| Along with the development of communication and information technologies, mobile multimedia broadcasting service is becoming an important application in the broadcasting and television industry. Various mobile multimedia broadcasting standards have been announced, among which China Mobile Multimedia Broadcasting (CMMB) standard is the one worth paying attention to. CMMB uses orthogonal frequency division multiplexing (OFDM) technique and realizes the high speed transmission of audio and video information by making full use of OFDM characteristics featured by high spectral efficiency and multipath immunity. However, compared with the single-carrier systems, CMMB system also has some technical barriers, one of which is synchronization. Therefore, this thesis focuses on investigating the frame (time-slot) synchronization and symbol synchronization techniques based on CMMB system.Firstly, this thesis introduces the architecture and key techniques of OFDM-based CMMB system.Then, the broadcasting environment is studied. Some typical channel models are selected for simulation according to the complex terrain conditions, which are possibly faced in the terrestrial transmission application of CMMB system. After that, this thesis analyzes the influences of frame (time-slot) synchronization error and symbol synchronization offset on the receiver. Based on the analysis, some criteria to evaluate the performance of synchronization algorithms are proposed.Via studying on the existing frame synchronization and symbol synchronization algorithms, this thesis finally proposes three novel algorithms including: the pretreatment-based frame (time-slot) synchronization algorithm, the low-complexity time-domain symbol synchronization algorithm, and the joint frame (time-slot) synchronization and symbol synchronization algorithm. The pretreatment-based frame (time-slot) synchronization algorithm integrates the existing algorithms' superiority so as to implement the accurate detection of frame (time-slot) data with lagre carrier frequency offset in high SNR conditions. The symbol starting point estimation performance of the proposed algorithm is better than that of SCA algorithm under the same carrier frequency offset condition, and is quite close to that of local-replica correlation algorithm with small carrier frequency offset caused only by Doppler effect. The low-complexity time-domain symbol synchronization algorithm is derived from traditional MMSE algorithm in the condition of small carrier frequency offset of fractional subcarrier spacing. The implementation complexity of the proposed algorithm is only about 1/4 of traditional MMSE algorithm with nearly the same estimation performance. The joint algorithm fully considers the characteristics of CMMB system and selected channel models and combines the above mentioned pretreatment-based frame (time-slot) synchronization algorithms with the low-complexity symbol synchronization. The ratio of estimated FFT window starting point locating behind the correct position and in the ISI region largely falls, and the number of symbol which causes ICI and ISI reduces as well. |
PDF Full Text Request