KR20190052838A - Method for transmitting and receiving signals in a visible light communication system and apparatus therefor - Google Patents

Abstract

The present specification is to provide a method for transmitting a signal using a spatial intensity modulation (SIM) scheme in a visible light communication system. The method performed by a transmitter of the present invention comprises the following steps: generating a blinking sequence for turning on or off at least one LED of an LED array for each specific time unit by using a SIM scheme on an input data stream; and transmitting the signal to a receiver through the generated blinking sequence. Accordingly, stable dimming control is performed, and a non-uniform lighting problem can be solved.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transmitting and receiving signals in a visible light communication system,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a method of transmitting and receiving a signal through a spatial modulation scheme in a visible light communication system and an apparatus for supporting the same.

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

By reusing coexisting LED infrastructures built for lighting, VLC provides LED lighting and communication capabilities.

Since lighting is a key feature of LED lighting devices, stable dimming control is a critical issue in VLC implementations. When varying the dimming level, the power saving and energy efficiency of the LED lighting system can be enhanced.

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), and Generalization are used to improve communication throughput by distributing the signal power for multiple channels, multiple input multiple output (MIMO) (GSM), and generalized SSK (GSSK) can be applied to the VLC system.

In SM, data is spatially encoded according to the illumination device (or luminaire index) and pulse amplitude modulation (PAM) intensity levels.

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

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

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

SM and SMP are special cases of GSM requiring higher transmission efficiency than GSSK method, and this method is mainly developed for communication function, not stable dimming quality.

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

Actual implementation of PAM for both data communication and lighting functions is very difficult because precise amplitude control through LED drive circuitry and stable lighting are affected by frequency, temperature, and so on.

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

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

In the case of the SSK and GSSK methods, dimming control is not provided even if a single or a few LEDs are activated, 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 illumination distribution.

It is an object of the present disclosure to provide a method of solving a non-uniform illumination problem using a spatial intensity modulation (SIM) technique and performing stable dimming control of the data stream.

The present disclosure also aims to provide a practical design of a dimmable SIM scheme by applying a multi-level inverse source coding scheme.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, unless further departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

A method for transmitting a signal in a visible light communication system, the method comprising the steps < RTI ID = 0.0 > of: < / RTI & Generating a blinking sequence that turns on or off at least one LED of the plurality of LEDs; And transmitting the signal to a receiver through the generated flicker sequence, wherein the spatial intensity modulation scheme comprises a set dimming ratio, a total number of LEDs constituting the LED array, and an intensity level on the basis of the generated intensity level code word for each intensity level based on the intensity level of each of the plurality of LEDs, And the position of the LED to be turned on or turned on.

In this specification, the number of intensity levels is determined based on the total number of LEDs.

In this specification, the turn-on probability of each intensity level is set to maximize the entropy according to the set dimming ratio.

Also, in this specification, the length of a codeword for each intensity level is longer as the turn-on probability for each intensity level is lower.

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

Also, in this specification, when the set dimming ratio is 0.72 and the total number of LEDs constituting the LED array is 4, the generated code words for each intensity level are 111, 110, 10 and 0, respectively .

In addition, the present invention relates to a transmitter for transmitting a signal in a visible light communication system, the transmitter comprising: an RF module for transmitting / receiving signals to / from outside; And a processor operatively coupled to the RF module, wherein the processor is operable to convert the input data stream to at least one LED of an array of LEDs by a specific time unit using a spatial intensity modulation (SIM) Generating a blinking sequence that turns on or off the flash memory; And to transmit the signal to the receiver through the generated flicker sequence.

The present specification has the effect of solving the problems that may occur in conventional PAM-based VLC such as unstable dimming control, uneven lighting function, and burden of channel prediction depending on the intensity of the SIM symbol determined only in the spatial domain and the target dimming level .

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

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the technical features of the invention.
FIG. 1 shows a system of a Visible Light Communication (VLC) system to which the present invention can be applied.
Figure 2 shows an example of a flicker sequence of an LED array based on the SIM scheme proposed herein.
FIG. 3 shows an optimal turn-on probability of maximizing entropy according to the dimming ratio when the total number of LEDs is set to 4 and 8.
4 shows an example of a binary tree of multi-level Huffman encoding to which the proposed method can be applied
FIG. 5 shows the turn-on probability using MISC according to the dimming ratio when the total number of LEDs is set to 4 and 8.
Figure 6 shows the dimming level of the SIM scheme that can be achieved based on an optimal turn-on probability and a practical MISC based approach.
Figure 7 shows a comparison of the entropy of the SIM method based on the optimal and actual turn-on probabilities with respect to the dimming ratio.
8 shows dimming capacities having various Nt numbers when the target dimming levels are 48% and 72%.
Figure 9 shows the dimming capacity of the SIM method, which depends on both the SNR and the dimming ratio.
10 is a flowchart showing an example of a method of transmitting and receiving a signal using the SIM technique proposed in the present specification.
11 shows an internal block diagram of a transmitting apparatus and a receiving apparatus operating in visible light communication to which the present invention can be applied.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details.

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

In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings and accompanying drawings, but the present invention is not limited to or limited by the embodiments.

Visible Light Communication (VLC) system

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

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

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

The transmission apparatus 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 matching the characteristics of the modulated signal .

The transmitting apparatus 110 includes a light source. Here, the light source may be turned on or off according to a predetermined speed (e.g., a pulse rate). At this time, the predetermined speed may be controlled by a user or a system. The transmitting device 110 can transmit data to the receiving device 120 using the on or off. For example, in the case of binary data, '1' may be represented using on, and '0' may be represented using off. Here, the light source may be a light emitting diode (LED).

The receiving apparatus 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 to obtain transmission data. The receiving device 120 may include a camera device.

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

Here, the receiving apparatus 120 may generate an image for the light source in a continuous frame according to a predetermined speed (e.g., a frame rate). At this time, the speed preset for the receiving apparatus 120 may be the same as or different from the speed previously set for the transmitting apparatus 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 (Internet Protocol camera), a smart phone, or the like.

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

The proposed method, i.e., the new method for existing PAM-based VLC and related MIMO VLC systems solves (1) amplitude-based modulation and non-uniform illumination problems, and (2) provides stable dimming control.

A plurality of LED arrays can be used for Visible Light Communication (VLC) to improve communication efficiency while maintaining smart illumination function through dimming control.

In this specification, 'spatial intensity modulation (SIM)' technique that can be applied to such VLC is newly defined.

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

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

Since the intensity and target dimming level of the SIM symbol are determined only in the spatial domain, 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 can be solved.

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

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

The present disclosure also provides a practical design of the dimmable SIM scheme 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, this specification provides a new VLC modulation scheme called 'spatial intensity modulation (SIM)', a new concept that provides a dimmable VLC solution to overcome the disadvantages of the existing VLC technique. Here, desired data modulation and stable dimming control are supported by activating the effective number of LEDs that are turned on.

Unlike conventional MIMO VLC schemes, the symbol intensity level is determined by counting the number of fully illuminated LEDs, not determined by the amplitude level of the VLC signal of each LED. Here, each LED emits light at the same amplitude level.

Since the data encoding of the SIM scheme is supported only in the spatial domain, careful setting of signal amplitude control and dimming control and data decoding without optical channel prediction can be supported.

Further, the method proposed in the present specification can change the number and shape (or arrangement) of LEDs spatially distributed 'ON' and 'OFF' around the target dimming level in time to satisfy a uniform illumination distribution in a target area .

In order to investigate the achievable communication speed considering the dimming level, the dimming capacity of the SIM scheme proposed herein can be represented by deriving the turn-on probability of maximizing the entropy.

In addition, this specification proposes a multilevel inverse source coding (MISC) applied to a dimmable SIM scheme for practical implementation.

The simulation results in parameter ranges such as the number of LEDs, the target dimming and the SNR (Signal-to-Noise Ratio) provide reference data confirming the performance and actual implementation of the SIM scheme proposed herein for the dimmable VLC.

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

First, we will discuss the theoretical design of SIM method.

The present disclosure contemplates a MIMO VLC system that includes multiple spatially distributed LEDs.

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

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

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

Figure 2 shows an example of a flicker sequence of an LED array based on the SIM scheme proposed herein.

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

To support a uniform illumination distribution, LEDs that are turned on must be equally distributed to all LEDs as in FIG. 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 .

To distinguish between the operating time and the non-operating time of a SIM based VLC system, a completely dark situation (in which all the LEDs are turned off), i.e., n = 0 (or In = 0) is not considered.

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

In order to satisfy the target dimming level during transmission of data, the probabilities of selecting the effective number of LEDs to be turned on, that is turn-on probability, must be determined.

Let p (n) be the turn-on probability for illumination with n turn-on LEDs.

로 표현될 수 있다.The discrete probability {p (1), ..., p (N t)} for n value of entropy is E {p (1), ... , p (N t)} =

. ≪ / RTI >

The normalization constraint is related to the sum of the turn-on probabilities. Also, the dimming limitation can be handled by changing 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 the given SIM scheme as: < EMI ID = 2.0 >

는 목표 디밍 비율(0≤

≤1) 이며, 목표 디밍 레벨은

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

0.0 > 0 < / RTI >

1), and the target dimming level is

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

Taking the second derivation provides 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), the turn-on probability and the Lagrange multiplier function are defined as in Equation 3 below.

Where [beta] and [gamma] are scalar Lagrange multipliers.

Taking the function result 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 ^* ) is the optimal value for the Lagrangian multiplier. By rearranging Equation (4) for p * (n), this can be expressed as Equation (7).

Equation (7) can be simplified as Equation (8) below.

here,

Substituting Equation (8) into Equation (5), it can be expressed simply as Equation (10) below.

Then, Equation (6) can be expressed as Equation (11) below.

From the equations (9) and (11), the optimal Lagrangian coefficients (? ^* ,? ^* ) Are determined. By using these coefficients, an optimal turn-on probability set {p ^* (1), ..., p ^* (N _t )} that maximizes the entropy with a given dimming limit can be obtained.

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

=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.In order to satisfy the target dimming ratio, the turn-on probability of maximizing the entropy for each SIM signal level is different. For example, N _t = 4,

= 0.72, the turn-on probability of maximizing the 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 should occur at a probability specified according to the target dimming rate.

In FIG. 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, we will look at a practical SIM design that uses multi-level inverse source coding.

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

However, in general, digital information bits represent an equal probability (50%). That is, '0' and '1' have approximately equal probability (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 as an average intensity level of approximately 0.5I _max .

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

This enables transmission of a SIM symbol that maximizes the entropy and, as a result, satisfies the turn-on probability according to the target dimming level.

The method proposed here is based on the assumption that inverse source coding of so-called " multi-level inverse source coding (MISC) " is used to satisfy the target dimming level of the SIM scheme from binary input data (0 Extend the concept.

This preserves the method to the maximum entropy while satisfying the dimming target.

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

In order to design the codewords of MISC, 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 a 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 symbols 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, where the largest turn-on probability value is located at the first location and the smaller turn-on probability value is located towards the right.

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

Since '0' and '1' have the same probability of 0.5 each, the turn-on probability in each codeword is expressed as (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.

That is, the lower the intensity level, the longer the codeword used.

In this example, the average of the dimming ratio can 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 the above Table 2, evenly configured binary data is transformed into data having '1' of 77%, and then the target dimming ratio can be achieved.

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

The probability value is scaled in order of 0.5 according to the length of the codeword, the turn-on probability of a particular range of dimming ratios giving the same value.

As Nt increases, the shape of the curve of Fig. 5 is close 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 on the receiving side, a mapping table is used that includes two attributes: codeword and intensity (or intensity) in Table 2. < RTI ID = 0.0 >

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 determined not by the amplitude level of the VLC signal but by calculating the effective number of turn-on LEDs in the SIM scheme.

Thus, the SIM scheme proposed herein prevents the necessity of channel prediction, which is essential for PAM-based VLC schemes.

Figure 6 shows the dimming level of the SIM scheme 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.

The use of MISC in the SIM method is practical for practical systems, since small differences in dimming levels can not be detected by the human eye.

Figure 7 shows a comparison of the 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 the dimming ratio.

This means that the SIM scheme using MISC always guarantees the robust performance of entropy.

The entropy of the SIM scheme increases as the total number of spatially distributed LEDs increases.

When Nt is 4, 8, and 16, the maximum number of bits required to provide the 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 is dependent on Nt.

The maximum value of the entropy can be observed since the turn-on probabilities of all the SIM symbols are the same at the intermediate intensity level.

Next, the dimming capacity analysis will be described.

In the following, the dimming capacity of the SIM scheme was investigated taking into account the VLC channel quality.

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

In order to express the dimming capacity, mutual information based on differential entropy can be used. Assuming an additive white Gaussian noise (AWGN), the received signal Y can be expressed as: < EMI ID = 12.0 >

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

The mutual information between X and Y can be expressed as Equation (13) below.

8 shows dimming capacities having various Nt numbers when the target dimming levels are 48% and 72%.

The signal to noise ratio (SNR) range is set from -10 dB to 20 dB in order to observe the change in the performance depending on the channel quality.

Here, the SNR is defined as Imax / sigma due to the optical communication link. A practical approach based on MISC achieves capacity performance very close to optimal performance results.

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

At high SNRs (> 20 db), the dimming capacity of both methods saturates.

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

Also, the performance gap in the three cases (Nt = 4, 8, 16) can be larger with increasing SNR (<15 dB).

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

Figure 9 shows the dimming capacity of the SIM method, which depends on both the SNR and the dimming ratio.

As the SNR increases, the dimming capacity saturates regardless of the dimming ratio.

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

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

Let's briefly summarize the contents we have already studied.

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 scheme is only provided 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 of maximizing the entropy of the SIM scheme is provided.

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

To analyze the achievable communication rate, we looked at the dimming capacity of the SIM scheme under the target dimming constraint.

Numerical results indicate that capacity performance based on optimal turn-on probability and practical MISC approach is close to the SNR range.

Also, it can be seen that the maximum capacity of the SIM scheme depends largely on the SNR, the total number of LED lights, and the target dimming level.

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

First, a transmitter generates a flicker sequence (or a flicker sequence) in which at least one LED of an LED array is turned on or off by a specific time unit using a spatial intensity modulation (SIM) blinking sequence (S1010).

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

The spatial intensity modulation scheme may include a code for each intensity level based on a set dimming ratio, a total number of LEDs constituting the LED array, and a turn-on probability for each intensity level. A codeword is generated, and at least one of the number of LEDs turned on or the LED position turned-on by the specific time unit is determined using the generated codeword for each intensity level to modulate the codeword .

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

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

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

In equation 7, p * (n) is the optimum turn-represents a whole probability, β ^* and γ ^* is Lagrangian deulyimyeo optimum values for the multiplier, N _t is the total number of the LED constituting the LED array, n is Indicates the effective number of LEDs that are turned on.

Also, the length of the code word 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 codeword for each intensity level is 111, 110, 10, and 10 as shown in Table 1 and Table 2, respectively. 0.

Transmitting apparatus and receiving apparatus

Next, a description will be made of an operation method of a transmitting apparatus and a receiving apparatus of a visible light communication system to which the presently proposed method can be applied, and an internal block diagram for implementing the method.

11 shows an internal block diagram of a transmitting apparatus and a receiving apparatus operating in visible light communication to which the present invention can be applied. Fig. 2 is merely for convenience of explanation and does not limit the scope of the present invention.

Referring to FIG. 11, a transmitting apparatus (or transmitter) 110 to which the present invention can be applied includes an RF module 111, a processor 112, and a memory 113. The elements of the transmitting apparatus shown in FIG. 11 are examples, and the transmitting apparatus may be composed of more or fewer components.

First, a radio frequency (RF) module 111 transmits and receives signals to and from the outside.

Next, the processor 112 is functionally coupled to the RF module and implements the functions, procedures, and / or methods suggested herein. The layers of the wired / wireless interface protocol may be implemented by a processor.

In particular, the processor may be configured to use a spatial intensity modulation (SIM) scheme to flick the input data stream such that the at least one LED of the LED array is turned on or off A blinking sequence, and controls the RF module to transmit the signal to the receiver through the generated flicker sequence.

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

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

First, a radio frequency (RF) module 121 transmits and receives signals to and from the outside.

Next, the processor 122 is functionally coupled to the RF module and implements the functions, procedures, and / or methods suggested herein. The layers of the wired / wireless interface protocol may be implemented by a processor.

Specifically, the processor controls the RF module to receive a flicker sequence transmitted from a transmitter.

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

The embodiments described above are those in which the elements and features of the present invention are combined in a predetermined form. Each component or feature shall be considered optional unless otherwise expressly stated. Each component or feature may be implemented in a form that is not combined with other components or features. It is also possible to construct embodiments of the present invention by combining some of the elements and / or features. The order of the operations described in the embodiments of the present invention may be changed. Some configurations or features of certain embodiments may be included in other embodiments, or may be replaced with corresponding configurations or features of other embodiments. It is clear that the claims that are not expressly cited in the claims may be combined to form an embodiment or be included in a new claim by an amendment after the application.

Embodiments in accordance with the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of 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) field programmable gate arrays, processors, controllers, microcontrollers, microprocessors, and the like.

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

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 characteristics thereof. Accordingly, the foregoing detailed description is to be considered in all respects illustrative and not restrictive. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

Claims (8)

A method for transmitting a signal in a visible light communication system, the method being performed by a transmitter,
A blinking sequence in which at least one LED of an LED array is turned on or off by a specific time unit using a spatial intensity modulation (SIM) ; And
And transmitting the signal to a receiver via the generated flicker sequence,
In the spatial intensity modulation method,
A codeword for each intensity level is generated based on a set dimming ratio, a total number of LEDs constituting the LED array, and a turn-on probability for each intensity level ,
And determining at least one of a number of LEDs turned on or a position of an LED turned on by the specific time unit using the generated code word for each intensity level. The method according to claim 1,
Wherein the number of intensity levels is determined based on the total number of LEDs. The method according to claim 1,
Wherein the turn-on probability for each intensity level is set to maximize entropy according to the set dimming ratio. The method of claim 3,
Wherein the turn-on probability for each intensity level is set by the following equation.

Here, p ^* (n) is the optimum turn-represents a whole probability, β ^* and γ ^* is Lagrangian deulyimyeo optimum values for the multiplier, N _t is the total number of the LED constituting the LED array, n is the turn-on The effective number of LEDs. The method according to claim 1,
Wherein the length of the code word for each intensity level is longer as the turn-on probability for each intensity level is lower. The method according to claim 1,
The generated code word for each intensity level is composed of at least one of '0' and '1'
Wherein the number of '0' or '1' included in the generated codeword for each intensity level is determined using a multi-level Huffman encoding binary tree technique. The method according to claim 6,
When the set dimming ratio is 0.72 and the total number of LEDs constituting the LED array is 4,
Wherein the generated code words for each intensity level are 111, 110, 10, and 0, respectively. A transmitter for transmitting a signal in a visible light communication system,
An RF module for transmitting and receiving signals to and from the outside; And
And a processor operatively coupled to the RF module,
A blinking sequence in which at least one LED of an LED array is turned on or off by a specific time unit using a spatial intensity modulation (SIM) Generate; And
And to transmit the signal to the receiver through the generated flicker sequence,
In the spatial intensity modulation method,
A codeword for each intensity level is generated based on a set dimming ratio, a total number of LEDs constituting the LED array, and a turn-on probability for each intensity level ,
And determines at least one of a number of LEDs turned on or a position of an LED turned on by the specific time unit using the generated codeword for each intensity level.

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