Nonlinear Optimization And Interference Suppression Of Visible Light Cellular Networks Based On PDSC

Green lighting equipment,light emitting diodes(LED),are developing rapidly.LED can use the visible light as a medium for high-bandwidth and high-rate communication,whlie they are used as a light source to meet the illumination demand.We utilize the fast-light-switching and electro-optical response characteristics of LED devices,which providing conditions for the modulation and transmission of information on the visible spectrum.The resulting visible light communication technology visible light communication(VLC)brings profound changes into indoor wireless communication.Compared with the increasingly crowded spectrum resources of RF communication,VLC has the advantages of abundant spectrum,environmental protection,anti-electromagnetic interference and high confidentiality,making it the most promising indoor access solution for next-generation mobile communication.In recent years,with the development of technologies such as the Internet of Things and virtual reality,the demand of the number of devices in the access network has increased rapidly,and the requirements for bandwidth and speed have also been continuously improved.However,due to the limitation of the nonlinear problem of the LED device and the technical limitations of the multiple access scheme,the number of access devices and the spectrum efficiency of the visible light cellular network cannot be well balanced.At the same time,in the cellular network environment,the signal interference of overlapping regions between different cells projected by multiple light sources has become a research hotspot in the field of cellular communication.To this end,this paper focuses on two important issues of nonlinear optimization and interference suppression.?A new visible light multiple access scheme is proposed:multiple access with polarity division sparse code(PDSC)In the field of wireless multiple access,large-scale terminal access has always been difficult.Traditional orthogonal multiple access technology is greatly limited by limited bandwidth,which limits the massive access of terminals.Especially in the visible light communication,visible light cannot transmit imaginary signals due to the switching characteristics of LED.At the same time,the nonlinear effect of LED increases the power peak-to-average ratio of the signal during propagation,which greatly affects the communication quality.Multiple access with polarity division sparse code(PDSC)proposed in this paper utilizes sparse coding on the transmitter,and uses non-orthogonal resource blocks to subtly exchange information of different users in the entire spectrum.The message passing algorithm(MPA)is used at the receiver.Intersymbol interference is avoided in non-orthogonal situations,which can expand the number of access devices.What is more,in the polarization separation modulation scheme,the positive and negative signals are transmitted separately using different transmitters,so that they are superimposed into a complete signal in free space,which can reduce the signal strength of each transmitter and avoid the nonlinear effect of the LED.The experiment proves that under the the same bandwidth,when bit error rate is fixed at 3.80×10-3,the capacity of PDSC network with overload rate of 1.50 is 1.48 times as same as that of OFDMA.?A visible light interference suppression network based on PDSC multiple access and space-time-color three-domain linkage is proposed.Due to the linear propagation characteristics of visible light,the user can receive signals only at a certain angle of view,resulting in a smaller area covered by visible light signals.Thus,in order to cover a larger area of the room and serve more terminals,the indoor visible light network needs to be arranged in a denser cell than the radio frequency cellular.Moreover,the shape of the cell in which the visible light of the LED is formed on the ground is circular.However,geometrically,the circle can no longer fill the entire planar area without overlapping and without blanks.Therefore,in a VLC network,overlapping between adjacent cells is easy.Signals from different LED light sources fr-om neighboring cells are simultaneously received,and these signals will cause serious interference with each other.Therefore,the signal interference between cells in the visible-light cellular network has always been a difficulty.It is the second key research content of this paper to ensure that there is no interference for the terminal in the overlapping area between adjacent cells performs cell selection and signal acceptance.The visible light interference suppression network based on PDSC multiple access and space-time-color three-domain linkage proposed in this paper adopts RGB three-color LED device and PDSC multiple access technology to perform color gamut segmentation.We combine it with time domain time slot technology and the virtual cell technology to propose a new architecture of access network,so that the terminals in the over-lapping area can eliminating interference.Theoretical calculations show that the network is below the capacity limit,and the bit error rate is only affected by noise.Experiments show that at 0.11lm,the center of the overlap region,the error rate of OFDMA is 2.84× 10-4,and the error rate of the interference suppression scheme based on the three-domain linkage is 3.21×10-5.The interference suppression performance has been greatly improved.The maximum rate of the OFDMA system is 77.32 Mb/s.The maximum rate of the system based on the three-domain linkage interference suppression scheme is 167.84 Mb/s,which is about 2.17 times that of OFDMA.