Yongqing Wu

Improvement of coordinate measuring machine probing accessibility

In this paper, the probe accessibility of coordinate measuring machines (CMM) in dimensional inspection is studied. Based on the previous methods of the accessibility map, the influence of the actual configuration of the probe on the accessibility is analyzed in detail. A method, which takes the effects of the probe length and volume into account, is proposed so that the shortcomings of abstracting the probe as an infinite half-line could be overcome completely. Finally, a feasible and efficient algorithm is given.

A simple distributed networking protocol for underwater acoustic networks

A simple distributed networking protocol for underwater acoustic networks is proposed. Each node in the network learns about the degrees of its separation to a certain destination node by passively analysis the packets transmitted from its immediate neighbors. The address of neighboring node with the least hops to a certain destination node will then be saved in a route table as the relay address for later communication with that destination. The route table is initialized with broadcast address and the relay address to a destination node will be reset to broadcast address if no packets from the destination have been heard through the corresponding neighbor for a given time. By applying such a decay mechanism, the routing information is locally updated to keep up with the topology changes of the network due to mobility, node failure, and channel variations. There is little overhead traffic for networking and the network-wide flooding only happens in the initialization process, the proposed protocol is ene...

Waveform design of geometric comb to extract target phase feature

The majority of active sonar systems to detect and classify a target based on the amplitude of the received echo strength or the induced Doppler shift. However, additional classification information is available from the phase shift introduced by some targets as a result of the acoustic boundary conditions. In this paper, waveform design of geometric comb using sub-band correlators is presented for measuring the phase shifts associated with certain stationary and moving targets when insonified by broadband transmissions. With the aim of providing improved range resolution, it maintains the amplitude of the transmission constant to maximize energy efficiency and compatibility with existing nonlinear power amplifiers. And the influences on target echo phase measurement are analyzed from reverberation gain achievable with broadband, Doppler sensitive geometric comb transmissions in littoral waters. At last, field trial results are given for a mine-like classification sonar system and a forward-looking sonar system designed for operation near the sea surface.

Time delay estimation in underwater positioning for pattern time delay shift coding

Based on the pattern time delay shift coding regime, a structure of positive and negative frequency modulation calling pulses of underwater ultra-short base line acoustic positioning system is given, and the second correlation method of time delay estimation is proposed in this paper. As the second correlation method improves the detectable signal-to-noise ratio of calling end to certain extent, it could accumulate the multipath reflections in the underwater channel on the energy including the direct wave effectively in the complex environment, so as to finish the peak detection accurately and to improve the accuracy of time delay estimation. At last, the sea trial results show that the second correlation method could suppress the multipath interference from interface reflections under different signal-to-noise (SNR) ratio efficiently.

The improvement of acoustic positioning of underwater vehicles based on synthetic long baseline navigation

Underwater navigation that relies solely on dead reckoning suffers from unbounded position error growth. In traditional positioning method, the cost and trouble of deploying, recovering, and assembly have become insuperable obstacle. Based on combination SLBL with an Argo float, a new positioning method of autonomous navigation is proposed in the paper. In order to improve the ranging accuracy, with the pattern time delay shift coding system, the second correlation method is given for time delay estimation in this paper. The superiority of the second cross-correlation method is that time delay could be estimated in a lower signal-to-noise ratio environment and in the complex multipath channels compared to the first cross-correlation method. Based on the measurements of distance and bearing, high-precision positioning of the AUV is achieved by using moving horizon estimation approach. At last, some field trial results show that the second correlation method could suppress the multipath interference in underwater channel efficiently, and that the position of moving vehicle is solved from point-to-point based on the estimation of bearing and ranging.

Reaearch on underwater integrated navigation system based on SINS/DVL/magnetometer/depth-sensor

For the long-range voyage and light Autonomous Underwater Vehicle (AUV), the high-precision navigation and positioning is the key point in the completion of the task. Therefore, this paper designs an underwater integrated navigation system, including the strapdown inertial navigation system (SINS), Doppler velocity loci (DVL), magnetometers and depth sensor. Based on the principle of each navigation sensor and the corresponding error model, the mathematic model of each sub-filter of the integrated navigation system is firstly established. Secondly, combining the combination filter and federated filtering theory, the integrated navigation system based on federated filtering is designed. Finally, to eliminate the influence of unknown or time-varying statistical characteristics on the Kalman filter (KF), a new federated filtering algorithm based on Sage-Husa adaptive KF is proposed to estimate each local filter. And the corresponding simulation results will show the performance of the research.

Doubly Weighted Average algorithm for DOA estimation on UCA with array failure

Failed elements will destroy the array performance, therefore methods to compensate for array element failures are important. Generally, there are two different lines to address this problem, reconstructing missing array element signals and reoptimize the weights of the remaining array elements according to a desired performance criterion. In this paper, a novel way termed Doubly Weighted Average (DWA) algorithm, which combines Weighted Average of Uniform Arc Arrays (WAUAA) algorithm and Non-uniform Circle Array (NCA) algorithm, is proposed for DOA estimation on Uniform Circle Array (UCA) with array failures. The theoretical derivation of its property is presented. This method is able to provide smaller Root Mean Square Error (RMSE) than NCA and even perfect UCA method. Simulation results show that DWA algorithm can substantially improve the DOA estimation performance. The RMSE of DWA is at least 1.5 dB less than WAUAA, which confirms the theoretical derivation. Especially with a small number of snapshots or a low source SNR, the proposed method provides more accurate estimates than the other compared methods. Furthermore, the DWA method can be used for multiple source and two-dimensional DOA estimation, and be expanded on the Uniform Linear Array (ULA).

An acoustic positioning of underwater vehicles using synthetic long baseline navigation

Underwater navigation that relies solely on dead reckoning suffers from unbounded position error growth. In traditional positioning method, the cost and trouble of deploying, recovering, and assembly have become insuperable obstacle. Based on combination SLBL with an Argo float, a new positioning method of autonomous navigation is proposed in the paper. In order to improve the ranging accuracy, with the pattern time delay shift coding system, the second correlation method is given for time delay estimation in this paper. The superiority of the second cross-correlation method is that time delay could be estimated in a lower signal-to-noise ratio environment and in the complex multipath channels compared to the first cross-correlation method. At last, some field trial results show that the second correlation method could suppress the multipath interference in underwater channel efficiently, and that the position of moving vehicle is solved from point-to-point based on the estimation of bearing and ranging.

Scattering phase analysis of dual-frequency plane wave by rigid and elastic spheres

Based on the scattering of dual-frequency transmission pulses and frequency-domain data processing, Philip R. Atkins has proposed a new method for standard-target phase calibration of sonar systems. This approach reduces the impact of unknown range and sound speed parameters upon phase calibration accuracy. However, since solutions to the phase of scattering of targets underwater are not offered, this approach is hard to be applied in practice. Phase information of the echo is necessary to use this approach, therefore mathematical models of rigid sphere and elastic sphere in the water are established and calculated. The phases of echoes resulting from a dual-frequency plane wave incident on these cases are analyzed. This paper deduces the phase difference of dual-frequency on the surface of rigid and elastic spheres. The simulations results of rigid and elastic spheres are given respectively.

Sonar detection performance with LFM-BPSK combined waveforms

As a sonar transmitted waveform, binary phase-shift keyed (BPSK) signal has a nearly ideal ambiguity function. The good Doppler and time resolution properties make BPSK signal advantageous for underwater targets detection. Under the Doppler perturbation situation, the property of good Doppler resolution will result in a sharp decline in detection performance. In recent years, waveform fusion has got extensive attentions. A novel waveform combining BPSK signal and a Doppler insensitive signal can improve the performance of target detection in case of perturbation. This article focuses on the study of ambiguity function, time and Doppler resolution of LFM-BPSK signal, furthermore we studied the detection performance of linear frequency-modulated (LFM), BPSK and LFM-BPSK signals in the presence of perturbation. Simulation results show that the LFM-BPSK signal has a stronger anti-perturbation proformance than BPSK signal.