Research On Timing Synchronization And Carrier Synchronization Algorithm Of High Order QAM

In recent years,with the development of high-speed information transmission,modern wired links and wireless networks need higher channel capacity,and now in the 5G era,the available spectrum resources are more and more scarce.Therefore,how to improve the information transmission rate is a research hotspot.Quadrature amplitude modulation(QAM)can transmit information in both amplitude and phase dimensions,so increasing the modulation order can obtain more capacity gain,which is widely used in high-speed microwave and other digital systems.However,the disadvantage of high order is that the sensitivity of the receiver is greatly reduced.When the QAM order is doubled,the receiver sensitivity will be reduced by-3d B.Therefore,how to improve the receiving performance of the receiver,and how to demodulate the amount of information correctly under the condition of channel damage such as timing delay and frequency offset,is a rese arch problem worthy of consideration.In this paper,1024 QAM is taken as the analysis object to study the classical algorithm of high-order QAM in timing synchronization and carrier synchronization module,as well as the improvement method for the characte ristics of high-order modulation.Firstly,in order to simplify the complexity of the system,an equivalent baseband mathematical model is established from the transmitter to the receiver,which includes channel damage such as delay and carrier offset;The n,the basic theories of loop filter and digital controlled oscillator in the synchronous feedback loop and the influence of frequency and phase offset on the signal are deeply analyzed,and the measurement standards of the two synchronization methods are established according to the actual situation,and the lower bounds of Cramer Rao estimation(MCRB)of the theoretical open-loop algorithm and closed-loop algorithm are given;Then,in the aspect of timing synchronization,the closed-loop Gardner algorithm and open-loop digital square filter(O&M)algorithm are mainly studied.The interpolator effect of the interpolation filter in Gardner algorithm is improved,and a group of interpolation coefficients are generated according to the basis function design,w hich makes the improved interpolation filter more in line with the ideal conditions;For O&M algorithm,a pre-filter is added to reduce the timing jitter.In the research of carrier synchronization,the open-loop frequency offset algorithm is used to compensate the frequency offset quickly.The DFT frequency offset estimation algorithm and the polarity decision open-loop algorithm are analyzed and compared respectively.Aiming at the residual error that cannot be eliminated introduced by the polarity decision algorithm,an improved algorithm of multi threshold is designed,and the DD algorithm is combined with the polarity decision algorithm in the structure of phase synchronization,A joint carrier synchronization algorithm is proposed.The final phase offset estimation accuracy is less than,and its performance is similar to that of high SNR in small SNR.