The use of multiple receive antennas as well as multiple transmit antennas has attracted worldwide attention to extend the performance of existing mobile communication systems. Therefore, it is of great importance to know the features of the real propagation channel. The real propagation channel is investigated by MIMO channel sounding, where high-resolution parameter estimation schemes are used to resolve the physical channel with respect to its spatial (and temporal) structure. However, due to narrow diffuse scatterers, the commonly used model of discrete wavefronts is no longer valid. We introduce a simple approach to model wavefronts with small angular spread. Additionally, we show that the ESPRIT (estimation of signal parameters by rotational invariance techniques) algorithm with a slight modification is applicable to estimate the direction of arrival and the angular spread jointly. The approach is based on the assumption of Gaussian distributed wavefronts.

In this article we introduce a novel multiple-input-multiple-output (MIMO) spatial filter (SF) which can be applied as a preprocessing scheme to uniform linear arrays in mobile communications, preserving the Vandermonde structure of the steering vectors while changing the amplitude and the phase gradient of the steering vector in a nonlinear fashion. The new scheme is therefore titled Vandermonde invariance transformation. The introduced degrees of freedom due to this preprocessing transformation can be used to beneficially influence the properties of the channel to achieve an enhanced performance of the subsequent signal processing algorithm.

We investigate the effects of both fading correlations and transmitter channel knowledge in multiple element antenna (MEA) communication systems. While, for independent and identically distributed fades between receive and transmit antennas, pioneering work showed that a huge increase in capacity is possible for MEA compared to a single antenna system, recent contributions warn that fading correlations destroy most of this advantage. While this is true for zero transmitter channel knowledge, we show however that long-term average channel state information enables the transmitter to efficiently use the fading correlations to its advantage and offers the potential to even increase capacity beyond the one possible for independent fading. A conceived transmit technique is presented that efficiently makes use of fading correlations, and also provides optimum choice of digital modulation schemes that carry the information.

Utilizing adaptive antenna arrays at the base stations of next generation mobile communication systems has been proposed as a promising approach to meet future requirements, e.g. spatio-temporal filtering techniques benefit from the detailed knowledge of the directional channel parameters. Unfortunately, in parameter estimation the computation of the signal subspace often turns out to be the most time-consuming part. However, the computational complexity of the subspace estimation can be significantly reduced by means of tracking. To this end, we propose a new technique which is merely based on the projector representation of the subspace. The presented results are based on the DSP implementation of two algorithms for tracking the azimuthal and elevation angles of impinging wavefronts in an alternating mobile communications system.

The pervasiveness of computers in everyday life coupled with recent rapid advances in computer technology have created both the need and the means for sophisticated human-computer interaction (HCI) technology. Despite all the progress in computer technology and robotic manipulation, the interfaces for controlling manipulators have changed very little in the last decade. Therefore human-computer interfaces for controlling robotic manipulators are of great interest. A flexible and useful robotic manipulator is one capable of movement in three translational degrees of freedom, and three rotational degrees of freedom. In addition to research labs, six degree of freedom robots can be found in construction areas or other environments unfavorable for human beings. This paper proposes an intuitive and convenient visually guided interface for controlling a robot with six degrees of freedom. Two orthogonal cameras are used to track the position and the orientation of the hand of the user. This allows the user to control the robotic arm in a natural way.