Limited-Feedback Precoding for Closed-Loop Multiuser MIMO OFDM Systems with Frequency Offsets
Limited-Feedback Precoding for Closed-Loop Multiuser MIMO OFDM Systems with Frequency Offsets
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DOI：
10.1109/t-wc.2008.060868
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发表时间：
2008-11
影响因子：
10.4
通讯作者：
Y. Fu;C. Tellambura;W. Krzymień
中科院分区：
文献类型：
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作者：
Y. Fu;C. Tellambura;W. Krzymień
频率偏移对闭环多输入多输出（MIMO）正交频分复用（OFDM）系统的性能有负面影响。特别是，当多个用户处于活动状态时，影响可能会很大。线性预编码和非线性Tomlinson-Harashima预编码（THP）因此被开发用于空间复用多用户OFDM和正交空时块编码（OSTBC） OFDM。所提出的预编码器采用有限反馈结构，该结构通过预编码矩阵的共享码本来实现，并且只将所选择的最优矩阵的索引反馈给发射机。传统的平坦衰落MIMO信道有限反馈设计准则仅适用于无频偏的单用户OFDM。我们表明，由于频率偏移的ICI矩阵不会影响用户单独预编码，并且可以在每个子载波的基础上进行预编码。利用这一特性，将传统设计推广到带频偏的多用户OFDM。非线性预编码使用模算术预编码矩阵（减少了线性预编码固有的功率效率损失，导致较低的错误率），优于线性预编码。我们的预编码器不仅提供显著的误码率（BER）改善的空间复用多用户MIMO OFDM频率偏移，但同样有效的OSTBC MIMO OFDM和空间相关信道。
Frequency offsets negatively impact the performance of closed-loop multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. Particularly, when multiple users are active, the impact can be high. Linear precoding and non-linear Tomlinson-Harashima precoding (THP) are thus developed for spatially-multiplexed multiuser OFDM and orthogonal space-time block-coded (OSTBC) OFDM. The proposed precoders employ a limited feedback structure, which is implemented with a shared codebook of precoding matrices, and only the index of the selected optimal matrix is fed back to the transmitter. The conventional limited feedback design criterion for flat-fading MIMO channels is only applicable to single-user OFDM without frequency offsets. We show that the ICI matrix due to frequency offset does not impact users precoding individually, and precoding on a per-subcarrier basis is possible. Exploiting this property, the conventional design is generalized to multiuser OFDM with frequency offsets. Nonlinear precoding uses a modulo arithmetic precoding matrix (which reduces the power efficiency loss inherent in linear precoding and leads to a lower error rate) and outperforms linear precoding. Our precoders not only offer significant bit error rate (BER) improvement for spatially-multiplexed multiuser MIMO OFDM with frequency offsets, but are equally effective for both OSTBC MIMO OFDM and spatially correlated channels.