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    • 专利摘要:
    Method, system and device for the reception of multiuser optical transmissions. The present invention relates to an optical receiver device for a multi-user optical system for transmitting information through light, comprising: two or more photodiodes arranged with different geometric orientations to receive optical signals; at least one optical filter associated with each of the photodiodes, to modify the amplitude of the received signals as a function of the angle of incidence; where the combination of the at least one filter and the geometric orientation of each of the photodiodes generates a linearly independent output signal in each of the photodiodes. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2713578A1
    申请号:ES201731342
    申请日:2017-11-21
    公开日:2019-05-22
    发明作者:Céspedes Máximo Morales；Armada Ana García；Luc André M Vandendorpe
    申请人:Universidad Carlos III de Madrid；
    IPC主号:
    专利说明:

    [0001]
    [0002] METHOD, SYSTEM AND DEVICE FOR THE RECEPTION OF MULTI-USER OPTICAL TRANSMISSIONS
    [0003]
    [0004] Technical field of the invention
    [0005]
    [0006] The present invention has application in the technical sector of the transmission of information through light and more specifically in the optical receivers of multi-user systems with multiple photodiodes, where the information is transmitted through light, which is known as Visible Light Communications (VLC) or Light Fidelity (LiFi).
    [0007]
    [0008] Background of the invention
    [0009]
    [0010] Currently, information transmission systems through light are a deeply active field of research within the framework of mobile communications and evolution towards 5G communications services. The degree of development of these technologies allows, at present, transmissions at low speed, but reaching high transmission speeds requires solving the interference problems between different luminous transmitters.
    [0011]
    [0012] Transmission through visible light requires a light receiver known as a photodetector. Usually these photodetectors are composed of a single sensor (photodiode) and optionally a filter capable of selecting certain wavelengths. In order to obtain sufficient coverage and offer an adequate quality of service, it is necessary to deploy multiple LiFi access points located at close distance between them. Therefore, as shown in FIG. 1, in a typical LiFi transmission scenario, a conventional photodetector (1) receives the contribution of several luminous transmitters (2-5), that is, the very close photodiodes (6) or Symmetric (7) are characterized by a very similar channel, which implies that interference is generated and considerably limits the performance of the link.
    [0013]
    [0014] This problem affects in particular the photodetectors composed of multiple photodiodes to increase the field of vision of the receiver or obtain diversity from receiving the same signal (information) through different channels. Taking into account transmission based on modulation of intensity and direct detection (IM / DD) in optical systems, the response to the channel between nearby photodiodes, as mentioned above, is highly correlated with each other, is dedr, is linearly dependent, which prevents the implementation of transmission schemes capable of sending several data streams simultaneously.
    [0015]
    [0016] Due to the nature of the transmission through visible light, the use of modulation by variation of intensity and direct detection (IM / DD), the signal received by a photodiode is not subject to changes on a small scale. Therefore, and in contrast to radio frequency-based transmission, where several variants of BIA schemes have been proposed using reconfigurable antennas capable of modifying their radiation diagram dynamically between different modes, the signal received between nearby photodiodes or Symmetric is highly correlated. Assuming a transmission structure as shown in Figure 2, the channel between luminous transmitter t and the photodiode k separated a distance dkt with a radiation angle tykt and an angle of incidence 9 ^ (which are determined by the vector vtk, that is, the vector between the light source t and the photodiode k is defined as
    [0017]
    [0018] and A (m +1)
    [0019] ht = T (9 kt) cosm (<ta) cos "(9 kt) sl 9 kt <Y c
    [0020] 2 ^ dkt
    [0021]
    [0022] where A and 7 is the detection area of the photodiode responsivity, respectively, T (9kt) is the filter / concentrator gain of the photodiode and the m and n parameters are related to the Lambertian modulus of the light transmitter and the coefficient associated with the field of vision of the photodiode ^ c. Thus, it can be verified that nearby photodiodes with the same orientation angle obtain the same channel response.
    [0023]
    [0024] The state of the art offers some proposals to manage the interference between LiFi transmitters, such as the use of topology to create amorphous cells to coordinate the transmission between different access points. However, this type of techniques requires a link between the luminous transmitters, as well as the sharing of data between all of them and their coordination through a central node, which supposes additional elements in the deployment, as well as a load of signaling.
    [0025]
    [0026] For all the above, since these problems of interferences between Nearby users also exist in conventional radio transmission and know techniques that can solve it efficiently, it would be desirable to adapt these techniques in the LiFi environment.
    [0027]
    [0028] Summary of the invention
    [0029]
    [0030] The present invention solves the aforementioned problems to apply interference canceling techniques in optical systems, offering linearly independent channel responses between the photodiodes of each user, which achieves a gain in multiplexing, that is, sending several data streams simultaneously.
    [0031]
    [0032] For this purpose, in a first aspect of the present invention, a configurable optical receiver device for a multi-user optical system for transmitting information through light, comprising: two or more photodiodes arranged with different geometrical orientations to receive two or more more optical signals, each with an angle of incidence, issued by different optical emitters; at least one optical filter associated with each of the two or more photodiodes, to modify the amplitude of the two or more optical signals received as a function of the angle of incidence; and where the combination of the at least one filter and the geometrical orientation of each of the two or more photodiodes generates a linearly independent output signal in each of the photodiodes.
    [0033]
    [0034] One of the embodiments of the invention additionally comprises a concentrator coupled to the at least one optical filter.
    [0035]
    [0036] A second aspect of the invention relates to a multi-user optical system for transmitting information through light, said system comprising: an optical receiver device according to any of the embodiments of the present invention; a signal selector module, with an input connectable to the two or more photodiodes to select the output signal of one and only one of said two or more photodiodes at each instant of time; and an interference cancellation module connected to the output of the selector module to cancel interferences between the output signals of the two or more photodiodes, where the output signal of the interference cancellation module at each instant of time corresponds to a single user of the system, according to a transmission pattern previously assigned to each of the users of the system.
    [0037]
    [0038] Additionally, in one of the embodiments of the present invention, the optical system multiuser of the present invention further comprises a decoder module connected to the output of the interference cancellation module to decode the output signal of said interference cancellation module.
    [0039]
    [0040] According to one of the particular embodiments of the invention, the interference cancellation module of the multi-user optical system of the present invention is a BIA module (acronym for the term "Blind Interference Alignment") for blind transmissions.
    [0041]
    [0042] In one embodiment of the present invention, the selector module comprises a pattern of selection of output signals of the two or more photodiodes based on a blind transmission scheme BIA.
    [0043]
    [0044] Optionally, in one of the embodiments of the invention, an equalizer module based on an equalizing technique is added, such as Zero Forcing. Advantageously, in this way the benefits of the present invention are exploited for vector transmission schemes based on knowledge of the channel, since in these schemes the high correlation of the channels of the users also greatly affects their performance.
    [0045]
    [0046] Another aspect of the invention relates to a method of receiving optical signals for a multi-user optical system for transmitting information through light comprising the steps of: receiving, in an optical receiver device with two or more photodiodes arranged with different geometrical orientations, two or more optical signals, each with an angle of incidence, emitted by different optical emitters; modifying, by at least one optical filter associated with each of the two or more photodiodes, the amplitude of the two or more optical signals received as a function of the angle of incidence; and generating a linearly independent output signal in each of the photodiodes based on the combination of the at least one filter and the geometrical orientation of each of the two or more photodiodes.
    [0047]
    [0048] Additionally, one of the embodiments of the present invention further comprises selecting the output signal linearly independent of one of said two or more photodiodes at each instant of time, by means of a signal selector module with an input connectable to the two or more photodiodes; and canceling interferences between the output signals of the two or more photodiodes, by means of a module of cancellation of interferences connected with the output of the selector module, where the output signal of the module of cancellation of interferences in each instant of time corresponds to a single user of the system, according to a transmission pattern previously assigned to each one of the users of the system.
    [0049]
    [0050] Finally, a computer program is presented comprising computer executable instructions for implementing the described method, when running on a computer, a digital signal processor, a specific integrated circuit of the application, a microprocessor, a microcontroller or any other form of programmable hardware. Said instructions may be stored in a digital data storage medium.
    [0051]
    [0052] The present invention implies, among other advantages, a considerable reduction in power compared to traditional multi-photodiode receivers. Thanks to the configurations of the reconfigurable photodetector of the present invention, BIA interference cancellation schemes can be implemented, which was not possible until now mainly due to the high correlation of signals from nearby and symmetric users, as well as to improve the performance of schemes of transmission based on precoding of the transmitted signal through knowledge of the state of the channel in transmission.
    [0053]
    [0054] For a more complete understanding of these and other aspects of the invention, its objects and advantages, reference may be made to the following specification and the accompanying drawings.
    [0055]
    [0056] Description of the drawings
    [0057]
    [0058] To complete the description that is being made, and in order to contribute to a better understanding of the characteristics of the invention, according to an example of one of the embodiments thereof, accompanying said description as an integral part thereof , some drawings are included in which, by way of illustration and not restrictively, the following is represented:
    [0059]
    [0060] Figure 1.- shows a typical LiFi transmission scenario of the art state.
    [0061] Figure 2 shows how the channel is characterized between a transmitter and a light receiver.
    [0062] Figure 3 shows a schematic of a reconfigurable photodetector based on a pyramidal structure, according to one of the possible embodiments of the present invention.
    [0063] Figure 4 shows in block diagram the architecture of a reconfigurable photodetector, according to a particular embodiment of the present invention.
    [0064] Figure 5.- shows an example scenario with two luminous transmitters and two users. Figure 6 shows a comparative graph that evaluates the performance of a traditional link versus links configured according to the present invention.
    [0065]
    [0066] Detailed description of the invention
    [0067]
    [0068] What is defined in this detailed description is provided to assist in a thorough understanding of the invention. Accordingly, persons of ordinary skill in the art will recognize that variations, changes, and modifications of the embodiments described herein are possible without departing from the scope of the invention. In addition, the description of functions and elements well known in the state of the art is omitted for clarity and concision.
    [0069]
    [0070] Of course, the embodiments of the invention can be implemented in a wide variety of architectural platforms, protocols, devices and systems, so the specific designs and implementations presented in this document are provided for illustration and comprehension purposes only, and never to limit aspects of the invention.
    [0071]
    [0072] The present invention discloses an optical receiver or photodetector composed of several photodiodes which, thanks to the combination of different filters and orientations thereof, are capable of providing linearly independent responses to the same angle of incidence of the light signals emitted from a plurality of light sources. Said responses are connected to a selector that provides a single line of signal processing and that extracts the signal received from one of the multiple photodiodes at each instant of time.
    [0073]
    [0074] Figure 3 shows a scheme of a reconfigurable photodetector based on a pyramidal structure, where each of the face of the pyramid corresponds to a photodiode, characterized by an orientation vector nk (v) (31), defined by the angle of rotation (32) and azimuth (33) in spherical coordinates.
    [0075]
    [0076] Assuming a photodetector receiver device with several photodiodes, the reconfigurable photodetector of the present invention varies the combination of the orientation of each of the photodiodes that compose it, as shown in Figure 3, and filters / concentrators, in order to obtain linearly independent responses to the channel between the photodiodes that compose it. The assignment of the photodiodes that make up the reconfigurable photodetector is done according to a determined structure. For example, continuing with the particular embodiment of Figure 3, a pyramidal structure. In this way, each of the photodiodes is associated with a different orientation, which generates different angles of incidence for the same user. Additionally, each of the photodiodes can be equipped with a filter / concentrator with different geometries, such as flat, hemispherical, polarized, etc., in order to guarantee the linear independence between the photodiodes.
    [0077]
    [0078] The receiver or reconfigurable photodetector offers a single user different configurations, called "modes" hereinafter. Thus, making use of these modes, which provide linearly independent responses, the reconfigurable photodetector enables the implementation of optimal transmission schemes in the absence of knowledge of the transmission channel, such as Blind Interference Alignment that mitigate or even eliminate the effect of the transmission. interference. Additionally, it allows the development of transmission strategies that improve the efficiency of vector transmission schemes based on knowledge of the channel such as Zero Forcing or Block Diagonalization, which contributes to obtain transmission speeds comparable or even higher than those obtained with the technologies conventional radio, such as WiFi or 4G.
    [0079]
    [0080] Figure 4 shows the architecture of a reconfigurable photodetector (41) according to a particular embodiment of the present invention. Each photodiode (42) is provided with a filter (43) to modify in amplitude the response to the channel depending on the angle of incidence of the luminous signal, a concentrator (44) and a certain orientation. In addition, the photodiodes are connected to a single selector (45) that assigns the response of one and only one of the available photodiodes in each symbol time. Therefore, the set of photodiodes is connected to a single branch of signal processing, cancellation of interference (46) and decoding (47), in which any transmission / reception scheme is applied, such as Blind Interference Alignment o Zero Forcing, where the mode selection pattern is set by the transmission strategy specified at the beginning of sending the information.
    [0081]
    [0082] Each of the photothodes of the reconfigurable photodetector of the present invention is connected to the selector, which is responsible for assigning one and only one of the available modes during each symbol period. The selector of each user follows a certain pattern known as supers ^ bolus, where this pattern is previously communicated to each user and determines the transmission structure that will be carried out. In this way, the present invention makes it possible to implement interference cancellation schemes, such as Blind Interference Alignment, reported hitherto exclusively for radiofrequency systems based on reconfigurable antennas.
    [0083]
    [0084] Figure 5 shows an example scenario, in which two luminous transmitters (51, 52) transmit four symbols (57-60) to two users (53, 54) equipped with a reconfigurable photodetector according to one of the embodiments of the invention. invention, wherein said photodetector provides two modes (55, 56). The super symbol corresponding to this example scenario can be seen in the following table, where h [k] (m) is the equivalent channel of user k in mode m in each symbol period:
    [0085]
    [0086]
    [0087]
    [0088]
    [0089] Assuming that this structure repeats in a specific manner throughout the transmission of a data stream, it can be verified that the mode of the reconfigurable photodetector of the user 1 (53) varies in each period of symbol, while the frequency of the user 2 ( 54) is of 2 periods of symbol. That is, there are two patterns that form a super symbol assigned to each user. This selection pattern allows to align or cancel the interference between users without the need of knowledge of the transmission channel or the use of orthogonal transmission schemes, such as division in time or frequency.
    [0090]
    [0091] For example, according to the transmission strategy shown in the previous table, the interference between optical users is aligned (or canceled) by transmitting four symbols during three periods of symbol. That is, it increases the gain of multiplexation in the absence of channel knowledge, which obtains 4/3 symbols per symbol period for the example shown in figure 5. It should be noted that the BIA techniques allow to obtain the gain of multiplexing in the absence of knowledge of the transmission channel.
    [0092] The reconfigurable photodetector is focused, according to a realization of the invention, to its adaptation for the use of BIA schemes, that is, in the absence of knowledge of the transmission channel, but its implementation is very useful also for other embodiments with schemas of vector transmission based on knowledge of the channel. As mentioned above, the transmission of data by visible light and its detection is subject to a high correlation of user channels, for example, symmetric users on the stage. This correlation greatly affects the application of vector transmission schemes such as Zero Forcing or Block Diagonalization in optical transmission. Advantageously, the use of reconfigurable photodetectors such as that described by the present invention allows the development of transmission strategies capable of eliminating this correlation, and therefore, considerably improving their performance.
    [0093]
    [0094] Figure 6 shows a graph that represents in its vertical axis the speed of transmission of data to each user in Mbps, in relation to the radius of coverage in meters of the access point LiFi represented on the horizontal axis. Specifically, the results of a first scenario (61) are presented in which the use of the reconfigurable photodetectors described in the present invention is introduced, BIA techniques are applied and the topology is known; a second scenario (62) in which the reconfigurable photodetectors described in the present invention are also used and BIA techniques are applied, but now without knowledge of the topology; and a third scenario (63) in which there is a perfect knowledge of the channel, and therefore also of the topology, with signal processing techniques applied to a receiver with a conventional photodetector.
    [0095]
    [0096] From the results obtained when evaluating the benefits obtained in a LiFi deployment, it can be observed how the use of BIA techniques, both with knowledge of the topology (61) and without the (62) obtains better transmission rates than a scheme ( 63) based on the perfect knowledge of the channel, and therefore also of the topology, with signal processing techniques applied to a receiver with a conventional photodetector.
    [0097]
    [0098] Therefore, the evaluation tests carried out demonstrate that the photodetectors described in the present invention contribute to providing transmission speeds of data and coverage much higher than those obtained by conventional photodetectors.
    [0099]
    [0100] Some preferred embodiments of the invention are described in the dependent claims which are included below.
    [0101] In this text, the word "comprises" and its variants (such as "understanding", etc.) must not be interpreted in an exclusive manner, that is, they do not exclude the possibility that what is described includes other elements, steps, etc.
    [0102]
    [0103] The description and the drawings simply illustrate the principles of the invention. Therefore, it should be appreciated that those skilled in the art could devise various provisions which, although not explicitly described or shown in this document, represent the principles of the invention and are included within its scope. In addition, all the examples described in this document are provided primarily for pedagogical reasons to help the reader understand the principles of the invention and the concepts contributed by the inventor (s) to improve the technique, and should be considered as non-limiting. with respect to such examples and conditions described specifically. In addition, everything set forth in this document related to the principles, aspects and embodiments of the invention, as well as the specific examples thereof, cover equivalences thereof.
    [0104]
    [0105] Although the present invention has been described with reference to specific embodiments, those skilled in the art should understand that the foregoing and various other changes, omissions and additions in the form and detail thereof may be made without departing from the scope of the invention. as defined by the following claims.
    权利要求:
    Claims (10)
    [1]
    An optical receiver device (41) configurable for a multi-user optical system for transmitting information through the light characterized in that it comprises:
    - two or more photodiodes (42) arranged with different geometrical orientations to receive two or more optical signals, each with an angle of incidence, emitted by different optical emitters;
    - at least one optical filter (43) associated with each of the two or more photodiodes, to modify the amplitude of the two or more optical signals received as a function of the angle of incidence;
    where the combination of the at least one filter and the geometrical orientation of each of the two or more photodiodes generates a linearly independent output signal in each of the photodiodes.
    [2]
    2. Device according to claim 1, which further comprises a concentrator (44) coupled to the at least one optical filter.
    [3]
    3. A multi-user optical system for transmitting information through light, characterized in that it comprises:
    - an optical receiver device (41) according to any of claims 1 or 2;
    - a signal selector module (45), with an input connectable to the two or more photodiodes to select the output signal of one and only one of said two or more photodiodes at each instant of time;
    - a module (46) for cancellation of interferences connected with the output of the selector module to cancel interferences between the output signals of the two or more photodiodes, where the output signal of the interference cancellation module at each instant of time corresponds to a single user of the system, according to a transmission pattern previously assigned to each of the users of the system.
    [4]
    4. System according to claim 3 further comprising a module (47) decoder connected to the output of the interference cancellation module to decode the output signal of said interference cancellation module.
    [5]
    System according to claim 4, wherein the interference cancellation module is a BIA module for blind transmissions.
    [6]
    6. System according to claim 5, wherein the selector module comprises a pattern of selection of output signals of the two or more photodiodes based on a blind transmission scheme BIA.
    [7]
    7. System according to claim 4, which also comprises an equalizer module based on a Zero Forcing equalizing technique.
    [8]
    8. A method of receiving optical signals for a multi-user optical system for transmitting information through light, characterized in that it comprises:
    a) receiving, in an optical receiver device with two or more photodiodes arranged with different geometrical orientations, two or more optical signals, each with an angle of incidence, emitted by different optical emitters;
    b) modifying, by at least one optical filter associated with each of the two or more photodiodes, the amplitude of the two or more optical signals received as a function of the angle of incidence; Y
    c) generating a linearly independent output signal in each of the photodiodes based on the combination of the at least one filter and the geometric orientation of each of the two or more photodiodes.
    [9]
    9. Method according to claim 8, which further comprises:
    d) selecting the output signal linearly independent of one of said two or more photodiodes at each instant of time, by means of a signal selector module with an input connectable to the two or more photodiodes; Y
    e) canceling interferences between the output signals of the two or more photodiodes, by means of an interference cancellation module connected to the output of the selector module, where the output signal of the interference cancellation module at each instant corresponds to a only user of the system, according to a transmission pattern previously assigned to each one of the users of the system.
    [10]
    10. A computer program characterized in that it comprises program code means adapted to perform the steps of the method according to any of claims 8 to 9, when said program is executed in a general purpose processor, a digital signal processor, an FPGA , an ASIC, a microprocessor, a microcontroller, or any other form of programmable hardware.
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