Matti H. A. J. Herben

Antenna-pattern diversity versus space diversity for use at handhelds

This paper investigates diversity for dual-antenna systems operating in indoor environments. First, an approximated equation of the diversity gain is derived for different combining techniques. These theoretical results show that the two-term approximation, as generally used in the literature , is too rough an estimate. Consequently, a new six-term approximation is derived. Next, it is demonstrated by a comparison of theoretical and experimental diversity gain values that, due to mutual coupling between the two antennas in practice, the diversity gain will not approach 0 dB if the distance between the two antennas approaches zero. Finally, it is concluded from measurements at 900 MHz that antenna-pattern diversity is a better choice than space diversity for use at handhelds.

Frequency Selectivity of 60-GHz LOS and NLOS Indoor Radio Channels

This paper analyzes the frequency selectivity, which is caused by multipath effects, of indoor line-of-sight (LOS) and non-LOS (NLOS) channels based on channel measurements in the frequency band of 60 GHz. The coherence bandwidth is determined to characterize frequency selectivity figures of the channels employing the combination of omnidirectional, fan-beam and pencil-beam antennas at transmitter (TX) and receiver (RX) sides. The results quantitatively show how far directional configurations are more effective for combating multipath effect than the omnidirectional ones for LOS channels. The frequency selectivity of the fan-beam-to-fan-beam configuration is less sensitive to misaligned TX-RX beams than the fan-beam-to-pencil-beam one. In addition, when omnidirectional antennas are used at both TX and RX side, the frequency selectivity of a NLOS channel is less sensitive to the TX-RX height difference than that of a LOS channel. Moreover, coherence bandwidth is empirically related to root-mean-squared delay spread. Lastly, the results presented in this paper lead to some useful insights into antenna configurations and beamformer designs for a 60 GHz radio system

Modal transmission-line modeling of propagation of plane radiowaves through multilayer periodic building structures

The modal transmission-line (MTL) method is used to analyze the shielding effectiveness of buildings, which is an important parameter for the accurate planning of microcellular communication networks. For that, the buildings are modeled as multilayer lossy periodic structures. After a description of the extended MTL-theory, the newly developed MTL model is applied to brick walls, reinforced-concrete walls and concrete block walls. From a comparison of the MTL-results with previously published theoretical or experimental results it is concluded that the MTL method is very well suited, because it is accurate as well as computational time-efficient.

A shaped reflector antenna for 60-GHz indoor wireless LAN access points

This paper addresses the design of a 60-GHz shaped reflector antenna that has to illuminate a predefined circular area without substantial spatial variation. At the boundary of this coverage area, the field strength has to fall off rapidly. Such efficient and confined illumination may be required in wireless networks that have to cope with a stringent link budget and/or require low channel dispersion. Typical examples are the emerging broadband wireless networks for customer premises and residential applications that will operate in the millimeter-wave frequency region. The particular property of the considered reflector is its diverging surface instead of the commonly applied converging shape. It is shown that the spatial variation within the defined coverage area can be within 1 dB, provided that the antenna is perfectly constructed. It is also shown that practical imperfections such as axial and lateral feed displacement and mispointing of the feed on top of effects due to blocking by the feed can contribute to spatial field variations on the order of a few decibels.

A shaped reflector antenna for 60-GHz radio access points

A shaped reflector antenna for a prototype 60-GHz wireless LAN access point has been designed and constructed. Its performance has been verified through measurements of the antenna far-field radiation patterns in the compact antenna test range. Near-field patterns have been reconstructed from the measured far-field data by using the Hankel transform. The results show that the amplitude across the footprint area remains within 6 dB of uniformity.

Impact Analysis of Directional Antennas and Multiantenna Beamformers on Radio Transmission

The impact of directional antennas and multiantenna beamformers on radio transmission is formulated in terms of the gain of the Rician -factor, the reduction of the root-mean-squared delay spread, and the gain of the signal-to-noise ratio at the receiver for Rician fading channels in multipath environments. The analysis is based on a double-directional channel model. For the analytical formulation, the joint channel spectrum is assumed to be decomposable into separate spectra in time and angular domains. By way of illustration, closed-form expressions for the impact of hypothetical cosine-shaped antenna patternsand conventional beamformers are derived for channels with uniform angular spectra and an exponential decaying delay spectrum. The impact factors are explicitly related to the antenna beamwidth and the number of antenna elements. In addition, the effect of misalignment between the antenna main beam and the direct path is included in the analysis. The quantitative analysis given in this paper is important for radio system design, particularly for the design of antennas and multiantenna beamformer configurations.

The Influence of the Probe Connection on mm-Wave Antenna Measurements

Commonly used connection methods for measuring antennas in the mm-wave range, like connectors or probes, influence the intrinsic behavior of the antenna under test (AUT). It is shown that nearby structures supporting the antenna and probe or connector cause strong interference on the measured antenna pattern. A new connection setup is proposed eliminating the interfering signal. This is confirmed by a detailed simulation model and verified with experimental results. Furthermore, the probe radiates significantly due to the discontinuity from the transitions of the probe tip to the microstrip line. This radiation influences the signal-to-noise ratio, i.e., the dynamic range. Measures are proposed to reduce this interference, resulting in an improved signal-to-noise ratio by approximately 15 dB.

Analysis of Clustered Multipath Estimates in Physically Nonstationary Radio Channels

This paper presents the results of angle-delay measurements in physically nonstationary radio channels. The multidimensional estimation data are obtained using a recently developed 3-D high-resolution channel sounder. For a better analysis, a hierarchical whole clustering method is presented that organizes the multidimensional estimation data into clusters. Furthermore, estimation results are compared with results obtained from a 3-D deterministic propagation prediction tool. The clustering method proposed here was successfully applied to multi-dimensional estimation data. The results show that it is vital to cluster these data in order to be able to correctly interpret the measurement results. Compared to the measurements, a large number of multipath clusters are missing in the predictions. Furthermore, the multipath clusters obtained from the measurement data tend to have larger time and angular spreads than predicted.

Accurate identification of scatterers for improved microcell propagation modelling

This paper describes a procedure for combined time delay/angle of arrival (AOA) measurements, which are needed for the development of improved microcell propagation models. The procedure requires a spread-spectrum channel sounder equipped with a receive antenna which can be moved along a circle. Using angular superresolution algorithms such as UCA-MUSIC and UCA-ESPRIT, accurate azimuth/elevation AOA information of individual multipath contributions arriving within subsequent time delay intervals can be extracted from the measured data. Simulations indicate that good results can be obtained (RMS AOA errors smaller than one degree), except for the case of highly correlated ground-reflected signals at grazing incidence. Measurement results obtained in a simple multipath environment are presented.

Analysis of Scattering in Mobile Radio Channels Based on Clustered Multipath Estimates

This paper presents the results of angle and delay measurements in physically nonstationary radio channels obtained in an outdoor urban environment. The multidimensional estimation data are obtained using a recently developed 3-D high-resolution channel sounder. The estimation results are compared with results obtained from a 3-D deterministic propagation prediction tool. For a better analysis, a hierarchical clustering method is presented that can separate and group the multidimensional estimation data into clusters. Measurements performed at a fixed position as well as along a trajectory are used to characterize the angular dispersion in both azimuth and elevation. The angular dispersion in terms of the rms cluster angular spread in both elevation and azimuth of the different clusters is analyzed over space and time and related to its physical scattering sources. Compared to the measurements, a large number of multipath clusters are missing in the predictions. Furthermore, it is observed from the measurements that different objects cause different angular spread values in azimuth and elevation. The results can be very helpful for the identification, improvement and calibration of deterministic propagation prediction models.