Abstract: A communications device such as a personal identity card is in the form of a badge or label worn on the outside of the wearer's clothing. The badge includes a first layer of a transparent material having an inner surface that is contoured with a retroreflecting repeating pattern. A second layer also of a transparent material has an inner surface with a reciprocating retroreflecting pattern. Sandwiched between the two layers is a layer of liquid crystal material the refractive index of which can be varied through the application of an electric field. When the refractive index of the layer is close to that of the first and second layers, incident radiation passes through the device with little scattering. However, as the refractive index of the layer is varied by application of an electric field, incident radiation is retroreflected from the contoured interface of the first layer with the layer.

Abstract: A master control station (10) includes a common antenna (12) which drives two, unsynchronized multi-channel GPS receivers (16, 18). The two receivers (16, 18) couple to a controller (24). The controller (24) commands the receivers (16, 18) to identify all GPS satellites in view, and then assigns (48) satellites to various channels in the receivers (16, 18). The assignment includes at least one common satellite between the two receivers. Location data are obtained from the two receivers for the common satellite and used to normalize (66) all pseudorange data from all channels to compensate for the lack of synchronization between the two receivers (16, 18). Differential GPS location resolution (84) may then occur using the normalized data.