Showing papers by "Mats Bengtsson published in 2004"

Modeling of wide-band MIMO radio channels based on NLoS indoor measurements

Abstract: In this paper, we first verify a previously proposed Kronecker-structure-based narrow-band model for nonline-of-sight (NLoS) indoor multiple-input-multiple-output (MIMO) radio channels based on 5.2-GHz indoor MIMO channel measurements. It is observed that, for the narrow-band case, the measured channel coefficients are complex Gaussian distributed and, consequently, we focus on a statistical description using the first- and second-order moments of MIMO radio channels. It is shown that the MIMO channel covariance matrix can be well approximated by the Kronecker product of the covariance matrices, seen from the transmitter and receiver, respectively. A narrow-band model for NLoS indoor MIMO channels is thus verified by these results. As for the wide-band case, it is observed that the average power-delay profile of each element of the channel impulse response matrix fits the exponential decay curve and that the Kronecker structure of the second-order moments can be extended to each channel tap. A wide-band MIMO channel model is then proposed, combining a simple COST 259 single-input-single-output channel model and the Kronecker structure. Monte Carlo simulations are used to generate indoor MIMO channel realizations according to the models discussed. The results are compared with the measured data using the channel capacity and good agreement is found.

From single link MIMO to multi-user MIMO

Abstract: For any given single link strategy for transmission over a MIMO channel with channel knowledge at both transmitter and receiver, we propose a general approach to reduce the interference when the strategy is used in an interference limited system. This solution has several interesting interpretations. The structure of the solution is shown to include the global optimum, even though it may be difficult to determine all parameters. However, a suboptimal choice is presented that can be implemented in practical systems using only local information. A numerical example illustrates the performance when trying to minimize the summed mutual information.

Spatially Spread Sources in Antenna Array Processing

Abstract: The use of multiple antennas and transceivers at the access points and/or terminals of wireless communication networks can greatly improve the per-formance or reduce the cost of these systems. Antenna arrays combined with the appropriate signal processing allows an increased spectral efficiency. Also, the coverage of the systems may be improved by extending the range of com-munications or lowering the power requirements on the terminals. Spectral efficiency can be improved in a combination of different ways, some of these include, interference rejection [1, 2], decreasing frequency reuse [3], spatial multiplexing [4], spatial division multiple access [5], space-time coding [6]. How to best exploit multiple antennas in wireless systems depends on the ser-vice requirements and system specifications. This is an active area of research and much remains to be understood [3, 7]. However, so-called smart antenna systems are already in commercial use in, for example, the Personal Handy Phone (PHS) system [8] as well as in GSM [9]. The UMTS system includes space-time coding schemes and spatially directive transmission exploiting multiple transmitter at the access point to provide high speed and reliable downlink communication.

On The Error of Kronecker Structure Based MIMO Channel Model

Abstract: Herein, we investigate the mismatch of the Kronecker structure based MIMO channel model. Finding the minimum mismatch is trivial and the result is always 0. The maximization problem, on the other hand, is not convex in general. Therefore we combine semidefinite programming with a grid search, to find a lower bound of the maximum mismatch. Numerical examples show that the bound is tight even for moderate number of points in the grid. The resulting worst case model error, is much larger than the model error previously observed in measurement campaigns, which confirms that the channel correlation matrix can, indeed, be well approximated by the Kronecker product of the correlation matrices at the transmitter and receiver for the measured NLOS indoor scenarios.

Table based performance evaluation for HIPERLAN/2 systems - a multi-parameter design

Abstract: This paper studies how to estimate the packet error rate (PER) of a HIPERLAN/2 link without using detailed link-level simulations. This is useful mainly for speeding up system-level simulations. An extension to MIMO is also considered. Two different 2D lookup table methods are evaluated, that take both the empirical mean sub-carrier quality across the frequencies and the frequency variability into account. Numerical validations show that these new methods are able to estimate the average PER more accurately than using a traditional 1D mapping. It is shown that these PER estimation methods are critical when characterizing the performance of MIMO transmission schemes where the frequency properties of the effective channel may deviate significantly from the SISO case.