Mille Millnert

An adaptive array for mobile communication systems

The use of adaptive antenna techniques to increase the channel capacity is discussed. Directional sensitivity is obtained by using an antenna array at the base station, possibly both in receiving and transmitting mode. A scheme for separating several signals at the same frequency is proposed. The method is based on high-resolution direction-finding followed by optimal combination of the antenna outputs. Comparison with a method based on reference signals is made. Computer simulations are carried out to test the applicability of the technique to scattering scenarios that typically arise in urban areas. The proposed scheme is found to have great potential in rejecting cochannel interference, albeit at the expense of high computational requirements. >

Ground Target Recognition Using Rectangle Estimation

We propose a ground target recognition method based on 3-D laser radar data. The method handles general 3-D scattered data. It is based on the fact that man-made objects of complex shape can be decomposed to a set of rectangles. The ground target recognition method consists of four steps; 3-D size and orientation estimation, target segmentation into parts of approximately rectangular shape, identification of segments that represent the targets functional/main parts, and target matching with CAD models. The core in this approach is rectangle estimation. The performance of the rectangle estimation method is evaluated statistically using Monte Carlo simulations. A case study on tank recognition is shown, where 3-D data from four fundamentally different types of laser radar systems are used. Although the approach is tested on rather few examples, we believe that the approach is promising

Identification of ARX models with markovian parameters

ABSTRACT Many different recursive identification methods for time-varying systems have been suggested in the literature. An assumption that the variations in the system parameters are slow is common for all the methods. When using the methods on systems with faster variations, one is forced to compromise between alertness to parameter variations on one hand and noise sensitivity on the other. The topic of this paper is to investigate if this compromise can be avoided for a special class of systems. The systems considered are such that their dynamic changes between some different typical modes. The philosophy behind the approach taken in the paper is to separate the observations into different sets corresponding to the different modes. The parameters of the different modes can then be estimated using the separated data sets. Technically, this parallel modelling is achieved by describing the system parameters as the realizations of a Markov chain. A parameter-identification algorithm for time-varying ARX mo...

Inverse glottal filtering using a parameterized input model

In this paper computational algorithms for inverse glottal filtering are studied. The objective of inverse glottal filtering is to estimate the driving source. A good model for the glottal pulse is useful for, e.g., speech synthesis, speech recognition and speaker diagnostics. One common approach is to use a parameterized model of the input signal, i.e., the glottal pulses. The algorithm presented enables simultaneous estimation of the parameters of the input signal and the parameters of the system transfer function, the vocal tract model. The presentation here is restricted to transfer functions of all-pole type, i.e., AR-models. The method can be extended to handle zeros in the transfer function. The computational burden would, however, increase significantly. The algorithm uses efficient numerical methods, as, for instance, QR-factorization through Householder transformations.

Coherent laser radar for vibrometry: robust design and adaptive signal processing

A coherent laser radar system based on semiconductor laser technology has been designed and built. The compact design and the absence of adjustments makes the system mechanically robust and easy to use. The present system has an output power of 50 mW and a line width of 280 kHz (HWHM). The laser radar system has been used in vibrometry measurements. For vibrometry of moving objects, adaptive signal processing is required in order to obtain the vibration signature. Especially for unresolved objects, interference between different vibrating parts will complicate the analysis. Model based estimation techniques are used to obtain the parameters which determine the dynamics of the reflecting object.

Terrain segmentation using laser radar range data.

A novel approach to segmentation of laser radar range images is presented. The approach is based on modeling horizontal and vertical scans of the terrain as piecewise-constant or piecewise-linear functions. The approach uses adaptive estimation based on Kalman filtering techniques. The performance of the segmentation algorithm is evaluated by application to laser range measurements. We also discuss how the output from the segmentation algorithm can be used for, e.g., object detection.

An approach to recursive identification of abruptly changing systems

A way to model systems with abruptly changing dynamics is suggested. The parameters of the system are described as realizations of a finite-state Markov chain. It is further discussed how to perform recursive parameter identification for this type of system. A crucial part in the identification algorithm is to estimate the present state of the Markov chain. The effects of some typical rules to do this estimation are examined. Also a procedure which reduces the need for a priori information is given.

Robust coherent laser radar design and signal processing for vibrometry

A CO2-ladar system is used for measurements. The signal from the system is a sinusoidal FM-modulated multi-component signal. To extract the modulating frequencies time-frequency representations, e.g., the Wigner-Ville distribution and the Choi-Williams distribution are used. The estimation method is applied both to simulated and real data. Estimation of the vibration frequencies is shown to be feasible even for low SNR, e.g., -4 db.

Three techniques for state order estimation of hidden Markov models

Three examples of techniques that can be used for state order estimation of hidden Markov models are given. The methods are also exemplified using real laser range data, and the computational burden of the three methods is discussed. Two techniques, maximum description length and maximum a posteriori estimate, are shown to be very similar under certain circumstances. The third technique, predictive least squares, is novel in this context.

A study of adaptive arrays for mobile communication systems

The application of adaptive antenna techniques to increase the channel capacity in mobile radio communication is discussed. Directional sensitivity is obtained by using an antenna array at the base station, possibly both in receiving and transmitting mode. A scheme for separating several signals at the same frequency is proposed. The method is based on high-resolution direction finding following by optimal combination of the antenna outputs. Comparisons to a method based on reference signals are made. Computer simulations are carried out to test the applicability of the technique to scattering scenarios that typically arise in urban areas. The proposed scheme is found to have great potential in rejecting cochannel interference, albeit at the expense of high computational requirements.<<ETX>>