KR102010640B1 - Apparatus of multi-user Full-duplex visible light communication - Google Patents

Abstract

Provided is a multi-user full duplex visible light communication system that can be applied to a smart home network in an indoor environment where a plurality of user devices and a plurality of smart devices are accessible. Gasing light communication apparatus of the visible light communication system according to an embodiment of the present invention includes a light emitting unit configured to emit visible light and a modulator configured to modulate a signal to be transmitted, wherein the light emitting unit is a red LED and green light emitting red light visible light And a green LED for emitting visible light in a band, wherein the modulator modulates the smart device signal to be transmitted to the smart device and the user device signal to be transmitted to the user device, respectively, to modulate each of the modulated smart device signal and the modulated user device signal. And to the red LED and the green LED to be transmitted through each of the red light emitted by the red LED and the green light emitted by the green LED.

Description

Apparatus of multi-user Full-duplex visible light communication

The present invention relates to visible light communication, and more particularly, to a visible light communication device to which a multi-user full duplex method is applied.

While wireless technology is working to meet demand, the number of networked devices is growing rapidly. Watching high-definition video and accessing cloud-based services through various network-connected devices comes at the expense of data capacity. Much of the consumption of data capacity occurs in indoor environments such as smart devices in homes, shopping malls, aircraft, and other vehicles. This high demand for data use is expected to continue to grow in the future. Efforts are being made to overcome the limitations of data transmission speed and capacity of the network. In the case of the radio frequency (RF) band, the Visible Light Communication (VLC) can be used to close the gap between user demand and capacity because it is used by various communication and network systems. Is attracting attention as a major technology.

The VLC uses a light emitting diode (LED) to provide a lighting function and perform data communication at the same time. VLC is showing its potential to be an integral part of the upcoming 5G network. In the case of 5G networks, data traffic is estimated to increase 1000 times, and 5G networks must rely on more efficient technologies to meet these demands. For example, technologies related to smaller at-cells, additional spectrum, energy efficient communications, and Het-Net integration are likely to be applied.

VLC has many advantages over traditional radio frequency (RF) wireless communications. The visible light spectrum is free, and visible light cannot pass through solid objects, which has security advantages when used in limited rooms. It can also be placed anywhere LEDs are installed, and typically have a high signal-to-noise ratio (SNR) because of the high illumination requirements.

The fact that VLC can provide high bandwidth densities can provide a solution to the high bandwidth challenges faced by upcoming RF-based networks. Considering the positive characteristics of VLC described above, VLC can be a suitable complement to Het-Nets in 5G networks.

As far as the multi-user full duplex VLC system is concerned, few studies have been reported in the literature. 'D. O'Brien. Optical wireless communications and potential applications in space. In Proceedings of the International Conference on Space Optical Systems and Applications (ICSOS), 2012. ' And 'K. Bandara, Y.H. Chung. Novel color-clustered multiuser visible light communication. Trans. Emerg. Telecommunication Technol. The authors of 2014, 25, 6, 579-590. Suggested a CSK-based downlink multi-user scheme, but the proposed scheme is a one-way communication scheme rather than a two-way scheme. 'A. Jovicic, J. Li, T. Richardson. Multiuser CSK scheme for indoor visible light communications. Opt. The authors of Express 2014, 22, 20, 24256-24267. 'Proposed bidirectional communication in a unidirectional user environment by proposing time division duplexing (TDD). Recently, a new user assignment scheme for bidirectional multi-user access for VLC networks is known as' Y.F. Liu, C.H. Yeh, C.W. Chow, Y. Liu, Y. L. Liu, H.K. Tsang. Demonstration of bidirectional LED visible light communication using TDD traffic with mitigation of reflection interference. Opt. Express 2012, 20, 21, 23019-23024. ',' A. Sewaiwar, S.V. Tiwari, Y.H. Chung. Novel user allocation scheme for full duplex multiuser bidirectional Li-Fi network. Opt. Commun. 2015, 339, 153-156. '. However, this method has a problem that it is very difficult to change / update the user since it restricts the user to operate in a specific color cluster. Therefore, there is a need for a robust multi-user full-duplex VLC system that can be easily integrated with smart home applications.

An object of the present invention is to provide an optical communication system applicable to a smart home network in an indoor environment.

The present invention has been made in an effort to provide a visible light communication device that enables full-duplex visible light communication for a plurality of user devices and a plurality of smart devices that can be connected to a smart home network.

In one aspect of the present invention, a visible light communication device operating in a smart home network of an indoor environment in which a plurality of user devices and a plurality of smart devices are accessible according to an embodiment of the present invention is a light emitting unit configured to emit visible light and to be transmitted And a modulator configured to modulate a signal, wherein the light emitter includes a red LED emitting red light in the visible band and a green LED emitting green light in the green band, and the modulator includes a smart device signal and a user device to be transmitted to the smart device. Modulating the user device signal to be transmitted to the red LED and the modulated smart device signal and the modulated user device signal, respectively, through the red light emitted by the red LED and the green light emitted by the green LED. Pass with green LED.

The smart device signal may be generated by combining coded data streams obtained by spreading data to be transmitted to each of the plurality of smart devices using unique orthogonal Walsh codes. The device signal may be generated by combining coded data streams obtained by spreading data to be transmitted to each of the plurality of user devices using a unique orthogonal Walsh code.

The smart device signal and the user device signal may be modulated by an Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) technique.

The apparatus may further include a light receiver configured to receive an optical signal from the plurality of smart devices and the plurality of user devices, and a demodulator configured to demodulate a received signal transmitted from the light receiver.

The light receiving unit may include a blue light filter having visible light in a blue light band as a pass band, and a photo-detector detecting the received signal from visible light in the blue light band passing through the blue light filter.

The received signal may be modulated by an on off keying (OOK) technique.

According to another aspect of the present invention, a visible light communication user device operating in a smart home network of an indoor environment in which a plurality of user devices and a plurality of smart devices are accessible includes a red light filter including visible light in a red light band as a pass band, and the red light. And a photo-detector for detecting a received signal from visible light in the red light band passing through the filter, and a demodulator for demodulating the received signal.

The visible light communication user device may further include a blue LED that emits visible light in a blue light band and a modulator that modulates a signal to be transmitted and transmits the signal to the blue LED to be transmitted through the blue light emitted by the blue LED.

The received signal may be modulated by an Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) technique, and the transmitted signal may be modulated by an on off keying (OOK) technique by the modulator.

In still another aspect of the present invention, a visible light communication smart device operating in a smart home network of an indoor environment in which a plurality of user devices and a plurality of smart devices are accessible includes a green light filter having visible light in a green light band as a pass band, and the green light. And a photo-detector for detecting a received signal from visible light in the green light band passing through the optical filter, and a demodulator for demodulating the received signal.

The smart device may further include a blue LED that emits visible light in a blue light band and a modulator that modulates a signal to be transmitted and transmits the signal to the blue LED to be transmitted through the blue light emitted by the blue LED.

The received signal may be modulated by an Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) technique, and the transmitted signal may be modulated by an on off keying (OOK) technique by the modulator.

Full-duplex visible light communication system for multiple users / devices enables uplink and downlink data transmission using only visible light communication system, enabling reliable data transmission / reception and relatively low network maintenance and maintenance costs Can be obtained.

1 illustrates an environment to which a multi-user full-duplex VLC system according to an embodiment of the present invention can be applied.
2 is a block diagram schematically illustrating a multi-user full-duplex VLC network according to an embodiment of the present invention.
3 is a block diagram briefly illustrating downlink transmission of a multi-user full-duplex VLC system according to an embodiment of the present invention.
4 is a block diagram of a OOK transmitter.
5A and 5B schematically show a Wi-Fi system and a hybrid VLC-Wi-Fi system, respectively.
6A and 6B show downlink and uplink bit error rate (BER) simulation results and data rates of a multi-user full duplex visible light communication system according to an embodiment of the present invention.
7 is a graph showing simulated average device cost and power consumption cost compared to data throughput of different signal processing devices.
8 shows the device cost versus data throughput of the system to be compared and the multi-user full duplex visible light communication system according to the embodiment of the present invention.
9 is a result of calculating the power cost for the data throughput.
10 shows the total cost for data throughput.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

1 illustrates an environment to which a multi-user full duplex VLC system may be applied according to an embodiment of the present invention. Multi-user full-duplex VLC system according to an embodiment of the present invention can be applied to various indoor environments, such as offices, cafes, libraries as well as the illustrated smart home environment.

As illustrated in FIG. 1, traffic to be considered in a multi-user full-duplex VLC system according to an embodiment of the present invention applied to a smart home may be classified into user data and data of a smart device. In other words, the downlink traffic is transmitted to a user device (eg, a smartphone, PDA, tablet, etc.) and a smart device that is connected to a network and is sent to a smart device that can automatically send and receive real-time data without human intervention. Can be divided into data. In addition, uplink traffic transmitted from the user terminal and the smart device may be considered. For convenience of explanation, hereinafter, the communication method in the VLC system according to the embodiment of the present invention will be described by dividing each in terms of uplink and downlink.

In one embodiment, a multi-user full-duplex VLC system may be applied with RGB LEDs to use red, green and blue light as the primary channels. Since blue light is more easily scattered than red and green light, red light and green light, which are less scattered and can be transmitted farther in the same condition, may be selected / used as a downlink channel. That is, the user data and the data of the smart device may be transmitted to the user terminal and the smart device through the red light and the green light. In one example, red light may be used for transmitting user data and green light may be used for transmitting smart device data. At this time, the blue light not used in the downlink is irradiated unmodulated. The illumination intensity of red light, green light, and blue light is adjusted / controlled so that the output light is white light, so that the human eye can easily adapt and function as an illumination that can perform daily tasks.

The downlink receiver may be equipped with a red or green optical filter to separate user data from device data. In an embodiment, an Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing (ACO-OFDM) scheme may be used to modulate the signal on the downlink channel. The description of the ACO-OFDM will be described later together with the reception process by the receiver.

In one embodiment, blue light may be used as an uplink channel. Phosphorus LEDs may be used to generate blue light. Phosphorus LEDs are basically blue LEDs coated with a phosphorus layer that emits white light. If red or green light is used for the uplink, it may act as an interference to the downlink data. Therefore, blue light not used for downlink transmission may be used for uplink transmission.

The uplink receiver includes a blue optical filter for receiving data. In order to reduce the complexity of the system and increase the reliability of transmission, an ON-OFF keying (OOK) scheme may be applied to data transmission through the uplink channel. In the case of a device for transmitting data through an uplink such as a user terminal (eg, a smart phone) and a smart device, available power may be limited. In order to extend the battery life of these devices and to efficiently utilize the computing power, the OOK method can be selected as an uplink modulation method.

2 is a block diagram schematically illustrating a multi-user full-duplex VLC network according to an embodiment of the present invention.

The VLC network according to the embodiment of the present invention illustrated in FIG. 2 may include a VLC communication device 100, at least one user device 200, and at least one smart device 300. 2 is a schematic diagram of the communication device 100, the user device 200, and the smart device 300, and the part that does not correspond to the features of the present invention in order to clarify the convenience of the description and the characteristic parts of the present invention. Is omitted.

The visible light communication device 100 operating in a smart home network of an indoor environment in which a plurality of user devices and a plurality of smart devices are accessible according to an embodiment of the present invention is configured to modulate a light emitting unit configured to emit visible light and a signal to be transmitted. Including a modulator, wherein the light emitting unit includes a red LED for emitting visible light of a red light band and a green LED for emitting visible light of a green light band, the modulator is a smart device signal and a user device 200 to be transmitted to the smart device 300 Modulating the user device signal to be transmitted to the red LED and transmitting the modulated smart device signal and the modulated user device signal, respectively, through the red light emitted by the red LED and the green light emitted by the green LED. Deliver to the green LED.

The smart device signal may be generated by combining coded data streams obtained by spreading data to be transmitted to each of the plurality of smart devices using unique orthogonal Walsh codes. The device signal may be generated by combining coded data streams obtained by spreading data to be transmitted to each of the plurality of user devices using a unique orthogonal Walsh code. The smart device signal and the user device signal may be modulated by an Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) technique. The apparatus may further include a light receiver configured to receive an optical signal from the plurality of smart devices and the plurality of user devices, and a demodulator configured to demodulate a received signal transmitted from the light receiver. The light receiving unit may include a blue light filter having visible light in a blue light band as a pass band, and a photo-detector detecting the received signal from visible light in the blue light band passing through the blue light filter. The received signal may be modulated by an on off keying (OOK) technique.

The visible light communication user device 200 operating in a smart home network in an indoor environment in which a plurality of user devices and a plurality of smart devices are accessible includes a red light filter having visible light in a red light band as a pass band and red light passing through the red light filter. And a photo detector for detecting a received signal from visible light in a band, and a demodulator for demodulating the received signal. The visible light communication user device 200 may further include a blue LED that emits visible light in a blue light band and a modulator that modulates a signal to be transmitted and transmits the signal to the blue LED to be transmitted through the blue light emitted by the blue LED. The received signal may be modulated by an Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) technique, and the transmitted signal may be modulated by an on off keying (OOK) technique by the modulator.

Visible light communication smart device 300 operating in a smart home network of the indoor environment that a plurality of user devices and a plurality of smart devices are accessible is a green light filter having the visible light of the green light band as a pass band, the green light passing through the green light filter And a photo detector for detecting a received signal from visible light in a band, and a demodulator for demodulating the received signal. The smart device 300 may further include a blue LED that emits visible light in a blue light band and a modulator that modulates a signal to be transmitted and transmits the signal to the blue LED to be transmitted through the blue light emitted by the blue LED. The received signal may be modulated by an Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) technique, and the transmitted signal may be modulated by an on off keying (OOK) technique by the modulator.

The multi-user full-duplex VLC system according to an embodiment of the present invention may be divided into a downlink part and an uplink part so that a user located in a smart home can make full use of the advantages of VLC in the downlink and uplink channels. have. As briefly described above, red and green LEDs may be used for the downlink. Red and green light may be used to convey user and device data, respectively. In the uplink, the phosphorus LED may be used. Hereinafter, the downlink and the uplink will be divided and described, respectively.

3 is a block diagram briefly illustrating downlink transmission of a multi-user full-duplex VLC system according to an embodiment of the present invention.

The downlink portion of a multi-user full duplex VLC system according to an embodiment of the present invention is composed of a transmitter and a receiver. The transmitter works in the following way. Data streams (user data and smart device data) are delivered to data spreading blocks. The block spreads user / smart device data using a unique orthogonal Walsh code. In the next step, all coded data streams are combined and delivered to the modulation block. In order to avoid DC biasing and increase power efficiency, the ACO-OFDM scheme may be applied to modulation as described above. The modulated signal passes through a DC bias to ensure that the entire output of the LED is bright white light. The signal is then propagated through the optical wireless channel and received by the user or smart device.

In the multi-user full-duplex VLC system according to an embodiment of the present invention, since the user data is transmitted through the red light region, the user receiver filters the received optical signal through the red optical filter. In the case of a smart device, the data transmitted to the smart device is transmitted through the green light region, and thus the received optical signal is filtered through the green optical filter.

After filtering the optical signal, the procedure described by the transmitter is reversed to restore the original data. Every user can have their own orthogonal Walsh code for added security and data can go through a spreading step to avoid interference and data corruption in the data transfer phase.

The main requirement for a working VLC system is to have a positive real number from the optical modulator, and typically an Intensity Modulation / Direct Detection (IM / DD) technique. ACO-OFDM also works with the IM / DD technique, making it relatively simple to implement. The main problem lies in the OFDM signal. Since OFDM signals are characterized as complex and bipolar, simple OFDM systems cannot be used with VLC systems. Therefore, it is necessary to make an OFDM signal unipolar and real, which can be performed by an ACO-OFDM modulator.

In the multi-user full-duplex visible light communication system according to an embodiment of the present invention, the following procedure may be followed to ensure that the output of the ACO-OFDM is real or unipolar. Only one of the N subcarriers is used to transmit data. At the transmitter, the source bits are first modulated using a gray coded M-ary quadrature amplitude modulation (QAM) mapping block to produce a complex bit stream. The encoded data is then subjected to a Hermitian symmetry block to maintain the actual OFDM symbol in the time domain. The data is then delivered to an Inverse Fast Fourier Transform (IFFT) block and a clipping block so that the data has an odd subcarrier and a positive value. Cyclic Prefix (CP) is added later to avoid Inter Symbol Interference (ISI). The addition of CP has a minor impact on the signal-to-noise ratio (SNR) and spectral efficiency of the VLC system. Two types of distortion can be applied to reduce the peak-to-average power ratio (PAPR): filtering can be applied to reduce out-of-band distortion and secondly, CP can be added to reduce in-band distortion. have. Note that only odd subcarriers are transmitted in the ACO-OFDM signal. The signal is converted from analog to digital using an analog-to-digital converter (ADC) and then transmitted over an optical wireless channel using intensity modulation (IM) data.

When Direct Detection (DD) is used at the receiver, the signal is received at the photo diode (PD). The signal received at the photodiode is converted from the light domain to the electrical domain. The estimated signal is passed to the ACO-OFDM demodulator block for demodulation, and the signal passes through a demapping block to recover the original data stream.

The signal received in the time domain at the receiver is represented by Equation 1.

In VLC, channel h can be line-of-sight (LOS) and non-line-of-sight (NLOS). The main attribute of channel h is that it always has a positive real value. The signal received in the frequency domain may be expressed as Equation 2.

인 간단한 가산 백색 가우스 잡음 (additive white Gaussian noise, AWGN)을 가정한다. 또한 송신기와 수신기는 완벽하게 동기화 되어있음을 가정한다.Where Xaco is the ACO-OFDM signal, H is the OWC channel response, and N is zero and variance

Assume a simple additive white Gaussian noise (AWGN). It is also assumed that the transmitter and receiver are perfectly synchronized.

When considering two kinds of optical channels; In i) LOS and ii) NLOS, two types of channels can be expressed as Equations 3 and 4 and the overall spread channel response can be obtained by Equation 6.

는 광 검출기 영역,

는 소스 빔의 지향성을 나타내는 램버트 모드 번호(lambert's mode number),

는 광 대역 통과 필터를 구비한 수신기,

는 집광기 이득,

는 방사 입사각,

는 송신기에 대한 각도, d는 송신기로부터의 거리, ΔA는 반사체의 면적, k는 실내의 반사체 총 수,

는 j의 반사 계수,

는 반사체와 수신기 사이의 k-1차 임펄스 응답이다.here

Light detector area,

Is a Lambert's mode number representing the directivity of the source beam,

Is a receiver having a wide band pass filter,

Condenser benefits,

Is the incident angle of radiation,

Is the angle to the transmitter, d is the distance from the transmitter, ΔA is the area of the reflector, k is the total number of reflectors in the room,

Is the reflection coefficient of j,

Is the k-first order impulse response between the reflector and the receiver.

In the case of uplink, since the apparatus for transmitting the uplink signal generally has limited resources (eg, power consumption depends on the battery), a simple but robust modulation / transmission scheme should be applied for the uplink period. In a multi-user full duplex visible light communication system according to an embodiment of the present invention, a simple OOK technique may be used to transmit data from a user or a smart device to a receiver. As described above, in LED may be used for uplink data transmission. Phosphorus LEDs are blue LEDs coated with phosphorus that emit white light. Since two other basic colors (red light and green light) are used for downlink except blue light, uplink data is transmitted and received using blue light.

4 is a block diagram of a OOK transmitter.

Data from the user or smart device first goes through a pre-emphasis circuit. This is done to improve the 3dB bandwidth of the VLC link. Since the pre-emphasis circuit is based on NPN transistors, the receiver sensitivity is increased. The signal then passes through the amplifier to increase the modulation depth and is superimposed on the LED bias current through the Bias-T block. The output of the Bias-T block is applied directly to commercially available phosphorescent LEDs. The signal then propagates through the optical radio channel and is received at a receiver with a blue optical filter. Directional lenses are used such that the emitted light is concentrated at the receiver so that the maximum light is exposed to the photodiode.

After receiving the optical signal filtered by the blue light filter on the receiver side through the photodiode, the electrical signal is amplified by the transimpedance amplifier. The amplified electrical signal passes through the post equalization block so that the signal level is amplified and original data is received.

Hereinafter, advantages and performances in terms of implementation cost and energy consumption will be described in comparison with a multi-user full-duplex visible light communication system according to an embodiment of the present invention and other systems of similar functions currently commercially available.

Multi-user full-duplex VLC systems require low implementation costs and high power efficiency for practical use. The communication systems to be compared are the Wi-Fi system and the hybrid VLC-Wi-Fi system, one of the most used wireless systems in the world today. Hybrid VLC-Wi-Fi system is basically proposed to solve the uplink problem of VLC. Downlink transmission may be VLC or Wi-Fi, but uplink is based on Wi-Fi technology.

5A and 5B schematically show a Wi-Fi system and a hybrid VLC-Wi-Fi system, respectively.

The Wi-Fi system consists of a router with a wireless access point (AP). Routers are connected to wide area networks (WANs) and transmit and receive data using radio frequency radiation. Hybrid VLC-Wi-Fi systems, on the other hand, offer improved system performance using both Wi-Fi and VLC technologies. Downlink transmission can be based on VLC or Wi-Fi, and uplink is based on Wi-Fi.

In order to implement a VLC system, the use of a signal processing device is essential. In this case, it is necessary to consider the type of signal processing apparatus required according to the size of the service area to be provided and the number of users. In the following, comparison is made using different types of signal processing devices based on different processing power, cost and power consumption.

Since VLC is not yet as popular as Wi-Fi systems, initial installation costs are approximate values included in simulations and results. Initial equipment prices for VLC systems are expected to be high at time of launch, but as technology becomes more common, costs will be significantly reduced, as with Wi-Fi systems.

In the performance comparison, the assumption is made using signal processing devices with different architectures. The architecture of the signal processing device may be different with respect to the parameters of the multiple cores and the general-purpose input / output (GPIO) registers. This can seriously affect the throughput and power consumption of the overall system. A high number of cores improves performance but increases product cost and power consumption, while a low number of cores lowers power consumption but also lowers performance. Therefore, consideration should be given to the selection of an appropriate signal processing device so that there is a balance between performance, cost and power consumption.

Table 1 shows some signal processing device architectures that differ in cost, power and processing power, resulting in power consumption and cost.

In Table 1, Architecture 1 has one core and four GPIOs, the most basic, low cost, and power efficient processing unit. Since the present invention assumes a smart home environment in one of the main embodiments, the signal processing device of the architecture 1 will be simulated. Since the number of subchannels is not yet defined in the VLC standard, it is assumed that there are 32 subchannels. Based on these assumptions, an Architecture 1 processing unit can accommodate 4 X 32 = 128 users and devices. This can be seen as sufficient for application in a smart home environment.

Table 2 shows power consumption and annual costs for the average US household. The device of Table 2 is an example of a device to which the VLC system can be applied.

We evaluated the performance of the three systems in terms of device cost and power consumption for data throughput. Since there are no commercial VLC products yet, the following environment is assumed for cost and power consumption comparison. The hybrid VLC-Wi-Fi and full-duplex VLC system according to the embodiment of the present invention are calculated based on the Texas Instruments (TI) DSP board series C6000 which is generally used for commercial communication system implementation. Long-term maintenance and electricity costs included. Indoor VLC environment simulation model is' M. T. Niaz, F. Imdad, H. S. Kim. Deployment methods of visible light communication lights for energy efficient buildings. Opt. Eng. 2016, 55, 10, 106113. ' The model of the literature was applied.

Under the above conditions / assumptions, the cost and power consumption calculation of the simple Wi-Fi system may be calculated as in Equations 7 and 8.

는 시뮬레이션 기간 동안 대체 된 LED 조명의 수,

는 특정 룸에서 사용 된 총 LED 수,

는 사용 된 LED의 비용,

는 Wi-Fi 장비 비용 및 사용 된 인터넷 연결 비용,

는 LED의 전력 소비량,

는 Wi-Fi 액세스 포인트 + 라우터의 전력 소비량이다.From here

The number of LED lights replaced during the simulation,

The total number of LEDs used in a particular room,

The cost of the used LED,

The cost of the Wi-Fi equipment and the cost of the internet connection used,

The power consumption of the LED,

Is the power consumption of the Wi-Fi access point + router.

The cost and power consumption calculation of the hybrid VLC-Wi-Fi system may be calculated as in Equations 9 and 10.

는 신호 처리 장치의 비용이고,

는 신호 처리 장치를 작동하는 데 소비되는 전력이며,

는 LED가 신호 처리 장치의 GPIO에 연결되고 연결된 LED의 수에 따라 전력을 끌어 오기 때문에 사용되는 LED 수의 인수와 곱해진다. LED를 연결하는 방식은 다양한 방식이 적용될 수 있다. 예를 들어, 각 GPIO가 각각 하나의 LED를 사용하는 방식으로 연결하거나, LED 조명의 배열을 만들고 한 방을 제공하는 배열을 특정 GPIO에 연결하는 방식이 적용될 수 있다. 이러한 방식으로, 전체 가정은 하나의 신호 처리 유닛을 사용하여 커버 될 수 있다. 앞서 가정한 바와 같이, VLC 부반송파가 32라면 간단한 1 코어 및 4 GPIO 기반 신호 처리 장치를 사용하여 총 128 개의 사용자 또는 스마트장치에게 데이터 전송/수신 서비스를 제공할 수 있다.From the equation above

Is the cost of the signal processing unit,

Is the power consumed to operate the signal processing device,

Is multiplied by a factor of the number of LEDs used since the LEDs are connected to the GPIO of the signal processing unit and draw power depending on the number of LEDs connected. Various methods may be used to connect the LEDs. For example, each GPIO may be connected using a single LED, or an array of LED lights may be connected and an array providing a room may be connected to a specific GPIO. In this way, the entire hypothesis can be covered using one signal processing unit. As previously assumed, if the VLC subcarrier is 32, a data transmission / reception service may be provided to a total of 128 users or smart devices using a simple 1 core and 4 GPIO based signal processing devices.

In the case of a full-duplex VLC system according to an embodiment of the present invention, cost and power consumption are calculated as in Equations 11 and 12.

The main difference from the hybrid VLC-Wi-Fi system is the removal of the Wi-Fi device.

In order to simulate the performance of a full-duplex VLC system according to an embodiment of the present invention, two main variables were investigated: data rate and bit error rate (BER). The room size is 5mX5mX3m and the LED lights are circularly placed on the ceiling to ensure optimized ROPD in the receiving plane and the receiving plane is assumed to have an average height of 0.8m. The system considers both LOS and NLOS signals and the resulting data is simulated with a total of 15 users for an average of 5 user devices and 10 smart devices. As described above, based on the downlink ACO-OFDM scheme, the uplink applied the OOK scheme.

6A and 6B show downlink and uplink BER simulation results and data rates of a multi-user full duplex visible light communication system according to an embodiment of the present invention.

As shown in FIG. 6A, the BER performance of the user and the smart device of the multi-user full-duplex visible light communication system according to the embodiment of the present invention are about the same. The performance of a multi-user full duplex visible light communication system according to an embodiment of the present invention is compared with a simple OOK based implementation of the same system for downlink. We can see that ACO-OFDM outperforms a simple OOK implementation. The fact that a multi-user full duplex visible light communication system according to an embodiment of the present invention performs better is due to the advantage of the application of ACO-OFDM and the added orthogonal Walsh code used to avoid multi-user interference. In the case of the uplink, the performance is the same as that of a typical OOK system, which shows that it is possible to ensure reliable data transmission while achieving high SNR for the uplink.

Next, look at the data rate performance of the multi-user full-duplex visible light communication system according to an embodiment of the present invention. In FIG. 6B, the data rate of the user device is displayed in red, the smart device is displayed in green, and the uplink data is displayed in blue. As can be seen in Figure 6b, the user data rate is higher than the device rate. This is generally more efficient in that users consume more data capacity than smart devices. Although the speed of uplink is the slowest, it should be considered that it is generally used less than downlink in home environment. You can also see that the data rate decreases as the number of users increases, which is the result of more users sharing the same bandwidth. In summary, the multi-user full-duplex visible light communication system according to the embodiment of the present invention can process user and smart device data and provide performance applicable to an average smart home environment.

Hereinafter, the cost and power consumption of the data throughput of the multi-user full-duplex visible light communication system according to an embodiment of the present invention will be described. Assuming the same environment as the above-mentioned environment, the subject of apostasy is also the same as the Wi-Fi system and the hybrid VLC-Wi-Fi system.

7 is a graph showing simulated average device cost and power consumption cost compared to data throughput of different signal processing devices.

It can be seen from FIG. 7 that the cost of the device also increases as the computing power of the DSP increases. Power consumption Consumption also increases with increasing computing power. The price mentioned here is an approximation as the DSP industry is now moving to efficient low-power boards, and device and power costs are expected to decrease as future power-efficient boards are introduced.

Based on the above description, the device cost for data throughput, power cost for data throughput, and total cost for data throughput of the comparison target system and the multi-user full-duplex visible light communication system according to the embodiment of the present invention are as follows.

8 shows the device cost versus data throughput of the system to be compared and the multi-user full duplex visible light communication system according to the embodiment of the present invention.

Although the device cost of the multi-user full-duplex visible light communication system according to the embodiment of the present invention is high, it can be seen that over time, the system becomes cheaper due to low maintenance costs. In FIG. 8, maintenance costs may be bulb replacement and hardware upgrade of the Wi-Fi device. However, for VLC, hardware upgrades are not necessary because they are expected to handle the data throughput required for the average smart home for at least five years, which can also lead to cost savings.

9 is a result of calculating the power cost for the data throughput.

As shown in FIG. 9, the Wi-Fi system and the hybrid VLC-Wi-Fi system consume relatively more power than data throughput, and thus are relatively expensive. In the multi-user full-duplex visible light communication system according to the embodiment of the present invention, in which a high efficiency DSP can be used, power cost for data throughput is low.

10 shows the total cost for data throughput.

The initial cost of the multi-user full-duplex visible light communication system according to the embodiment of the present invention is higher than that of the comparison target system, but it shows that the lowest cost after four years.

Claims (12)

A visible light communication device operating in a smart home network in an indoor environment where a plurality of user devices and a plurality of smart devices are accessible,
A light emitting unit configured to emit visible light; And
A modulator configured to modulate a signal to be transmitted;
The light emitting unit includes a red LED for emitting visible light in a red light band and a green LED for emitting visible light in a green light band,
The signal to be transmitted is transmitted to a user device signal to be transmitted to a user device equipped with a red light filter without a green light filter, and to a smart device equipped with a green light filter without a red light filter and capable of transmitting and receiving data without human intervention. Being divided into a smart device signal, the user device detects the user device signal from the visible light of the red light band passing through the red light filter mounted on the user device and the smart device is the green light filter mounted on the smart device The modulator modulates the user device signal and transmits the modulated user device signal to the red LED to be transmitted through the red light emitted by the red LED to detect the smart device signal from visible light in the green light band that has passed through. And modulate the smart device signal and modulate the smart A device signal to the visible light communication device transmitted to the green LED to be transmitted through the green light emitted by the green LED. According to claim 1,
The smart device signal is generated by combining coded data streams obtained by spreading data to be transmitted to each of the plurality of smart devices using unique orthogonal Walsh codes.
And the user device signal is generated by combining coded data streams obtained by spreading data to be transmitted to each of the plurality of user devices using a unique orthogonal Walsh code. According to claim 1,
And the smart device signal and the user device signal are modulated by an Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) technique. According to claim 1,
A light receiving unit configured to receive an optical signal from the plurality of smart devices and the plurality of user devices; And
And a demodulator for demodulating the received signal transmitted from the light receiver. The method of claim 4, wherein
The light receiving unit includes a blue light filter having visible light in a blue light band as a pass band;
And a photo-detector for detecting the received signal from the visible light in the blue light band passing through the blue light filter. The method of claim 5,
And the received signal is modulated by an OOK (On Off Keying) technique. delete delete delete delete delete delete

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