Research On The Key Technology Of DMB SFN And The System Realization

Digital Multimedia Broadcast(DMB)has been evolved from its initial usage,broadcast only,to various new applications such as emergency warning,public information announcement and data transmission.The new applications call for higher receiving quality.In many situations,Single Frequency Network(SFN)is needed to get better coverage without increasing the transmit power.The traditional DMB SFN is complicated and expensive because it needs dedicated data transmission network.This has seriously affected the promotion of the DMB new applications.This thesis proposes a low cost small-scale DMB SFN solution based on the high integration DMB transmitters developed by Chongqing University of Posts and Telecommunications(CQUPT).The proposed DMB SFN uses GPS as time and frequency reference,and can work in a common local area network(LAN).Firstly,the DMB ensemble data is transferred from the multiplexer to each transmitter in Server/Client mode,with the multiplexer as the server and each transmitter as the clients.A point-to-point TCP connection is established between the server and each client to keep the data transmission reliable even in a common LAN,at a cost of slight higher bandwidth.Secondly,each transmitter is synchronized by the synchronization control circuit added in the FPGA of the transmitter.The circuit counts the frequency deviation of the system clock of each transmitter using the PPS signal from a GPS receiving module,and then regulates the cycle time of a new clock divided by 4 of the system clock.With the assistance of the UTC time read from the GPS receiver,the new clock generates the timing control signals to each computing block of the transmitter.The ensemble data fed to each transmitter are then modulated synchronously by comparing the timing control signals of the transmitter and the time stamps inside each ensemble frame.Finally,laboratory test using RF combiner and filed test in wireless environment were carried on using two DMB transmitters.The test results show that:(1)the two transmitters can be correctly synchronized with time deviation less than 1us and frequency deviation less than 0.5Hz;(2)in the overlapped area,the receiving PBER in SFN mode can be significantly reduced than that in MFN mode.The test results prove the proposed design is correct and efficient.