1.
Beckman, Claes, 1962-
(författare)
Plausibility of assuming ideal arrays for direction of arrival estimation
1996
Ingår i: IEEE Antennas and Propagation Society International Symposium. 1996 Digest. ; , s. 1364-1367 vol.2
Konferensbidrag (refereegranskat) abstract
In order to fulfil the increasing demands on capacity and coverage of mobile communication systems smart or intelligent antennas have been suggested. These antennas increase the spectral efficiency of a wireless system by using arrays of antenna elements to shape RF signals in particular directions. Generally, smart antennas can be divided into two approaches: switched multi-beam and adaptive. Adaptive antennas utilize sophisticated signal processing algorithms to continuously distinguish between the desired signal, multipath and interfering signal as well as to calculate their direction of arrival (DOA). This makes it possible to smoothly track users with main lobes and interferers with nulls and thereby constantly maximizing the SINR (signal-to-interference and noise ratio). The DOA is one of the most important parameter for an adaptive antenna system to estimate. It is also the main subject of this paper. We establish whether or not it is plausible to assume the array to be ideal (which is often assumed in array signal processing theory) when the received signals are actually collected with a physical array consisting of standard folded dipoles. In doing so we first measured the element patterns (or steering vectors) of a twelve element antenna array. The results were then used in array signal processing simulations. The performance of two DOA estimation algorithms, MUSIC and ESPRIT, are studied and compared.
2.
Bengtsson, Mats, 1967-, et al.
(författare)
Signal Waveform Estimation from Array Data in Angular Spread Environment
1996
Ingår i: 30:th Asilomar Conference on Signals, Systems & Computers. - : IEEE. ; , s. 355-359
Konferensbidrag (refereegranskat) abstract
We analyze different direction based signal copy algorithms for a model of angular spread caused by local scattering around each signal source. Optimal algorithms, in terms of signal to interference and noise ratio, are derived for both rapidly and slowly time varying angular spread and a low complexity an-hoc algorithm is suggested. Simulations show that these algorithms outperform traditional signal copy algorithms in terms of signalto interference and noise ratio as well as outage probability.
3.
Viberg, Mats, 1961, et al.
(författare)
Maximum Likelihood Array Processing in Spatially Correlated Noise Fields Using Parameterized Signals
1997
Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1941-0476 .- 1053-587X. ; 45, s. 996-1004
Tidskriftsartikel (refereegranskat) abstract
This paper deals with the problem of estimating signal parameters using an array of sensors. This problem is of interest in a variety of applications, such as radar and sonar source localization. A vast number of estimation techniques have been proposed in the literature during the past two decades. Most of these can deliver consistent estimates only if the covariance matrix of the background noise is known. In many applications, the aforementioned assumption is unrealistic. Recently, a number of contributions have addressed the problem of signal parameter estimation in unknown noise environments based on various assumptions on the noise. Herein, a different approach is taken. We assume instead that the signals are partially known. The received signals are modeled as linear combinations of certain known basis functions. The exact maximum likelihood (ML) estimator for the problem at hand is derived, as well as a computationally more attractive approximation. The Cramer Rao lower bound (CRB) on the estimation error variance is also derived and found to coincide with the CRB, assuming an arbitrary deterministic model and known noise covariance.
4.
Lindeberg, Tony, 1964-, et al.
(författare)
Scale-space with causal time direction
1996
Konferensbidrag (refereegranskat) abstract
This article presents a theory for multi-scale representation of temporal data. Assuming that a real-time vision system should represent the incoming data at different time scales, an additional causality constraint arises compared to traditional scale-space theory—we can only use what has occurred in the past for computing representations at coarser time scales. Based on a previously developed scale-space theory in terms of noncreation of local maxima with increasing scale, a complete classification is given of the scale-space kernels that satisfy this property of non-creation of structure and respect the time direction as causal. It is shown that the cases of continuous and discrete time are inherently different.
5.
Gustavsson, Jan-Olof, et al.
(författare)
Simultaneous Channel and Symbol Maximum Likelihood Estimation in Laplacian Noise
1998
Ingår i: [Host publication title missing]. - Beijing : IEEE, Piscataway, NJ, USA. - 0780343255 ; , s. 81-84
Konferensbidrag (refereegranskat) abstract
This paper treats channel estimation and signal detection in Laplacian noise. The received signal is assumed to be a transmitted signal which has been corrupted by an unknown channel, modeled as a FIR filter, the output being further disturbed by additive independent Laplacian noise. The transmitted signal is assumed to depend on an unknown parameter belonging to a known finite set. The simultaneous maximum likelihood (ML) estimator of the unknown parameter, as well as of the FIR filter coefficients, is derived. The ML estimate of the channel can be obtained by using a linear programming approach and the decision about the parameter is based on the output from a set of generalized matched filters. Simulation results are included in order to illustrate the performance of the proposed receivers.
6.
Lindmark, B., et al.
(författare)
Dual-polarized array for signal-processing applications in wireless communications
1998
Ingår i: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 46:6, s. 758-763
Tidskriftsartikel (refereegranskat) abstract
A novel dual-polarized antenna array designed for a spatial division multiple access (SDMA) system working in the 1850-1990-MHz band is designed and built. The antenna is designed to have similar element patterns, and measurements of S-parameters and radiation patterns are presented. The array signal processing performance of the array using all elements and with no compensation for mutual coupling or differences in element patterns is studied through direction-of-arrival (DOA) estimation using total least squares estimation of signal parameters via rotational invariance techniques (TLS-ESPRIT). The results show that the accuracy of the DOA estimates is quite acceptable for wireless communication applications.
7.
Jansson, Magnus, et al.
(författare)
Robust Weighted Subspace Fitting in the Presence of Array Model Errors
1998
Ingår i: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. ; , s. 1961-1964
Konferensbidrag (refereegranskat) abstract
Model error sensitivity is an issue common to all high resolution direction of arrival estimators. Much attention has been directed to the design of algorithms for minimum variance estimation taking only finite sample errors into account. Approaches to reduce the sensitivity due to array calibration errors have also appeared in the literature. Herein, a weighted subspace fitting method for a wide class of array perturbation models is derived. This method provides minimum variance estimates under the assumption that the prior distribution of the perturbation model is known. Interestingly enough, the method reduces to the WSF (MODE) estimator if no model errors are present. On the other hand, when model errors dominate, the proposed method turns out to be equivalent to the “model-errors-only subspace fitting method”. Unlike previous techniques for model errors, the estimator can be implemented using a two-step procedure if the nominal array is uniform and linear, and it is also consistent even if the signals are fully correlated.
8.
Hansson, Maria
(författare)
On Signal Dependent Basis Functions, Estimation of Event Related Potentials and Multiple Window Spectrum Analysis
1996
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The three parts of this thesis are different examples of utilization of signal dependent basis functions in the estimation procedure. The first part surveys a number of parametric methods applied to estimation of single ERP (P300). The basis functions of the sERP are the damped sinusoids where the frequency and damping factor are estimated from the signal. The algorithms for white noise disturbance are known, and they are here also developed for coloured noise disturbance. Evaluations are made for simulated sERP conditions, i.e., short data sequences with low-frequency content and low signal-to-noise ratio. The algorithms are also applied to real data measurements. In the second part, a new system for automatic tracking of the depth of anaesthesia is proposed. The amplitude and latency of the Nb-trough are used as tracking parameters. Signal dependent basis functions are obtained by filtering a long average in a bandpass-filterbank. The basis functions are adapted to a shorter average, and the waveform of the AEP is estimated. The system detects changes in the state of consciousness with a maximum delay of 52 s. A multiple window method where the windows are matched to a peaked power density spectrum is proposed in the third part. The advantage of the method is that model assumptions of the measured spectrum are unnecessary. The windows are derived as Karhunen-Loeve basis functions of a known peaked power density spectrum. With a penalty function, the optimization procedure can be constrained with resulting control of sidelobes. Suppression of sidelobes outside the predetermined resolution bandwidth will prevent leakage from frequencies outside the mainlobe width.
9.
10.
Edfors, Ove, et al.
(författare)
OFDM channel estimation by singular value decomposition
1996
Ingår i: Mobile technology for the human race. - Piscataway, NJ : IEEE Communications Society. - 0780331575 ; , s. 923-927
Konferensbidrag (refereegranskat) abstract
A new approach to low-complexity channel estimation in orthogonal-frequency division multiplexing (OFDM) systems is proposed. A low-rank approximation is applied to a linear minimum mean-squared error (LMMSE) estimator that uses the frequency correlation of the channel. By using the singular-value decomposition (SVD) an optimal low-rank estimator is derived, where performance is essentially preserved - even for low computational complexities. A fixed estimator, with nominal values for channel correlation and signal-to-noise ratio (SNR), is analysed. Analytical mean-squared error (MSE) and symbol-error rates (SER) are presented for a 16-QAM OFDM system.
