KR20160128881A - Optical Camera Communications Based on Compressed Sensing - Google Patents

Abstract

Provided is an optical camera communication system which receives light emitting diode (LED) optical data based on a camera sensor. The optical camera communication system includes: a transmission apparatus for transmitting a visible light signal of a first rate as an optical rate; and a reception apparatus for receiving the visible light signal at a second rate less than the first rate. The transmission apparatus includes: a signal modulation module for modulating source data in an M-ary pulse position modulation (PPM); a pseudo noise (PN) code generation module for generating a PN code to randomly project the signal modulated by the signal modulation module; an LED driving module for generating a driving signal to control an on or off state of at least one LED according to the randomly projected signal; and an LED module for transmitting the visible light signal through the at least one LED according to the driving signal. The reception apparatus includes: a camera module having a second rate as a frame rate; an interest region detection module for detecting a transmission region of the visible light signal in the frame received through the camera module; and a signal detection module for detecting the source data in the visible light signal transmitted through the detected interest region.

Description

Technical Field [0001] The present invention relates to an optical camera communication based on compression sensing,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical camera communication method based on compression sensing and an apparatus for supporting the same.

Optical Camera Communication (Optical Camcom) is a new concept technology that receives LED (Light Emitting Diode) optical data based on camera sensor.

LED light data generated from at least one LED can be detected by a camera sensor. Unlike conventional Visible Light Communications (VLC), which uses a photodiode as a receiver component, the Optical Camcom of this disclosure adds an additional cost to the application to cameras mounted on cellular phones, electronic devices such as CCTV I do not.

For data communication based on LED light, the transmitting device must provide a wider range of dimming levels for data modulation and no flicker.

Here, the flicker phenomenon refers to a phenomenon in which the flicker of the light is perceived by a human eye. In general, when the LED is flickered at a frequency of 100 Hz or less, the flickering can be perceived by a human eye. Therefore, in order to prevent such a flickering phenomenon, the LED of the Optical Camcom can be flickered to a frequency exceeding 100 Hz. In the IEEE 802.15.7 VLC standard, the maximum flickering time period (MFTP) is reported to be 5 ms.

The capture rate (or frame rate) of a typical CMOS (Complementary Metal Oxide Semiconductor) camera is only about 30 frames per second. As a result, the Optical Camcom acquires the signal at a sampling rate lower than the data transmission rate. As a result, unsampled data is generated, resulting in data loss, thereby significantly reducing the probability of correct signal detection. In addition, in implementing a high-speed ADC (Analog-to-Digital Converter) included in the camera, adverse effects may occur in terms of cost and complexity.

To solve this problem, an RGB coding method has been proposed in LED-LCD camera communication.

Here, the RGB coding method is a coding method in which a QR (Quick Response) code is extended to a color space. However, in the RGB coding method, there is a disadvantage that the LED / LCD functions only as a data transmitter and does not perform a general display function.

Considering the LED light source for performing the display function and the communication function, a flicker-free optical Camcom scheme including a specific CMOS image sensor may be proposed.

The specific CMOS image sensor can respond instantaneously to changes in intensity of light.

Here, a specific CMOS image sensor may include at least one communication pixel composed of a photodiode. However, there is a disadvantage that such a specific CMOS image sensor can not be directly applied to a cost effective general CMOS image sensor.

In order to solve this problem, an undersampled frequency shift ON-OFF keying (UFSOOK) scheme using an aliasing characteristic has recently been proposed. However, this scheme can only decode the signal assuming a certain pattern of frequencies. This limits the flexibilty of the system.

Recently, Candes et al. And Donoho developed a compression sensing theory that restores the signal at a low sampling rate. Based on the sparse generation characteristics of the probability signal, the compression sensing makes it possible to restore the signal with a high bit rate to a sampling rate lower than the Nyquist rate.

According to an embodiment of the present invention, there is provided an optical camera communication system, comprising: a transmitter for transmitting a visible light signal having a first rate at an optical rate; And a receiving device for receiving the visible light signal at a second rate lower than the first rate, wherein the transmitting device modulates the source data using an M-ary pulse position modulation (PPM) method Signal modulation module; A PN code generation module for generating a PN code (Pseudo Noise code) for random projection of a signal modulated through the signal modulation module; An LED driving module for generating a driving signal for controlling an on or off state of at least one light emitting diode according to the randomly projected signal; And an LED module for transmitting a visible light signal through the at least one LED according to the driving signal, wherein the receiving device comprises: a camera module having the second rate at a frame rate; A region of interest detection module that detects a transmission region of the visible light signal in a frame received through the camera module; And a signal detection module for detecting the source data in a visible light signal transmitted through the detected ROI.

The second rate may be determined according to the length of the PN code.

Further, the signal modulation module may convert the source data into pulse positions in any one of a plurality of time intervals within each time frame.

In addition, the signal modulation module outputs the input signal as a K-sparse signal having K non-zero values through the M-ary pulse position modulation (PPM) method .

In a transmitting apparatus for transmitting a signal in an optical camera communication system according to another embodiment of the present invention, source data is modulated by using M-ary Pulse Position Modulation (PPM) Signal modulation module; A PN code generation module for generating a PN code (Pseudo Noise code) for random projection of a signal modulated through the signal modulation module; An LED driving module for generating a driving signal for controlling an on or off state of at least one LED according to the randomly projected signal; And an LED module that transmits a visible light signal through the at least one LED according to the driving signal.

Further, the signal modulation module may convert the source data into pulse positions in any one of a plurality of time intervals within each time frame.

In addition, the signal modulation module outputs the input signal as a K-sparse signal having K non-zero values through the M-ary pulse position modulation (PPM) method .

In an optical camera communication method according to an embodiment of the present invention, a signal is transmitted using a PPM method and a PN code in a transmitting apparatus, thereby improving the signal restoration performance even at a low sampling rate in a receiving apparatus using a camera There is an effect that can be.

In addition, the optical camera method according to an embodiment of the present invention can perform signal detection at a sampling rate lower than a Nyquist rate through random projection using a PN code, thereby reducing the complexity of implementation of a receiving apparatus. A compression sensing based signal detection scheme can be provided.

In addition, since the optical camcom method according to the embodiment of the present invention does not limit the downsampling rate to a specific rate, there is an advantage that it is possible to freely design an optical camcom system.

1 is a diagram illustrating a structure of an optical camera communication (Optical CamCom) based on a compression sensing (CS) according to an embodiment of the present invention.
2 is a diagram illustrating a transmission signal structure using a 4-ary PPM scheme according to an embodiment of the present invention.
3A and 3B are graphs illustrating an example of a signal detection probability result graph according to various down sampling rates (DSR).
4 is a diagram showing the detection probability of a signal according to the length of the PN code and the DSR in a three-dimensional image.

As used herein, terms used in the present specification are taken into consideration in considering the function of the present invention. However, this may vary depending on the intention of the person skilled in the art, custom or the emergence of a new technique. Also, in some cases, there may be a term selected arbitrarily by the applicant, and in this case, the meaning will be described in the description of the corresponding embodiment. Therefore, it is intended that the terminology used herein should be interpreted relative to the meaning of the term rather than to the nomenclature of the term, and the entire content of the specification.

Furthermore, the embodiments are described in detail below with reference to the accompanying drawings and the accompanying drawings, but are not limited or limited by the embodiments.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

compression Sensing (Compressed Sensing: CS ) theory

Compression sensing theory is a "sparse" signal in which most of the signals in nature are zero, most of which are zero when transformed into a specific signal space.

Here, when a signal is displayed on an xy graph, a signal having a y value of non-zero at a relatively small number of x values and y is zero at most x values It says.

Also, the number of non-zero numbers in the original signal is called 'sparsity'. That is, the number of non-zero values in the original signal is defined as 'sparsity', and the sparsity can be expressed by a specific variable.

According to the compression sense (CS) theory, the sparse signal can restore the original signal almost perfectly even with only a very small number of linear measurements.

Hereinafter, a method of optical camera communication (Optical CamCom) based on compression sensing will be described.

First, the Optical Camcom system requires that the data transmission signal be real-valued and positive-valued. This is because LEDs are used to transmit data using the intensity of light (or light).

Consider the NX1 signal vector X.

Here, X is a signal vector having a real number and a positive number, and having a finite length.

가 성립하는 특정 신호 벡터 X는 NX1의 기본 벡터(

)로 표현될 수 있다고 가정한다. 이 경우, 상기 신호 벡터 X는 아래의 수학식 1과 같이 표현될 수 있다.

Is the base vector of NX1 (

). ≪ / RTI > In this case, the signal vector X can be expressed by the following equation (1).

Herein, the basic vector of NX1 means a vector capable of expressing all natural signals.

[Equation 1]

,

,

는 계수 세트(coefficient set)를 나타내며, 기본 벡터 앞에 곱해지는 스칼라(scalar) 값이다. here,

Represents a coefficient set and is a scalar value that is multiplied before the base vector.

로 표현될 수 있다.When the NX1 signal vector X is expressed in a matrix form

. ≪ / RTI >

는 기본 벡터들과

로 구성된 NXN 행렬을 나타낸다.here,

Lt; RTI ID = 0.0 >

Gt; NXN < / RTI >

는

의 전치 행렬(transposed matrix)을 나타낸다.here,

The

(Transposed matrix).

According to compression sensing theory, if X can be represented as a linear combination of K (= N) basis vectors, X can be defined as a K-sparse signal.

가 K개의 논-제로(non-zero) 요소(element)들을 가지며, 나머지 요소들은 제로 임을 의미한다.The coefficient vector

Has K non-zero elements, and the remaining elements are zero.

및

로부터 선택된 K 벡터들의 선형 결합으로서 재표현될 수 있으며, 이는 수학식 2와 같다. Thus, the signal X

And

Lt; RTI ID = 0.0 > K < / RTI >

&Quot; (2) "

,

,

,

,

는 자연수 세트를 나타낼 수 있다. here,

Can represent a set of natural numbers.

If the NX1 signal vector x is not directly a K-sparse signal, it may be represented as a K-sparse signal through a specific linear transformation process as shown in Equation (3) below.

를 DXN(D=cK, c≥1이고, D는 N보다 작은 자연수) 랜덤 측정 행렬(random measurement matrix)라고 하고, y를 DX1 크기의 압축 측정 벡터라고 했을 때, y는 행렬

를 기초로 프로젝션 변형(projection transformation)되어 이하의 수학식 3과 같이 표현될 수 있다. Specifically,

Is a DXN (D = cK, c? 1, D is a natural number less than N) random measurement matrix, and y is a DX1 compression measurement vector, y is a matrix

And can be expressed by the following equation (3). &Quot; (3) "

&Quot; (3) "

는 수신 장치에서의 다운 샘플링을 의미하며,

는 송신 장치에서의 랜덤 프로젝션을 의미하며,

는 K-sparse 신호를 의미한다.here,

Quot; means downsampling in the receiving apparatus,

Quot; refers to random projection in a transmitting apparatus,

Means a K-sparse signal.

라는 K-sparse 신호를 랜덤 프로젝션한 뒤, 다운 샘플링한 결과를 나타낸다. That is, y in the equation (3)

And a downsampling result after randomly projecting a K-sparse signal called " K-sparse "

의 요소들 및 계수 벡터

의 스파시티 레벨(Sparsity level)에 의해 결정될 수 있다. 이때, 압축률(D/N)은 대응하는 다운 샘플링 비율(down sampling ratio)과 관련될 수 있다.According to Equation (3), the sampling rate (or number of measurements)

And the coefficient vector

And the sparsity level of the signal. At this time, the compression ratio (D / N) may be related to a corresponding down sampling ratio.

Hereinafter, a CS-based optical camera communication method (optical camcom) proposed by the present invention will be described in detail with reference to the related drawings based on the above-mentioned contents.

That is, the present invention outputs an input signal satisfying a sparse signal condition (for example, Ristricted Isometry Property: RIP) as (1) a K-sparse signal using a pulse position modulation (PPM) ) This method provides a method of restoring or detecting a sparse signal transmitted from a camera-based receiving apparatus having a low sampling rate by random projection through a PN code.

1 is a diagram illustrating an example of a structure of an optical camera communication (Optical CamCom) based on a compression sense (CS) proposed in the present specification.

Referring to FIG. 1, an optical camera system 100 includes a transmitter 110 and a receiver 120.

The transmitter 110 generates a K-sparse signal using the PPM modulation and the PN code of the input signal, and transmits the visible light signal output through the at least one LED (through the channel) to the outside.

Hereinafter, the components of the transmission apparatus 110 will be described in more detail.

The transmission device 110 includes a signal modulation module 111, a PN code generation module 112, an LED driving module 113, and an LED module 114.

The components of the transmission apparatus 110 shown in FIG. 1 are examples, and the transmission apparatus 110 may be implemented with components having fewer or fewer components.

The signal modulation module 111 modulates an input signal using an M-ary PPM scheme.

At this time, the input signal may be a signal satisfying a RIP (Ristricted Isometry Property) condition to be a sparse signal. The input signal may be represented by input data, input bits, source data, or the like.

That is, the signal modulation module 111 converts the input signal into a pulse position in any one of a plurality of time intervals within each time frame.

Here, the signal modulated with the pulse position is a K-sparse signal, and the K-sparse signal means a signal having a non-zero value K, as shown in FIG.

는 상기 신호 변조 모듈을 통해 출력되는 신호에 해당한다.In equation (3), PPM signal vector

Corresponds to a signal output through the signal modulation module.

2, if the 4-ary PPM scheme is used, the K-sparse signal output from the signal modulation module may be a 1-sparse signal.

에 포함된 M 요소(element)들 중 논-제로(non-zero) 요소들의 개수가 하나이기 때문이다.The reason is as follows.

The number of non-zero elements among the M elements included in the matrix is one.

The PN code generation module 112 generates a PN (pseudo noise) code for randomly projecting the modulated PPM signal (based on the CS theory).

The PN code is used to digitize a downsampled signal including randomness and random numbers of a signal transmitted from a transmitting apparatus.

By randomly projecting the K-sparse signal using the PN code, even if the transmission signal in the transmission apparatus 110 is down-sampled, the randomness of the signal received by the reception apparatus can be maintained at the same level.

That is, since the transmission signal itself in the transmission apparatus 110 has a random characteristic, the reception apparatus 120 can transmit the K-sparse transmission even if the reception apparatus 120 does not accurately catch the sync signal transmitted from the transmission apparatus 110 It is not a big problem in restoring the signal.

In addition, the transmission apparatus 110 can improve the restoration performance of the downsampled signal in the reception apparatus 120 by adjusting the length of the PN code.

In addition, the transmitter 110 can eliminate the flicker that may occur in the VLC by adjusting the length of the PN code.

The transmission apparatus 110 combines the PPM modulation signal and the PN code to generate a transmission signal X from Equation (1) to Equation (3).

The PPM modulation signal and the PN code have incoherent properties.

를 랜덤 기초 벡터 셋트(random basis vector set)로 프로젝션하기 위해

를 (Ns+(M-1))XM 크기의 랜덤 프로젝션 행렬(random projection matrix)

와 곱할 수 있다. 이때, 랜덤 프로젝션 행렬

와 관련하여, 랜덤 시퀀스로서 통계적으로 모델링된 PN 코드가 고려될 수 있다.More specifically, the transmitting apparatus 110 transmits a sparse signal vector

To project on a random basis vector set < RTI ID = 0.0 >

(Ns + (M-1)) XM-sized random projection matrix.

≪ / RTI > At this time, the random projection matrix

, A statistically modeled PN code as a random sequence can be considered.

는 첫 번째 열을 (

)로 가지는 순환(circulant) 행렬로 결정될 수 있다.The random projection matrix

Is the first column (

) Can be determined as a circulant matrix.

Here, C denotes a PN code vector having a length of Ns, and 0 denotes a zero vector having a length of (M-1) X1.

를

와 곱함으로써 전송 신호 X를 생성하게 된다.That is, the transmitting apparatus 110 transmits

To

To generate a transmission signal X.

The transmission signal x generated through the transmission device 110 is input to the LED driving module 113.

The LED driving module 113 generates a driving signal for controlling on and off states of at least one LED according to the modulated signal and outputs the driving signal to the LED module 113.

In particular, the LED driving module 113 controls an LED corresponding to a region of interest (ROI) (or located in an ROI) so that the LED module 113 can output an optical signal corresponding thereto .

For example, the LED driving module 113 can control the light intensity, the optical frequency (or flickering frequency) of at least one LED located in the ROI, and thereby output the optical signal from the LED module 114 have.

The LED module 114 is turned on in response to a driving signal of the LED driving module 113 to generate a visible light modulation signal using light emitted from at least one LED and transmits the visible light modulation signal to the outside.

The LED module 114 may include at least one LED.

Here, the LED driving module 113 and the LED module 114 may be implemented as one light emitting module.

The receiving device 120 receives the down-sampled signal through the camera module 121, and restores the input signal through ROI detection (Region-Of-Interest Detection).

Hereinafter, the components of the receiving apparatus 120 will be described in more detail.

The receiving apparatus 120 includes a camera module 121, an ROI detecting module 122, and a signal detection module 123.

The components of the receiving device 120 shown in FIG. 1 are examples, and the receiving device 120 may be implemented with fewer or more components.

The camera module 121 receives a visible light signal transmitted from the transmission device 110.

The camera module 121 may be a CCD camera module.

The received visible light signal is sampled at the frame rate (or capture rate) of the camera module 121.

Since the frame rate of the camera module 121 is smaller than the optical rate of the LED, the visible light signal received through the camera module 121 corresponds to a downsampled signal.

에 의해 모델링될 수 있다.The signal received through the camera module 121 is a measurement matrix having a size of DX (Ns + M-1)

Lt; / RTI >

는 (Ns+M-1) X (Ns+M-1) 크기의 단위 행렬로부터 D개의 행을 선택적으로 포함하는 행렬을 나타낸다.Here,

Represents a matrix including D rows from (Ns + M-1) X (Ns + M-1) -type unitary matrices.

는 랜덤 프로젝션 프로시져(random projection procedure), 채널 이득(channel gain) 및 프레임-레이트(frame-rate) ADC를 포함하는 행렬이 될 수 있다.in this case,

May be a matrix that includes a random projection procedure, a channel gain, and a frame-rate ADC.

The ROI detection module 122 detects a region in which a visible light signal for communication is transmitted, that is, a region of interest (ROI), among frame regions received through the camera module 121.

The ROI detection module 122 may detect the ROI using a simple image processing scheme.

That is, the ROI detection module 122 detects a delayed time based on the frame start time and a specific optical signal for performing communication.

The signal detection module 123 restores or detects an input signal through a demodulation scheme corresponding to the modulation scheme (PPM).

2 is a diagram illustrating a transmission signal structure using a 4-ary PPM scheme according to an embodiment of the present invention.

이 tc와 같다고 가정하기로 한다. 이 경우, 심볼 듀레이션(symbol duration) ts는 이하의 수학식 4와 같이 정의될 수 있다. As shown in FIG. 2, the chip duration of the PN code is defined as tc (= 1 / optical rate), and the PPM pulse interval

Is equal to tc. In this case, the symbol duration ts can be defined as Equation (4) below.

&Quot; (4) "

ts = tc X (Ns + 3)

Here, Ns represents the length of the PN code. Hereinafter, for convenience of explanation, the case where Ns is 5 will be described as an example.

For an M-ary structure, a block containing a bit (s) represents an M = 2 ^ a position interval (interval position or position interval) in a time frame of length Ns + (M-1).

Thus, a-bits data can be identified in the frame through the location of the PN code. For example, as shown in FIG. 2, a block including two bits may be located at four different positions within a time frame of length 5 + 4-1 = 8.

That is, the block including the 2 bits can be represented by a total of 2 2 = 4 position intervals. As we have seen, the position of the PN code within the time frame represents the data.

), PN 코드의 길이(Ns), 및 PPM ary(M)에 의해 결정될 수 있으며, 이를 수식으로 표현하면 수학식 5와 같다.From the symbol structure of the present invention, the bit rate can be expressed as an optical rate,

), The length of the PN code (Ns), and the PPM ary (M), which can be expressed by Equation (5).

&Quot; (5) "

To satisfy the RIP condition of the compression sensing theory, the PN code entry may be generated based on Gaussian distributions or Bernoulli distributions. Here, the RIP condition indicates the degree of robustness to noise in the compression sensing theory.

을 갖는 i.i.d.(Independent and Identically Distributed) 가우시안 엔트리를 포함할 수 있다. 다른 실시예로서, PN 코드는 유니폼 베르누이 분포(Uniform Bernoulli distribution)로부터 i.i.d.로서 0 과 1의 랜덤 변수들을 포함할 수 있다. More specifically, in one embodiment, the PN code has an average value of 0.5, a variance value

Lt; RTI ID = 0.0 > (iid) < / RTI > As another example, the PN code may contain random variables of 0 and 1 as iid from the Uniform Bernoulli distribution.

Under such conditions of PN code generation, the present invention can provide a dimming light level close to 50%. This is because, in general, when the time frame length is Ns + (M-1) and the condition of tc = ts is satisfied, the light level is greatly influenced by the statistical characteristic of the PN code. To ensure a wider range of dimming levels, analog dimming control may be applied to the present invention.

에 의해 모델링될 수 있다. 여기서 측정 행렬

는 (Ns+M-1) X (Ns+M-1) 크기의 단위 행렬로부터 D개의 행을 선택적으로 포함하는 행렬을 나타낸다. 이 경우,

는 랜덤 프로젝션 프로시져, 채널 이득 및 프레임-레이트 ADC를 포함하는 행렬이 될 수 있다. The optical signal received via the channel may be sampled at the frame rate (or capture rate) of the camera. At this time, the frame rate (or capture rate) may be less than the optical rate of the transmitter LED. At this time, the received optical signal is a measurement matrix having a size of DX (Ns + M-1)

Lt; / RTI > Here,

Represents a matrix including D rows from (Ns + M-1) X (Ns + M-1) -type unitary matrices. in this case,

May be a matrix that includes a random projection procedure, a channel gain, and a frame-rate ADC.

Before detecting the optical signal transmitted from the transmitting apparatus, the receiving apparatus can perform the ROI detection algorithm. The ROI detection algorithm is an algorithm for detecting a ROI in which a specific optical signal for performing communication among the LEDs of the transmitting apparatus that outputs various optical signals is outputted.

The VLC data contained in the LED optical signal output from the ROI may have a variety of distributions within successive frames captured by the receiving device camera. Using this characteristic, the receiving apparatus can detect the ROI by applying a simple image processing scheme (e.g., weighted differential image). As a result, the receiving apparatus detects the delayed time based on the frame start time and the specific optical signal received from the transmitting apparatus, and obtains data corresponding to the optical signal received from the transmitting apparatus.

In addition, the present invention can borrow a frame header composed of a square wave having a high frequency (for example, a frequency of 10 kHz or more) for corse synchronization. In this case, the residual synchronization offset may remain between the down sampling interval (1 / frame rate). The present invention uses a PN code to digitize a downsampling signal composed of a randomness of a transmission signal and random numbers. Therefore, even if the transmission signal is downsampled, the randomness can be maintained at the same level. That is, since the transmission signal itself has a random characteristic, there is not much problem in restoring the original signal even if the transmission signal is not accurately synchronized.

과 랜덤 측정 행렬

이 incoherent property를 갖는 경우, 압축된 신호 y로부터 원본 신호가 성공적으로 복원될 수 있다고 본다. 변조된 PPM 신호는 스파스한 특성을 가지며, PN 코드

는 incoherent property를 가지므로, 컨벡스 최적화(covex optimization)을 해결함으로써 원본 신호가 복원될 수 있다. 이를 수식으로 표현한 식은 이하의 수학식 6과 같다.According to compression sensing theory,

And a random measurement matrix

If we have this incoherent property, we see that the original signal can be successfully recovered from the compressed signal y. The modulated PPM signal has sparse characteristics, and the PN code

Has an incoherent property, so that the original signal can be reconstructed by solving the covex optimization. The equation expressed by the equation is shown in Equation (6) below.

&Quot; (6) "

는 복원된 K-sparse 계수를 의미한다. 수신 장치는 컨벡스 최적화가 가장 잘되는

값을 선택하여 적용할 수 있다. here,

Is the reconstructed K-sparse coefficient. The receiving device may be a

Value can be selected and applied.

의 최대 크기(또는 진폭)의 위치를 검출함으로써 PPM 신호는 성공적으로 복원(또는 복조)될 수 있게 된다.This convex optimization problem can be solved by applying a linear programming technique if the transmitted signal is in real form.

The PPM signal can be successfully restored (or demodulated) by detecting the position of the maximum size (or amplitude) of the PPM signal.

Unlike conventional sampling theory, which is based on a band-limited signal that needs to be sampled at a Nyquist rate, the present invention provides a technique for down-sampling a signal at a rate lower than the Nyquist rate can do.

In this case, the sampled signal may be a signal having a sparse characteristic. This means that at least one LED of the transmitting apparatus can modulate the optical signal with a higher modulation period so that the optical signal can be transmitted without the occurrence of a visually recognizable flicker phenomenon. The receiving apparatus requires only a camera having a low frame rate ADC function in order to detect an optical signal outputted from the transmitting apparatus, so that no additional manufacturing cost is required, which is advantageous in terms of manufacturing cost and product applicability.

Simulation result

In order to prove the above, a simulation was performed on the detection performance of the optical camcom based on the compression sensing theory. In connection with this simulation, the down-sampling ratio (DSR) refers to the sampling interval relative to the optical rate (or flicker rate) of the camera of the receiving device.

For example, if the DSR is 5, the sampling rate for signal demodulation is 1/5 of the optical rate of the LED. This means that when the optical rate of the optical signal output from the LED of the transmitting apparatus is 150/300 Hz, the sampling rate of the receiving apparatus camera becomes 30/60 Hz.

은 0.25로 설정하였다. 채널 DC 이득은 광 신호의 파워 감쇄를 고려하여 0.6으로 설정하였다. In the case of the PN code based on the Gaussian distribution in this simulation,

Was set to 0.25. The channel DC gain was set to 0.6 in consideration of the power attenuation of the optical signal.

In the data detection process, the presence of timing offset due to course synchronization has been considered. In order to evaluate the signal restoration performance of the present invention, the likelihood of successful detection of the PPM signal was obtained using Monte Carlo simulation.

3A and 3B are graphs of detection probability results of signals according to various DSRs. More specifically, FIG. 3A is a graph of detection probability of a signal according to various DSRs of an 8-PPM signal, and FIG. 3B is a graph of a result of demodulating a 16PPM signal with various DSRs.

According to the simulation results shown in Figs. 3A and 3B, it can be seen that the detection probability (or demodulation performance, demodulation probability) of a PN code having a Gaussian distribution is higher than that of a PN code having a Bernoulli distribution. Also, it can be seen that in all the DSR values, the length Ns of the PN code is proportional to the length of the measurement vector. The length of the measurement vector is an important factor in data demodulation. Therefore, the length Ns of the PN code may increase for a high signal detection probability.

Referring to the simulation result graph of FIG. 3A, it can be seen that the detection probability of PN codes having Gaussian distribution or Bernoulli's distribution is maintained at over 93% even when DSR is 6 when Ns is 27 or more. In this simulation, if the length Ns of the PN code is in the range of 20 to 36, the range of the frame length can be 27 to 43 by the expression of Ns + M-1 (M = 8).

Referring to the simulation result graph of FIG. 3B, it can be seen that the length Ns of the PN code must be 30 or more so that the detection probability of about 90% or more is maintained at 6 in DSR. 3A, the detection probability is maintained at 90% or more when Ns is 24 or more. This means that high order modulation is advantageous for data rates with fixed target detection probability, frame rate and flickering frequency. In this simulation, if the length Ns of the PN code is in the range of 20 to 36, the range of the frame length can be 35 to 51 by the expression of Ns + M-1 (M = 16).

3A and 3B, it can be seen that the present invention provides a degree of freedom in signal modulation rate selection in consideration of the target detection probability. It can also be seen that if the transmission signal is sparse, the original signal can be reconstructed with a sampling rate lower than the Nyquist rate.

FIG. 4 is a three-dimensional image showing the detection probability according to the length of the PN code and the DSR in consideration of the 8-PPM signal and the 0.6-channel gain based on the PN code having the Gaussian distribution.

Referring to FIG. 4, when the length of the PN code is more than 30 and the DSR is 6 or less, the detection probability is saturated. This means that if an 8-PPM signal based on a PN code having a length of 30 is transmitted at an optical rate of 180/360 Hz, it can also be detected by a general camera having a frame rate of 30/60 Hz. If the length of the PN code is more than three times the PPM interval position, the signal is restored with a detection probability of about 95% even at a very low DSR.

conclusion

In the foregoing, a method of optical camera communication (optical camcom) based on the compression sensing proposed in the present invention has been described.

That is, the CS-based optical camera communication method proposed by the present invention is a method for restoring a transmission signal at a low sampling rate using a PPM scheme and a PN code.

In order to solve the problem that the signal restoration performance of a receiver is degraded due to a low frame rate of a commercial camera as compared with a flickering light source of a fast flickering, the present invention provides a K-sparse signal represented by a PPM-based PN code Respectively.

In addition, the present invention can perform a simple implementation of a receiving apparatus by performing a random projection using a PN code in a transmitting apparatus, and can detect a transmission signal even at a low sampling rate in a receiving apparatus.

In addition, the simulation results of FIGS. 3 and 4 show that the signal restoration can be successfully performed even at a sampling rate much lower than the Nyquist rate.

Further, the present invention has the advantage of increasing the freedom of selecting the LED flicker frequency in the transmitting apparatus, and simultaneously improving display and communication performance.

Although the drawings have been described for the sake of convenience of explanation, it is also possible to design a new embodiment by incorporating the embodiments described in each drawing. In addition, the present invention is not limited to the configuration and method of the embodiments described above, but the embodiments described above may be modified such that all or some of the embodiments are selectively combined .

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It should be understood that various modifications may be made by those skilled in the art without departing from the spirit and scope of the present invention.

100: Optical camera communication system
110: Transmitting device
120: Receiver

Claims (7)

In an optical camera communication system,
A transmitter for transmitting a visible light signal having an optical rate at a first rate; And
And a receiving device for receiving the visible light signal at a second rate lower than the first rate,
The transmitting apparatus includes:
A signal modulation module for modulating the source data using an M-ary Pulse Position Modulation (PPM) scheme;
A PN code generation module for generating a PN code (Pseudo Noise code) for random projection of a signal modulated through the signal modulation module;
An LED driving module for generating a driving signal for controlling an on or off state of at least one light emitting diode according to the randomly projected signal; And
And an LED module for transmitting a visible light signal through the at least one LED according to the driving signal,
The receiving apparatus includes:
A camera module having the second rate as a frame rate;
A region of interest detection module that detects a transmission region of the visible light signal in a frame received through the camera module; And
And a signal detection module for detecting the source data in a visible light signal transmitted through the detected region of interest. The method according to claim 1,
And the second rate is determined according to the length of the PN code. The method according to claim 1,
Wherein the signal modulation module comprises:
And said source data is switched into a pulse position in any one of a plurality of time intervals within each time frame. The method of claim 3,
Wherein the signal modulation module comprises:
And outputs the input signal as a K-sparse signal having K non-zero values through the M-ary Pulse Position Modulation (PPM) scheme. . A transmitting apparatus for transmitting a signal in an optical camera communication system,
A signal modulation module for modulating the source data using an M-ary Pulse Position Modulation (PPM) scheme;
A PN code generation module for generating a PN code (Pseudo Noise code) for random projection of a signal modulated through the signal modulation module;
An LED driving module for generating a driving signal for controlling an on or off state of at least one LED according to the randomly projected signal; And
And an LED module for transmitting a visible light signal through the at least one LED according to the driving signal. 6. The method of claim 5,
Wherein the signal modulation module comprises:
And said source data is switched into a pulse position in any one of a plurality of time intervals within each time frame. 6. The method of claim 5,
Wherein the signal modulation module comprises:
And outputs the input signal as a K-sparse signal having K non-zero values through the M-ary pulse position modulation (PPM) scheme.

Images