FMT系统中的同步方法研究

【作者】 许峰；

【导师】 高振明；

【作者基本信息】 山东大学 ， 通信与信息系统， 2005， 硕士

【摘要】 随着科技的进步,生活水平的不断提高,人们对信息量的需求越来越大。无线移动通信业务从语音、数据到图像,对服务质量(QoS)和传输速率的要求也越来越高,宽带化已成为当今通信技术领域的主要发展方向;而且,无线通信业务还必须满足用户的移动性要求,所有这些都对移动通信系统的性能提出了更高的要求。 由于传输媒介的不同,各种信道传输信息的能力也不尽相同,无线信道的相干带宽是限制无线信道传输能力的主要因素之一。在短波电离层反射信道、对流层散射信道、移动信道、广播信道等实际信道中,由于云层、山脉、城市中林立的高层建筑的影响所造成的多径衰落现象,会引起严重的码间干扰(ISI),限制了信息传输速率的提高。在高达几兆bps的传输速率下,传输符号的符号周期小于信道的时延扩展,从而产生ISI。因此在利用传统的单载波调制方式进行高速率无线通信时需使用多抽头均衡器,从而使系统的复杂度大大增加。研究表明,如果多径信道的时延扩展(信道记忆长度)远小于一个传输符号的符号周期,则由多径传播造成的符号间干扰可以忽略不计。所以,可以利用多载波传输技术在不降低信息传输速率的条件下使信道中的传输符号的符号周期远大于多径信道的时延扩展,从而可以有效地对抗由多径传播造成的ISI。 正交频分复用(OFDM)技术是当今4G研究中的一个热点。作为一种多载波技术,它具有抗多径干扰能力强、频谱利用率高等优点。然而OFDM技术也存在着一些缺点,如容易受频率偏移影响、符号同步困难以及有较大的峰值平均功率比(PAPR)等,这些问题都制约着OFDM在无线信道中的应用,现在人们对OFDM所进行的研究也主要集中在这些领域。 滤波多音调制(FMT)是基于滤波器组(filter banks)的多载波技术。该技术的主要特点是各子信道具有很高的频谱约束性,对系统频率偏差不敏感。FMT克服了OFDM易受频率偏差影响的弱点,但FMT系统需要引入子信道均衡技术来消除滤波器组的影响。本课题的研究受到国家自然科学基金(60372029)的资助。更多还原

【Abstract】 With the advancement of technology and the continual development of living standard, the requisition for information is more than ever. The high QoS and transmission speed in wireless communication business is highly needed in the field of voice, data and image. The broadband technologies lead the main development direction in communication field. Moreover, many transactions provided by communication systems must provide mobile services. All these put forward higher requirement for the performance of mobile communication systems.The transmittability of every kind of channel is different due to the different medium. The coherence bandwidth of wireless channels is an important factor which limits the transmittability. In built-up urban areas, multi-path fading occurs because of high surrounding structures, so there is severe intersymbol interference (ISI) which can decrease the performance of communication system. When the data rate is more than several Mbps, the ISI is generated for the signal duration is shorter than the channel delay spread. So for conventional single-carrier modulation, the system complexity will increase greatly due to the multi-taps equalizer used in high data rate wireless communication. The effect of the ISI is negligible so long as the delay spread of the multi-path channel is significantly shorter than the duration of one transmitted symbol. Therefore, multicarrier transmission technology can be used to overcome this limitation.Nowadays, Orthogonal Frequency Division Multiplexing (OFDM) is a key technology in the 4th generation mobile communication system. As one of the multicarrier transmission technologies, OFDM can reduce the multipath fading effect with high frequency efficiency. However, there are some disadvantages in OFDM system such as the sensitivity to frequency offset caused by oscillator inaccuracy and time variance of wireless channel, symbolsynchronization and high peak-to-average dynamic range of output symbols caused by summation of multiple subcarrier. All of these limit the application of OFDM in the wireless environment.Filtered Multitone (FMT) Modulation is a new multicarrier technology based on filter banks. In FMT system, the spectrum of each subchannel has a high level of spectral containment. So the inter-channel interference(ICI) is negligible compared with other noise, while it often appears in OFDM system because of its sensitivity to frequency offset. However, sub-channel equalization is needed in order to reduce the remaining ISI introduced by the filter banks. This research is inbursed by the National Natural Science Foundation of China (60372029) .In this thesis we introduce FMT transmission technology and derive the practical efficient implementation structure. In the following research, we investigate the influence of time and frequency offset. The receiver constellation and bit error rates are shown.In the chapter 3, we investigate some familiar timing synchronization schemes of multicarrier systems and schemes of FMT. We give a new timing synchronization scheme of FMT system in wireless communication and simulate the performance of some of the schemes with computer.In the chapter 4, we investigate frequency synchronization schemes of multicarrier systems. We modify SCA to accomplish frequency synchronization with only one training symbol, instead of two, without performance degradation. The redundancy of the training sequence is reduced to half. This reduction is critical especially in burst data transmission, for example, in WLAN.Because of the limitation of the time and some objective conditions, only parts of the synchronization schemes are simulated. And there are many topics which are not studied including sample timing, tracking algorithm, etc. Further study on these topics will be done in future work.更多还原