Robust Beamforming Design for Ultra-Dense User-Centric C-RAN in the Face of Realistic Pilot Contamination and Limited Feedback
Robust Beamforming Design for Ultra-Dense User-Centric C-RAN in the Face of Realistic Pilot Contamination and Limited Feedback
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DOI：
10.1109/twc.2018.2882442
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发表时间：
2018-04
影响因子：
10.4
通讯作者：
Cunhua Pan;Hong Ren;M. Elkashlan;A. Nallanathan;L. Hanzo
中科院分区：
文献类型：
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作者：
Cunhua Pan;Hong Ren;M. Elkashlan;A. Nallanathan;L. Hanzo
考虑在网络中密集部署远程无线电头的超密集云无线接入网UD-CRAN。为了减少信道估计开销，我们重点研究了以用户为中心的分频双工udp - crans的鲁棒发射波束形成设计，其中只有有限的信道状态信息（CSI）可用。具体来说，我们设想了一个完整的获取CSI的程序，其中包括两个关键步骤：信道估计和信道量化。在相干协同传输中，相位模糊度（PA）也被量化。在此基础上，在用户速率要求和前传容量约束下，优化波束形成矢量，使总发射功率最小。利用多不确定项的统计性质，导出了可实现数据速率的封闭表达式。然后，我们提出了一种基于连续凸逼近技术的低复杂度迭代算法来求解这一问题。在每次迭代中，采用拉格朗日双分解方法获得最优波束形成向量。在此基础上，提出了一组低复杂度的用户选择算法，保证了问题的可行性。仿真结果验证了鲁棒算法在满足速率要求方面的准确性。最后，我们的仿真结果验证了使用单个比特量化PA获得了良好的性能。
The ultra-dense cloud radio access network (UD-CRAN), in which remote radio heads are densely deployed in the network, is considered. To reduce the channel estimation overhead, we focus on the design of robust transmit beamforming for user-centric frequency division duplex UD-CRANs, where only limited channel state information (CSI) is available. Specifically, we conceive a complete procedure for acquiring the CSI that includes two key steps: channel estimation and channel quantization. The phase ambiguity (PA) is also quantized for coherent cooperative transmission. Based on the imperfect CSI, we aim to optimize the beamforming vectors in order to minimize the total transmit power subject to the users’ rate requirements and fronthaul capacity constraints. We derive the closed-form expression of the achievable data rate by exploiting the statistical properties of multiple uncertain terms. Then, we propose a low-complexity iterative algorithm for solving this problem based on the successive convex approximation technique. In each iteration, the Lagrange dual-decomposition method is employed for obtaining the optimal beamforming vector. Furthermore, a pair of low-complexity user selection algorithms is provided to guarantee the feasibility of the problem. The simulation results confirm the accuracy of our robust algorithm in terms of meeting the rate requirements. Finally, our simulation results verify that using a single bit for quantizing the PA achieves good performance.