摘要
随着通信技术的发展,数字调制技术得到广泛的应用。其中,正交频分复用(OFDM)技术成为该领域中的一项热门研究项目。但是由于无线信道存在时变性和多普勒频移,易破坏OFDM子载波间的正交性,降低其系统性能。对此梁德群教授提出了一种时移非正交多载波调制(TS-NMT)技术,不但继承了OFDM的频分复用的原理而且还突破了正交性的限制,使得在相同的带宽条件下可以排列更多的子信道,并且每个子信道可以携带更多的子载波,这样就大大提高了信息传输率,相对于OFDM有更高的频谱利用率。同时带来了两个技术优势：一是TS-NMT不像OFDM那样对频率偏差敏感,二是峰值均值比也有所降低。由于人类社会生活对通信的需求标准越来越高,迫切地需要一种更好的调制方式,而TS-NMT的出现正迎合了无线通信发展的需求。
目前,在梁德群教授的带领下,已经完成了TS-NMT在有线、无线、移动、卫星信道上的仿真研究和在有线物理信道上的实验验证,证明了TS-NMT的可行性和先进性。然而,我们的研究还存在一个缺口：未进行实际的无线信道的实验验证,而恰恰无线通信具有更为广阔的市场前景,所以本论文的目的就是对TS-NMT在实测的无线信道上进行仿真研究,并与现有的OFDM调制技术进行对比,以验证TS-NMT技术的优越性,为以后的实际应用打下基础。
本文介绍了TS-NMT的基本原理,分析了TS-NMT在理论信道和实验信道上的系统仿真结果。其中,在理论信道的系统仿真中,基于前几届研究生的信道估计的算法,本文提出了一种插入冲激信号直接测量信道的算法。在实验信道的系统仿真中,首先介绍了实际信道模型的测量方法；其次,为了更加有效的模拟无线信道的时变性,在仿真中采用多测量几组数据,每隔五个码元换一次信道的方法来实现。并且在相同条件下,对TS-NMT和OFDM的系统性能进行对比,证明了TS-NMT的优势。最后,将MATLAB仿真程序转化成C语言程序,为下一步仿真算法向DSP移植提供技术支持。
Along with the fast development of the communications technology, digital modulation techniques are widely used. Orthogonal Frequency Division Multiplexing (OFDM) techniques become a top research project in this domain. However, due to wireless channel has variability and doppler frequency shift, it make OFDM orthogonality that between subcarriers are easily damaged, so that system performance greatly degrade.Professor Dequn Liang brought forward the Time Shift Non-Orthogonal Multi-Modulation Technology (TS-NMT) not only inherited the frequency division multiplexing principles, but also breaks through the limitation of orthogonality, which makes it can arrange more sub-channel under the same bandwidth and each sub-channel can have more sub-carriers than OFDM, thus greatly improving the information transmission rate and spectrum efficiency. At the same time, it bring two technical advantages:TS-NMT not like OFDM that sensitive to the frequency deviation., and also reduce the Peak-to-Average Ratio. Because human social life are growing demand for communication and urgent need for a better modulation, so the appearance of TS-NMT is catered to the needs of the development of wireless communications.
Currently, Under the leadship of Professor Dequn Liang, Many simulation researches had been completed, including simulation on the wired, wireless, mobile, satellite channle, and made experiments on the physical channel, which proved its feasibility and superiority. However, our study also has a gap, not do the experiments on the real wireless channel, and TS-NMT has a more broad market prospects in the wireless communication. Therefore, the purpose of this thesis is do simulation study in the measured wireless channel and compare to OFDM modulation technique to prove its superiority and to lay the foundation for future practical appplocations.
In this thesis, introduced the basic principle of TS-NMT, and do system simulation respectively in the theoretical and practical channel. In the simulation of theoretical channle, based on channel estimation algorithm made by previous graduate, this thesis presents a algorithm of direct measurement channel, which insert impulse signal in the send signal. In the simulation of practical wireless channle, this thesis first describes the method of how to measure channel, and in order to simulate the wireless channel's time-varying characteristics, it is necessary to measure sets of data and change channel at intervals of five yards in the simulation. Then, compare TS-NMT and OFDM system performance in the same condition, results show the advantages of TS-NMT. Lastly, convert MATLAB program into C language program, in order to provide technical support to simulation algorithm transplant to DSP.
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