outdoor path loss models for IEEE 802.16

1. Outdoor Path loss models for IEEE 802.16
in suburban and campus-like environments
Damiano De Luca(b), Fabio Fiano(d), Franco Mazzenga(a), Cristiano Monti(b), Stefano Ridolfi(e), Francesco Vallone(c)
(a)
Dipartimento di Ingegneria Elettronica, University of Rome Tor Vergata, Via del Politecnico 1, 00133, Roma, Italy
(b)
Consorzio Universit`a Industria Laboratori di Radiocomunicazioni, RadioLabs
(c)
Ericsson Telecomunicazioni
(d)
University of Rome Tor Vergata
(e)
British Telecom Italia
Contact author: F. Mazzenga, email: mazzenga@ing.uniroma2.it
Abstract— Wireless metropolitan area networks (WMANs)
based on IEEE 802.16 standard are widely deployed to provide
users with wireless network connectivity, anytime, anyplace. In
particular IEEE 802.16 standard has been developed to provide
fixed and mobile broadband applications at lower costs for
installation as compared with traditional wired infrastructures.
In this paper we present the main results of a measurement
campaign on propagation at 3.5 GHz conducted by BT Italy
and Ericsson with the University of Rome Tor Vergata. Path
loss channel model obtained from experimental data are also
presented.
I. INTRODUCTION
The evolution of broadband Internet access anywhere, at
any time, can became a reality thanks to the novel broadband
technologies such as WiMAX. WiMAX promises to open new,
economically viable market opportunities for operators, wire-
less Internet service providers and equipment manufacturers.
The flexibility of wireless technology, combined with high
troughput, scalability and long-range features of the IEEE
802.16 standard helps to fill the broadband coverage gaps
and reach millions of new residential and business customers
worldwide. IEEE 802.16 [2],[3] is a specification for fixed
broadband wireless metropolitan access networks (MANs) that
can use a point-to-multipoint architecture. The Worldwide
Microwave Interoperability Forum is a non-profit consortium
dedicated to promoting the adoption of this technology and
ensuring that different vendors’ products will interoperate. In
the typical operation mode the WiMAX system consists of
two parts: a WiMAX base station and a WiMAX receiver,
also referred as customer premise equipment (CPE) that can
be fixed on mobile. The 802.16 devices operating in the
3.5 − 3.8 GHz band, are designed for easy, fast and low cost
installation. However accurate planning for outdoor cellular-
like WMAN is required in order to obtain maximum system
capacity and an estimate of the number of BSs required to
cover a service area for a specified quality of service. Current
practice of network planning is based on the path loss models
that are specific of the propagation environment around the
BSs. Up to now only few results on propagation models in
the 3.5 − 3.8 GHz band have been presented in the literature
[4]. In this paper we present the main results of a measurement
campaign on propagation at 3.5 GHz conducted by BT-Italia
and Ericsson with the University of Rome Tor Vergata. The
considered tests area are depicted in fig.1 and Fig.2.
Fig. 1. Measurement test area - BT Italy
In both cases up to 200 measurements (mainly acquired in
NLOS conditions) of the received power have been collected
during the measurement campaign but about 170/180 only
have been used to evaluate the parameters of path loss models.
The paper is organized as a follows: section II and section
III the measurement setup and data process are respectively
described; section IV shows the outdoor path loss channel
model while in section V the results are described. As an
example of application the section VI shows the link budget.
II. MEASUREMENT SETUP
The area in Fig.1 includes the BT Italy employee’s building
in Rome and it is representative of a typical suburban propaga-
tion environment. The buildings are not higher than 43 m and
the width of the streets can vary from 4 up to 10 m. The Base
Station antenna was positioned on the most visible building
1-4244-0353-7/07/$25.00 ©2007 IEEE
This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings.
4902

2. Fig. 2. Measurement test area - Ericsson campus
Fig. 3. Measured path loss for each point (BT Italy)
(see Fig.1) and the measurement equipment was installed on a
car that moved in the area. The receiver antenna gain was 3 dB
and the equipment operates at 3.5 GHz. Received power was
measured parking the car in the areas evidenced in Fig.1. The
car is also equipped with a GPS receiver used to determine its
position for each measure.
The area in Fig.2 includes the Ericsson research laboratories
in Rome and it is representative of a typical campus-like
propagation environment. The buildings are not higher than
16 m and the width of the streets can vary from 2 up to
8 m. The transmitting antenna was positioned on the highest
building (see the red arrow in Fig.2) and the measurement
equipment was installed on a van that moved in the area. The
receiver antenna gain was 3 dB and the equipment operates at
3.5 GHz with a signal bandwith of 3.5 MHz.
The measurement equipment consisted of: one IEEE 801.16-
2004 Base Station model Airspan Macromax equipped with
at 60-degree antenna and a portable PC with an IEEE 802.16-
2004 Self Install CPE designed to sit next to a computer
on a desktop. CPE antenna containing four 90-degree with
high-gain directional antennas providing 360 degree coverage
(CPE selects antenna with best RF reception). The values
of the received power were extracted from the CPE using a
software provided by BT Italy. The test consisted on hold the
position of the Base Station and CPE too and measuring the
power received with an EIRP of 23dBm (200mW). Outdoor
measurements are collected by driving around map shown in
Fig.1 and Fig.2 for about 1 Km maximum from the Base
Station. Every point over the map represents a fixed position of
the CPE where we collected about 30 samples of the received
power for a total measurement time interval of 100s. Graphics
in fig.3 and in fig.4 show the path loss values for each point
where samples were collected for both scenarios.
Fig. 4. Measured path loss for each point (Ericsson campus)
III. DATA PROCESS
For each set of measured values and for both scenarios we
have preliminarily removed some sample that were considered
too far from the majority of values (outlier) as shown in
the next figures representing the model fitting. We also have
excluded the samples with too large standard deviation. This
remedy tries to remove the environment variability measure-
ment noise caused by the presence of cars, bus, etc. during
the measure.
IV. OUTDOOR PATH LOSS CHANNEL MODEL
The path loss model considered in this paper are summa-
rized in this Section. Most models aim to predict the median
This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings.
4903

3. path loss, i.e. the loss not exceeded at fixed percent of locations
and/or for fixed percent of the time. This fixed value is tied
to the service to provide. Knowledge of the signal statistics
then allows the estimation of the variability of the signal
so to determine the percentage of the specified area that
has an adequate signal strength. The One Slope (OS) model
assumes a linear dependence between the path loss (dB) and
the logarithm of distance. In the formulation for (OS) model
1, d is distance between the transmitter and the receiver i.e.
and usually expressed in meters
L(d) = l0 + 10γ log(d), (dB) (1)
and l0 is the path loss at 1 meter distance, γ is the power
decay index or the path loss exponent dual (γ=2 is free space)
with
l0 = −27.5 + 20 log(f), (dB) (2)
V. RESULTS
The parameters of the model (1) have been obtained through
best square fitting with collected data. The statistics of data
points in the scenarios are represented as follows (Table I,
Table II). Parameters were obtained considering only the data
showing the RSSI standard deviation.
γ RSSI Standard Deviation (σ) l0
Free space 2 1.348 129.01
OS 3.032 1.348 41.10
TABLE I
PATH LOSS EXPONENT, RSSI STANDARD DEVIATION AND l0 (BT ITALY)
γ RSSI Standard Deviation (σ) l0
Free space 2 0.6525 103.28
OS 3.533 0.6525 9.711
TABLE II
PATH LOSS EXPONENT, RSSI STANDARD DEVIATION AND l0 (ERICSSON)
Subsequently, starting from the fitting obtained from the
path loss models in (1), we show the typical parameters of
the models considered at 3.5 GHz with experimental data. To
evaluate the goodness of the model with respect to data, we
considered the R-Square and RMSE. The first parameter called
R-Square measures how successful the fit is in explaining
the variation of the data e.g R-square is the square of the
correlation between the response values and the predicted
response values. It is also called the square of the multiple
correlation coefficient and the coefficient of multiple determi-
nation. R-square is defined as the ratio of the sum of squares
of the regression (SSR) and the total sum of squares (SST),
where SST = SSR + SSE. Given these definitions, R-square
is expressed as R − SQUARE = 1 - SSE/SST. R-square
can take on any value between 0 and 1, with a value closer to
1 indicating a better fit. The second parameter is called Root
Mean Squared Error and is also known as the fit standard
error and the standard error of the regression. A RMSE value
closer to 0 indicates a better fit. To evaluate the goodness of the
model with respect to data we also considered the fitting of the
experimental data with a free space alike model considering
the constant l0 as an unknown and γ=2. Results have been
reported in table III and IV.
A. First Area : BT ITALY
This test refers at BT ITALY area shown in Fig.1. In this
case the 1 becomes
L(d) = l0 + 10γ log(d) (dB) (3)
with l0 representing a constant that provides the lower error
in the fitting calculation.
The l0 value is shown in table I. The cumulative distribution
of the model error is shown in fig.5.
R SQUARE RMSE
OS 0.3713 6.927
Free Space 0.3283 7.137
TABLE III
SUMMARY BT ITALY
Table III shows the two statistic parameters described pre-
viously.
Fig. 5. Cumulative distribution of the model error - OS model -
Relatively to Free Space model (γ = 2) the value of
parameter l0 is shows in table I and the statistic result fitting
for Free Space model is shows in fig.6; R-SQUARE and
RMSE are lists in table III.
A qualitative comparison between the models is shown in
fig. 7
B. Second Area : Ericsson Campus
With respect to the Ericsson Area test shown in Fig.2,
starting from the 1
This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings.
4904

4. Fig. 6. Cumulative distribution of the model error - Free Space model -
Fig. 7. Comparison between the models
where l0 represents a constant that provides the lower error
in the fitting calculation.
The l0 value is shows in table II. The cumulative distribution
of the model error is shown in fig.8.
Relatively to Free Space model (γ = 2) the value of
parameter l0 is shows in table II and the statistic result fitting
for Free Space model is shows in fig.9; R-SQUARE and
RMSE are lists in table IV.
VI. LINK BUDGET
In this section we show a comparison between the measured
and calculated path loss with the models described above.
Moreover we show an example of the coverage map calculated
with parameters obtained from OS model for both environ-
ments. For suburban environment as BT ITALY scenario we
show the results in Table V and fig.11 obtained using a
software tool provided by RadioLabs.
For campus-like environments as Ericsson research labora-
tories campus the Table VI and fig.12 show the results obtained
R SQUARE RMSE
OS 0.7083 7.280
Free Space 0.5749 8.765
TABLE IV
SUMMARY ERICSSON
Fig. 8. Cumulative distribution of the model error - OS model -
Fig. 9. Cumulative distribution of the model error - Free Space model -
from software provided by RadioLabs.
Finally we show a link budget example to determine the
maximum coverage ray with the receiver power sensitivity
fixed at -100 dBm. The used equation is
PT xGT xGRx/L(d) = Psensitivity
The result of link budget is shown in Table VII.
VII. CONCLUSIONS
The characterization of outdoor path loss is an important
step in wireless network design in order to estimate the radio
This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings.
4905

5. Fig. 10. Comparison between the models
Distance(m) Pathloss(dB) OS(dB) FS(dB)
1 188.62 108.26 110.10 118.18
2 294.88 117.54 115.98 122.06
3 396.39 129.52 119.88 124.63
4 445.85 121.68 121.42 125.65
5 495.04 122.92 122.80 126.56
6 548.22 116.71 124.15 127.44
7 604.07 135.56 125.42 128.29
8 695.08 116.49 127.27 129.50
9 751.24 127.00 128.290 130.18
10 863.03 125.450 130.120 131.38
TABLE V
COMPARISON PATH LOSS (BT ITALY)
Fig. 11. Coverage map with OS model (BT ITALY)
coverage and the costs. In this paper we used measured
data to evaluate the parameters of several path loss channel
models some of them proposed in the current literature. In
particular, Free space and One Slop models were analyzed
and results have been provided for two different categories
Distance(m) Pathloss(dB) OS(dB) FS(dB)
1 23.714 69.377 58.290 74.579
2 54.337 69.759 71.012 81.781
3 80.825 66.569 77.105 85.230
4 93.981 90.687 79.418 86.540
5 137.11 92.614 85.214 89.821
6 222.56 91.265 92.646 94.028
7 240.51 97.633 93.837 94.702
8 261.15 94.897 95.099 95.417
9 346.11 95.828 99.422 97.863
10 390.98 93.500 101.29 98.922
TABLE VI
COMPARISON PATH LOSS (ERICSSON)
Fig. 12. Coverage map with OS model (Ericsson Campus)
BTITALY ERICSSON
model distance(m) distance (m)
OS 996 1570
FS 927 1849
TABLE VII
LINK BUDGET: MAXIMUM RAY COVERAGE
of environments: sub-urban and campus-like environment.
The comparison between the parameters of the models have
been shown and the cumulative distribution of the considered
models error are also shown. Furthermore in this work is
also shown a link budget example calculated with parameters
obtained from OS model for both environments.
REFERENCES
[1] The Business of WiMAX. Deepak Pareek. John Wiley and Soons June
2006.
[2] Standard IEEE 802.16d-2004 available on site
http://www.ieee802.org/16
[3] Standard IEEE 802.16e-2005 available on site
http://www.ieee802.org/16 published on 28 February
[4] V. Erceg, K. V. S. Hari, et al., ”Channel models for fixed wireless
applications,” tech. rep., IEEE 802.16 Broadband Wireless Access
Working Group, January 2001
[5] A Survey of Various Propagation Models for Mobile Communication
Tapan K. Sarkar, Zhong Ji, Kyungjung Kim, Abdellatif Medouri, and
Magdalena Salazar-Palma IEEE Antennas and Propagation Magazine,
Vol.45, No.3,June 2003
This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings.
4906