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The self-alignment process for the strapdown inertial navigation system (SINS) is performed mainly to achieve an accurate initial attitude only using the measurements from the inertial measurement unit (IMU). Different from conventional self-alignment methods, a gradient descent optimization-based SINS self-alignment method, which can determine the initial attitude without using the latitude information, is proposed in this paper. According to certain geometry constraints of the earth rate vector in the navigation frame, we use the measurements from the IMU to represent the earth rate vector instead of directly using the latitude information. To overcome the sensor noise disturbance, we also construct a quaternion-based nonlinear objective function with the estimated earth rate vector, which is formulated as seeking the least square solution of a Wahba problem. Thus, we employ the gradient descent optimization to achieve the optimal solution of the nonlinear objective function. The simulation and experiment results verify the alignment performance and flexibility of the proposed self-alignment method for SINS stationary alignment without using a priori local latitude information. [ABSTRACT FROM AUTHOR]

To solve the self-alignment problem of strapdown inertial navigation system (SINS) for underwater vehicles, a novel gravitational apparent motion (GAM)-based method is proposed. Different from conventional GAM methods, the proposed GAM method can complete SINS self-alignment under swaying conditions without using the a priori local latitude information. First, we determine the gravity vector in the earth frame and the local latitude by using the gradient descent optimization and certain geometry constraints. Then, the self-alignment process is formulated as an optimization-based alignment quaternion determination problem by constructing an objective function with the estimated gravity vector. We employ gradient descent optimization to achieve the least square solution of the objective function. Thus, the attitude quaternion can be determined according to the quaternion product chain rule. The simulation and experiments results demonstrate the proposed GAM method without using the local latitude achieves an alignment accuracy close to conventional GAM methods during the coarse alignment process. [ABSTRACT FROM AUTHOR]

Estimation of signal-to-noise ratio (SNR) plays an important role in many fields of communications. This paper addresses the SNR estimation of multiple phase-shift keying (MPSK) signals in Nakagami- $m$ fading channels. A family of SNR estimators with closed-form expressions is developed based on the relationship among different orders of moments. Compared with the existing algorithms, the estimator, which exploits the minimum order of moments, exhibits the best performance in general. We also propose a joint estimation algorithm for SNR and the fading factor when it is unknown. Simulation results verify the feasibility and superiority of the proposed algorithms. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate parameter estimation for generalized frequency division multiplexing (GFDM) signals over frequency-selective fading channels. Based on the characteristics of the second-order cyclostationary statistics of GFDM signals, we develop algorithms to blindly estimate pure block duration, overall block duration, symbol duration, and number of subcarriers. The proposed algorithms are robust to timing, phase, and carrier frequency uncertainties and do not require any a priori knowledge of the received signal. Simulation results verify the feasibility of the proposed algorithms. [ABSTRACT FROM AUTHOR]

With a considerable ratio of the world?s mobile users, China has been actively promoting research on 5G, in which the spectrum issue is of great interest. New 5G characteristics put forward a lot of requirements for spectrum in terms of total amount, candidate bands, as well as new challenges for spectrum usage methods and management. Based on China?s current situation, this article first discusses the 5G vision, spectrum demands, and potential candidate bands. Furthermore, it is indicated that spectrum sharing will bring many benefits for 5G systems, and different sharing scenarios are summarized. Finally, based on the current framework of spectrum management in China, potential services classification and spectrum assessment are proposed to accommodate new 5G requirements. [ABSTRACT FROM PUBLISHER]