Research Of The High-speed Nonlinearly Amplified 16QAM Modulation By Folding Two QPSK Signals

High-speed digital modulation is one of the key technologies in communication system. Now the QPSK is the most common in space communication in the world, but it's spectral efficiency is only 2b/s/Hz. With the developing of the space communication, the frequency spectral becomes more and more crowded, so the QPSK becomes a bottleneck. The spectral efficiency of 16QAM is 4b/s/Hz, which higher than it of QPSK. But the conventional method, that is Quadrature Amplitude Modulation, must be adopting linear amplifier because the 16QAM signal is multilevel. The linear amplifier can only work in un- saturated state then the efficiency is very low so result in the precious energy resource in spacecrafts was wasted. From now, only the INTELSAT did the 16QAM experiments in space communication, and their 16QAM is made by conventional method, and its data rate is not high.For QAM be applied in space communication, This paper study an unconventional method of folding two QPSK modulated signals to make a 16QAM modulated signal which is fit for transmitting high-speed data in the satellites. This paper presents how to make 16QAM signal by folding two QPSK signals. Different from the conventional QAM, the method of folding two QPSK is to generate the strong 16QAM signal by combining two QPSK signals which have been amplified by each saturated amplifier. This method can not only improve the spectral efficiency, but also make full use of the precious energy on satellites. The 16QAM generated by this method is named NLA-16QAM. The data rate of the NLA-16QAM exceed 200Mb/s in L band when EVM less than 8.59%.For the more, In the paper, I have studied the more advanced NLA-16SQAM, IJF-NLA-16QAM, IJF-NLA-16SQAM which extended from NLA-16QAM.My main innovative research is the following:First, I have lucubrated QPSK/SQPSK, designed the scheme and realized them. Then we compare the performance and implementation between QPSK and SQPSK and finally reached meaningful conclusions from fruit of the experiments.Second, I have lucubrated how to obtain the NLA-16QAM by folding two QPSK signals and designed the scheme and realized them. First, a serial data stream is split into four parallel streams that form two in-phase and quadrature-phase signal pairs. Each pair of signals are converted from absolute codes into relative codes, and then sent into each QPSK modulator. Two QPSK signals are amplified by their own saturated amplifier, which produce a 6dB difference in their voltage levels, and then sent into a power synthesizer to obtain NLA-16QAM signals. I researched the NLA-16SQAM by folding two SQPSK simultaneously. Then we compare the performance and implementation between NLA-16QAM and NLA-16SQAM and finally reached meaningful conclusions from fruit of the experiments.Third, I have researched high-speed pseudo random numbers generator, PLL frequency synthesizer, wideband signal amplifier, microtrip power synthesizer, raised cosine filters, and so on. So the subject has the rudiment of a transmitter.From now, there are no space communication system adopted high-speed (>100Mb/s) 16QAM and can amplified by saturated amplifiers in the world, so the high-speed NLA-16QAM/SQAM is meaningful for the development of space communication.