Showing papers by "Mats Viberg published in 2008"

Least-Squares based channel estimation for MIMO relays

Abstract: A least-squares based channel estimation algorithm is proposed for relay-assisted wireless multiple-input multiple-output (MIMO) channels. The method consists of a sequence of LS-problems with the purpose to arrive to a computationally efficient solution. The performance of the proposed algorithm is evaluated as a function of the input signal-to-noise ratio (SNR) for randomly generated Rayleigh flat fading channels. Finally, we study the effect of the channel estimation error on the performance of a MIMO zero-forcing receiver in order to verify the presented analysis.

On the Resolution Probability of MUSIC in Presence of Modeling Errors

Abstract: The problem of resolving closely spaced signal sources using an antenna array remains a difficult one, although several estimation methods are available in the literature. When the array correlation matrix is known, the resolution capability of subspace algorithms is infinitely high. However, in the presence of modeling errors the resolution deteriorates, even for a known correlation matrix. In this paper, we analyze the MUSIC method, by way of three different definitions of the resolution. Assuming Gaussian circular random modeling errors, we determine the corresponding expressions of the probability of source resolution versus the model mismatch. A first series of simulations validates the mathematical expression of the three resolution probabilities. A second series of simulations is used to select among them the tightest one to the empirical one. The results are useful, e.g., for determining the necessary antenna calibration accuracy to achieve a target performance.

Performance Prediction of Maximum-Likelihood Direction-of-Arrival Estimation in the Presence of Modeling Errors

Abstract: This paper provides new analytic expressions for the root mean-square (RMS) error and bias of the maximum-likelihood (ML) direction-of-arrival (DOA) estimator in the presence of steering vector modeling errors. Previous work has provided a first-order approximation of these performance measures, which is valid for small modeling errors. In order to take into account larger errors and provide tools for designing an experimental setup, a more accurate (but still easy-to-use) performance analysis is necessary. For such an investigation, the DOA estimation errors are expressed as a Hermitian form with a stochastic vector composed of the modeling errors. Closed-form expressions relating the bias and RMS errors to the statistical moments of the modeling error are then deduced from the statistics of this Hermitian form. Simulations are provided to illustrate the usefulness of the theoretical results.

Adaptive channel prediction based on polynomial phase signals

Abstract: Motivated by recently published physics based scattering SISO and MIMO channel models in mobile communications [1, 2], a new adaptive channel prediction based on non-stationary polynomial phase signals is proposed. To mitigate the influence of the time-varying amplitudes and to reduce the computation complexity, an iterative estimation of the polynomial phase parameters using the Non-linear instantaneous LS criterion is proposed. Given the polynomial phase parameters, the time-varying amplitudes are estimated using the Kalman filter. The performance of the new predictor is evaluated by Monte Carlo simulations in SISO scenarios with multiple scattering clusters. The new predictor outperforms the classical Linear Prediction and previous prediction methods based on sinusoidal modeling.

A new method based on dynamic programming for boundary detection in ultrasound image sequences

Abstract: Dynamic programming has previously been used when measuring Lumen Diameter (LD) and Intima-Media Thickness (IMT) in single frame ultrasound carotid artery images [1]. An extension to multiframe detection of that procedure is proposed in this paper. Our new method transforms a three dimensional problem into multiple two dimensional problems that can again be solved by dynamic programming. First, several “candidate boundaries” are detected in each image. Then, one boundary from each image in the sequence is selected in such a way that the sequence of boundaries is optimal among the considered possibilities. A model of the movements of the boundaries is used in the second step. Our proposed method shows promising performance on both synthetic and real ultrasound data.

Simulation of MIMO antenna systems in simulink and embedded Matlab

Abstract: Multi-Input Multi-Output (MIMO) has emerged as a hot topic in wireless communications during the last decade. This is due to possible dramatic increases in reliability and capacity as compared to single-antenna solutions. However, much of the existing theoretical results are based on very simplistic models of the antennas and transciever circuitry. Within the Strategic Research Center on Atenna Systems Charmant at Chalmers, we are developing a systems simulator for making more realistic studies of MIMO systems. Models of different complexity can be used for the different components. For the linear components, S-parameters are used as the interface. These can come from theoretical models, electromagnetic field simulations, or directly from measurements. For the non-linear components, simple memoryless models can be used, as existing in the RF Toolbox. However, wideband applications demand more elaborate models. We have implemented a so-called memory polynomial model, which has been found to match measurements of nonlinear wideband power amplifiers well. Since RF Toolbox cannot handle multi-port scattering matrices (yet), the MIMO part is here computed in a Matlab function, and then implemented as a MIMO transfer function. The paper describes an implementation of a transciever chain including mixers, filters, PA/LNA, matching network, MIMO antennas and channel models. The simulator can be used for a wide range of wireless communication applications.

Simulation of a wideband reconfigurable multi-antenna system with space-time coding

Abstract: Multiple-Input Multiple-Output (MIMO) systems will play a crucial role in the future of wireless systems, for example multiple antenna techniques can be a key to boost the performance of modern wireless systems. In order to study the performance and complexity of MIMO systems, a suitable simulation tool is essential. Simulation is important in system architecture exploration, algorithm optimization and bottleneck detection. Simulation is also a powerful tool when designing various components in an antenna system like electromagnetic solvers for radiation patterns and circuit simulation for amplifiers, but simulating an entire antenna system is not usual. In this paper the capabilities of MathWorks Simulink as a simulation platform for MIMO systems have been investigated and a typical MIMO-WCDMA link has been developed. Some of the blocks were used from the WCDMA library and others were developed accordingly. The Space-Time encoder and decoder for a general MIMO link were also developed. Furthermore, in order to be able to test different antenna types in a system, the antenna block is separated from the channel. Henceforth a double directional channel has been developed based on the SCM (spatial channel model) proposed by 3GPP (3rd Generation Partnership Project), which is an environmental channel independent from the antenna. The results of the simulation shows that Simulink is a capable platform for simulation of an entire communication link.

Modeling error sensitivity of the MUSIC algorithm conditioned on resolved sources

Abstract: When the correlation matrix is known, the resolution power of subspace algorithms is infinite. In the presence of modelling errors, even if the correlation matrix is known, sources can no longer be resolved with certainty. Focusing on the MUSIC algorithm [1], the purpose of this work is to provide closed form expression of bias and variance versus the model mismatch (these errors can be different for each source). Unlike previous work, these performance measures are derived conditioned on the success of a certain source resolution test. Among the resolution definitions proposed in [2], we investigate which one is more suitable for our purposes. Numerical results support the theoretical investigations. Our findings are of a great interest for the determination of the necessary antenna calibration accuracy to achieve specifications on the estimator performance.

Analysis of 3-D shape estimation using bistatic multi-channel radar systems

Abstract: We estimate the radius of a perfect electric conductor (PEC) half-sphere placed on a ground plane, given six bi-conical antennas that suffer from manufacturing errors. The results are complemented by an analytical model of the sensor system and the scatterer. The analytical model includes the front-end electronics in combination with the antenna radiation impedance and the radiation field function.