KR102045867B1 - Method for transmitting and receiving signals in a visible light communication system and apparatus therefor - Google Patents

Abstract

The present specification provides a method for transmitting a signal using a SIM technique in a visible light communication system.
A method performed by the transmitter proposed in the present specification, the input data stream by using a spatial intensity modulation (Spatial Intensity Modulation (SIM)) method for turning on at least one LED of the LED array (array) for each specific time unit (On) Or generating a blinking sequence to turn off; And transmitting the signal to a receiver through the generated blink sequence.
Through this, the present specification can solve the problem of stable dimming control and non-uniform illumination.

Description

METHOD FOR TRANSMITTING AND RECEIVING SIGNALS IN A VISIBLE LIGHT COMMUNICATION SYSTEM AND APPARATUS THEREFOR}

The present invention relates to a method for transmitting and receiving a signal through a spatial modulation scheme in a visible light communication system and an apparatus supporting the same.

In recent years, as a complementary candidate for radio frequency (RF), visible light communication (VLC) technology has generated considerable interest in the field of future wireless communication systems.

By reusing the coexisting LED infrastructure built for lighting, VLC brings together LED lighting and communication capabilities.

Since lighting is a key feature of LED lighting devices, reliable dimming control is an important issue for VLC implementation. By varying the dimming level, the power saving and energy efficiency of the LED lighting system can be increased.

In addition, emotional lighting, which changes the dimming level according to factors related to the surrounding environment such as atmosphere, music, food, and temperature, has become an important lighting method in many applications.

Spatial modulation (SM), spatial multiplexing (SMP), spatial shift keying (SSK), generalization to improve communication throughput by distributing signal power over multiple channels, multiple input multiple outputs (MIMO) SM (GSM), and Generalized SSK (GSSK) can be applied to the VLC system.

In SM, data is spatially encoded according to a lighting device (or lighting device) luminaire index and a pulse amplitude modulation (PAM) intensity level.

In SMP, independent data streams are encoded in PAM and emitted simultaneously at all transmitters.

SSK activates only one LED of the total LEDs for a given channel.

The GSSK modulation method differs from classical SSK in that one or more LEDs can be activated to determine the spatial location corresponding to the unique data symbol.

SM and SMP are special cases of GSM that require higher transmission efficiency than the GSSK method, which was developed primarily for communication functions, not for reliable dimming quality.

Conventional PAMs used in SM, SMP and GSM schemes also suffer from unstable control of LED intensity.

Accurate amplitude control and stable lighting through LED drive circuits are affected by frequency, temperature, etc., so the actual implementation of PAM for both data communication and lighting functions is very difficult.

In addition, PAM is susceptible to noise because noise affects amplitude.

Here, amplitude is where information is stored in the PAM signal. Therefore, information about accurate intensity attenuation along multiple channels is required for data decoding.

For the SSK and GSSK methods, activating a single or just a few LEDs does not provide dimming control, resulting in uneven illumination of the target area.

Since the main function of LED lighting devices is high quality lighting, VLC systems with multiple LEDs must provide a uniform distribution of light.

An object of the present specification is to provide a method of solving a non-uniform lighting problem by using a spatial intensity modulation (SIM) technique and performing a stable dimming control.

It is also an object of the present specification to provide a practical design of a dimmable SIM technique by applying a multi-level inverse source coding method.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

In the present specification, a method for transmitting a signal in a visible light communication system, wherein the method performed by a transmitter includes an array of LEDs for a specific time unit using an input data stream using a spatial intensity modulation (SIM) scheme. Generating a blinking sequence to turn on or off at least one of the LEDs; And transmitting the signal to the receiver through the generated blinking sequence, wherein the spatial intensity modulation scheme includes a set dimming ratio, total number information of the LEDs constituting the LED array, and an intensity level ( generating a codeword for each intensity level based on a turn-on probability per intensity level, and using the generated codeword for each intensity level to turn on the specific time unit. It is characterized by determining at least one of the number or the position of the LED is turned on.

In addition, the number of the intensity level in the present specification is characterized in that it is determined based on the total number information of the LED.

Further, in the present specification, the turn-on probability for each intensity level is set to maximize entropy according to the set dimming ratio.

Further, in the present specification, the length of the codeword for each strength level is longer as the turn-on probability for each strength level is lower.

In addition, in the present specification, the generated codeword for each strength level is composed of at least one combination of '0' or '1', and the number of '0' or '1' included in the generated codeword for each strength level. Is determined using the binary tree technique of multi-level Huffman encoding.

In the present specification, when the set dimming ratio is 0.72 and the total number of LEDs constituting the LED array is 4, the generated codewords for each intensity level are 111, 110, 10, and 0, respectively. .

In addition, the present specification is a transmitter for transmitting a signal in a visible light communication system, RF module for transmitting and receiving a signal with the outside; And a processor operatively connected to the RF module, wherein the processor comprises: inputting the at least one LED of the array of LEDs on a specific unit of time using a spatial intensity modulation (SIM) scheme; Generate a blinking sequence to turn On or Off; And transmitting the signal to a receiver through the generated blink sequence.

The present specification has the effect of solving problems that may occur in the conventional PAM-based VLC, such as unstable dimming control, non-uniform illumination function and the burden of channel prediction according to the strength and target dimming level of the SIM symbol determined only in the spatial domain. .

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description. .

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as part of the detailed description in order to provide a thorough understanding of the present invention, provide embodiments of the present invention and together with the description, describe the technical features of the present invention.
1 shows a system of visible light communication (VLC) to which the present invention can be applied.
2 shows an example of a blink sequence of the LED array based on the SIM scheme proposed in the present specification.
3 shows the optimal turn-on probability of maximizing entropy according to the dimming ratio when the total number of LEDs is set to 4 and 8. FIG.
4 shows an example of a binary tree of multi-level Huffman encoding to which the method proposed in this specification can be applied.
FIG. 5 shows turn-on probability using MISC according to dimming ratio when the total number of LEDs is set to 4 and 8. FIG.
6 illustrates the dimming level of the SIM technique that can be achieved based on an optimal turn-on probability and a practical MISC based approach.
7 shows a comparison of entropy of the SIM method based on the optimal and actual turn-on probabilities with respect to the dimming ratio.
8 shows dimming capacity with various Nt numbers when the target dimming level is 48% and 72%.
9 shows the dimming capacity of the SIM method depending on both SNR and dimming ratio.
10 is a flowchart illustrating an example of a method of transmitting and receiving a signal using the SIM technique proposed in the present specification.
11 is an internal block diagram of a transmitter and a receiver operating in visible light communication to which the present invention can be applied.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates that the present invention may be practiced without these specific details.

In some instances, well-known structures and devices may be omitted or shown in block diagram form centering on the core functions of the structures and devices in order to avoid obscuring the concepts of the present invention.

In addition, although the embodiments of the present invention are described in detail with reference to the accompanying drawings and the contents described with reference to the accompanying drawings, the present invention is not limited or limited by the embodiments.

Visible Light Communication (VLC) System

1 shows a visible light communication system to which the present invention can be applied. 1 is merely for convenience of description and does not limit the scope of the invention.

Referring to FIG. 1, the visible light communication system 100 to which the present invention may be applied includes at least one transmitting device 110 and a receiving device 120.

Here, the transmitting device 110 and the receiving device 120 may be implemented with the component (s) shown in FIG.

The transmitting device 110 generates a modulated signal by applying various modulation schemes to the transmission data, and transmits the modulated signal using a light source through a wavelength band suitable for the characteristics of the modulated signal. .

The transmitting device 110 includes a light source. Herein, the light source may be turned on or off according to a preset speed (eg, a pulse rate). In this case, the preset speed may be controlled by a user or a system. The transmission device 110 may transmit data to the reception device 120 by using the on or off. For example, in the case of binary data, '1' may be represented by using on and '0' may be represented by using off. Here, the light source may be configured as a light emitting diode (LED).

In addition, the reception device 120 receives data transmitted through a light source, and demodulates data by applying a demodulation scheme corresponding to various modulation schemes to the received data, thereby obtaining transmission data. The receiving device 120 may include a camera device.

Here, the receiving device 120 may generate an image of a light source included in the transmitting device 110 by using the camera device and extract data from the image.

Here, the receiving device 120 may generate an image of the light source as a continuous frame according to a preset speed (eg, a frame rate). In this case, the preset speed for the receiving device 120 may be the same as or different from the preset speed for the transmitting device 110.

The receiving device 120 may be a device equipped with a camera such as a digital camera, a closed circuit television (CCTV), a network camera (for example, an IP protocol camera), a smartphone, or the like.

Hereinafter, a method of transmitting and receiving a signal using Spatial Intensity Modulation (SIM) proposed in the present specification will be described.

The method proposed in this specification, namely the new method for the existing PAM-based VLC and related MIMO VLC system, (1) solves the amplitude-based modulation and non-uniform illumination problem, and (2) provides stable dimming control.

A plurality of LED arrays may be used for visible light communication (VLC) to increase communication efficiency while maintaining smart illumination function through dimming control.

In this specification, a 'Spatial Intensity Modulation (SIM)' technique that can be applied to such a VLC is newly defined.

The effective number of LEDs turned on in the SIM technique is used for data modulation and dimming control in the VLC system.

Unlike conventional pulse amplitude modulation (PAM), the symbol intensity level is not determined by the amplitude level of the VLC signal from each LED, but by counting the number of turned on LEDs illuminating at a single amplitude level.

Since the strength and target dimming level of the SIM symbol are determined only in the spatial domain, it can solve the problems of conventional PAM-based VLC and related MIMO VLC techniques such as unstable dimming control, non-uniform illumination function and burden of channel prediction.

By varying the number and shape (or placement) of LEDs turned on around the target dimming level in time, the SIM method can ensure uniform illumination across the target area.

Dimming capacity analysis, which is the communication rate achievable at the target dimming level of the VLC, can be provided by deriving a turn-on probability that maximizes the entropy of the SIM-based VLC system.

In addition, the present specification provides a practical design of the dimmable SIM technique by applying a multi-level inverse source coding (MISC) method.

To verify the performance of the dimmable SIM scheme proposed in this specification and its application in real systems, the simulation results provide reference data under a wide range of parameters.

That is, the present specification provides a new VLC modulation scheme called 'Spatial Intensity Modulation (SIM)', a new concept for providing a dimmable VLC solution to overcome the disadvantages of the conventional VLC technique. Here, desired data modulation and stable dimming control are supported by activating the effective number of LEDs that are turned on.

Unlike the conventional MIMO VLC scheme, the symbol intensity level is not determined by the amplitude level of the VLC signal of each LED, but by counting the total number of LEDs found. Here, each LED emits light at the same amplitude level.

Because the data encoding of the SIM technique is only supported in the spatial domain, it can support dimming control and data decoding without careful setting of signal amplitude control and fiber channel prediction.

In addition, the method proposed herein changes the number and shape (or arrangement) of spatially distributed 'ON' and 'OFF' LEDs around a target dimming level in time to satisfy a uniform distribution of light in the target area. Let's do it.

In order to investigate the attainable communication speed in consideration of the dimming level, the dimming capacity of the SIM scheme proposed in this specification may be represented by deriving a turn-on probability of maximizing entropy.

In addition, the present specification proposes multi-level inverse source coding (MISC) applied to dimmable SIM technique for practical implementation.

Simulation parameters in parameter ranges such as LED count, target dimming and signal-to-noise ratio (SNR) provide reference data confirming the performance and actual implementation of the SIM scheme proposed herein for dimmable VLC.

Next, the theoretical design of the SIM technique, the actual implementation of the SIM system using MISC, and the evaluation of the theoretical and actual dimming capacity analysis will be discussed in detail.

First, the theoretical design of the SIM technique is discussed.

This disclosure contemplates a MIMO VLC system comprising multiple LEDs spatially distributed.

To generate the SIM symbol, the data stream is converted into a blinking sequence depicted in the spatial domain.

Each SIM symbol is provided by an effective number of fully lit LEDs.

Here, the arrangement of the turned-on LED may vary with time. For the dimming function of the LED lighting device, the time average of the intensity level of the SIM symbol is set to the target dimming level.

2 shows an example of a blink sequence of the LED array based on the SIM scheme proposed in the present specification.

Here, Nt is the total number of available LEDs (or the total number of LEDs constituting the LED array), and n is the effective number of LEDs turned on. n is time-varying and is determined by the corresponding turn-on probability.

To support uniform illumination distribution, the turned-on LEDs should be equally distributed to all LEDs as shown in FIG. 4. The total Nt possible intensity levels of the LED array are given by Equation 1 below.

Where I _max represents the maximum intensity of the LED array and Nt represents the effective number of LEDs that are turned on.

For example, when Nt = 4, the possible intensity levels are I _max / 4, I _max / 2, 3 * I _max / 4, I _max .

In order to distinguish between operating time and non-operating time of a SIM based VLC system, a completely dark situation (all LEDs are off), i.e. n = 0 (or In = 0), is not taken into account.

Unlike the PAM based modulation employed in the conventional MIMO VLC, the SIM symbol intensities are determined only in the spatial domain by counting the effective number of LEDs that are 'ON'.

In order to meet the target dimming level during data transmission, the probabilities of selecting an effective number of LEDs to be turned on, i.e., turn-on probability, must be determined.

We can denote p (n) as the turn-on probability for lighting with n turned-on LEDs.

로 표현될 수 있다.The entropy of discrete probabilities {p (1), ..., p (N _t )} for n values is E {p (1), ..., p (N _t )} =

It can be expressed as.

Normalization constraints are related to the sum of turn-on probabilities. In addition, the dimming limit can be addressed by varying the number of turn-on LEDs according to the corresponding probability in time.

Here, the entropy-maximization probability distribution of the turn-on LED according to the dimming level requirement is derived. The distribution is obtained by maximizing the entropy of a given SIM technique as shown in Equation 2 below.

는 목표 디밍 비율(0≤

≤1) 이며, 목표 디밍 레벨은

*100[%]가 된다. 제한된 최적화 문제를 해결하기 위해, 라그랑즈(Lagrange) multiplier 방법이 사용된다.here,

Is the target dimming ratio (0≤

≤1) and the target dimming level is

* 100 [%]. To solve the limited optimization problem, the Lagrange multiplier method is used.

Taking the second derivative gives a diagonal Hessian with a value of -1 / p (n).

Therefore, the objective function 2 is concave.

This means that the probability obtained from Equation 2 provides a global solution.

The increased objective function L (x), turn-on probability and Lagrange multiplier function are defined as in Equation 3 below.

Where β and γ are scalar Lagrange multipliers.

Taking the function output of equation (3) for the variables can be obtained by the following equations.

Where p * (n) is the optimal turn-on probability and (β ^* , γ ^* ) are the optimal values for the Lagrange multiplier. By rearranging Equation 4 with respect to p * (n), it can be expressed as Equation 7.

Equation 7 may be simplified as in Equation 8 below.

here,

Substituting Equation 8 into Equation 5 can be expressed simply as in Equation 10 below.

Then, Equation 6 may be expressed as Equation 11 below.

The optimal Lagrangian coefficients (β ^* , γ ^* ) are determined from equations (9) and (11). By using these coefficients, an optimal set of turn-on probabilities {p ^* (1), ..., p ^* (N _t )} that maximizes entropy with a given dimming limit can be obtained.

3 shows the optimal turn-on probability of maximizing entropy according to the dimming ratio when the total number of LEDs is set to 4 and 8. FIG.

=0.72일 때, 엔트로피를 최대로 하는 턴-온 확률은 p(1)=0.098, p(2)=0.165, p(3)=0.276, p(4)=0.461로 설정된다.To meet the target dimming ratio, the turn-on probability of maximizing the entropy for each SIM signal level is different. For example, N _t = 4,

When = 0.72, the turn-on probability of maximizing entropy is set to p (1) = 0.098, p (2) = 0.165, p (3) = 0.276, p (4) = 0.461.

This means that each SIM symbol must occur at a specified probability according to the target dimming ratio.

3, it can be seen that the curve is symmetrical with respect to the dimming ratio corresponding to the intermediate intensity.

=0.625, N_t = 8에 대해

= 0.563)(For N _t = 4

= 0.625, for N _t = 8

= 0.563)

Next, a practical SIM design using multi-level inverse source coding is described.

As we saw earlier, the turn-on probability provides different values depending on the target dimming ratio.

In general, however, digital information bits represent an equal probability (50%). That is, '0' and '1' have approximately equal probabilities (50% each).

If dimming control is not considered, the probability of all SIM symbols that can occur in a single attempt is the same, which is calculated at an average intensity level of approximately 0.5I _max .

Therefore, a method of providing dimming control function during the transmission of SIM symbols is required for the implementation of the actual SIM design.

This enables the transmission of SIM symbols with maximum entropy and consequently satisfies the turn-on probability according to the target dimming level.

The method proposed herein uses a method of reverse source coding called so called 'multi-level inverse source coding (MISC)' to satisfy the target dimming level of the SIM scheme from binary input data (0 (s) and 1 (s)). Extend the concept.

This preserves the way up to maximum entropy while meeting the dimming target.

In addition, this method changes the symbol probability of '0' and '1', which are 50% each, to appropriate values, and helps performance approach maximum entropy.

To design the codewords of the MISC, the Huffman code used for source coding can be used.

An example of a multi-level Huffman table using four different symbols is shown in Table 1, and the corresponding tree representation is shown in FIG.

SIM symbols may be represented as binary data based on multi-level Huffman encoding.

Similar to the general Huffman tree structure, the value of each node in FIG. 4 is the sum of the children values of each node.

In this example, the average intensity level of the SIM symbol is 0.72 * Imax (Imax * 0.461 + 3Imax / 4 * 0.276 + Imax / 2 * 0.165 + Imax / 4 * 0.098).

In FIG. 4, the values located at the bottom of the Huffman tree structure are turn-on probability values, the largest turn-on probability value is located at the first position, and a smaller turn-on probability value is located toward the right.

Table 2 shows an example of MISC when Nt = 4.

Since '0' and '1' each have the same probability of 0.5, the turn-on probability in each codeword is represented by (0.5) ^x . Where x represents the length of the codeword.

In Table 2, the length of each codeword is inversely proportional to the probability of the corresponding intensity level.

In other words, the lower the intensity level, the longer the codeword used.

In this example, the average dimming ratio may be calculated as 0.77 * I _max (I _max * 0.5 + 3I _max /4*0.25+I _max /2*0.125+I _max /4*0.125).

By using Table 2 above, the evenly organized binary data is transformed into data with '1' having 77%, and then the target dimming ratio can be achieved.

FIG. 5 shows turn-on probability using MISC according to dimming ratio when the total number of LEDs is set to 4 and 8. FIG.

The probability value is scaled in order of 0.5 depending on the length of the codeword, the turn-on probability of a particular range of dimming ratios that give the same value.

As Nt increases, the shape of the curve of FIG. 5 becomes closer to the curve of FIG.

This means that the entropy of the MISC-based approach can be maximized by increasing the total number of available LEDs.

To decode the original information at the receiving side, a mapping table is used that includes two attributes of code words and strength (or strength) in Table 2.

After the symbol strength is received, a candidate codeword may be selected from the mapping table.

Unlike the conventional PAM scheme, the symbol intensity level is not determined by the amplitude level of the VLC signal, but by calculating the effective number of turn-on LEDs in the SIM scheme.

Therefore, the SIM scheme proposed herein avoids the need for channel prediction, which is essential for the PAM-based VLC technique.

6 illustrates the dimming level of the SIM technique that can be achieved based on an optimal turn-on probability and a practical MISC based approach.

Referring to FIG. 6, it can be seen that there is a slight performance gap between the curves based on the optimal measurement probability and the practical turn-on probability. However, as Nt increases, the performance difference becomes insignificant.

Since small differences in dimming levels cannot be detected by the human eye, the use of MISC in the SIM method is practical for practical systems.

7 shows a comparison of entropy of the SIM method based on the optimal and actual turn-on probabilities with respect to the dimming ratio.

It can be seen that the curve based on the optimal and practical turn-on probability is close to the range of dimming ratios.

This means that a SIM technique using MISC always guarantees robust entropy performance.

The entropy of the SIM technique increases as the total number of spatially dispersed LEDs increases.

When Nt is 4, 8, 16, the maximum number of bits needed to provide illumination amplitude is 2, 3 and 4, respectively.

The dimming ratio that provides the maximum entropy is the dimming ratio that corresponds to the medium intensity of the entire LED and depends on Nt.

Since the turn-on probability of all SIM symbols is the same at the medium intensity level, the maximum value of entropy can be observed.

Next, the dimming capacity analysis will be described.

In the following, the dimming capacity of the SIM technique was investigated in consideration of the VLC channel quality.

Dimming capacity refers to the communication rate achievable based on the modulation scheme and the target dimming constraint.

To represent the dimming capacity, mutual information based on differential entropy can be used. Assuming additional white Gaussian noise (AWGN), the received signal Y may be expressed as in Equation 12 below.

Where X is the transmitted signal and Z to N (0, σ ² ).

Mutual information between X and Y may be expressed by Equation 13 below.

8 shows dimming capacity with various Nt numbers when the target dimming level is 48% and 72%.

The signal to noise ratio (SNR) ranges from -10dB to 20dB to observe changes in performance that depends on channel quality.

Here, SNR is defined as Imax / σ due to the optical communication link. MISC-based practical approaches achieve capacity performance very close to optimal performance results.

As the SNR increases, the achievable communication rate of both the dimmable SIM technique and the MISC approach based on the optimal turn-on probability increases.

At high SNR (> 20db), the dimming capacity of both methods is saturated.

If the dimming level is set to 48% and the SNR is high, then the SIM technique with Nt = 16 and Nt = 4 can provide approximately 4 bits / symbol and 2bits / symbol, respectively.

In addition, in three cases (Nt = 4, 8, 16), the performance gap can become larger as the SNR increases (<15 dB).

Since the median intensity of the SIM symbol is at maximum entropy (see FIG. 9), the dimming capacity of 48% dimming level is greater than the dimming capacity of 72%.

9 shows the dimming capacity of the SIM method depending on both SNR and dimming ratio.

As the SNR increases, the dimming capacity is saturated regardless of the dimming ratio.

However, the maximum dimming capacity increases as the number of available space LEDs Nt increases.

When the number of space LEDs available is large, the SNR value due to saturation of the dimming capacity becomes large.

The following is a brief summary of the findings.

The present disclosure provides a spatial light modulation (SIM) method that encodes data using an effective number of turn-on LEDs and supports target dimming.

Since the data encoding of the SIM technique is provided only in the spatial domain, it is possible to avoid the careful configuration of signal amplitude control, non-uniform illumination performance and optical channel prediction, which are strongly required for conventional PAM based and related MIMO VLC methods.

By solving the optimization problem, a turn-on probability is provided that maximizes the entropy of the SIM technique.

For practical implementation of the SIM technique with dimming requirements, multi-level inverse source coding (MISC) is also provided.

In order to analyze the achievable communication rates, the dimming capacity of the SIM technique was examined under the target dimming constraint.

The numerical results indicate that capacity performance based on optimal turn-on probability and a practical MISC approach was close in the SNR range.

In addition, it can be seen that the maximum capacity of the SIM technique depends heavily on the SNR, the total number of LED lights and the target dimming level.

10 is a flowchart illustrating an example of a method of transmitting and receiving a signal using the SIM technique proposed in the present specification.

First, the transmitter transmits an input data stream using a spatial intensity modulation (SIM) scheme to turn on or off at least one LED of an array of LEDs by a specific time unit. A blinking sequence is generated (S1010).

Thereafter, the transmitter transmits the signal to the receiver through the generated blink sequence (S1020).

The spatial intensity modulation scheme is a code for each intensity level based on a set dimming ratio, total number information of LEDs constituting the LED array, and a turn-on probability for each intensity level. Generating a word (word), and by using the generated code word for each intensity level to determine at least one of the number of the LED is turned on by the specific time unit or the position of the LED is turned on and modulates. .

The number of intensity levels may be determined based on the total number information of the LEDs.

The turn-on probability for each intensity level may be set to maximize entropy according to the set dimming ratio.

Specifically, the turn-on probability for each intensity level may be set by the Salping Equation 7 above.

In Equation 7, p * (n) represents an optimal turn-on probability, β ^* and γ ^* are optimal values for Lagrange multiplier, N _t is the total number of LEDs constituting the LED array, and n is Indicates the effective number of LEDs that are turned on.

In addition, the length of the codeword for each intensity level becomes longer as the turn-on probability for each intensity level is lower.

For example, when the set dimming ratio is 0.72 and the total number of LEDs constituting the LED array is 4, the generated codewords for each intensity level are 111, 110, 10 and 10 as shown in Table 1 and Table 2, respectively. It becomes zero.

Transmitter and receiver

Next, an operation method of a transmitter and a receiver of a visible light communication system to which the method proposed in the present specification can be applied and an internal block diagram for implementing the same will be described.

11 is an internal block diagram of a transmitter and a receiver operating in visible light communication to which the present invention can be applied. 2 is merely for convenience of description and does not limit the scope of the invention.

Referring to FIG. 11, a transmission device (or transmitter, transmitter, 110) to which the present invention may be applied includes an RF module 111, a processor 112, and a memory 113. Components of the transmitting apparatus shown in FIG. 11 are one example, and the transmitting apparatus may be configured with more or fewer components.

First, the RF module 111 transmits and receives a signal to and from the outside.

Next, the processor 112 is functionally connected to the RF module, and implements the functions, processes, and / or methods proposed herein. Layers of the wired / wireless interface protocol may be implemented by a processor.

Specifically, the processor blinks the input data stream by turning on or off at least one LED of the LED array by a specific time unit by using a spatial intensity modulation (SIM) scheme. And control the RF module to transmit a signal to the receiver through the generated blinking sequence.

The memory 113 is connected to the processor and stores various information for driving the processor.

In addition, the reception apparatus (or receiver, receiver, 120) to which the present invention may be applied includes an RF module 121, a processor 122, and a memory 123. Components of the receiving apparatus illustrated in FIG. 2 are one example, and the receiving apparatus may be configured with more or fewer components.

First, the RF module 121 transmits and receives a signal with the outside.

Next, the processor 122 is functionally connected to the RF module, and implements the functions, processes, and / or methods proposed herein. Layers of the wired / wireless interface protocol may be implemented by a processor.

Specifically, the processor controls the RF module to receive a blink sequence sent from a transmitter.

The memory 123 is connected to the processor and stores various information for driving the processor.

The embodiments described above are the components and features of the present invention are combined in a predetermined form. Each component or feature should be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. In addition, it is also possible to combine the components and / or features to form an embodiment of the present invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment, or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation in the claims, or may be incorporated into new claims by post-application correction.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a hardware implementation, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), and FPGAs ( field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code may be stored in memory and driven by the processor. The memory may be located inside or outside the processor, and may exchange data with the processor by various known means.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

Claims (9)

A method for transmitting a signal in a visible light communication system, the method performed by a transmitter,
By using spatial intensity modulation (SIM) method, the input data stream generates a blinking sequence to turn on or off at least one LED of the LED array at a specific time unit. Generating; And
Transmitting the signal to a receiver through the generated blink sequence;
The spatial intensity modulation scheme,
Generate a codeword for each intensity level based on a set dimming ratio, total number of LEDs constituting the LED array, and turn-on probability for each intensity level; ,
The intensity level is calculated based on the ratio of the maximum intensity of the LED array, the effective number of LEDs turned on among the total number of LEDs constituting the LED array,
And determining at least one of the number of turned-on LEDs or the position of the turned-on LEDs by the specific time unit using the generated code word for each intensity level.
delete The method of claim 1,
And the turn-on probability per intensity level is set to maximize entropy according to the set dimming ratio. The method of claim 3,
The turn-on probability for each intensity level is set by the following equation.

Where p ^* (n) represents the optimal turn-on probability, β ^* and γ ^* are the optimal values for the Lagrange multiplier, N _t is the total number of LEDs constituting the LED array, and n is the turn-on Indicates the effective number of LEDs being. The method of claim 1,
The length of the codeword for each intensity level is longer as the turn-on probability for each intensity level is lower. The method of claim 1,
The generated code word for each strength level is composed of at least one combination of '0' and '1',
The number of '0' or '1' included in the generated power level codeword is determined using a binary tree technique of multi-level Huffman encoding. The method of claim 6,
When the set dimming ratio is 0.72 and the total number of LEDs constituting the LED array is 4,
The generated intensity level codewords are 111, 110, 10 and 0, respectively. A transmitter for transmitting a signal in a visible light communication system,
RF module for transmitting and receiving a signal with the outside; And
A processor functionally connected to the RF module, wherein the processor includes:
Blinking sequence for turning on or off at least one LED of the LED array by a specific time unit using the spatial intensity modulation (SIM) method of the input data stream. Generate; And
In order to control the signal to be transmitted to the receiver through the generated blink sequence,
The spatial intensity modulation scheme,
Generate a codeword for each intensity level based on a set dimming ratio, total number of LEDs constituting the LED array, and turn-on probability for each intensity level; ,
The intensity level is calculated based on the ratio of the maximum intensity of the LED array, the effective number of LEDs turned on among the total number of LEDs constituting the LED array,
And determining at least one of the number of LEDs that are turned on for each specific time unit or the location of the LEDs that are turned on by using the generated intensity level codewords.
The method of claim 1,
And the intensity level is set by the following equation.

Here, Imax represents the maximum intensity of the LED array, Nt represents the total number of LEDs constituting the LED array, and n represents the effective number of LEDs turned on.

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