Browsing by Author "Vilaipornsawai, U."
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- Combined adaptive time reversal and DFE technique for time-varying underwater communicationsPublication . Vilaipornsawai, U.; Silva, A.; Jesus, S. M.This work presents a combined geometry-adapted passive Time Reversal (pTR) and Decision Feedback Equalizer (DFE) technique for time-variant underwater communications. We consider sustainable high data rate communications between a moving source and/or a moving receiver array, i.e. there is the presence of geometry changes such as range and depth changes. Such geometry changes can be partially compensated by employing a proper frequency shift on the probe impulse response in the pTR processing. We then refer to the geometry-adapted pTR as Frequency Shift pTR (FSpTR). With dense and long receiver array, a pTR-based technique possesses pulse compression property and can eliminate Inter-Symbol Interference (ISI) problem in multipath static channels. However, with a practical-size array and time-varying channels, a residual ISI always exists. Hence, in this work, we apply an adaptive DFE to further mitigate the residual ISI from the FSpTR, and call the technique as FSpTR-DFE. Performance of the FSpTR-DFE is evaluated using both experimental and simulated data, where an information rate of 2000 bps and BPSK signaling are considered. The RADAR’07 experimental data and the simulated data of the south Elba site are considered. In both data sets, a fast moving source with speed of 1.5 m/s is considered. The results show that the FSpTR-DFE technique outperforms the FSpTR as well as the technique combining the conventional pTR with DFE.
- Experimental testing of Asymmetric Underwater Acoustic NetworksPublication . Vilaipornsawai, U.; Silva, António; Jesus, S. M.The coordinated operation of multiple vehicles within the framework of multipoint non-cabled observatories and offshore activities sprung the necessity for complex underwater acoustic networks (UANs). An example of such UAN consisting of fixed and mobile underwater nodes, was recently developed and tested at sea. A star-shaped network topology was adopted, where wide area network (WAN) integration was ensured through an asymmetric underwater master node composed of an acoustic modem, for low-data-rate downlink from WAN to UAN, and a multiple receiver antenna for single-input-multiple-output (SIMO) high-priority high-data-rate uplink, from UAN to WAN. This paper focuses on the performance of the high-priority SIMO uplink combining multichannel geometry-adapted passive Time Reversal (pTR) and single Decision Feedback Equalizer (DFE). High data-rate and sustainable communications for mobile and fixed nodes were considered. Two experimental data sets were used: one from the UAN10 sea trial (Pianosa island, Italy, September 2010) for a moving source and UAN11 (Trondheim Fjord area, Norway, May 2011) for a fixed source. BPSK/QPSK signaling, data-rate upto 4000 bps and a source speed upto 0.5 m/s, were considered for carrier frequencies ranging from 5kHz to 25.6kHz. Temporal coherence is shown to be a key factor, determining the performance of pTR-based techniques. Moreover, the geometry-adapted pTR is shown to sustain the temporal coherence in case of geometry changes.
- UAN - Engineering Test: P2P CommunicationsPublication . Vilaipornsawai, U.; Silva, A.This report describes the P2P communication setup and results from the engineering test conducted at Pianosa island, Italy during September 7-25, 2010.
- Underwater communications for moving source using geometry-adapted time reversal and DFE UAN10 dataPublication . Vilaipornsawai, U.; Silva, A.; Jesus, S. M.This work presents an improved version of our previously proposed technique, i.e. the combined geometryadapted passive Time Reversal (pTR) and Decision Feedback Equalizer (DFE) for underwater communications between a moving source and a fixed receiver array (implying a range change) [1]. Since the geometry change can be compensated by employing a proper frequency shift on the probe Impulse Response (IR) in the pTR processing, the geometry-adapted pTR is called Frequency Shift pTR (FSpTR). A slot-based FSpTR processing is performed, where frequency shifts applied to the IRs can change over slots to compensate for geometry changes over time. The FSpTR output is the concatenation of slots of the processed signals. With different frequency shifts for consecutive slots, there are phase jumps in the FSpTR output. In this work, we propose a new phase-jump correction method, which is stable with respect to IR time-window selection. After the phase correction, a standard phase synchronization method and the DFE can then be applied subsequently to the FSpTR processing to further improve the performance. The developed technique is named FSpTR-DFE. Experimental data collected off Pianosa island, Italy in September 2010 for Underwater Acoustic Network (UAN) project, is called UANI0 data and used in the evaluation of the FSpTR-DFE performance. An information rate up to 2400 bps and BPSK signaling are considered. The results show that the FSpTR-DFE technique outperforms the FSpTR as well as the technique combining the conventional pTR with DFE when there exist strong range changes.