Application Of Filtered-OFDM In Visible Light Communication

With the advent of 5G era,the demand for spectrum resource becomes more and more high.It also puts forward higher requirements on all kinds of wireless communication technology.The visible light communication has received widespread attention in the field of wireless communications because of its green environmental protection,rich spectrum resources and strong confidentiality.The transmission rate of the visible light communication is limited because the modulation bandwidth of white LED is relatively narrow.In order to solve this problem,a suitable modulation scheme is needed to be designed.In this paper,we studied various modulation technologies in visible light communication system,including OOK modulation,PPM/PMW modulation,DMT modulation,CAP modulation and OFDM modulation.We introduce the technology principle,advantages and disadvantages of various modulation technologies in detail.Optical OFDM technology inherits the advantages of OFDM technology in the field of radio frequency.It uses IFFT/FFT for orthogonal carrier modulation,which greatly simplifies the structure of the system.At the same time,it can effectively withstand ICI and ISI.O-OFDM is a key modulation technology in the field of VLC.In the research of 5G communication technology,a single scenario setting can no longer meet 5G's needs because the current application scenarios are complex.So a variety of new multi-carrier modulation technologies that can meet the needs of multi-carrier have attracted extensive attention.For example,FBMC,UFMC and F-OFDM.In this paper,the respective implementation principles,advantages and disadvantages are introduced in detail.We find that F-OFDM has good system performance by comparing with other method.F-OFDM technology can effectively inhibit the out-of-band leakage of OFDM signals.Different suppression effects can be achieved by adding different window functions to OFDM signals.The selection of window functions can be judged according to specific requirements.To apply F-OFDM technology to the visible light communication,we need to change its structure.The improved F-OFDM divides the channel into different sub-band,each sub-band can set up different sub-carrier spacing.length of symbols,the CP length according to different scenario.Compared with ACO-OFDM and DCO-OFDM,the improved F-OFDM has better system performance.Under the same SNR,F-OFDM has a lower error rate.QAM modulation order has an impact on bit error rate.The lower the order is,the lower the bit error rate will be.However,the lower order will affect the performance of the system,we need to choose proper order according to the requirement.In F-OFDM technology,the design of filter is a key step.The quality of the filter can affect the out-of-band attenuation of the signal,as well as the sub-band interval.The frequency response masking filter can design a very narrow transition band.Due to the use of masking filter,FRM has fewer filter coefficients and lower complexity.By using FRM to replace the filter in F-OFDM,the system will have lower complexity and narrower transition bandwidth.F-OFDM has multiple sub-bands,which will lead to the problem of multiple rates.The application of polyphase filter banks can perfectly solve the problem of multiple sampling rates,effectively reduce the number of calculations,and improve the operation rate of the system.In the F-OFDM system,the use of FRM-based polyphase filter banks can greatly reduce the number of multiplier and system complexity under the same transition bandwidth.Polyphase filter banks based on IFIR require the least number of multipliers to achieve the same filter effect.