Mhaj Matti Herben

Channel characteristics and transmission performance for various channel configurations at 60 GHz

Extensive measurements are conducted in room environments at 60 GHz to analyze the channel characteristics for various channel configurations. Channel parameters retrieved from measurements are presented and analyzed based on generic channel models. Particularly, a simple single-cluster model is applied for the parameter retrieval and performance evaluation. By this model, power delay profiles are simply described by a-factor, a root-mean-squared delay spread, and a shape parameter. The considered channels are configured with the combination of omnidirectional, fan-beam, and pencil-beam antennas at transmitter and receiver sides. Both line-of-sight (LOS) and non-LOS (NLOS) channels are considered. Further, to evaluate the transmission performance, we analyze the link budget in the considered environments, then design and simulate an OFDM system with a data rate of 2 Gbps to compare the bit-error-rate (BER) performance by using the measured and modeled channels. Both coded and uncoded OFDM systems are simulated. It is observed that the BER performance agrees well for the measured and modeled channels. In addition, directive configurations can provide sufficient link margins and BER performance for high data rate communications. To increase the coverage and performance in the NLOS area, it is preferable to apply directive antennas.

A tree-scattering model for improved propagation prediction in urban microcells

This paper presents a model for the scattering of radiowaves from the canopy of a single tree. The canopy is modeled as a cylindrical volume containing randomly distributed and oriented cylinders, representing the branches, and thin disks, representing the leaves. A simple expression for the incoherent scattered field outside the canopy is obtained using Twerskys multiple scattering theory. This expression is shown to agree well with results of scattering measurements on a live tree typical of those found in urban environments. The scattering model can be readily incorporated in ray-based propagation prediction tools that assist the planning of microcellular radio networks. This involves the use of so-called tree-scattered rays, which interact at the tree centers. Path loss predictions generated with the aid of the new model are shown and compared with measured data to illustrate the considerable improvement in prediction accuracy that can be achieved in realistic urban microcellular scenarios by taking into account the scatter from trees.

Effect of internal reflections on the radiation properties and input impedance of integrated lens antennas-comparison between theory and measurements

This paper presents the effect of internal reflections on the beam pattern and input impedance of integrated lens antennas. A silicon lens was designed and manufactured, and measurements were conducted at a frequency of 100 (impedance) and 500 GHz (beam pattern). A frequency-dependence characterization of the beam pattern clearly showed the existence and impact of internal reflections. The measurements confirmed that most of the frequency variations of the beam pattern could be attributed to internal reflections, as predicted by the model. An on-wafer measurement strategy for determining the antenna impedance at millimeter-wave frequencies is presented. The validity of the model was also proven by an excellent match of the input impedance measurements and predictions. Not only the level, but also the oscillation on the impedance curve was predicted accurately. Initial space qualification was performed in the form of thermal cycling.

High-resolution angle-of-arrival measurement of the mobile radio channel

The accurate planning of microcellular mobile radio networks requires a thorough understanding of the mechanisms that govern radio wave propagation in urban environments. Combined measurements of time delays and angles-of-arrival (AoAs), both in azimuth and elevation, of individual multipath contributions are expected to he very helpful in the validation and improvement of existing ray-tracing propagation models. To this end, we have applied the uniform circular array (UCA)-MUSIC angular superresolution algorithm to complex impulse response measurement data obtained from a synthetic uniform circular array. Beamspace processing and forward/backward averaging were applied to cope with strongly correlated signals. The presented experimental results show that our approach is capable of identifying the dominant multipaths in actual mobile propagation environments.

Effect of internal reflections on the radiation properties and input admittance of integrated lens antennas

This paper begins with the modeling of the reflected waves within integrated lens antennas, which consist of a dielectric lens on which a planar antenna is mounted. It is demonstrated that if the relative dielectric constant of the lens is small (/spl epsi//sub r//spl les/4), the single- and double-reflected waves are sufficient to analyze the effect of the internal reflections. For small angles around boresight, these unwanted reflected fields mainly affect the cross-polar far-field pattern, while for large observation angles, both the co-polar and cross-polar patterns are significantly disturbed. It appears that by neglecting the internally reflected field contributions, the beam efficiency may be overestimated more than 10%. In this paper, two types of matching layers are analyzed in order to reduce these unwanted reflections. It is demonstrated that the radiation performances of the integrated lens antennas with optimum-thickness and quarter-wavelength matching layer are almost equal. Even for low dielectric-constant lenses, the beam efficiency can be increased by over 10%. Finally, it is demonstrated that the internal reflections may also have a strong effect on the antenna admittance, which can only be reduced partly by the use of a matching layer.

Millimeter-wave antenna measurement

A novel approach is presented to accurately measure the scattering parameters as well as the radiation pattern of planar antennas that operate in the millimeter-wave frequency band. To avoid interconnection problems, RF probes have been used to connect to the antenna. These RF probes are normally used for the characterisation of devices on a semiconductor wafer. Here, they are used to characterise antennas that can be realised in any planar manufacturing technology. A completely planar transition is designed to transform the coplanar waveguide transmission line that is required by the RF probe to a microstrip line. It is shown that this transition can be de-embedded from the measurements. Moreover, a measurement setup has been built for the measurement of the far-field radiation pattern of millimeter-wave antennas and antenna arrays. This setup allows to connect the antenna under test with an RF probe and can measure the radiation pattern in the whole upper hemisphere.

Characterization of radio wave propagation into buildings at 1800 MHz

The paper presents the results of signal strength measurements at 1800 MHz in four office buildings in The Hague, illuminated by an outdoor base station with an antenna above the rooftop. The objectives of these experiments are to study the behavior of the received signal strength at different floors of a building and to determine the main characteristics concerning cell coverage, namely, signal attenuation and variation within these buildings. It is shown that large fluctuations occur between average signal levels in line-of-sight (LOS) and non-LOS areas of multifloor buildings.

Indoor Channel Measurements and Analysis in the Frequency Bands 2 GHz and 60 GHz

This paper describes the wideband measurements conducted at the frequencies 58 GHz and 2.25 GHz in an indoor environment. Normalized received power (NRP) and root-mean-squared (RMS) delay spread are calculated and used to compare the characteristics of radio wave propagation in both line-of-sight and non-line-of-sight areas at the two frequencies. The results show that on top of the difference in free space, the NRP at 58 GHz is several dBs lower than at 2.25 GHz in average. This difference is also reflected in the fitted log-(virtual) distance NRP models. In the deep shadow region, the poor diffraction level at 58 GHz will reduce the power level, but meanwhile the reflected waves from walls have a strong contribution to the received signal. In addition, it is observed that the radio channel at 58 GHz shows much less time dispersion in terms of RMS delay spread. The results can be quite useful for the 60 GHz system design, which might be very different from the design of conventional systems which operate in the lower frequency bands

Impact of antenna pattern and reflective environment on 60 GHz indoor radio channel characteristics

Wideband channel measurements at the 60-GHz frequency band in a reflective environment with different antenna heights are presented. The log-distance model of the normalized received power (NRP) is used to fit the measured data for both line-of-sight (LOS) and nonline-of-sight (NLOS) cases. Also, the impact of the biconical antennas and the reflective environment on the channel properties is analyzed and explained. Results show that the most favorable NRP values are found in the case that the Tx and Rx antennas are at the same height. Also, in most cases, the scatter paths have more contributions on the total received power than the direct path. In addition, in the LOS case, the NRPs become less dependent on the Tx-Rx separation owing to the combined effect of the antenna and the reflective environment. In the NLOS region, the contribution level of the strongest path becomes less dominant with increasing virtual Tx-Rx separation. The analysis of these results can be instructive for the deployment of a 60-GHz system in a reflective environment.

High-Resolution Angle-of-Arrival Measurements on Physically-Nonstationary Mobile Radio Channels

A high-resolution measurement system for the characterization of the delay and angle-of-arrival properties of all significant multipath components on mobile radio channels is presented. The system uses complex impulse response data obtained from a novel 3-D tilted cross switched antenna array as input to an improved version of 3-D Unitary ESPRIT. Results from simulations and measurements show that the approach is capable of accurately characterizing the delay and angle-of-arrival characteristics of the dominant multipath components at moderate urban speeds along a trajectory in mobile propagation environments with high resolution in both azimuth and elevation.