| 1. |
- Hoeher, Peter, et al.
(författare)
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Channel estimation with superimposed pilot sequence
- 1999
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Ingår i: Proc. IEEE GLOBECOM '99, Rio de Janeiro, Brazil, December 1999. - 0780357965 ; 4, s. 2162-2166
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Konferensbidrag (refereegranskat)abstract
- For the purpose of various synchronization tasks (including carrier phase, time, frequency, and frame synchronization), one may add a known pilot sequence, typically a pseudo-noise sequence, to the unknown data sequence. This approach is known as a spread-spectrum pilot technique or as a superimposed pilot sequence technique. In this paper, we apply the superimposed pilot sequence technique for the purpose of channel estimation (CE). We propose and verify a truly coherent receiver based on the Viterbi algorithm, which is optimal in the sense of per-survivor processing. We also suggest a generic low-cost receiver structure based on reduced-state sequence estimation. Among the distinct advantages compared to conventional pilot-symbol-assisted CE are (i) a lack of bandwidth expansion and (ii) a significantly improved performance in fast fading environments. The proposed Viterbi receiver may also be used as an alternative receiver for pilot-symbol-assisted CE
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| 2. |
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| 3. |
- Mietzner, Jan, et al.
(författare)
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Analysis of the expected error performance of cooperative wireless networks employing distributed space-time codes
- 2004
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Ingår i: IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE. ; , s. 2854-2858
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Konferensbidrag (refereegranskat)abstract
- In this paper, typical uplink scenarios in a cellular system are considered, where two cooperating mobile stations (serving, for example, as mobile relays) are transmitting the same information to a base station by using a distributed space-time coding scheme. Due to the distributed nature of the system, the transmitted signals are typically subject to different average path losses. For fixed distances between the mobile stations and the base station, the error performance of the distributed space-time coding scheme is determined analytically. Then, based on considerations concerning the spatial distribution of the mobile stations, analytical expressions for the distribution of the average path losses are derived and verified by means of simulations. These results are then used in order to compute the expected error performance of the system. It is shown that in most scenarios the average performance loss compared to a conventional multiple-antenna system with colocated antennas is less than 2 dB at a bit error rate of 10(-3). The most significant performance losses occur for a large path-loss exponent.
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| 4. |
- Tufvesson, Fredrik, et al.
(författare)
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OFDM Time and Frequency Synchronization by Spread Spectrum Pilot Technique
- 1999
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Ingår i: Proc. 8th IEEE Communication Theory Mini Conference in conjunction to ICC'99, Vancouver, Canada, June 7-10, 1999. - 0780356535 ; , s. 115-119
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Konferensbidrag (refereegranskat)abstract
- Correct time and frequency synchronization is important for the performance of orthogonal frequency division multiplex (OFDM) systems. We evaluate a system where a pseudonoise sequence (PN-sequence) is used for estimation of these synchronization parameters. The PN-sequence is superimposed on the OFDM signal. The system is evaluated by means of the variance of the frequency estimation error and the probability for correct timing synchronization. Both theoretical and simulated results are presented. The proposed technique is very flexible and works also at low signal to noise ratios. The frequency offset range has been significantly increased compared to conventional OFDM synchronizer schemes
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| 5. |
- Zhang, Siwei, et al.
(författare)
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Distributed Direct Localization Suitable for Dense Networks
- 2020
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Ingår i: IEEE Transactions on Aerospace and Electronic Systems. - 1557-9603 .- 0018-9251. ; 56:2, s. 1209-1227
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Tidskriftsartikel (refereegranskat)abstract
- Traditional network localization algorithms contain ranging and localization steps, which have systematic disadvantages. We propose an algorithm dubbed direct particle filter based distributed network localization (DiPNet). A node's location is directly estimated from the received signals, incorporating location uncertainty of neighboring nodes. The propagation effects on DiPNet become insignificant for dense networks, due to the massive-link collective physical layer processing. DiPNet achieves a near-optimal performance with low complexity, which is particularly attractive for realtime dense-network localization.
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| 6. |
- Zhang, Siwei, et al.
(författare)
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Self-Aware Swarm Navigation in Autonomous Exploration Missions
- 2020
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Ingår i: Proceedings of the IEEE. - 1558-2256 .- 0018-9219. ; 108:7, s. 1168-1195
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Forskningsöversikt (refereegranskat)abstract
- A multitude of autonomous robotic platforms collectively organized as a swarm attracts increasing attention for remote sensing and exploration tasks. A navigation system is essential for the swarm to collectively localize itself as well as external sources. In this article, we propose a self-aware swarm navigation system that is conscious of the causality between its position and the localization uncertainty. This knowledge allows the swarm to move in a way to not only account for external mission objectives but also enhance position information. Position information for classical navigation systems has already been studied with the Fisher information (FI) and Bayesian information (BI) theories. We show how to extend these theories to a self-aware swarm navigation system, particularly emphasizing the collective performance. In this respect, fundamental limits and geometric interpretations of localization with generic observation models are discussed. We further propose a general concept of FI and BI based information seeking swarm control. The weighted position Cramer-Rao bound (CRB) and posterior CRB (PCRB) are employed flexibly as either a control cost function or constraints according to different mission criteria. As a result, the swarm actively adapts its position to enrich position information with different emerging collective behaviors. The proposed concept is illustrated by a case study of a swarm mission for gas exploration on Mars.
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