CN109150308A - A kind of application method of Multicarrier DS CDMA technology in visible light positioning system - Google Patents
A kind of application method of Multicarrier DS CDMA technology in visible light positioning system Download PDFInfo
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- H—ELECTRICITY
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
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- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
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Abstract
The invention discloses a kind of indoor visible light localization methods based on Multicarrier DS CDMA technology, this method is first that each user distributes a specific spreading code, serial to parallel conversion is carried out to the serial data stream of transmission, time domain spread spectrum is carried out to parallel data by specific spread spectrum code, then progress Fast Fourier Transform Inverse (IFFT) in different sub-carrier is moved to the sequence after spread spectrum to, first spread-spectrum signal is mapped to before Fast Fourier Transform Inverse and meets the symmetrical signal of hermitian, make in its odd subcarriers comprising information, it is zero in even subcarriers, guarantee to export after IFFT is operated is real signal, clipping is carried out to signal later, add cyclic prefix, the operation such as parallel serial conversion.This method will be applied in indoor visible light positioning system after OFDM technology and DS-CDMA technological incorporation, effectively reduce intersymbol interference caused by multi-path delay spread in traditional indoor positioning, the positional accuracy of raising system solves the problems, such as that bipolar signal cannot be transmitted in visible light communication.
Description
Technical Field
The invention relates to application of a multi-carrier DS-CDMA technology in a visible light positioning system, belonging to the technical field of visible light positioning.
Background
The visible light communication technology is that high-frequency signals which cannot be identified by human eyes are loaded on the LED for transmission, and compared with the traditional positioning technology, the indoor positioning accuracy based on visible light is high, no electromagnetic pollution exists, the deployment is relatively easy, the illumination requirement is met, and the power consumption and the cost are reduced. With the development of the next generation of green LED lighting technology, the indoor positioning technology based on visible light will be a promising indoor positioning alternative.
Direct sequence code division multiple access (DS-CDMA) modulation achieves signal separation in both time and frequency domains by utilizing orthogonality of spreading codes, thereby achieving code division multiplexing and solving the problem of intersymbol interference caused by multiple reference points in a VLC positioning system, but DS-CDMA is difficult to achieve high-speed data transmission due to multiple access interference and intersymbol interference.
Orthogonal Frequency Division Multiplexing (OFDM) adopts a parallel transmission technology, burst damage caused by fast fading is effectively dispersed into a plurality of symbols, rather than a plurality of adjacent symbols are completely destroyed; in addition, the parallel processing technology of OFDM prolongs the symbol period of the transmission signal, and reduces the sensitivity of the signal to the multipath diffusion of the channel.
Spread spectrum Code Division Multiple Access (CDMA) technology has undoubted competitiveness due to its multiple access capability, robustness against fading, strong interference resistance, and the like. However, since the capacity of spread spectrum CDMA is limited by multiple access interference and multipath interference, and the multi-carrier technique is robust to multipath and inter-symbol interference, it has been explored to apply the multi-carrier technique to the CDMA system.
OFDM-CDMA is a technology that combines CDMA and OFDM recently proposed, it combines the advantages of OFDM and CDMA, after each orthogonal subcarrier is directly spread, it is similar to single carrier DS-CDMA system, it has stronger anti-multipath and anti-fading ability, and for the wireless transmission of high-speed data, its anti-intersymbol interference performance is obviously superior to traditional single carrier CDMA. The multi-carrier CDMA scheme may be divided into frequency domain spreading and time domain spreading. Frequency domain spreading is commonly referred to as multi-carrier CDMA (MC-CDMA). The time domain spread spectrum is divided into two different construction methods, namely multi-carrier DS-CDMA (MC-DS-CDMA) and multi-tone modulation CDMA (MT-CDMA).
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to solve the technical problem of application of a multi-carrier DS-CDMA technology in a visible light positioning system, mainly provides a method for combining OFDM and DS-CDMA aiming at the defects in the background technology, and is applied to indoor visible light positioning, thereby overcoming the influence of multipath effect on positioning error, realizing high-speed transmission, improving the frequency spectrum utilization rate of the system, and simultaneously meeting the requirement of an intensity modulation direct detection system on nonnegative real number signals.
The technical scheme is as follows: a method for applying multi-carrier DS-CDMA technology in a visible light positioning system comprises the following steps:
step 1: serial data stream containing position information generated by a sending device is converted into parallel data stream in a serial-to-parallel mode;
step 2: taking the bipolar codes with high autocorrelation value and low cross correlation value as spreading codes, generating the spreading codes through a sequence generator arranged at a sending end, distributing a specific spreading code for each user, and generating a composite code sequence after modulo two addition of a parallel data stream and a high-speed spreading code to expand the bandwidth of parallel data and generate a spreading signal;
and step 3: carrying out Hermite mapping operation on the spread spectrum signals in the step 2, wherein the output signals after mapping meet Hermite symmetry;
and 4, step 4: modulating the signals meeting Hermite symmetry characteristics generated in the step 3 onto different subcarriers through inverse fast Fourier transform, and carrying out amplitude limiting on the signals after fast Fourier transform;
and 5: adding a cyclic prefix to the amplitude-limited signal, performing parallel-to-serial conversion, performing digital-to-analog conversion, and sending the signal to a channel in an optical form through an LED driver;
step 6: visible light signals from different light sources received by a receiving end through a photoelectric detector are converted into electric signals, the electric signals are discretized through analog-to-digital conversion, and fast Fourier transform is carried out after serial-to-parallel conversion and cyclic prefix deletion operation;
and 7: and (3) performing related despreading on the output signal subjected to the fast Fourier transform by using a pseudorandom sequence synchronized with a transmitting end, recovering transmitted information, and positioning the position of a receiver by using a triangulation positioning algorithm.
Further, step 1 is specifically that serial data flows through the demultiplexer and then is changed into K paths of parallel output, and the sending information is am(t) converting the serial data stream into K parallel data streams through the demultiplexer:
wherein, αmkFor the k-th line of parallel data of the m-th transmission data, q (t-iT)0) Is a rectangular wave at time T, T0Is the period length of a square wave, αmIs a matrix representation of the mth transmission data.
Further, in step 2, each path of data is spread by the same spreading code, and then modulated onto K adjacent subcarriers, specifically:
spread the parallel data stream to xm(t)：
Wherein,pi∈[-1，+1]，pm(T) is the spreading code allocated to the mth user, TcIs the chip length and G is the spreading code length.
Further, the spread-spectrum modulated signal is subjected to Hermitian mapping and fast-speed in step 3An inverse Fourier transform operation, mapping to make the signal satisfy the condition that the odd number sub-carrier contains information, and the even number sub-carrier is 0, then the mapped signal is Xm：
WhereinAnd xm(G-1) signals X which are conjugate symmetric functions of each other and satisfy hermitian symmetrymThe real signal X is output after IFFT conversion operationIFFT：
XIFFT＝FHXm
XIFFT(k)＝-XIFFT(k+N/2) k＝0，1，2....N/2-1
Where F is an NxN normalized discrete Fourier transform matrix, N is the length of the Inverse Fast Fourier Transform (IFFT), and H represents the conjugate transpose of the matrix.
Further, the signal is clipped in step 4, XIFFTDeleting values less than zero to obtain unipolar real number signal Xclip(k)：
Wherein n isclip(k) For clipping noise, the frequency domain signal corresponding to the clipped signal is:
as can be seen from the above equation, the signal X is mappedmContaining information in odd bits and 0 in even bits, the useful signal being on odd subcarriers and the amplitude beingHalf of the frequency domain signal is not clipped, while the clipping noise falls on the even-bit subcarriers.
Has the advantages that:
1. the single carrier DS-CDMA-based indoor visible light positioning system is easily influenced by the multipath effect of the system, and the DS-CDMA and the OFDM are combined, so that the advantages of easy realization, strong anti-interference capability, good confidentiality and the like of the DS-CDMA are reserved, and the problem of intersymbol interference caused by the multipath effect of the system is effectively reduced.
2. The DS-CDMA-based indoor visible light positioning system has the advantages that the capacity of the system is greatly influenced by multiple access interference, when the number of LED lamps of the system is large, the system is greatly influenced by the multiple access interference, so that the positioning error is large, and the system capacity can be effectively improved by adopting a multi-carrier DS-CDMA technology.
3. In the traditional code division multiple access-based indoor visible light positioning system, an intensity modulation direct detection technology is adopted, non-negative real signals are transmitted by the system, the multiple access interference resistance of the system is determined by the correlation of spread spectrum codes, in order to improve the multiple access interference resistance, a bipolar pseudo-random code is generally selected, therefore, the problem of converting bipolar signals into unipolar signals is solved, in a multi-carrier DS-CDMA system, the spread spectrum modulated signals are mapped to have hermitian symmetry, and then IFFT operation is carried out, so that the problem of converting bipolar signals into unipolar codes can be effectively solved.
Drawings
FIG. 1 is a block diagram of a transmitter of an indoor visible light positioning system;
FIG. 2 is a schematic block diagram of a conventional multi-carrier DS-CDMA;
fig. 3 is a block diagram of a receiver of an indoor visible light positioning system.
Detailed Description
The invention is further explained below with reference to the drawings.
The invention provides an application method of a multi-carrier DS-CDMA technology in a visible light positioning system, which is an improvement of the existing indoor positioning technology, and is characterized in that data sent by each indoor LED lamp is subjected to direct sequence spread spectrum (DS-CDMA), and output spread spectrum information is carried to mutually orthogonal subcarriers to realize Orthogonal Frequency Division Multiplexing (OFDM). The scheme applies the direct sequence spread spectrum technology and the orthogonal frequency division multiplexing technology to an indoor positioning system in an iteration mode, can effectively overcome positioning errors caused by multiple access interference and multipath effect of the system, simultaneously realizes the process of converting bipolar complex signals into unipolar real signals by Hermite mapping and amplitude limiting operation of data before and after IFFT conversion, and solves the problem that a visible light positioning system cannot transmit the bipolar signals. The receiving end detects information from different light sources through a photoelectric detector, separates out the position information of the different light sources by separating out the information of the different light sources and demodulating the information and the like, and determines the position information of the receiver through an RSS positioning algorithm.
Fig. 1 is a block diagram of a transmitter of an indoor visible light positioning system, which first splits a serial data stream and converts the serial data stream into a plurality of parallel data streams, the system is provided with 2 identical pseudo-random sequence generators, which respectively act on spread spectrum modulation at a transmitting front end and spread spectrum demodulation at a receiving front end, the sequence generator at the transmitting end generates a pseudo-random sequence as a spreading code, the spreading code is multiplied by the parallel data streams to perform spreading, and inverse fast fourier transform is performed on the spread data. In order to correctly perform the despreading processing of the signal, after the receiver receives the signal, the receiver captures the accurate phase of the transmitted spreading code through a code synchronization technology, thereby generating a despreading code which is completely consistent with the phase of the transmitted pseudo random code so as to accurately recover the transmitted information.
Fig. 2 is a schematic block diagram of a conventional multi-carrier DS-CDMA, which combines DS-CDMA and OFDM technologies and is applied to an indoor visible light positioning system. The transmitted serial data stream passes through a serial-to-parallel conversion operation device (S/P),outputting parallel data, parallel data and assigned spreading code Cm(N-1), which implements direct sequence spreading of the data. The orthogonal frequency division multiplexing in the system is realized by Inverse Fast Fourier Transform (IFFT) operation, before the IFFT operation, the mapping operation is carried out on the data after the frequency spreading, so that the spread spectrum information meets the Hermite symmetry characteristic, namely the odd number sub-carriers contain information, the even number sub-carriers are 0, the signal meeting the Hermite symmetry characteristic is a real number signal output after the IFFT conversion, then the amplitude limiting operation is carried out on the signal, the bipolar signal is converted into the unipolar signal, and the subsequent transmission is facilitated. And then, the parallel-serial conversion, cyclic prefix adding, digital-to-analog conversion and other operations are carried out, and then the electric signals are converted into optical signals through the LED driver and transmitted into a channel for transmission.
Fig. 3 is a schematic block diagram of a receiving end of the system, wherein the receiver receives visible light signals from different light sources, converts the visible light signals into electric signals, discretizes the signals through analog-to-digital conversion, and then performs serial-to-parallel conversion and fast fourier transform after deleting the cyclic prefix operation. And (3) performing related despreading on the output signal subjected to the fast Fourier transform and a pseudorandom sequence synchronized with a transmitting end to recover the transmitted signal.
The traditional indoor visible light positioning technology generally adopts a frequency identification and time slot rotation method, which is similar to the frequency division multiplexing and time division multiplexing technology in wireless communication in concept, but the two methods occupy a larger frequency range and have high clock synchronization precision, so that the positioning error of the system is larger, and therefore, the method proposes an idea that: the application of multi-carrier DS-CDMA in positioning introduces CDMA technology into a positioning system, thereby improving the performance of the system to a great extent, the system adopts spread spectrum codes with better correlation, different light source information can be effectively distinguished at a receiving end, the introduction of OFDM can reduce the influence of multipath effect on the system, improve the system capacity and improve the positioning accuracy.
A method for applying multi-carrier DS-CDMA technology in a visible light positioning system comprises the following steps:
step 1: and converting serial data streams containing the position information generated by the sending equipment into parallel data streams in a serial-to-parallel mode. Step 1 is specifically that serial data flow is changed into K paths of parallel output after flowing through a demultiplexer, and the sending information is am(t) converting the serial data stream into K parallel data streams through the demultiplexer:
wherein, amkFor the k-th line of parallel data of the m-th transmission data, q (t-iT)0) Is a rectangular wave at time T, T0Is the period length of the square wave, amIs a matrix representation of the mth transmission data.
Step 2: the method comprises the steps of taking a bipolar code with a high autocorrelation value and a low cross-correlation value as a spread spectrum code, generating the spread spectrum code through a sequence generator arranged at a sending end, distributing a specific spread spectrum code for each user, performing modulo two addition on a parallel data stream and a high-speed spread spectrum code to generate a composite code sequence, expanding the bandwidth of parallel data and generating spread spectrum signals. Each path of data is spread by the same spreading code and then modulated to K adjacent subcarriers respectively, specifically:
spread the parallel data stream to xm：
Wherein,pi∈[-1,+1]，pm(T) is the spreading code allocated to the mth user, TcIs the chip length and G is the spreading code length.
And step 3: and (3) carrying out Hermite mapping operation on the spread spectrum signals in the step (2), wherein the output signals after mapping meet Hermite symmetry. In step 3 toCarrying out Hermite mapping and inverse fast Fourier transform operation on the signal after spread spectrum modulation, wherein the signal after mapping meets the condition that information is contained on odd subcarriers and 0 is contained on even subcarriers, and the signal after mapping is Xm：
WhereinAnd xm(G-1) signals X which are conjugate symmetric functions of each other and satisfy hermitian symmetrymThe real signal X is output after IFFT conversion operationIFFT：
XIFFT＝FHXm
XIFFT(k)＝-XIFFT(k+N/2) k＝0，1，2·…N/2-1
Where F is an NxN normalized discrete Fourier transform matrix, N is the length of the Inverse Fast Fourier Transform (IFFT), and H represents the conjugate transpose of the matrix.
And 4, step 4: and (3) modulating the signals meeting Hermite symmetry characteristics generated in the step (3) to different subcarriers through inverse fast Fourier transform, and limiting the signals after fast Fourier transform. In step 4, the signal is limited, XIFFTDeleting values less than zero to obtain unipolar real number signal Xclip(k):
Wherein n isclip(k) For clipping noise, the frequency domain signal corresponding to the clipped signal is:
as can be seen from the above equation, the signal X is mappedmThe odd bits containing information and the even bits 0, the useful signal on the odd subcarriers having an amplitude which is half that of the non-clipped frequency domain signal and the clipping noise on the even subcarriers
And 5: adding a cyclic prefix to the amplitude-limited signal, performing parallel-to-serial conversion, performing digital-to-analog conversion, and sending the signal to a channel in an optical form through an LED driver;
step 6: visible light signals from different light sources received by a receiving end through a photoelectric detector are converted into electric signals, the electric signals are discretized through analog-to-digital conversion, and fast Fourier transform is carried out after serial-to-parallel conversion and cyclic prefix deletion operation;
and 7: and (3) performing related despreading on the output signal subjected to the fast Fourier transform by using a pseudorandom sequence synchronized with a transmitting end, recovering transmitted information, and positioning the position of a receiver by using a triangulation positioning algorithm.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (5)
1. A method for applying multi-carrier DS-CDMA technology in a visible light positioning system is characterized by comprising the following steps:
step 1: serial data stream containing position information generated by a sending device is converted into parallel data stream in a serial-to-parallel mode;
step 2: taking the bipolar codes with high autocorrelation value and low cross correlation value as spreading codes, generating the spreading codes through a sequence generator arranged at a sending end, distributing a specific spreading code for each user, and generating a composite code sequence after modulo two addition of a parallel data stream and a high-speed spreading code to expand the bandwidth of parallel data and generate a spreading signal;
and step 3: carrying out Hermite mapping operation on the spread spectrum signals in the step 2, wherein the output signals after mapping meet Hermite symmetry;
and 4, step 4: modulating the signals meeting Hermite symmetry characteristics generated in the step 3 onto different subcarriers through inverse fast Fourier transform, and carrying out amplitude limiting on the signals after fast Fourier transform;
and 5: adding a cyclic prefix to the amplitude-limited signal, performing parallel-to-serial conversion, performing digital-to-analog conversion, and sending the signal to a channel in an optical form through an LED driver;
step 6: visible light signals from different light sources received by a receiving end through a photoelectric detector are converted into electric signals, the electric signals are discretized through analog-to-digital conversion, and fast Fourier transform is carried out after serial-to-parallel conversion and cyclic prefix deletion operation;
and 7: and (3) performing related despreading on the output signal subjected to the fast Fourier transform by using a pseudorandom sequence synchronized with a transmitting end, recovering transmitted information, and positioning the position of a receiver by using a triangulation positioning algorithm.
2. The method as claimed in claim 1, wherein the step 1 is that serial data flows through the demultiplexer and then becomes K-path parallel output, and the transmission information is am(t) converting the serial data stream into K parallel data streams through the demultiplexer:
wherein, αmkFor the k-th line of parallel data of the m-th transmission data, q (t-iT)0) Is a rectangular wave at time T, T0Is the period length of the square wave, amIs a matrix representation of the mth transmission data.
3. The method as claimed in claim 2, wherein in step 2, each path of data is spread by the same spreading code and then modulated onto K adjacent sub-carriers, specifically:
spread the parallel data stream to xm(t)：
Wherein,pm(T) is the spreading code allocated to the mth user, TcIs the chip length and G is the spreading code length.
4. A method as claimed in claim 3, wherein the spread spectrum modulated signal is subjected to hermitian mapping and inverse fast fourier transform in step 3, the mapping being such that the signal satisfies the condition that information is contained in odd subcarriers and 0 is contained in even subcarriers, the mapped signal is Xm：
WhereinAnd xm(G-1) are conjugate symmetric functions of each other，Signal X satisfying Hermite symmetrymThe real signal X is output after IFFT conversion operationIFFT：
XIFFT＝FHXm
XIFFT(k)＝-XIFFT(k+N/2)k＝0,1,2….N/2-1
Where F is an NxN normalized discrete Fourier transform matrix, N is the length of the Inverse Fast Fourier Transform (IFFT), and H represents the conjugate transpose of the matrix.
5. Method for applying multi-carrier DS-CDMA technique in a visible light positioning system according to claim 4, characterized in that in step 4 the signal is limited, X is limitedIFFTDeleting values less than zero to obtain unipolar real number signal Xclip(k):
Wherein n isclip(k) For clipping noise, the frequency domain signal corresponding to the clipped signal is:
as can be seen from the above equation, the signal X is mappedmThe odd bits contain information and the even bits are 0, the useful signal is on the odd subcarriers with an amplitude that is half that of the non-clipped frequency domain signal and the clipped noise falls on the even subcarriers.
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| CN110581732A (en) * | 2019-09-30 | 2019-12-17 | 山东建筑大学 | Multi-objective optimization system and method for indoor visible light communication based on neural network |
| CN111541459A (en) * | 2019-12-11 | 2020-08-14 | 西安英诺视通信息技术有限公司 | Data transmission method and system for actively utilizing multipath effect |
| CN114944868A (en) * | 2022-03-22 | 2022-08-26 | 江苏科大亨芯半导体技术有限公司 | Top adjusting system of passive optical network |
| CN115189715A (en) * | 2021-04-02 | 2022-10-14 | 湖南工商大学 | Optical transmission device and method based on direct spread spectrum time division multiplexing |
| WO2023051278A1 (en) * | 2021-09-30 | 2023-04-06 | 华为技术有限公司 | Signal transmission method and apparatus |
| CN116366091A (en) * | 2022-12-23 | 2023-06-30 | 北京环佳通信技术有限公司 | Distributed frequency domain spreading method and despreading method for self-organizing network scene |
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| WO2023051278A1 (en) * | 2021-09-30 | 2023-04-06 | 华为技术有限公司 | Signal transmission method and apparatus |
| CN114944868A (en) * | 2022-03-22 | 2022-08-26 | 江苏科大亨芯半导体技术有限公司 | Top adjusting system of passive optical network |
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