KR20110139350A - Apparatus and method for obtaining optical rate using multiple led transmitter in visible light communication system - Google Patents

Abstract

PURPOSE: A device and a method for obtaining optimized transmission rate by using multi light emitting diode are provided to transmit data by calculating maximum transmission rate with each data when transmitting two different data at the same tiem. CONSTITUTION: A controller performs singular value decomposition about provided channel if a plurality of data is inputted. The controller calculates the modulation size value of many data through the performed specified value decomposition. The controller calculates the transmission rate of the data by using the modulation size value. Two modulators(211,213) modulates data according to the obtained modulation size and transmission rate. A transmission unit transmits the modulated data.

Description

Apparatus and method for obtaining optimal transmission rate using multiple light emitting diodes in visible light communication system {APPARATUS AND METHOD FOR OBTAINING OPTICAL RATE USING MULTIPLE LED TRANSMITTER IN VISIBLE LIGHT COMMUNICATION SYSTEM}

TECHNICAL FIELD The present invention relates to a visible light communication system, and more particularly, to an apparatus and a method for obtaining an optimal transmission rate using multiple light emitting diodes.

Visible light wireless communication refers to a technology for communicating by using a modulation and demodulation technique using fast blinking of light emitting diodes as lighting such as incandescent bulbs and fluorescent lights are replaced with light emitting diode lighting by digital semiconductors. In other words, visible light communication is a fusion entity of lighting and communication as a technology that can use lighting as a communication light source as the semiconductor is also used as lighting. Currently, standards for the physical layer and the media control access layer are actively progressing, and the light emitting diode lighting infrastructure can be used to provide communication services such as intelligent transportation systems, wireless home networks, and high precision indoor positioning.

Visible light wireless communication is usually performed in the visible light band from 380nm to 780nm, and an important feature of visible light communication is basically a lighting function, and it is possible to communicate only up to the light source's reach for high security. It can be summarized as being harmless and having no regulation on the visible light band. Recently, a light emitting diode has been spotlighted as a light source used in wireless visible light communication, and has advantages of low power consumption, long life, and environment-friendliness compared to other light sources.

Representative modulation and demodulation techniques that can be used in such visible light communication can be classified into a baseband modulation technique that is modulated in the baseband and a subcarrier modulation that uses subcarriers. Typical baseband modulation techniques include line coding and pulse modulation using pulse characteristics (position, width, spacing, etc.), and subcarrier modulation techniques include common M-ary PSK / PAM / QAM / OOK modulation techniques. . Modulation techniques currently considered in visible light communication include On-Off Keying (OOK) modulation and pulse position modulation (PPM), which are already used in infrared communication. The modulation technique is described below with reference to FIG. 1.

1 is a diagram illustrating an exemplary modulation technique considered in conventional visible light communication.

Referring to FIG. 1, the OOK is a basic form of an amplitude modulation technique, which transmits data by turning on / off an electrical signal for a specific time according to binary information. OOK is used in cases where high noise immunity is not required because of its relatively simple implementation and high frequency efficiency compared to other modulation schemes, and it is often considered in portable applications because it reduces transmission power when the electrical signal is turned off. That's the way. The pulse position modulation method is used to change the position of a pulse in accordance with binary information and transmit it.

Current visible light communication has a transmission structure for transmitting one data to a plurality of light emitting diodes. However, when a plurality of light emitting diodes are considered as a transmitting unit, by transmitting a plurality of data to the light emitting diodes, a visible light communication system having a higher transmission rate can be designed than when transmitting a single data. In addition, when transmitting a plurality of data at the same time by using a plurality of light emitting diodes, how to consider the transmission rate of each data according to the channel when intensity modulation of each data, how much light output value should be assigned to each data modulator There was no research on whether or not. Therefore, the design of a transmission system using a plurality of light emitting diodes has different conditions from that of a conventional multiplex transmission system.

First, in the case of the transmission power, which is the most basic reference, in the case of radio frequency communication, information to be sent is transmitted in a size or phase of a signal transmitted from a transmitter. In this case, the signal power of the transmitted signal may be obtained as follows.

Unlike in the above formula, which is generally used to obtain the power of an electrical signal, in the case of visible light communication using a light emitting diode, the data is encoded in an optical output corresponding to the strength of the signal transmitted, that is, the power of the electrical signal. Is generally transmitted. Therefore, the power of the signal transmitted at this time can be obtained as follows.

It can be seen that the power reference for the electrical signal of Equation 1 is considered to be strictly different from the power reference in visible light communication such as Equation 2, and therefore, a transmission scheme suitable for multiplexing transmission that meets the light output criterion must be found.

Next, consider the intensity modulation generally used in visible light communication. Intensity modulation is a technique for transmitting data on the intensity of a signal as described above. The transmitted signal itself means a signal corresponding to power. Therefore, the transmitted signal should always have a positive value as shown in Equation 3 below.

This restriction is not necessary in a typical radio frequency communication system. However, since the transmission signal of the visible light communication using the intensity modulation must satisfy the above conditions, in order to allocate the optical power in the multiple light emitting diode transmission system having the multiplexing gain, optimization must be performed under the above conditions.

The present invention proposes a transmission system capable of simultaneously transmitting two different data when transmitting data to a hand-held mobile device such as a cellular phone through intensity modulation using a plurality of light emitting diodes. For a given channel H, convert the channel into a parallel channel (H = UΛV ^T ) through singular value decomposition (SVD), taking into account the singular value matrix (V) of the transmitter and the data being modulated in each channel Based on the conditions to be determined, what is the optimal modulation size, what is the offset value of the modulation scheme according to the singular value matrix (V), and what is the transmission rate at this time. We propose a new algorithm and a transmission and reception system.

According to an aspect of the present invention, in a method for obtaining an optimal transmission rate using multiple light emitting diodes in a visible light communication system, a process of simultaneously receiving a plurality of data, performing singular value decomposition for a given channel, and Obtaining a modulation size value of the plurality of data by performing singular value decomposition; obtaining a transmission rate of the plurality of data using the modulation size value; and determining the plurality of data according to the obtained modulation size value and transmission rate. And modulating the data.

According to another aspect of the present invention, in a device for obtaining an optimal transmission rate using multiple light emitting diodes in a visible light communication system, when a plurality of data is input, singular value decomposition is performed on a given channel, and the performed singularity A control unit for obtaining a modulation size value of the plurality of data through value decomposition, and obtaining a transmission rate of the plurality of data using the modulation size value, and modulating the plurality of data according to the obtained modulation size value and transmission rate. And a transmitter for transmitting the modulated plurality of data.

According to the present invention, when two different data are simultaneously transmitted, data is transmitted by calculating the maximum data rate of each data, thereby optimizing the data rate without interruption in data transmission.

1 is a diagram illustrating a representative modulation technique considered in conventional visible light communication.
2 is a block diagram illustrating a transmission system using multiple light emitting diodes according to an exemplary embodiment.
3 is an exemplary view illustrating an operation of determining a modulation size, an offset position, and a transmission rate of data in a transmitter according to an embodiment of the present invention.
4 is a diagram illustrating an offset region satisfying a condition of intensity modulation according to an embodiment of the present invention.
5 is a diagram illustrating an area where all symbols of intensity modulation are formed and an area where a maximum data rate can be obtained according to an embodiment of the present invention;
6 is a flowchart illustrating a process of determining a modulation size, an offset position, and a transmission rate in a transmitter according to an embodiment of the present invention.
7 is a graph illustrating a result after intensity modulation according to an embodiment of the present invention;
8 is a graph illustrating a change in an average data rate according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific details such as specific components are shown, which are provided to help a more general understanding of the present invention, and the specific details may be changed or changed within the scope of the present invention. It is self-evident to those of ordinary knowledge in Esau.

2 is a block diagram illustrating a transmission system using multiple light emitting diodes according to an exemplary embodiment. When a channel using multiple light emitting diodes is defined as H 201, channel H 201 may be represented in a matrix form, and the value of each matrix has a positive real value according to the characteristics of the visible light communication channel. The channel H 201 may singular value decomposition into a product H = UΛV ^T of three matrices according to unique characteristics. It will be described with reference to the following equation.

In Equation 4, U denotes a right singular matrix of the channel matrix, and V denotes a left singular matrix of the channel matrix. Λ is a diagonal matrix having singular values of the channel matrix as elements of the diagonal matrix. In this case, the mathematical operator (*) ^T means Transpose.

(209)를 결정하여 다중 안테나 채널을 병렬 채널로 만들 수 있다. 이러한 병렬 채널을 구성할 수 있기 때문에 송신 단에서는 최대 2개의 데이터를 동시에 전송할 수 있다. 따라서 두 개의 데이터가 동시에 각 변조기(211, 213)를 거치고 송신 매트릭스와 곱해진 후 전송이 된다. 변조가 이루어진 데이터들은 사각 펄스를 기저 함수로 이용하여 실제 송신되는 송신 신호를 형성하게 된다. 이후 수신부(205)에서는 수신된 송신 신호를 복조기(215, 217)를 통하여 복조한다.The transmitter 203 knows the channel H 201, and each transmitter 203 and the receiver 205 has a transmission matrix V 207 and a receiving matrix according to the characteristics of the channel.

209 may be determined to make the multiple antenna channel a parallel channel. Since the parallel channel can be configured, the transmitting end can transmit two data at the same time. Therefore, two data are simultaneously passed through each modulator 211 and 213, multiplied by the transmission matrix, and then transmitted. The modulated data forms a transmission signal that is actually transmitted using a square pulse as a basis function. Thereafter, the receiver 205 demodulates the received transmission signal through the demodulators 215 and 217.

Although not shown in the drawing, when the number of light emitting diodes is two or more, the grouping may be divided into two groups, and thus the same method as in the case of using two light emitting diodes may be applied.

3 is an exemplary diagram illustrating an operation of determining a modulation size, an offset position, and a transmission rate of data in a transmitter 203 according to an embodiment of the present invention.

As shown in FIG. 3, when two different data are respectively input to different modulators 211 and 213, at zero on the constellation of the transmission rate Ki of the pulse amplitude intensity modulation (hereinafter referred to as PAM) and the symbol space of the PAM calculated by the proposed technique. A symbol S'i is formed based on the distance Δi between the furthest symbols and the offset P'i is added to the modulation symbols S1 (= S'1 + P'1) and S2 (= S ') to be sent to the transmission matrix V. 2 + P'2). That is, the output value of the modulator to which the offset is applied can be expressed as follows.

In this case, the signal x transmitted to the receiving end through the light emitting diode may be multiplied by the transmission matrix V 207 as shown in FIG.

After the channel, white noise (AWGN) is added to give the following received signal:

(209)를 곱해주면 다음과 같은 2개의 병렬 수신 신호를 얻을 수 있다.Receive matrix to the above received signal

By multiplying (209), two parallel received signals are obtained.

에 의해 변형된 수신신호와 그 때의 백색 잡음을 의미하고, 백색 잡음의 확률 분포는 수신 행렬과 관계없이 변하지 않는다.In equation (8), r and z are reception matrices

It means that the received signal modified by and the white noise at that time, the probability distribution of the white noise does not change regardless of the reception matrix.

Since the receiver 205 knows Λ and P ', it is possible to remove ΛP' from the above signal and make new received signals r'1 and r'2 as follows.

The two received signals of Equation 9 may be ML decoded and demodulated as follows.

과

은 ML Decoding을 하여 가능한 송신 심볼 중에서 거리가 가장 가까운 거리의 송신 심볼을 찾아 결정한 복조 심볼을 의미한다. 수학 연산자 arg max는 최대값을 찾기 위한 집합 내의 변수값들 중에서 최대값을 갖게 하는 변수값을 찾는 연산자이다.At this time,

and

Denotes a demodulation symbol obtained by finding and transmitting the nearest transmission symbol among the possible transmission symbols by ML decoding. The mathematical operator arg max is an operator that finds the variable value that has the maximum value among the variable values in the set for finding the maximum value.

In addition, singular value decomposition (SVD, 305) of the fed back channel H may be performed, and a water rate, modulation magnitude, and offset may be obtained using the water filling technique 307. In the case of discontinuous PAM having an integer value as the modulation rate, the bit loading scheme is used instead of the water filling technique. If so, the following describes how to calculate the rate k, modulation magnitude value Δ, and offset p 'applied to the modulators 211 and 213 above.

First, the conditions for the transmission signal considered in the present invention will be described.

<Condition of Intensity Modulation>

First, a vector to be sent to the transmission matrix of the transmitter 203 through the modulator is defined as follows.

Bit information entering the modulator is modulated by s 'intensity modulation, and the position of the modulated symbol can be changed by adding an arbitrary p' value. In the present invention, a pulse intensity modulation technique having a plurality of levels is assumed as an intensity modulation technique. When the transmission matrix is passed, the transmission vector is as follows.

Since the modulation is assumed in the present invention, the transmission signal may be referred to as a signal for power and should have a positive value. Therefore, the following two conditions must be satisfied.

Here, E [x (t)] means an operator to find the mean value of the random variable. Also, the inequality of a vector equal to or greater than zero means that the elements of each vector are equal to or greater than zero.

<Condition for Transmitted Light Output>

In the present invention, it is assumed that the maximum transmit light output value that can be used by the transmitting end is limited by a given value P _opt . You can condition it as follows:

<Condition for Bit Error Rate of Modulation Technique>

If there is a bit error rate that can be obtained by using two modulation schemes of s'1 and s'2, it is assumed in the present invention that the bit error rate must be smaller than an arbitrary threshold value to enable reliable communication. If the bit error rates obtained by two modulation schemes, s'1 and s'2, are defined as BER1 and BER2, they can be conditioned as follows.

If the transmission rates obtained by the two modulations of s'1 and s'2 are k1 and k2, respectively, the present invention seeks to maximize the transmission rates of the two modulations under the above conditions. In addition, when solving the problem of obtaining the maximum data rate, it is possible to determine how many levels of PAM to use, how much light output to give to each modulation scheme, and how the offset value of each modulation scheme should be given. . If the optimization problem is raised under the above three conditions, the following problem should be solved.

Looking at the optimization problem solving process according to the three conditions presented in the equation (16) as follows. First, a process of deriving an offset region of p 'satisfying conditions (II) and (III) of Equation 16 will be described.

According to the equation (II) of Equation 16, two straight lines can be obtained as follows.

이기 때문에 V(207)를 적절히 변형하여 다음과 같은 영역에서만 고려하면 다른 영역의 최적화 문제도 동일하게 해결 할 수 있다.Where a is a value calculated by the elements of the transmission matrix V 207 as defined in the horizontal direction. Four lines are generated according to the two straight lines of Equation 17, and the direction of the inequality is changed according to the transmission matrix V 207 so that only one of the four areas can obtain an offset value satisfying condition (II). It becomes an area.

Therefore, if V 207 is properly modified and considered only in the following areas, optimization problems in other areas can be solved in the same way.

일 경우를 살펴보면 E.g,

If you look at

로 동일한 특이값 분해임을 알 수 있고, 여기서 구한

는 수학식 18의 조건을 만족시킨다는 것을 알 수 있다. 따라서 다른 조건들을 수학식 18과 같은 동일한 조건으로 변형하여 최적화 문제를 해결할 수 있다.Transforming to

We can see that the same singular value decomposition

It can be seen that satisfies the condition of Equation 18. Accordingly, the optimization problem may be solved by modifying other conditions to the same condition as in Equation 18.

The offset region satisfying the conditions (II) and (III) of Equation 16 under the condition of Equation 18 is as follows.

The third condition of Equation 20 is derived from condition (III) of Equation 16, and the process is as follows.

Looking at the area to meet this through the following drawings.

4 is a diagram illustrating an offset region that satisfies the condition of intensity modulation according to an embodiment of the present invention. Looking at the area that satisfies Equation 21, for example, it can be seen that the shaded area shown in Figure 4, the arbitrary offset value should always be in the shaded area.

Next, a process of defining the size of the modulation scheme under condition (I) will be described.

를 만족시켜야 하기 때문에 두 개의 선 위에 존재해야 한다. 이를 하기의 도 5에 나타내었다.As described above, the modulation of s'1 and s'2 is performed through two modulators. The modulation is formed on the left and right sides up and down as shown in FIG. As in condition (I), the modulated and formed points always

It must be above two lines because it must satisfy. This is shown in Figure 5 below.

FIG. 5 is a diagram illustrating a region where all symbols of intensity modulation are formed and a region where a maximum data rate can be obtained according to an embodiment of the present invention. As shown in FIG. 5, the constellation region formed when two modulation techniques are used around the p 'point is formed in a rectangle.

When calculating the rectangular area that can form the constellation, it can be considered by dividing it into two ranges, a> 1 and 0 <a <1, depending on the value of a.

As shown in FIG. 5, the area of p 'for solving the optimization problem can be reduced. The reason is as follows. Among the areas where the actual p 'point can be formed, the size of the modulation technique that can maximize the transmission rate can be found among the shaded portions as shown in the above figure. When there is an offset value in the portion to the left of the shaded region of FIG. 5 among the offset regions of FIG. 4, the transmission rate is always lower than when the offset value is at the left edge of the triangular region of the shaded region of FIG. 5. Therefore, the offset region located to the left of the shaded region does not need to be considered. Similarly, when the offset is formed in the region to the right of the shaded region of FIG. 5 among the shaded regions of FIG. 4, the transmission rate is always lower than when the offset value is formed at the right edge of the triangle shaded region of FIG. 5. Therefore, this area does not need to be considered.

Accordingly, the shaded areas considered for optimization as shown in FIG. 5 are as follows. In FIG. 5, the straight line 501 corresponds to a set of points having the same distance from the two straight lines p'2 = ap'1 and p'2 = p'1 / a to the p'1 axis for an arbitrary p'2 value. do. In addition, it can be said that the set of center points that can form the maximum constellation in the p'1 direction. Such a straight line is obtained by calculating the values of the p'1 axes of the two straight lines with respect to the p'2 value and saying that the distances are the same from p'1.

In FIG. 5, the straight line 503 has p'1 = 0. Therefore, the shaded area can be formulated as follows.

Next, when a random offset value is determined, the size of the modulation scheme should be formed to maximize the transmission rate.

The size of the modulation scheme is the largest modulation size when the constellation points formed by Δ1 and Δ2, which are half the size of each modulation scheme, reach p'2 = ap'1 and p'2 = -p'1 / a. To form. When the constellation point formed by Δ1 and Δ2 touches p'2 = ap'1 and p'2 = -p'1 / a, the point touching each straight line is the point that touches p'2 = ap'1 first. Becomes (p'1 + Δ1, p'2-Δ2) and the point where p'2 = -p'1 / a becomes (p'11Δ1, p'2-Δ2). When each point is put in a straight line, the equation is as follows.

If Equation 24 is arranged, the following relation between p 'and Δ can be obtained.

So far, we have looked at the case of a> 1. If 0 <a <1, the size of the modulation scheme for maximizing the transmission rate can be found when the p 'point is formed in the region shown in Equation 26 below. The optimization problem can be solved in the same manner as in the case of a> 1.

The relation between p 'and Δ is the same as that obtained when a> 1.

Next, a process of forming a modulation scheme that satisfies the target bit error rate according to condition (IV) of Equation 16 will be described.

When Δ1 and Δ2 are determined and transmitted to any M-ary PAM, the bit error rate must satisfy condition (IV). To determine the M value that satisfies this, the bit error rate according to arbitrary Δ and M is first calculated. If the M-ary PAM for any Δ is formed, the constellation may be considered such that the distance between adjacent symbols is 2Δ / (M-1). The average symbol energy is obtained as follows.

At this time, assuming that the variance value of the white noise is 1, the bit error rate of the M-ary PAM when passing through a channel having a symbol energy of Es and a channel gain of λ can be approximated as follows.

은 다음과 같은 식을 만족시켜야 한다.Therefore, in order to satisfy the minimum target bit error rate BER _tgt which is intended to be satisfied in the present invention, the transmission rate of ki can be obtained according to the size Δi of each modulation scheme.

Must satisfy the following equation:

If this is expressed for ki:

Using the newly obtained conditions, the optimization problem for p 'may be replaced by the optimization problem for Δ. First, the optimization problem for p 'is as follows.

인 첫 번째 조건과,

인 두 번째 조건과,

인 세 번째 조건으로 나누어 최적화 문제를 살펴볼 수 있다. 이를 p'와 Δ간의 관계식을 사용하여 바꾸면 다음과 같은 Δ에 대한 최적화 문제로 치환할 수 있다. 첫 번째 조건은 다음과 같이 치환할 수 있다.As in Equation 31 above

With the first condition that is,

With the second condition,

Dividing by the third condition, we can look at the optimization problem. This can be changed by using the relation between p 'and Δ as an optimization problem for Δ as follows. The first condition can be substituted as follows.

The second condition can be substituted as follows.

The third condition can be substituted as follows.

Therefore, the above optimization problem can be replaced by the following optimization problem for Δ.

If we assume a continuous level of PAM, i.e., if the rate of PAM can have any real value, then the optimization problem of Eq. 35 can be calculated using the following water-filling technique: have. Water-filling algorithms are commonly used in the physical layer, and it is already known to obtain bit rates using existing water-filling algorithms or to obtain bit rates to be applied to each modulation scheme using bit-loading algorithms. The derivation process of the water-filling solution is as follows. The above optimization problem can be achieved using the Lagrange multiplier to obtain the following cost function.

To get the maximum value for Δi, we need to find a value where the derivative is zero when we differentiate C into each Δi. This can be found through the following equation.

로 정의할 경우, 다음과 같은 최적의 Δ값을 얻을 수 있다. 여기에서 구한 Δi의 합이 C가 되도록 하는 μ를 찾고, 이를 대입하여 각 변조기의 크기를 구할 수 있다.

If it is defined as, the optimal Δ value can be obtained. We find μ such that the sum of Δi obtained here is C, and substitute these to obtain the size of each modulator.

로 정의된다.Operator here Is

Is defined as

Accordingly, the optimum p 'can also be obtained by substituting Δ * above in the relation (31) between p' and Δ.

In addition, the modulation scheme to be used for transmission may be determined as follows by substituting Δ * in Equation 29.

), 4PAM (

), 8PAM (

) 등과 같은 불연속적인 PAM만을 사용할 경우에는 Levin-Campello의 비트 로딩 알고리즘과 같은 불연속적인 PAM에 대한 최적화 문제를 푼 알고리즘을 이용하여야 한다.If we calculate the optimal Δ for the actual arbitrary channel H and obtain the data rate as in Equation 40, we get the real value ki *. If 2PAM (

), 4PAM (

), 8PAM (

In case of using only discrete PAM such as), we have to use algorithm that solves optimization problem for discontinuous PAM such as Levin-Campello's bit loading algorithm.

6 is a flowchart illustrating a process of determining a modulation size, an offset position, and a transmission rate in a transmitter according to an embodiment of the present invention. When given the channel H and the optical output level P _opt, look at the process of determining the position and rate of the size of the offset value of the modulation by an algorithm proposed by the present invention will be described.

In step 601, the channel H is fed back, and in step 603, matrix V and Λ are calculated through singular value decomposition for the given channel H. If you configure the system assuming a continuous rate, Go to step 605 Obtain the water-filling solution using V and Λ . The process is as follows.

If a discrete rate is assumed, Levin Campello bit loading is applied instead of water filling to calculate Δ. From this, Δ is used to find the data rate and offset. In step 607, k1 and k2 are obtained, and in step 609, p1 and p2 are obtained. The equation to find is as follows.

과

을 더하여 송신 행렬 V에 곱할 벡터

를 형성한다.Subsequently, in step 611, a modulation scheme is determined according to the transmission rate ki * and the modulation size Δi *, and the data is modulated. After that, the process proceeds to step 613 to the modulated values.

and

To multiply the transmission matrix V by

To form.

Next, a process of transmitting two signals simultaneously by performing singular value decomposition on a specific channel will be described with reference to the following embodiments.

7 is a graph illustrating a result after intensity modulation according to an embodiment of the present invention.

에 대해 P_opt=15의 광출력을 사용할 경우에 대한 실시 예를 보여준다. 위의 채널을 특이값 분해 할 경우에 다음과 같다. Any given channel

An example of using the optical power of P _opt = 15 is shown. The singular value decomposition of the above channel is as follows.

,

,

로 계산될 수 있다. 이 값을 수학식 39에 대입하여

와

를 얻을 수 있다. 또한 수학식 40에 대입하여

비트와

비트의 전송률을 얻을 수 있고 이에 따라 각 변조기에서 최소한 2-PAM과 8-PAM이 사용될 수 있다.Assuming the bit error rate is 10 ^-3 , K = 0.4344, and at this time, the value is calculated according to Equation 38

,

,

It can be calculated as Substitute this value in (39)

Wow

Can be obtained. Also, by substituting Equation 40

Bit and

Bit rates can be obtained so that at least 2-PAM and 8-PAM can be used in each modulator.

의 오프셋이 더해진 것을 볼 수 있고, 왼쪽 아래의 신호에는 8-PAM에

의 오프셋이 더해진 것을 볼 수 있다. 또한 오른쪽은 신호 파형들은 송신 매트릭스 V를 거친 후 볼 수 있는 신호 파형으로 세기 변조를 이용하였을 경우 만족시켜야 하는 x(t)>0의 조건을 충족시키고 있다는 것을 보여준다.At this time, the signal waveform in which the centers of the two signals are changed according to each offset value is shown on the left. The upper left signal has a 2-PAM

You can see the offset of, plus 8-PAM for the lower left signal

You can see that the offset of is added. The right hand side also shows that the signal waveforms meet the condition of x (t)> 0 which must be met when intensity modulation is used as the signal waveform seen after the transmission matrix V.

8 is a graph illustrating a change in an average data rate according to an embodiment of the present invention.

를 사용하는 경우를 비교하였다. 최적화 문제를 풀 경우에

인 조건에 따라서

로 동일한 경우에 대한 값을 구할 수 있고 이 값을 이용하여 전송하였을 경우를 최적화된 경우와 비교하였다. 그림과 같이 최적화된 Δ*를 사용하는 경우가 낮은 광출력 값에 비하여 최대 2 dB 이득을 보인다는 것을 볼 수 있다. 이는 동일한 전송률을 보낼 수 있는 시스템을 구성할 경우 최대 2dB의 광출력 값을 절약할 수 있다는 것을 의미한다.The change of the average transmission rate according to the light output value _Popt is examined through simulation. The distribution of H used in the simulations was randomly assumed to follow the Rayleigh amplitude distribution. The target bit error rate assumed in the simulation is 10 ^-3 . At this time, the same method as using the optimized p 'and Δ *

The case of using was compared. If you solve the optimization problem

Depending on conditions

The values for the same case can be obtained and compared with the optimized case. As shown in the figure, the use of the optimized Δ * shows a maximum gain of 2 dB compared to the low light output value. This means that up to 2dB of light output value can be saved if the system is configured to send the same data rate.

Meanwhile, in the above description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be defined by the described embodiments, but by the claims and equivalents of the claims.

Claims (15)

What is claimed is: 1. A method for obtaining an optimal data rate using multiple light emitting diodes in a visible light communication system.
Receiving a plurality of data at the same time,
Performing singular value decomposition for a given channel and obtaining modulation magnitude values of the plurality of data through the singular value decomposition performed;
Obtaining a data rate of the plurality of data using the modulation size value;
And modulating the plurality of data according to the obtained modulation size value and transmission rate. The method of claim 1,
Obtaining an offset for shifting the centers of the symbols of the plurality of data using the modulation magnitude value;
And transmitting the offset by adding the offset to the modulated plurality of data. The method of claim 1,
And performing the singular value decomposition to convert the given channel into a parallel channel to transmit the two different data simultaneously. The method of claim 1, wherein the obtaining of the modulation magnitude value comprises
A method for obtaining an optimal transmission rate, characterized in that the distance between the symbols farthest from 0 is calculated on a symbol constellation of a PAM. 5. The method of claim 4, wherein the modulation magnitude value is
A method for obtaining an optimal transmission rate, characterized by the use of water filling or bit loading techniques. According to claim 1, wherein the rate is a condition for having a maximum value
The two different data have a positive value, the maximum transmission optical power is less than the preset optical power, and the bit error rate that can be obtained by using a modulation technique that modulates the two different data is arbitrary. A method for obtaining an optimal rate, characterized in that less than the threshold of. The method of claim 1, wherein the modulating of the two different data is performed.
And determining a modulation scheme according to the obtained transmission rate and modulation size to modulate the two different data with pulse amplitude intensity. An apparatus for obtaining an optimal transmission rate using multiple light emitting diodes in a visible light communication system,
When a plurality of data is input, singular value decomposition is performed on a given channel, a modulation magnitude value of the plurality of data is obtained by performing the singular value decomposition performed, and a transmission rate of the plurality of data using the modulation size value is obtained. A control unit for obtaining
Two modulators for modulating the plurality of data according to the obtained modulation magnitude value and data rate;
And a transmitter for transmitting the modulated plurality of data. The method of claim 8, wherein the control unit
And an offset for shifting the centers of the symbols of the plurality of data by using the modulation size value. The method of claim 9, wherein the transmitting unit
And transmit the offset by adding the offset to the plurality of modulated data. The method of claim 8, wherein the control unit
And performing the singular value decomposition to convert the given channel into a parallel channel to simultaneously transmit the two different data. 9. The method of claim 8, wherein obtaining the modulation magnitude value is
The apparatus for obtaining an optimal transmission rate, characterized in that the distance between the symbols of the furthest distance from 0 on the symbol constellation of the PAM. 13. The method of claim 12, wherein the modulation magnitude value is
Apparatus for obtaining an optimal transmission rate characterized by the use of water filling or bit loading techniques. The method of claim 8, wherein the rate is a condition for having a maximum value
The two different data have a positive value, the maximum transmission optical power is less than the preset optical power, and the bit error rate that can be obtained by using a modulation technique that modulates the two different data is arbitrary. And an apparatus for obtaining an optimal transmission rate, characterized in that it is less than a threshold of. 9. The method of claim 8, wherein modulating the two different data is
And determining a modulation scheme according to the obtained transmission rate and modulation size to modulate the pulse amplitude intensity of the two different data.

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