. Therefore, the minimum received optical power can be expressed as:

[0070]

[0071] Where R is the responsivity of the PD (i.e., photodiode), is the total noise variance and can be expressed as:

[0072]

[0073] In the formula, is the shot noise variance, represents the amplifier noise variance.

[0074] Step S20, calculating the overall channel attenuation of the uplink and downlink links according to the user location information and the optical fiber transmission distance;

[0075] In a feasible implementation, the step of calculating the overall channel attenuation of the uplink and downlink based on the user location information and the optical fiber transmission distance includes: determining the location information of the side-emitting optical fiber transmitter, the location information of the flashing optical fiber receiver and the uplink and downlink optical fiber transmission loss based on the optical fiber transmission distance; determining the uplink and downlink free space channel gain based on the user location information, the location information of the side-emitting optical fiber transmitter, the location information of the flashing optical fiber receiver and the visible light free space channel model; determining the overall channel attenuation of the uplink and downlink based on the uplink and downlink optical fiber transmission loss and the uplink and downlink free space channel gain.

[0076] In a specific implementation, the uplink and downlink channel attenuation may be calculated based on the uplink and downlink optical fiber transmission losses and the visible light free space channel model.

[0077] In a feasible implementation manner, the step of determining the location information of the side-emitting optical fiber transmitter, the location information of the flashing optical fiber receiver, and the uplink and downlink optical fiber transmission losses according to the optical fiber transmission distance includes: determining the transmission length of the uplink second optical signal in the flashing optical fiber of the visible light communication system according to the optical fiber transmission distance; determining the uplink transmission loss according to the transmission length, transmission ratio, attenuation coefficient, and correction factor; determining the optical fiber radius of the side-emitting optical fiber in the downlink of the visible light communication system; and determining the downlink transmission loss according to the optical fiber radius, scattering coefficient, and correction factor.

[0078] It should be noted that in the uplink, the transmission loss L of the optical signal after it is transmitted over a length z in SF is SF It can be expressed as:

[0079]

[0080] Among them, α SF is the transmission ratio of light from the surface to the fiber core, α ac represents the attenuation coefficient, c f is the correction factor.

[0081] It should be noted that the transmission loss L of SEF in the downlink SEF It can be expressed as:

[0082]

[0083] Where k is the scattering coefficient, r SEF is the radius of SEF, c f is the correction factor.

[0084] Step S30, determining the minimum transmission power of the uplink and downlink when the expected bit error rate is met according to the minimum received optical power and the overall channel attenuation of the uplink and downlink, so as to dynamically adjust the visible light communication system based on the minimum transmission power.

[0085] In the specific implementation, Figure 4 As shown in the figure, when the user's position is fixed and needs to meet a certain transmission BER (bit error rate), the minimum received optical power is first estimated based on the user's BER requirement and the noise power; secondly, the channel attenuation is calculated according to the designed transmission loss and the visible light free space channel model; finally, the received optical power and channel attenuation are combined to obtain the minimum transmitted optical power of the uplink and downlink when the transmission information BER threshold is met.

[0086] In a feasible implementation manner, the step of determining the uplink and downlink free space channel gains according to the user location information, the location information of the side-emitting fiber transmitter, the location information of the scintillation fiber receiver and the visible light free space channel model includes: determining the first link distance between the second laser 201 of the user terminal 10 in the visible light communication system and the scintillation fiber receiver of the visible light communication system according to the user location information and the location information of the scintillation fiber receiver; determining the receiver field of view angle, the first radiation intensity, the receiver effective detection area and the divergence angle of the second laser, wherein the first radiation intensity is determined according to the Lambert emission order and the half-power intensity angle of the light source, and the receiver effective detection area is determined according to the scintillation fiber radius, the first link distance and the divergence angle of the second laser; determining the uplink free space channel gain according to the first link distance, the receiver field of view angle, the radiation intensity, the receiver effective detection area and the divergence angle of the second laser.

[0087] In the uplink of the present invention, the channel gain h between the i-th user and the j-th SF receiver is i,j It can be expressed as:

[0088]

[0089] Where, d i,j is the link distance between the i-th uplink transmitter (the second laser 201 in the uplink) and the j-th receiver, φ is the uplink transmitter divergence angle, ψ i,j is the incident angle of light on the optical fiber, Ψ FoV is the field of view of the receiver, and R(φ) is the first radiation intensity.

[0090] It should be noted that in the uplink, R(φ)=[(m lam +1) / 2π]cos m (φ), where:

[0091] represents the Lambertian emission order, Φ 1 / 2 is the half-power intensity angle of the light source.

[0092] It should be noted that the effective detection area A of the receiver Rx It can be written as:

[0093] A Rx =r SF ×d i.j ×tan(φ),

[0094] Among them, r SF is the flashing fiber radius.

[0095] In a specific implementation, the uplink channel attenuation can be expressed as:

[0096] Ltotal=LPOF×hi,j

[0097] Where, L POF represents the transmission loss of the scintillation optical fiber 104 (i.e., the uplink transmission loss), h i,j Represents the uplink free space channel gain.

[0098] It should be noted that, finally, the minimum received optical power and the uplink channel attenuation are combined to obtain the minimum transmitted optical power of the uplink when the transmission information BER threshold (expected bit error rate) is met, where the minimum transmitted optical power P of the uplink transmitter is t It can be expressed as:

[0099]

[0100] In a feasible implementation manner, the step of determining the uplink and downlink free space channel gains based on the user location information, the location information of the side-emitting fiber transmitter, the location information of the scintillation fiber receiver, and the visible light free space channel model includes: determining the second link distance between the side-emitting fiber transmitter and the second photodiode 202 in the user terminal 10 based on the user location information and the location information of the side-emitting fiber transmitter; determining the second photodiode field of view angle, the second radiation intensity, and the second photodiode effective detection area, wherein the second radiation intensity is determined based on the initial light flux of the transmitter, the scattering coefficient of the side-emitting fiber, and the radius of the side-emitting fiber, and the second photodiode effective detection area is determined based on the refractive index of the optical concentrator and the area of ​​the detector; determining the downlink free space channel gain based on the second link distance, the second photodiode field of view angle, the second radiation intensity, and the second photodiode 202 effective detection area.

[0101] In the downlink, the channel gain h between the i-th SEF transmitter and the j-th user is i,j It can be expressed as:

[0102]

[0103] Where, d i,j is the link distance between the i-th SEF transmitter and the j-th downlink receiver (the second photodiode 202 in the downlink), φ is the transmitter irradiance angle, ψ i,j is the incident angle of light on the optical fiber, Ψ FoV is the field of view of the downlink receiver, and R(φ) is the second radiation intensity.

[0104] It should be noted that, in the downlink, the second radiation intensity may be:

[0105] It is estimated that, where φ0 represents the initial luminous flux of the transmitter.

[0106] It should be noted that the effective detection area A of the downlink receiver is Rx It can be written as:

[0107]

[0108] Among them, n β is the refractive index of the optical concentrator, A d is the area of ​​the detector.

[0109] In a specific implementation, the downlink channel attenuation can be expressed as:

[0110] L total =L POF ×h i,j

[0111] Where, L POF represents the transmission loss of the side-emitting optical fiber 103 (ie, the downlink transmission loss), h i,j Represents the downlink channel gain.

[0112] It should be noted that, finally, the minimum received optical power and the downlink channel attenuation are combined to obtain the minimum transmitted optical power of the downlink when the transmission information BER threshold (expected bit error rate) is met. Among them, the minimum transmitted optical power P of the SEF transmitter is t It can be expressed as:

[0113]

[0114] In the specific implementation, a typical indoor environment with a size of 5m×5m×3m is considered, and the distance between the transmitting plane and the receiving plane is 2.15m. Here, the upper left corner of the room is taken as an example for simulation analysis, and its coordinates are (0,2.5,0.85). Figure 5 and Figure 6 The results show the minimum transmission power required for the uplink and downlink to meet a certain BER in different background light illumination scenarios under the same terminal position. From the results, it can be seen that whether it is uplink or downlink, as the background light illumination increases, its noise power increases accordingly. If the BER is to remain unchanged, the transmitter needs a larger transmission power to offset the influence of background light noise, thereby meeting its signal-to-noise ratio requirements.

[0115] In addition, by comparing Figure 5 and Figure 6 It can be found that under the same conditions, the transmission power required for the downlink is much greater than that for the uplink. This is because the transmission loss of SEF is much greater than that of SF. Under the same optical fiber transmission distance, SEF requires a larger transmission power to meet its transmission rate requirements.

[0116] This embodiment determines the minimum received optical power according to the expected bit error rate; calculates the uplink and downlink channel attenuation according to the user location information and the optical fiber transmission distance; determines the minimum transmission power of the uplink and downlink when the expected bit error rate is met according to the minimum received optical power and the uplink and downlink channel attenuation, so as to dynamically adjust the visible light communication system based on the minimum transmission power. Combining the special design material of SF (doped phosphor) and the mechanism of SEF using scattering for side emission, the transmission loss model of SF and SEF is given, which can more accurately calculate the minimum transmission power.

[0117] It should be noted that the above examples are only used to understand the present application and do not constitute a limitation on the low-power transmission method of the present application. More simple transformations based on this technical concept are all within the scope of protection of the present application.

[0118] The above descriptions are only some embodiments of the present application, and are not intended to limit the patent scope of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A visible light communication system based on a distributed passive front end, characterized in that: The visible light communication system includes an access point AP and a user terminal. The access point AP and the user terminal communicate indoors via an uplink and a downlink. The access point AP includes a first laser, a first photodiode, a side-emitting optical fiber, and a flashing optical fiber. The user terminal includes a second laser and a second photodiode. The side-emitting optical fiber is used to receive a first optical signal emitted by the first laser and then emit it sideways, so that the second photodiode receives the first optical signal transmitted through a free space channel to achieve downlink communication. The flashing optical fiber is used to receive a second optical signal emitted by a second laser transmitted through a free space channel, so that the first photodiode receives the second optical signal and achieves uplink communication.

2. The system according to claim 1, characterized in that The side-emitting optical fiber includes a plurality of first optical fiber segments connected in sequence, and any one of the first optical fiber segments is configured as a side-emitting optical fiber transmitter.

3. The system according to claim 1, characterized in that The scintillation optical fiber includes a plurality of second optical fiber segments connected in sequence, and any one of the second optical fiber segments is configured as a scintillation receiver.

4. The system according to claim 1, characterized in that The first laser and the second laser have different emission wavelengths.

5. A low power transmission method, characterized in that: The low-power transmission method is applied to the visible light communication system according to any one of claims 1 to 4, and the method comprises: Determine the minimum received optical power according to the expected bit error rate; Calculate the overall channel attenuation of uplink and downlink based on user location information and fiber transmission distance; According to the minimum received optical power and the overall channel attenuation of the uplink and downlink, the minimum transmit power of the uplink and downlink when the expected bit error rate is met is determined, so as to dynamically adjust the visible light communication system based on the minimum transmit power.

6. The method according to claim 5, characterized in that The step of determining the minimum received optical power according to the expected bit error rate comprises: Determine a signal-to-noise ratio according to the expected bit error rate and a Gaussian error function; Determine the shot noise variance based on the background light noise power; Determine the amplifier noise variance based on the amplifier noise density and the amplifier bandwidth; determining a total noise variance based on the shot noise variance and the amplifier noise variance; The minimum received optical power is determined according to the photodiode response rate, the total noise variance and the signal-to-noise ratio.

7. The method according to claim 5, characterized in that The step of calculating the overall channel attenuation of the uplink and downlink links according to the user location information and the optical fiber transmission distance comprises: Determine the location information of the side-emitting optical fiber transmitter, the location information of the flashing optical fiber receiver, and the uplink and downlink optical fiber transmission losses according to the optical fiber transmission distance; Determine uplink and downlink free space channel gains according to the user location information, the location information of the side-emitting optical fiber transmitter, the location information of the scintillation optical fiber receiver, and a visible light free space channel model; The uplink and downlink overall channel attenuation is determined according to the uplink and downlink optical fiber transmission losses and the uplink and downlink free space channel gains.

8. The method according to claim 7, characterized in that The step of determining the location information of the side-emitting optical fiber transmitter, the location information of the flashing optical fiber receiver, and the uplink and downlink optical fiber transmission losses according to the optical fiber transmission distance comprises: Determine the transmission length of the second optical signal of the uplink in the visible light communication system in the scintillation optical fiber according to the optical fiber transmission distance; Determining uplink transmission loss according to the transmission length, transmission ratio, attenuation coefficient and correction factor; Determining the fiber radius of the side-emitting optical fiber in the downlink of the visible light communication system; The downlink transmission loss is determined according to the optical fiber radius, the scattering coefficient and the correction factor.

9. The method according to claim 7, characterized in that The step of determining the uplink and downlink free space channel gains according to the user location information, the location information of the side-emitting optical fiber transmitter, the location information of the scintillation optical fiber receiver, and the visible light free space channel model comprises: Determine a first link distance between a second laser at a user end of the visible light communication system and a scintillation optical fiber receiver of the visible light communication system according to the user location information and the location information of the scintillation optical fiber receiver; Determine the receiver field of view angle, the first radiation intensity, the receiver effective detection area and the divergence angle of the second laser, wherein the first radiation intensity is determined according to the Lambertian emission order and the light source half-power intensity angle, and the receiver effective detection area is determined according to the scintillation fiber radius, the first link distance and the second laser divergence angle; An uplink free space channel gain is determined according to the first link distance, the receiver field of view angle, the radiation intensity, the receiver effective detection area, and the divergence angle of the second laser.

10. The method according to claim 7, characterized in that The step of determining the uplink and downlink free space channel gains according to the user location information, the location information of the side-emitting optical fiber transmitter, the location information of the scintillation optical fiber receiver, and the visible light free space channel model comprises: Determine a second link distance between the side-emitting optical fiber transmitter and a second photodiode in the user terminal according to the user location information and the location information of the side-emitting optical fiber transmitter; Determine a second photodiode field of view angle, a second radiation intensity, and an effective detection area of ​​the second photodiode, wherein the second radiation intensity is determined according to an initial luminous flux of a transmitter, a scattering coefficient of a side-emitting optical fiber, and a radius of the side-emitting optical fiber, and the effective detection area of ​​the second photodiode is determined according to a refractive index of an optical concentrator and an area of ​​a detector; A downlink free space channel gain is determined according to the second link distance, the second photodiode field of view, the second radiation intensity, and the second photodiode effective detection area.

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