MIMO-OFDM快衰落信道的稀疏自适应感知估计

Sparsity adaptive channel sensing estimation of fast fading MIMO-OFDM systems

在多输入多输出(MIMO)-正交频分复用(OFDM)系统中,怎样在较高频谱利用率的情况下对快时变信道进行较为准确的估计是一个具有挑战性的课题。该文在利用压缩感知理论可提高系统频谱利用率的基础上,提出了一种适合于快时变环境下MIMO-OFDM系统的稀疏自适应信道估计方法。该方法不再受到奈奎斯特采样频率条件约束,避免了传统导频辅助信道估计方法频谱利用率低的缺点。该文方法通过构建多天线群时频结构特征稀疏基,利用多天线间和群时变OFDM符号内信道冲激响应具有更强稀疏性的特点,对MIMO-OFDM快衰落信道进行稀疏变换。由于实际MIMO-OFDM快衰落信道往往处于频率选择性、时变性和多种干扰并存的复杂环境,受到干扰的信道参数对系统而言是未知,采用该方法克服了现有基于压缩感知理论的信道估计方法需要预先知道信道冲激响应稀疏度才能重构信道参数的不足,在信道稀疏度未知道的情况下,运用稀疏自适应的方法来对不同时频结构特征的信道参数进行估计。仿真结果表明所提估计方法具有对快时变信道参数估计的鲁棒性和较高频谱利用率,且均方误差小。

Fast fading of propagating channels degrades the performance of multiple-input multiple-output（MIMO） orthogonal frequency-division multiplexing（OFDM） systems.The theoretical benefits of MIMO-OFDM systems may not be fully achieved in broadband high mobile applications because the channels are both rapidly time-varying and frequency-selective.The theory of compressed sensing（CS） shows that fast fading channels in high-dimensional spaces can be recovered from a relatively small number of random plots.The relatively nonzero channel coefficients are tracked by random pilots at a sampling rate significantly below the Nyquist rate. However,existing CS-based channel estimations require the sparsity as a prior for exact recovery.The sparsity of fast fading channels could not be well-defined.In actual fast fading environments,the MIMO-OFDM channels are often frequency selective and time-varying delay.The sparsity of fast fading channel Impulse responses on MIMO-OFDM the system is unknown.A sparsity adaptive estimation of fast fading MIMO-OFDM channels based on CS is given in this paper.The sparsity adaptive estimation enjoys a potentially higher sparsity level from transmit-receive antennas and multi-symbol processing.The multi-antenna structure and sparse time-frequency basis is constructed.The time-varying channel impulse responses within the multiple antennas and group OFDM symbols have a more sparse nature. The fast fading channel coefficients within the multiple antennas and group OFDM symbols can be represented by a few coefficients, which reduces the number of channel measurements.The fast fading channels are estimated by a sparsity adaptive compressive sensing technique without prior information of the sparsity,when the channel sparsity is rapidly varying and not available in MIMO-OFDM systems.The simulation results show that the new channel estimator can provide a considerable performance improvement in esti- mating fast fading channels.The proposed estimation method for fast time-varying channels has strong robustness and high spectral efficiency, and small the mean square error.