滤波多音调制系统中的自适应技术研究

【作者】 王少波；

【导师】 高振明；

【作者基本信息】 山东大学 ， 通信与信息系统， 2006， 硕士

【摘要】 目前，第三代移动通信系统(3G)逐步走向商用化，下一代移动通信系统正成为研究的热点，其目标就是实现无所不在的、高质量的、高速率的移动多媒体传输。而移动通信频谱资源的有限性决定了下一代的移动通信必须采用频谱利用率高的抗衰落技术来提高系统的性能，从而支持高速率多媒体业务的传输。多载波调制(MCM)就是一种有效的信息传输技术，它是用多个子载波并行地传输信息符号，使每个子信道内的符号时间大大延长，系统就可以有效地克服信道造成的符号间干扰(ISI)，达到更高的数据传输速率。 正交频分复用(OFDM)技术是一种特殊的多载波调制技术，可以充分的利用频谱资源，有效地对抗多径时延扩展，并且已经被多个标准(IEEES02．11a，HIPERLAN／2等)采用。但是OFDM技术也存在着一些缺点，如容易受频率偏移影响和符号同步困难等，本文研究了一种新型的多载波调制技术——滤波多音(FMT)调制。该技术通过滤波器组将整个信道划分成若干个频带有限且互不重叠的子信道，因此FMT系统具有高度的频谱约束性，有效的抑制了信道间干扰(ICI)，从而避免了无线通信中OFDM系统对频偏敏感性强这一难以解决的问题，但是由于滤波器组的使用引入了ISI，所以FMT系统需要引入子信道均衡技术来消除ISI的影响。 自适应技术是移动宽带通信系统的核心技术之一。它的基本思想就是通过检测当前信道的状况，动态地改变发射功率、符号传输速率、调制信号的星座大小、编码效率、编码结构等参数，以便最充分的利用当前信道的环境。自适应技术已经被广泛的认为是有效地提高频谱利用率的重要手段之一，并且已在包括CDMA2000、WCDMA的第三代移动通信标准中使用。因此，将自适应技术与多载波(OFDM、FMT等)技术相结合，必将能更有效地提高系统的性能，也亦将会成为当今通信的发展趋势。 本文首先介绍了无线信道的基本特征，并简要回顾了多载波技术的产生背景及发展状况。然后介绍了滤波多音调制技术的基本原理，分析了FMT系统优缺点，并给出了可实用的高效的实现形式。接着，本文对自适应技术的基本原理进行了简单的介绍，从理论上分析和推导了自适应系统的模型，然后重点研究了多载波更多还原

【Abstract】 Up to now, 3G has been launched into business in many countries, and researches are focused on the next generation communication system, called 4G, which is expected to provide ubiquitous, high-quality, and high-rate mobile multimedia transmission. The next generation communication system has to support the transmission of high rate data and multimedia applications in the radio spectrum, which is already extremely scarce. As one of the effective transmission technologies, Multi-carrier modulation (MCM) transmits the data information parallel with several sub-carriers, and it makes symbol duration of each sub-channel much longer than the delay spread of the multipath channel. Therefore, MCM can provide high data rate and efficiently avoiding intersymbol inference (ISI) arosing by multipath propagation.As one of the multicarrier techniques, Orthogonal Frequency Division Multiplexing (OFDM) can make the best use of radio spectrum and efficiently reduce the multipath fading. OFDM has been adopted in several standards, such as IEEE802.11a, HIPERLAN/2. However, there are some disadvantages in OFDM system such as sensitivity to frequency offset, symbol synchronization and so on. We investigate a new multi-carrier modulation technique: Filtered Multitone (FMT) modulation. It divides the whole channel into several sub-channels with filter bank, so the spectrum of each subchannel has a high level of spectral containment in FMT system. And Inter-channel Interference (ICI) is effectively reduced, so FMT overcomes the weakness of being sensitive to frequency offset in OFDM system. However, the using of filter banks brings ISI to the system. Therefore, subchannel equalization is necessary to reduce the remaining ISI introduced by the filter banks.Adaptive technology is one of the crucial techniques for the mobile broadband systems. Its basic idea is that the transmitted power level, symbol transmission rate, constellation size, coding rate/scheme or any combination of these parameters can be adaptively adjusted by the current channel state information (CSI). By this way, adaptive technology can make the best use of the current channel environment.更多还原