CN110071770B

CN110071770B - Visible light communication receiver

Info

Publication number: CN110071770B
Application number: CN201910406965.3A
Authority: CN
Inventors: 陈清祥; 黄显扬; 穆罕默德凯南吉帕; 徐丽妮
Original assignee: Shaoxing Aifenghuan Communication Equipment Co ltd
Current assignee: Shaoxing Aifenghuan Communication Equipment Co ltd
Priority date: 2019-05-16
Filing date: 2019-05-16
Publication date: 2021-12-24
Anticipated expiration: 2039-05-16
Also published as: CN110071770A

Abstract

The invention discloses a visible light communication receiver, which is connected with an external visible light communication emitter, wherein the visible light communication emitter comprises an emitter circuit and a modulation light source connected with the emitter circuit, the visible light communication receiver comprises a receiver circuit, a photoelectric detector connected with the receiver circuit and a Fresnel lens, the receiver circuit is connected with the photoelectric detector, the Fresnel lens is convex, and the Fresnel lens is used for diffracting light generated by the modulation light source to the photoelectric detector so that the photoelectric detector receives light signals under a plurality of focuses or at different positions of the detector. Compared with the prior art, the invention improves the visible light communication efficiency and the visual field of the coverage range of the visible light receiver.

Description

Visible light communication receiver

Technical Field

The invention relates to the field of photoelectric devices, in particular to a visible light communication receiver.

Background

As shown in fig. 1, current visible light communication systems typically include transmitter and receiver circuitry, as well as light emitting diodes and photodetectors, to transmit and receive data over an optical link. When the optical link becomes unavailable, the Wi-Fi link may be selected as a backup, continuing to send and receive data.

Fig. 2 shows a photodiode coupled to a receiver circuit in an existing visible light communication system paired with a lens that can increase the light intensity to be received by the photodiode. This increased light intensity translates into an increased power density received by the photodiode and receiver circuitry, thus further improving the signal-to-noise ratio (SNR) of the received signal. This is due to the fact that the lens converts the wide beam into a converging beam with a minimum focal length radius.

In current visible light communication systems, line of sight (LOS) connections are typically required for the transmitter and receiver in order to provide high data transmission efficiency.

However, in practical situations, line-of-sight connections do not always exist, as the field of view (FOV) of the receiver may change if its position is moved.

If the receiver's received signal orientation changes, it may result in an alignment between the field of view of the transmitter and the receiver not being achieved.

Disclosure of Invention

The invention mainly aims to provide a visible light communication receiver, aiming at improving the visible light communication efficiency and the visual field of the coverage range of the receiver and improving the receiving power of a visible light communicator.

In order to achieve the above object, the present invention provides a visible light communication receiver, the visible light communication receiver is connected to an external visible light communication transmitter, the visible light communication transmitter includes a transmitter circuit, a modulation light source connected to the transmitter circuit, the visible light communication receiver includes a receiver circuit, a photodetector connected to the receiver circuit, and a fresnel lens, the receiver circuit is connected to the photodetector, wherein the fresnel lens is convex, and the fresnel lens is configured to diffract light generated by the modulation light source to the photodetector, so that the photodetector receives light signals at a plurality of focuses or at different positions of the detector.

Wherein the photodetector is positioned at the highest point of the light incident plane generated by the modulated light source and the photodetector.

The modulation light source is one of a light emitting diode, a laser or an optical modulator.

Wherein the photodetector is one of a photodiode, an array charge coupled device, an array CMOS, an avalanche photodiode, or an APD detector array.

The visible light communication receiver further comprises a first microcontroller connected with the receiver circuit, the visible light communication transmitter further comprises a second microcontroller connected with the transmitter circuit, and the first microcontroller is connected with the second microcontroller through WIFI.

The visible light communication receiver further comprises a first modulator connected with the first microcontroller, and the visible light communication receiver further comprises a second modulator connected with the second microcontroller.

The invention has the beneficial effects that: according to the visible light communication receiver, the convex Fresnel lens is adopted through the technical scheme, so that the visible light communication efficiency is improved, and the visual field of the coverage range of the visible light receiver is improved. The convex fresnel lens can improve the reception power of the visible light communication receiver by placing the photodiode at multiple focal points. The use of a convex fresnel lens also improves the transmission distance between the light emitting diode and the photodiode. The convex fresnel lens can also be used bi-directionally, with multiple focal points on either side of the convex fresnel lens fabricated in the visible light communications receiver.

Drawings

Fig. 1 is a block diagram of a system configuration of a visible light communication transmitter and a visible light communication receiver without a fresnel lens in the related art;

FIG. 2 is a schematic diagram of a convex lens and a photodiode pair connected to a receiver circuit in a prior art visible light communication system;

FIG. 3 is a block diagram of a system configuration of a visible light communication transmitter and a visible light communication receiver having a Fresnel lens according to the present invention;

fig. 4 is a block diagram of a visible light communication receiver circuit with a modified fresnel lens and a photodiode connected to a microcontroller and demodulator.

FIG. 5 is a top view of a convex Fresnel lens;

FIG. 6 is a bottom view of a convex Fresnel lens;

FIG. 7 is a front view of a convex Fresnel lens;

FIG. 8 is a schematic of the minimum number of focal points that exist when using a straight Fresnel lens;

FIG. 9 is a schematic illustration of the multiple focal points that exist when a convex Fresnel lens is used;

FIG. 10 shows a shaped Fresnel lens showing the diffraction of an incident optical signal into multiple focal points;

FIGS. 11(a) and 11(b) illustrate various lenses used in experiments to determine the most effective Fresnel lens;

fig. 12 is a schematic diagram of an experimental setup for determining the efficiency of a visible light communication system at direct line of sight at different distances.

Fig. 13 is a schematic diagram of an experimental setup for determining the efficiency of a visible light communication system for different transmission angles between light emitting diodes and photodiodes.

Fig. 14 is a schematic diagram of an experimental setup for determining the efficiency of a visible light communication system for different photodiode locations (not in a direct line-of-sight connection).

Fig. 15 is a schematic diagram of an experimental setup for determining the efficiency of a visible light communication system within the coverage area of light emitting diode transmissions.

Fig. 16 is a schematic diagram of an experimental setup for determining the visible light communication efficiency of the led footprint within the cone radius R when the photodiode is moved.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Referring to fig. 1 to 16, the present invention provides a visible light communication receiver, the visible light communication receiver is connected to an external visible light communication transmitter, the visible light communication transmitter includes a transmitter circuit and a modulation light source connected to the transmitter circuit, the visible light communication receiver includes a receiver circuit, a photodetector connected to the receiver circuit, and a fresnel lens, the receiver circuit is connected to the photodetector, and the fresnel lens is convex.

It will be appreciated that a convex fresnel lens may diffract light generated by the modulated light source to the photodetector such that the photodetector receives the light signal at multiple focal points or at different locations on the detector.

As an embodiment, the invention positions the photodetector at the highest point between the light incident plane generated by the modulated light source and the photodetector, so that the visual field detected by the visible light communication receiver can be improved.

In one embodiment, the modulated light source used may be a standard light emitting diode, and the photodetector may be a high sensitivity silicon-based photodiode. The modulated light source may also employ a laser diode, or a laser, or a light modulator (SLM) with a backlight, or any modulated light source. In addition, the photodetector may also employ one of a photodiode, an array Charge Coupled Device (CCD), an array CMOS, an Avalanche Photodiode (APD), or an APD detector array to detect the high bandwidth optical signal. The following description will mainly use the light emitting diode as the modulation light source and the photodiode as the photo detector.

It is understood that in the present invention, the convex shaped fresnel lens may provide multiple focal points to diffract light from the light emitting diode to the photodiode. Thereby, the photodiodes may be placed at different positions, as the multiple focal points increase the light transmission angle in the visible light communication receiver and the transmission distance between the light emitting diode and the photodiode.

Compared with the prior art, the transmission distance between the light emitting diode and the photodiode is longer, and the efficiency of receiving power by the photodiode is improved. The relative transmission angle between the light emitting diode and the photodiode is wider, and the efficiency of receiving power by the photodiode is improved. In the present invention, the fresnel lens may also be used in both directions to provide multiple focal points in the visible light communication receiver.

As an embodiment, when manufacturing the fresnel lens, it is necessary to use a specific size container to complete the lens manufacturing process by heating the lens or other mechanical means or a combination of both.

Specifically, the lens to be prepared is placed in a container (such as a bowl) filled with preheated cooking oil, the heating is carried out for 3-5min within the temperature range of 80-90 ℃, the heated lens to be prepared is placed in a container with a preset diameter, the pressure is applied, the lens to be prepared is molded into a preset shape within 10-12 seconds, and then the lens to be prepared molded into the preset shape is cooled at room temperature to obtain the Fresnel lens. The heated lens to be prepared is placed in a container with a preset diameter, so that lenses with different sizes can be conveniently produced, and the lens to be prepared is molded into a preset shape within 10-12 seconds, so that the Fresnel lens can be ensured to be soft.

In other embodiments, the formation and modification of the Fresnel lens may also be shaped by other heating methods, deposition methods, or other mechanical methods, or a combination of both, as desired.

Further, in the invention, the visible light communication receiver further comprises a first microcontroller connected with the receiver circuit, the visible light communication transmitter further comprises a second microcontroller connected with the transmitter circuit, and the first microcontroller and the second microcontroller are connected through WIFI.

Further, the visible light communication receiver further comprises a first modulator connected with the first microcontroller, and the visible light communication receiver further comprises a second modulator connected with the second microcontroller.

The structure and the operation principle of the visible light communication receiver of the present invention are further explained below.

As shown in fig. 3, the present invention proposes a Visible Light Communication (VLC) receiver for use with a visible light communication transmitter. The visible light communication system as shown in fig. 1 (without the use of a lens) and fig. 3 (with the use of a fresnel lens) includes a set of transceiver circuits that interface with a Microcontroller (MCU). The transmitter circuit is connected with the modulated light source, and the receiver circuit is connected with the photoelectric detector. In this example, as shown in fig. 3, a light emitting diode LED is used as the modulated light source, and a photodiode is used as the electric detector. An input optical signal from a light emitting diode LED is sensed by a photodiode and its optical signal is converted into an electrical signal, and then the transmitted data is processed by a receiver circuit. The two WiFi transceivers provide and control a communication link between the two circuits on the circuits of the transmitter and receiver.

Fig. 4 further illustrates that the visible light communication receiver includes a photodiode and a fresnel lens modified to be curved in a convex shape such that light from the light emitting diode LED, when diffracted by the fresnel lens, creates multiple focal points at which the light signal is received by the photodiode.

In other words, the photodiodes may be positioned at multiple focal points to receive the incident optical signal. This improves the field of view (FOV) of detection of the visible light communication receiver. It is noted, however, that the photodiode is typically positioned so that the photodiode receives the highest received power, that is, the highest point at which the incident optical signal is incident relative to the plane of incidence of the photodiode, that will be the optimal location for the photodiode. The light emitting diode LED used is a standard commercial LED, and a silicon point contact (PIN) photodiode is used due to its high sensitivity. The light source used may further be selected from a laser diode, a laser, a Spatial Light Modulator (SLM) with a backlight or any modulated light source. In terms of the photodetectors used, they may be selected from photodiodes, photodiode arrays, Charge Coupled Device (CCD) arrays, CMOS arrays, Avalanche Photodiodes (APD) and APD detector arrays, and the like, which allow the detection of high bandwidth optical signals.

To improve the performance of the visible light communication system described above, a fresnel lens is used to improve the field of view of the visible light communication receiver. FIG. 5 shows a top view of the modified Fresnel lens and FIG. 6 shows a bottom view of the modified Fresnel lens. FIG. 7 shows a front view of a Fresnel lens with a reduced diameter after modification.

Fig. 8 and 9 show the difference in the effect of the fresnel lens on the passing light signal. Figure 8 shows a known fresnel lens used to pass an optical signal to produce a minimum number of focal points. When a straight fresnel lens receives an incident light signal, the lens converges parallel incident light rays at one point, referred to as the primary focal point. FIG. 9 shows a Fresnel lens modified by a curved lens. Since the fresnel lens is shaped to reduce the diameter of the lens, the incident parallel beams will converge in a random fashion due to the intersecting rays (as shown in fig. 10) to create multiple focal points at different locations. This is in contrast to the known use of fresnel lenses, which produce fewer focal points. This optical fourier effect can improve signal quality by creating multiple optical foci through the fresnel lens with various wavefront radiations. The advantage of using a modified lens is that individual photodiodes can be placed at different positions to increase the light transmission angle in the system, as well as to increase the different distances between the light emitting diode LED and the photodiode. This can be seen in the experiments to be performed below.

As shown in table 1 below, table 1 shows 7 different types of fresnel lenses that were used in the following experiments as shown in fig. 11(a) before lens modification and fig. 11(b) after lens modification.

Fig. 12 shows an experimental setup of an optical visible light communication receiver, where the photodiode is placed directly in line of sight of the light emitting diode LED (0 ° angle between the light emitting diode LED and the photodiode). The modified fresnel lens is placed in front of the photodiode in the same line of sight. The photodiode is further connected to a receiver circuit. The transmitter circuit and the receiver circuit are further connected to a computer for generating signals and processing the received signals. Experiments were performed by adjusting the distance between the light emitting diode LED and the photodiode to be between 30 cm and 285 cm.

To determine lens performance, the experiment was sent from the light emitting diode LED to the receiver circuit through different sized files or data.

TABLE 1

As shown in table 2, table 2 shows the experimental results in which lens B and lens C are modified fresnel lenses that also achieve the highest efficiency. Graph 2 shows the overall lens efficiency (distance range 30 cm to 285 cm) at 0 ° angle between the LED (101) and photodiode (105)

Fig. 13 shows a similar experimental setup for an optical visible light communication receiver, where the photodiode is placed directly in line of sight of the light emitting diode LED.

In this arrangement, the angle between the light emitting diode LED and the photodiode is adjusted in 10 degree increments to gradually change the angle from 10 to 100. A method of non-automatic/manual movement is used to adjust the angle between the light emitting diode LED and the photodiode to thereby achieve the desired angle. To determine lens performance, experiments will be sent from the light emitting diode LED to the receiver circuit through different sized files or data.

Lens	VLC Efficiency (visible light communication system Efficiency)
		Lens-free	13.70％
Lens A	62.47％
		Lens B	94.08％
Lens C	98.96％
		Lens D	53.83％
Lens E	50.00％
		Lens F	50.00％
Lens G	48.799％

TABLE 2

As shown in table 3, table 3 shows the lens efficiency or total visible light communication system efficiency at a fixed 75 cm distance and at different emission angles.

Table 3 shows the results of the experiment in which lenses B and C are improved fresnel lenses with the highest efficiency.

Fig. 14 shows a similar experimental setup for an optical visible light communication receiver, where the photodiode is placed at a certain distance from the line of sight of the light emitting diode LED, such that the angle between the light emitting diode LED and the photodiode is adjusted in 10 degree increments gradually changing the angle from 10 to 100 °. An example of a specific distance used is 40.5 centimeters. The experiments were performed at a fixed distance of 30 cm between the light emitting diode LED and the photodiode.

To determine lens performance, experiments will be sent from the light emitting diode LED to the receiver circuit through different sized files or data.

Lens	Total VLC Efficiency (Total visible light communication System Efficiency)
		Lens-free	0.00％
Lens A	82.19％
		Lens B	92.86％
Lens C	89.46％
		Lens D	86.60％
Lens E	80.00％
		Lens F	85.89％
Lens G	70.26％

TABLE 3

As shown in table 4, the lens efficiency was performed at a fixed distance of 30 cm between the LED and photodiode, with the LED footprint shifting the photodiode position.

Table 4 shows the experimental results that almost all lenses showed high efficiency.

Fig. 15 shows an experimental setup of an optical visible light communication receiver in order to determine the coverage area of the light emitting diode LED and the detection field of view (FOV) of the visible light communication system receiver. The experiments were performed using three different fixed distances of 30 cm, 150 cm and 225 cm between the light emitting diode LED and the photodiode. As shown in fig. 16, the photodiode and fresnel lens are moved over the LED cone radius R footprint.

To determine lens performance, experiments will be sent from the light emitting diode LED to different photodiode locations through different sized files or data.

Lens	Total VLC Efficiency (Total visible light communication System Efficiency)
		Lens-free	61.09％
Lens A	100.00％
		Lens B	100.00％
Lens C	100.00％
		Lens D	100.00％
Lens E	100.00％
		Lens F	100.00％
Lens G	98.51％

TABLE 4

Table 5 shows the results of the experiment using lens B and lens C. Lenses B and C show the best maximum beam angle when the LED is 150 cm from the photodiode compared to when no lens is used, while having a larger radius of 121 cm or 130 cm.

Thus, the modified Fresnel lens provides an improved field of view compared to other lenses or compared to no lens used.

TABLE 5

As shown in table 6, table 6 shows that lens B and lens C exhibit the highest efficiency in the visible light communication receiver.

	Lens and lens assembly	Overall VLC Efficiency% (Total visible light communication System Efficiency)
			1	B	94.341％
2	C	89.530％
			3	A	81.280％
4	F	77.782％
			5	D	72.609％
6	E	70.059％
			7	G	61.843％
8	Lens-free	33.292％

As shown in tables 7 and 8, table 7 provides a summary of the performance of lens B in the visible light communication receiver, and fig. 8 provides a summary of the performance of lens C in the visible light communication receiver.

TABLE 7

TABLE 8

As shown in table 9, table 9 presents the characteristics of the fresnel lens after the experimental results are improved.

TABLE 9

It will be appreciated that the fresnel lens employed in the present invention is also suitable for use in a hybrid visible light communication system in which Li-Fi is used to transmit downlink data and WiFi is used to transmit uplink data.

Under normal conditions where Li-Fi is used to transmit downlink data transmissions, the hybrid system will automatically switch to WiFi use when the link is blocked or obstructed.

The microcontroller processes data transmitted or received by the LiFi to process, modulate and demodulate. The hybrid visible light communication system provides better security than a pure WiFi system because the hybrid visible light communication system does not readily recognize that personal data is accessed. The hybrid visible light communication system also provides wider bandwidth capabilities and higher immunity to electromagnetic interference (EMI) than existing WiFi systems. The use of the fresnel lens in a hybrid visible light communication system allows the system to compensate for the lack of line-of-sight connections.

The visible light communication receiver has the advantages that by adopting the technical scheme and the convex Fresnel lens, the visible light communication efficiency is improved, and the visual field of the coverage range of the visible light receiver is improved. The convex fresnel lens can improve the reception power of the visible light communication receiver by placing the photodiode at multiple focal points. The use of a convex fresnel lens also improves the transmission distance between the light emitting diode LED and the photodiode. The convex fresnel lens can also be used bi-directionally, with multiple focal points on either side of the convex fresnel lens fabricated in the visible light communications receiver.

The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A visible light communication receiver is characterized in that the visible light communication receiver is connected with an external visible light communication transmitter, the visible light communication transmitter comprises a transmitter circuit and a modulation light source connected with the transmitter circuit, the visible light communication receiver comprises a receiver circuit, a photoelectric detector connected with the receiver circuit and a Fresnel lens, the receiver circuit is connected with the photoelectric detector, the Fresnel lens is convex, and the Fresnel lens is used for diffracting light generated by the modulation light source to the photoelectric detector so that the photoelectric detector receives light signals under a plurality of focuses or at different positions of the detector; the Fresnel lens provides a plurality of focuses, and the front surface and the back surface of the Fresnel lens are provided with a plurality of focuses; the photoelectric detector at least comprises a plurality of photodiodes, and the photodiodes are positioned on two sides of the Fresnel lens or positioned at different positions.

2. The visible light communication receiver of claim 1, wherein the photodetector is positioned at a highest point of the plane of incidence of light generated by the modulated light source and the photodetector.

3. The visible light communication receiver of claim 2, wherein the modulated light source is one of a light emitting diode, or a laser, or a light modulator.

4. The visible light communication receiver of claim 2, wherein the photodetector is one of a photodiode, an array charge coupled device, an array CMOS, an avalanche photodiode, or an APD detector array.

5. The visible light communication receiver of claim 1, further comprising a first microcontroller coupled to the receiver circuit, wherein the visible light communication transmitter further comprises a second microcontroller coupled to the transmitter circuit, and wherein the first microcontroller and the second microcontroller are connected via WIFI.

6. The visible light communication receiver of claim 5, wherein the visible light communication receiver further comprises a first modulator connected to the first microcontroller, and wherein the visible light communication transmitter further comprises a second modulator connected to the second microcontroller.