A wireless optical communication and positioning system

Abstract

The present invention relates to a wireless optical communication and positioning system, including a wireless optical communication device and a wireless optical positioning device, wherein the wireless optical communication device includes a signal transmitting end for transmitting signals and a signal receiving end for receiving signals, and the wireless optical positioning device is used to position a mobile terminal. The system of the present invention does not need to send additional positioning information, and can simultaneously realize communication and positioning using only communication signals. Not only does it not have the problem of signal interference, but it also greatly improves the utilization rate of spectrum resources, so that mobile communication and positioning can be deployed simultaneously in the same indoor system, realizing the real integration of communication and positioning.

Description

Technical Field

[0001] The present invention relates to the field of communication and positioning technology, and in particular to a wireless optical communication and positioning system. Background Art

[0002] White light-emitting diodes (LEDs) are developing rapidly in the lighting market. In addition to lighting, LEDs can also be used in wireless optical communications or wireless optical positioning. On the one hand, wireless optical communication based on white light LEDs has become a promising indoor wireless communication technology. On the other hand, wireless optical positioning has also received widespread attention. However, wireless optical communication and wireless optical positioning are usually designed and deployed separately. When the two work at the same time, they cannot coexist because they occupy each other's spectrum resources. Therefore, the integration of the two has been a hot topic of research in recent years.

[0003] Existing technologies include:

[0004] First, the traditional indoor wireless optical positioning method, such as the indoor wireless optical positioning method based on received signal strength (RSS). This method uses the received signal strength to estimate the distance between transceivers, and then uses three-sided positioning to estimate the location coordinates of the terminal. However, when implementing the wireless optical positioning method, the real-time mobility of the terminal is usually ignored, and most of them only consider the case where the receiver is fixed, that is, the receiver is fixed at various discrete points indoors to receive the wireless optical positioning signal.

[0005] Second, for mobile communication terminals, some wireless optical communication solutions have been proposed. For example, the patent "A mobile visible light communication channel equalization method" (patent number: ZL201811231920.9). This method takes into account the single-input single-output (SISO) scenario. In the SISO scenario, different transmitters send the same optical signal to the receiver. At this time, the optical channel is relatively simple. By taking the inverse of different subcarrier channels, the received signal can be restored.

[0006] Third, in addition, in indoor wireless optical communication and wireless optical positioning systems, the simultaneous operation of wireless optical communication and wireless optical positioning systems will interfere with each other, so it is often necessary to stagger the spectrum resources occupied by the two systems through time division multiplexing or frequency division multiplexing so that they can work simultaneously. For example, in the conference paper "Visible light positioning and communication cooperative systems" of ICOCN 2017, two cooperative systems for wireless optical positioning and wireless optical communication were proposed based on the spread spectrum plug-in (OPID) for optical identification. In scheme 1, if the system only needs wireless optical positioning, the spread spectrum code can be simply used as OPID to identify different LEDs. In scheme 2, OPID contains transmitter information, all of which is spread with different spread spectrum codes and interspersed in the wireless optical communication signal. It is considered to be a good solution to overcome the mutual exclusion between wireless optical positioning and wireless optical communication systems.

[0007] The disadvantages of the prior art are as follows:

[0008] First, in the traditional indoor wireless optical positioning based on received signal strength, the receiver is fixed at a discrete position to receive the wireless optical positioning signal, and the continuous process of terminal movement is not taken into account. For a mobile receiver, when performing wireless optical positioning during movement, the estimated channel state information is inaccurate due to channel changes, which inevitably reduces the positioning accuracy in the motion trajectory.

[0009] Second, a mobile visible light communication channel equalization method, this technology can solve the problem of inaccurate channel estimation under mobile channels, but this method can only be applied to single-input single-output (SISO) scenarios, and the system capacity is greatly limited; and there is no such method in MIMO scenarios, so the system transmission quality will still deteriorate due to the time-varying nature of the channel when the terminal moves. In addition, this method only considers communication performance and only has communication functions, not positioning functions. When other positioning systems are deployed, they will still interfere with them, making it difficult to achieve effective integration of communication and positioning.

[0010] Third, based on the spread spectrum plug-in of optical recognition, a collaborative system for wireless optical positioning and wireless optical communication is proposed. This system seems to combine wireless optical communication and wireless optical positioning together, but in fact, the information used for positioning by the system still needs to occupy the spectrum resources of the communication system, and it does not truly achieve the integration of communication and positioning. In addition, this technology uses code division multiple access technology (CDMA), which requires strict synchronization between transmitters and between transmitters and receivers, and the system complexity is high; specific communication resources are still required to send positioning information, and the utilization rate of spectrum resources is low.

[0011] In summary, the existing technology has not really combined wireless optical positioning and wireless optical communication effectively. Summary of the invention

[0012] To this end, the technical problem to be solved by the present invention is to overcome the problem in the prior art that wireless optical positioning and wireless optical communication cannot be effectively combined.

[0013] In order to solve the above technical problems, the present invention provides a wireless optical communication and positioning system, including a wireless optical communication device and a wireless optical positioning device;

[0014] The wireless optical communication device comprises a signal transmitting end and a signal receiving end;

[0015] The signal transmitting end is used to transmit a signal, and includes a signal source module, a mapping module, a first STBC encoding module, an IFFT module, a CP adding module, a parallel-to-serial conversion module, a digital-to-analog conversion module and an LED light source connected in sequence;

[0016] in,

[0017] Source module: used to generate bit stream data;

[0018] Mapping module: used to convert the bit stream data generated by the source module into corresponding OFDM symbols, and then send them to the STBC encoding module;

[0019] The first STBC encoding module is used to perform STBC encoding on the OFDM symbols obtained by the mapping module to form an STBC matrix X n (k), and then sent to the IFFT module;

[0020] IFFT module, CP adding module, parallel-to-serial conversion module, digital-to-analog conversion module: used to convert X n (k) performing IFFT transformation, adding cyclic prefix, parallel-to-serial conversion, and digital-to-analog conversion;

[0021] LED light source: used to send out the signal after digital-to-analog conversion;

[0022] The signal receiving end is used to receive signals, including a photodetector PD, an analog-to-digital conversion module, a serial-to-parallel conversion module, a CP removal module, an FFT module, a mobile channel estimation module, an STBC decoding module, a subcarrier symbol decision module, an inverse mapping module and a destination module connected in sequence, the output end of the subcarrier symbol decision module is also connected to a second STBC encoding module, and the output end of the second STBC encoding module is connected to a mobile channel estimation module;

[0023] in,

[0024] Photodetector PD: used to receive the signal from the LED light source;

[0025] Analog-to-digital conversion module, serial-to-parallel conversion module, CP removal module, and FFT module: used to convert the signal received by the photodetector PD into analog-to-digital, serial-to-parallel, remove the cyclic prefix, and obtain the signal through FFT transformation Send to the mobile channel estimation module;

[0026] Mobile channel estimation module: used to estimate the mobile channel and estimate the channel state information Send to STBC decoding module for symbol decoding;

[0027] STBC decoding module: used to decode the signal and channel state information estimate Calculate the estimated value of the transmitted signal

[0028] Subcarrier symbol decision module: used to estimate the value of the transmitted signal Make a symbol decision and record the decision value as

[0029] The second STBC encoding module: used for the decision value Perform STBC encoding to obtain a new estimated decoding matrix The new estimated decoding matrix Together with the newly received signal, it is used for the next channel estimation of the mobile channel estimation module;

[0030] Inverse mapping module: used to convert the decision value The inverse mapping restores the bit stream form of the transmitted signal;

[0031] Sink module: used to receive the bit stream of the restored signal and complete the communication;

[0032] The wireless optical positioning device comprises a channel DC gain estimation module, a distance measurement module and a three-sided positioning module connected in sequence;

[0033] in,

[0034] Channel DC gain estimation module: used to estimate the value using channel state information Estimate the channel DC gain;

[0035] Distance measurement module: calculates the distance between the photodetector PD and the LED light source using the estimated value of the channel DC gain;

[0036] Three-side positioning module: used to estimate the coordinate positions of two photoelectric detectors PD, and use the position coordinates between the two photoelectric detectors PD as the estimated coordinates of the mobile terminal to complete the positioning.

[0037] In one embodiment of the present invention, it also includes:

[0038] Power monitoring module: used to control the weight calculation module and the observation length control module according to the power of the terminal. When the power of the terminal is lower than the set threshold power E, the power monitoring module directly sends control information to the weight calculation module, using the equal weight distribution in formula (4). At the same time, the power monitoring module sends control information to the observation length control module to select the default observation length L. 1 ; When the power of the terminal is higher than the set threshold power E, the control information will enter the speed sensor module, so that the speed sensor module that is closed will enter the working state;

[0039] Speed ​​sensing module: used to control the weight calculation module and the observation length control module according to the terminal's moving speed. When the terminal's moving speed is lower than the set threshold speed V 1 >0, the speed sensing module sends control information to the weight calculation module, using the equal weight distribution in formula (4); when the terminal speed is higher than the set threshold speed V 1 When the terminal moves at a speed less than or equal to V, the unequal weight distribution in formula (5) is used. At the same time, the speed sensing module sends control information to the observation length control module: 1 When the observation length L is selected 1 ; When the terminal moves at a speed of V 1 and V 2 When the observation length L is between 2 ; When the terminal moves at a speed of V 2 and V 3 When the observation length L is between 3 , when the terminal's moving speed is greater than V 3 When the observation length L is selected 4 , where V 1 <V 2 <V 3 , L 1 <L 2 <L 3 <L 4 ; The observation length is the number of the first n STBC matrices of the current signal used to solve the channel state information;

[0040] The observation length control module is used to send the generated observation length to the weight calculation module;

[0041] The weight calculation module is used to calculate the weight assigned to each channel state information according to the control information sent by the power monitoring module or the speed sensing module in combination with the observation length selected by the observation length control module, and send the weight to the mobile channel estimation module;

[0042] The mobile channel estimation module performs mobile channel estimation according to the received weights.

[0043] In one embodiment of the present invention, the FFT module obtains a signal through FFT transformation. The formula is:

[0044]

[0045] Where j represents the jth photodetector PD, n represents the nth STBC matrix, in is the kth transmitted subcarrier symbol of the lth OFDM symbol at the i-th LED, i = 1, 2, ... N T ,l=1,2,...N T ; in is the kth received subcarrier symbol of the lth OFDM symbol; in is the channel response between the i-th LED and the j-th PD, is the noise matrix.

[0046] In one embodiment of the present invention, the STBC decoding module is based on the signal and channel state information estimate Calculate the estimated value of the transmitted signal The formula is:

[0047]

[0048] Where, formula (2) satisfies N T =4.

[0049] In one embodiment of the present invention, the estimated value of the transmitted signal In N T =2, it is expressed as:

[0050]

[0051] In one embodiment of the present invention, the equal weight distribution of formula (4) is performed when the terminal's moving speed V≤V 1 When: the channel state information from n-L+1th to nth is summed and the average value is taken as the value of the n+1th channel state information, then the channel estimation of the mobile channel estimation module is expressed as:

[0052]

[0053] Where L is the observation length of the STBC matrix and its value is L 1 .

[0054] In one embodiment of the present invention, the unequal weight allocation of formula (5) satisfies: for the n-L+1th to nth channel state information, the weight allocated to each channel state information is normalized and expressed as Then the channel estimation of the mobile channel estimation module is expressed as:

[0055]

[0056] Where L is the observation length of the STBC matrix, V is the speed of the terminal uniform motion, when V 1 <V≤V 2 When L is L 2 ; When V 2 <V≤V 3 ,L takes the value of L 3 ; When V>V 3 When L is L 4 .

[0057] In one embodiment of the present invention, the distance measurement module calculates the distance between the photodetector PD and the LED light source using the estimated value of the channel DC gain, and the formula is:

[0058]

[0059] Where m is the Lambertian emission order, a R is the effective area of ​​PD, T s (ψ) is the filter gain, g(ψ) is the concentrator gain, h is the vertical distance between LED and PD, is the estimated value of the channel DC gain between the i-th LED and the j-th PD.

[0060] In one embodiment of the present invention, the estimated value of the DC gain of the channel between the i-th LED and the j-th PD is Specifically:

[0061] The channel state information estimate obtained by formula (5) is The elements in the matrix are constructed using the formula:

[0062]

[0063] Where N P is the number of OFDM subcarriers; then after time-frequency transformation, the channel DC gain is extracted from the channel impulse response, the formula is:

[0064]

[0065] In one embodiment of the present invention, the three-side positioning module estimates the coordinate positions of the two photodetectors PD, and uses the position coordinates between the two photodetectors PD as the estimated coordinates of the mobile terminal to complete the positioning, specifically:

[0066] Based on formulas (6), (7), and (8), the jth PD is trilaterally positioned to obtain its position coordinates:

[0067]

[0068] Then the estimated coordinate formula of the mobile terminal is:

[0069]

[0070] In the formula, is the two-dimensional position coordinate of the first photodetector PD, is the two-dimensional position coordinate of the second photodetector PD.

[0071] The above technical solution of the present invention has the following advantages compared with the prior art:

[0072] The present invention performs positioning while communicating. This solution does not need to occupy additional communication resources to transmit positioning information, greatly improving the utilization rate of spectrum resources and realizing the integration of communication and positioning. In addition, this solution does not need to adopt any multiplexing technology, does not require strict synchronization between transceivers, and has low system complexity;

[0073] The present invention can adapt to time-varying channels, improve the problem of decreased communication and positioning performance under mobile channels, and at the same time, the present invention can dynamically track and locate the terminal when it moves in real time;

[0074] In the present invention, the former uses multiple LEDs and multiple PDs to increase the communication capacity and communication quality; at the same time, in the process of decision feedback channel estimation, the present scheme uses STBC coding to reconstruct the decoded signal into an STBC matrix, avoiding the feedback matrix during channel estimation. Irreversible situations may occur, which ensures that this solution can work properly in MIMO systems;

[0075] The present invention optimizes the traditional equal-weight channel estimation method, specifically utilizes a power monitoring module and a speed sensing module, controls a weight calculation module and an observation length control module according to different situations, and selects a better weight distribution method, which can ensure that a portion of the noise is averaged and make the estimated channel more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0077] Figure 1 is a block diagram of a wireless optical communication and positioning system in an embodiment of the present invention;

[0078] Figure 2 is a comparison chart of bit error rate performance when using or not using the system of the present invention under different LED transmission powers in an embodiment of the present invention;

[0079] Figure 3 is a comparison diagram of bit error rate performance of using or not using the system of the present invention at different moving speeds in an embodiment of the present invention;

[0080] Figure 4 It is a schematic diagram of positioning results of a receiver along different test routes when the method of the present invention is used or not used in an embodiment of the present invention. DETAILED DESCRIPTION

[0081] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0082] Embodiment 1

[0083] Reference Figure 1 As shown, the present invention relates to a wireless optical communication and positioning system, comprising a wireless optical communication device and a wireless optical positioning device; the wireless optical communication device comprises a signal transmitting end and a signal receiving end;

[0084] (1) A signal transmitting end is used to transmit a signal, and includes a signal source module, a mapping module, a first STBC encoding module, an IFFT module, a CP adding module, a parallel-to-serial conversion module, a digital-to-analog conversion module, and an LED light source connected in sequence; wherein:

[0085] Source module: used to generate bit stream data;

[0086] Mapping module: used to convert the bit stream data generated by the source module into corresponding OFDM symbols, and then send them to the STBC encoding module;

[0087] The first STBC encoding module is used to perform STBC encoding on the OFDM symbols obtained by the mapping module to form an STBC matrix X n (k), and then sent to the IFFT module;

[0088] IFFT module, CP adding module, parallel-to-serial conversion module, digital-to-analog conversion module: used to convert X n(k) performing IFFT transformation, adding cyclic prefix, parallel-to-serial conversion, and digital-to-analog conversion;

[0089] LED light source: used to send out the signal after digital-to-analog conversion;

[0090] (2) A signal receiving end is used to receive a signal, including a photodetector PD, an analog-to-digital conversion module, a serial-to-parallel conversion module, a CP removal module, an FFT module, a mobile channel estimation module, an STBC decoding module, a subcarrier symbol decision module, an inverse mapping module and a destination module connected in sequence, wherein the output end of the subcarrier symbol decision module is also connected to a second STBC encoding module, and the output end of the second STBC encoding module is connected to a mobile channel estimation module; wherein

[0091] Photodetector PD: used to receive the signal from the LED light source;

[0092] Analog-to-digital conversion module, serial-to-parallel conversion module, CP removal module, and FFT module: used to convert the signal received by the photodetector PD into analog-to-digital, serial-to-parallel, remove the cyclic prefix, and obtain the signal through FFT transformation Send to the mobile channel estimation module;

[0093] Mobile channel estimation module: used to estimate the mobile channel and estimate the channel state information Send to STBC decoding module for symbol decoding;

[0094] STBC decoding module: used to decode the signal and channel state information estimate Calculate the estimated value of the transmitted signal

[0095] Subcarrier symbol decision module: used to estimate the value of the transmitted signal Make a symbol decision and record the decision value as

[0096] The second STBC encoding module: used for the decision value Perform STBC encoding to obtain a new estimated decoding matrix The new estimated decoding matrix Together with the newly received signal, it is used for the next channel estimation of the mobile channel estimation module;

[0097] Inverse mapping module: used to convert the decision value The inverse mapping restores the bit stream form of the transmitted signal;

[0098] Sink module: used to receive the bit stream of the restored signal and complete the communication;

[0099] (3) The wireless optical positioning device includes a channel DC gain estimation module, a distance measurement module and a three-sided positioning module connected in sequence; wherein:

[0100] Channel DC gain estimation module: used to estimate the value using channel state information Estimate the channel DC gain;

[0101] Distance measurement module: calculates the distance between the photodetector PD and the LED light source using the estimated value of the channel DC gain;

[0102] Three-side positioning module: used to estimate the coordinate positions of two photoelectric detectors PD, and use the position coordinates between the two photoelectric detectors PD as the estimated coordinates of the mobile terminal to complete the positioning.

[0103] The following is a general introduction to the system of this embodiment:

[0104] The whole system is divided into three parts, namely the transmitter, the channel and the receiver (i.e. the mobile terminal). At the transmitter, only the wireless optical communication signal is transmitted for communication data transmission. At the receiver, channel estimation is performed to restore the wireless optical communication signal, thereby realizing the transmission of communication data. While performing channel estimation, the channel state information (CSI) obtained by the way will be further used to obtain the position of the receiver indoors, thereby realizing positioning. Therefore, through this idea, the system simultaneously realizes the dual functions of wireless optical communication and wireless optical positioning. The system schematic diagram is shown in the figure. Figure 1 shown.

[0105] At the transmitter, the system converts N T LEDs are installed on the ceiling of the room as transmitting antennas. After the data stream is mapped, it enters the STBC encoding module, and the encoded parallel data stream is then converted into a serial data stream. Finally, these STBC symbols are modulated into OFDM symbols and emitted by each LED light source. After passing through the MIMO channel, these wireless optical communication signals will reach the mobile receiver.

[0106] At the receiver, N R A photodetector PD is installed on the mobile receiver as a receiving antenna. After capturing the received signal, the PD converts these serial data streams into parallel data streams. Then, these parallel OFDM data are sent to the STBC decoding module for decoding. The decoded signal is re-STBC encoded after symbol judgment to obtain a new estimated decoding matrix. Then, this matrix and the newly received signal are used together for the next channel estimation. By repeating the above process continuously, dynamic estimation of the mobile channel can be achieved.

[0107] At the same time, thanks to the improvement of channel estimation accuracy, CSI can be further used to estimate the position of the mobile terminal. This embodiment uses the CSI estimated during the communication process and the Lambertian radiation model to calculate the distance between the i-th LED and the j-th PD. Then, through the three-sided positioning algorithm, this embodiment can easily obtain the position coordinates of each of the two PDs. Finally, the position coordinates between the two PDs are used as the estimated coordinates of the mobile terminal. Thus, real-time positioning can be performed while the mobile terminal is communicating.

[0108] System modules and connections:

[0109] (1) A signal transmitting end, which is used to transmit a signal and includes:

[0110] Source module: generates bit stream data.

[0111] Mapping module: converts the bit stream data generated by the source into corresponding OFDM symbols and then sends them to the STBC encoding module.

[0112] STBC encoding module: This module performs STBC encoding on the OFDM symbols obtained after mapping to form an STBC matrix X n (k), and then sent to the IFFT module.

[0113] IFFT module, CP adding module, parallel-to-serial conversion module, digital-to-analog conversion module: X n (k) After IFFT transformation, a cyclic prefix is ​​added, and after parallel-to-serial conversion and digital-to-analog conversion, the signals are sent out through different LED light sources.

[0114] (2) A signal receiving end, the signal receiving end is used to receive a signal, including:

[0115] Photodetector PD: used to receive signals.

[0116] Analog-to-digital conversion module, serial-to-parallel conversion module, CP removal module, FFT module: The signal received by the photodetector PD is first converted to analog-to-digital, serial-to-parallel, and then the cyclic prefix (CP) is removed. After FFT conversion, the signal is Enter the next module.

[0117] Power monitoring module: This module controls the weight calculation module and the observation length control module according to the power of the terminal. When the power of the terminal is lower than the set threshold power E, the module directly sends control information to the weight calculation module and uses the equal weight distribution in formula (4) (the algorithm is simple and more power-saving than the unequal weight method). At the same time, the module sends control information to the observation length control module and selects the default observation length L. 1When the power level of the terminal is higher than the set threshold power level E, the control information will enter the speed sensing module, making the speed sensing module that was originally turned off enter the working state.

[0118] Speed ​​sensor module: This module is turned off by default. It will only work when the power level is higher than the set threshold power level E. The speed sensor module controls the weight calculation module and the observation length control module according to the terminal movement speed V. When the terminal movement speed is lower than the set threshold speed V, the speed sensor module will start to work. 1 (V 1 >0), the module sends control information to the weight calculation module, using the equal weight distribution in formula (4); when the terminal speed is higher than the set threshold speed V 1 When the terminal speed is less than or equal to V 1 When the observation length L is selected 1 (The observation length is the number of the first n STBC matrices of the current signal used to solve the channel state information); when the speed is V 1 and V 2 Between (including V 2 ), select the observation length L 2 ; When the speed is V 2 and V 3 Between (including V 3 ), select the observation length L 3 , when the speed is greater than V 3 When the observation length L is selected 4 (Where V 1 <V 2 <V 3 , L 1 <L 2 <L 3 <L 4 ). These parameters can be set to appropriate values ​​according to different usage scenarios.

[0119] Observation length control module: This module selects the appropriate observation block length based on various factors (such as terminal movement speed, terminal power), and the generated observation length control information is sent to the weight calculation module to calculate the weight assigned to each channel state information. In general, the faster the terminal moves, the shorter the observation length.

[0120] Weight calculation module: This module calculates the weight assigned to each channel state information based on the control information sent by the power monitoring module or the speed sensing module and the observation length selected by the observation length control module. Then, these weights will be sent to the mobile channel estimation module for subsequent channel estimation modules.

[0121] Mobile channel estimation module: This module estimates the mobile channel based on the parameters transmitted by each module, and then uses the channel state information estimation value Feed into the next module for symbol decoding.

[0122] STBC decoding module: by receiving signal and the channel state information estimate obtained by the channel estimation module Calculate the estimated value of the transmitted signal

[0123] Subcarrier symbol decision module: sends the estimated value of the signal The symbol decision is made, and its decision value is recorded as

[0124] Inverse mapping module, sink module: The inverse mapping restores the bit stream and transmits it to the sink module.

[0125] (3) Wireless optical positioning device

[0126] Channel DC gain estimation module: This module uses channel state information to estimate the value Estimate the channel DC gain.

[0127] Distance measurement module, three-sided positioning module: After calculating the distance between the photodetector PD and the LED light source using the estimated value of the channel DC gain, the coordinate position of the photodetector PD is estimated through the three-sided positioning module.

[0128] The following describes the two parts of communication and positioning:

[0129] (1) Communication method:

[0130] At the transmitting end, the serial data stream is converted into several parallel data streams, which are then mapped and sent to the STBC encoder. These STBC symbols are then modulated into OFDM symbols and emitted by each LED light source. It is worth noting that the form of the STBC encoding matrix depends on the number of transmitting antennas N. T In this work, this example uses N T =4 scenario example. T The same is true for other values. Simply replace formula (2) with the corresponding decoding formula. After passing through the MIMO channel, the wireless optical communication signal reaches the mobile receiver and is captured by the photodetector PD. After the wireless optical communication signal undergoes photoelectric conversion and time-frequency conversion, for the kth subcarrier in the OFDM symbol, the nth STBC matrix (i.e., X n (k)) can be expressed in the frequency domain as:

[0131]

[0132] In the formula, in is the kth transmitted subcarrier symbol of the lth OFDM symbol at the i-th LED, i = 1, 2, ... N T ,l=1,2,...N T ; in is the kth received subcarrier symbol of the lth OFDM symbol; in is the channel response between the i-th LED and the j-th PD, is the noise matrix.

[0133] Next, after passing through the STBC decoding module, the nth STBC matrix (i.e., X n The decoded symbol of the kth subcarrier in the OFDM symbol in (k)) can be expressed as:

[0134]

[0135] The same method can also be used in N T When N is other values, we only need to derive the corresponding decoding formula (2) based on the corresponding STBC encoding matrix. It is worth noting that this encoding matrix must be a square matrix. In particular, when N T =2, formula (2) becomes the following form, and the rest of the steps remain unchanged:

[0136]

[0137] However, when N T =2, in order to meet the conditions of three-sided positioning, at least two groups of LED light sources are required to complete the positioning through time division multiplexing.

[0138] The decoded symbols are divided into two paths after symbol judgment: one path is demapped and finally converted into a serial data stream to reach the destination module to complete the communication. The other path is re-encoded by STBC in the second STBC encoding module for subsequent channel estimation. The specific steps are as follows:

[0139] It can be seen from formula (2) that before performing STBC decoding, the receiver needs to obtain prior knowledge of CSI. Usually, training symbols are used in the header of each OFDM data packet to estimate CSI, and the channel state information in the entire data packet is often considered to be constant. However, for mobile terminals, the channel exhibits time-varying characteristics. Therefore, the CSI obtained by the training symbols will be different from the CSI experienced by subsequent data symbols. This will lead to CSI estimation errors, thereby affecting the performance of the system. In order to track dynamic channels and obtain more accurate CSI, this embodiment proposes a new decision feedback channel estimation scheme in the system. The scheme first uses training symbols to estimate the initial CSI of each OFDM data packet header. Then, the estimated CSI is calculated by formula (2) Then, the receiver Perform symbol decision to obtain the decision value Restore the original transmitted signal. In addition, the STBC encoder Encode again to regenerate an estimated signal matrix It can be regarded as the transmitted signal matrix X n Finally, use and Channel estimation is performed for subsequent STBC decoding. It should be emphasized that the coding matrix based on STBC, It is always reversible, which ensures the feasibility of formulas (4) and (5).

[0140] In order to reduce the impact of noise on channel estimation, an observation length L is often set, and the terminal moving speed V≤V 1 When , the channel state information from the n-L+1th to the nth is summed and the average value is taken as the value of the n+1th channel state information:

[0141]

[0142] Where L is the observation length of the STBC matrix and its value is L 1 .

[0143] However, this processing method assumes that the weights assigned to each channel state information are equal by default, which is obviously unreasonable. Because for the n+1th channel state information, the nth channel state information is the closest to it, so a larger weight needs to be assigned. To this end, this embodiment designs two modules (power monitoring module and speed sensing module), controls the weight calculation module and the observation length control module according to different situations, and selects a better weight allocation method. The specific process has been given in the introduction of system modules and connections. When the unequal weight allocation method of formula (5) is selected, for the n-L+1th to nth channel state information, the weight assigned to each channel state information is normalized and expressed as Therefore, the channel estimation formula can be expressed as:

[0144]

[0145] Where L is the observation length of the STBC matrix, V is the speed of the terminal uniform motion, when V 1 <V≤V 2 When L is L 2 ; When V 2 <V≤V 3 ,L takes the value of L 3 ; When V>V 3 When L is L 4 To average out the noise, equation (5) contains L sets of STBC matrices Such a process will be repeated to recover the subsequent STBC matrix until the end of each OFDM data packet. This can effectively track and eliminate the channel changes between adjacent STBC blocks, thereby improving the accuracy of channel estimation.

[0146] (II) Positioning method:

[0147] At the same time, thanks to the improvement of channel estimation accuracy, CSI can be further used to estimate the position of the mobile terminal. This embodiment uses three-sided positioning to estimate the coordinates of the PD. Therefore, ranging between the LED and the PD is essential. Considering the Lambertian radiation model, the distance between the i-th LED and the j-th PD can be estimated based on the RSS scheme:

[0148]

[0149] Where m is the Lambertian emission order, a R is the effective area of ​​PD, T s (ψ) is the filter gain, g(ψ) is the concentrator gain, h is the vertical distance between LED and PD, is the estimated value of the DC gain of the channel between the i-th LED and the j-th PD. That is, in order to estimate the distance between the LED and the PD, this embodiment needs to first estimate Therefore, the channel state information estimation value obtained by formula (5) in this embodiment is The elements in construct the following matrix:

[0150]

[0151] Where N P is the number of OFDM subcarriers. Then, after time-frequency transformation, the channel DC gain can be easily extracted from the channel impulse response:

[0152]

[0153] Based on formulas (6), (7), and (8), each PD can be three-sided positioned to obtain its position coordinates. Here, this embodiment takes PD1 and four LEDs as an example, and the following equations can be listed:

[0154]

[0155] In this system, this embodiment assumes that the height of each PD is known and the same. Therefore, this embodiment only needs to estimate the two-dimensional position coordinates of the PD. Through the above equations, the two-dimensional position coordinates of PD1 can be solved The same method can be used to find the two-dimensional position coordinates of another PD2 Finally, the middle position of the two PDs is used as the position coordinates of the mobile terminal to complete the two-dimensional positioning:

[0156]

[0157] Experimental comparison

[0158] In order to evaluate the performance of the above scheme, a specific 4×2 MIMO indoor communication positioning scenario is considered. The indoor size is 5m×5m×3m (length×width×height). The light source is LED lamp and the photodetector is PD. The LED lamp is deployed on the ceiling. The power of each lamp is 20W, the modulation index is 0.15, the coordinates of LED1 are (1.5, 1.5, 3), the coordinates of LED2 are (1.5, 3.5, 3), the coordinates of LED3 are (3.5, 1.5, 3), and the coordinates of LED4 are (3.5, 3.5, 3). Two PDs are installed on the mobile receiver. The receiver moves at a speed of 2m / s along two different test routes at one quarter of the receiving plane: Route 1 from (2.5, 2.5, 1) to (4.5, 2.5, 1) and Route 2 from (2.5, 4, 1) to (4.5, 4, 1). The power threshold E is set to 20%, L1 ~L 4 Set to 10, 20, 30 and 40 respectively, V 1 ~V 3 Set to 1m / s, 2m / s and 3m / s respectively.

[0159] At the transmitting end, parallel quadrature phase shift keying (QPSK) symbols are generated and encoded through STBC, then modulated into direct current biased light (DC-OFDM), and finally loaded onto four LEDs. For each LED, each OFDM data packet has 20 training symbols, followed by 19980 data symbols. Therefore, the total duration of each OFDM data packet is 0.1s. After passing through the mobile MIMO channel, the wireless optical communication signal is detected and recovered. At the same time, the CSI obtained by wireless optical communication is further used for ranging and wireless optical positioning. The positioning time interval of mobile wireless optical positioning is set to 10 milliseconds. This embodiment evaluates the communication performance and positioning performance of the system proposed in this embodiment. In order to reduce the complexity of the system and verify the feasibility of the scheme proposed in this embodiment, this scheme only considers the line-of-sight (LOS) link.

[0160] This embodiment first evaluates the communication performance of the system when the terminal moving speed is 2 m / s and the power level is greater than the power threshold of 20%. Figure 2 The bit error rate performance of the system when using the method proposed in this embodiment and not using the method proposed in this embodiment is compared when the LED transmission power is different. This embodiment finds that the unequal weight allocation method proposed in this embodiment can improve the communication performance of the system to a certain extent. For example, when the LED transmission power is 20W, when the receiver moves along route 1 and route 2, the bit error rates when not using the method of this embodiment (only using formula (4)) are 4.4×10 -5 and 5.8×10 -4 When the unequal weight allocation method proposed in this embodiment is adopted (Formula (5)), the bit error rates of route 1 and route 2 are reduced to 2.4×10 -5 and 3.8×10 -4 This is because decision feedback improves the channel estimation accuracy and can effectively track the time-varying channel. In addition, the bit error rate of route 1 is better than that of route 2. The reason is that route 1 is closer to the center of the room and has a higher corresponding signal-to-noise ratio (SNRs).

[0161] Next, this embodiment evaluates the communication performance of the terminal at different moving speeds when the terminal power is greater than the power threshold of 20%. Figure 3 As shown in the figure, when the receiver moves along route 1 and route 2 at 3 m / s, the bit error rates when the method of this embodiment is not used (only formula (4) is used) are 5.5×10 -5 and 8.4×10 -4When the unequal weight allocation method (Formula (5)) proposed in this embodiment is adopted, the bit error rates of route 1 and route 2 are reduced to 3.4×10 -5 and 5.4×10 -4 .

[0162] Secondly, this embodiment evaluates the positioning performance of the system. Figure 4 It is the positioning result when the receiver moves along different test routes. Figure 4 As shown, in both routes, when only the training sequence is used to estimate the channel, the positioning results are only distributed in discrete positions near the moving trajectory. This is because using only training symbols for channel estimation causes the estimated CSI in the entire OFDM data packet to remain unchanged, so the positioning results in each packet overlap at the same position. After using the method proposed in this embodiment, continuous positioning results can be observed, which are closer to the true position. This is because feedback can dynamically estimate the channel to obtain more accurate CSI. This precise CSI can further improve the positioning accuracy of the entire system. In addition, since the signal-to-noise ratio received by the terminal on route 1 is higher, the positioning accuracy of route 1 is higher than that of route 2. Therefore, dynamic decision feedback can benefit from a higher signal-to-noise ratio.

[0163] It is not difficult to find that the present invention has many advantages compared with the traditional solution:

[0164] 1) The system of the present invention takes into account the continuous process of terminal movement and can dynamically track and locate the terminal. Compared with traditional wireless optical positioning technology, this solution can adapt to time-varying channels, so that the receiver can still maintain a high positioning accuracy during the movement process.

[0165] 2) The information used for positioning by the system of the present invention does not need to occupy the spectrum resources of the communication system, realizing the real integration of communication and positioning. In addition, the technology does not require strict synchronization, and the system complexity is low; no specific communication resources are required to send positioning information, and the spectrum resource utilization rate is high.

[0166] 3) The system of the present invention considers combining space-time block coding and multiple-input multiple-output technology to make the system capacity larger and the communication quality higher. At the same time, by proposing a method of performing STBC coding again in the feedback stage, the problem that the traditional decision feedback method cannot work properly in the MIMO system is effectively solved.

[0167] The present invention optimizes the traditional equal weight distribution channel estimation method. The system uses a power monitoring module and a speed sensing module to control a weight calculation module and an observation length control module according to different situations, and selects a better weight distribution method. This can ensure that a part of the noise is averaged and the estimated channel is more accurate.

[0168] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0169] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A wireless optical communication and positioning system, characterized in that: It includes a wireless optical communication device and a wireless optical positioning device; The wireless optical communication device comprises a signal transmitting end and a signal receiving end; The signal transmitting end is used to transmit a signal, and includes a signal source module, a mapping module, a first STBC encoding module, an IFFT module, a CP adding module, a parallel-to-serial conversion module, a digital-to-analog conversion module and an LED light source connected in sequence; in, Source module: used to generate bit stream data; Mapping module: used to convert the bit stream data generated by the source module into corresponding OFDM symbols, and then send them to the STBC encoding module; The first STBC encoding module is used to perform STBC encoding on the OFDM symbols obtained by the mapping module to form an STBC matrix X n (k), and then sent to the IFFT module; IFFT module, CP adding module, parallel-to-serial conversion module, digital-to-analog conversion module: used to convert X n (k) performing IFFT transformation, adding cyclic prefix, parallel-to-serial conversion, and digital-to-analog conversion; LED light source: used to send out the signal after digital-to-analog conversion; The signal receiving end is used to receive signals, including a photodetector PD, an analog-to-digital conversion module, a serial-to-parallel conversion module, a CP removal module, an FFT module, a mobile channel estimation module, an STBC decoding module, a subcarrier symbol decision module, an inverse mapping module and a destination module connected in sequence, the output end of the subcarrier symbol decision module is also connected to a second STBC encoding module, and the output end of the second STBC encoding module is connected to a mobile channel estimation module; in, Photodetector PD: used to receive the signal from the LED light source; Analog-to-digital conversion module, serial-to-parallel conversion module, CP removal module, and FFT module: used to convert the signal received by the photodetector PD into analog-to-digital, serial-to-parallel, remove the cyclic prefix, and obtain the signal through FFT transformation Send to the mobile channel estimation module; Mobile channel estimation module: used to estimate the mobile channel and estimate the channel state information Send to STBC decoding module for symbol decoding; STBC decoding module: used to decode the signal and channel state information estimate Calculate the estimated value of the transmitted signal Subcarrier symbol decision module: used to estimate the value of the transmitted signal Make a symbol decision and record the decision value as The second STBC encoding module: used for the decision value Perform STBC encoding to obtain a new estimated decoding matrix The new estimated decoding matrix Together with the newly received signal, it is used for the next channel estimation of the mobile channel estimation module; Inverse mapping module: used to convert the decision value The inverse mapping restores the bit stream form of the transmitted signal; Sink module: used to receive the bit stream of the restored signal and complete the communication; The wireless optical positioning device comprises a channel DC gain estimation module, a distance measurement module and a three-sided positioning module connected in sequence; in, Channel DC gain estimation module: used to estimate the value using channel state information Estimate the channel DC gain; Distance measurement module: calculates the distance between the photodetector PD and the LED light source using the estimated value of the channel DC gain; Three-side positioning module: used to estimate the coordinate positions of two photoelectric detectors PD, and use the position coordinates between the two photoelectric detectors PD as the estimated coordinates of the mobile terminal to complete the positioning.

2. The wireless optical communication and positioning system according to claim 1, characterized in that: Also includes: The power monitoring module is used to control the weight calculation module and the observation length control module according to the power of the terminal. When the power of the terminal is lower than the set threshold power E, the power monitoring module directly sends control information to the weight calculation module, using the equal weight distribution in formula (4). At the same time, the power monitoring module sends control information to the observation length control module to select the default observation length L1. When the power of the terminal is higher than the set threshold power E, the control information will enter the speed sensing module, so that the closed speed sensing module will enter the working state. Speed sensing module: It is used to control the weight calculation module and the observation length control module according to the moving speed of the terminal. When the moving speed of the terminal is lower than the set threshold speed V1>0, the speed sensing module sends control information to the weight calculation module and uses the equal weight distribution in formula (4); when the speed of the terminal is higher than the set threshold speed V1, the unequal weight distribution in formula (5) is used. At the same time, the speed sensing module sends control information to the observation length control module: when the moving speed of the terminal is less than or equal to V1, the observation length L1 is selected; when the moving speed of the terminal is between V1 and V2, the observation length L2 is selected; when the moving speed of the terminal is between V2 and V3, the observation length L3 is selected; when the moving speed of the terminal is greater than V3, the observation length L4 is selected, where V1<V2<V3 and L1<L2<L3<L4; the observation length is the number of the first L STBC matrices of the current signal used to solve the channel state information; The observation length control module is used to send the generated observation length to the weight calculation module; The weight calculation module is used to calculate the weight assigned to each channel state information according to the control information sent by the power monitoring module or the speed sensing module, combined with the observation length selected by the observation length control module, and send the weight to the mobile channel estimation module; The mobile channel estimation module performs mobile channel estimation according to the received weight; The equal weight distribution of formula (4) satisfies when the moving speed V of the terminal is V≤V1: the sum of the (n-L+1)-th to the n-th channel state information is averaged as the value of the (n+1)-th channel state information, then the channel estimation of the mobile channel estimation module is expressed as: In the formula, L is the observation length with respect to the STBC matrix and takes the value of L1; The unequal weight allocation of formula (5) satisfies: For the channel state information from the n-L+1th to the nth, the weight allocated to each channel state information is normalized and expressed as Then the channel estimation of the mobile channel estimation module is expressed as: In the formula, L is the observation length with respect to the STBC matrix, V is the moving speed of the terminal. When V1<V≤V2, L takes the value of L2; when V2<V≤V3, L takes the value of L3; when V>V3, L takes the value of L4.

3. The wireless optical communication and positioning system according to claim 1, characterized in that: The FFT module obtains the signal through FFT transformation The formula is: Where j represents the jth photodetector PD, n represents the nth STBC matrix, in is the kth transmitted subcarrier symbol of the lth OFDM symbol at the i-th LED, i = 1, 2, ... N T ,l=1,2,...N T ; in is the kth received subcarrier symbol of the lth OFDM symbol; in is the channel response between the i-th LED and the j-th PD, is the noise matrix.

4. The wireless optical communication and positioning system according to claim 3, characterized in that: The STBC decoding module is based on the signal and channel state information estimate Calculate the estimated value of the transmitted signal The formula is: Where, formula (2) satisfies N T =4.

5. The wireless optical communication and positioning system according to claim 4, characterized in that: The estimated value of the transmitted signal In N T =2, it is expressed as:

6. The wireless optical communication and positioning system according to claim 1, characterized in that: In the ranging module, the distance between the photodetector PD and the LED light source is calculated using the estimated value of the channel DC gain. The formula is: Where m is the Lambertian emission order, a R is the effective area of ​​PD, T s (ψ) is the filter gain, g(ψ) is the concentrator gain, h is the vertical distance between LED and PD, is the estimated value of the channel DC gain between the i-th LED and the j-th PD.

7. The wireless optical communication and positioning system according to claim 6, characterized in that: The estimated value of the DC gain of the channel between the i-th LED and the j-th PD is Specifically: The channel state information estimate obtained by formula (5) is The elements in the matrix are constructed using the formula: Where N P is the number of OFDM subcarriers; then after time-frequency transformation, the channel DC gain is extracted from the channel impulse response, the formula is:

8. The wireless optical communication and positioning system according to claim 7, characterized in that: In the trilateral positioning module, the coordinate positions of two photodetectors PD are estimated, and the position coordinate in the middle of the two photodetectors PD is used as the estimated coordinate of the mobile terminal to complete the positioning. Specifically: Based on formulas (6), (7), and (8), trilateral positioning is performed on the j-th PD to obtain its position coordinates: Then the estimated coordinate formula of the mobile terminal is: In the formula, is the two-dimensional position coordinate of the first photodetector PD, is the two-dimensional position coordinate of the second photodetector PD.

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