Time filter

Source Type

Storrs, CT, United States

Chen Y.,Xiamen University | Wang Z.,University of Connecticut | Wang Z.,Michigan Technological University | Wan L.,University of Connecticut | And 3 more authors.
IEEE Journal of Oceanic Engineering

Dynamic coded cooperation (DCC) allows relay diversity without altering the transmission procedure from the source to the destination. In this paper, we propose a practical orthogonal frequency-division multiplexing (OFDM)-modulated DCC scheme for underwater relay networks, where OFDM modulation accommodates multipath fading channels with large delay spread. Two cooperation strategies are studied, where the relay transmits either identical or different OFDM blocks as the source during the cooperation phase. The block-level synchronization between the OFDM blocks from the source and the relay is achieved by a delay control mechanism at the relay, by knowing the distances among the source, relay, and destination. Two OFDM-DCC design examples are presented, one based on nonbinary rate-compatible low-density parity-check (LDPC) codes applied across multiple OFDM blocks, and the other using layered interblock erasure correction and intrablock error-correction coding. In addition to simulation studies, one particular design has been implemented on practical OFDM modems, and tested in a swimming pool and in a recent sea experiment. The proposed OFDM-DCC scheme is particularly appealing to underwater acoustic (UWA) networks where a relay node with abundant resources (e.g., a surface buoy) can enhance communications among underwater nodes without changing their transmission procedure. © 1976-2012 IEEE. Source

Carroll P.,University of Connecticut | Domrese K.,University of Connecticut | Zhou H.,Aquatic Sensor Network Technology | Zhou S.,University of Connecticut | Willett P.,University of Connecticut
Proceedings of the 9th ACM International Conference on Underwater Networks and Systems, WUWNET 2014

In this short paper, we look at a real-world implementation of an algorithm to enhance localization of a moving object in an underwater distributed antenna system. We utilize OFDM modems which are capable of estimating the Doppler shift of a message when it is received and combine this with a time-difference-of-arrival (TDOA) estimate. This combination serves to both enhance the position estimate and provide an accurate estimate of the velocity of the mobile network element, thus providing a full-state point estimate. A Kalman Filter (KF) is implemented to compare the accuracy of the full-state and position-only estimates. Basic simulations show that the full-state estimate provides an improvement, and this is verified using data from several pool tests. © 2014 ACM. Source

Carroll P.,University of Connecticut | Domrese K.,University of Connecticut | Zhou H.,Aquatic Sensor Network Technology | Zhou S.,University of Connecticut | Willett P.,University of Connecticut
Physical Communication

In this paper, we consider a problem of localizing a moving object in the context of an underwater distributed antenna system. All the distributed nodes record the time-of-arrivals of a single message from the moving object and obtain the Doppler speed estimates used in the decoding process. Conventional methods have relied only on the time-of-arrival measurements to obtain position estimates, on top of which filtering methods can be further applied for tracking purposes. In this work, we explore the usefulness of Doppler speed information. The combination of time-of-arrival measurements and Doppler speed estimates associated with a single message enhances the accuracy of position estimation and provides an estimate of the velocity of the mobile object. A Kalman Filter (KF) and a Probabilistic Data Association Filter (PDAF) are further implemented processing the point estimates. Simulations show that the proposed Doppler-aided methods improve both the point estimation and tracking filter performance, which is verified using data from pool tests. © 2015 Elsevier B.V. Source

Wan L.,University of Connecticut | Zhou H.,Aquatic Sensor Network Technology | Wilson D.,Caribbean Wind LLC | Hanson J.,Aquatic Sensor Network Technology | Zhou S.,University of Connecticut
Marine Technology Society Journal

Underwater acoustic orthogonal-frequency-division-multiplexing (OFDM) modems have been deployed in an environmental monitoring application in the Chesapeake Bay, maintained by the National Oceanic and Atmospheric Administration (NOAA)Chesapeake Bay Office, bringing sensory data from underwater instruments to surface on an hourly basis since March 2012. This paper analyzes the recorded datasets collected over a 2-month period to understand the OFDM performance in this particular application. During online operations, there were 221 data files failed in decoding out of 1,310 data files recorded, with a packet success rate of 83.1%.Various offline processing techniques are applied to evaluate the possible performance improvement when the receiver complexity and processing delays are not of concern, including (i) iterative processing while treating inter carrier interference (ICI)as additive noise, (ii) explicit ICI mitigation in a progressive fashion, and (iii) data driven sparsity factor optimization and effective noise weighting for improved channel estimation and multi channel data fusion. With these offline processing techniques, the packet success rate can be improved to nearly 97.0%. Both online and offline data analyses confirm that there were large temporal dynamics, and large wind speed and wave height led to low pilot signal-to-noise ratios that directly deteriorate the decoding performance. Through the study, we suggest several possible approaches to improve the communication reliability for long-term deployments in challenging shallow water environments. © 2014, Marine Technology Society Inc. All rights reserved. Source

Zhang Y.,Northwestern Polytechnical University | Zhang Y.,University of Connecticut | Huang Y.,University of Connecticut | Wan L.,Aquatic Sensor Network Technology | And 4 more authors.
2014 Oceans - St. John's, OCEANS 2014

Multiuser communication has been an important research area of underwater acoustic communications and networking. This paper studies the use of adaptive OFDMA in a multiuser downlink scenario, where a central node sends data to multiple distributed nodes simultaneously. The reduction of channel feedback via clustering and quantization is considered, and an interleaved power-bit loading algorithm is presented to jointly assign the data subcarriers to different users and allocate the power and bits on each subcarrier. Simulation results show the performance improvement due to subcarrier allocation with and without additional power and bit loading. An experiment conducted in a swimming pool illustrates potential benefits and challenges of harvesting the multiuser diversity through adaptive subcarrier allocation. © 2014 IEEE. Source

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