摘要
正交频分复用-码分多址是一种把正交频分复用和码分多址相结合的技术。它具有正交频分复用系统能有效对抗多径衰落的优点，同时码分多址比其它传统多址技术能提供更多用户容量。但是在快速时变信道中，正交频分复用码分多址系统对于信道估计误差很敏感。针对上述问题，本文重点研究了正交频分复用码分多址接收机中的快速信道估计算法。采用梳状导频进行信道估计，提出了一种低复杂度、基于离散傅立叶变换的最小均方误差的信估计算法。在系统同步条件下，首先使用最小平方方法来估计信道响应，然后利用离散傅利叶变换的性质把信道响应信息和信道噪声分离，并在时域按最小均方误差准则做加权处理。分析和仿真表明，该算法计算复杂度低并能及时跟踪快速时变信道，并由于这两个主要特点使该算法可以有效适应无线快速时变信道，顺利完成系统的快速信道估计工作。
OFDM-CDMA is a technology that combines OFDM and CDMA. It inherits the anti-multipath fading ability of OFDM technology as well as the high user capacity of CDMA. However, the OFDM-CDMA system is vulnerable to channel estimation errors in fast varying channels. Hence, this paper focuses on fast channel estimation algorithms for OFDM-CDMA receivers. We use comb pilots to estimate the channel response, and propose a low-complexity discrete Fourier transform based MMSE channel estimator. After the system has been synchronized, we first use the Least Square method to make channel estimation, then separate the channel response information from the channel noises by DFT. A weighting function based on the Minimum Mean Square Error (MMSE) criteria can be applied to the time domain channel impulse response. Analysis and simulation results show that this algorithm has much lower complexity and is able to track the fast time varying channels in time. With such two advantages, this algorithm can efficiently adopt wireless fast varying channels and successfully achieve the fast channel estimation for OFDM-CDMA systems.
引文
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