Research On Filter-Bank Multicarrier Technology In Indoor VLC

Indoor visible light communication(VLC)loads information onto white light LEDs to transmit data.Under the indoor circumstance,VLC simultaneously realizes both illumination and communication functions.With the advantages of high bandwidth,low power consumption,high spatial multiplexing rate,and no electromagnetic interference,VLC has become one of the important access technologies of next generation communication networks.OFDM is a classical multi-carrier transmission scheme with high transmission rate,which has been introduced into VLC systems.Next-generation communication networks require waveforms with high spectral efficiency to save valuable spectrum resources.OFDM technology relies on adding a CP before multi-carrier symbols to ensure orthogonality between subcarriers under non-ideal channels.The CP carrying the repeated information reduces the effective rate of the transmitted data,so the indoor VLC system calls for a new multi-carrier waveform to meet the spectrum utilization requirements of the next generation communication scenario.Filter-Bank Multicarrier(FBMC)is a new multi-carrier waveform that uses a prototype filter with good time-frequency characteristics to ensure orthogonality between subcarriers.CP is replaced by the use of filter bank at transceiver in FBMC system,which is superior to the traditional OFDM technology in spectrum efficiency.However,as a system using the IM/DD mechanism,transmitted signals in VLC system must be with real-valued,single-polarization characteristics.Combining the VLC scene with the FBMC waveform will face the unique oversampling symbol structure of the FBMC signal,which makes the real-valued method of the signal in the traditional optical OFDM scheme not directly applicable to the design of the optical FBMC waveform.The optical signal is direct and cannot penetrate the wall,which enables the VLC system to achieve a high spatial multiplexing rate and also ensures a certain degree of security.However,the indoor optical channel is a non-dedicated wireless channel.In a multi-user scenario,the VLC network may have an illegal eavesdropping user to capture and intercept confidential information,which poses a certain threat to the user data security of the VLC system.Therefore,the VLC multicarrier system needs to rely on the physical layer security technology with good security performance to encrypt the data.Based on the theory of time-frequency analysis of signals and multicarrier theory,the newmulti-carrier implementation scheme of FBMC and the indoor VLC system are combined together in this paper.Under the constraints of Nyquist criterion and the evaluation of ambiguity function,the shortcomings of the time-frequency location of rectangular window function are considered,and several prototype filter impulse responses with good time-frequency location characteristics are given,including constant and variable coefficient filter.Under the premise of using the filter with good time-frequency location characteristic,and for the requirements of VLC communication scene and the unique structure of FBMC transceiver system,the oversampled symmetrical vector is used to realize the real value of FBMC signal.After the signal with overlapped and summed structure is DC-biased to achieve single polarization of the signal,a new optical multicarrier system,DCO-FBMC system,is designed and analyzed in various aspects of performance.DCO-FBMC can achieve the performance of traditional DCO-OFDM system in terms of bit error rate and sensitivity to carrier frequency offset,and is significantly better than traditional DCO-OFDM system in effective data rate.In the multi-user VLC network where there may be illegal eavesdropping users,the VLC physical layer security model is analyzed.Since the DCO-FBMC system uses filter banks in the transceiver,the physical layer encryption of the VLC system has a new degree of operational freedom.Considering that when the transceiver filter does not match,the signal will be greatly interfered.With the variable coefficient prototype filter in the case of different coefficients and different functional forms of different prototype filters,the level of mismatch of the transceiver filter will increase.A multi-filter mixed filter hopping mechanism is proposed based on DCO-FBMC system to realize the system encryption of legitimate user data.The data is encrypted by the filter and its coefficient sequence in the filter hopping mechanism,and the cipher sequence is encrypted by asymmetric cryptography algorithm.This multi-filter mixed filter hopping mechanism provides a larger set of optional filters for the system compared to a single variable-coefficient prototype filter hopping,reflecting a higher system security capacity from the difference in BER performance between the illegitimate receiving end and the legitimate receiving end.