Interference Exploitation Precoding for Multi-Level Modulations: Closed-Form Solutions
Interference Exploitation Precoding for Multi-Level Modulations: Closed-Form Solutions
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DOI：
10.1109/tcomm.2020.3031616
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发表时间：
2021-01-01
影响因子：
8.3
通讯作者：
Swindlehurst, A. Lee
中科院分区：
文献类型：
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作者：
Li, Ang;Masouros, Christos;Swindlehurst, A. Lee
研究了多用户多输入单输出(MU-MISO)系统下行链路中多级调制的闭式干扰利用预编码。我们考虑了两种不同的情况：首先，当服务用户数不大于基站的发射天线数时，我们从数学上推导出基于Karush-Kuhn-Tucker(KKT)条件的最优预编码结构。通过建立对偶问题的形式，将预编码问题转化为使用二次规划(QP)优化的预缩放操作。我们进一步考虑其中服务的用户数大于BS处的发射天线数的情况。利用伪逆，我们证明了预尺度向量的最优解等价于对应于零奇异值的右奇异向量的线性组合，并导出了等价的QP公式。我们还给出了多路复用比发射天线数目更多的流是可以实现的条件。对于这两种情况，我们提出了一种改进的迭代算法来获得最优的预编码矩阵，以及一种次优的闭合形式的预编码器。数值结果验证了我们关于多级调制最优预编码结构的推导，并证明了干扰利用预编码在两种情况下的优越性。
We study closed-form interference-exploitation precoding for multi-level modulations in the downlink of multi-user multiple-input single-output (MU-MISO) systems. We consider two distinct cases: first, when the number of served users is not larger than the number of transmit antennas at the base station (BS), we mathematically derive the optimal precoding structure based on the Karush-Kuhn-Tucker (KKT) conditions. By formulating the dual problem, the precoding problem is transformed into a pre-scaling operation using quadratic programming (QP) optimization. We further consider the case where the number of served users is larger than the number of transmit antennas at the BS. By employing the pseudo inverse, we show that the optimal solution of the pre-scaling vector is equivalent to a linear combination of the right singular vectors corresponding to zero singular values, and derive the equivalent QP formulation. We also present the condition under which multiplexing more streams than the number of transmit antennas is achievable. For both considered scenarios, we propose a modified iterative algorithm to obtain the optimal precoding matrix, as well as a sub-optimal closed-form precoder. Numerical results validate our derivations on the optimal precoding structures for multi-level modulations, and demonstrate the superiority of interference-exploitation precoding for both scenarios.