Research Of Key Technology In Filter Bank Multi-carrier For Optical Wireless Communication

With the gradual integration of radio frequency communications and optical wireless communications,the development of future optical wireless communication networks compatible with the next generation mobile communication systems has become the direction of the industry.The research on related communication theories and technologies has urgent practical needs and important scientific value.Compared with the single-carrier transmission scheme,the main advantages of the optical orthogonal frequency division multiplexing(OOFDM)scheme include its excellent ability to resist inter-symbol interference and nonlinear interference,simple equalization,and allowing separate coding,modulation,and power control of low-speed data streams on each subcarrier.At present,the multi-carrier communication scheme mainly represented by OOFDM is gradually becoming the mainstream communication mode in the field of optical wireless communication except single-carrier modulation.However,the existing OOFDM transmission scheme has some inherent defects that are difficult to overcome,including slower out-of-band attenuation,higher requirement for frequency synchronization,and incapability of acquiring the overall channel capacity when the channel conditions on each subcarrier are different.In view of this,the transmission scheme based on filter bank multi-carrier technology in optical wireless communication has begun to attract industry attention in the past few years.This paper focuses on the key technologies of filter bank multi-carrier in optical wireless communications.Firstly,it summarizes the development of filter bank multi-carrier technology in optical wireless communications,the channel modeling of optical wireless communication systems and the basic principle of filter bank multi-carrier.Furthermore,two existing optical filter bank multi-carrier communication schemes,namely direct current-biased and non-direct current biased optical filter bank multi-carrier,are introduced.Secondly,in view of the complex filter design and the poor transmission performance in multi-user networks of the existing optical filter bank multi-carrier transmission scheme,this paper proposes a direct current biased optical filter bank multiple access(DCO-FBMA)scheme for optical wireless communication uplink multi-user networks.It adopts a common low-pass filter as a prototype filter,which is no longer limited by the perfect reconstruction/nearly perfect reconstruction constraint,and the multi-user access is performed by using narrow-banded subcarriers and wide-banded subcarriers respectively,and the receiver performs signal demodulation by joint subband frequency domain equalization.Then,the signal is subjected to a critical down-sampling operation in the analysis filter bank in the above proposed scheme,which may cause the signal at the edge of the filter to be “folded” into the passband after down-sampling,resulting in information loss.Two improved receiver designs for optical filter bank multi-carrier communication scheme are proposed.Firstly,considering the over-sampling signal for data detection at the receiver,we propose a receiver based on over-sampling analysis filter bank.Then,further consider abandoning the analysis filtering process,we propose a down-sampling frequency domain receiver.In addition,in order to obtain better system detection performance,an iterative multi-user interference cancellation technique is introduced at the receiver.Finally,because of the fact that the transmission signal of each user in the above proposed scheme is only loaded into a certain frequency range,the transmitted signal may be seriously distorted by the random fading channel,especially the channel with strong frequency selectivity.An optical filter bank multiple access system based on dual-band structure is proposed.It allows each user to transmit their signals on two subbands,that is,each subband simultaneously transmits information of two users,which can increase the frequency diversity gain of the system.In addition,since the proposed scheme introduces inter-user interference information,the receiver performs joint subband frequency domain equalization operation by means of minimum mean square error estimation and iterative parallel interference cancellation to achieve correct signal demodulation.In summary,this paper mainly studies the key technologies of the filter bank multiple access scheme in optical wireless communication systems.Firstly,a DCO-FBMA scheme for optical wireless communication multi-user uplink networks is proposed,including wide subband and narrow subband access modes.Then,based on the wide-banded DCO-FBMA scheme,two improved schemes are proposed for the receiver.Finally,a wide-banded DCOFBMA scheme based on dual-band structure is proposed.Theoretical analysis and simulation results show that compared with the conventional DCO-FBMA and the DC-biased optical orthogonal frequency division multiple access,the proposed wide-banded DCO-FBMA scheme has lower peak-to-average power ratio and better bit error ratio performance.