The problem of recovering a one-dimensional signal from its Fourier transform
magnitude, called Fourier phase retrieval, is ill-posed in most cases. We
consider the closely-related problem of recovering a signal from its phaseless
short-time Fourier transform (STFT) measurements. This problem arises naturally
in several applications, such as ultra-short laser pulse characterization and
ptychography. The redundancy offered by the STFT enables unique recovery under
mild conditions. We show that in some cases the unique solution can be obtained
by the principal eigenvector of a matrix, constructed as the solution of a
simple least-squares problem. When these conditions are not met, we suggest
using the principal eigenvector of this matrix to initialize non-convex local
optimization algorithms and propose two such methods. The first is based on
minimizing the empirical risk loss function, while the second maximizes a
quadratic function on the manifold of phases. We prove that under appropriate
conditions, the proposed initialization is close to the underlying signal. We
then analyze the geometry of the empirical risk loss function and show
numerically that both gradient algorithms converge to the underlying signal
even with small redundancy in the measurements. In addition, the algorithms are
robust to noise.

本文研究从相位不完整的短时傅里叶变换 (STFT) 测量中恢复信号的问题，其中当使用最小二乘问题的解来构造一个矩阵的主特征向量作为初始值，该问题可以由两种基于非凸优化的本地优化算法解决，其中第一种算法是基于最小化经验风险损失函数，第二种算法是基于最大化相位流形上的二次函数，这两种梯度算法均可以对信号进行收敛，并且对噪声具有抗干扰性。