A position and orientation determining system includes a first radio frequency (RF) device including at least one antenna configured to receive and transmit RF signals, a first radio unit in communication with the at least one antenna, and an inertial measurement unit (IMU). The system further includes a second RF device includes a constellation of antennae including at least three receiving antennae, a second radio unit in communication with the constellation of antennae, and a processor configured to determine a three-dimensional position and three-axis angular orientation of the first RF device relative to the second RF device based on computing at least two of three angles in the second RF device coordinate frame (XY, XZ and YZ) computed from carrier phase difference (CPD) measurements taken between each pair of the at least three receiving antennae when receiving a single RF signal transmitted from the at least one antenna of the first RF device, and estimating a direction of a gravity vector generated by the IMU.