KEYWORDS: Design, Digital signal processing, Transducers, Acoustics, Transmitters, Receivers, Tunable filters, Signal processing, Signal filtering, Bandpass filters
Underwater acoustic (UWA) modem is an important part of underwater information transmission field, which is widely used in underwater wireless sensor network, coral reef and ocean monitoring. At present, most commercial modems are expensive and bulky, which limits their large-scale application. It is based on the low cost, miniaturization, robust UWA modem this demand, first of all, this paper takes NXP iMXRT1062 MCU as the core processor, designed the corresponding receiving and transmitting circuit, secondly, in the design of hardware based on the realization of UWA FH-2FSK communication algorithm. The actual lake test results show that the designed modem can achieve a communication rate of 100 bps in the complex shallow water area, and the communication distance is 70 m.
The ultra-short baseline (USBL) acoustic positioning systems, characterized by their compactness and ease of installation, are extensively employed to augment efficiency in marine engineering tasks. Nevertheless, the diminutive size of USBL systems inherently leads to escalated positioning inaccuracies as the operational range expands. Conventional positioning systems based on ternary and quaternary arrays are compromised by suboptimal positioning accuracy and inadequate robustness. While adopting more intricate array configurations, such as three-dimensional arrays, or an increased number of elements, such as octonary arrays, can enhance the system's accuracy and reliability, such measures inevitably raise the hardware requirements and computational demands. In response to the dichotomy between the need for precision and computational efficiency, this study introduces a novel five-element planar array USBL positioning approach. Executed on a low-power, fixed-point TI TMS320C6416T digital signal processor (DSP), this five-element array positioning algorithm adeptly mediates between the requisites for high positioning accuracy, manageable computational complexity, and affordability. Experimental outcomes from controlled pool tests affirm that the devised scheme attains a positioning accuracy of 0.6%, illustrating its efficacy and potential applicability in marine engineering endeavors.
KEYWORDS: Doppler effect, Signal to noise ratio, Tunable filters, Signal detection, Detection and tracking algorithms, Education and training, Field programmable gate arrays, Acoustics, Signal processing, Receivers
Underwater acoustic (UWA) communication (UWAC) and positioning technology plays an important role in the field of underwater resource utilization and development. UWA multi-user detection and positioning technology is the core issue in UWAC and positioning systems. The time-varying ocean environment provides UWA multi-user detection, Doppler estimation and compensation and time delay estimation pose great challenges. First of all, in response to the requirements of multi-user UWAC and positioning technology, this article proposes a multi-user detection and delay estimation scheme based on Direct Sequence Spread Spectrum technology, using a 7th-order sequence as the spread spectrum code; secondly, in order to overcome the Doppler problem caused by high-speed motion, this article proposes a Doppler estimation and compensation technology based on ambiguity functions; then, based on the actual FPGA hardware platform, joint multi-user detection and multi-user detection are implemented. Doppler estimation and compensation and high-precision delay estimation algorithm; finally, the simulation and experiment results show that the solution proposed in this article can realize multi-user detection, Doppler estimation and compensation and high-precision delay estimation under 4-user conditions in real time. The delay estimation accuracy is less than 12us when the signal-to-noise ratio is 3dB, and the multi-user detection probability is greater than 90%.
The application of underwater acoustic communication (UWAC) technology in the field of marine resource development and utilization is increasingly in demand, and UWA MFSK-OFDM technology has attracted much attention because of its superior anti-interference. However, in the multitasking and high real-time requirements, FPGA has a greater parallelism advantage over the traditional DSP. In this paper, we first analyze the principle and characteristics of the UWA MFSKOFDM communication algorithm, and propose a UWA MFSK-OFDM algorithm suitable for real-time implementation on FPGA, which is based on the band-pass sampling theorem to finish the frame synchronization and demodulation of MFSKOFDM, and greatly reduces the computational complexity of the system, and secondly, we propose a scheme to reduce the computational complexity of the system, which is based on the frame synchronization and demodulation based on conventional Nyquist sampling theorem. Second, according to the proposed UWA MFSK-OFDM algorithm structure, relying on the advantages of FPGA in parallel computing, the UWA MFSK-OFDM communication system is realized in real-time through reasonable resource allocation and task scheduling. Finally, the pool experimental results show that the proposed algorithm improves the communication efficiency while maintaining the stability and real-time performance of the system, and the uncoded BER is 10-3 when the signal-to-noise ratio is around 8 dB, and the BER after decoding of the Turbo code with 1/2 code rate is 0. In addition, the consumption of FPGA hardware resources is greatly reduced compared with the conventional scheme.
KEYWORDS: Phase measurement, Field programmable gate arrays, Signal processing, Analog electronics, Phase shift keying, Linear filtering, Design, Phase modulation, Data conversion, Data transmission
In the multi-channel receiving system, the consistency of the phase and amplitude of the hardware circuit has a great impact on the signal processing results at the back end. Therefore, it is very important to ensure the consistency of the phase and amplitude between multiple channels. The high-precision measurement of the phase and amplitude of each channel is the premise of adjusting the circuit parameters. In order to provide a reliable and accurate parameter adjustment basis for the phase and amplitude adjustment of multiple channels, a convenient, effective and high-precision five-channel phase and amplitude consistency measurement scheme is presented in this paper. Firstly, the hardware circuit of the five-channel receiving system is designed, including signal preprocessing module, phase modulation module, A/D sampling module, FPGA control module, network port data transmission module, etc. Secondly, based on the designed hardware circuit, the FPGA program of 5-channel high-speed data acquisition and transmission is programmed. With the help of the data of the designed measurement scheme, by adjusting the parameters of the all-pass filter of the phase modulation circuit, the mean phase difference between the five channels is controlled within 0.1°, and the amplitude consistency is controlled within ±0.1dB.
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