|Session:||Session 3A08P - Channel Characterisation for Urban and Indoor Environments (08g1)|
|Date:||Wednesday, November 08, 2006|
|Time:||08:30 - 12:20|
Verification of 3D Ray Tracing with Measurements in Urban Macrocellular Environments
Fügen, T.1; Porebska, M.2; Maurer, J.2; Knörzer, S.2; Wiesbeck, W.2
1Institut für Höchstfrequenztechnik und Elektronik, Universität Karlsruhe (TH), GERMANY;
2Universität Karlsruhe (TH), GERMANY
Successful design of future wireless communications systems requires a detailed knowledge of the radio propagation channel. 3D ray tracing has meanwhile advanced to a performance that it can provide channel information with high accuracy. This paper demonstrates the capability of 3D ray tracing for defining parameter sets of future wireless communications systems. Moreover it shows that the proposed model can be used in order extract channel parameters for the specification of MIMO channel models. In the first part of the paper the 3D ray tracing model is described. Then comparisons with wide-band non-directional and directional measurements at 2 GHz and 5.2 GHz respectively are presented showing a good agreement.
The 3D ray tracing model consists of a realistic model of the propagation environment and a model to calculate the multi-path wave propagation between the transmitter and the receiver. As environment a digital model of a part of the city of Karlsruhe, Germany, is used. It includes buildings, trees and the street floor. The wave propagation model is based on ray optics. It distinguishes between different multipath components. Each path is represented by a ray, which may consecutively experience several different propagation phenomena, like combinations of multiple reflection, multiple diffraction and scattering. Fig. 1 shows the result of the ray tracing procedure for a single snapshot calculated in the digital Karlsruhe scenario. The receiver is placed on top of an exposed building and the transmitter is positioned at a road crossing 1.7m above ground. It is clearly seen that the wave propagation scenario is very complex and gives rise to numerous mult-path components.
In order to verify the model, it is compared to wide-band non-directional and directional propagation measurements. The MEDAV RUSK ATM vector channel sounder is used as measurement platform. The urban measurements are performed in the city of Karlsruhe, Germany. Two different receiver positions are chosen on top of an approx. 38.5 m high building. The transmitter is placed in a vehicle (van) and is moved along 5 different measurement routes. Characteristic narrow-band and wide-band channel parameters are considered for the non-directional comparison between the simulated and measured channel. The narrow-band comparison includes not only the long-term behavior of the channel but also the statistical properties of the short-term fading component. Fig. 2 shows the measured and simulated receive power for one of the measurement routes. It will be shown in the final paper, that the deviation of the simulated receive power of all other measurement routes is in the same order of magnitude. The time-variance of the channel is compared by the measured and simulated Doppler spectrum and its characteristic properties (mean Doppler shift, mean Doppler spread). The comparison of the wide-band channel behavior is based on the power delay profile, and the resulting delay spread. Finally the spatial behavior of the measured and
simulated channel is compared by the angular power spectrum and its characteristic properties (angular spread, mean angle).
Measurements and Channel Modeling for Short Range Indoor UHF Applications
Mayer, L. W.; Wrulich, M.; Scholtz, A. L.; Rupp, M.
Vienna University of Technology, AUSTRIA
The recent emergence of short range applications, e.g. RFID, requires careful investigation of wave propagation and adequate description of the radio channel. In this contribution, we present indoor channel measurements that expose the transition between the near and far field as well as the effects of fading. Furthermore, we develop a statistical single bounce channel model that is parameterized by the characteristics of the scenario and we verify the results by measurement data.
Adaptive Channel Characterization for Wireless Sensor Network Performance
Moïse, N.1; Babar, S.1; Gilles Y, D.2
1National Research Council, CANADA;
2International Institute of Telecommunications, Montreal, CANADA
This paper provides a theoretical yet accurate and flexible proposal of propagation modeling for wireless sensor networks. The proposed modeling approach can be used for free-space and multipath environments and provides means to handle radio irregularities in radio range caused by path losses and heterogeneous communication ranges due to various reasons like hardware calibration and energy depletion over time. Where most of the propagation models are either overly simple and generic or accurate and hardware specific, this model tries to bridge the gap between these two approaches. A basic simulator of a hybrid channel model has been built, both for free space and multipath environments. This model has been imported into the WSN (Wireless Sensor Network) simulator with various simulation setups and topologies to study the effects of channel modeling approach on different layers of wireless sensor networks.
Figure 2 represents a comparison of packet reception rate versus distance in free space, with an empirical  study using Crossbow sensor kits (Mica2 and Mica2dot). Figure 3 shows the effects of packet size on roundtrip time and packet drop rate for a multihop routing based WSN application. In this particular case, the simulation results are obtained using the conditions of mutipath environment illustred in figure 1.
This paper sets out a proposal for an adaptive radio propagation approach that can be used for heterogeneous wireless sensor networks in multipath environment. The effects of various radio wave propagation parameters on packet delivery performance were studied. More simulation and empirical results, comparisons and details will be provided in full paper as well as in the conference.
 A. Anastasi, et al., "Understanding the Real Behavior of Mote and 802.11 Ad Hoc Networks: An Experimental Approach", Pervasive and Mobile Computing Journal, Vol 1, no. 2, June 2005.
Simulation and Measurement of the Satellite to Indoor Propagation Channel in S-Band
Hoppe, R.1; Heyn, T.2; Widmer, H.3
1AWE Communications, Boeblingen, GERMANY;
2Fraunhofer Institute IIS, Erlangen, GERMANY;
The satellite to indoor propagation channel in L and S bands is becoming of significant importance as future satellite mobile communication, broadcast and navigation systems (as e.g. S-DMB and Galileo) are aiming at optimum performance in all kind of environments, i.e. even in indoor scenarios. Furthermore, the indoor scenarios are of special relevance for the attractiveness of new MSS services in order to provide ubiquitous coverage over all environments.
The satellite to indoor propagation channel depends strongly on the layout and the material properties, i.e. the construction materials used for walls, windows, and ceilings of the building where the receiver is located. Therefore it is important to first categorise the buildings into relevant types and to define typical material properties for each of the categories defined. A possible classification could be the distinction of residential houses with 1-2 storeys, multi-storey residential buildings (e.g. apartment blocks), office buildings, and commercial buildings as factories, stations and airports. Other important parameters influencing the satellite to indoor propagation are given by the satellite elevation angle and the orientation of the building towards the satellite. Besides the varying attenuation of the direct satellite signal depending on the penetration loss, multipath contributions are introduced by the building walls (e.g. reflection on the floor) leading to Rice or Rayleigh fading distributions depending on the location of the receiver inside the building.
Due to the high amount of parameters influencing the satellite to indoor propagation channel, wave propagation models are mandatory for analysing the various effects in detail, as this can not be achieved by measurement campaigns only. For the accurate simulation of the satellite to indoor propagation channel a ray-optical model for the coverage prediction in terrestrial networks (included in the radio planning tool of AWE Communications) has been upgraded to consider satellite transmitters (in the framework of the ESA funded S-DMB Phase A study). This deterministic model is based on 3D vector data of buildings and considers the different propagation phenomena as direct path, reflection, diffraction and penetration by using the principles of geometrical optics. Accordingly, the ray-optical model allows a site-specific prediction of the satellite to indoor radio channel for each point inside the corresponding building. Numerous simulations of the satellite to indoor channel for various buildings have been performed.
In the framework of the EU FP6 project MAESTRO, the Fraunhofer Institute IIS (in Erlangen) has carried out several measurement campaigns of the satellite to indoor channel for different types of buildings. These measurements show different zones of signal penetration depending on the location inside the building with respect to the satellite (see Figure). The measurements have been used to compare and verify the ray-optical model implemented in the radio planning tool.
The Influence of Building Material Humidity on Wedge Diffraction
Valtr, P.; Kucera, J.; Bartik, H.; Pechac, P.
Czech Technical University in Prague, CZECH REPUBLIC
The aim of the paper is to show the influence of humidity contained in real building materials on diffraction part of the field in the vicinity of a wedge-shaped obstacle. Field measurement around both dry and wet wedge formed by real building material was performed in the frequency range of 4 - 40 GHz to get an idea what the influence of humidity contained in building material is upon the field around a building obstacle. The measured results are compared with theoretical prediction by Uniform Theory of Diffraction (UTD).
The experiments of field measurement around a wedge both in anechoic chamber  and around a real building  show a good agreement between UTD prediction and measurement. Rather than to compare measured results with UTD prediction we focused here on the electrical properties of the building material. There have been numerous papers published on electrical parameters of building materials but relatively small amount of work has been done concerning the influence of water content within building materials on propagation prediction.
As an illustration, Fig. 1 shows angular dependency of received field at frequency of 40 GHz for several types of wedges and for vertical polarization. The depicted dependencies represent perfectly conducting wedge, dry building material and wet building material. The paper presents the measurement results for the whole frequency bands and draws some conclusions regarding the influence of the material water content on the diffraction.
Fig. 1. Field amplitude around wedge-shaped obstacle
The Shower Curtain Effect in Time-Reversal Wireless Communications
Kyritsi, P.1; Papanicolaou, G.2
1Aalborg University, DENMARK;
2Stanford University, UNITED STATES
Time reversal (TR) is a scheme that has its origin in wideband transmission in underwater acoustics and ultrasound: in TR, the signal to be transmitted is filtered through a filter that is the time reversed and phase conjugated channel impulse response (CIR). The resulting signal focuses tightly on the intended receiver in both space and time. Due to these properties, TR has recently appeared as a promising technique for secure, wideband, wireless communications. Specifically temporal focusing is important for systems where delay spread is a fundamental limitation.
TR filtering is commonly applied in Multiple Input- Single Output (MISO) situations, i.e. where there are M transmit antennas and one receive antenna. Let gm(t)=A hm*(-t) denote the TR filter employed at the mth transmitter antenna, where hm(t) is the CIR from that antenna element to the intended receiver and * is the complex conjugate operator. A is a scaling factor so that the TR filters introduce unity gain. The equivalent C heq(t) is
heq(t) = A hm*(-t) X hm(t) ,
where X denotes the convolution operation.
In general, the delay spread (ds) is given as the second moment of the average power delay profile (pdp). We can similarly define the ds of the equivalent CIR as the second central moment of the equivalent pdp.  investigated the efficiency of TR at reducing the perceived ds of the channel, based on actual channel measurements. It showed that the efficiency of TR depends on the scattering situation around the acting transmitters and receivers. Specifically two situations were defined:
a. Cluttered to clear: the intended receiver is in a less scattering environment than the acting transmitter array,
b. Clear to cluttered: the intended receiver is in the clutter.
The measurements showed that the advantage of applying MISO TR increases as the separation between the two ends of the communication link increases, when the intended receiver is in the clear and the acting transmitters are in the higher clutter situation. The opposite occurs when the receiver is in the cluttered situation and the acting transmitters are in the clear. This trend can be explained in terms of the shower-curtain effect. Indeed  has mathematically analyzed this effect in the regime of turbulent propagation.  has investigated the influence of the shower curtain effect on the spatial focusing properties of TR.
In this paper we reproduce the experimentally observed temporal focusing results using simulations of the wireless channel. Specifically we use the ring of scatterers modeling approach. We investigate the effects of bandwidth, number of transmit antennas, and transmit antenna spacing on the efficiency of TR as a means to reduce the perceived ds of the channel.
1. P. Kyritsi, G. Papanicolaou, P. Eggers, and A. Oprea, "MISO Time Reversal and Delay-Spread Compression for FWA Channels at 5 GHz", in Antennas and Wireless Prop. Letters,Vol. 3, No 6, 2004, pp.96-99.
2. A. Fannjiang, "Information Transfer in Disordered Media by Broadband Time Reversal: Stability, Resolution and Capacity," e-print: arxiv.org/abs/physics/0509158
3. A. Ishimaru, S. Jaruwatanadilok, and Y. Kuga, "Time reversal in random media and super resolution with shower curtain effects and backscattering enhancement," in Proc. URSI General Assembly Meeting 2005.
Percolation-Based Approaches for Ray-Optical Propagation in Inhomogeneous Random Distributions of Discrete Scatterers
Martini, A.1; Franceschetti, M.2; Massa, A.1
1University of Trento, ITALY;
2University of California at San Diego, UNITED STATES
In principle, electromagnetic wave propagation is governed and fully described by Maxwell equations. However, in several fields of applied science, such as mobile communications, remote sensing and radar engineering, we often have to deal with very complex propagation media, whose characteristics fluctuate randomly in time and space, and providing an analytical solution by applying the classic electromagnetic theory turns out to be an impracticable or, at least, very time-expensive way to solve the problem. In order to overcome such drawbacks, a possible approach consists in developing random models of the area of interest, characterized by a few parameters. Waves in such environments vary randomly in amplitude and phase and are accordingly described in terms of statistical averages and probabilities densities.
In such a framework, we consider the problem of optical ray propagation in a half-plane percolation lattice . The idea of applying such model for characterizing a medium of disordered scatterers was proposed for the first time in , where urban environment is described in terms of a uniform random lattice. We consider a far field scenario, where a plane monochromatic wave impinges on the grid with a prescribed incidence angle. The wave is modeled in terms of a collection of parallel rays that undergo specular reflections on the occupied cells. The aim is analytically estimating the probability a ray penetrates up to a prescribed level inside the lattice before being reflected back in the above empty half-plane.
We will present and compare two different mathematical approaches, by taking into account the most general case of an inhomogeneous grid where scatterers’ density varies with the lattice depth. The first approach is an extension of the one proposed in  and is based on the theory of Martingale random processes. We will show limitations of such an approach when dealing with widely varying obstacles’ density distributions and we will propose as a solution an innovative approach based on the theory of the Markov chains . Selected numerical tests and experiments carried out in a real controlled environment will assess the validity of the proposed solutions. Finally, we will present recent advances, where electromagnetic phenomena not considered yet are included in the propagation model, allowing application of the percolation approach to a wider ensemble of real propagation problems.
A Dynamic Way of Simplifying Objects by Homogenization for Electromagnetic Field Prediction in Urban Environment
Dauron, G.1; Richalot, E.2; Wong, M.F.1; Picon, O.2; Wiart, J.1
1France Telecom, FRANCE;
The prediction of the electromagnetic field in the urban environment is a fundamental step for developing radio network coverage and estimating the human exposure levels. The urban environment modeling may have different complexity levels depending on whether the model is highly detailed or not. We present in this paper a simplification procedure of a building wall model using homogenization. The process is divided in two steps and must be repeated for each observation point.
Verifying 3G Licence Requirements When Every dB Is Worth a Billion
Beckman, C.1; Eklund, L.2; Karlsson, B.3; Lindmark, B.4; Ribbenfjärd, D.4; Wirdemark, P.5
1University of Gävle, SWEDEN;
2Post och Telestyrelsen, SWEDEN;
4Royal Institute of Technology, SWEDEN;
5Canaima Communications, SWEDEN
Background: In the year 2000, the Swedish Telecom regulator, Post&Telestyrelsen (PTS) granted four licenses for 3G mobile operations in Sweden. All four licensees committed themselves to build networks that cover a population of 8.860.000. The definition of coverage specifies that the field strength outdoor at a height of 1.7m above ground from the primary common pilot channel, CPICH, measured over 5MHz should be 58 dBµV/m with an area probability of 95% .
To verify the coverage PTS has developed a test procedure where the field strength is measured in a drive test. However, designing such test constitutes a number of challenges:
First of all the requirement is for covered area while a drive test only measures along a route. In order to convert measurements data from drive testing to probability of area being covered, one need a statistical model based on population density and geography.
For practical reasons, PTS needs to verify the coverage through measurements using vertically polarized antennas. This is the standard way of verifying radio networks.
Typically one antenna for each operator would be mounted on each of the corners on the roof of a standard car. The antennas are then connected to receivers for each operator’s individual frequency band. This set up makes the drive test very easy to conduct. However, one needs to be aware that such a set up is filled with errors due to e.g. the size limitations of the car roof which is assumed to act as a perfect ground plane. In GSM this does not constitute much of a problem since the coverage requirements are not so stringent. However, in 3G the accuracy in the measurement needs to be extremely high since even a small systematic error of 1dB could have the consequence that each operator would have to build an extra ~1000 sites at a staggering cost of 1bilion SEK!
The present paper gives an overview of the considerations behind the design of a highly accurate test method for verification of 3G licence requirements. In particular we analyse: 1. The relationship between the requirement set for the CPICH outdoors and data rates indoors;
2. The power needed to be allocated to the CPICH.
3. A statistical model based on population density and geography to be used in order to convert data from drive testing to 95% area probability is presented and discussed.
4. The antenna designed for the measurements and the influence of the ground plane on polarization, frequency response and gain.
5. The use of polarization diversity at the BTS antennas and its influence on downlink coverage .
 Tillståndsgivningen för UMTS i Sverige, Stockholm, Sweden: Swedish Post- and Telecom Agency (PTS), 2001.
 David Ribbenfjärd, Björn Lindmark, Bo Karlsson, Lars Eklund. "Omnidirectional Vehicle Antenna for Measurement of Radio Coverage at 2 GHz". IEEE Antennas and Wireless Propagation Letters, November 2004.
 Björn Lindmark and Claes Beckman "Recommendations for compensation of polarization mismatch in 3G networks" R-S3-SB-0325. Royal Institute of Technology, Stockholm Sweden, 2003