| Research task is about the Orthogonal Frequency Division Multiplexing (OFDM) technique that works as the key to the high speed data transmission in the railway circumstance. After the comparison among several OFDM systems, our research choose the Digital Audio Broadcast (DAB) for a reference to the railway circumstance research. Research carry on under the Modulator part in the DAB standard with the Digital Intermediate Frequency (DIF) Technique for the design of Intermediate Frequency (IF).Research follows the general step that is system simulation first, then designing a hardware circumstance, finally development of software.In the simulation step, do research in the system simulation according to the parameters of mode I of DAB for baseband and digital frequence converter for IF. Then, do research in the system performance simulation under channel of the AWGN and multipath. In the hardware design step, design the PCB for system realization includes the transmitter part and receiver part, and due to the many high speed digital signals, take many high speed circuit manners to prevent from the circuit noise. From the final tests, we can see, it is very useful to the system performance with these methods. In the software development step, it focus on DSP, FPGA/CPLD, and digital upconverter (DUC) & digital downconverter (DDC). With DSP development, it main completes the baseband process in accordance to DAB standard. With the FPGA/CPLD development, it main completes system clock design, high speed data buffer between the baseband and IF, and specific application bus for the ASIC. With the DUC&DDC development, it main completes the DAB IF signal output, and data collections in receiver. Finally, research give the debug results and test results, and then point out the next step work in the future. |
