Future wireless systems are moving to high frequencies for additional bandwidth and frequency reuse. This makes it very important to have accurate and time-efficient models for system planning. We have previously published measurement results for an indoor channel investigation from 2.4 GHz to 24 GHz. We now propose a new combined E/H-plane 2D ray tracing method. This method includes 2D ray-tracing calculations from both horizontal and vertical sections (E/H-planes). The method predicts loss accurately for both line-of-sight (LOS) and non-line-of-sight (NLOS) paths at five frequency bands from 2.4 GHz to 24 GHz. In addition, it predicts the delay spread for line-of-sight paths well, but fails for non-line-of-sight paths

Lu, Dai

Rutledge, David

Caltech Authors - Main

Indoor Wireless Channel Modeling from 2.4 to 24GHz Using a 
Combined EIH-Plane 2D Ray Tracing Method 
Dai Lu and David Rurledge 
Depament o f  Electrical Engineering, Caltech 
Pasadena, CA 91 125-9300 
Email: dailu@caltech.edu 
Abstract: Fufure wireless systems are moving to high frequencies for additional bandwidth and frequcncy 
reuse. This makes it very imponant to have accurate and time-efficient models for system planning. In the 
past, we have published measurement results for an indoor-channel investigation from 2.4 CHI to 24 GHz. 
In this paper, we propose a new combined E/€-plane 2D ray tracing method. This method includes 2D 
ray-tracing ~ a l c ~ l a t i o n ~  from both horizontal and vertical sections (VH planes). The method predicts loss 
ac~urately for bath line-of-sight (LOS) and non-line-of-right (NLOS) paths at five frequency bands from 
2.4 GHz to 24GHr. In addition, it predicts delay spread for line-of-sight paths well, but fails for non-line- 
of-sight paths. 
1. INTRODUCTION 
C u r ”  wireless network standards s u p p m  data rates from 2Mbps to over 50Mbps. The IEEE 802.1 I (a, b 
and g) syrfems have been widely used. They are currently operating 8: 2.4 GHz and 5 GHz. In addition, 
fuNre wireless systems have been proposed at 17 GHz (HIPERLAN 11) and 60 GHz for the large 
bandwidth and high data rate. We have previously published measurement  result^ of an indoor-channel 
investigation for five Selectcd frequency bands from 2.4 to 24 CHI [I]. In addition IO 2.4, 5 and 17 GHz, 
the 10 GHz (amateur radio) and 24 GHz (Indus!iial, Scientific and Medical) bands have been added for 
comparison. The indoor measurements were done in the Moore Lab at Calteeh. For the purpose af  system 
planning, a prediction tool would be valuable to avoid time-consuming measurements. 3D ray tracing 
methods [2-31 can handle these problems but need detailed 3D information and long processing time. In 
this paper, a new combined VH-plane 2D my-h-acing method is proposed. It gives quite good results in 
predicting the measurement data and reducing processing time. 
11. COMBINE0 EM-PLANE ZD RAY TRACING METHOD 
We did indoor channel measurements in the hallway of the 3“ floor ofthe Moore building. Since the width 
of the hallway is not too large, there exist strong reneetion paths fmm the walk on both sides. Also, many 
air ducts and light strips on the ceiling contribute strong additional multipaths to the channel. It is almost 
impossible to get a reasonable prediction of the channel by any 2D ray-tracing method. However, a general 
3D ray-wcing requires more time for both geometry input and numerical computation. Therefore, a 
combined EJH-plane 2D ray tracing method has been developed to save time and retain accuracy. 
In the LOS scenario ofthii  method, hvo planes (vertical and horizontal) are cut through both the transmitter 
(Tx) and the receiver (h), (Fig. I). The 2D ray tracing code is applied to both these planer and the rsults 
are summed up far a complete set of signal paths. By considering these hvo principle planes, most strong 
multipaths are included except the ZM and high order paths that cmss the planes. The processing time i s  
now proportianal to (2”) instead o f  (”) as required for a general 3D ray-tracing method. Even though 
some accelerating algorithms have been developed recently for 3D ray-tracing [4], this combined 2D 
method i s  still a very promising way 10 handle the complex indoor environment with reasonable time and 
accuracy. Another advantage of this method is that the my calculations can be naNmlly divided for parallel 
processing. This further reduces the simulation time, which is exeemely helpfil for a large problem. 
For the NLOS scenario, there is no way to cut the vertical plane to include both hanrminer and receiver. 
We have defined new Iransminer sources to handle this problem (Fig. 2). All additional sources are 
generated by diffrastion from the original Tn, or its image reflected by the ceiling or floor. All have a LOS 
0-7803-8302-8/04/$20.00 2004 IEEE 3641 
path to the Rx. After finding the  value^ of these sources from diffraction formulas, we can apply the 
normal 2D ray-tracing method as hefore and sum them with the horizontal ray-tracing results. This 
procedure is quite similar to the LOS case. The only difference here is that each new murce requires the 
consideration of  an additional vertical plane. This calculation is also included as an option in the numerical 
ray-tracing code. The NLOS case has a computation time proportional to mN', where m is an inleger (m > 
2), depending on haw many diffraction SOUTC~S are taken into account. Environment geometry determines 
the number of diffraction sources necessary. 
The formula for the link performance Calculation i s  given in (1 .I), where R, is the product of the reflection. 
transmission and diffraction coefficients associated with the i' path, L, is the total length of the i' path, and 
GT' and G" are antenna pallem functions for the transminer and receiver. Panem measurements were 
made in an anechoic chamber. The Hann window and IFFT are applied to find the time domain profile to 
calculate the RMS delay spread. 
A graphical user interface program har been developed using MATLAB. It takes the positions of the 
transminer and receiver and the 2D EIH cutting plane geometry files as input parameten for ray-tracing 
calculations. Different code is used for the LOS and NLOS scenarios as described before. 
Hallway 
A-A' E-Plane Cut 
Fig. 1 Combined 2D ray tracing for LOS. 
111. EXPERIMENTAL SETUP 
We have made WO indoor channel measurements: path loss and RMS delay spread. Far the path loss 
measurement, an An"tsu 68197 signal generator provided the signal for the transmitter and an HP 8561 
specmm analyzer measured the signal at the receiver. An HP8722 vector network analyzer was used for 
delay spread measurements. HP8149B and Linon TWT amplifiers were used to improve the signal-to- 
noise ratio. A pair of AEL broadband hom antennas that cover all bands of interest with a gain of 8-10 dB 
were wed. We mote  LABVIEW programs to extract measucment data from those instraments and also 
control the movement of the receiver cart using the GPIB. This gave us the ability to take data for a signal 
plot over a long distance. 
Fig. 2 Modified ZD ray tracing for NLOS. 
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Measurements were made to extract electrical parameten for indoor construction materials. A goad 
material model is very impoitant for accurate my-tracing. In the pait, people have published result3 an the 
electtical properties of materials at microwave frequencies [ 5 ] ,  [6]. For this work, we made free-space 
TRL measuremenrs to find the microwave pmpetries of three conrmction materials (plaiterboard, glass 
and wood) at five selected frequency bands. The measurement data is shown in Fig. 3. They are 
comparable to the results that have been published before. 
Fig. 3 Comparison of three different mafenals: glass, wood and plasterboard 
W .  SIMULATION VS MEASUREMENT 
Simulafions were performed and measurements made for the 3" floor of Moore building (Fig. 4). In the 
LOS scenario, the transminer is located in the center of the hallway, and in the NLOS scenario, the 
transminer is located in one of the side rooms. The receiver is moved along the hallway conuolled by the 
computer on the cart, while path loss and power delay profile data were measured. The cas is moving 
quite rlowly to avoid frequency shills. The cart can also be controlled in step mode to take measurements 
while stopped. 
Fig. 5 shows the path loss at 24GHs for both LOS and NLOS. As can be seen from the figure, Ule 
algorithm gives a good prediction of path 1055 in both LOS and NLOS environment. The simulation does 
not have ai many fluctuations as the measurement due to the limited number of paths considered. The path 
loss TeSultS are Similarly good for the other four frequency bands, not shown here. 
Fig. 4 3" floor OfCaltech's Moore building (Depamnent ofEleettica1 Engincenng) 
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Fig. 6 gives the cumulative distribution function of the RMS delay spread at 24GHz for both LOS and 
NLOS. As can be seen, the simulation is good for the LOS but is not so close in the NLOS scenario. That 
may be due m the absence of some of the higher order paths in the NLOS model and also because of noise 
when the signal i s  quite weak. The power delay profile for NLOS has shown that some delayed paths are 
missing in the NLOS model presented here. We will show Ule path loss and RMS delay spread plots for all 
five frequency bands at the conference. Only the 24-GHz data i s  given here due to space constramts. 
V. CONCLUSION 
In this paper, we have developed a combined UH plane 2D ray-rracing method. This method predict IOU 
accurately far both line-of-sight and non-line-of-sight paths. In addition, it predicts RMS delay spread for 
line-of-sight well, but fails for non-line-of-night. The ~imulation and measurement were done at five 
selected frequencybandsfmm 2.410 24 CHI. 
VI. ACKNOWLEDGEMENT 
We would like to thank the Lee Center for Advanced Networking far the support of this research work 
REFERENCES 
[I]. Dai Lu and Dave Rutledge, "Investigation of indoor radio channels fmm 2.4 GHz to 24 G W ,  IEEE 
Antennarr and Propagation Symposium (APSNRSI) June, 2003, Columbus OH. 
121. K.Rizk, A. Mawiia, J.F. Wagen and F. Gariol, "Propagation in urban micmcclls with high rise 
buildings", IEEE VTS 46" Vehicular Tech Conf,, Atlanta, CA, pp. 859-863, April, 1996. 
131. Geoge Liang and Hew L. Benoni, "A new approach to 3D ray tracing for propagation prediction in 
cities", IEEE Trans on Antennas and Propagations, Vo1.46, No.6, pp. 883-863, June 1998. 
[4]. F.A. Agelet et.al, "Efficient ray-tracing a~celeration techniques for radio propagation modeling", IEEE 
Trans an Vehicular Technology, Vo1.49. No.6, pp.2089-2104, November 2000. 
[SI. V.V. Varadan, R.D. Hollinger, D.K. Ghodgaonkar and V.K. Varadan, "Frec-space, broadband 
measwemenu of high-temperature, complex dielectric pmperties at microwwe frequencies," IEEE Trans. 
Inst". ~eas.,vo1.4n,pp.842-846, Oct. 1991. 
[6]. lnigo Cuinas and Manuel Garcia Sanchez, "Building material eharacteriration fmm complex 
transmissivity measurement at 5.8 GHz," IEEE Trans. Antennas and Propagation, ~01.48, "0.8, pp.1269- 
1271, Aug. 2000. 
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Indoor wireless channel modeling from 2.4 to 24 GHz using a combined E/H-Plane 2D ray tracing method

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Indoor wireless channel modeling from 2.4 to 24 GHz using a combined E/H-Plane 2D ray tracing method

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