Int. J. Communications, Network and System Sciences, 2013, 6, 377-380
http://dx.doi.org/10.4236/ijcns.2013.68040 Published Online August 2013 (http://www.scirp.org/journal/ijcns)
Call Admission Control in HAP W-CDMA
Cellular Systems
Behnaz Behzadi
Faculty of Engineering, Islamic Azad University, South Branch, Tehran, Iran
Received June 15, 2013; revised July 15, 2013; accepted July 25, 2013
Copyright © 2013 Behnaz Behzadi. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Among various radio sources which control different dependencies/functions, in this article, we will talk about the Call
Admission Control (CAC), and we are supposed to confine our concentration on W-CDMA which is based on high
raised platforms, since during the recent years remarkable amount of attention has been focused on platforms located in
stratosphere layer [1]. Firstly, we study the capacity of uplink from HAP (High Altitude Platform) W-CDMA and we’ll
work on estimation and power control defects in a new conversation added to current conversations. We’ll enhance the
Call Admission Control (CAC) based on the side effects of power control defects and users’ stimulus and then compare
the CAC which has been measured by using of momentary energy on bit in the spectral density form (Eb/N0). Then we
examine the mentioned charts for two different criteria which the decision will be made by these criteria in order to de-
cide if exchanged calls are to be admitted or not. The first criterion is based on the minimum of (Eb/N0) of the first row
cells meanwhile the second criterion is based on the average of (Eb/N0) of first row-cells.
Keywords: High Raised Platforms; Call Admission Control; Quality of Services; Power Control Defects
1. Introduction
The HAPS internal potentials will be appeared gradually,
HAPS (High Altitude Platform Station) is the name of a
technology which provides far distance communication
between wide and narrow fiber.
The aim of HAPS is to offer the services to the users
using planes with pilot or none pilot running planes, or
balloons. These platforms are available for several us-
ages and will be used in estratosphery zone in the height
range of 20 - 50 km [2].
It’s not a cutting-edge innovation to use platforms as a
none-polluter and cheap and flexible. These platforms
can be accordant with satellite and also earth-established
equipments since they can be an organizer as a founda-
tion. Also HAPS can be used in a special event such as
Olympics to be covered when there’ll be lots of crowd.
Daily enhancement of demands for telecommunication
systems and having new systems with a wide range of fi-
bers has turned the trend to the use of more high-tech
systems to meet the demand. The third generation of mo-
bile cellular telecommunication and the following gen-
eration have been designed in a wide telecommunication
and several sided accessibility with pass code, plus hav-
ing more capacity in comparison with current systems, to
be able to provide a sending with different rates.
This paper investigates a HAP W-CDMA cellular sys-
tem based on a high platform. One of the radio sources
that controls the HAP W-CDMA system’s functions. In
this article, we concentrate on call admission control
which it means to admit or to reject a call will be admit-
ed when it receives the service quality from the net and
no good to be mentioned that this issue will affect on call
service quality that is being used. At the same time, it’s
possible that QoS rejects the current calls.
Lots of issues are engaged in call admission but the
power control is above the qualification and possibility.
In real systems, the control defects power will lead to
some alterations in receiving power by a central station
which consequently lead to some alterations in ratio of
receiving energy per bit to spectral density of power-
noise of (Eb/N0). Call admission will be done based on
measures of (Eb/N0). Two thresholds will be considered
for new transferred calls and exchanged calls.
The process will be as below in the second ward. We
will analyze the call admission control. The third part
contains an explanation of the offering plan and laying
matters. In the forth part, the simulated results have been
offered and the point of discussion. And lastly, the result
C
opyright © 2013 SciRes. IJCNS

B. BEHZADI
378
and observations are in the fifth section.
2. Review on Call Admission Control
Performance
Considering the advantages of this crucial talk, the call
admission control charts are the point of this research. In
this part, we will specify the prominent features of CDMA.
Our study is based on linear alterations of time field [3-6].
The all CAC can’t cease the power control defects and
according to studies, receiving power by each central
station from a user is stable and equal to other users. In
spite of this, practical power control defects lead to al-
terations in receiving power which cause the net function
to get worse [2,7].
Signal to-interference ratio (SIR) is one of the effec-
tive parameters in QoS in each telecommunication and
communication system. In CDMA systems, the SID meas-
uring can promote function of CAC by predicting the
effect of each new call on current call quality in the same
or neighboring cells. All the CAC measuring SIR is es-
timated considering that power control is completed. But
in authentic systems power control defects will increase
the doubts about the function. We are going to compare
the result of the both CAC with completed power control
and defects considering CAC. So we illustrate the effects
of power control on system function.
3. Offering Plan for Call Admission Control
In this article, we analyze the CAC which is based on the
average management concept in a short period of time
which will be done in average SIR estimation of current
calls in order to decline any possible fault. Then we com-
pare the out coming results with completed power con-
trol. We will estimate this in a cellar system HAPW-
CDMA with multi-functional service, one of the most
noticeable advantages of such systems is flexibility, re-
construction features, cheap practicality, having low ra-
diation delay, extended covering [1].
Designing the Parameters
In this study, we consider a HAP in the height of 20 km
with an antenna having fuzzy arrays based on ITU The-
ory (Equation (1)) [8].


2
34.83,for 04.53
1.57
9.8,for 4.535.87
55.9560log,for 5.8737
38.2,for 3790
G

 



















(1)
The cell radius will be selected in a way that the gain in
edges of cell to be 10 dB less than the maximum gain. In
our study, we investigate a group of services which their
specifications are as follows: (Table 1) [9,10].
At first the capacity of HAP-WCDMA cellular system
will be estimated based on the probability of an interrup-
tion for two states having perfect power control and de-
fect power control. In this section, the probability of in-
terruption will be defined considering Eb/N0 being less
than the needed (Eb/N0) min. There is not need to men-
tion that the least needed energy for each bit (Eb) in per
service group will be provided based on the signal power
on bit rate.
Eb/N0 shows the quality as Equation (2)

01
ci
b
Pe
EN WR
I
intra nth


 (2)
From the right order the formula represents the power
of a user which has been received by a central station,
although it returns back to when we consider the power
control defects [11-14]. Power control defects have been
considered as a long-normal distribution. So the receiving
power by a station could be shown as ci Pe


. Pci defines a
nominal receiving power of its class of a user by an ideal
power control and α equals to ln10
10 and θk is a Gaussian
random variable with zero mean and σp represents stan-
dard deviation. Rb is information rate and W is sending
band width which is equal to 5 MHz. Intercellular inter-
ference (Iintra) is originated from the interference be-
tween users which are located in the same cell. β will
show the performance of the central station with multiuser
clarifying. nth is the power of thermal noise. The per-
formance of multiuser clarifying method is percentage of
Iintra which in this paper β will be equal to zero. Also we
assume 11dB
c
P
nth  All the interfering signals are un-
der the effect of power control with same statistical speci-
fication of any signal.
10
1
1
M
c
i
I
intraP e



 (3)
M10 is the number of user of group 1 which are effec-
tive on cellular interference. Receiving power from the
user hasn’t been considered. Considering the users dis-
tributions, we imagine we would have equal distribution
in each cell. Also the number of users has a poison dis-
tribution.
Table 1. Service class specifications.
Information
bitrate
Minimum
required Eb/N0
Power
factor
Typical
applications
12.2 kb/s 5 dB 0 dB Voice

B. BEHZADI 379

!
n
n
Pne n



 (4)
λ is the average users in each cell. So by this formula the
number of users in each cell depends on the number of
users in others. The average of Eb/N0 will be taken for
each cell and group-service and will be recorded for each
2.5 S on Eb/N0. With any new call demand or transferred
calls these measures will be compared with predefined
threshold [2].
Here we simulate for a 2-second period of time, with
having mostly 8 saved measures. Receiving a new call or a
transferred call request is based on the average of Eb/N0
and will be counted by the average of 8 saved equivalent
values. This method will be done both for nominated cell
to be used for call service and the first-row cells [15].
Based on the average value of Eb/N0 cells of the first
row should be in a way to provide the quality of current
calls and to ensure that a new call in its first try won’t fail.
In our method, all the first-row cells should specify the
whole admitting criteria since now on. We refer to mini-
mum maker criteria which are the items that count the least
average of Eb/N0 of first-row cells for each service group
and compare it with predefined thresholds. In other words,
the algorithm calculates average of Eb/N0 for each group-
service in each cell and selects the smallest value. In the
suggested algorithm, transferred calls are in higher prior-
ity rather than new calls in which the smaller levels are for
transferred calls and bigger ones are for call requests.
Table 2 shows the CAC parameters. The aim of choos-
ing the appropriate measurements for threshold levels is
to make the possible interruption of each service group
like a reasonable one. The values of these threshold lev-
els are greater than minimum of required Eb/N0.
So our suggested model is as follows: measurement of
Eb/N0 should be done each 2.5 S. A new call request or an
already received transferred call measures the amount for
nominated cells for service and the first-row cells which
are to be average. This measurement gives two values as
result. The first one is the average of Eb/N0 for each ser-
vice group in selected cells to service the calls and the
second one is the average of Eb/N0 for each service in
first-row cells. When we have 2 outcomes, we can use 2
approaches as: one is minimum maker and the other is
average making and these 2 measurements will be com-
pared with two predefined thresholds.
We will review four different CAC plans which have
been explained as follows:
Table 2. CAC parameters.
Threshold for E
b/N0
New calls-same cell 7 dB
New calls-1st tier cells 6.7 dB
Handoff class-1 calls-same cell 6.65 dB
Handoff class-1 calls-1st tier cells 6.60 dB
1-AM: based on an average measurement of Eb/N0
based on the least criteria.
2-IM: based on instantaneous measurement of Eb/N0
based on the least criteria.
3-AA: based on an average measurement of Eb/N0 based
on with average criteria.
4-IA: based on instantaneous measurement of Eb/N0
based on with average criteria.
4. Simulation Environment
Experiments in this article are done with the aim of esti-
mating the function of defected power control in four
methods of completed power control. A 4*4 cellar sys-
tem will be used. HAP is located directly above the 6th
cell. We are to estimate n unlimited net which is next to
each cell in all directions of neighboring cells. A call is
added to the net it’s interval will be created by chart dis-
tribution in first of call the terminal’s style are monoto-
nous on simulating zone, and their direction is from to
360˚ by chance time between two steady alterations di-
recting toward users has a chart distribution of 40 s. The
new created direction accordant with a steady distribu-
tion is on −45˚ and 45˚ to the ex-direction. And also the
user pace in very first of the call is steady and will be the
steady during the entire call. Simulation parameters in
Table 3 are considered.
Simulation Results
We count the Grade of Service (GoS) in order to have a
better parameter comparison. GoS is defined as follows:
GoS = Call blocking probability + 10 Ca ll dropping
probability
Figure 1 shows the Grade of Service (GoS) to the rate
of incoming calls with imperfect power control with an
average standard. Figure 2 shows GoS to the rate of in-
coming calls with imperfect power control and minimum
standard and compares it with Figure 1.
5. Conclusions
In this paper, we propose a call admission control scheme
for cellular systems HAP W-CDMA.
Funding for this project was based on measurements
of Eb/N0. The mechanisms used to achieve the proposed
scheme provide better performance.
Parameters of the CAC, as required by the simulation
Table 3. Simulation parameters.
Parameters Calls
Mean call duration 180 s
Minimum user velocity 0 m/s
Maximum user velocity 20 m/s
σp 1 dB

B. BEHZADI
380
[2] S. Karapantazis and F.-N. Pavlidou, “Broadband Commu-
nications via High-Altitude Platforms—A Survey,” IEEE
Communications Surveys & Tutorials, Vol. 7, No. 1, 2005,
pp. 2-31. doi:10.1109/COMST.2005.1423332
[3] S. Karapantazis and F.-N. Pavlidou, “The Role of High
Altitude Platforms in beyond 3G Networks,” IEEE Wire-
less Communications, Vol. 12, No. 6, 2005, pp. 33-41.
doi:10.1109/MWC.2005.1561943
[4] Z. Liu and M. Zarki, “SIR-Based Call Admission Control
for DSCDMA Cellular Systems,” IEEE Journal on Se-
lected Areas in Communications, Vol. 12, No. 4, 1994, pp.
638-644. doi:10.1109/49.286670
[5] S. Shin, C.-H. Cho and D. Sung, “Interference-Based
Channel Assignment for DS-CDMA Cellular Systems,”
IEEE Transactions on Vehicular Technology, Vol. 48, No.
1, 1999, pp. 233-239. doi:10.1109/25.740098
[6] S. Shin and D. Sung, “DS-CDMA Reverse Link Channel
Assignment Based on Interference Measurements,” Elec-
tronics Letters, Vol. 31, No. 22, 1995, pp. 1897-1899.
doi:10.1049/el:19951319
Figure 1. GoS to the rate of incoming calls with imperfect
power control with average standard.
[7] J. M. Romero-Jerez, C. Tellez-Labao and A. Diaz-Estrella,
“Effect of Power Control Imperfections on the Reverse
Link of Cellular CDMA Networks under Multipath Fad-
ing,” IEEE Transactions on Vehicular Technology, Vol.
53, No. 1, 2004, pp. 61-71. doi:10.1109/TVT.2003.819638
[8] ITU-R, “Minimum Performance Characteristics and Op-
erational Conditions for High Altitude Platform Stations
Providing IMT-2000 in the Bands 1885 - 1980 MHz,
2010 - 2025 MHz and 2110 - 2170 MHz in Regions 1 and
3 and 1885 - 1980 MHz and 2110 - 2160 MHz in Region
2,” Rec. ITU-R M.1456, 2000.
[9] 3GPP TS 22.105, “Services and Service Capabilities,” v.
6.2.0, 2003.
[10] 3GPP TS 23.107, “Quality of Service (QoS) Concept and
Architecture,” v. 6.1.0, 2004.
[11] A. M. Viterbi and A. J. Viterbi, “Erlang Capacity of a
Power Controlled CDMA System,” IEEE Journal on Se-
lected Areas in Communications, Vol. 11, No. 6, 1993, pp.
892-900.
Figure 2. GoS to the rate of incoming calls with imperfect
power control with minimum standard.
are chosen. In deciding whether to accept or reject calls,
the proposed move of two criteria is based on the mini-
mum and the other one is based on the average. It is
based on a minimum measurement of Eb/N0 and an aver-
age criteria (AA) at the lowest level of GoS. According
to the results, AA is the best.
[12] A. J. Viterbi and R. Padovani, “Implications of Mobile
Cellular CDMA,” IEEE Communications Magazine, Vol.
30, No. 12, 1992, pp. 38-41.
[13] F. D. Priscoli and F. Sestini, “Effects of Imperfect Power
Control and User Mobility on a CDMA Cellular Net-
work,” IEEE Journal on Selected Areas in Communica-
tions, Vol. 14, No. 9, 1996, pp. 1809-1817.
Although the hybrid schemes at HAP W-CDMA cel-
lular system are evaluated, they can also be used as
ground-CDMA systems.
[14] G. E. Corazza, G. D. Maio and F. Vatalaro, “CDMA Cel-
lular Systems Performance with Fading, Shadowing, and
Imperfect Power Control,” IEEE Transactions on Vehi-
cular Technology, Vol. 47, No. 2, 1998, pp. 450-459.
doi:10.1109/25.669083 REFERENCES
[15] N. Dimitriou, G. Sfikas and R. Tafazolli, “Quality of Ser-
vice for Multimedia CDMA,” IEEE Communications Ma-
gazine, Vol. 38, No. 7, 2000, pp. 88-94.
doi:10.1109/35.852036
[1] S. Karapantazis and F.-N. Pavlidou, “Call Admission
Control in Multiservice High Altitude Platform (HAP)
W-CDMA Cellular Systems,” Computer Networks, Vol.
51, No. 12, 2007, pp. 3491-3506.
doi:10.1016/j.comnet.2007.02.003