Radiation Analysis for Co-exisiting GSM900 and UMTS900 Networks Chan-Keong Chio, Sio-Weng Ting, Kam-Weng Tam
Tapan K. Sarkar
Department of Electrical and Computer Engineering University of Macau Macau, China
Department of Electrical and Computing Engineering
Syracuse University NY, USA
Abstract — a
three-dimensional model is created for a building structure to study the radiation exposure from base-station antenna operating under a coexistence of GSM900 and UMTS900. This model can be used to analyze the radiation distribution of the building structure in the frequency bands of GSM900 and UMTS900 and predict the level of field variation due to the deployment of UMTS900. Full wave electromagnetic simulation using Integral-equation based Method of Moments with higher order basis functions (HOB) is used in this simulation for acquiring higher accuracy with less computation time. Localized measurements were carried out to verify the simulation results and good agreements were shown.
I.
created to study the radiation exposure for a building structure illuminated by a base-station antenna operating for both GSM900 and UMTS900 mobile communication; and analyze the effect on field due to the deployment of UMTS900. The full wave EM simulation using Integral-equation based Method of Moments (MoM) is used for acquiring a higher accuracy. In order to enable this big dielectric structure to be simulated successfully with MoM, higher order basis functions and the technique of parallel computation are used [5].
I NTRODUCTION
Since 2005, 3GPP has released the specification to allow the deployment of UMTS radio technology in the GSM900 frequency band. Such action spurs operators and vendors around the world to start accessing the benefits and challenges due to this deployment. The motivation behind putting UMTS to the lower frequency band of 900MHz is to achieve better signal propagation and indoor penetration in contrast to the standard UMTS2100 band. In addition, it was reported that the number of cell sites of UMTS900 can be reduced by 60% for covering the same area and also the indoor data transfer rate can be improved by 50% [1]. When there is a coexistence of GSM900 and UMTS900 networks in the frequency band around 900 MHz, it was found that the total radiation in this whole frequency band should become larger. As shown in Fig. 1, a measured spectrum in the downlink frequency range (935 MHz – 960 MHz) clearly shows that additional radiation is exhibited from 947.5 MHz to 951.5 MHz by UMTS900, whilst GSM900 keeps radiation at its original bands centered at 945 MHz and 952.5 MHz. This extra radiation due to the UMTS900 deployment leads to a concern on radiation safety. Traditional radiation assessment method is performed by onsite measurements according to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) standard [2]. Recently, a new method for the analysis of radiation from base-station antennas based on electromagnetic electromagnetic (EM) simulation was proposed [3-4]. The advantage of the simulation approach is the capability to predict the radiation variation in the vicinity of the base station due to some kinds of assumption. However, this kind of simulation suffers from the challenge of heavy computation and thus usually needed to simply the structure or using some numerical methods with low accuracy. In this work, a 3-dimensional prediction model is
978-1-4673-5317-5/13/$31.00 ©2013 IEEE
1528
Figure 1. Measured spectrum shows the radiation radiation exposure due to a coexistence of GSM and UMTS at around 900 MHz.
II.
MODEL OF BUIDLING STRUCTURE WITH BASE-STATION A NTENNA
The corridor of a building in University of Macau, with size of 6.55 × 66.44 × 11.4 at 949.2 MHz, is selected to be studied. The dimensions of the model are given in Fig. 2. It is assumed that all the walls of the corridor are made by concrete. The thickness of the wall is assumed to be 20 cm. The basestation antenna is located 33.6 m apart from the corridor at a height of 24.5 m. The antenna main beam direction is 135 degrees with respect to x-axis and down tilt of 45 degrees.
Figure 2. Model of the building structure structure and the base-station antenna.
The antenna consists of three parts which are a group of six dipole antennas, excitation and the back plate. The function of the back plate acts as a reflector which can increase the gain of the antenna and the directivity of the radiation pattern. As
AP-S 2013
shown in Fig. 3, the six dipole antennas are placed in front of o the back plate with polarization of ±45 , and are arranged with vertical alignment. The length of dipole is /2 at the operating frequency. The separation between the centers of each pair of dipole elements is equal and is around 0.6 λ and the distance between dipoles and back plate is around λ/5. The back plate is extended and bent to the front (as marked in red in Fig. 3) in order to improve the radiation patterns and front to back radio. It is assumed that the excitations to the six dipole antennas are fed by the same source and no loss from cables and the power dividers. This antenna was simulated at 944 and 949.2 MHz which are the GSM and UMTS downlink frequency respectively. The simulated horizontal and vertical radiation pattern is shown in Fig. 3. Moreover, the simulated parameters of this antenna are listed in Table I and are compared with the manufacturer specification; good agreements are shown. Structure
Vertical
(a)
Unit: V/m
(b)
Unit: V/m
Figure 4. The simulated E-field distribution inside the corridor at (a) 944 MHz (GSM900) and (b) 949.2 MHz (UMTS900).
(a)
Horizontal
(b) Figure 3. Antenna structure and radiation patterns. TABLE I. PARAMETERS OF THE ANTENNA MODEL AGAINST SPECIFICATION. Operating frequency Polarization Front-to-bac k ratio Gain 3dB Horizontal BW 3dB Vertical BW
Specification 890 ~960 MHz +45 and -45 >30dB 10 dBi 65 32 ∘
∘
∘
∘
Simulation Model 944 MHz, 949.2 MHz +45 and -45 30 dB 11.3 dBi 68 36 ∘
IV.
∘
∘
∘
In the following sections, the 3D model for the corridor together with the antenna is then simulated. The model was simulated in both 944 and 949.2 MHz, and both of them have around 500,000 unknowns and require 3.64 TB memories. The total simulation times are about 162 hours when a blade server with 64 cores of 2.6 GHz running in parallel is used. III.
Figure 5. Compasion between simulation and measurement at (a) 944 MHz (GSM900) and (b) 949.2 MHz (UMTS900).
SIMULATION AND MEASUREMENT R ESULTS
The Field Nose System is used to measure the E-field strength. Fig. 4 shows the simulated E-field distribution inside the corridor with 1.5 m in height at 944 and 949.2 MHz respectively. The simulated maximum E-field strengths in 944 and 949.2 MHz are about 0.457 and 0.0889 V/m respectively, and they are far below the standard in [2]. The simulated and the measurement results at 12 different locations (along y-axis and fixed at x =1.2 m and z = 1.5 m in height) are compared in Fig. 5. It is clear that good agreements are obtained in terms of the overall distribution. The level of field variation due to UMTS900 network is much lower than those from GSM900 network. Therefore, it shows that the major radiation is generated from GSM900 network. In addition, the E-field strength in the entire region can also be obtained through the simulation model whereas measurement can only provide information at some particular locations.
1529
CONCLUSION
In this paper, the radiation levels at a corridor of a building from base-station antenna operating under a coexistence of GSM900 and UMTS900 nearby were measured and modeled. The EM simulation is based on the Method of Moments (MoM) with the higher-order basis function (HOBs), parallel computation and out-of-core technique in order to have high accuracy and computational efficiency. Both the simulated and measured radiation levels were found compliant to ICNIRP. It shows a good agreement of the prediction model when comparing with the measurement result. ACKNOWLEDGEMENT This work is supported by the Science and Technology Development Fund of Macau SAR Government and University of Macau under the projects: FDCT/033/2010/A2 and MYRG147(Y1-L2)-FST11-TSW. [1]
R EFERENCES H. Holma, T. Ahonpaa, E. Prieur, "UMTS900 Co-Existence with GSM900," IEEE VTC2007-Spring, April 2007.
[2]
“ICNIRP Guidelines for Limiting Exposure to Time -varying Electric, Magnetic, and Electromagnetic Fields (up to 300 GHz)”, Health Physics, vol.74, no. 4, pp. 494-522, April 1998.
[3]
A. Karwowski, “Comparision of simple models for predicting radio frequency fields in vicinity of base station antennas,” Electronic Letters, Vol. 36, no. 10, 11th May 2002, pp. 851-861.
[4]
Lala, A., Kamo, B., Cela, S., “A Method of GSM Antenna Modeling for the Evaluation of the Exposed Field in the Vicinity”, NBiS, pp. 513 – 516, Sep. 2011.
[5]
Y. Zhang, T. K. Sarkar, X. Zhao, D. Garcia- Donoro, W. Zhao, M. Salazar-Palma, and S. W. Ting, Higher Order Basis Based Integral Equation Solver (HOBBIES). Wiley-IEEE, 2009.
