Showing papers by "Milica Stojanovic published in 2002"
01 Aug 2002
TL;DR: Using Neural Networks in Underwater Acoustic Signal Processing with Statistical Signal Processing for Echo Ensembles and Advanced Coding for Underwater Communications.
Abstract: Preface. 1. High-Speed Unterwater Acoustic Communications M. Stojanovic. 2. Synthetic Aperture Mapping and Imaging M.E. Zakharia, J. Chatillon. 3. Integrated Programmable Underwater Acoustic Biotelemetry System R.S.H. Istepanian. 4. Digital Underwater Voice Communications H. Sari, B. Woodward. 5. Applications of Neural Networks in Underwater Acoustic Signal Processing Z. Zhaoning, P.R. Nanjing. 6. Statistical Signal Processing of Echo Ensembles J. Penrose, T. Pauly. 7. Advanced Coding for Underwater Communications H. Junying, G. Haihong. Reference.
63 citations
29 Oct 2002
TL;DR: A networking algorithm for communication within a group of AUVs deployed on a cooperative mission in an area covering several square kilometers is proposed, based on a time-scheduled operation which enables the AUVs to locate each other by measuring the inter-vehicle signal propagation delays and by exchanging localization maps.
Abstract: With maturing of AUV technology and underwater acoustic modem technology, networks of AUVs have come into the focus of research on future systems for ocean observation and monitoring. In this paper, we propose a networking algorithm for communication within a group of AUVs deployed on a cooperative mission in an area covering several square kilometers. The algorithm is based on a time-scheduled operation which enables the AUVs to locate each other by measuring the inter-vehicle signal propagation delays and by exchanging localization maps. The vehicles transmit high-rate PSK signals which can directly be used for delay measurements. At the end of every time-slot, assigned for transmission from a single vehicle, each of the receiving vehicles updates its map based on the newly measured delay from the transmitting vehicle, the stored value of own map, and the value of the map as known by the currently transmitting vehicle. The so-built map may be used directly for localization, and also in a routing table for subsequent location-based dynamic routing of data packets. An example system provides a delay resolution on the order of tenth of a millisecond, and a map updating interval on the order of ten seconds. The basic algorithm operation is demonstrated using a network of several vehicles.
47 citations
01 Jan 2002
TL;DR: The design of high-speed digital communication systems, which rely on powerful equalization and multiple sensor signal processing methods is treated, and phase-coherent detection, which offers better efficiency in bandwidth utilization, is the subject of this chapter.
Abstract: Underwater acoustic communications are a rapidly growing field of research and engineering, driven by the expansion of applications which require underwater data transmission without wired connections. In this chapter, we explore the problems of underwater acoustic communications in three parts. The first part presents an overview of modern applications in underwater data transmission and today’s achievements in this area. System requirements are reviewed, and propagation characteristics of underwater acoustic channels are given. It is shown that the majority of underwater acoustic channels are severely band-limited, with signal distortions depending on the link configuration, and ranging from benign to extreme ones caused by time-varying multipath propagation and signal phase variations. Examples of existing systems are given, with emphasis on the methods used for intersymbol interference mitigation. Most of these systems use noncoherent or a differentially coherent signal modulation and detection methods. Phase-coherent detection, which offers better efficiency in bandwidth utilization, is the subject of the second part of this chapter. In this part, the design of high-speed digital communication systems, which rely on powerful equalization and multiple sensor signal processing methods is treated.
38 citations
29 Oct 2002
TL;DR: Two promising receivers, a RAKE based receiver and a hypothesis-feedback equalization based architecture are presented and the performance of the proposed receiver structures are compared based on simulations and also actual field test data.
Abstract: Direct sequence spread spectrum (DSSS) techniques for low probability of intercept (LPI) and multi-user communications applications for underwater acoustic communications are investigated. Two promising receivers, a RAKE based receiver and a hypothesis-feedback equalization based architecture are presented. The performance of the proposed receiver structures are compared based on simulations and also actual field test data.
37 citations
07 Aug 2002
TL;DR: It is demonstrated that a large improvement over a non-adaptive system is available provided an appropriately designed adaptation scheme that makes use of the channel fading statistics.
Abstract: Adaptive power and rate control for efficient use of satellite channels in the Ka band are considered. Fading due to rain is modeled as a log-normally distributed, autoregressive process with known statistics. Adaptation policies based on MMSE channel estimation are designed taking into account the effect of channel estimation errors in an optimal manner so as to satisfy the required outage probability for given fading dynamics. Analytical results show average power savings or average bit rate increase that are available from adaptive techniques. It is demonstrated that a large improvement over a non-adaptive system is available provided an appropriately designed adaptation scheme that makes use of the channel fading statistics. Finally, practical methods based on adaptive modulation level selection in a fixed-bandwidth system are evaluated analytically in terms of average bandwidth efficiency.
16 citations