Cellular RF Coverage Design and

Optimization Using Cloudrf Bangladesh Perspective

Sehtab Hossain1 and Saleh Faruque2

,Ph.DDepartment of Electrical Engineering, University of North Dakota,

Grand Forks, ND-58202, U.S.A2Assosciate Professor, Department of Electrical Engineering, University

of North Dakota, Grand Forks, ND-58202, U.S.A

1sehtab@yahoo.com, 2saleh.faruque@engr.und.edu

ABSTRACT: Cellular RF coverage design and optimization are critical to sustain networkperformance, subscriber growth and revenue generation. Day by day subscriber for cellular phone is increasing rapidly, as a result the service needed to be upgraded otherwise the company will lose their profit and subscriber will roam from one companyto another. Therefore, the company has to make extensive plan for cell, cluster and delicate reckon on Traffic Engineering. This paper presents a method of cellular RF design and optimization techniques using Cloudrf in conjunction with GoogleTMearth. Experimental results are presented to illustrate the concept and a tradeoff between loss in profit and customer satisfaction has been derived.

Keywords: Cloudrf, Cellular Coverage, Antenna directivity, Trunking Efficiency

1. Introduction

During the last two decades, therehas been explosive growth in thetelecommunications industry. Withthe addition of e-mail and Internetbrowsing, there will be exponentialincrease in demand, putting theexisting network resources underextreme pressure. As such, servicesfor the cellular network need to beimproved.

In this paper, we present a cost-effective method of improvingexisting cellular RF coverage by

means of “Cloudrf”. “Cloudrf” is afree software which can be operatedin the environment of GoogleTM

earth. That means we can use“Cloudrf” as a plug-in forGoogleTMearth. All the configurationfor Omnidirectional and directionalantenna with several angle downtiltis a feature of this software. Firstwe have to locate the area where wewant to know the coverage footprint.

After sweeping the location inGoogleTMearth “Cloudrf” will showthe coverage footprint of that areawithin few seconds. Generally, cellconsists it spectrum byomnidirectional antenna.Omnidirectional antenna spreadssignal all around it; that’s whysignal spread everywhere but withless power. As a result, oftensubscriber’s line get disconnected.For this case, we should useunidirectional antenna which willprovide more power than that and wehave to reckon Trunking Efficiencywhich is the indicator of revenueand we have to compensate betweenrevenue and cellular coverage forcustomer satisfaction which isdiscussed in section 4.

2. Experimental Procedure

We used “Cloudrf” software in the environment of GoogleTM earth for getting the powerspectrum ofCellular network. Then we sweep “Cloudrf” through Suburban area like Dhaka University,Dhaka, Bangladesh and also denselyurban area like Rifle Square, Rd#3 ,Dhanmondi, Dhaka, Bangladesh and seethe result. First,we useOmnidirectional Antenna then we useDirectional Antenna tilted with theangle of 20˚and 22˚.Then wecalculate Traffic Efficiency toinvestigate the quality of cellularnetwork.

3. Simulated Results

First, we swapped through Dhaka University with Omnidirectional

Antenna and we see that it cover a vast area which is of 5 km radius and 900 MHz Frequency; there are some remote coverage near the main coverage.(Fig.:1)

Fig.1: Coverage footprint of 900 MHz systemin Dhaka University campus.

The configuration for transmitter and receiver antenna is given in Fig:2

Fig.2: Transmitter and receiver configurationfor 900 MHz system.

Then we use unidirectional antenna tilted with 20˚ angle and we get that the area got shrank but power increased and for that network quality got updated. (Fig. 3) Here we also see some remote coverage near the main coverage.

Fig.3: Coverage footprint of 900 MHz systemhaving directional Antenna with 200 downtilt.

Then we go for 1800 MHz Omni directional Antenna and we see that the cellular coverage got smaller but signal power has been improved.(Fig.4)

Fig.5 depict the configuration of Transmitter and Receiver Antenna of 1800 MHz.

Fig.4: Coverage footprint of 1800 MHz system having Omni directional Antenna

Fig.5: Configuration of Transmitter and Receiver of 1800 MHz system

After simulating for unidirectional antenna tilted with 20˚ we see that the area coverage shifted to right and has shrunk more side but with better coverage quality. (Fig.6)

With 22˚ tilted angle the area get more shrank as we use unidirectionalantenna and that’s why subscriber will get better network quality. (Fig.7)

Fig.6: Coverage footprint of 1800 MHz systemhaving Unidirectional antenna with downtilt 20˚

Fig.7: Coverage footprint of 1800 MHz systemhaving Unidirectional antenna with downtilt 22˚

From the simulation it is seen that 22˚ tilted angle has better coveragequality than 20˚ tilted angle coverage.

For the case of Suburban area like Dhaka University we do not need so much planning and antenna designing.But the case of dense urban area like Rifle Square we need extensive planning of Cell Coverage.

For this case we simulated 900MHz Omni directional antenna in Rifle Square. (Fig: 8)

Fig.8: Coverage footprint of 900 MHz system

We didn’t see any remote coverage area near the main coverage area as it is a densely populated area (Dense Urban Area).

For 22˚ tilted Unidirectional are weget smaller area with better coverage. (Fig: 9)

Fig.9: Coverage footprint of 900 MHz systemhaving Unidirectional antenna with downtilt 22˚

For the case of 1800 MHz we get larger area than 900MHz (Fig: 10) but when we use unidirectional antenna area get shrunk. (Fig: 11)

Fig.10: Coverage footprint of 1800 MHz system

Fig.11: Coverage footprint of 1800 MHz systemhaving Unidirectional antenna with downtilt 22˚

4. Trunking Efficiency

As we increase our cellular coverage

Trunking efficiency comes to play.

Trunking Efficiency is the indicator

of Revenue in which a cellular company

solely depends on. Trunking efficiency

(channel utilization efficiency) is

known as a measure of base station

efficiency. It is determined by the

amount of traffic per channel, defined

as:

Efficiency(% )=Traffic in ErlangsNumber of Channels

×100

From the Erlang table with Grade of

Service (GOS) = 2%, we obtain the graph

of Fig.12, which shows the relationship

between efficiency and capacity .We see

that for a given GOS, the efficiency

increases as the number of trunks

(voice circuits) increases. A cell site

having < 15 voice circuits(channels)

is generally inefficient, less cost-

effective and generates poor revenue.

Figure12. Trunking efficiency

curve

To illustrate this further, we consider

an OMNI cell having 48 channels, which

are then sectorized into three as shown

in Fig.13. Although the total number of

channels in the sectorized cell remains

the same, the traffic capacity of the

OMNI cell is higher than the sectorized

cell due to trunking efficiency.

Efficieny (%)

Number of Channels

0102030405060708090

GOS = 2%

0

10

20

30

40

50

60

Capacity(Erlang)

Efficiency curve

Capacity curve

48 channels16 ch.

16 ch.16 ch.

Fig.13 Illustration of trunking

efficiency. ( a) OMNI Cell and (b)

Sectorized Cell

For the Omni Site:k Total number ofchannels available = 48. With GOS=

0.02, the traffic intensity in Erlang

will be= 38.4 Erlang. Therefore

trunking efficiency = 38.4/48 = 0.8

(80%).

For the Sectorized Site, the available

48 channels are divided into three

groups, 16 channels per group.Theefore

with 16 channels per grout, GOS =

0.02, the traffic intensity/group in

Erl.= 9.83. Total traffic in three

sectors(3 x 9.83) = 29.49 Erl.

Therefore trunking efficiency =

29.49/48=0.714 (71.4%).

We see that there is a loss of Trunking Efficiency in sectorized cell. Yet, there is a performance benefit as we shall see in the next section.

5. Carrier to Interference Ratio (C/I)

Now, we calculate Carrier to interference ratio and compare thesetwo scenarios.

For the case of Omnidirectional antenna which has 7 cell cluster will have 6 interferer.then

C/I (dB) = 10log[1/6*(D/R)γ]=18 dB(approximately)

Where ,D/R=√(3N)=√(3x7) = 4.58, D=distance between 2 cell, R= radiusof a cell, N= no. of cells in a cluster, γ = 4 (urban).

For the case of 120˚ sectorized unidirectional antenna, C/I becomes,

C/I = 10log[1/3(√(3xN))γ]= 10log[1/3(√(3x3))4]= 21dB (approx).

Though Trunking efficiency decreasedthen revenue will decrease but network will be improved as C/I ratio is improved, which is a good compromise.

6. Conclusions

From experimental data andsimulation above we can concludethat for the case of suburban areawe can render better service with22˚ tilted directional antennas;decrement of trunking efficiencywill not affect the service. But forthe case of dense urban area we haveto keep in mind about this issue andwe need to cell split to renderbetter service. For that case, totake care of Revenue we can use lessdirectional antenna oromnidirectional antenna in suburbanarea as subscriber are less therethan Densely urban or urban area. Inthis way we can compensate ourrevenue. As “Cloudrf” is a freesoftware for that case cost for theplanning and cellular coveragedesigning will be nullified and only

installation cost will be present.So this is a very cost effectivemethod.

Acknowledgement

This work was supported by the USFulbright Scholar Program 2011-12.

References

[1]www.google.com/googleearth

[2]www.cloudrf.com

[3] Bernard Sklar, “Digital Communications Fundamentals and Applications”, Prentice Hall, 1988.

[4]Saleh Faruque,”Cellular mobile Systems Engineering”, Artech House,1996

[5] Theodore S rapaport ,”Wireless Communications-Principles and Practice”,PrenticeHall,2000

[6] Saleh Faruque, et al., “Broadband Wireless Access Based on Code Division Parallel Access”, US Patent No. 6208615,March 27, 2001

[7] Saleh Faruque, et al., “Frequency Planning for Cellular Network”, US Patent No. 5483667, Jan 9, 1996