Research On Sequence Design And Its Application In OFDM System

As a multi-carrier technology,OFDM has the advantages of high spectrum utilization,strong anti-interference ability,and simple system structure.It has been widely used in the field of wireless communications.However,in the OFDM system,there are high PAPR and sensitivity to timing offset problem.Complementary sequences have good correlation characteristics.Applying them to OFDM systems can not only reduce PAPR in the system,achieve accurate synchronization,but also not distort the transmission signal.However,currently there are fewer design methods for this sequence and the length is limited.For this reason,this article designs the complementary sequence,and studies the application of the sequence in PAPR suppression and synchronization techniques in OFDM systems.The main work is as follows:(1)Two new 16 QAM complementary sequence design methods are proposed: based on binary Golay complementary sequences,new mapping relationships and cascades can be used to construct new Golay complementary sequences;based on complete sequences and Hadamard orthogonal matrix,new periodic complementary sequences can be obtained.The two newly proposed design methods allow a binary sequence to generate a sixteen-element sequence through a new mapping relationship,and can flexibly obtain a variety of different complementary sequences according to the number of cascades and the parameters of the Hadamard orthogonal matrix.Theoretical analysis shows that the two newly designed complementary sequences have good correlation characteristics.(2)Aiming at the problem of too high PAPR in OFDM system,the newly designed complementary sequence is applied to the system,and it is proved that if the complementary sequence with good correlation is used to reduce the PAPR of the OFDM system,the PAPR value of the system is only equal to the complementary sequence neutron.The number of sequences is related to the length of the sequence.The random OFDM signal is compared with the encoded OFDM signal.The simulation results show that the two newly designed complementary sequences can effectively reduce the PAPR in the system.(3)As the OFDM system is more sensitive to timing offset,two improved synchronization algorithms based on complementary sequences and CAZAC sequences are proposed.Algorithm 1 improves the training sequence,and uses two sets of sequences to redesign the training sequence structure in the synchronization algorithm.Algorithm 2improves the sliding window,and uses two sets of sliding windows to perform correlation operations on different training sequences respectively.The two newly proposed improved algorithms both use conjugate symmetric structures,so they can reduce the computational complexity in the synchronization algorithm.At the same time,simulation experiments show that compared with the classical synchronization algorithm,the two improved algorithms can still achieve accurate synchronization at low SNR,which can effectively reduce the interference of the secondary peaks to the main peaks,and the root mean square error is small.The two sets of new complementary sequences designed in this paper can effectively reduce the PAPR of OFDM systems.Two improved synchronization algorithms based on complementary sequences can achieve accurate synchronization of the system.