【作者】 孔令坤；

【导师】 赵春明；

【作者基本信息】 东南大学 ， 通信与信息系统， 2006， 硕士

【摘要】 正交频分复用(OFDM)技术由于能有效对抗多径且具有较高的频谱利用率,因而被最新的无线城域网(WirelessMAN)标准IEEE802.16e采用,并成为下一代移动通信系统的候选方案。由于IEEE802.16e标准融合了移动宽带无线接入,它要求系统在高速移动的情况下实现数据的高速率、高质量传输,这就对OFDM系统的信道估计和跟踪技术提出了更高的要求。因此本文重点研究了OFDM系统的信道估计技术,并应用到IEEE802.16e系统中。首先,论文讨论了固定宽带无线接入系统下的信道估计算法,比较了现有导频信道估计算法在SUI典型慢变信道下的性能。在此基础上,论文给出一种适用于虚载波(Virtual Carriers)系统的基于DFT变换的信道估计算法。它利用导频子载波上信道最小二乘(LS)估计值估计出虚导频子载波上的信道传输函数,随后再进行全频域导频长度的IDFT变换得出信道时域冲击响应(CIR)。仿真结果表明,该算法以较小的算法复杂度实现了良好的信道估计性能。其次,论文针对固定无线接入系统的六种SUI测试信道模型,给出一种便于工程实现的基于模型匹配判决的信道估计算法。该算法通过有限的初始信道估计样本对信道Profile作出判决,随后根据判决出的信道统计特性进行模型匹配的MMSE信道估计。这之后,论文针对WiMAX-OFDM系统帧结构设计了一种残余相位跟踪校正算法,它能跟踪校正由同步不准确引起的残余相位噪声且性能好于传统的时域线性插值方法。最后,论文讨论了移动宽带无线接入系统下的信道估计算法。给出了一种改进型的基于傅立叶变换的信道估计器。它通过预先循环右移信道冲击响应(CIR)来减小非整数倍采样信道中功率泄漏引起的信道估计误差。与直接的DFT估计算法相比,改进型算法在算法复杂度接近的前提下大大提高了信道估计的性能,避免了由信道估计误差引起的“错误平底”。更多还原

【Abstract】 Due to its features of multipath immunity and bandwidth efficiency, OFDM (Orthogonal Frequency Division Multiplexing) has been favored for IEEE 802.16e, which is the newly published standard for fixed and mobile broadband wireless access systems, and has become a prime candidate for next generation mobile communications systems. The requirements for IEEE 802.16e mobile broadband wireless access systems such as high data rate, high quality and high mobility make channel estimation and channel tracking techniques more important. Hence this thesis mainly focuses on channel estimation and its application in IEEE 802.16e systems.Firstly, channel estimation in fixed broadband wireless access systems is discussed. We give their performance comparison of some conventional pilot-symbol-aided channel estimation algorithms in SUI channels which are typically slow fading. Further, a DFT-based channel estimation algorithm for systems with virtual carriers is proposed. We present LS method to estimate the CTF at virtual pilots by exploiting the estimated CTF of pilots. Simulation result shows that the DFT-based channel estimator incorporating the CTF estimation at virtual carriers performs well with low complexity.Secondly, for the SUI testing channel models of fixed broadband wireless access systems, we present a model-based judging method which can make a decision of current channel profile via limited estimated samples. As a correct decision is made, a matching MMSE estimation algorithm is applied to OFDM systems. Afterwards, a residual phase correction mechanism for the specific subframe structure of WiMAX-OFDM system is investigated. It gives a better tracking performance than the time-domain linear interpolation.Finally, channel estimation in mobile broadband wireless access systems is taken into our account. We analyse the channel estimators for nonsample-spaced channels where aliased spectral leakage exists. Based on this, an improved DFT-based estimation algorithm is designed by pre-shifting the channel impulse response right. Compared to the direct-DFT method, it has been simulated and proved to be high-efficient and avoids the occurrence of error floor caused by aliased spectral leakage with nearly equal complexity in nonsample-spaced channels.更多还原