Approximating User Distributions in WCDMA Networks Using 2-D Gaussian Page: 1
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CCCT 05: INTERNATIONAL CONFERENCE ON COMPUTING, COMMUNICATIONS, AND CONTROL TECHNOLOGIES
Approximating User Distributions in WCDMA
Networks Using 2-D Gaussian
Son NGUYEN and Robert AKL
Department of Computer Science and Engineering
University of North Texas
Denton, TX, 76203
In this paper, we present an analytical model for ap-
proximating the user distributions in multi-cell third gen-
eration WCDMA networks using 2-dimensional Gaussian
distributions by determining the means and the standard
deviations of the distributions for every cell. This allows
us to calculate the inter-cell interference and the reverse-
link capacity of the network. We compare our model with
simulation results and show that it is fast and accurate
enough to be used efficiently in the planning process of
large WCDMA networks.
Keywords: Inter-cell interference, Capacity, WCDMA,
User distribution, 2-D Gaussian distribution.
Wideband Code Division Multiple Access (WCDMA) is
an air interface that is proposed for third generation wireless
networks that provides a vast range of data services with
bit rates of up to 2Mbps with varying quality of service
requirements. Since CDMA was first introduced in 1989
by QUALCOMM, the number of subscribers has grown to
more than 240 million globally. The ability to offer greater
capacity, multi-rate transmission with backward compati-
bility, effortless integration, and easy migrating path to 3G
cellular systems, has created the widespread deployment of
CDMA systems all over the world .
It has been shown in , , ,  that the capacity
of a CDMA network is reverse link limited, and therefore
our study is focused on reverse link capacity. One of the
principal characteristics of a WCDMA network is that the
capacity of the system is a function of the total interference
experienced by the network, and is upper bounded by
the cell experiencing the most interference. Thus, it is
imminent to characterize the total inter-cell interference
seen by a single cell in terms of the user distribution in all
other cell for determining the capacity in that single cell.
Traditionally, the total interference contributed by a cell has
been viewed as an approximation, determined by simply
multiplying the number of users in that cell by the average
interference offered by that cell . In other words, a user
placed anywhere within a cell generated the same amount of
interference. Clearly, a more realistic approach will use per-
user interference as a function of its actual distance to the
point of interest. There is a dearth of literature where actual
distance was used in the interference model. In , even
though interference was calculated using actual distance,
the capacity calculations were done using mean value of
interference. User positions were varied over time, but the
number of users was kept constant.
In this paper, we present an analytical model for the ap-
proximation of the user distribution in multi-cell WCDMA
networks using 2-dimensional Gaussian distributions by
determining the means and the standard deviations of the
distributions for every cell. Once the user distributions are
approximated, the average inter-cell interferences can be
determined similar to what was done in . We compare
our model with simulation results presented in  and show
that it is fast and accurate enough to be used efficiently in
the planning process of large WCDMA networks.
The remainder of this paper is organized as follows. In
section 2, we use the 2-D Gaussian function for modeling
user distributions and calculating the average inter-cell
interference. In section 3, we compute the capacity of
a WCDMA network. Numerical results are presented in
section 4. Finally, our conclusions are given in section 5.
2. AVERAGE INTER-CELL INTERFERENCE
MODEL USING 2-D GAUSSIAN DISTRIBUTION
It is assumed that each user is always communicating
and is power controlled by the base station (BS) that has
the highest received power at the user. Let r (x, y) and
rj(x, y) be the distance from a user to BS i and BS j,
respectively. This user is power controlled by BS j in the
cell or region Cj with area Aj, which BS j services. It is
assumed that both large scale path loss and shadow fading
are compensated by the perfect power control mechanism.
Let Ijit be the average inter-cell interference that all users
nj,t using services t with activity factor vt and received
signal St at BS j impose on BS i. Modifying the average
inter-cell interference given by , we have
J "(x, y)
w(x, y) dA(x, y),
where 1 = ln(10)/10, os is the standard deviation of
the attenuation for the shadow fading, m is the path loss
exponent, and w(x, y) is the user distribution density at
e( ) /2
Iji,t = Stvtnj,t
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Nguyen, Son & Akl, Robert G. Approximating User Distributions in WCDMA Networks Using 2-D Gaussian, paper, July 2005; [Hertfordshire, England]. (digital.library.unt.edu/ark:/67531/metadc30820/m1/1/: accessed June 28, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Engineering.