Algorithm And Design Of Downward Compatible Digital AM Broadcasting

With the development of the society, multimedia has seeped into every aspect of people’s lives. Traditional AM broadcasting which can only provide audio program will no longer meet the needs of people and cannot make full use of the valuable spectrum occupied. There is an urgent need for digital transformation of AM broadcasting. Although there have been some digitization proposals recognized internationally, they are not in line with China’s current situation. Based on this, a backward-compatible digital AM broadcasting system was proposed. This thesis further studies and improves this MPPSK/ DSB-AM hybrid modulation based system in terms of modulation methods, demodulation algorithms of audio and data flow, and transmission way, and channel coding is introduced making the demodulation performance better.An efficient modulation method MPPSK (the M-ary Position Phase Shift Keying) was introduced and its spectrum and demodulation performance is analyzed. Improved MPPSK modulation method and its advantages are described. A comparison of transfer rates, bandwidth and demodulation performance is made between the original MPPSK modulation and its improved version. Key technology for the MPPSK demodulation is discussed.The system consists of transmitter and receiver. Appropriate parameter is selected for transmitter based on MPPSK/DSB-AM scheme to achieve high data rate in the specified bandwidth, and an equivalent is made to the transmitter’s output matching network. The receiver is divided into audio demodulation and digit demodulation. Several audio demodulation schemes are put forward and methods that can improve the audio quality demodulated are used. All these schemes and methods are validated both in subjective aspect and in objective aspect. Band-pass filter is designed to separate digital signal in coherent receiver for digit flow. Some improved symbol judgement methods are proposed and proved to be effective in simulation. Two possible receivers of the overall system are described and a single sideband transmission mode is putfoward based on the second one, which can effectively reduce the error rate and show good applicability for low SNR environment with the guarantee of no damage to other properties.Finally channel model is established after some research on AM broadcasting. Channel coding is introduced in order to enhance the anti-interference capability in multipath fading cases of the system. Convolutional coding used in DRM and IBOC standards is compared with LDPC coding in simulation experiments, which demonstrates that the LDPC coding has stronger error-correction performance in this system.