| Summary: | 碩士 === 國立高雄第一科技大學 === 電腦與通訊工程系碩士專班 === 106 === When continuous phase modulation (CPM) has an infinite number of different pairs of input data sequences, but there’s only a limited Euclidean distance in its corresponding output signal, we call it catastrophic sequence, and this modulation is called Catastrophic CPM. Due to the two most commonly used continuous phase modulations: LREC CPM and LRC CPM are mostly catastrophic continuous phase modulation. (REC represents rectangle frequency shape pulse, and RC represents raised cosine frequency shape pulse). Studying the effects of catastrophic sequences on CPM is a meaningful and interesting work.
In general, the minimum normalized squared Euclidean distance (MNSED) can be used to estimate the bit error rate (BER) of the modulator in the white noise channel. We have shown in recent studies that such catastrophic sequences tend to produce smaller MNSEDs, and it has made poor performance of many architectures in LREC and LRC systems. In past studies, although catastrophic sequences could be converted to non-catastrophic sequences using precoders. Even if the catastrophic CPM becomes a non-catastrophic CPM, this method does not change the MNSED of the modulator. According to the results of Professor Yang Hsinhsyong’s research, this study has found that the problem of catastrophic CPM can be solved by asymmetrical frequency shaping pulse. And can effectively extend the constraint length, which can increase the probability of CPM generating a larger MNSED, thereby improving the error performance of CPM.
This study is based on the principle of asymmetrical frequency shaping pulse (AFSP) production proposed by Professor Yang and several different AFSPs for MNSED and bandwidth simulation. Under the comparison of energy-bandwidth, we get a new non-catastrophic CPM with a coding gain of up to 3.5dB compared to traditional CPM at the same bandwidth.
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