Research On High Accuracy Turbo Synchronization Algorithm At Low Signal-to-Noise Ratio For Short Burst Communication Systems

With the development of communication system, Wireless communication systemsare required to provide services based on high data rates burst-mode packet-datatransmission, capable of operating at very low Signal-to-Noise Ratio and large Dopplerfrequency offset conditions. Recently, pepople pay great attention to Shannon code forhigh coding gain and low Signal-to-Noise Ratio, however, Shannon code’s decodingprocess is very sensitive to carrier synchronization errors, requiring exact knowledge ofthe carrier frequency and phase, it is very importance for communication to obtainaccurate carrier synchronization. Therefore, it is a key that how to realize effectivecarrier synchronization with short pilot symbols at low Signal-to-Noise Ratio (SNR)and large frequency offset conditions.Based on research of data frame and carrier synchronization algorithms at homeand abroad, firstly, we introduce the encoding/decoding algorithms of Turbo code andextended Turbo decoder suit for joint Turbo iterative decoding and carriersynchronization, and main factors affecting the decoding performance are alsodiscussed; secondly, based on theoretical performance analysis for carrier parameterswith only pilot symbols, the Cramer-Rao bound (CRB) and modified Cramer-Raobound (CRB) of carrier parameters are deduced with joint pilot symbols and datainformation; thirdly, based on existed data frame structures and time-domain correlationestimation algorithm, variable distance data frame structure is proposed, which cansatisfy the system’s requirement for estimation accuracy and range by flexibly changingdistance between two pilot blocks, and verifies the structure is suitable for short burstcommunication system; finally, joint pilot and iterative decoding soft-output carriersynchronization algorithms are proposed, and choose proper data frame structure forsystem’s requirement, based on time-domain correlation estimation method, pilotsymbols are utilized to perform coarse synchronization, pilot symbols and decodingsoft-output are used to perform fine synchronization, Theoretical analysis andsimulation results show that the algorithms have low computation complexity and cancorrect large range frequency offset with only very short pilot symbols, which can maketurbo code achieve optimal BER performance.