Research On Reception Performance Of SFN For DTT Using Synchronous Technology Based On Modulated Wave And Device For Synchronization

Nowadays construction of single frequency network for digital terrestrial television(DTT) has two modes: the synchronous technology based on baseband mode and the synchronous technology based on modulated-wave mode. Modulation diversity between transmitting stations in Baseband synchronous system cause the co-channel interference resulting in reception performance degradation. While the synchronous technology based on modulated-wave uses "once modulated, multiple distributing" approach, each transmission station is no longer separately modulated, while using the device which has high-precision and high-bandwidth processing capability to ensure SFN time synchronization. In this paper, the two parts work based on characteristics and application requirements of the modulated-wave synchronization technology have done.Firstly, the relationship between the reception performance of the synchronization system based on modulated-wave and the factors-the IQ imbalance and nonlinear characteristics of amplifier was focused on. The simulation results show that when the signal to noise ratio less than 13 dB, the factors have tiny influence to the reception performance of synchronous technology based on modulated wave. As the SNR increasing, the influence of these factors on the performance of the system gradually increases. Meanwhile, the influence of the time synchronization accuracy also was analyzed, providing a reference and basis for performance analysis on synchronization technology based on modulated-wave.Then, the design scheme based on polyphase filtering technique for the high efficiency channelized RF device for synchronization was proposed. There are two key components in this device: a channelization control module and delay control module. In the design of channelization control module, the direct parallel filters banks, tree-liked filter banks, polyphase filter banks used in this paper were compared in computational complexity. Simulation results show that in the realization of the 8-channel control, the polyphase filter banks used in this paper has significantly lower addition and multiplication calculation times than the other two algorithms; In the FPGA implementation, resource consumption saves about 60% than the method direct parallel filter banks approach; In the design of the delay control module, synchronous FIFO was used to achieve the delay accuracy about 100 ns.