| 1. |
- Backén, Staffan, et al.
(författare)
-
A novel software defined research receiver architecture
- 2009
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Ingår i: Proceedings of the 13th IAIN World Congress. - : Nordic Institute of Navigation.
-
Konferensbidrag (refereegranskat)abstract
- Software defined receivers (SDR) are an increasingly important tool within the GNSS research community as the high level of flexibility offer a significant advantage over traditional hardware implementations. Over the last decade, software receivers have been used to investigate techniques as diverse as bi-static radar (additional correlators), multipath mitigation techniques, GPS/INS integration and array processing.Mentioned above are only a few examples of features that could be required of an SDR, other include support for new signals (Galileo, GPS L5), multiple data file formats, high sensitivity and support for very long data sets. The large number of available features should ideally be coupled with program simplicity (such that other people can understand the program) and efficiency. This paper discusses these issues and proposes several solutions such asgeneralized data buffers (that is trivial to extend for new data formats) and a unified tracking structure (regardless of signal modulation). Examples are given using a Matlab implementation based on the Borre/Akos book Ä Software-Defined GPS and Galileo Receiver", however with significant modifications. Where critical, Java is used to increase performance while maintaining cross platform compatibility. Near real-time operation is available under optimal circumstances and the receiver currently supports GPS C/A- and GPS P-code signals.
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| 2. |
- Backén, Staffan, et al.
(författare)
-
Post-processing dynamic GNSS antenna array calibration and deterministic beamforming
- 2008
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Ingår i: Proceedings of the 21th International Technical Meeting of the Satellite Division of the Institute of Navigation. ; , s. 1311-1319
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Konferensbidrag (refereegranskat)abstract
- An array processing GNSS (Global Navigation Satellite System) receiver may provide increased accuracy, reliability and integrity by forming beams towards satellites and nulls towards interference or reflective surfaces. Also, software defined receivers have proven themselves versatile and provide a convenient environment to implement novel algorithms.This paper first describes the gain/phase calibration of a seven element custom array antenna and proceeds to compare the single antenna performance to that of the performance attained by forming beams towards the satellites. IF (Intermediate Frequency) data, high rate samples representing the received signal in a narrow band around the GPS L1 frequency, from an array antenna have been recorded both in an environment with open sky conditions and also in more challenging areas (central Boulder, Colorado). Simultaneously, data from a high quality GPS based INS was recorded in order to obtain accurate estimates of position/ orientation. Calibration of the system (including antennas and front-ends) was performed using data from the benign environment, and based on this information, deterministic beams were formed towards the satellites using data from the semi-urban dataset. The single antenna accuracy was then compared to the position obtained by processing after forming beams.
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| 3. |
- Bergquist, Bjarne, et al.
(författare)
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A Bayesian analysis of unreplicated two-level factorials using effects sparsity, hierarchy, and heredity
- 2011
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Ingår i: Quality Engineering. - : Informa UK Limited. - 0898-2112 .- 1532-4222. ; 23:2, s. 152-166
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Tidskriftsartikel (refereegranskat)abstract
- This article proposes a Bayesian procedure to calculate posterior probabilities of active effects for unreplicated two-level factorials. The results from a literature survey are used to specify individual prior probabilities for the activity of effects and the posterior probabilities are then calculated in a three-step procedure where the principles of effects sparsity, hierarchy, and heredity are successively considered. We illustrate our approach by reanalyzing experiments found in the literature.
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| 4. |
- Birk, Wolfgang, et al.
(författare)
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Project: iRoad
- 2011
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Annan publikation (populärvet., debatt m.m.)
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| 5. |
- Bossér, Daniel, et al.
(författare)
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A Statistically Motivated Likelihood for Track-Before-Detect
- 2022
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Ingår i: 2022 IEEE INTERNATIONAL CONFERENCE ON MULTISENSOR FUSION AND INTEGRATION FOR INTELLIGENT SYSTEMS (MFI). - : IEEE. - 9781665460262 - 9781665460279
-
Konferensbidrag (refereegranskat)abstract
- A theoretically sound likelihood function for passive sonar surveillance using a hydrophone array is presented. The likelihood is derived from first order principles along with the assumption that the source signal can be approximated as white Gaussian noise within the considered frequency band. The resulting likelihood is a nonlinear function of the delay-and-sum beamformer response and signal-to-noise ratio (SNR). Evaluation of the proposed likelihood function is done by using it in a Bernoulli filter based track-before-detect (TkBD) framework. As a reference, the same TkBD framework, but with another beamforming response based likelihood, is used. Results from Monte-Carlo simulations of two bearings-only tracking scenarios are presented. The results show that the TkBD framework with the proposed likelihood yields an approx. 10 seconds faster target detection for a target at an SNR of -27 dB, and a lower bearing tracking error. Compared to a classical detect-and-track target tracker, the TkBD framework with the proposed likelihood yields 4 dB to 5 dB detection gain.
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| 6. |
- Bossér, Daniel, et al.
(författare)
-
A Statistically Motivated Likelihood for Track-Before-Detect
- 2022
-
Ingår i: 2022 IEEE International Conference on Multisensor Fusion and Integration for Intelligent Systems (MFI). - : IEEE. - 9781665460279 - 9781665460262
-
Konferensbidrag (refereegranskat)abstract
- A theoretically sound likelihood function for passive sonar surveillance using a hydrophone array is presented. The likelihood is derived from first order principles along with the assumption that the source signal can be approximated as white Gaussian noise within the considered frequency band. The resulting likelihood is a nonlinear function of the delay-and-sum beamformer response and signal-to-noise ratio (SNR).Evaluation of the proposed likelihood function is done by using it in a Bernoulli filter based track-before-detect (TkBD) framework. As a reference, the same TkBD framework, but with another beamforming response based likelihood, is used. Results from Monte-Carlo simulations of two bearings-only tracking scenarios are presented. The results show that the TkBD framework with the proposed likelihood yields an approx. 10 seconds faster target detection for a target at an SNR of -27 dB, and a lower bearing tracking error. Compared to a classical detect-and-track target tracker, the TkBD framework with the proposed likelihood yields 4 dB to 5 dB detection gain.
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| 7. |
- Bossér, Daniel, et al.
(författare)
-
Underwater Environment Modeling for Passive Sonar Track-Before-Detect
- 2023
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Ingår i: OCEANS 2023 - LIMERICK. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350332278 - 9798350332261
-
Konferensbidrag (refereegranskat)abstract
- Underwater surveillance using passive sonar and track-before-detect technology requires accurate models of the tracked signal and the background noise. However, in an underwater environment, the signal channel is time-varying and prior knowledge about the spatial distribution of the background noise is unavailable. In this paper, an autoregressive model that captures a time-varying signal level caused by multi-path propagation is presented. In addition, a multi-source model is proposed to describe spatially distributed background noise. The models are used in a Bernoulli filter track-before-detect framework and evaluated using both simulated and sea trial data. The simulations demonstrate clear improvements in terms of target loss and improved ability to discern the target from the noisy background. An evaluation of the track-before-detect algorithm on the sea trial data indicates a performance gain when incorporating the proposed models in underwater surveillance and tracking problems.
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| 8. |
- Carlson, Johan, et al.
(författare)
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Measurement of methane content in upgraded biogas using pulse-echo ultrasound
- 2008
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Ingår i: Proceedings of the International Congress on Ultrasonics.
-
Konferensbidrag (refereegranskat)abstract
- In this paper we present an ultrasonic pulseecho technique for estimating the methane (CH4) content in binary mixtures of CH4 and carbon dioxide (CO2). The method is based on parametric estimation of phase velocity and frequency dependent attenuation in combination with Partial Least-Squares Regression (PLSR). The technique is verified using experiments on mixtures with a volume fraction of CO2 in the range of 0 % -10 %. The experiments show that the CH4 content can be accurately estimated with high repeatability.
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| 9. |
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| 10. |
- Hostettler, Roland, et al.
(författare)
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A system identification approach to modeling of wave propagation in pavements
- 2012
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Ingår i: 16th IFAC Symposium on System Identification. - : IFAC, International Federation of Automatic Control. - 9783902823069 ; , s. 292-297
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Konferensbidrag (refereegranskat)abstract
- In this paper, modeling of the pavement as a wave propagation medium and estimation of the corresponding model parameters is approached from a system identification perspective. A model based on the physical background is proposed and the corresponding parameters are then estimated from measurement data. In order to achieve the latter, two estimators are proposed, their performance evaluated, and then applied to the measurement data. It is found that the proposed methods are applicable and the results show that different eigenmodes of the structure are excited.
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| 11. |
- Hostettler, Roland, et al.
(författare)
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Extended Kalman filter for vehicle tracking using road surface vibration measurements
- 2013
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Ingår i: IEEE 51st Annual Conference on Decision and Control. - Piscataway, NJ : IEEE Communications Society. - 9781467320658 - 9781467320641
-
Konferensbidrag (refereegranskat)abstract
- This paper addresses a novel method for vehicle tracking using an extended Kalman filter and measurements of road surface vibrations from a single accelerometer. First, a measurement model for vibrations caused by vehicular road traffic is developed. Then the identifiability of the involved parameters is analyzed. Finally, the measurement model is combined with a constant speed motion model and the Kalman filter is derived. Simulation and measurement results indicate that the approach is feasible and show where further development is needed.
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| 12. |
- Hostettler, Roland, et al.
(författare)
-
Feasibility of road vibrations-based vehicle property sensing
- 2010
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Ingår i: IET Intelligent Transport Systems. - : Institution of Engineering and Technology (IET). - 1751-956X .- 1751-9578. ; 4:4, s. 356-364
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Tidskriftsartikel (refereegranskat)abstract
- This article discusses a novel approach to vehicle property sensing based on traffic-induced road surface vibrations and investigates the feasibility of this approach. Road surface vibrations from real-life experiments are acquired using three-axis accelerometers and the data are analysed. Based on the assessment of the data, a first coarse scheme for axle detection of passing vehicles is developed. The scheme is then evaluated using measurement data from a highway with moderate traffic intensity but diverse traffic. It is found that the proposed approach is feasible and the estimation scheme yields promising results. Furthermore, delimitations, encountered problems and identified research challenges are discussed and future research directions are given.
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| 13. |
- Hostettler, Roland, et al.
(författare)
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Joint Vehicle Trajectory and Model Parameter Estimation using Road Side Sensors
- 2015
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Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 15:9, s. 5075-5086
-
Tidskriftsartikel (refereegranskat)abstract
- This article shows how a particle smoother based system identification method can be applied for estimating the trajectory of road vehicles. As sensors, a combination of an accelerometer measuring the road surface vibrations and a magnetometer measuring magnetic disturbances mounted on the side of the road are considered. First, sensor models describing the measurements of the two sensors are introduced. It is shown that these depend on unknown, static parameters that have to be considered in the estimation. Second, the sensor models are combined with a two-dimensional constant velocity motion model. Third, the system identification algorithm is introduced which iteratively runs a Rao-Blackwellized particle smoother to estimate the vehicle trajectory followed by an expectation-maximization step to estimate the parameters. Finally, the method is applied to both simulation and measurement data. It is found that the method works well in general and some issues when real data is considered are identified as future work.
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| 14. |
- Hostettler, Roland, et al.
(författare)
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Maximum Likelihood Estimation of the Non-Parametric FRF for Pulse-Like Excitations
- 2016
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Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 61:8, s. 2276-2281
-
Tidskriftsartikel (refereegranskat)abstract
- This technical note introduces the closed form maximum likelihood estimator for estimating the coefficients of the non-parametric frequency response function from system identification experiments. It is assumed that the experiments consist of repeated pulse excitations and that both the excitation and system response are measured which leads to an error-in-variables setting. Monte Carlo simulations indicate that the estimator achieves efficiency at low signal-to-noise ratios with only few measurements. Comparison with the least-squares estimator shows that better, unbiased results are obtained.
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| 15. |
- Hostettler, Roland, et al.
(författare)
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Surface mounted vehicle property sensing for cooperative vehicle infrastructure systems
- 2009
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Ingår i: 16th World Congress and Exhibition on Intelligent Transport Systems 2009. - Red Hook : Curran Associates, Inc.. - 9781617385896
-
Konferensbidrag (refereegranskat)abstract
- This paper presents first results for vehicle detection and vehicle property estimation based on the assessment of traffic induced vibrations in the road surface. A surface mounted 3D accelerometer device is used to register the vibrations in the surface. Acquired data from experiments on roads are used to design methods that are able to detect vehicle passages, estimate the number of axles of a vehicle and also deduce the wheel-base for passenger cars. Evaluation of the methods indicate that the accelerometer based approach is feasible and should be further developed in order to deduce vehicle properties like vehicle speed and distance to sensing device from one device. Moreover, results for the vehicle detection on real-life traffic data from the E4 in northern Sweden are summarized.
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| 16. |
- Hostettler, Roland, et al.
(författare)
-
The pavement as a waveguide: modeling, system identification, and parameter estimation
- 2014
-
Ingår i: IEEE Transactions on Instrumentation and Measurement. - 0018-9456 .- 1557-9662. ; 63:8, s. 2052-2063
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents modeling of wave propagation in pavements from a system identification point of view. First, a model based on the physical structure is derived. Second, experiment design and evaluation are discussed and maximum-likelihood estimators for estimating the model parameters are introduced, assuming an error-in-variables setting. Finally, the proposed methods are applied to measurement data from two experiments under varying environmental conditions. It is found that the proposed methods can be used to estimate the dispersion curves of the considered waveguide and the results can be used for further analysis
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| 17. |
- Isoz, Oscar
(författare)
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Interference detection and localization in the GPS L1 frequency band
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The usage of Global Navigation Satellite Systems (GNSS) in general and the American GPS in particular increases everyday and so does the number of applications where it is used. The GNSS receivers relies on receiving signals from satellites orbiting the earth at an altitude of about 20 000 km and the signals received by the receiver are signicantly weaker then the background noise. Due to the weak signals it is fairly easy to intentionally or accidentally make it very hard or even impossible for a receiver to detect and track the satellites.With this in mind there is a need to develop cost eective methods to detect and localize interference so that appropriate counter measures can be taken. A number of methods have been proposed to detect and localize these sources. The complexity of these methods ranges from requiring future cellphones to contain software to monitor the GNSS environment to dedicated systems with multiple antennas and complicated hardware. In this thesis, two complementary methods will be presented which can detect and also localize interference in the GNSS bands using minimum amount of equipment. The equipment is based around a type of GNSS "receiver" that only samples the GNSS frequency so that it can be processed using a software dened GNSS eceiver. It will be shown that it is capable of detecting and localizing interference sources while also be cost eective and easily deployable. The rst technique is based on measuring the received power level. Since the GNSS signals are below the noise oor, the number of visible satellites will not aect the received power level. Instead the received power level will be aected by changes in the spectrum and changes in the receiver hardware. The GNSS signal is fairly robust against interference so an interferer usually has to have a signicantly higher signal power than the received power from the satellites in order to cause problems for the receiver. By monitoring the received signal power using multiple receivers it is possible to both detect interference and estimate the position of the transmitter. This method requires very little bandwidth but since the signal is measured in the analog domain it is sensitive to process variations between dierent receivers. Also, the nonlinear behaviour of the analog components in the receiver limits the accuracy of the position estimations. To improve the accuracy of the interference localization, a second method has been evaluated. In this method the GNSS samples recorded by dierent receivers at different locations is compared. When a GNSS receiver calculates a position it is actually calculating the time it takes for the signals to travel from the satellite to the receiver. This made it possible to synchronize data from multiple independent receivers both in time and frequency and then estimate the time dierence of arrival of the interfering signal between the dierent receivers. Both localization methods were evaluated during experiments done with assistance from the Swedish armed forces research agency (FOI). It will be shown that the signal power measurement can be used as a detector for interference and that the GPS signal can be used to synchronize data from independent stations so that the dierence in distance to a wideband transmitter can be estimated. To determine the amount of interference in the GPS L1 band two measurement campaigns were made. The rst campaign, measured where interference might be present in an urban area using a car mounted receiver. The other campaign took place at two airports in the summer and fall of 2011 and measured the interference level from xed antennas over an extended period of time.All research was done using the GPS L1 signal but the methods can easily be applied to other GNSS signals as well.
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| 18. |
- Johansson, Gustav, et al.
(författare)
-
Simulation of post-ADC digital beamforming for large aperture array radars
- 2010
-
Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 45:RS3001
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents simulations and methods developed to investigate the feasibility of using a Fractional-Sample-Delay (FSD) system in the planned EISCAT_3D incoherent scatter radar. Key requirements include a frequency-independent beam direction over a 30 MHz band centered around 220 MHz, with correct reconstruction of pulse lengths down to 200 ns. The clock jitter from sample to sample must be extremely low for the integer sample delays. The FSD must also be able to delay the 30 MHz wide signal band by 1/1024th of a sample without introducing phase shifts, and it must operate entirely in baseband. An extensive simulation system based on mathematical models has been developed, with inclusion of performance-degrading aspects such as noise, timing error, and bandwidth. Finite Impulse Response (FIR) filters in the baseband of a band-pass-sampled signal have been used to apply true time delay beamforming. It has been confirmed that such use is both possible and well behaved. The target beam-pointing accuracy of 0.06° is achievable using optimized FIR filters with lengths of 36 taps and an 18 bit coefficient resolution. Even though the minimum fractional delay step necessary for beamforming is ∼13.1 ps, the maximum sampling timing error allowed in the array is found to be σ ≤ 120 ps if the errors are close to statistically independent.
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| 19. |
- Johansson, Jonny, et al.
(författare)
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Project: EISCAT 3D
- 2007
-
Annan publikation (populärvet., debatt m.m.)
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| 20. |
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| 21. |
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| 22. |
- Lidström, Viktor, et al.
(författare)
-
A Framework For Testing Data Driven Underwater Link Adaptation
- 2022
-
Ingår i: 2022 Sixth Underwater Communications And Networking Conference (UCOMMS). - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- To make full use of the underwater acoustic channel, a high degree of adaptivity is typically required. A novel framework for efficient evaluation of link adaptation employing channel replay simulation with Watermark and a lookup table is proposed. The approach is used to compare link adaptation based on SNR and CRC feedback using measured sea data. The best performance is obtained with a CRC criterion since it detects if a communication link has poor behaviour. The method is further improved by introducing a memory mechanism that disables a link with repeated low reliability.
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| 23. |
- Lidström, Viktor, 1991-, et al.
(författare)
-
Non-Coherent Acoustic Modulation for Energy Constrained Underwater Platforms
- 2019
-
Ingår i: OCEANS 2019 - Marseille, OCEANS Marseille 2019. - : Institute of Electrical and Electronics Engineers Inc..
-
Konferensbidrag (refereegranskat)abstract
- With regards to energy constrained Autonomous Underwater Vehicles (AUVs), and difficulties inherent to the acoustic underwater communication channel, a non-coherent method is investigated in order to improve energy consumption and reliability over traditional Frequency Shift Keying (FSK), without increasing the bandwidth. A proposed method of adapting Trellis Coded Modulation (TCM) to constant amplitude Permutated Frequency Shift Keying (PFSK) symbol constellations is evaluated. A system implementation of two PFSK methods is simulated in an Additive White Gaussian Noise channel, and field tested in an underwater channel in the Stockholm archipelago, where a binary FSK reference method is used as a comparison. The main interest is comparing electrical bit energy and bit error rate (BER) for the methods. Time variability of frequency fading, related to wind speed, is also evaluated from the field tests.
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| 24. |
- Lidström, Viktor, 1991-
(författare)
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On the Design of Noncoherent Acoustic Underwater Communication
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The underwater domain is an environment hostile to humans due to the hydrostatic pressure that rapidly increases with water depth, which has led to underwater robotics becoming an emerging technological field with many commercial-, environmental-, and security-related applications. A major challenge to untethered autonomous underwater vehicles (AUVs) is communicating robot-to-robot and robot-to-topside operator since it must, in most cases, be done acoustically. Meanwhile, the underwater acoustic (UWA) channel is widely considered one of nature's most difficult communication mediums due to the limited frequency range, complicated sound propagation physics, prolonged- and time-varying multipath, and, in some situations, non-Gaussian background noise. The wide variety of UWA channels observed in different locations, and in the same location at different times, also poses a challenge to the research methodology since sea experiments become inherently difficult to repeat. However, replay simulation of recorded channels using the public benchmark Watermark allows direct comparison between publications and is employed extensively in this thesis, complemented by sea experiments for verifying the internal validity of simulation results.No link solution is perfect for all channels, and a toolbox consisting of methods with varying information rates and robustness is necessary for an adaptive network to exploit the full capability of the channel encountered in situ. A link is called channel-agnostic if its robustness is limited by the ratio of signal power to noise (SNR), rather than the channel characteristics, thereby being robust to many channels one might encounter. The proven information rates for such link methods are relatively low; this, together with recent advancements in other areas, such as error correction codes and joint synchronisation and decoding, motivates the focus on noncoherent methods in this thesis. The second focus is link adaptation and the necessary mechanisms for its implementation in adaptive UWA networks.The thesis provides a background on various approaches to acoustic signalling, both coherent and noncoherent, and other key components of a noncoherent UWA link, such as symbol alphabets, receiver data models, error correction codes, and time-Doppler synchronisation. The topic of link adaptation in a UWA network is discussed, as is the methodology for research in UWA communication. The included papers provide a set of channel-agnostic link methods with spectral efficiencies in the range 0.02-0.22 (bit/s/Hz), with varying requirements on the SNR and the length of the communication frame, which are enabled by the presented improvements to link methods. Using a Rice-fading model for soft decoding, the robustness to parameter time variation is found to increase substantially by limiting the SNR of the likelihood parametrisation; this result applies to all methods that employ frequency shift keying (FSK). Furthermore, a novel noncoherent symbol alphabet with 1 (bit/s/Hz) maximum spectral efficiency is presented, whose dimensionality M increases the soft decoder performance, specialising to on-off keying (OOK) for M=1. A joint synchronisation and decoding framework is proposed, allowing robust time-Doppler detection with low overhead; its viability is demonstrated in an adverse shallow-water channel with relative platform velocities in the range +/- 4 (m/s). Moreover, a framework for efficient evaluation of link adaptation algorithms is presented, and a link-adaptive ad-hoc UWA network using low-latency implicit feedback is demonstrated through sea experiments.The research presented herein has been conducted as part of the Swedish Maritime Robotics Centre (SMaRC), a national cross-disciplinary research centre funded by the Swedish Foundation for Strategic Research (SSF).
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| 25. |
- Lin, Jing, et al.
(författare)
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Bayesian survival analysis in reliability for complex system with a cure fraction
- 2011
-
Ingår i: International Journal of Performability Engineering. - 0973-1318. ; 7:2, s. 109-120
-
Tidskriftsartikel (refereegranskat)abstract
- In traditional methods for reliability analysis, one complex system is often considered as being composed by some subsystems in series. Usually, the failure of any subsystem would be supposed to lead to the failure of the entire system. However, some subsystems' lifetimes are long enough and even never fail during the life cycle of the entire system. Moreover, such subsystems' lifetimes will not be influenced equally under different circumstances. In practice, such interferences will affect the model's accuracy, but it is seldom considered in traditional analysis. To address these shortcomings, this paper presents a new approach to do reliability analysis for complex systems. Here a certain fraction of the subsystems is defined as a "cure fraction" under the consideration that such subsystems' lifetimes are long enough and even never fail during the life cycle of the entire system. By introducing environmental covariates and the joint power prior, the proposed model is developed within the Bayesian survival analysis framework, and thus the problem for censored (or truncated) data in reliability tests can be resolved. In addition, a Markov chain Monte Carlo computational scheme is implemented and a numeric example is discussed to demonstrate the proposed model
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| 26. |
- Lin, Jing, et al.
(författare)
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Spares demand system with consideration of integration management and optimization
- 2011
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Ingår i: 2011 International Conference on Mechanical, Industrial, and Manufacturing Engineering. - 9780983169314 ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- Inventory management differs from other manufacturing inventory managements, mainly due to its specialists in function with maintenance. So far, enormous attention has been paid by standing on spares’ manufacturingfactories, sales companies, end users’ purchasing departments, or maintenance engineers, separately. However, not only “bullwhip effect” in forecasting spares demands, but also deteriorated relationships among the spares supply chains have shown that, spares optimization strategies with isolated consideration couldonly bring short-term or partial improvements. In this paper, the spares demand system with consideration of integration management is promoted, the new Solid-Net relationships among four main components are elaborated. Then, the root causes of ineffective in spares demand system are analyzed. Also, distinctoptimization policies are illustrated. What’s more, successful stories in practice are cited.
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| 27. |
- Ling, Jun, et al.
(författare)
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Efficient channel equalization for MIMO underwater acoustic communications
- 2010
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Ingår i: 2010 IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM). - Piscataway, NJ : IEEE Communications Society. - 9781424489787 - 9781424493951 ; , s. 73-76
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Konferensbidrag (refereegranskat)abstract
- Linear minimum mean-squared error (LMMSE)-based channel equalization is widely used in multi-input multioutput (MIMO) underwater acoustic communications (UAC). The practical challenge of LMMSE based schemes is the necessity of matrix inversion which generally imposes heavy computational burden on the receiver. To obtain the LMMSE filters efficiently, we exploit the conjugate gradient method and the diagonalization properties of circulant matrices. The proposed scheme is based on fast Fourier transform operations and can be implemented in parallel, which makes it a promising candidate for real-time MIMO underwater acoustic communications. Both numerical and SPACE'08 experimental examples are presented to demonstrate the effectiveness of the proposed approach.
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| 28. |
- Ling, Jun, et al.
(författare)
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Enhanced channel estimation and efficient symbol detection in MIMO underwater acoustic communications
- 2009
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Ingår i: Conference Record of the Forty-Third Asilomar Conference on Signals, Systems and Computers. - : IEEE Communications Society. - 9781424458257 ; , s. 600-604
-
Konferensbidrag (refereegranskat)abstract
- Effective training sequences and reliable channel estimation algorithms are essential for enhancing the performance of multi-input multi-output (MIMO) underwater acoustic communications (UAC). Also, effective interference cancellation schemes are crucial for reliable symbol detection. In this paper, the problem of designing MIMO training sequences is considered. Moreover, we present a sparse learning via iterative minimization (SLIM) algorithm for enhanced channel estimation and reduced computational complexity. Furthermore, RELAX-BLAST, a linear minimum mean-squared error based symbol detection scheme, is implemented efficiently by exploiting the conjugate gradient method and diagonalization properties of circulant matrices. The proposed MIMO UAC techniques are evaluated using both simulated and experimental examples.
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| 29. |
- Ling, Jun, et al.
(författare)
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Multi-input multi-output underwater communications over sparse and frequency modulated acoustic channels
- 2011
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 130:1, s. 249-262
-
Tidskriftsartikel (refereegranskat)abstract
- This paper addresses multi-input multi-output (MIMO) communications over sparse acoustic channels suffering from frequency modulations. An extension of the recently introduced SLIM algorithm, which stands for sparse learning via iterative minimization, is presented to estimate the sparse and frequency modulated acoustic channels. The extended algorithm is referred to as generalization of SLIM (GoSLIM). The sparseness is exploited through a hierarchical Bayesian model, and because GoSLIM is user parameter free, it is easy to use in practical applications. Moreover this paper considers channel equalization and symbol detection for various MIMO transmission schemes, including both space-time block coding and spatial multiplexing, under the challenging channel conditions. The effectiveness of the proposed approaches is demonstrated using in-water experimental measurements recently acquired during WHOI09 and ACOMM10 experiments.
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| 30. |
- Ling, Jun, et al.
(författare)
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On Bayesian channel estimation and FFT-based symbol detection in MIMO underwater acoustic communications
- 2014
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Ingår i: IEEE Journal of Oceanic Engineering. - 0364-9059 .- 1558-1691. ; 39:1, s. 59-73
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Tidskriftsartikel (refereegranskat)abstract
- Reliable channel estimation and effective interference cancellation are essential for enhancing the performance of multiple-input-multiple-output (MIMO) underwater acoustic communication (UAC) systems. In this paper, an efficient user-parameter-free Bayesian approach, referred to as sparse learning via iterative minimization (SLIM), is presented. SLIM provides good channel estimation performance along with reduced computational complexity compared to iterative adaptive approach (IAA). Moreover, RELAX-BLAST, which is a linear minimum mean-squared error (MMSE)-based symbol detection scheme, is implemented efficiently by making use of the conjugate gradient (CG) method and diagonalization properties of circulant matrices. The proposed algorithm requires only simple fast Fourier transform (FFT) operations and facilitates parallel implementations. These MIMO UAC techniques are evaluated using both simulated and in-water experimental examples. The 2008 Surface Processes and Acoustic Communications Experiment (SPACE08) experimental results show that the proposed MIMO UAC schemes can enjoy almost error-free performance even under severe ocean environments.
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| 31. |
- Lundberg Nordenvaad, Magnus, et al.
(författare)
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A map based estimator for inverse complex covariance matricies
- 2012
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Ingår i: 2012 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). - 1520-6149. - 9781467300469 ; , s. 3369-3372
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Konferensbidrag (refereegranskat)abstract
- A novel approach to estimate (inverse) complex covariance matrices is proposed. By considering the class of unitary invariant estimators, the main challenge lies in estimating the underlying eigenvalues from sampled versions. By exploiting that the distribution of the sample eigenvalues can be derived in closed form, a Maximum A Posteriori (MAP) based scheme is then derived. The performance of the derived estimator is simulated and results indicate that the proposed scheme shows performance similar to one of the best estimators known to date. The main advantage lies in that the proposed solution only requires numerical optimization over a P-dimensional space where P is the size of the covariance matrix.
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| 32. |
- Lundberg Nordenvaad, Magnus, et al.
(författare)
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Broadband synchronization of underwater acoustic communication signals using superimposed pilots
- 2012
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Ingår i: OCEANS, 2012 - YEOSU. - 9781457720918
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Konferensbidrag (refereegranskat)abstract
- A low-complex methodology to synchronize broadband underwater acoustic channels is proposed. The aim of the scheme is to process the received signal in such a way that the highly time-varying discrete-time channel turns time-invariant. Suggested is an LMS-like strategy based on superimposed pilots. Simulations on realistic models show that the proposed scheme is able to maintain very stable channel properties throughout long data frames. This indicates that the derived strategy is a highly attractive component for various underwater communication applications as channel variation is often the limiting factor in system performance.
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| 33. |
- Ma, Xiaoliang, Docent, et al.
(författare)
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DigiWays: A Digitalisation Testbed for Sustainable Traffic Management on Swedish Motorways
- 2023
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Ingår i: 2023 IEEE World Forum on Internet of Things: The Blue Planet: A Marriage of Sea and Space, WF-IoT 2023. - : Institute of Electrical and Electronics Engineers Inc..
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Konferensbidrag (refereegranskat)abstract
- Motorway traffic management system plays important roles for modern Intelligent Transport Systems (ITS). The Swedish motorways near large cities such as Stockholm are equipped with a large number of sensors for traffic monitoring and advanced traffic management purposes. This paper introduces our recent experiments of digitalising motorway traffic system using vehicle-to-everything (V2X) communication and other sensors deployed for measuring road traffic and road-side air pollutants. In addition to the deployment of V2X testbed, a Cyber-Physical system (CPS) framework is presented to integrate the deployed sensors with the computational models for estimation and prediction of traffic and road-side environmental conditions. A digital twin of motorway traffic flow is established using traffic flow models of different levels. The computation in experiment of the cyber space shows that traffic states can be estimated using V2X sensing data by applying the model-based estimation approach.
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| 34. |
- Nilsson, Bernt, et al.
(författare)
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Active sonar methods : Bistatic sonar, Synthetic aperture sonar and Space-time adaptive processing
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this report is to present work on threee processing methods with the potential to improve the performance of active sonar systems. Advantages of the processing methods are discussed and illustrated with simulation results.In addition, simulation packages are presented. Further work needed for a more detailed evaluation of the methods is indicated. We describe the development of software for an active sonar processor for a monostatic transceiver and a bistatic receiver including Doppler processing. Combined mono- and bistatic processing yields advantages in terms of covert operation of the bistatic receiver. Improved detection probability can be achieved and increased resilience to countermeasures. The objective has been to obtain a reference for comparison with new advanced sonar processors and a tool for accurate performance predictions.In addition, initial results from two promising methods are included.Synthetic Aperture Sonar (SAS) processing, commonly used in advanced mine hunting sonars, is here utilized at lower frequencies for surveillance applications.Space-Time Adaptive Processing (STAP), a signal processing technique used in radars to enhance the ability to detect targets that might otherwise be obscured by clutter or by jamming, can be applied in active sonar in order to reject reverberation. SAS has potential for improving the detection and classification performance of conventional sonars.Simulations made under idealised conditions indicate that good results can be obtained for relevant distances and frequencies. Fully adaptive STAP processing requires large amounts of training data, which is not always readily available in sonar applications. We present some alternative approaches that require less training data, with promising results.
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| 35. |
- Nordenvaad, Magnus Lundberg
(författare)
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A hierarchical approach to noise-adaptive estimation
- 2010
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Ingår i: 2010 IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM). - Piscataway, NJ : IEEE Communications Society. - 9781424493951 - 9781424493951 ; , s. 161-164
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Konferensbidrag (refereegranskat)abstract
- This paper presents a noise-adaptive estimator for the linear model. The strategy is based on a hierarchical approach where in each step, a decreasing number of unbiased estimates for the parameter of interest is produced. In this way, the complexity is greatly reduced compared to standard estimators, like the adaptive maximum likelihood (AML) estimator. Also, since the method combines solutions to sub-problems of smaller dimensionality, the required size of the noise training data set is also reduced. As a result, the derived scheme performs better than AML for small sample support. The results are verified by simulations and show that the derived scheme is a very appropriate choice for a large class of problems with high dimensionality.
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| 36. |
- Nordenvaad, Magnus Lundberg, et al.
(författare)
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Iterative reception for acoustic underwater MIMO communications
- 2006
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Ingår i: Oceans 2006. - : IEEE Communications Society. - 1424401143
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Konferensbidrag (refereegranskat)abstract
- This paper presents a soft input/soft output linear equalizer for Alamouti encoded MIMO signals. The derived structure allows for simultaneous equalization of MIMO channels and decoding of Alamouti coded signals. The equalizer/decoder is here used within the turbo equalization framework to exploit the complex and rich characteristics of the acoustic underwater channel. Such schemes can operate ate very low signal-to-noise ratio (SNR) levels enabling high transmission rates over long distances. We investigate the viability of the technique by using a simulation example and by studying its behavior for a real scenario, using data collected in the Baltic Sea
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| 37. |
- Pezeshki, Ali, et al.
(författare)
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Eigenvalue beamforming using a multirank MVDR beamformer and subspace selection
- 2008
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 56:5, s. 1954-1967
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Tidskriftsartikel (refereegranskat)abstract
- We derive eigenvalue beamformers to resolve an unknown signal of interest whose spatial signature lies in a known subspace, but whose orientation in that subspace is otherwise unknown. The unknown orientation may be fixed, in which case the signal covariance is rank-1, or it may be random, in which case the signal covariance is multirank. We present a systematic treatment of such signal models and explain their relevance for modeling signal uncertainties. We then present a multirank generalization of the MVDR beamformer. The idea is to minimize the power at the output of a matrix beamformer, while enforcing a data dependent distortionless constraint in the signal subspace, which we design based on the type of signal we wish to resolve. We show that the eigenvalues of an error covariance matrix are fundamental for resolving signals of interest. Signals with rank-1 covariances are resolved by the largest eigenvalues of the error covariance, while signals with multirank covariances are resolved by the smallest eigenvalues. Thus, the beamformers we design are eigenvalue beamformers, which extract signal information from eigenmodes of an error covariance. We address the tradeoff between angular resolution of eigenvalue beamformers and the fraction of the signal power they capture.
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| 38. |
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| 39. |
- Sangfelt, Erland, et al.
(författare)
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Underwater communication in the Baltic Sea using iterative equalization
- 2007
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Ingår i: 2nd International Conference & Exhibition on "Underwater Acoustic Measurements: Technologies & Results". ; , s. 617-624
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Konferensbidrag (refereegranskat)abstract
- We introduce a multi-channel soft input/soft output receiver for underwater communication that performs joint iterative channel estimation, linear equalization, and decoding. The transmitted symbols were encoded using a turbo coded bit-sequence. Our method exploits the gain present in the turbo code through a feed-back of soft information from the decoder to the channel estimator and to the equalizer. The use of several receiving hydrophones makes the method more robust to frequency selective or low-SNR channels, or can improve reception in channels with very large delay spreads. We give examples of such channels measured in the Baltic Sea at two different sea trials during 2005 and 2006. Properties like time variations of the channel impulse response or channel Doppler spread are given, as well as decoding examples using our method. It is shown that the multi-channel version of the receiver achieve error free reception of 4000 coded symbols per second up to 60 km through channels featuring very large delay spreads. The maximum transmitter source level used was 180 dB re 1μPa at 1m at the carrier frequency 12 kHz.
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| 40. |
- Skog, Isaac, et al.
(författare)
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Signals-of-Opportunity-Based Hydrophone Array Shape and Orientation Estimation
- 2024
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Ingår i: IEEE Journal of Oceanic Engineering. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0364-9059 .- 1558-1691.
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Tidskriftsartikel (refereegranskat)abstract
- A signal-of-opportunity-based method to automatically calibrate the orientations and shapes of a set of hydrophone arrays using the sound emitted from nearby ships is presented. The calibration problem is formulated as a simultaneous localization and mapping problem, where the locations, orientations, and shapes of the arrays are viewed as the unknown map states, and the position, velocity, etc., of the source as the unknown dynamic states. A sequential likelihood ratio test, together with a maximum a posteriori source location estimator, is used to automatically detect suitable sources and initialize the calibration procedure. The performance of the proposed method is evaluated using data from two 56-element hydrophone arrays. Results from two sea trials indicate that: 1) signal sources suitable for the calibration can be automatically detected; 2) the shapes and orientations of the arrays can be consistently estimated from the different data sets with shape variations of a few decimeters and orientation variations of less than 2(degrees) and 3) the uncertainty bounds calculated by the calibration method are in agreement with the true calibration uncertainties. Furthermore, the bearing time record from a sea trial with an autonomous mobile underwater signal source also shows the efficacy of the proposed calibration method. In the studied scenario, the root-mean-square bearing tracking error was reduced from 4(degrees) to 1(degrees) when using the calibrated array shapes compared to assuming the arrays' to be straight lines. Also, the beamforming gain increased by approximately 1 dB.
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| 41. |
- Svensson, Lennart, 1976, et al.
(författare)
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The Reference Prior for Complex Covariance Matrices With Efficient Implementation Strategies
- 2010
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Ingår i: IEEE Transactions on Signal Processing. - 1941-0476 .- 1053-587X. ; 58:1, s. 53-66
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Tidskriftsartikel (refereegranskat)abstract
- The paper derives the reference prior for complex covariance matrices. The reference prior is a noninformative prior that circumvents some of the weaknesses of common alternatives in multidimensional settings. As a consequence, inference based on this prior renders well-behaving solutions that in many cases outperform traditionally used approaches. The main obstacle is that inference based on this prior require integration over high-dimensional spaces which have no closed form solutions. A focus of the paper is therefore to discuss efficient implementation strategies based on Markov chain Monte Carlo methods. It is identified that certain structures can be treated analytically both for the case where the parameter of interest is the covariance matrix itself but also for cases in which the covariance matrix is a nuisance parameter that characterizes noise color. Evaluation in both these settings also verify the superior performance obtained by using the proposed prior as compared to traditional techniques to treat unknown covariance matrices.
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| 42. |
- Öberg, T., et al.
(författare)
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Underwater communication link with iterative equalization
- 2006
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Ingår i: OCEANS 2006. - : IEEE Communications Society. - 1424401143
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Konferensbidrag (refereegranskat)abstract
- In this paper an acoustic underwater communication link is presented. The channel has severe inter symbol interference, which is dealt with by an iterative linear equalizer and a Turbo code. Experiments has been performed in the Baltic Sea using a 4QAM signal with bandwidth 4 kHz at a center frequency of 12 kHz. The raw data rate is 8 kbit/s but after reduction for error correction coding the net bit rate is 2.88 kbit/s. With a source level of 180 dB re. 1mu/Pa @ 1m and a single hydrophone receiver, a reliable communication is shown up to a distance of 60 km. Very important for a successful decoding is the initial synchronization, which also is discussed.
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