Study On Key Techniques In Visible Light Communication Based Indoor Positioning

With the popularity of internet technology,indoor positioning technique has developed rapidly due to the demand for various indoor location-based services in location and navigation,robot control,expensive equipment monitoring and so on.However,the mature global positioning system(GPS)cannot be used in indoor settings because its signals are easily blocked by buildings.Meanwhile,radio frequency(RF)-,infrared-,Bluetooth-,geomagnetic field-based indoor positioning systems cannot be widely used for the disadvantages of low positioning accuracy,high cost and so on.Recently,the indoor positioning technique based on visible light communication(VLC),namely,the “VLC-based positioning system(VPS)” is a new research field for indoor positioning,and has the advantages of high positioning accuracy,no electromagnetic interference,compatibility with lighting facility,and good security.Therefore,VPS will be one of the competitive solutions in future indoor positioning.Our thesis focuses on the researches of the key techniques of VPS,including modulation-demodulation scheme,multiple beacons receiving scheme,and single LED-based positioning scheme.Based on these schemes,a VLC-based indoor positioning system is realized.The details are discussed as follows: 1.Research of modulation-demodulation scheme in VPSTransmition of positioning beacon signals is the primary issue for a VPS.Because VPS tendency is fusing the functions of green illumination,high-speed communication,and high-accuracy positioning to realize a multi-functional VLC system,a novel modulation-demodulation scheme is needed for the future VPS,which can realize the simultaneous transmition of low-speed beacon signals and high-speed communication data.As for this issue,our thesis has researched modulation-demodulation scheme in VPS.The details are as follows:1)A 2ASK-OFDM(2-Amplitude Shift Key-Orthogonal Frequency Division Multiplexing)-based modulation-demodulation scheme is proposed.In this scheme,2ASK signals are modulated by low-speed beacon signals,while OFDM signals are modulated by high-speed data.To realize transmission of two modulated signals on one system,OFDM symbol energy is modulated by 2ASK signals further.In this way,beacon signals can be extracted with a simple receiver,which meets the requirement of portability in positioning applications.2)A real-time VLC system based on 2ASK-OFDM is established.The 2ASK-OFDM algorithm is achieved in FPGA(Field Programmable Gate Array),and a VLC optical link is set up.The experimental results show that,the bit error rates of 2ASK and OFDM signals are both much lower than the forward error correction line,which demonstrates the good performance of this system.2.Research of multiple beacons receiving scheme in VPSIn indoor settings,LED beacons are close to each other which would induce a dramatical multiple beacons interference(MBI),so the multiple beacons receiving(MBR)scheme is needed for a VPS to insure beacon signals to be received correctly under MBI.However,in the large scale indoor settings with numerous LEDs mounted,like mall or exhibition hall,the classic MBR scheme,like time division-MBR(TD-MBR)and frequency division-MBR(FD-MBR)would induce a long delay for receiving beacon signals and a high complexity in receiver.To solve these issues,our thesis has researched the low-delay,low-complexity MBR scheme:1)A LED block-based MBR scheme is proposed.In this scheme,LEDs are divided into several blocks and transmit beacon signals in their time slots or channels.When the LEDs on the same sites of different blocks share the same time slot or channel,the time slot or channel reuse can be realized.2)The performance of the proposed MBR scheme in TD-MBR is researched.The emitted signals are encoded by the extended BCD(Binary Coded Decimal)codes to reduce MBI.The feasibility of this scheme is verified by simulation and the influence of various parameters is investigated.At last,a comparison between this scheme and the classic TD-MBR about the received beacon signals delay is achieved,and the results show that,as the LED number increases,our scheme's delay has a slow growth compared with the linear increase of TD-MBR's delay.As an example,when the LED number is 530,our scheme's delay is only 3 ms while TD-MBR's delay is up to 100 ms.3)The performance of the proposed MBR scheme in FD-MBR is researched.The receiver's structure is designed.The influence of various parameters is investigated by simulation,and the maximum receiver's tilted angle is determined.Moreover,an experimental platform is set up to verify the feasibility and the experimental results coincide with the simulations.At last,the positioning performance comparison between our scheme and the classic FD-MBR is achieved,and the results demonstrate that in the indoor setting with 81 LEDs mounted,the positioning accuracy of 9.8 cm and 2.5 cm,and the used filter numbers of 9 and 81,can be achieved in our scheme and FD-MBR respectively.Although our scheme has a lower accuracy,the complexity is much lower than the one of FD-MBR.3.Research of single LED-based positioning scheme in VPSThe key issue of a positioning system is positioning scheme.At present,most of VPSs have the limitation of multiple LEDs involved in one positioning process,which would make the VPSs disabled when beacon signals are blocked by objects or the indoor settings have only one LED mounted,like small partition,stairs,or corridors.Meanwhile,the existed single LED beacon-based indoor positioning schemes have the disadvantages of low accuracy,complicated receiver's structure,and no compatibility with the off-the-shelf devices.For these issues,this thesis has researched the high-accurate single LED beacon-based indoor positioning scheme compatible with mobile devices.The details are as follows:1)A novel high-accurate single LED beacon-based indoor positioning scheme using a photodetector(PD),an image sensor,and a gyroscope is proposed.In this scheme,PD is used to receive arrival optical signals;image sensor is used to measure arrival light angles;and gyroscope is used to measure receiver's gesture.These devices have been integrated in a smart mobile terminal,so our scheme has a good compatibility.2)The key techniques about AOA measurement and single LED-based positioning algorithm are researched.Specifically,an angle-of-arrival(AOA)measurement based on image processing is presented,and a novel received-signal-strength and angle-of-arrival(RSS/AOA)-based positioning algorithm is proposed.4.Realization of VLC-based indoor positioning systemThe aim of this thesis is to develop the VLC-based indoor positioning technique with advantages of high accuracy,low cost,and good compatibility.Based on the research of the key techniques of modulation-demodulation scheme,multiple beacons receiving scheme,and single LED-based positioning scheme,a VLC-based indoor positioning system is realized.This system is not only applied in the indoor settings with multiple LEDs mounted,but also applied in one LED mounted settings.The influence of RSS and AOA measurements on system accuracy is researched by experiment.The system performance is demonstrated in the cases of the ceiling-mounted and the wall-mounted LED.The system complexity and the influence of a tilted receiver performance are both discussed.The experimental results show that,the maximum accuracy of 7.3 cm can be achieved.Meanwhile,the performance with the ceiling-mounted LED is better than the one with the wall-mounted case.Moreover,due to the influence of reflect light,the performance at the center of room is better than the one in the edge of room.