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

Abstract

This application discloses a visible light communication system and low-power transmission method based on a distributed passive front-end, relating to the field of visible light communication technology. The visible light communication system includes an access point (AP) and a user terminal. The AP and the user terminal communicate indoors via uplink and downlink. The AP includes a first laser, a first photodiode, a side-emitting optical fiber, and a scintillating optical fiber. The user terminal includes a second laser and a second photodiode. The side-emitting optical fiber receives a first optical signal emitted by the first laser and then emits it from the side, enabling the second photodiode to receive the first optical signal transmitted through a free-space channel and achieve downlink communication. The scintillating optical fiber receives a second optical signal emitted by the second laser, transmitted through a free-space channel, enabling the first photodiode to receive the second optical signal and achieve uplink communication. This reduces the complexity of the visible light communication system.

Description

Technical Field

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

[0002] For IoT applications, the topology of a Visible Light Communication (VLC) system should be simple enough and use low-cost components. A typical VLC network includes multiple front-end access points, each consisting of a light-emitting diode (LED) and a photodiode (PD). The corresponding photoelectric and electro-optical conversions are performed at the front end, and the electrical signal is sent back to the residential gateway. To reduce the complexity of VLC networks, the concept of a passive optical front end has been proposed. In an indoor communication system based on a passive optical front end, plastic optical fiber is used as a feeder in the room ceiling. For the downlink, the light generated by the residential gateway is emitted from the plastic optical fiber (POF) end for data transmission. For the uplink, the light collected by a lens propagates 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 indoor coverage requires multiple optical front ends, this optical front end-based system still remains highly complex in practical applications.

[0003] The above content is only used to help understand the technical solution of this application and does not represent an admission that the above content is prior art. Summary of the Invention

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

[0005] To achieve the above objectives, this application proposes a visible light communication system based on a distributed passive front-end. The visible light communication system includes an access point (AP) and a user terminal. The AP and the user terminal communicate indoors via uplink and downlink. The AP includes a first laser, a first photodiode, a side-emitting optical fiber, and a scintillating optical fiber. The user terminal includes a second laser and a second photodiode. The side-emitting optical fiber receives a first optical signal emitted by the first laser and then emits it from the side, enabling the second photodiode to receive the first optical signal transmitted through a free space channel and achieve downlink communication. The scintillating optical fiber receives a second optical signal emitted by the second laser transmitted through a free space channel, enabling the first photodiode to receive the second optical signal and achieve uplink communication.

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

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

[0009] To achieve the above objectives, this application also proposes a low-power transmission method, which is applied to the visible light communication system described above, the method comprising:

[0010] Determine the minimum received optical power based on the expected bit error rate;

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

[0012] Based on the minimum received optical power and the overall channel attenuation of the uplink and downlink, the minimum transmit power of the uplink and downlink is determined to meet the expected bit error rate, 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 based on the expected bit error rate includes:

[0014] The signal-to-noise ratio is determined based on the expected bit error rate and the 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 amplifier bandwidth;

[0017] The total noise variance is determined based on the shot noise variance and the amplifier noise variance;

[0018] The minimum received optical power is determined based on the photodiode responsivity, the total noise variance, and the signal-to-noise ratio.

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

[0020] The location information of the side-emitting fiber optic transmitter, the location information of the scintillation fiber optic receiver, and the uplink and downlink fiber optic transmission losses are determined based on the fiber optic transmission distance.

[0021] The uplink and downlink free space channel gains are determined based on the user location information, the location information of the side-emitting fiber optic transmitter, the location information of the scintillation fiber optic receiver, and the visible light free space channel model.

[0022] The overall channel attenuation of the uplink and downlink is determined based on the uplink and downlink fiber transmission loss and the uplink and downlink free space channel gain.

[0023] In one embodiment, the step of determining the location information of the side-emitting fiber optic transmitter, the location information of the scintillation fiber optic receiver, and the uplink and downlink fiber optic transmission losses based on the fiber optic transmission distance includes:

[0024] The transmission length of the uplink second optical signal in the scintillating optical fiber in the visible light communication system is determined based on the optical fiber transmission distance.

[0025] The uplink transmission loss is determined based on the transmission length, transmission ratio, attenuation coefficient, and correction factor.

[0026] Determine 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 based on the fiber radius, scattering coefficient, and correction factor.

[0028] In one embodiment, the step of determining the uplink and downlink free-space channel gain based on the user location information, the location information of the side-emitting fiber optic transmitter, the location information of the scintillation fiber optic receiver, and the visible light free-space channel model includes:

[0029] The first link distance between the second laser at the user end of the visible light communication system and the scintillation fiber optic receiver is determined based on the user location information and the location information of the scintillation fiber optic receiver.

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

[0031] The uplink free-space channel gain is determined based on the first link distance, the receiver field of view, 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 gain based on the user location information, the location information of the side-emitting fiber optic transmitter, the location information of the scintillation fiber optic receiver, and the visible light free-space channel model includes:

[0033] The second link distance between the side-emitting fiber optic transmitter and the second photodiode in the user terminal is determined based on the user location information and the location information of the side-emitting fiber optic transmitter.

[0034] The field of view of the second photodiode, the second radiation intensity, and the effective detection area of ​​the second photodiode are determined. 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. The effective detection area of ​​the second photodiode is determined based on the refractive index of the optical condenser and the area of ​​the detector.

[0035] The downlink free space channel gain is determined based on the second link distance, the field of view of the second photodiode, the second radiation intensity, and the effective detection area of ​​the second photodiode.

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

[0037] This application proposes a visible light communication system and low-power transmission method based on a distributed passive front-end. The visible light communication system includes an access point (AP) and a user terminal. The AP and the user terminal communicate indoors via uplink and downlink. The AP includes a first laser, a first photodiode, a side-emitting optical fiber, and a scintillating optical fiber. The user terminal includes a second laser and a second photodiode. The side-emitting optical fiber receives the first light signal emitted by the first laser and then emits it from the side, enabling the second photodiode to receive the first light signal transmitted through a free-space channel and achieve downlink communication. The scintillating optical fiber receives the second laser signal transmitted through a free-space channel. The emitted second optical signal enables the first photodiode to receive the second optical signal and achieve uplink communication. This solves the technical problem that visible light communication systems based on passive optical front-ends still have great complexity in practical applications. Compared with the prior art, this application uses two different novel special plastic optical fibers for signal transmission in the uplink and downlink. The downlink uses side-emitting optical fiber, which can emit optical signals from the side of the optical fiber, thereby increasing the coverage area of ​​visible light communication. The uplink uses scintillating optical fiber, which can increase the intensity of the incoming light and thus improve the received optical power. Moreover, this visible light communication system does not require the use of lenses for optical focusing, thereby effectively reducing the complexity of the visible light communication system. Attached Figure Description

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

[0039] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a block diagram of the visible light communication system based on a distributed passive front end, as described in this application.

[0041] Figure 2 This is a block diagram of the visible light communication system based on a distributed passive front end, as described in this application.

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

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

[0044] Figure 5 This is a simulation diagram of the minimum transmit power of the uplink in the low-power transmission method provided in Embodiment 2 of this application;

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

[0046] Figure label:

[0047] 10-Access Point (AP); 20-User Terminal; 101-First Laser; 102-First Photodiode; 103-Side-emitting Fiber Optic; 104-Scintillating Fiber Optic; 201-Second Laser; 202-Second Photodiode.

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

[0049] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.

[0050] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0051] This application provides a visible light communication system based on a distributed passive front end.

[0052] Reference Figure 1 In this embodiment of the 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 communicate indoors via uplink and downlink. The access point AP10 includes a first laser 101, a first photodiode 102, a side-emitting fiber 103, and a scintillating fiber 104. The user terminal 20 includes a second laser 201 and a second photodiode 202. The side-emitting fiber 103 receives a first light signal emitted by the first laser 101 and emits it from the side, so that the second photodiode 202 receives the first light signal transmitted through a free space channel and achieves downlink communication. The scintillating fiber 104 receives a second light signal emitted by the second laser 201 transmitted through a free space channel, so that the first photodiode 102 receives the second light signal and achieves uplink communication.

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

[0054] It should be noted that both types of plastic optical fibers are installed on the ceiling, with a length equal to the length of the room, while the PD used to detect optical signals in the uplink and the laser used to transmit optical signals in the downlink are located in the side walls.

[0055] In one feasible implementation, 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 (e.g., 5cm), and each fiber segment will be regarded as a transmitter, thereby improving the communication coverage area.

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

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

[0059] In one possible implementation, the first laser 101 and the second laser 201 emit different wavelengths.

[0060] It should be noted that, 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, to reduce geometric losses 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 towards the ceiling and that the beams on the receiving plane do not overlap. In this case, the SF can be regarded as several receiving segments, each receiving only the LOS signal emitted by the nearest transmitter. For the downlink, 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 portion of the SEF is visible, while the SEF outside the field of view is ignored.

[0061] This embodiment provides a visible light communication system based on a distributed passive front-end. The visible light communication system includes an access point (AP10) and a user terminal (10). Indoor communication between the AP10 and the user terminal (10) is achieved via uplink and downlink. The AP10 includes a first laser 101, a first photodiode 102, a side-emitting fiber 103, and a scintillating fiber 104. The user terminal (10) includes a second laser 201 and a second photodiode 202. The side-emitting fiber 103 receives the first light signal emitted by the first laser 101 and then emits it laterally, enabling the second photodiode 202 to receive the first light signal transmitted through a free-space channel and achieve downlink communication. The scintillating fiber 104 receives the second laser 201 transmitted through a free-space channel. The second optical signal emitted by the first photodiode 102 enables uplink communication after receiving the second optical signal. This solves the technical problem that visible light communication systems based on optical front-ends still have great complexity in practical applications. Compared with the prior art, this application uses two different novel special plastic optical fibers for signal transmission in the uplink and downlink. The downlink uses a side-emitting optical fiber 103, which can emit optical signals from the side of the optical fiber, thereby increasing the coverage area of ​​visible light communication. The uplink uses a scintillating optical fiber 104, which can increase the intensity of the incoming light and thus improve the received optical power. Moreover, this visible light communication system does not require the use of lenses for optical focusing, effectively reducing the complexity of the visible light communication system. It has the advantages of large communication coverage, simple structure, low cost, flexible construction and convenient maintenance.

[0062] Based on this, embodiments of this application also provide a low-power transmission method, referring to... Figure 3 , Figure 3 This is a flowchart illustrating the first embodiment of the low-power transmission method of this 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: Determine the minimum received optical power based on the expected bit error rate;

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

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

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

[0068]

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

[0070]

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

[0072]

[0073] In the formula, For the variance of shot noise, This represents the amplifier noise variance.

[0074] Step S20: Calculate the overall channel attenuation of uplink and downlink based on user location information and fiber optic transmission distance;

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

[0076] In practical implementation, uplink and downlink channel attenuation can be calculated based on uplink and downlink fiber transmission loss and visible light free space channel model.

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

[0078] It should be noted that in the uplink, the optical signal experiences a transmission loss L after traveling a length z along the SF path. SF It can be represented as:

[0079]

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

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

[0082]

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

[0084] Step S30: Based on the minimum received optical power and the overall channel attenuation of the uplink and downlink, determine the minimum transmit power of the uplink and downlink while meeting the expected bit error rate, so as to dynamically adjust the visible light communication system based on the minimum transmit power.

[0085] In specific implementations, such as Figure 4 As shown, when the user's location is fixed and a certain transmission BER (bit error rate) needs to be met, the minimum received optical power is first estimated based on the user's BER requirement and noise power; then, the channel attenuation is calculated based on the designed transmission loss and the visible light free space channel model; finally, by combining the received optical power and the channel attenuation, the minimum transmit optical power of the uplink and downlink when the transmission information BER threshold is met is obtained respectively.

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

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

[0088]

[0089] In the formula, d i,j Let φ be the link distance between the i-th uplink transmitter (the second laser 201 in the uplink) and the j-th receiver, φ be the divergence angle of the uplink transmitter, and ψ be the distance between the i-th uplink transmitter and the j-th receiver. i,j Ψ is the angle of incidence of light at the fiber optic cable. FoV R(φ) 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] Φ represents the Lambert emission order. 1 / 2 The angle 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] Where, r SF The radius of the scintillation fiber.

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

[0096] Ltotal = LPOF × hi,j

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

[0098] It should be noted that, finally, by combining the minimum received optical power and the uplink channel attenuation, the minimum transmit optical power of the uplink that satisfies the expected bit error rate (BER) threshold is obtained, where P is the minimum transmit optical power of the uplink transmitter. t It can be represented as:

[0099]

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

[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 represented as:

[0102]

[0103] In the formula, d i,j Let φ be the link distance between the i-th SEF transmitter and the j-th downlink receiver (the second photodiode 202 in the downlink), φ be the transmitter irradiance angle, and ψ be the irradiance angle. i,j Ψ is the angle of incidence of light at the fiber optic cable. FoV R(φ) represents the field of view of the downlink receiver, and R(φ) represents the second radiation intensity.

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

[0105] The estimated value is φ0, which represents the initial optical flux of the transmitter.

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

[0107]

[0108] Where, n β A is the refractive index of the optical concentrator. d Let be the area of ​​the detector.

[0109] In practical implementation, downlink channel attenuation can be expressed as:

[0110] L total =L POF ×h i,j

[0111] In the formula, L POF h represents the transmission loss (i.e., downlink transmission loss) of the side-emitting fiber 103. i,j This indicates the downlink channel gain.

[0112] It should be noted that, finally, by combining the minimum received optical power and downlink channel attenuation, the minimum transmit optical power of the downlink that satisfies the expected bit error rate (BER) threshold is obtained. Here, the minimum transmit optical power P of the SEF transmitter... t It can be represented as:

[0113]

[0114] In the specific implementation, a typical indoor environment with dimensions of 5m×5m×3m is considered, and the distance between the transmitting plane and the receiving plane is 2.15m. Here, the simulation analysis is carried out using the upper left corner of the room as an example, with coordinates (0,2.5,0.85). Figure 5 and Figure 6 The results demonstrate the minimum transmit power required for uplink and downlink to meet a certain BER in scenarios with different background illumination levels at the same terminal location. The results show that, for both uplink and downlink, the noise power increases with increasing background illumination. To maintain a constant BER, the transmitter needs greater transmit power to offset the impact of background light noise and thus meet the signal-to-noise ratio requirements.

[0115] Furthermore, through comparison Figure 5 and Figure 6 It can be observed that, under the same conditions, the downlink requires much more transmit power than the uplink. This is because the transmission loss of SEF is much greater than that of SF. For the same fiber transmission distance, SEF requires more transmit power to meet its transmission rate requirements.

[0116] This embodiment determines the minimum received optical power based on the desired bit error rate; calculates the uplink and downlink channel attenuation based on user location information and fiber transmission distance; and determines the minimum transmit power of the uplink and downlink while meeting the desired bit error rate based on 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 transmit power. Combining the special design materials of SF (doped phosphor) and the mechanism of SEF (side emission via scattering), transmission loss models for SF and SEF are given, which can calculate the minimum transmit power relatively accurately.

[0117] It should be noted that the above examples are only for understanding this application and do not constitute a limitation on the low-power transmission method of this application. Any simple modifications based on this technical concept are within the protection scope of this application.

[0118] The above description is only a part of the embodiments of this application and does not limit the patent scope of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this 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 AP and the user terminal communicate indoors via uplink and downlink. The AP includes a first laser, a first photodiode, a side-emitting optical fiber, and a scintillating optical fiber. The user terminal includes a second laser and a second photodiode. The side-emitting optical fiber receives a first light signal emitted by the first laser and then emits it from the side, enabling the second photodiode to receive the first light signal transmitted through a free space channel and achieve downlink communication. The scintillating optical fiber receives a second light signal emitted by the second laser transmitted through a free space channel, enabling the first photodiode to receive the second light signal and achieve uplink communication. The visible light communication system is used to implement a low-power transmission method, which includes: The minimum received optical power is determined based on the expected bit error rate, which is determined based on the user's bit error rate. The minimum received optical power is estimated by combining the expected bit error rate and the noise power. Calculate the overall channel attenuation of uplink and downlink based on user location information and fiber optic transmission distance; Based on the minimum received optical power and the overall channel attenuation of the uplink and downlink, the minimum transmit power of the uplink and downlink is determined to meet the expected bit error rate, so as to dynamically adjust the visible light communication system based on the minimum transmit power.

2. The system as described in claim 1, characterized in that, The side-emitting optical fiber includes several 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 as described in claim 1, characterized in that, The scintillation fiber includes several second fiber segments connected in sequence, and any one of the second fiber segments is configured as a scintillation receiver.

4. The system as described in 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 a visible light communication system as described in any one of claims 1-4, the method comprising: The minimum received optical power is determined based on the expected bit error rate, which is determined based on the user's bit error rate. The minimum received optical power is estimated by combining the expected bit error rate and the noise power. Calculate the overall channel attenuation of uplink and downlink based on user location information and fiber optic transmission distance; Based on the minimum received optical power and the overall channel attenuation of the uplink and downlink, the minimum transmit power of the uplink and downlink is determined to meet the expected bit error rate, so as to dynamically adjust the visible light communication system based on the minimum transmit power.

6. The method as described in claim 5, characterized in that, The step of determining the minimum received optical power based on the expected bit error rate includes: The signal-to-noise ratio is determined based on the expected bit error rate and the 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 amplifier bandwidth; The total noise variance is determined based on the shot noise variance and the amplifier noise variance; The minimum received optical power is determined based on the photodiode responsivity, the total noise variance, and the signal-to-noise ratio.

7. The method as described in claim 5, characterized in that, The step of calculating the overall uplink and downlink channel attenuation based on user location information and fiber optic transmission distance includes: The location information of the side-emitting fiber optic transmitter, the location information of the scintillation fiber optic receiver, and the uplink and downlink fiber optic transmission losses are determined based on the fiber optic transmission distance. The uplink and downlink free space channel gains are determined based on the user location information, the location information of the side-emitting fiber optic transmitter, the location information of the scintillation fiber optic receiver, and the visible light free space channel model. The overall channel attenuation of the uplink and downlink is determined based on the uplink and downlink fiber transmission loss and the uplink and downlink free space channel gain.

8. The method as described in claim 7, characterized in that, The steps of determining the location information of the side-emitting fiber optic transmitter, the location information of the scintillation fiber optic receiver, and the uplink and downlink fiber optic transmission losses based on the fiber optic transmission distance include: The transmission length of the uplink second optical signal in the scintillating optical fiber in the visible light communication system is determined based on the optical fiber transmission distance. The uplink transmission loss is determined based on the transmission length, transmission ratio, attenuation coefficient, and correction factor. Determine the fiber radius of the side-emitting optical fiber in the downlink of the visible light communication system; The downlink transmission loss is determined based on the fiber radius, scattering coefficient, and correction factor.

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

10. The method as described in claim 7, characterized in that, The step of determining the uplink and downlink free-space channel gain based on the user location information, the location information of the side-emitting fiber optic transmitter, the location information of the scintillation fiber optic receiver, and the visible light free-space channel model includes: The second link distance between the side-emitting fiber optic transmitter and the second photodiode in the user terminal is determined based on the user location information and the location information of the side-emitting fiber optic transmitter. The field of view of the second photodiode, the second radiation intensity, and the effective detection area of ​​the second photodiode are determined. 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. The effective detection area of ​​the second photodiode is determined based on the refractive index of the optical condenser and the area of ​​the detector. The downlink free space channel gain is determined based on the second link distance, the field of view of the second photodiode, the second radiation intensity, and the effective detection area of ​​the second photodiode.

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