FRFD MIMO系统：有限反馈预编码V-BLAST与非正交STBC MIMO
FRFD MIMO Systems: Precoded V-BLAST with Limited Feedback Versus Non-orthogonal STBC MIMO
摘要：
全速率（FR）和全分集（FD）是MIMO系统中具有吸引力的特征。我们将同时实现FR和FD的系统称为FRFD系统。非正交空时分组码可以在无反馈的情况下实现FRFD，但其ML译码复杂度较高。没有预编码的V-BLAST实现了FR而不是FD。FRFD可以在V-BLAST中通过在发射机处给定完整信道状态信息（CSIT）的情况下进行预编码来实现。然而，在有限反馈预编码的情况下，V-BLAST实现了FD，但是具有一些速率损失。我们在本文中的贡献是双重的：$i)$我们提出了一种有限反馈（LFB）预编码方案，其在$2\times 2$、$3\times 3$和$4\times 4$ V-BLAST系统中实现FRFD（我们将该方案称为FRFD-VBLAST-LFB方案），以及$ii)$比较FRFD-VBLAST-LFB方案和没有反馈的非正交STBC（例如，Golden码，完美码）在ML解码下，我们表明，在具有4-QAM/16-QAM的$2\times 2$ MIMO系统中，FRFD-VBLAST-LFB方案优于Golden码约0.6 dB;在$3\times 3$和$4\times 4$ MIMO系统中，FRFD-VBLAST-LFB方案的性能与完美码的性能相当。FRFD-VBLAST-LFB方案是有吸引力的，因为1）ML解码与非正交STBC的解码相比变得不那么复杂，2）实现上述性能所需的反馈比特的数量很小，3）在慢衰落中，仅偶尔发送反馈比特就足够了，以及4）在大多数实际无线系统中，反馈信道通常是可用的（例如，用于自适应调制、速率/功率控制）。
英文摘要：
Full-rate (FR) and full-diversity (FD) are attractive features in MIMO systems. We refer to systems which achieve both FR and FD simultaneously as FRFD systems. Non-orthogonal STBCs can achieve FRFD without feedback, but their ML decoding complexities are high. V-BLAST without precoding achieves FR but not FD. FRFD can be achieved in V-BLAST through precoding given full channel state information at the transmitter (CSIT). However, with limited feedback precoding, V-BLAST achieves FD, but with some rate loss. Our contribution in this paper is two-fold: $i)$ we propose a limited feedback (LFB) precoding scheme which achieves FRFD in $2\times 2$, $3\times 3$ and $4\times 4$ V-BLAST systems (we refer to this scheme as FRFD-VBLAST-LFB scheme), and $ii)$ comparing the performances of the FRFD-VBLAST-LFB scheme and non-orthogonal STBCs without feedback (e.g., Golden code, perfect codes) under ML decoding, we show that in $2\times 2$ MIMO system with 4-QAM/16-QAM, FRFD-VBLAST-LFB scheme outperforms the Golden code by about 0.6 dB; in $3\times 3$ and $4\times 4$ MIMO systems, the performance of FRFD-VBLAST-LFB scheme is comparable to the performance of perfect codes. The FRFD-VBLAST-LFB scheme is attractive because 1) ML decoding becomes less complex compared to that of non-orthogonal STBCs, 2) the number of feedback bits required to achieve the above performance is small, 3) in slow-fading, it is adequate to send feedback bits only occasionally, and 4) in most practical wireless systems feedback channel is often available (e.g., for adaptive modulation, rate/power control).
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