Abstract: In a method for feeding back combination information of transmitted signals in a multiple-input multiple-output (MIMO) system using a multiple space-time block coding technique, mean square error values are computed in relation to the combination information pieces of the transmitted signals. An index of a combination having a minimum mean square error value from among the mean square error values is fed back.

Abstract: A high-precision displacement measurement device and linear or rotational displacement measurement method using a unit displacement sensor based on a confocal theory. This device is simpler in construction, lower in cost and superior in resolution to other displacement measurement devices, and is capable of measuring a much wider area than other measurement equipment. The present device is adapted to project a spot of light from a light source on an object whose displacement is to be measured and measure a relative displacement of the object from a displacement of the projected light spot.