11.
Berbyuk, Viktor, 1953
(författare)
Multibody dynamics and optimization problems of an above-knee prostheses
1996
Konferensbidrag (övrigt vetenskapligt/konstnärligt) abstract
New prosthetic materials and designs have resulted in many prostheses of lower limbs which are presently available for the amputee to use. As a result, it is becoming more difficult for the prosthetists and the physicians to choose which prosthesis is the best for the individual amputee. Presently, there is limited information about how the prosthesis performs dynamically in achieving optimal symmetrical gait for amputee. To provide insight into the interaction between dynamics and control in biotechnical systems and for optimizing the prosthesis's structure the energy-optimal control problem of the human locomotor system (HLS) wearing an above-knee prosthesis has been considered. The algorithm based on multibody dynamics approach and special conversion of the optimal control problem for nonlinear dynamic system model of the HLS into a standard nonlinear programming problem has been proposed. A number of the energy-optimal control problems of human locomotion with an artificial leg and the optimization problems of the constructive parameters of an above-knee prostheses under different boundary conditions and constraints have been solved.
12.
13.
Berg, Miguel
(författare)
Concept for hybrid random/dynamic radio resource management
1998
Ingår i: Proceedings of the 1998 9th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC '98. Part 3; Boston, MA, USA; 8 Sept. - 11 Sept. 1998. Vol. 1. - New York : IEEE. ; , s. 424-428, s. 424-428
Konferensbidrag (refereegranskat) abstract
Third generation mobile communication systems will allow many different services with varying demands on data rate and delay. For those systems, the fixed radio resource management (RRM) techniques used in today's low rate systems will not be appropriate to ensure efficient utilization of the radio spectrum. Dynamic RRM is necessary in order to cope with the large variations in data rate. We study the bunch concept which is a hybrid between random and dynamic RRM. Within a small synchronized cluster (bunch) we use dynamic radio resource allocation combined with SIR-based power control and between the bunches we use time/frequency hopping to average the interference. We propose an improved RRM algorithm and evaluate the performance of the bunch concept for a Manhattan scenario with mixed traffic. The performance is improved while the computational complexity is reduced compared to our previously published results for the bunch concept. We also show that the performance of a single bunch system is close to the theoretical upper bound.
14.
Berg, Miguel
(författare)
Maintaining high Capacity for Centralized DCA with Limited Measurements and Signaling
1999
Ingår i: Proceedings of the 1999 10th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC '99, Osaka, Japan, Sept 12 - 15, 1999. - New York : IEEE.
Konferensbidrag (refereegranskat) abstract
Centralized dynamic channel allocation strategies can, in theory, achieve very high capacity in terms of achievable load at a certain quality level. Unfortunately, these strategies have often been considered non-feasible in practice due to the massive amount of measurements and signaling typically required. In this paper we evaluate some methods to maintain high performance while drastically reducing the measurement and signaling requirements. Our DCA algorithm is based on measurements of the link gain matrix. We show that for a microcellular Manhattan environment, only the gains from the three strongest beacons have to be measured and signaled by each mobile in order to achieve almost the same capacity as an ideal system where all beacons can be measured.
15.
Viberg, Mats, et al.
(författare)
Source Localization in the Presence of Model Uncertainties
1992
Ingår i: Proceedings of the 2nd Workshop on Adaptive Algorithms in Communications.
Konferensbidrag (refereegranskat) abstract
In many signal processing applications high accuracy signal parameter estimation from sensor array data is a significant problem. Much of the recent work in array processing has focused on methods for high-resolution location estimation. Model based estimation techniques requre accurate knowledge of the so-called array manifold. In practise, the array response is often determined by measuring the array response when only one emitter is radiating and the signal parameters of which are allowed to vary in a known way. This paper addresses some of the practical issues that arise in generating the so-called array manifold from a finite collection of caibration vectors. For high-resolution signal parameter estimation techniques to be successful, the interpolated array manifold has to satisfy certain smoothness conditions. A paradigm for generating an array model from noise corrupted calibration vectors is developed. The key idea is to use a local parametric model of the sensor responses. The potential improvement using the suggested scheme rather than an ideal array model is demonstrated on real data collected from a full-scale hydro-acoustic array.
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17.
Ottersten, Björn, 1961-, et al.
(författare)
Performance Analysis of the Total Least Squares ESPRIT Algorithm
1991
Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 39:5, s. 1122-1135
Tidskriftsartikel (refereegranskat) abstract
The asymptotic distribution of the estimation error for the total least squares (TLS) version of ESPRIT is derived. The application to a uniform linear array is treated in some detail, and a generalization of ESPRIT to include row weighting is discussed. The Cramer-Rao bound (CRB) for the ESPRIT problem formulation is derived and found to coincide with the asymptotic variance of the TLS ESPRIT estimates through numerical examples. A comparison of this method to least squares ESPRIT, MUSIC, and Root-MUSIC as well as to the CRB for a calibrated array is also presented. TLS ESPRIT is found to be competitive with the other methods, and the performance is close to the calibrated CRB for many cases of practical interest. For highly correlated signals, however, the performance deviates significantly from the calibrated CRB. Simulations are included to illustrate the applicability of the theoretical results to a finite number of data.
18.
Berbyuk, Viktor, 1953, et al.
(författare)
Internal torques of human upper extremity during its optimal motion in vertical plane
1997
Ingår i: The Tenth Biomechanics Seminar. - 1100-2247. ; 10, s. 66-83
Konferensbidrag (refereegranskat) abstract
In the paper a number of optimal control problems for the motion of the human upper extremity (HUE), for different types of working tasks, are considered. The performance index used in these problems is the integral over the duration of the working task of the sum of the square of the controlling stimuli acting at the joints of the human arm. Under some conditions this performance index can be used for evaluation of the muscles' energy expenditure during human movements. The HUE is simulated by a plane multibody system of rigid masses. The system comprises the three elements with mass and rotatory inertia modelled the upper arm, the forearm and the hand. The controlled motions of the mechanical system are described in terms of joint angles and Cartesian coordinates of the shoulder joint, through the application of Lagrange's equations. The main aim of the study is an investigation of the interaction between the gravity forces and the internal torques acting at the joints during goal-directed extremal motions of the HUE. The analysis of the internal torques, energetic and viscoelastic characteristics of the shoulder, the elbow and the wrist joints for the exstremal controlled motions of the human arm under the external load acting on the hand has been done.
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