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Inertial navigation system (INS) is a practical method for indoor pedestrian navigation without pre-installation of infrastructure. Based on the fundamentals of human bipedal motion, zero velocity update (ZUPT) is a pervasive approach to tackle the accumulated error of inertial measurement units (IMU). While zero velocity detection plays a vital role in the algorithm, existing fixed-threshold methods to pick these pseudo-measurements of error-state Kalman Filter (ESKF) have the doubtful capability to fit various individuals in different motions. To address this issue, we propose the Symmetrical-Net leveraging deep Recurrent Convolutional Neural Networks (RCNNs) to detect the zero velocity interval adaptively. Additionally, two RCNNs are constructed in the symmetrical framework considering bidirectional IMU readings, which further improves the performance of the model. A comprehensive evaluation containing 87 different trajectories from 27 individuals has been conducted. The results show that the detection accuracy is up to 99.5% and 96.5% on the training and validation sets, respectively. It is verified that the precise and robust Symmetrical-Net can be a viable approach for the ZUPT-aided INS system. [ABSTRACT FROM AUTHOR]

This letter presents a novel analog predistortion circuit based on two Schottky diodes that can suppress both the third- and fifth-order nonlinear distortions simultaneously. This circuit is simple, of low cost, and of low power consumption. The predistortion circuit is verified in two radio over fiber (RoF) transmission systems. It is shown that spurious free dynamic range is improved significantly from 1 to 6 GHz. Using the circuit for Wi-Fi wireless signal over RoF, error vector magnitude is improved by up to 3.9 dB. [ABSTRACT FROM PUBLISHER]

A dual Schottky diode-based ultrabroadband predistortion circuit (PDC) is designed and experimentally verified to linearize both directly and externally modulated radio-over-fiber (RoF) transmission systems. A monolithic dual Schottky diode is used in the PDC to reduce the footprint and improve the bandwidth. The measured S-parameters show that the circuit is able to work for up to 40 GHz. The theory of third order intermodulation distortion (IMD3) generation by the PDC is established, and calculated IMD3 agrees well with the measured. Two measures are used to verify the PDC: spurious-free dynamic range (SFDR) and error vector magnitude (EVM) for WiFi signal at 2.4 GHz. For a directly modulated RoF transmission linearized by the PDC, the SFDR is improved by ∼12 dB. For an externally Mach–Zehnder modulator (MZM) modulated RoF transmission linearized by the PDC, the SFDR is improved by higher than 5 dB from 2 to 30 GHz, and in particular higher than 12 dB from 2 to 5 GHz. For 2.4–GHz WiFi signal over the externally modulated RoF transmission linearized by the PDC, the EVM for WiFi signal is improved by up to 5.1 dB for back-to-back and 3.5 dB for 20-km SMF transmission. [ABSTRACT FROM PUBLISHER]

The dual wavelength linearization (DWL) technique using two lasers with different wavelengths is for the first time comprehensively studied theoretically and experimentally to improve output signal power and suppress second- and third-order nonlinearities in radio-over-fiber (RoF) systems using an electro-absorption modulator (EAM). Spurious-free dynamic ranges (SFDRs) are calculated and measured. Both the calculation and experiments show that not only the RF signal power is significantly increased, but also both the second- and third-, as well as fifth-order nonlinearities are suppressed. For our considered EAM, when the second-order nonlinearity is suppressed maximally, the SFDRs with respect to second-order harmonic distortion and second-order intermodulation distortion are improved by 11.5 and 8.5 dB, respectively. In the mean time, the SFDRs with respect to third-order harmonic distortion (HD3) and third-order intermodulation distortion (IMD3) are improved by 1.8 and 1.3 dB, respectively. When the third order is suppressed maximally, the SFDRs with respect to HD3 and IMD3 are improved by 8.1 and 20.4 dB, respectively. The fifth-order intermodulation distortion is also suppressed at the same time. The RoF transmissions for WiFi signals are also verified. As a result, 3.5 dB at 2.4-GHz improvement and 2.8 dB at 5-GHz improvement of error vector magnitude are obtained for an RoF system by using the DWL technique. [ABSTRACT FROM AUTHOR]

A low-cost broadband analog predistortion circuit (PDC) is designed and experimentally verified in a radio over fiber (RoF) system. A miniature hybrid microwave integrated circuit technique is used to reduce the size and parasitics of PDC. Only two zero bias GaAs beam lead detector diodes and capacitors are used in the PDC. The diodes can be biased at <3~mA due to zero bias characteristic so that power consumption is reduced. No broadband matching network is required because of high series resistance of the zero bias diodes. The linearization performance is evaluated using an RoF system without and with the PDC. It is shown that the PDC improves the input 1-dB compression power by 0.4–2.2 dB from 7 to 18 GHz; and spurious free dynamic ranges are improved by \sim10~dB from 7 to 14 GHz and \sim6~dB from 15 to 18 GHz, limited by fifth order nonlinear distortion. [ABSTRACT FROM PUBLISHER]