论文标题

基于在线期望最大化的频率和相位共识

Online Expectation-Maximization Based Frequency and Phase Consensus in Distributed Phased Arrays

论文作者

Rashid, Mohammed, Nanzer, Jeffrey A.

论文摘要

分布式的相分阵列由单独的较小天线系统组成,它们相互协调以支撑朝着目的地的相干波束形成。但是,由于振荡器的频率漂移和相位抖动,以及节点处引起的频率和相位估计误差,因此存在降低波束成式过程的腐蚀性。在未指向网络的先前工作中提出了分散的频率和相位共识(DFPC)算法,其中节点与邻居在本地共享其频率和相位以达到同步。 Kalman滤波(KF)还与DFPC(KF-DFPC)集成在一起,以降低收敛时的总残留相误差。由于这些基于DFPC的算法依赖于平均共识协议,因此它们不收敛于有向网络。在本文中,我们建议针对有向网络的基于推和的频率和相位共识(PSFPC)算法。 PSFPC的残余相误差理论上也是衍生得出的。 Kalman滤波也与PSFPC集成,所得的KF-PSFPC算法显示,收敛时残留相误差显着降低。 KF假设已知模型参数,即测量噪声和创新噪声协方差矩阵。由于在实践中可能不知道它们,因此我们开发了一种基于在线的算法(EM)算法,该算法以在线方式迭代地计算未知矩阵的最大可能性(ML)估计值。 EM与KF-PSFPC集成,以提出EM-KF-PSFPC算法。在分析不同分布式阶段阵列的基于PSFPC的算法的性能并将其与其他算法进行比较的情况下,包括模拟结果。

Distributed phased arrays are comprised of separate, smaller antenna systems that coordinate with each other to support coherent beamforming towards a destination. However, due to the frequency drift and phase jitter of the oscillators, as well as the frequency and phase estimation errors induced at the nodes, there exists decoherence that degrades the beamforming process. A decentralized frequency and phase consensus (DFPC) algorithm was proposed in prior work for undirected networks in which the nodes locally share their frequencies and phases with their neighbors to reach synchronization. Kalman filtering (KF) was also integrated with DFPC (KF-DFPC) to lower the total residual phase error upon convergence. Since these DFPC-based algorithms rely on the average consensus protocol, they do not converge for directed networks. In this paper, we propose a push-sum based frequency and phase consensus (PsFPC) algorithm for the directed networks. The residual phase error of PsFPC is theoretically derived as well. Kalman filtering is also integrated with PsFPC and the resulting KF-PsFPC algorithm shows a significant reduction in the residual phase error upon convergence. KF assumes that the model parameters, i.e., the measurement noise and innovation noise covariance matrices, are known. Since they may not be known in practice, we develop an online expectation maximization (EM) based algorithm that iteratively computes the maximum likelihood (ML) estimate of the unknown matrices in an online manner. EM is integrated with KF-PsFPC to propose the EM-KF-PsFPC algorithm. Simulation results are included where the performance of the PsFPC-based algorithms is analyzed for different distributed phased arrays and is compared to other algorithms.

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