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Robust RF Beamforming for Millimeter Wave MIMO-OFDM Systems

机译:毫米波MIMO-OFDM系统的稳健RF波束成形

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In conventional multiple-input multiple-output systems, each antenna is connected to a radio-frequency (RF) chain. Due to the tiny wavelength of millimeter waves (mmWave), tens of antennas can be packed into a small area in mmWave transceivers. However, implementing an RF chain for each antenna is impractical due to the high cost and power of mixed-signal devices. In order to reduce the cost and get benefit from the antennas, an analog RF beamformer is implemented using variable gain amplifiers and analog phase shifters. In this paper, we propose a novel spatial diversity scheme for mmWave RF beamforming. The transmitter is assumed to have partial knowledge of the channel to the receiver. We formulate the spatial diversity problem as maximizing the geometric mean of the projections of the RF precoder on the transmit steering vectors and the geometric mean of the projections of the RF combiner on the receive steering vectors. To solve the optimization problem of the RF beamformers, we propose two solution algorithms. The first algorithm is based on semidefinite relaxation (SDR). Due to the high computational complexity of the SDR algorithm, we propose a simpler second algorithm, which is gradient ascent algorithm. Simulation results show that the proposed spatial diversity scheme outperforms the conventional spatial diversity schemes in case of no blockage and in case of blockage to any propagation path regardless of the number of propagation paths.
机译:在常规的多输入多输出系统中,每个天线都连接到射频(RF)链。由于毫米波(mmWave)的波长极小,因此数十个天线可以封装在mmWave收发器的一小块区域中。但是,由于混合信号设备的高成本和功率,为每个天线实现RF链是不切实际的。为了降低成本并从天线中受益,使用可变增益放大器和模拟移相器实现了模拟RF波束形成器。在本文中,我们提出了一种用于毫米波射频波束成形的新型空间分集方案。假设发射机对接收机的信道有部分了解。我们将空间分集问题表述为最大化RF预编码器在发射导向向量上的投影的几何平均值和RF组合器在接收导向向量上的投影的几何平均值。为了解决射频波束形成器的优化问题,我们提出了两种求解算法。第一种算法基于半确定松弛(SDR)。由于SDR算法的计算复杂度高,我们提出了一种更简单的第二算法,即梯度上升算法。仿真结果表明,所提出的空间分集方案在没有阻塞的情况下以及对任何传播路径的阻塞情况下均优于传统的空间分集方案,而与传播路径的数量无关。

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