Performance Optimization Of DRM Broadcasting And Transplantation To Mobile Platforms

The rise of a variety of advanced wired and wireless digital communication makes it possible for people to conveniently enjoy different kinds of digital data service in high speed, and this trend distracts people from traditional analog communication schemes, and AM(Amplitude Modulation) broadcasting is such an example. In order to energize the tradition AM broadcasting, the concept of digital audio broadcasting is proposed accordingly, and DRM (Digital Radio Mondiale) is one representative. With the modification of the equipments of analog AM broadcasting, DRM can realize the transmission of digital information. Thus, the cost of DRM can be kept low, and DRM has great potentials.For the purpose of understanding the principles of DRM, improving its performance and promoting its application, this thesis focuses on the following 3 aspects:First, DRM employs OFDM (Orthogonal Frequency Division Multiplexing) to provide robustness in fading channels. Since OFDM is quite sensitive to errors in synchronization, DRM receiver should stress a special emphasis on the design and implementation of the synchronization of OFDM signals. This thesis introduces the theoretic foundation as well as the implementation of frequency synchronization, time synchronization and channel estimation in DRM receiver. These contents will be especially instrumental in understanding the principle of DRM and in analyzing its theoretic performance.Second, DRM standard adopts MLC (Multilevel Coding) as the encoding structure in its channel coding module and uses RCPC (Rate Compatible Punctured Convolutional) codes as the sub codes in each level. In order to lower the BER (Bit Error Rate) of DRM system to guarantee a reliable transmission, this thesis replaces RCPC codes with LDPC(Low-Density Parity Check) codes in channel coding. According to the MF and HF channels in which DRM signals are transmitted, this thesis designs the code rates distribution of MLC over such channels and simulates the performance in the typical channels. Simulation results verify the efficacy of LDPC codes in improving the BER performance. Meanwhile, as a subtype of LDPC codes, Quasi-Cyclic LDPC (QC-LDPC) codes have special properties in structure which can be utilized to save memory in storing the parity check matrices as well as to reduce the encoding complexity. On account of this, this thesis replaces the general LDPC codes with QC ones to promote the efficiency of the channel coding module in DRM system. Aiming at constructing QC-LDPC codes by cyclic lifting of protograph, this thesis proposes efficient algorithms in construction, and the simulation reveals that the codes constructed by the proposed algorithm have better performance in the low BER region. In addition, in order to further exploit the structural properties of QC-LDPC codes, this thesis proposes a new encoding method of QC-LDPC codes, which decomposes the encoding of a QC-LDPC code into the encoding of several base codes, reducing the complexity of preprocessing the parity check matrices in encoding significantly and saving the memory in storing the encoding matrices. The encoding complexity of the proposed method is also analyzed in detail.At last, DRM receiver can be implemented in two ways:the first one is to use specific hardware equipments to demodulate DRM signals, and the other one is to receive DRM signals by AM radio and demodulate them through software by inputting the signals into PC. The cost of the software scheme is lower, while it lacks enough flexibility because of the prerequisite of a PC. In order to promote the application DRM receiver, this thesis transplants the DRM receiver software to Android and iOS, two of the most popular operation systems of smart mobile devices nowadays. Then DRM signals can be received and demodulated by the combination of a traditional AM radio with a smart mobile device at any time and any place, further reducing the cost of DRM broadcasting.