Showing papers by "Mats Viberg published in 2001"

Superimposed periodic pilots for blind channel estimation

Abstract: Multipath is a major impairment in a wireless communications environment. Blind channel estimation methods are of interest because they avoid training and thus make efficient use of the available bandwidth. In the past few years, we have seen an evolution from higher-order statistics-based, to cyclic second-order statistics based approaches for blind channel estimation. We propose here a simple, alternative scheme which employs only a first-order statistic. Pilot symbols are periodically added to the intended symbol stream prior to transmission. There is no loss of information rate in our approach, and neither is there any restriction on the FIR channel to be identified. We derive the variance expression of our linear channel estimate and compare with the Cramer-Rao Bound (CRB). Numerical examples indicate that the variance approaches the CRB at high SNR.

A robust frequency domain subspace algorithm for multi-component harmonic retrieval

Abstract: Multi-component harmonic retrieval finds applications in many fields, including radar, sonar and wireless communications. In previous years, several high-resolution subspace-based techniques have been proposed to overcome the spectral leakage problems inherent in the conventional periodogram. However, these methods require high SNR and/or white noise, and are highly computationally intensive in scenarios with a large number of spectral components. We propose a frequency domain subspace algorithm which overcomes these limitations. The method is computationally efficient in providing estimates of the frequencies within a user-selected sub-band. The estimates are exact in the noise-free case, and exhibit low sensitivity to out-of-band signals and colored noise.

A Radio Channel Model for Multielement Antenna Systems

Abstract: A realistic Multi-Input Multi-Output (MIMO) spatiotemporal radio channel model for simulation of MultiElement Antenna (MEA) systems is presented. The model is based on fundamental theory from ElectroMagnetic (EM) scattering where the properties of the transmit and receive antennas are included. Both the direction and amplitude of the electromagnetic field are included in the model. Furthermore, mutual coupling between the antenna elements is also accounted for since the typical MIMO system most likely will use closely spaced antenna elements. Surprisingly, it is found that mutual coupling actually decorrelates the received signals. Thus, mutual coupling may, contrary to common belief, sometimes increase the communication capacity.