【作者】 董晶；

【导师】 乐光新；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2006， 硕士

【摘要】 随着Internet的发展，数据通信业务增长迅速，而无线的数据通信更给人以全新的感受。目前的无线通信系统如3G、WLAN在数据速率、业务能力及成本、覆盖范围、移动性等方面各有其应用的局限，因此，移动宽带无线接入(MBWA,Mobile Broadband Wireless Access)越来越受到重视。 当前针对3G系统和B3G系统设计的DSSS(直接序列扩频)和Turbo编码已经不能满足未来无线移动通信系统所预计的更高的数据的要求。为了支持50～100Mbit／s，甚至高达1Gbit／s的传输速率，需要采用全新的更加高效的物理层技术。由于实现如此高速的数据传输速率，因此与所占据的信道带宽相比，相干带宽就非常小，从而要求更加复杂的多径处理技术，以解决更多可分解、但又是随机的多径信号。 正交频分复用(Orthogonal Frequency Division Multiplexing，OFDM)技术能在频谱效率、频率分集、低速并行数据处理和抗干扰、实现复杂度等方面占有一定优势，使OFDM技术受到广泛关注，并作为新一代移动通信系统的候选方案。基于OFDM技术的发射信号，经过移动通信信道时，将有频率选择性衰落特点，同一用户的不同子载波有不同的衰落；同时，不同用户的衰落又可看成是独立的。为了进一步发挥OFDM技术的特点，利用信息论的注水原理，提出了OFDM的自适应编码调制与子载波功率分配算法。但是，要实现每个子带上精确的功率控制，有较大的实现复杂度与算法的收敛性问题，在具体系统中实现起来较困难。 由于正交频分多址(Orthogonal Frequency Division Multiple Access，OFDMA)系统提供了时间与频率二维资源，可采用OFDM的频分与时分的多址技术即OFDMA来实现系统的多址接入。美国高通公司的HDR(High DataRate，HDR)通信标准采用了在基站按最大功率发射，移动台按接收功率的强弱实现不同的编码调制方案，得到不同速率的数据通信，同时在分配时隙单元上满足一定的公平性原则。这种方法在功率控制上较为简单，但对功率有一定浪费。本文的算法将这种方法与OFDM系统的特点相结合：在比例公平性原则下，按用户数据速率与信道条件进行资源调度，通过对用户子载波组的平均信道参数进行相应的自适应编码调制代替对每个子载波进行功率控制，在降低了实现复杂度的同时，使系统的总的吞吐量为最大。本文通过OPNET仿真工具更多还原

【Abstract】 As the rapid progress of Internet, data services have grown up fast, and all these have brought new taste of the wireless networks. But nowadays wireless systems, such as 3G, WLAN, have some defects in respect of speed, cost, range and mobility. So the mobile broadband wireless access (MBWA) has got more and more attention.The mobility provided by the transmission of speech and data without the need of a cable connection has lead to the wide integration of mobile telephones and computers in every day’s life. With the increase in transmission speed and quality, provided by these techniques new interesting services, e.g. video telephony or the ubiquitous usage of the Internet can be provided to the mobile user. However, the benefit of mobility adds a certain cost to the system. Unlike cable connections, wireless systems suffer from a high variance of the delay and the attenuation of the transmitted signals. This effect varies over time and frequency and rises with the data-rate. In order to assure the fault-tolerant transmission, while providing high data rates Orthogonal Frequency Division Multiplexing (OFDM) has been developed. With OFDM the spectrum is separated into small sub-bands, the so-called sub-carriers, which are placed in order to assure a high utilization of the given bandwidth.OFDM technology has gained much attention these years for its excellent behavior in spectrum utilization, parallel data processing, anti-interfere, etc. And OFDM has been listed as one of the candidate technologies of the next generation communication system. When the signal based on OFDM transmits through the wireless channel, it undergoes the frequency selective loss, and different sub-carriers of one更多还原