Research And Implementation Of Optical Camera Communication System Under Uncontrolled Conditions

LED has become the mainstream technology for indoor lighting,and LED-based Visible Light Communication(VLC)is considered to be the best candidate for indoor dedicated communication in next-generation wireless networks due to its advantages of wide frequency bandwidth,strong confidentiality,and green security.Optical Camera Communication(OCC)technology,as a branch technology of VLC,not only inherits its advantages,but also attracts extensive attention due to its high penetration rate and low cost of receiving equipment.In the existing LED-based OCC communication systems,most of the receivers are set to a static state or move according to a predetermined trajectory to communicate.However,when the OCC is applied to the actual scene,the receivers are in an uncontrolled situation.The random swaying of the receiver or the change of the receiving position will affect the performance of the OCC system,and the uncontrolled condition will bring about the distortion of the stripes.It will greatly increase the difficulty of demodulation and reduce the reliability of the system.Starting from the OCC demodulation in the above-mentioned uncontrolled situation,and aiming at universality,lightness and robustness,this paper proposes pilot-based stripe area estimation(P-SAE)decoding algorithm,and constructs an actual OCC system for effect verification.In addition,for the swaying of the receiver,this paper constructs the swaying model of the receiver.Starting from the OCC channel model,based on the measured swaying data,the effective capacity of the OCC system under the swaying scene is simulated and analyzed.The main research results of this paper are as follows:1.For the problem of stripes distortion caused by users in uncontrolled situations and photon overflow in OCC system resulting in different widths of bright and dark stripes,a lightweight pilot-based stripe area estimation decoding algorithm is proposed,combined with pixel rearrangement scheme and the bright and dark stripe separation decision logic mechanism are applied in the OCC system.Through experimental verification and bit error rate(BER)analysis,the scheme proposed in this paper can significantly reduce the bit error rate caused by uncontrolled situations,and its bit error rate can basically reach the order of 10^-4.It can effectively improve the reliability of the system.2.For the construction of the actual system,this paper designs the communication system according to the IEEE802.15.7 optical wireless communication standard.For the transmitter,the Physical Layer and the MAC Layer of the OCC are summarized.For the Physical Layer,this paper gives some device selections,coding and modulation methods,and hardware workflows;for the MAC layer,according to IEEE802.15.7,the basic functions of the MAC layer of VLC are changed,which are encapsulation into frame,transparent transmission,error control,synchronization and data padding.For the receiver,based on the Android Studio development platform,this paper develops an APP that can independently support OCC communication,and cooperates with the transmitter to successfully realize the communication.By building a complete OCC system,it provides hardware and software support for the experiments,simulations,algorithms in this paper and practical application of OCC.3.For the situation of uncontrolled of receiver,this paper constructs a random swaying model,deduces the effective capacity of the OCC system through the channel model and the measured data,and analyzes the change curve of the effective capacity of the OCC system with the Qo S indexthrough simulation.It is used to describe the achievable transmission rate of users under the constraint of statistical delay Qo S.In this way,the theory and practice can be combined to further promote the development of OCC.