Research On Key Technologies Of Filter Bank Multicarrier With Offset Quadrature Amplitude Modulation

Filter bank multicarrier(FBMC)is a candidate waveform for mobile communications in the future.Based on orthogonal frequency division multiplexing(OFDM),FBMC employs a pulse shaping by involving a prototype filter at each subcarrier to suppress the out-of-band radiation and reduce adjacent channel interference.Accordingly,FBMC can provide a flexible frequency band resource usage and is supposed to be applicable to the asynchronous networks and fractional spectrum utilization scenarios,such as massive machine-type communications and cognitive radio.To maintain a high bandwidth efficiency,offset quadrature amplitude modulation(OQAM)is usually adopted in FBMC systems to achieve the maximum data symbol density in the time-frequency plane while maintaining good time-frequency localization,whereas the orthogonality of the OQAM signal is restricted only to the real field.Owing to these system features,FBMC-OQAM faces some specific signal processing problems need to be addressed.Several important issues of FBMC-OQAM,e.g.,the bit error probability(BEP)analysis,synchronization,channel estimation,and the system scheme for low peak-to-average power ratio(PAPR),are mentioned in this dissertation.For a waveform technology,an important performance metric is the BEP over multipath channels.To evaluate the BEP performance fast and accurately,the BEP theoretical analysis method is firstly studied in this dissertation.Based on the general baseband system model of FBMC-OQAM and OFDM,the cumulative distribution function of the received data symbol can be converted to the conditional probability of a Gaussian Hermite variable,and then a probability calculation method for the received data symbols is proposed to cover both Rician and Rayleigh fading channels.According to the symbols mapping and bit error decision rules of the Gray coding,the explicit BEP expressions are derived for the signal with arbitrary constellation sizes.Simulation results validate the proposed theoretical analysis method.Some key signal processing issues,e.g.,synchronization and channel estimation,are important factors for the performance of communication systems.In FBMC-OQAM,the prototype filter causes a symbol overlapping effect,especially in the case of continuousmode transmission.Thus,the synchronization sequence design needs to involve multiple symbols,which may add computation complexity and decrease bandwidth efficiency.Owing to the real orthogonality of the OQAM modulation,the received signal suffers intrinsic imaginary interference,which complicates the frequency domain channel coefficient estimation.To address the synchronization issue in the case of continuous-mode transmission,a synchronization method with a high bandwidth efficiency is proposed by exploiting the conjugate symmetry of the OQAM signal.First of all,by using successive symbols with specific values to counteract the destructive effects of pulse shaping and symbol overlapping on the conjugate symmetry of the OQAM signal,a sequence pattern is proposed to generate a conjugate symmetric signal in the time domain.Then,considering the conjugate symmetry,the synchronization sequence,as a variant of the Zadoff-Chu sequence,is designed for time-frequency synchronization.By virtue of the properties of the proposed synchronization sequence,a combined timing algorithm is proposed by considering both auto-correlation and replica-based correlation detection to achieve a high detection signal-to-noise ratio and be applicable to the large carrier frequency offset cases.For the channel estimation,in the several schemes have been investigated in the literature,the training sequences for channel estimation and synchronization are usually designed separately,which will cause a large bandwidth efficiency loss.In this dissertation,a joint symbol timing and channel estimation method for FBMC-OQAM systems is proposed.A new training sequence pattern with a high bandwidth efficiency is designed.In this scheme,a pilot symbol and two auxiliary data symbols are used to generate a conjugate symmetric sequence in the time domain while protecting the pilots from the intrinsic interference.Thus,channel estimation can be performed directly by the pilots,and an auto-correlation symbol timing algorithm is introduced by exploiting the conjugate symmetry property.The simulation results demonstrate that the proposed scheme achieves good performances in terms of timing accuracy and channel estimation.In particular,a pulse tail truncation scheme is proposed for burst-mode transmission to further improve bandwidth efficiency while maintaining good orthogonality and low out-of-band radiation.As a multicarrier modulation technology,FBMC-OQAM also faces a high PAPR problem.Owing to that the OQAM preprocessing splits the complex data into real and imaginary parts,just combining discrete Fourier transform(DFT)spreading and OQAM can not achieve the same PAPR performance as a singlecarrier signal.To addressthis problem,this dissertation proposes a DFT-spread scheme based on a data conjugate symmetric mapping.According to this scheme,the OQAM preprocessing can be avoided,and a better PAPR reduction can be achieved.In addition,the effect of the prototype filter on PAPR is studied via numerical simulation and a trade-off exists between the PAPR and out-of-band performances.Compared with the original FBMC-OQAM,the proposed scheme also benefits from the frequency diversity provided by the DFT spreading,and thus can achieve a lower BEP for the signal with a small constellation size over multipath fading channels.