| The PCM/FM (Pulse Code Modulation/Frequency Modulation) system adopts pre-modulation filter, limiting the signal bandwidth and gathering up useful transmitted power. And the way of non-coherent demodulation including limit-frequency discrimination is used, easy for engineering application and suitable for fading channel difficult to carry out phase-coherent detection, capable of suppressing amplitude fading and phase distortion, becoming a common method of code modulation in our country's area of telemetry. But it has a low bit rate up to 2Mbit/s at most, unable to meet the need of new telemetering plan. Furthermore, some problems such as frequency-selective fading and intersymbol interference deteriorate under the condition of high bit rate.Firstly, The paper reviews the history of PCM/FM system and summarizes the related basic theory. Secondly, two algorithms of non-coherent and coherent demodulation are introduced. Finally, based on the two algorithms above, software simulation proceeds for PCM/FM signals'modulation and demodulation with a bit rate of 10Mbit/s and its results and analysis are given. This simulation can be referred while the high-speed telemetering signal's performance of demodulation is to be improved. |
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