Andreas Hutter

Analysis of MIMO capacity gains for indoor propagation channels with LOS component

We analyse typical indoor propagation scenarios with respect to the capacity gain made available through the use of multiple transmit and receive antennas. In particular, we investigate propagation channels with a strong line of sight component, as evident when the transmit array is in the same room as the receive array. It is found that the capacity gain for the pure LOS component depends highly on the array geometry and the receiver location, such that the capacity gain vanishes rapidly with receiver distance. We show that the existence of stochastic scattering components is beneficial to obtain the maximum capacity gain, thus reducing the dependence on the array geometry and the receiver location. This benefit exists even for a strong LOS component. Quantitative results are provided for wireless LAN systems operating at carrier frequencies around 5 GHz.

Alamouti-Based Space-Frequency Coding for OFDM

We investigate space-frequency block coding for OFDM systems with multiple transmit antennas, where coding is applied in the frequency domain (OFDM carriers) rather than in the time domain (OFDM symbols). In particular we consider Alamoutis code, which was shown to be the optimum block code for two transmit antennas and time domain coding. We show that the standard decoding algorithm results in significant performance degradation depending on the frequency-selective nature of the transmission channels, such that a low coherence bandwidth results in a huge degradation. The optimum decoding algorithm that alleviates this problem is the maximum-likelihood decoder for joint symbol detection. We present a performance analysis for the investigated space-frequency decoders in terms of the achievable BER results. Furthermore we compare space-time and space-frequency coding and discuss the respective advantages and drawbacks of the different decoding algorithms in terms of their complexity. It should be noted that for the space-time approach we introduce the so-called matched-filter receiver, which shows significantly lower complexity compared to the maximum-likelihood decoder known from literature. The HIPERMAN system serves as an example OFDM system for quantitative comparisons.

On the multiple input multiple output capacity of Rician channels

We consider a wireless system with multiple antennas at both the transmitter and the receiver and operating in a Rician propagation environment. For fixed bandwidth and total transmitted power, the Rician channel matrix can be seen as the sum of two contributions. The first contribution is related to the deterministic component of the channel, which is given by the line-of-sight (LOS) path only. The second contribution denotes the stochastic component of the channel given by the Rayleigh fading paths, in which case the corresponding elements in the channel matrix are modeled as random variables. We focus on the averaged Rician channel capacity expression and its behavior according to the contribution of the deterministic and stochastic part of the channel. We derive an upper bound on the averaged Rician channel capacity and we show that a limit of this capacity is given by the sum of the capacities corresponding to the LOS and Rayleigh components when they are considered separately. Simulations results are given to support our claims.

UWB Transmission and MIMO Antenna Systems for Nomadic Users and Mobile PANs

Personal Area Networks (PANs) are expected to play an important role in future mobile communications and information systems. A proliferation of low data rate sensor and control devices is envisioned. These devices must be able to communicate across various networks in order to provide seamless end-to-end service. At the physical and link level, several factors are critical in order to realize a nomadic PAN: co-existence with other systems, efficient use of increasingly scarce spectrum resources and capacity, robustness in the presence of interference, as well as, the availability of low cost individual user devices. In this paper, we examine a concept for nomadic PANs employing low cost, low data rate ultra wideband (UWB) communication links between personal devices and a handset, or mobile bridge, coupled with a multiple input multiple output (MIMO) antennas for communication from a mobile bridge to other networks. Key issues are identified and potential capacity and quality-of-service (QoS) enhancements are evaluated.

A wideband equivalent SPICE circuit for a monopole antenna and its usefulness for UWB applications

This paper presents a transmission line based electrical equivalent schematic of a ¿/4 monopole antenna for co-simulation with electrical circuits in simulators like ELDO and SPICE. The antenna model is derived from TDR (time domain) measurements and yields fast and accurate results for the antenna impedance from DC up to 3 times the 1st resonant frequency f0.