Real-Time Demodulatio Of Composite Modulation Radios

As the development of the diversity of the modern transmission media, digital communication has been the inevitable trend. As a result of specific application environment and requirements, the digital development process of analogue amplitude modulated (AM) radio is quire slow, which is a traditional information transfer mode. Considering the large amount of AM radio listeners and analogue broadcasting equipment, it will be such significant if we could promote digital broadcasting which is compatible with the analogue amplitude modulation radio.This paper will put forward a hybrid modulation system, which can transmit digital information without changing the modulation of the current AM radio. We use the efficient modulation signal, which has the character of crunch spectrum, to take the place of the sine carrier in traditional DSB-AM modulation, and then, this digital signal with constant envelope wile bear the amplitude modulation from analogue audio. While the receiver it, this particular modulation signal will be divided into two different parts:one part can reproduce the analogue audio directly through the envelope detector in current radio sets; the other one is digital demodulation, which can use either coherent or non-coherent manner.Firstly, this paper explains the fundamental principle of EBPSK modulation which is proposed and improved by the laboratory, and gives an introduction about MPPSK based on EBPSK; then detailed analyzes the coherent demodulation and non-coherent demodulation of EBPSK and MPPSK; finally, according to the requirements of AM radio's transmitting, MPPSK is chosen as digital modulation in our communication system, and several appropriate modulation parameters are provided.Next, the principle and realization of the entire MPPSK/DSB-AM hybrid broadcasting system are introduced. In the transmitting end we have discussed about how we balance digital signal and analogue signal as well as a series of measures respond to the AM transmitting mask; and the receiving end concludes recovery of analogue audio, coherent and non-coherent demodulation of digital signal and the real-time phase synchronization during the judgment. After all a simulation under certain parameters is proposed, as well as the realization on hardware platform SDR is given.At last, this paper provides two other methods to implement digital broadcasting. For the purpose of transmitting both digital signal and analogue signal at the same time, frequency division multiplexing (FDM) is adopted. These methods can base on the traditional AM radio system and be applied for more situations.