337 research outputs found
Mixed numerologies interference analysis and inter-numerology interference cancellation for windowed OFDM systems
Extremely diverse service requirements are one of the critical challenges for the upcoming fifth-generation (5G) radio access technologies. As a solution, mixed numerologies transmission is proposed as a new radio air interface by assigning different numerologies to different subbands. However, coexistence of multiple numerologies induces the inter-numerology interference (INI), which deteriorates the system performance. In this paper, a theoretical model for INI is established for windowed orthogonal frequency division multiplexing (W-OFDM) systems. The analytical expression of the INI power is derived as a function of the channel frequency response of interfering subcarrier, the spectral distance separating the aggressor and the victim subcarrier, and the overlapping windows generated by the interferer's transmitter windows and the victim's receiver window. Based on the derived INI power expression, a novel INI cancellation scheme is proposed by dividing the INI into a dominant deterministic part and an equivalent noise part. A soft-output ordered successive interference cancellation (OSIC) algorithm is proposed to cancel the dominant interference, and the residual interference power is utilized as effective noise variance for the calculation of log-likelihood ratios (LLRs) for bits. Numerical analysis shows that the INI theoretical model matches the simulated results, and the proposed interference cancellation algorithm effectively mitigates the INI and outperforms the state-of-the-art W-OFDM receiver algorithms
Fine timing synchronization based on modified expectation maximization clustering algorithm for OFDM systems
A novel fine timing synchronization method based on the modified expectation-maximization (EM) clustering algorithm is proposed for orthogonal frequency-division multiplexing systems. Using the cross-correlation metrics of one preamble symbol, the cross-correlation peaks corresponding to the channel arriving paths are identified by the proposed modified EM clustering algorithm, the position of the first coherent cross-correlation peak is then chosen as the start of the frame. Computer simulations show that the proposed method is robust in multipath dispersive channels and achieves superior performance to existing techniques in terms of timing accuracy
Smartphones: A Game Changer for Psychological Research
As technology continues to advance and smartphones continue to grow in popularity, we argue that smartphones have rapidly evolved as a suitable tool for psychological research. In this editorial, we will first briefly introduce the technological and social features possessed by smartphones that are ideal for psychology research. Then we distinguish two approaches to use smartphones for research, highlighting the external and internal validity of each approach. We further discuss computer skills and analysis methods needed for research with smartphones
Calibration of the in-orbit center-of-mass of TaiJi-1
Taiji program is a space mission aiming to detect gravitational waves in the
low frequency band. Taiji-1 is the first technology demonstration satellite of
the Taiji Program in Space, with the gravitational reference sensor (GRS)
serving as one of its key scientific payloads. For accurate accelerometer
measurements, the test-mass center of the GRS must be positioned precisely at
the center of gravity of the satellite to avoid measurement disturbances caused
by angular acceleration and gradient. Due to installation and measurement
errors, fuel consumption during in-flight phase, and other factors, the offset
between the test-mass center and the center-of-mass (COM) of the satellite can
be significant, degrading the measurement accuracy of the accelerometer.
Therefore, the offset needs to be estimated and controlled within the required
range by the center-of-mass adjustment mechanism during the satellite's
lifetime. In this paper, we present a novel method, the Extended Kalman Filter
combined with Rauch-Tung-Striebel Smoother, to estimate the offset, while
utilizing the chi-square test to eliminate outliers. Additionally, the
nonlinear Least Squares estimation algorithm is employed as a crosscheck to
estimate the offset of COM. The two methods are shown to give consistent
results, with the offset estimated to be mm, mm, and mm. The results indicate a significant
improvement on the noise level of GRS after the COM calibration, which will be
of great help for the future Taiji program.Comment: 8 pages, 9 figure
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