Research On Joint Estimation Algorithm Of Time Offset And Channel Response Of PDM CO-FBMC-OQAM System

In recent years,fifth-generation mobile communication systems have become commercially available,while new application scenarios such as the Internet of Things and cloud computing are emerging.People are putting higher and higher demands on the rate and quality of service of communication systems.Due to limitations such as the need to use cyclic prefixes,high peak-to-average power ratio,and severe out-of-band energy leakage,the orthogonal frequency division multiplexing technology widely used in fourth-generation mobile communication systems is no longer able to meet the further demand for future communication systems.In order to remedy the shortcomings of orthogonal frequency division multiplexing technology,several new multi-carrier communication techniques have been developed,and filter bank multi-carrier technology is a typical representative of them.FBMC-OQAM's pulse-shaping filter has better time-frequency focusing characteristics and therefore lower out-of-band energy leakage.It does not require the use of cyclic prefixes and has higher spectral efficiency.Currently,the technology has received more and more attention.Coherent optical FBMC-OQAM communication system with polarization multiplexing(PDM CO-FBMC-OQAM)is a convergence of polarization multiplexing technology and FBMC-OQAM technology,which can increase channel capacity significantly.However,as a multi-carrier communication system,it is still heavily affected by timing deviations,while factors such as polarization mode dispersion,chromatic dispersion,and noise can also interfere with the optical signal transmission process.The object of this paper is a joint estimation method for timing synchronization and channel response of PDM CO-FBMC-OQAM system.First,the FBMC-OQAM system uses non-rectangular pulse waveform,which causes the overlapping of multiple symbols in the time domain and makes the design of timing synchronization algorithm more difficult.And the timing synchronization method of traditional multi-carrier communication system is not compatible with the signal processing flow of FBMC-OQAM,which requires additional training sequence overhead for channel estimation.To address this problem,this paper analyzes the signal characteristics of the CO-FBMC-OQAM system and examines in detail the conditions that need to be satisfied for conjugate symmetry to appear in the time domain waveform.Based on this,a binary pseudo-random sequence-assisted timing synchronization algorithm is proposed,which is fully compatible with the signal processing flow of FBMC-OQAM and can effectively suppress the interference of side peaks to the timing synchronization process.Secondly,there are two frequency-domain channel estimation methods for PDM CO-FBMC-OQAM communication system.They are Half Load method and Full Load method.Full Load method has stronger ability to resist noise and polarization mode dispersion.Based on the dual-dependent pilot principle,we redesigned the training sequence and the calculation rules of the channel response matrix for the Full Load method.The advantage of this method is that by combining with our proposed timing synchronization algorithm,the training sequence used in this method is able to perform not only the channel estimation task of the CO-FBMC-OQAM system,but also the timing synchronization task,realizing the joint estimation of timing offset and channel response.