Conjugate Phase Retrieval on ${\mathbb C}^M$ by real vectors

In this paper, we will introduce the notion of {\it conjugate phase retrieval}, which is a relaxed definition of phase retrieval allowing recovery of signals up to conjugacy as well as a global phase factor. It is known that frames of real vectors are never phase retrievable on ${\mathbb C}^M$ in the ordinary sense, but we show that they can be conjugate phase retrievable in complex vector spaces. We continue to develop the theory on conjugate phase retrievable real frames. In particular, a complete characterization of conjugate phase retrievable real frames on ${\mathbb C}^2$ and ${\mathbb C}^3$ is given. Furthermore, we show that a generic real frame with at least $4M - 6$ measurements is conjugate phase retrievable in ${\mathbb C}^M$ for $M \ge 4.$