System Design And Implementation Of Downward Compatible Digital AM Broadcasting

With the continuous development of modern communication technology, digitalization has become a mainstream trend. All kinds of new type of digital system has gradually replaced analog communication system. However, the traditional analog amplitude modulation (AM) broadcasting, its digital development process is very slow. Considering our country still has many AM radio listeners and AM radio in the event of sudden emergency still plays an irreplaceable role, therefore, it is very urgent and great significant to promote digital AM broadcasting.Our laboratory through many years research, puts forward a digital amplitude modulation broadcasting system to realize the digitalized transmission which is compatible with the analogue AM broadcast. At the transmitter of this system, the M-ary phase position keying (MPPSK) modulated signal with low sidelobe of power spectrum, is adopted to replace the sine carrier to bear the amplitude modulation of analogue audio. While at the receiver the composite modulated signal received is divided into two parts:one part directly follows the envelope detector used in current radio sets to reproduce the analogue audio and to achieve the backward compatibility; and another part can get the data through the non-coherent and coherent manner. The system can transmit analogue audio and data simultaneously within the existing AM broadcasting scheme, except for a slight modification to current analogue AM broadcasting transmitters.This thesis first introduces the EBPSK, MPPSK and full hopping MPPSK modulations. Then make a detailed analysis of the demodulation core module, i.e. the impact filter, in efficient modulation techniques. Both the non-coherent receiver and the coherent receiver are described, and their performance are compared via simulations.Next, the entire digital AM broadcasting system is introduced. Make an analysis of the digital AM radio transmitter system including the parameter selection of "digital carrier", hybrid modulation technique and the transmitter resonant loop shaping filter simulation. Then, briefly describe the RS coding and intertleaveing used in the system. Besides, expound the downward compatible with the audio demodulation, focusing on the pretreatment module for audio compensation. Analyze the two kinds of receiver of the digital AM broadcasting system and give their performance comparisons.Finally, in order to verify the feasibility of digital AM broadcasting system, we use the Lyrtech SFF SDR DP platform to achieve a composite modulation scheme that mixes the full transition MPPSK modulation and the analog audio programs, and to successfully demodulate the two signals. Successful implementation of the hardware platform shows that the system has a good performance, and is expected to become the framework of China’s digital AM broadcasting.