Receiving system for high speed and large coverage optical wireless communication

Abstract

To meet the application requirements of high data rates and large coverage range in optical wireless communication systems, an optical front-end sub-system (100) is disclosed in the present invention. The optical front-end sub-system (100) comprises a first photodiode (110) having a first active surface area and a second photodiode (120) having a second active surface area, wherein the second active surface area is larger than the first active surface area. Depending on the received signal strength, either the branch with the first photodiode (110) or the branch with the second photodiode (120) is selected to provide an output signal of the optical front-end sub-system (100). By utilizing the first photodiode to support high speed communication and the second photodiode to support large coverage range communication, receiver diversity is achieved.

Description

Technical Field

[0001] This invention relates to the field of optical wireless communication networks, such as Li-Fi networks. More particularly, this document discloses various methods, apparatuses, systems, and computer-readable media related to systems with receiver diversity to support high-speed and wide-coverage optical wireless communication. Background Technology

[0002] To enable a growing number of electronic devices, such as laptops, tablets, and smartphones, to wirelessly connect to the internet, wireless communication faces unprecedented demands for data rates and link quality, and these demands continue to grow year after year, given the emerging digital revolution associated with the Internet of Things (IoT). Radio frequency (RF) technologies, such as Wi-Fi, have limited spectrum capacity and cannot meet this demand. Meanwhile, Light Fidelity (Li-Fi) is attracting increasing attention due to its inherent enhanced security and ability to support higher data rates across the available bandwidth of the visible, ultraviolet (UV), and infrared (IR) spectra. Furthermore, compared to Wi-Fi, Li-Fi is directional and shielded by light-blocking materials, making it possible to deploy a larger number of access points in densely populated areas by spatially reusing the same bandwidth. These key advantages compared to wireless RF communication make Li-Fi a promising and secure solution for alleviating radio spectrum congestion for IoT applications and indoor wireless access. Other potential benefits of Li-Fi include guaranteed bandwidth for specific users and the ability to operate securely in areas susceptible to electromagnetic interference. Therefore, Li-Fi is a very promising technology for enabling next-generation immersive connectivity.

[0003] Several related terms exist in the field of lighting-based communications. Visible light communication (VLC) transmits data via intensity-modulated light sources such as light-emitting diodes (LEDs) and laser diodes (LDs), faster than the persistence of the human eye. VLC is typically used to embed signals into light emitted by a lighting source, such as everyday lamps, for example, indoor or outdoor lighting, thus allowing the lighting from the lamp to serve as a carrier of information. Therefore, the light can include a visible lighting component used to illuminate a target environment such as a room (often the primary purpose of light), and an embedded signal used to provide information to the environment (often considered a secondary function of light). In this case, modulation can typically be performed at a sufficiently high frequency to exceed human perception, or at least make any visible transient light artifacts (such as flicker and / or stroboscopic artifacts) sufficiently weak and not noticeable or at least tolerable to humans at a sufficiently high frequency. Therefore, the embedded signal does not affect the primary lighting function; that is, the user only perceives the overall lighting, not the effect of the data modulated into that lighting.

[0004] The IEEE 802.15.7 Visible Light Communication Personal Area Network (VPAN) standard maps anticipated applications to four topologies: peer-to-peer, star, broadcast, and coordinated. Optical Wireless PAN (OWPAN) is a more general term than VPAN, as it also allows communication over invisible light, such as UV and IR. Therefore, Li-Fi is often considered a derivative of Optical Wireless Communication (OWC) technology, which utilizes a wide range of spectra to support bidirectional data communication.

[0005] In Li-Fi systems, signals are embedded by modulating the properties (typically intensity) of light, using any of a variety of suitable modulation techniques. For high-speed communication, infrared (IR) is often used instead of visible light. Although ultraviolet and infrared radiation are invisible to the human eye, the techniques for utilizing these spectral regions are the same, although variations can occur as a result of wavelength dependence (such as in the case of refractive index). In many instances, using ultraviolet and / or infrared is advantageous because these frequency ranges are invisible to the human eye and can introduce more flexibility into the system. Of course, ultraviolet quanta have higher energy levels than infrared and / or visible light, which in turn may make the use of ultraviolet light undesirable in certain situations.

[0006] Based on modulation, any suitable light sensor or photodetector can be used to detect information in light. For example, a light sensor can be a photodiode. A light sensor can be a dedicated photocell (point detector), a photocell array possibly with lenses, reflectors, diffusers, or phosphor converters (for lower speeds), or a photocell (pixel) array and lenses for forming an image on the array. For example, a light sensor can be a dedicated photocell included in a dongle inserted into a user device such as a smartphone, tablet, or laptop, or the sensor can be integrated and / or dual-purpose, such as an infrared detector array originally designed for 3D facial recognition. Either way, this allows applications running on the user device to receive data via light.

[0007] While Li-Fi systems have the potential to support very high data rates with their unlicensed bandwidth in the THz range, currently commercially achievable bit rates are typically in the hundreds of Mbps range due to the low inherent bandwidth (10-20 MHz) of LEDs (visible light or IR) and the use of spectrally efficient modulation such as OFDM. Furthermore, enabling Li-Fi systems to support large coverage areas (e.g., 30-60 degrees depending on the full width at half maximum (FWHM)) is very attractive. However, the requirement for large coverage areas typically leads to a significant reduction in received optical power (high path loss, which keeps the TX power below eye-safe limits), and thus may further limit the total throughput. On the other hand, Li-Fi systems based on lasers or vertical-cavity surface-emitting lasers (VCSELs) can support large modulation bandwidths. However, due to eye safety concerns, the total power emitted by the laser / VCSEL is very limited, and therefore large coverage areas remain difficult to achieve.

[0008] US2009027658A1 relates to a detector system for wavelength division multiplexing optical signals, comprising an array of various types of detectors. Summary of the Invention

[0009] For LED-based optical wireless communication systems, low to medium data rates can be achieved with relatively large FoV and long communication distances. For laser / VCSEL-based optical wireless communication systems, higher data rates can be achieved with relatively small coverage areas (narrow beams) and short communication distances. To take advantage of the strengths of both systems, the inventors propose employing diversity on the active surface region of the photodiode on the receiver side. Therefore, the optical receiver possesses the flexibility to support high-speed and wide-coverage optical wireless communication.

[0010] In view of the above, this disclosure relates to methods, apparatus, systems, computer programs, and computer-readable media for providing receiver diversity so that a receiving system can achieve both high speed and wide coverage. More particularly, the object of the invention is achieved by means of an optical front-end system, an optical receiver, an optical wireless communication system, a method of an optical front-end system, and a computer program.

[0011] According to a first aspect of the present invention, an optical front-end system is provided, wherein the optical front-end system for receiving optical wireless communication signals comprises: a first photodiode having a first active surface region configured to receive a first optical signal; a second photodiode having a second active surface region configured to receive a second optical signal; a sniffer circuit configured to compare the received signal strength of the first optical signal with a predefined reference value; and a switch configured to select the received first optical signal as the output signal of the optical front-end system when the received signal strength of the first optical signal is higher than the predefined reference value, and otherwise select the received second optical signal as the output signal of the optical front-end system; wherein the second active surface region is larger than the first active surface region.

[0012] A photodiode is a semiconductor device that converts light into current or voltage based on its operating mode. Sometimes, photodiodes are also called photodetectors, photodetectors, or photosensors. Photodiodes can include filters, built-in lenses, and can have large or small surface areas. As the surface area of ​​a photodiode increases, its response time generally becomes slower. Depending on the device's structure, photodiodes can be classified into different types, such as PN photodiodes, Schottky photodiodes, PIN photodiodes, and avalanche photodiodes. Although different types of photodiodes may operate slightly differently, their basic operation remains the same. Advantageously, an optical front-end system includes at least two photodiodes, a first photodiode and a second photodiode. Here, the first and second photodiodes can be the same type or different types of photodiodes, photodetectors, photodetectors, or photosensors.

[0013] The active surface region of a photodiode can also be referred to as the effective active region or surface region. The first photodiode and the second photodiode have different active surface regions, resulting in different device characteristics that allow them to be adapted to different receiving scenarios. A sniffer circuit is used to compare a first optical signal received from the first photodiode with a first predefined reference value. When the received signal strength of the first optical signal is higher than the predefined reference value, the received first optical signal is selected as the output signal of the optical front-end subsystem. Otherwise, the received second optical signal is selected as the output signal of the optical front-end subsystem. The first predefined reference value can be configured in a factory preset, and this value can be specific to the type of the first photodiode. Given the size of the first active surface region, the first predefined reference value can also be specific to the type of the first photodiode. The first predefined reference value can also be configured during the actual physical installation of the optical front-end subsystem. In another example, the first predefined reference value can be configured by the user according to system settings, user scenario, application requirements, or user preferences. By adjusting the first predefined reference value, or essentially adjusting the selection criteria, the optical front-end subsystem can preferentially select either the first optical signal received by the first photodiode or the second optical signal received by the second photodiode.

[0014] Preferably, the second active surface region is at least twice the size of the first active surface region.

[0015] A larger active surface area allows the photodiode to generate a larger current in response to incident light, but at the cost of higher junction capacitance and therefore lower speed or narrower signal bandwidth. This invention aims to employ a first photodiode and a second photodiode with sufficiently different active surface area sizes to suit different application scenarios.

[0016] As mentioned earlier, LED-based optical wireless communication systems are characterized by relatively long communication distances and wide coverage, but are low for medium data rates; while VCSEL-based optical wireless communication systems are characterized by high data rates, but have relatively small angular coverage with a narrow FoV. Therefore, when the received first optical signal is used as the output signal of the optical front-end system, it can be used in conjunction with a VCSEL-based transmitter. When the received second optical signal is used as the output signal of the optical front-end system, it can be used in conjunction with an LED-based transmitter. When the transmitter is a hybrid configuration (e.g., a hybrid front-end with both LEDs and VCSELs), the optical front-end system can adaptively select the optimal photodiode based on the received signal strength of the optical signal detected by the photodiode. This is because the influence of the actual user scenario, such as the actual distance from the transmitter, the angle of incidence of light, the intensity of light, and path loss, are ultimately reflected in the signal strength of the optical signal detected by the photodiode.

[0017] Advantageously, the first photodiode is further configured to receive a first optical signal within a first signal collection region, and the second photodiode is further configured to receive a second optical signal within a second signal collection region, wherein the second signal collection region is larger than the first signal collection region.

[0018] The signal collection area of ​​a photodiode should be understood as the coverage area within which the photodiode receives optical signals. Sometimes, the coverage area is also defined as the angular coverage area or field of view (FoV). Typically, a bare photodiode without any lens has a relatively wide FoV (e.g., 120 degrees), and then a lens on it will define the final or actual FoV. This lens can be an internal lens of the photodiode.

[0019] Note that only incident light projected onto the active surface area can be collected by the photodiode and converted into an electrical signal in the form of a current or voltage signal. Typically, small-area photodiodes collect less light and require additional optics (lenses) to increase optical signal collection. The lens focuses the incident beam onto this small active area. However, if a large angle of incidence (wide FoV) is required, the image size produced by the lens also increases, and part of the focused beam misses the active area. Therefore, a trade-off must be made between the angular incident coverage and the amount of light collected. Thus, for efficient optical signal collection, it is advantageous for the first photodiode, with its smaller active surface area, to also have a narrower FoV compared to the second photodiode.

[0020] In the preferred configuration, the first signal collection area is completely covered by the second signal collection area.

[0021] It is known that non-uniformity at the edges of the active surface region of a photodiode or photodetector can generate unwanted capacitance and resistance, which distorts the time-domain response of the photodiode. Therefore, it is also preferable that the incident light on the photodiode is located exactly at the center of the active surface region or the active region. Thus, it may be advantageous to have the first signal collection region completely covered by the second signal collection region. Furthermore, it is also advantageous to have the first and second signal collection regions centered at the same point.

[0022] Advantageously, the first photodiode is configured to support a higher data rate than the second photodiode.

[0023] As mentioned above, junction capacitance has a profound impact on the bandwidth and response speed of a photodiode. Junction capacitance is proportional to the active surface area. A large active surface area of ​​a photodiode encompasses a larger junction volume and increased junction capacitance. Therefore, compared to the second photodiode, the smaller active surface area of ​​the first photodiode allows for a larger signal bandwidth. Consequently, the first photodiode can support higher data rates.

[0024] Preferably, the sniffer circuit further includes a root mean square (RMS) detector configured to estimate the strength of the received signal.

[0025] The sniffer circuit needs to measure the signal strength of the received first optical signal and compare it to a predefined reference value. Therefore, the sniffer circuit includes a signal strength detector. In a preferred example, the signal strength detector is a root mean square (RMS) detector. In another example, the signal strength detector could be a peak detector, although for OFDM-based systems, peak values ​​are a poorly defined statistical variable. In yet another example, the signal strength detector could be an AC component averaging detector.

[0026] The switch can be a MOSFET or a transistor.

[0027] In one embodiment, the optical front-end system further includes: a first amplifier connected to a first photodiode and configured to amplify a received first optical signal using a first amplifier circuit tailored to the characteristics of the first photodiode; and a second amplifier connected to a second photodiode and configured to amplify a received second optical signal using a second amplifier circuit tailored to the characteristics of the second photodiode; and wherein the sniffer circuit is further configured to compare the received signal strength of the first optical signal with a second predefined reference value after the first optical signal has been amplified by the first amplifier.

[0028] Given that the output electrical signal from a photodiode is typically very small, an amplifier is usually employed to amplify this small signal, making it large enough for further processing in the receiver chain. The amplifier is typically tailored and / or configured based on the properties of the photodiode preceding it, ensuring that signal quality is not degraded by thermal noise introduced by the amplifier itself and maintaining sufficient signal bandwidth to preserve the information carried by the signal. For example, the amplifier should provide sufficient gain to avoid SNR degradation. However, on the other hand, excessive gain can lead to unnecessary complexity, cost, and power consumption. Furthermore, the second-order effect of the photodiode capacitance can cause excessive noise gain at higher frequencies, which may even degrade signal quality at higher frequency ranges. Additionally, one or more other parameters—such as total input capacitance, photodiode signal range, required bandwidth, and minimum signal swing—can be considered. It can be seen that there are many design trade-offs in customizing and / or optimizing the amplifier for a single photodiode. Therefore, to benefit from an optimized design of the first amplifier, it may be advantageous to have a sniffer circuit compare the received signal strength of the first optical signal with a reference value after the amplification stage.

[0029] Preferably, the first amplifier and / or the second amplifier is a transimpedance amplifier (TIA).

[0030] A TIA is a current-to-voltage converter that is typically used with a sensor (when the sensor has a current response that is more linear than a voltage response). A TIA is often used as a first-stage amplifier to regulate the received signal from a photodiode.

[0031] In another embodiment, the optical front-end subsystem further includes: a third photodiode having a third active surface region configured to receive a third optical signal, wherein the third active surface region is larger than a first active surface region but smaller than a second active surface region; and wherein the sniffer circuit is further configured to compare the received signal strength of the third optical signal with a predefined third reference value; and the switch is further configured to select the received first optical signal as the output signal of the optical front-end subsystem when the signal strength of the received first optical signal is higher than the predefined reference value; and to select the received third optical signal as the output signal of the optical front-end subsystem when the received signal strength of the first optical signal is not higher than the predefined reference value and the received signal strength of the third optical signal is higher than the third predefined reference value, and otherwise, to select the received second optical signal as the output signal of the optical front-end subsystem.

[0032] Preferably, the second active surface area is at least twice the size of the first active surface area. This ratio may be much larger than twice. For example, the second active surface area may be more than 10 times the size of the first active surface area to meet different application requirements. A third photodiode may also be deployed in the optical front-end system, having an active surface area larger than the first active surface area but smaller than the second active surface area. Therefore, the sniffer circuit is configured to first check the received signal strength of the first optical signal against a predefined reference value, and if the requirement is met, select the received first optical signal as the output of the optical front-end system. Otherwise, the sniffer circuit is configured to further check the received signal strength of the third optical signal against a predefined third reference value, and if the requirement is met, select the received third optical signal as the output of the optical front-end system. Otherwise, the received second optical signal is selected as the output. In this way, the optical front-end system is configured to preferentially activate the receiving path with the highest possible bandwidth. Note that additional photodiodes can be used in the optical front-end system as long as the diversified application requirements justify the additional hardware cost.

[0033] A third photodiode is configured to receive a third optical signal within a third signal collection region. Preferably, the third signal collection region is larger than the first signal collection region but smaller than the second signal collection region.

[0034] According to a second aspect of the invention, an optical receiver is provided. An optical receiver for receiving optical wireless communication signals includes: an optical front-end subsystem according to the invention; an analog front-end component configured to receive an input signal from the optical front-end subsystem for analog processing; and a modem component configured to perform baseband processing on the output of the analog-processed signal from the analog front-end component.

[0035] The disclosed optical front-end subsystem can be coupled with an analog front-end and modem to complete an optical receiver chain. Since only one receive path is enabled after selection in the optical front-end subsystem, the analog front-end and modem can be the same as those in a conventional optical receiver.

[0036] According to a third aspect of the invention, an optical wireless communication system is provided. The optical wireless communication system includes: an optical receiver according to the invention; an optical transmitter including one or more optical front ends, wherein each of the one or more optical front ends includes a light source; and wherein the optical receiver is configured to receive an optical wireless communication signal emitted by the optical transmitter.

[0037] The disclosed optical receiver can handle different transmitter settings and provide optimal reception capabilities adapted to specific application scenarios. In the disclosed optical wireless communication system, the transmitter may include one or more optical front ends, each of which includes a light source. The light source may be a light-emitting diode (LED), a laser diode, a vertical-cavity surface-emitting laser (VCSEL), or a hybrid front end incorporating both LEDs and VCSELs.

[0038] According to a fourth aspect of the present invention, a method for an optical front-end system is provided. A method for receiving an optical wireless communication signal using an optical front-end system, the method comprising: receiving a first optical signal via a first photodiode having a first active surface region; receiving a second optical signal via a second photodiode having a second active surface region; comparing the received signal strength of the first optical signal with a predefined reference value; and when the received signal strength of the first optical signal is higher than the predefined reference value, selecting the received first optical signal as an output signal of the optical front-end system, and otherwise selecting the received second optical signal as an output signal of the optical front-end system; wherein the second active surface region is larger than the first active surface region.

[0039] Advantageously, the method further includes an optical front-end subsystem: receiving a third optical signal via a third photodiode having a third active surface region, wherein the third active surface region is larger than a first active surface region but smaller than a second active surface region; comparing the received signal strength of the third optical signal with a predefined third reference value; and selecting the received first optical signal as the output signal of the optical front-end subsystem when the received signal strength of the first optical signal is higher than the predefined reference value; or selecting the received third optical signal as the output signal of the optical front-end subsystem when the received signal strength of the first optical signal is not higher than the predefined reference value and the received signal strength of the third optical signal is higher than the third predefined reference value; or selecting the received second optical signal as the output signal of the optical front-end subsystem when the received signal strength of the first optical signal is not higher than the predefined reference value and the received signal strength of the third optical signal is not higher than the third predefined reference value.

[0040] The invention can also be embodied in a computing program that includes a code device, which, when executed by an optical front-end system including a processing device, causes the processing device to perform the method of the optical front-end system as disclosed in this invention. Attached Figure Description

[0041] In the accompanying drawings, similar reference numerals are used throughout. Figure 1 Generally, the same parts are referred to. Furthermore, the accompanying drawings are not necessarily to scale; instead, the focus is usually on illustrating the principles of the invention.

[0042] Figure 1 This illustrates one possible system configuration of the optical front-end system of the present invention;

[0043] Figure 2 The concept of receiver diversity generated by different active surface regions is demonstrated;

[0044] Figure 3 An example of the arrangement of the first signal collection area and the second signal collection area is shown;

[0045] Figure 4 Another possible system configuration of the optical front-end system of the present invention is shown;

[0046] Figure 5 Another possible system configuration of the optical front-end system of the present invention is shown;

[0047] Figure 6 The basic components of the optical receiver of the present invention are schematically depicted.

[0048] Figure 7 A flowchart illustrating a method for an optical front-end terminal system is shown;

[0049] Figure 8 A flowchart illustrating a method for an optical front-end terminal system is shown. Detailed Implementation

[0050] Now it will be based on such Figure 1Various embodiments of the present invention are described using an optical front-end system 100 as illustrated. As a basic setup, the optical front-end system 100 includes a first photodiode 110, a second photodiode 120, a sniffer circuit 140, and a switch 150. The first photodiode 110 and the second photodiode 120 can be photodiodes of the same or different types. Here, photodiode should be understood broadly, such as a photoelectric sensor, light sensor, or photodetector, which has an active surface area. The difference between the first photodiode 110 and the second photodiode 120 lies in the size of their active surface areas. The second active surface area of ​​the second photodiode 120 is larger than the first active surface area of ​​the first photodiode 110. Therefore, the first photodiode 110 and the second photodiode 120 provide different response times. Thus, the first photodiode 110, with its smaller active surface area compared to the second photodiode 120, is able to support higher data rate communication. When the distance from the optical transmitter increases, for example, according to comparison results obtained by the sniffer circuit, the received signal strength of the first photodiode may be insufficient. The optical front-end system 100 is configured to harvest energy from a second signal collection region or a wider FoV region compared to the first signal collection region using a second photodiode. Because the second photodiode has a larger active surface area, it is configured for optical reception for low- to medium-data-rate communications.

[0051] Ideally, the first photodiode is paired with a high-speed, narrow-beam optical emitter (e.g., a VCSEL-based optical emitter). The second photodiode is paired with a medium- to low-speed, wide-beam optical emitter (e.g., an LED-based optical emitter). Thus, by utilizing active region diversity features, the disclosed optical front-end system can adaptively enjoy the benefits of both high-speed and wide-coverage optical communication upon selection.

[0052] In traditional segmented optical receivers, more than one uniform photodiode or optical detector is simultaneously activated, each pointing in a different orientation and combined to cover a wide FoV. Normally, to achieve good coverage, an optical receiver may require four or more photodiodes. To achieve high data rates, each photodiode may have a very narrow FoV, and then even more photodiodes may be needed to cover the entire signal collection area. Therefore, the disclosed system offers advantages in flexibility, low hardware cost, and low power consumption compared to segmented solutions.

[0053] Figure 2The receiver diversity is shown, generated by different active surface regions of the first and second photodiodes. In the left figure, the x-axis represents the distance D between the optical front-end system and the optical transmitter, and the y-axis represents the normalized power |P| of the received optical signal. ref This indicates a predefined reference value, which serves as a threshold for comparison with the received signal strength of the optical signal. In the right figure, the x-axis represents the normalized power |P| of the received optical signal, and the y-axis represents the data rate R to be supported. The curve is formed by 1 st and 2 nd This is indicated to differentiate the characteristics between the first and second photodiodes. From... Figure 2 As can be seen, at the same distance from the optical transmitter, the second photodiode can collect more energy than the first photodiode because it has a larger active surface area. In other words, to collect the same amount of energy, the first photodiode either has a short communication distance or a narrow FoV. However, at the same normalized received power, the first photodiode can support a higher data rate because it has a smaller junction capacitance and a shorter response time. In this sense, the first photodiode is used to cover applications with relatively short distances but high data rate communication, while the second photodiode is used to cover applications with relatively long communication distances but low to medium data rate communication.

[0054] Taken together, the disclosed optical front-end system can cover both wide coverage and high data rate application requirements. It offers improved flexibility with relatively low hardware cost and system complexity.

[0055] A first photodiode is configured to receive a first optical signal within a first signal collection region Z1, and a second photodiode is configured to receive a second optical signal within a second signal collection region Z2. This is for illustrative purposes only. Figure 3 An example of the arrangement of the first signal collection region Z1 and the second signal collection region Z2 is provided. Z1 and / or Z2 can have symmetrical shapes, but they can also have irregular shapes. In this example, both Z1 and Z2 have symmetrical shapes, and Z1 is completely covered by Z2. In another example, Z1 and Z2 can partially overlap, or they can not overlap at all. The size and shape of the first signal collection region Z1 and the second signal collection region Z2 are primarily determined by the lenses on the first and second photodiodes. The lens design should take into account the active surface area of ​​the individual photodiodes to achieve good efficiency in collecting light energy.

[0056] Figure 4Another possible system configuration of the optical front-end system of the present invention is shown. In this configuration, a first amplifier 160, customized for the characteristics of a first photodiode 110, is connected to the first photodiode 110 to amplify the received first optical signal before the sniffer circuit 140 evaluates the first optical signal. Similarly, a second amplifier 170, customized for the characteristics of a second photodiode 120, is connected to the second photodiode 120 to amplify the received second optical signal. One or more characteristics or parameters associated with a single photodiode can be considered here, such as total input capacitance, photodiode signal range, required bandwidth, and minimum signal swing required. Therefore, in this example, the evaluation of the sniffer circuit is based on the optical signal received after being conditioned by the amplifier. Since the output electrical signal of a photodiode is typically very small, amplifying this small signal from the photodiode to a sufficiently large signal is beneficial for further processing. Using the first amplifier 160 dedicated to the first photodiode 110 and the second amplifier 170 dedicated to the second photodiode 120, a customized design can be applied to the amplifiers, taking into account the characteristics of the photodiode preceding them. Therefore, compared to the option of placing another amplifier after the switch to process the received first optical signal or the received second optical signal, the optical front-end system is further optimized in both branches, depending on the choice made.

[0057] Figure 5 Another possible system configuration of the optical front-end system of the present invention is shown. A third photodiode 130 is employed, having a third active surface area larger than the first active surface area of ​​the first photodiode but smaller than the second active surface area of ​​the second photodiode. As already disclosed, the second active surface area is at least twice the size of the first active surface area, and this ratio can be as large as 10 times or more. Therefore, the third photodiode has a third active surface area whose size is between the first and second active surface areas. The optical front-end system is further enhanced by adding a fine-tuning receiver chain to provide a balance between system complexity and the requirements of covering a wide variety of application scenarios. In another scenario, the optical front-end system can be further extended with additional photodiodes, provided that hardware cost and complexity meet application requirements.

[0058] It should be noted that Figure 5 The settings in are based on, for example Figure 1 The system settings disclosed in the document are at the top. Embodiments employing the third photodiode 130 can also be compared with... Figure 4 The embodiments shown are used in combination, wherein the third amplifier is placed directly after the third photodiode 130 and before the sniffer circuit 140.

[0059] Figure 6The basic components of the optical receiver 200 of the present invention are schematically depicted. The optical receiver 200 includes at least the optical front-end subsystem 100, analog front-end component 210, and modem component 220 disclosed above. The analog front-end component receives input signals from the optical front-end subsystem 100 for analog processing; and the modem component is configured to perform baseband processing on the output of the analog-processed signal from the analog front-end component 210. Although the optical front-end subsystem 100 includes more than one photodiode to provide receive diversity, the selection of the more than one photodiode is implemented within the optical front-end subsystem 100, and only a single output signal is provided to the next component in the receiver chain (analog front-end component 210). Therefore, the analog front-end component and modem component can use the same hardware used in conventional optical receivers, although the processing power (such as bandwidth and clock speed) should be sufficient to process the signal received from the first or second photodiode.

[0060] The optical receiver 200 can be used to establish an optical communication link with an optical transmitter in an optical communication system. Given the flexibility provided by the optical receiver, the optical transmitter may also include one or more optical front ends. A single optical front end includes a light source for transmitting optical signals. The light source may be an LED, a laser diode, a VCSEL, or a hybrid front end incorporating both LEDs and VCSELs.

[0061] Figure 7 A flowchart of a method 500 for receiving an optical front-end terminal system 100 for receiving optical wireless communication signals is shown. Method 500 includes the optical front-end terminal system 100: in step S501, receiving a first optical signal through a first photodiode 110 having a first active surface region; in step S502, receiving a second optical signal through a second photodiode 120 having a second active surface region. Then, in step S503, the optical front-end terminal system 100 compares the received signal strength of the first optical signal with a predefined reference value; and in step S504, when the signal strength of the received first optical signal is higher than the predefined reference value, selecting the received first optical signal as the output signal of the optical front-end terminal system; and otherwise, selecting the received second optical signal as the output signal of the optical front-end terminal system 100; wherein the second active surface region is larger than the first active surface region.

[0062] Figure 8A flowchart illustrating another embodiment of a method 500 for an optical front-end system 100 is shown. Method 500 includes the optical front-end system 100: in step S501, receiving a first optical signal via a first photodiode 110 having a first active surface region; in step S502, receiving a second optical signal via a second photodiode 120 having a second active surface region. Then, in step S503, the optical front-end system 100 compares the received signal strength of the first optical signal with a predefined reference value. In step S505, the method includes the optical front-end system 100 receiving a third optical signal via a third photodiode 130 having a third active surface region, wherein the third active surface region is larger than the first active surface region but smaller than the second active surface region. In step S506, the optical front-end system 100 compares the received signal strength of the third optical signal with a predefined third reference value; and in step S507:

[0063] • When the received signal strength of the first optical signal is higher than a predefined reference value, the received first optical signal is selected as the output signal of the optical front-end subsystem, or

[0064] • When the received signal strength of the first optical signal is not higher than a predefined reference value and the received signal strength of the third optical signal is higher than a third predefined reference value, the received third optical signal is selected as the output signal of the optical front-end subsystem, or

[0065] • When the received signal strength of the first optical signal is not higher than a predefined reference value and the received signal strength of the third optical signal is not higher than a third predefined reference value, the received second optical signal is selected as the output signal of the optical front-end subsystem.

[0066] A third photodiode is configured to receive a third optical signal within a third signal collection region. Preferably, the third signal collection region is larger than the first signal collection region Z1, but smaller than the second signal collection region Z2.

[0067] The method according to the invention can be implemented on a computer as a computer-implemented method, or in dedicated hardware, or in a combination of both.

[0068] The executable code of the method according to the invention can be stored on a computer / machine-readable storage device. Examples of computer / machine-readable storage devices include non-volatile storage devices, optical storage media / devices, solid-state media, integrated circuits, servers, etc. Preferably, the computer program product includes non-transitory program code means stored on a computer-readable medium for executing the method according to the invention when the program product is executed on a computer.

[0069] Methods, systems, and computer-readable media (transitory and non-transitory) may also be provided to implement selected aspects of the above embodiments.

[0070] The term "controller" is used generally herein to describe various means relating to the operation of one or more network devices or coordinators—among other functions. A controller can be implemented in a variety of ways (e.g., such as with dedicated hardware) to perform the various functions discussed herein. A "processor" is an example of a controller employing one or more microprocessors, which can be programmed using software (e.g., microcode) to perform the various functions discussed herein. A controller can be implemented with or without a processor, and can also be implemented as a combination of dedicated hardware performing some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) performing other functions. Examples of controller components that can be employed in various embodiments of this disclosure include, but are not limited to, conventional microprocessors, application-specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0071] In various embodiments, the processor or controller may be associated with one or more storage media (collectively referred to herein as "memory," such as volatile and non-volatile computer memories, such as RAM, PROM, EPROM, and EEPROM, compact disks, optical disks, etc.). In some embodiments, the storage media may be encoded with one or more programs that, when executed on one or more processors and / or controllers, perform at least some of the functions discussed herein. Various storage media may be fixed within the processor or controller, or may be transportable, such that one or more programs stored thereon may be loaded into the processor or controller to implement various aspects of the invention discussed herein. The terms "program" or "computer program" are used herein in a general sense to refer to any type of computer code (e.g., software or microcode) that can be used to program one or more processors or controllers.

[0072] As used herein, the term “network” refers to any interconnection of two or more devices (including controllers or processors) that facilitates the transport of information (e.g., for device control, data storage, data exchange, etc.) between any two or more devices and / or between multiple devices coupled to the network.

Claims

1. An optical front-end subsystem (100) for receiving optical wireless communication signals, the optical front-end subsystem (100) comprising: - A first photodiode (110) having a first active surface region configured to receive a first optical signal; - A second photodiode (120) having a second active surface region configured to receive a second optical signal; The optical front-end system (100) is characterized in that: The optical front-end system (100) also includes: - A sniffer circuit (140) configured to compare the received signal strength of the first optical signal with a predefined reference value; and - A switch (150) is configured to select the received first optical signal as the output signal of the optical front-end system (100) when the received signal strength of the first optical signal is higher than the predefined reference value; and otherwise, select the received second optical signal as the output signal of the optical front-end system (100). The second active surface region is larger than the first active surface region.

2. The optical front-end terminal system (100) according to claim 1, characterized in that, The second active surface region is at least twice the size of the first active surface region.

3. The optical front-end terminal system (100) according to claim 1 or 2, characterized in that, The first photodiode (110) is further configured to receive the first optical signal within a first signal collection region (Z1), and the second photodiode (120) is further configured to receive the second optical signal within a second signal collection region (Z2). The first signal collection region (Z1) is the coverage area of ​​the first photodiode (110) receiving the optical signal, and the second signal collection region (Z2) is the coverage area of ​​the second photodiode (120) receiving the optical signal. The second signal collection region (Z2) is larger than the first signal collection region (Z1).

4. The optical front-end terminal system (100) according to claim 3, characterized in that, The first signal collection area (Z1) is completely covered by the second signal collection area (Z2).

5. The optical front-end terminal system (100) according to claim 1 or 2, characterized in that, The first photodiode (110) is configured to support a higher data rate than the second photodiode (120).

6. The optical front-end terminal system (100) according to claim 1 or 2, characterized in that, The sniffer circuit (140) also includes a root mean square (RMS) detector configured to estimate the strength of the received signal.

7. The optical front-end terminal system (100) according to claim 1 or 2, characterized in that, The optical front-end system (100) also includes: - A first amplifier (160), connected to the first photodiode (110), and configured to amplify the received first optical signal using a first amplifier circuit tailored to the characteristics of the first photodiode (110); and - A second amplifier (170), connected to the second photodiode (120), is configured to amplify the received second optical signal using a second amplifier circuit tailored to the characteristics of the second photodiode (120); and The sniffer circuit (140) is further configured to compare the received signal strength of the first optical signal with a second predefined reference value after the first optical signal is amplified by the first amplifier (160).

8. The optical front-end terminal system (100) according to claim 7, characterized in that, The first amplifier (160) and / or the second amplifier (170) are transimpedance amplifiers (TIAs).

9. The optical front-end terminal system (100) according to claim 1 or 2, characterized in that, The optical front-end system (100) also includes: - A third photodiode (130) having a third active surface region configured to receive a third optical signal, wherein the third active surface region is larger than the first active surface region but smaller than the second active surface region; and The sniffer circuit (140) is further configured to - Compare the received signal strength of the third optical signal with a predefined third reference value; and The switch (150) is also configured to - When the received signal strength of the first optical signal is higher than the predefined reference value, the received first optical signal is selected as the output signal of the optical front-end subsystem (100); and when the received signal strength of the first optical signal is not higher than the predefined reference value and the received signal strength of the third optical signal is higher than the third predefined reference value, the received third optical signal is selected as the output signal of the optical front-end subsystem (100), and otherwise, the received second optical signal is selected as the output signal of the optical front-end subsystem (100).

10. An optical receiver (200) for receiving optical wireless communication signals, characterized in that, The optical receiver includes: -Optical front-end terminal system (100) according to any one of claims 1-9. - Analog front-end component (210), which is configured to receive input signals from the optical front-end subsystem (100) for analog processing; and - A modem component (220) configured to perform baseband processing on the output of an analog-processed signal from the analog front-end component (210).

11. An optical wireless communication system, characterized in that, The optical wireless communication system includes: - The optical receiver (200) according to claim 10; - An optical emitter comprising one or more optical front ends, wherein each of the one or more optical front ends comprises a light source; And the optical receiver is configured to receive optical wireless communication signals emitted by the optical transmitter.

12. A method (500) for receiving optical wireless communication signals, the method being applied to an optical front-end subsystem (100), the method comprising: - A first optical signal is received (S501) by a first photodiode (110) having a first active surface region; - The second optical signal is received (S502) by a second photodiode (120) having a second active surface region; The method (500) is characterized in that: The method (500) further includes: - Compare the received signal strength of the first optical signal with a predefined reference value (S503); and - When the received signal strength of the first optical signal is higher than the predefined reference value, the received first optical signal is selected (S504) as the output signal of the optical front-end system; otherwise, the received second optical signal is selected as the output signal of the optical front-end system. The second active surface region is larger than the first active surface region.

13. The method (500) according to claim 12, characterized in that, The method (500) further includes: - A third optical signal is received (S505) by a third photodiode (130) having a third active surface region, wherein the third active surface region is larger than the first active surface region but smaller than the second active surface region; - Compare the received signal strength of the third optical signal with a predefined third reference value (S506); and • When the received signal strength of the first optical signal is higher than the predefined reference value, the received first optical signal is selected (S507) as the output signal of the optical front-end subsystem, or • When the received signal strength of the first optical signal is not higher than the predefined reference value and the received signal strength of the third optical signal is higher than the third predefined reference value, the received third optical signal (S507) is selected as the output signal of the optical front-end subsystem, or • When the received signal strength of the first optical signal is not higher than the predefined reference value and the received signal strength of the third optical signal is not higher than the third predefined reference value, the second optical signal received in (S507) is selected as the output signal of the optical front-end subsystem.

14. A computer program product comprising a code device or program, characterized in that, When the code device or program is executed by an optical front-end terminal system (100) including a processing device, the processing device performs the method of any one of claims 12-13.

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