| 1. |
- Backén, Staffan, et al.
(author)
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A novel software defined research receiver architecture
- 2009
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In: Proceedings of the 13th IAIN World Congress. - : Nordic Institute of Navigation.
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Conference paper (peer-reviewed)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.
(author)
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Post-processing dynamic GNSS antenna array calibration and deterministic beamforming
- 2008
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In: Proceedings of the 21th International Technical Meeting of the Satellite Division of the Institute of Navigation. ; , s. 1311-1319
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Conference paper (peer-reviewed)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. |
- Carlson, Johan, et al.
(author)
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Measurement of methane content in upgraded biogas using pulse-echo ultrasound
- 2008
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In: Proceedings of the International Congress on Ultrasonics.
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Conference paper (peer-reviewed)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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| 4. |
- Hostettler, Roland, et al.
(author)
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Surface mounted vehicle property sensing for cooperative vehicle infrastructure systems
- 2009
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In: 16th World Congress and Exhibition on Intelligent Transport Systems 2009. - Red Hook : Curran Associates, Inc.. - 9781617385896
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Conference paper (peer-reviewed)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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| 5. |
- Johansson, Jonny, et al.
(author)
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Project: EISCAT 3D
- 2007
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Other publication (pop. science, debate, etc.)
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| 6. |
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| 7. |
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| 8. |
- Ling, Jun, et al.
(author)
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Enhanced channel estimation and efficient symbol detection in MIMO underwater acoustic communications
- 2009
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In: Conference Record of the Forty-Third Asilomar Conference on Signals, Systems and Computers. - : IEEE Communications Society. - 9781424458257 ; , s. 600-604
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Conference paper (peer-reviewed)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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| 9. |
- Nilsson, Bernt, et al.
(author)
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Active sonar methods : Bistatic sonar, Synthetic aperture sonar and Space-time adaptive processing
- 2008
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Reports (other academic/artistic)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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| 10. |
- Nordenvaad, Magnus Lundberg, et al.
(author)
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Iterative reception for acoustic underwater MIMO communications
- 2006
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In: Oceans 2006. - : IEEE Communications Society. - 1424401143
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Conference paper (peer-reviewed)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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| 11. |
- Pezeshki, Ali, et al.
(author)
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Eigenvalue beamforming using a multirank MVDR beamformer and subspace selection
- 2008
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In: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 56:5, s. 1954-1967
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Journal article (peer-reviewed)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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| 12. |
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| 13. |
- Sangfelt, Erland, et al.
(author)
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Underwater communication in the Baltic Sea using iterative equalization
- 2007
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In: 2nd International Conference & Exhibition on "Underwater Acoustic Measurements: Technologies & Results". ; , s. 617-624
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Conference paper (peer-reviewed)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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| 14. |
- Öberg, T., et al.
(author)
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Underwater communication link with iterative equalization
- 2006
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In: OCEANS 2006. - : IEEE Communications Society. - 1424401143
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Conference paper (peer-reviewed)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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