A method for indoor visible light positioning using NLOS suppression and OCDMA

Abstract

The present invention discloses a NLOS-suppressed OCDMA indoor visible light positioning method, which is based on OCDMA (Optical Code Division Multiple Access) technology, and effectively alleviates the problem of poor positioning performance at the edges and corners of a room due to the influence of multipath effects in a traditional indoor visible light positioning system. The core idea of ​​the present invention is to assign an optical address code with good orthogonality to each LED, use the orthogonality between codes to distinguish different LED signals at the receiving end, calculate the correlation value, and use the correlation value in combination with the corresponding positioning algorithm to complete the positioning. The difference between this design and the traditional positioning method is that the traditional positioning method directly uses the received power at the receiving end and combines the channel model for positioning, while the present design realizes positioning by calculating the correlation value between the mixed signal and the local optical address code at the receiving end. Due to the low correlation between the NLOS (Non-Line-of-Sight) signal and the LOS (Line-of-Sight) signal, the influence of the NLOS signal on the result after the correlation calculation is almost negligible, so the positioning performance of the room edge, corner area and other areas that are greatly affected by the NLOS signal can be improved, which makes up for the defects of the traditional positioning method to a certain extent.

Description

Technical Field

[0001] The present invention belongs to the technical field of visible light communication, and is particularly suitable for positioning in an indoor visible light model where the room positioning performance is greatly affected by multipath reflection. Background Art

[0002] Unlike traditional indoor visible light positioning systems, which usually rarely consider the impact of multipath reflection in the room, this technology fully considers the impact of multipath reflection on indoor positioning performance, especially the edges and corners of the room, which are severely affected by reflection. The reason for taking this approach is that, in actual scenarios, multipath reflection is inevitable in the room, and there will be more or less diffuse reflection on the four walls. This is based on actual scenarios. Reason two, OCDMA technology does not require strict synchronization between transceivers, and does not require complex filter design. It has the advantages of strong anti-interference ability, random access, and good confidentiality. Reason three, in fact, the positioning performance of the indoor positioning system is greatly affected by multipath reflection, which is usually the main source of indoor positioning error. It is very valuable to analyze and suppress the impact of multipath reflection. This technology can greatly reduce the impact of multipath reflection.

[0003] With the development of mobile communications, the demand for positioning-based applications and services has increased dramatically, which has also promoted the continuous development and research of new indoor positioning technologies. Common indoor visible light positioning algorithms include TOA (Time of Arrival), TDOA (Time Difference of Arrival), AOA (Angle of Arrival), and RSS (Received Signal Strength). At present, the indicators for measuring positioning performance are: positioning accuracy, complexity, scalability, and equipment cost. Since the RSS positioning algorithm is simple to implement, flexible and scalable, and has low hardware requirements, this positioning algorithm has been studied more at this stage, but the RSS-based positioning system is usually affected by multipath reflection, resulting in poor positioning performance in the edge and corner areas of the room. Usually, the traditional visible light positioning system that uses the received signal strength requires three LEDs to complete the positioning process, obtains the power of the three optical signals at the receiving end, and then uses the received signal power and channel model to inversely solve the distance between different LEDs and the receiver, and then uses the trilateral measurement method to achieve positioning. This method is simple and easy to use, and has a good positioning effect in the center of the room. However, due to the diffuse reflection of light in the room, the edge of the room has a poor positioning effect due to the superposition of reflected power, and the farther away from the center of the room, the worse the positioning effect. The optical signal is transmitted in the wireless channel and finally received by the photodetector (PD) at the receiving end, and superimposed as a mixed signal at the receiving end. The three signals interfere with each other at the receiving end, so it is impossible to directly separate each LED signal from the mixed signal, and positioning cannot be completed. Multiplexing technology is usually used to solve this problem. Traditional multiplexing technologies usually include frequency division multiplexing, time division multiplexing and code division multiplexing.

[0004] So far, a large number of scholars have conducted in-depth research on indoor positioning technology based on frequency division multiplexing, and have achieved great results, but it usually has the problem of filter design. Later, some scholars proposed to use DSP processing instead of filter design, but the problem is that a large number of additional equipment is introduced, which greatly increases the system cost. In addition, in the positioning system of frequency division multiplexing, frequency adjustment is very inconvenient, especially when there are a large number of LED lights in the LED network, it is impractical to adjust the frequency for each LED light. Therefore, some scholars proposed an indoor positioning system based on time division multiplexing technology. This system does not have these problems faced by the frequency division multiplexing system, but it requires strict synchronization between the receiver and the transmitter, which is difficult to achieve in practical applications, especially in today's high-speed data transmission. It is very difficult to achieve strict synchronization of the system. Code division multiplexing uses the orthogonality between codes to distinguish different signals. There is no filter design, frequency adjustment, and synchronization problem, but the address code used in the traditional code division multiplexing system is mostly bipolar, which is not suitable for optical systems. Summary of the invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to propose a method for indoor visible light positioning based on OCDMA with NLOS suppression based on correlation detection in view of the shortcomings of the background technology. This design scheme mainly provides a simple, effective, novel and feasible design scheme for indoor visible light positioning in rooms that are greatly affected by multipath reflection. It uses correlation values ​​instead of received power for positioning, effectively suppresses the influence of NLOS components on the positioning system, and improves the positioning accuracy of room edges and corners.

[0006] Technical solution: The present invention proposes a NLOS suppression OCDMA indoor visible light positioning method based on correlation detection, which specifically includes the following steps:

[0007] Step 1, select an optical address code pattern, and select a corresponding number of code words from the code set as pre-selected code words according to the number of LED lights in the LED network in the room, let them be T1, T2, T3, ..., Tn, and the corresponding optical address code used for recovery at the receiving end is R1, R2, R3, ..., Rn;

[0008] Step 2, respectively calculate and draw the autocorrelation curves of T1, T2, T3, ..., Tn. If the autocorrelation curves all have a higher autocorrelation peak value and a lower autocorrelation side lobe, proceed to step 3, otherwise return to step 1;

[0009] Step 3, respectively calculate and draw the cross-correlation curves between T1, T2, T3, ..., Tn. If the cross-correlation curves have a lower cross-correlation threshold, proceed to step 4, otherwise return to step 1;

[0010] Step 4, perform OOK modulation on T1, T2, T3, ..., Tn respectively, and the modulated signals are respectively set to S1, S2, S3, ..., Sn;

[0011] Step 5, respectively send S1, S2, S3, ..., Sn to the driving circuit to drive the LED and send a signal by flashing;

[0012] Step 6: After the receiver receives the mixed signal of multiple LED signals, it undergoes photoelectric conversion and OOK demodulation to obtain the signal r(t);

[0013] Step 7, calculate the correlation value between r(t) and R1 to obtain the correlation value θ1;

[0014] Step 8: Repeat step 7 to obtain Θ2, Θ3, ..., Θ n ;

[0015] Step nine, obtaining the positioning result according to the OCDMA indoor visible light positioning algorithm.

[0016] The NLOS suppression OCDMA indoor visible light positioning method based on correlation detection of the present invention is characterized in that: in step 1, since the indoor visible light positioning system needs to complete positioning, the receiving end needs to receive at least 3 LED light signals, so the number of LED lights in the LED network in the room must be no less than 3;

[0017] The NLOS suppression OCDMA indoor visible light positioning method based on correlation detection of the present invention is characterized in that: in step 2, the autocorrelation characteristic satisfies:

[0018]

[0019] w is the optical address code weight, τ is the quantized optical address code delay, λ a is the maximum autocorrelation sidelobe, N is the length of the optical address code, and λ is required a As small as possible, so that the receiver can quickly find the synchronization position based on the autocorrelation peak;

[0020] The NLOS suppression OCDMA indoor visible light positioning method based on correlation detection of the present invention is characterized in that: in step three, the cross-correlation characteristic satisfies:

[0021]

[0022] Where λ c is the maximum cross-correlation threshold, requiring λ c As small as possible, this is to reduce the multiple access interference introduced by the mutual interference between the optical address codes, which largely determines the positioning performance of the system;

[0023] The NLOS suppression OCDMA indoor visible light positioning method based on correlation detection of the present invention is characterized in that: in step 4, the pre-selected code words T1, T2, T3, ..., Tn should satisfy the following code selection rules:

[0024] 1) Code sets should have larger autocorrelation peaks and smaller autocorrelation sidelobes;

[0025] 2) After all codewords in the code set are shifted, specific codewords can still be identified through relevant characteristics;

[0026] 3) All codewords in the code set can be identified from other mixed codewords, that is, a small cross-correlation threshold is required;

[0027] The NLOS suppression OCDMA indoor visible light positioning method based on correlation detection of the present invention is characterized in that: in step nine, the indoor visible light positioning algorithm of the OCDMA mode is essentially derived based on the traditional positioning algorithm, and the positioning calculation formula is as follows:

[0028]

[0029]

[0030] In the above formula, P ri is the power of the i-th LED lamp received by the receiver, P ti is the emission power of the ith LED lamp, λ i is the correlation value between Ti and Ri, P NLOS is the sum of all reflected powers, It is the multiple access interference introduced when the correlation characteristics between optical address codes are not ideal. error It is the distance error caused by multiple access interference;

[0031]

[0032] D i is the distance between the ith LED: (xi,yi,zi) and the receiver Rx: (x,y,z),

[0033] m=-ln2 / ln(cos(φ 1 / 2 )),

[0034] m is the Lambert index;

[0035] After obtaining the transmission distance, the positioning result can be obtained according to the trilateration method.

[0036] Beneficial effects:

[0037] The present invention is based on the existence of multipath reflection in the room, proposes to use OCDMA to build an indoor visible light positioning system, provides a calculation method for the positioning function, and uses correlation values ​​for positioning, which makes up for the defect that the traditional indoor positioning system is greatly affected by multipath reflection and improves the performance of indoor positioning;

[0038] 1. The present invention establishes an indoor optical positioning system model based on OCDMA. The solution is based on OCDMA technology and does not require complex filter design, frequency adjustment, and system synchronization. The positioning process is simple and easy, and the positioning result has high accuracy, which meets the indoor positioning requirements;

[0039] 2. The present invention performs positioning based on correlation values, which can effectively suppress the influence of NLOS on positioning performance and improve the positioning accuracy of room edges and corners. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the OCDMA indoor positioning room model diagram

[0041] Figure 2OCDMA indoor visible light positioning principle block diagram

[0042] Figure 3 This is the concept diagram of OCDMA indoor visible light positioning DETAILED DESCRIPTION

[0043] The purpose, advantages and features of the present invention will be illustrated and explained by the non-limiting description of the following preferred embodiments. These embodiments are only typical examples of the application of the technical solution of the present invention, and any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection claimed by the present invention.

[0044] The present invention proposes a NLOS suppression OCDMA indoor visible light positioning method based on correlation detection, such as Figure 1 , is the model diagram of the scheme. The room model in the figure is 5m*5m*3m, and the height of the receiver is 0.85m. The address code generated by the address code generator is required to meet the code selection rules. After signal processing, such as OOK modulation, the address code is sent to the drive circuit to drive the LED to emit light and transmit data. After a certain amount of processing, the receiving end obtains the information required by the positioning algorithm of the scheme and performs positioning.

[0045] like Figure 2 This is the principle block diagram of the solution. The address code that meets the requirements is sent to the drive circuit to drive the LED after OOK modulation. The signal is transmitted through the wireless channel and finally received at the PD receiving end. After photoelectric conversion and OOK demodulation, it is correlated with the local optical address code and finally the obtained correlation value is sent to the positioning module to perform the positioning operation.

[0046] like Figure 3 This is a conceptual diagram of the positioning of the present invention. The diagram reveals that, unlike the traditional positioning concept, the present invention uses correlation values ​​instead of received power for positioning, and does not require filter design. It only requires an integrator at the receiving end to implement relevant calculations. The present invention can effectively suppress the interference of NLOS to the positioning system.

[0047] The specific implementation steps of the present invention are as follows:

[0048] Step 1, select an optical address code pattern, and select a corresponding number of code words from the code set as pre-selected code words according to the number of LED lights in the LED network in the room, let them be T1, T2, T3, ..., Tn, and the corresponding optical address code used for recovery at the receiving end is R1, R2, R3, ..., Rn;

[0049] Step 2, respectively calculate and draw the autocorrelation curves of T1, T2, T3, ..., Tn. If the autocorrelation curves all have a higher autocorrelation peak value and a lower autocorrelation side lobe, proceed to step 3, otherwise return to step 1;

[0050] Step 3, respectively calculate and draw the cross-correlation curves between T1, T2, T3, ..., Tn. If the cross-correlation curves have a lower cross-correlation threshold, proceed to step 4, otherwise return to step 1;

[0051] Step 4, perform OOK modulation on T1, T2, T3, ..., Tn respectively, and the modulated signals are respectively set to S1, S2, S3, ..., Sn;

[0052] Step 5, respectively send S1, S2, S3, ..., Sn to the driving circuit to drive the LED and send a signal by flashing;

[0053] Step 6: After receiving the mixed signal of multiple LED signals, the receiver performs photoelectric conversion and OOK demodulation to obtain the signal r(t);

[0054] Step 7, perform correlation calculation on r(t) and R1 to obtain correlation value θ1;

[0055] Step 8: Repeat step 7 to obtain Θ2, Θ3, ..., Θ n ;

[0056] Step nine, obtaining the positioning result according to the OCDMA indoor visible light positioning algorithm.

[0057] Taking the three-light positioning system as an example, the transmitter uses the optical address code T1, T2, T3. In this example, it is assumed that T1, T2, T3 have ideal orthogonal characteristics. The codewords are modulated by OOK to obtain S1, S2, S3. The corresponding optical address codes restored by the receiver are R1, R2, R3. Assuming that the transmission power of the i-th LED light is P ti , then S i It can be simply expressed as:

[0058] S i (t) = P ti T i (t),

[0059] r(t) is the mixed signal received by the PD receiver:

[0060] r(t)=S1(t)H 01 +S2(t)H 02 +S3(t)H 03 +S NLOS

[0061] =P t1 H 01 T1(t)+P t2 H 02 T2(t)+P t3 H 03 T3(t)+S NLOS ,

[0062] Among them, H 0i S represents the DC gain of the channel from the ith LED to the receiver. NLOS Represents the sum of all reflected signals of multipath propagation. If the transmission power of all LEDs is equal, P t1 =P t2 =P t3 =P, then:

[0063] r(t)=P t (H 01 T1(t)+H 02 T2(t)+H 03 T3(t))+S NLOS ,

[0064] Take the calculation of Θ1 as an example:

[0065] Θ1=r(t)⊙R1(t)=P t (H 01 T1(t)⊙R1(t)+H 02 T2(t)⊙R1(t)+H 03 T3(t)⊙R1(t))+S NLOS ⊙R1(t),

[0066] Among them, ⊙ represents the relevant calculation, R i (t) represents the light address code corresponding to the i-th LED for restoration. Let the last term in the above formula, i.e. S NLOS ⊙R1(t), is E NLOS Due to the low correlation between NLOS and LOS signals, E NLOS Very small.

[0067] Let λ i T i (t) and R i (t), then:

[0068] θ1=P t (λ1H 01 +λ2H 02 +λ3H 03 )+E NLOS

[0069] =P t λ1H 01 +E NLOS =λ1P r1 +E NLOS ,

[0070] Where P NLOSIndicates the NLOS power reaching the receiver after being reflected by the wall.

[0071] Similarly, P ri =Θ i / λ i +P NLOS , according to the channel model, the transmission distance D is inversely solved i ,

[0072]

[0073] Where D error is the distance error. Let the horizontal distance between the i-th LED and the PD receiver be l i ,

[0074]

[0075] According to the trilateral measurement method, the following set of equations can be listed:

[0076] (xx i ) 2 +(yy i ) 2 = l i 2 ,

[0077] Where i = 1, 2, 3. The above equation is transformed into a matrix form, and the coordinates of the position of the point to be measured are obtained by least squares estimation: X = [x, y] T :

[0078] X=(A T A) -1 A T B,

[0079] in

Claims

1. A NLOS suppression OCDMA indoor visible light positioning method, characterized in that: The specific steps include: Step 1, select an optical address code pattern, and select a corresponding number of code words from the code set as pre-selected code words according to the number of LED lights in the LED network in the room, let them be T1, T2, T3, ..., Tn, and the corresponding optical address code used for recovery at the receiving end is R1, R2, R3, ..., Rn; Step 2, respectively calculate and draw the autocorrelation curves of T1, T2, T3, ..., Tn. If the autocorrelation curves all have a higher autocorrelation peak value and a lower autocorrelation side lobe, proceed to step 3, otherwise return to step 1; Step 3, respectively calculate and draw the cross-correlation curves between T1, T2, T3, ..., Tn. If the cross-correlation curves have a lower cross-correlation threshold, proceed to step 4, otherwise return to step 1; Step 4, perform OOK modulation on T1, T2, T3, ..., Tn respectively, and the modulated signals are respectively set to S1, S2, S3, ..., Sn; Step 5, respectively send S1, S2, S3, ..., Sn to the driving circuit to drive the LED and send a signal by flashing; Step 6: The receiver receives the mixed signal of multiple LED signals, converts them into photoelectric signals, and performs OOK demodulation to obtain the signal r(t); Step 7, calculate the correlation value between r(t) and R1 to obtain the correlation value θ1; Step 8: Repeat step 7 to obtain Θ2, Θ3, ..., Θ n ; Step nine, obtaining the positioning result according to the OCDMA indoor visible light positioning algorithm; In step 2, the autocorrelation curve satisfies: w is the weight of the optical address code, x is the codeword in the code set, is a modulo N operation, R xx is the calculated autocorrelation value, τ is the quantized optical address code delay, λ a is the maximum autocorrelation sidelobe, N is the length of the optical address code; In step 3, the cross-correlation curve satisfies: Where λ c is the maximum cross-correlation threshold, x and y are both codewords in the code set, is a modulo N operation, R xy is the calculated cross-correlation value, τ is the quantized optical address code delay, λ a is the maximum autocorrelation sidelobe, N is the length of the optical address code; In step 4, the pre-selected code words T1, T2, T3, ..., Tn have the following characteristics: 1) There are larger autocorrelation peaks and smaller autocorrelation sidelobes between code sets; 2) After all codewords in the code set are shifted, a specific codeword can be identified by its correlation characteristics; 3) All codewords in the code set can be identified from other mixed codewords with a small cross-correlation threshold; In step nine, the indoor visible light positioning algorithm of OCDMA mode, the positioning calculation formula is as follows: In the above formula, P ri is the power of the i-th LED lamp received by the receiver, P ti is the emission power of the ith LED lamp, λ i is the correlation value between Ti and Ri, P NLOS is the sum of all reflected powers, It is the multiple access interference introduced when the correlation characteristics between optical address codes are not ideal. error is the distance error caused by multiple access interference; A r is the effective area of ​​the receiver; g is the gain of the optical concentrator, P ti is the emission power of the ith LED, h i is the height of the i-th LED from the receiver; D i is the distance between the ith LED: (xi,yi,zi) and the receiver Rx: (x,y,z), m=-ln2 / ln(cos(φ 1 / 2 )), m is the Lambert index; After the transmission distance is obtained, the coordinates of the point to be measured are calculated according to the trilateration method.

2. The NLOS suppression OCDMA indoor visible light positioning method according to claim 1, characterized in that: In step 1, the receiving end receives at least 3 LED light signals, and the number of LED lights in the LED network in the room is not less than 3.

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