1.
Stigwall, Johan, 1977, et al.
(författare)
Photonic GHz to THz tunable signal generation by chirped-pulse mixing
2006
Ingår i: 2006 European ISIS Workshop, Emerging Optical Broadband Technologies, Boppard am Rhein, Germany, May 29 - June 1, 2006.
Konferensbidrag (refereegranskat) abstract
Frequency-tunable generation of pulsed tones in the millimeter to sub-millimeter range was demonstrated by mixing of two chromatically dispersing femtosecond laser pulses split up in time by an adjustable differential group delay (DGD) and a polarizer. The signal frequency was set by adjusting the amount of DGD and the amount of dispersion, and was here tuned from below 1 GHz to 0.9 THz. Time-domain measurements were conducted using a sampling oscilloscope for the lower frequencies and an auto-correlator for the higher frequencies. Near 100% modulation depth was obtained, and the signal phase was very stable, being locked to the pulses from the femtosecond laser. The line-width of the mm-wave waveform was found to be transform-limited if the signal chirp induced by higher order dispersion was compensated for. Suggested applications for this system are for instance THz spectroscopy, characterization of high performance photo-diodes and real-time dispersion measurements.
2.
Stigwall, Johan, 1977, et al.
(författare)
Non-linear Signal Retrieval in Wide-Band Photonic Time-Stretch Systems Using the Gerchberg-Saxton Algorithm
2006
Ingår i: International Topical Meeting on Microwave Photonics, Grenoble, France, Oct. 3-6, 2006. - 1424402042 ; , s. 88-
Konferensbidrag (övrigt vetenskapligt/konstnärligt) abstract
The Gerchberg-Saxton algorithm, which is often used for phase retrieval in free space diffractive optics, is here applied to the problem of signal retrieval in dualoutput (phase-diverse) photonic time-stretch systems. Using wide band noise covering the first two fading frequencies as an input signal we numerically analyze the proposed algorithm for different numbers of iterations, measurement noise levels, mis-estimation of system parameters and optical modulation depths. We show that the algorithm can successfully compensate for non-linear distortion of the signal due to chromatic dispersion, that it is robust to noise and mis-estimated system parameters, and that it converges very rapidly (within ten iterations). For lower signal-to-noise ratios and/or smaller modulation depths it also provides a non-iterative method of retrieving the inputsignal.
3.
Ranjbar, Parivash, 1968-
(författare)
Vibrotactile identification of signal-processed sounds from environmental events presented by a portable vibrator : a laboratory study
2009
Annan publikation (övrigt vetenskapligt/konstnärligt) abstract
Objective: To evaluate different signal-processing algorithms for tactile identification of environmental sounds in a monitoring aid for the deafblind. Subjects: Two men and three women, sensorineurally deaf or profoundly hearing impaired with experience of vibratory experiments, age 22-36 years. Method: A closed set of 45 representative environmental sounds were processed using two transposing (TRHA, TR1/3) and three modulating algorithms (AM, AMFM, AMMC) and presented as tactile stimuli using a portable vibrator in three experiments. The algorithms TRHA, TR1/3, AMFM and AMMC had two alternatives (with and without adaption to vibratory thresholds). In Exp. 1, the sounds were preprocessed and directly fed to the vibrator. In Exp. 2 and 3, the sounds were presented in an acoustic test room, without or with background noise (SNR=+5 dB), and processed in real time. Results: In Exp. 1, Algorithm AMFM and AMFM(A) consistently had the lowest identification scores, and were thus excluded in Exp. 2 and 3. TRHA, AM, AMMC, and AMMC(A) showed comparable identification scores (30%-42%) and the addition of noise did not deteriorate the performance. Conclusion: Algorithm TRHA, AM, AMMC, and AMMC(A) showed good performance in all three experiments and were robust in noise; they can therefore be used in further testing in real environments.
4.
Liu, Yang, et al.
(författare)
A Study Towards Reliability- and Delay-Critical Wireless Communication for RoboCup Robotic Soccer Application
2007
Ingår i: 2007 International Conference on Wireless Communications, Networking and Mobile Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1424413117 - 9781424413119 - 1424413125 - 1424413125 - 1424413117 ; , s. 633-636
Konferensbidrag (refereegranskat) abstract
RoboCup is an international competition for a team of multiple fast-moving robots under a dynamic environment to autonomously play soccer game against another team. Due to the nature of the competition, the requirements and constraints for the wireless communication are extremely tight. The challenge is that wireless communication is involved in the control loop and therefore the reliability and propagation delay are vital factors which directly affect the team performance. Beside, various interferences with known and unknown frequency / transmission power usually exist at the competition site, which are hazardous environment to achieve reliable and low latency performance for wireless communication. This paper investigates the performance strengths and weaknesses of wireless communication means e.g. RF, IEEE 802.11a/b, IEEE 802.15.4, DECT, Linx, etc, which are commonly used nowadays in different RoboCup teams and propose improvements towards reliable and delay-critical wireless communication.
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6.
Selén, Yngve, et al.
(författare)
Optimal bayesian RAKE receiver for sparse channels
2005
Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1424401313 - 9781424401314 ; , s. 121-125
Konferensbidrag (refereegranskat) abstract
In this article we derive the optimal (soft) RAKE MRC (maximum ratio combiner) under a sparse channel model. In contrast to many previous approaches, we do not separate the problem of channel estimation and symbol detection. Instead we treat the problem of symbol detection given data and a training sequence together. We illustrate the performance of our approach by numerical examples.
7.
Bollen, Math, et al.
(författare)
Classification of Underlying Causes of Power Quality Disturbances: Deterministic versus Statistical Methods
2007
Ingår i: Eurasip Journal on Applied Signal Processing. - : Springer Science and Business Media LLC. - 1110-8657 .- 1687-0433 .- 1687-6172 .- 1687-6180. ; , s. 17 pages (Article ID 79747)-
Tidskriftsartikel (refereegranskat) abstract
This paper presents the two main types of classification methods for power quality disturbances based on underlying causes: deterministic classification, giving an expert system as an example, and statistical classification, with support vector machines as an example. An expert system is suitable when one has limited amount of data and sufficient power system expert knowledge, however its application requires a set of threshold values. Statistical methods are suitable when large amount of data is available for training. Two important issues to guarantee the effectiveness of a classifier, data segmentation and featureextraction, are discussed. Segmentation of a sequence of data recording is pre-processing to partition the datainto segments each representing a duration containing either an event or transition between two events. Extraction of features is applied to each segment individually. Some useful features and their effectiveness are then discussed. Some experimental results are included for demonstrating theeffectiveness of both systems. Finally, conclusions are given together with the discussion of some future research directions.
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