Research Of Carrier Aggregation In LTE-Advanced Downlink

In response to International Telecommunications Union Radiocommunication Sector(ITU-R) on the fourth generation communication technology requirements,3GPP officiallylaunched the follow-up evolution project of LTE—LTE-Advanced in March2008,assubmitted IMT-Advanced candidate technology to the ITU-R. LTE-Advanced system havegreatly improved in the peak data rate,the peak spectral efficiency, symtem bandwidth,andcompatibility etc.In order to achieve the performance targets of LTE-Advancedsystem,LTE-Advanced introduces many new key technologies on the basis of the LTE.Carrier aggregation is one of the key technologies in LTE-Advanced.It is aggregatingcontinuous or discrete LTE system carrier into the lager bandwidth LTE-Advanced systemcarrier.It is presented to solve the problem of shortage of radio spectrum resources,not onlymeet the LTE-Advanced bandwidth needs,but also improve the utilization of the discretespectrum. At the same time,Carrier aggregation technology also realizes the smoothtransition of the LTE system to LTE-Advanced system,maintains the system’s backwardcompatibility,reduces the commercial time.This paper first introduces the related concepts of carrier aggregation in detail,including the classification of carrier aggregation, carrier aggregation schemes and carrieraggregation issues to be considered.Then the related performance of the carrier aggregationis studied from two aspects,the one hand is the impact of guard band on the carrieraggregation system performance, the other hand is multi-carrier aggregation and directwideband aggregation comparison.The former shows that guard band setting can reduceinterferences between the adjacent carriers.The latters shows that direct widebandaggregation is better than multi-carrier aggregation,due to the better flexibility andcompatibility,The combined use of the two aggregations shoule be considered in practice.As LTE-Advanced downkink adopts OFDM technology,the system is sensitive tosynchronzation errors genetated by multipath delay and oscillator instability etc, includingSampling Timing Offset, Symbol Timing Error and Carrier Frequency Offset.Therefore,thispaper focuses on the suppression of synchronization errors based on non-continuous carrieraggregation system in the final.Firstly,this paper describes the impact of synchronizationerrors on the system.Then,for the suppression of synchronization errors,this paper proposes two methods of synchronization errors suppression,respectively are block type pilot andtraining sequence based on synchronization errors suppression algorithm.The formerexploites a special CAZAC sequence as the pilot pattern,and the latter uses Zadoff-Chusequence as the training sequence.According to the simulation analysis show that the twoalgorithms both can suppress the synchronization errors of the non-continuous carrieraggregation system, achieve a good effect of suppressing synchronization errors,andimprove the system performance.