Call Admission Control in HAP W-CDMA Cellular Systems

doi:10.4236/ijcns.2013.68040

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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

Email: [email protected]

Received June 15, 2013; revised July 15, 2013; accepted July 25, 2013

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

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].



34.83,for 04.53

1.57

9.8,for 4.535.87

55.9560log,for 5.8737

38.2,for 3790



































(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)



EN WR

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





. 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

nth  All the interfering signals are un-

der the effect of power control with same statistical speci-

fication of any signal.

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



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

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[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