An important goal of indoor positioning systems is to improve positioning accuracy as well as reduce power consumption. In this paper, we propose an indoor positioning method based on the received signal strength (RSS) fingerprint. The proposed method used a certain criterion to select fixed access points (FPs) in an offline phase instead of an online phase for location estimation. Principal component analysis (PCA) was applied to reduce the features of the RSS measurements but retain the most information possible for establishing the positioning model. Then, a kernel-based ridge regression method was used to obtain the nonlinear relationship between the principal components of the RSS measures and the position of the target. We thoroughly investigated the performance of the proposed method in realistic wireless local area network (WLAN) and wireless sensor network (WSN) indoor environments and made comparisons with recently developed methods. The experimental results indicated that the proposed method was less dependent on the density of the reference points and had higher positioning accuracy than the commonly used positioning methods, and it adapts to different application environments.
A roll-angle interferometer with high sensitivity is presented in this Letter. Two sets of centrosymmetric beams are used to travel through the measurement and reference arms of the roll-angle interferometer, which contains two specific optical devices: wedge prism assembly and wedge mirror assembly. Changes of the optical path in the interferometric arms caused by roll are differential and converted into phase shift through a particular interferometer system. The interferometric beams are a completely common path for the adoption of the centrosymmetric measurement structure, and the cross talk of the straightness, yaw, and pitch errors is avoided. The dead path is minimized, so the stability and the accuracy of the measurement can be greatly enhanced. The experimental results fit well with the theoretical analysis, and a measurement resolution of sub-microradian is achieved experimentally.
This paper presents an enhanced differential plane mirror interferometer with high resolution for measuring straightness. Two sets of space symmetrical beams are used to travel through the measurement and reference arms of the straightness interferometer, which contains three specific optical devices: a Koster prism, a wedge prism assembly, and a wedge mirror assembly. Changes in the optical path in the interferometer arms caused by straightness are differential and converted into phase shift through a particular interferometer system. The interferometric beams have a completely common path and space symmetrical measurement structure. The crosstalk of the Abbe error caused by pitch, yaw, and roll angle is avoided. The dead path error is minimized, which greatly enhances the stability and accuracy of the measurement. A measurement resolution of 17.5 nm is achieved. The experimental results fit well with the theoretical analysis.
A method for high resolution roll angle measurement of linear displacement stages is developed theoretically and tested experimentally. The new optical configuration is based on a special differential plane mirror interferometer, a wedge prism assembly, and a wedge mirror assembly. The wedge prisms assembly is used as a roll angle sensor, which converts roll angle to the changes of optical path. The special interferometer, composed a polarization splitter plane, a half wave plate, a beam splitter, a retro-reflector and a quarter wave plate, is designed for high resolution measurement of the changes of the optical path. The interferometric beams are a completely common path for the adoption of the centrosymmetrical measurement structure, and the cross talk of the straightness, yaw, and pitch errors is avoided. The angle measurement resolution of the proposed method is 3.5 μrad in theoretical with a phase meter which has a resolution of 2π/512. The experimental result also shows the great stability and accuracy of the present roll angle measurement system.
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