© 2005 Bechtel Corporation. All rights reserved. 57

INTRODUCTION

Radio planning in third-generation (3G)networks [1] is fundamentally different from

radio planning in second-generation (2G)networks. The major difference is that networkcarriers expect to be able to reuse most of theirexisting 2G site infrastructure for 3G deployment.When 2G networks were originally designed anddeployed, all or most of the sites weregreenfields; in 3G networks, on the other hand,carriers want only a small portion of greenfieldsites. This is, of course, due to business andfinancial considerations, since developinggreenfield sites is associated with higher costsand longer time to market, compared toupgrading existing 2G sites. The percentage ofexisting 2G sites in 3G networks typically rangesfrom 70 to 95. Consequently, one cannot speak ofradio design for 3G in the same terms as for 2G.In 3G, the starting point for radio design is thecoverage achieved using existing 2G sites; newsites are used to “fill the holes” and providecontinuous 3G coverage in accordance with thedesired key performance indicators (KPIs). Thisapproach generally results in a less-than-optimaldesign and puts more emphasis on the pre-launchand post-launch optimization phases.

The opportunity to use 2G drive test data in theradio design of 3G networks is advantageous.Since the existing 2G sites constitute most of the3G network sites, the drive test data from the 2Gnetwork can be used to pinpoint areas where theexisting 2G sites cannot provide adequate 3Gcoverage. This data, accompanied by the analysisperformed using radio planning tools, can then

be used to determine the number and bestlocations of new 3G sites. The importance of drivetest data rises in areas inherently unfriendly toradio planning tools, such as dense urban areas.

To be used in the 3G radio planning process, 2Gdrive test data must be scaled to 3G signal levels.Also, since 3G planning is equally based oncommon pilot channel (CPICH) coverage plotsand on CPICH power-to-total-interference pluscarrier-to-interference (notationally, Ec/Io) noiseratio plots, Ec/Io coverage needs to be estimatedfrom the 2G drive test data. This paper presentsthe method for doing so.

A case study is also presented illustrating the useof 2G drive test data for the radio design of a 3Guniversal mobile telecommunications system(UMTS) network in a large central businessdistrict (CBD). This approach provides crucialinsight into the validity of the radio design whenthe design based on the radio planning toolsproves to be unreliable due to low propagationmodel resolution and the very nature of urbandowntown clutter. This approach also allowseach proposed new site to be analyzed andcoverage holes and areas with potential qualityissues to be predicted, resulting in an increasedoverall level of confidence in the radio design.

While this paper focuses on the use of globalsystem for mobile communication (GSM) drivetest data, the approach can be applied easily toother 2G technologies. In fact, it is even bettersuited for code division multiple access (CDMA)systems, such as those based on theTelecommunications Industry Association (TIA)

USING 2G DRIVE TEST DATA FOR 3G UMTS RADIO PLANNING IN A LARGE CBD:A CASE STUDY

USING 2G DRIVE TEST DATA FOR 3G UMTS RADIO PLANNING IN A LARGE CBD:A CASE STUDY

Abstract—This paper presents a method for using GSM BCCH drive test data to estimate CPICH coverageand Ec/Io coverage in 3G UMTS or CDMA networks. The benefits of the presented method are twofold: first,it can be used to estimate coverage achievable using the existing 2G sites only. Second, it can complementpredictions obtained using radio planning tools in scenarios where the predictions are inherently less reliable,such as dense urban areas. The results obtained from applying this method to the radio design of a 3G UMTSnetwork in a large CBD are also presented.

Issue Date: August 2005Issue Date: August 2005

Suvath Lee slee@bechtel.com

Amer Catovicacatovic@bechtel.com

Bechtel Telecommunications Technical Journal 58

Interim Standard 95 (IS-95). In general, it is safe tosay that 2G drive test data can be used as astandard procedure to enhance UMTS andCDMA radio frequency (RF) designs, especiallyin downtown and other difficult areas.

PROBLEM STATEMENT

Anew 3G UMTS network was to be designedfor a large, grid-like CBD with many

extremely tall buildings and a population of morethan 3 million people (Figure 1).

According to existing 2G estimates, between 30 and 40 percent of users were located in theCBD, accounting for most of the high-data-rateservices and making the CBD the major revenue-generating area. This must be kept inmind when performing radio design.

The two major design criteria used in the firstiteration of radio design to fix site count andrough site locations are CPICH signal strengthand Ec/Io level. (In later iterations, simulations ofdifferent services based on specific trafficdistribution are used for fine-tuning andoptimization.) For the case study, the targetoutdoor values for these two parameters for anunloaded network in a CBD were set to –81 dBmand –10 dB, respectively.

Radio design based on CPICH signal strengthand Ec/Io level is usually performed using aradio planning tool. However, for the case study,only a propagation model with a 50 m x 50 mresolution was available. In CBDs, thiscorresponds to one street block and is highlyunreliable. Hence, conventional radio planningbased on a planning tool was not feasible. On theother hand, even when a high-resolution model isavailable, it is difficult to accurately model theradio environment in CBDs. First, the radio signalpropagates differently at low heights than at highheights; using the same propagation model forboth results in an inaccurate design. Also, UMTSis extremely sensitive to inter-site interference,whereby even adjacent sites interfere with eachother. In CBDs, this situation is hard to model.Finally, strong multipath, which is the majorcharacteristic of downtown clutter, is impossibleto model accurately. So, for the case study it wasessential that the design be supported byalternative, creative methods.

In the case study, planners had originally reliedon site visits to perform analyses. They haddiligently scouted the entire CBD, taking manyphotos and marking important objects andlandmarks, as well as potential problem areas.They also shot videos and developed a goodgrasp of the techniques used to obtain 360-degreepanoramic views from important locations.During the desktop analysis, they combined thephotos, videos, and propagation maps to producea radio design. Unfortunately, although thisapproach is diligent and provides good insightinto the geographical characteristics of an area, itlacks the technical insight obtainable onlythrough solid, reliable radio analysis.

An additional constraint placed on the casestudy’s design was that existing 2G network sites

ABBREVIATIONS, ACRONYMS, AND TERMS

2G second generation

3G third generation

BCCH broadcast control channel

CBD central business district

CDMA code division multipleaccess

CPICH common pilot channel

Ec/Io ratio of the signal energy within one chip duration ofthe pilot signal to the powerspectrum of the interference and noise

GSM global system for mobilecommunication

KPI key performance indicator

RF radio frequency

RSCP received signal code power

UMTS universal mobile telecommunications system

Figure 1. CBD Map

August 2005 • Volume 3, Number 1 59

had to be used to the extent possible. It should benoted that network-wide 2G use of these siteswas approximately 85 percent.

The original radio design for the CBD gridconsisted of 23 sites (Figure 2), of which 12 were existing and 11 were new. However, theradio planning team’s efforts to provide crediblejustification for each site were hampered by theabsence of solid radio analysis. Furthermore, thisnumber seemed high, especially because theinitial forecast was for 17 sites and an existing 3Gcarrier had 17 sites in its CBD design. On theother hand, the reported call failure rate in theexisting 3G carrier’s network was 18 percent,which pushed that carrier to announce plans toadd 7 or 8 CBD sites. Because the number of sitesequally affects quality, cost, and time to market, itwas decided for the case study to conduct athorough design review and site-by-sitejustification for the 23-site count.

Analysis based on radio measurements of theexisting 2G site coverage, extrapolated to 3Gradio conditions, was proposed. Measurementsfrom 2G GSM 1800 MHz drive tests were used toderive the equivalent CPICH power and Ec/Ioplots for a UMTS RF signal. The resulting benefitsof this analysis were twofold: first, threeproposed new sites were removed from thedesign without affecting the quality, generatinghuge cost and time-to-market savings; second, the radio planning team successfullyused the analysis in its report to justify the sitecount on a site-by-site basis.

The approach described in this paper focused onanalyzing the 3G coverage achievable by usingexisting 2G sites. The GSM 1800 MHz broadcastcommon channel (BCCH) drive test measurementswere used to predict the CPICH and Ec/Iocoverage for UMTS 2100 MHz, thereby exposingany coverage holes to be filled with new sites.Using this method, it was possible to see whethercoverage overlapped among existing 2G sites andproposed new sites. If the coverage (either CPICHor Ec/Io) provided by existing 2G sites had a holeat the same location where a new site was

proposed, then the new site was considered to be justified. On the other hand, it would have been hard to justify the existence of a new site where existing 2G sites already provided good coverage.

First, a GSM 1800 MHz drive test wasperformed. Then, the results were post-processedto obtain estimates of the UMTS 2100 MHzCPICH and Ec/Io coverage. Finally, an analysiswas performed to justify the existence of eachnew site.

GSM 1800 MHz Drive TestThe GSM 1800 MHz BCCH drive test wasperformed in idle mode to capture all recordablecarriers at each location in the CBD. GSM BCCHnumbers were obtained from the performanceengineers, and the drive test results wererecorded (see Figure 3). For each measurement,the best server BCCH was retained as thereceived signal strength, i.e., best BCCH equalsreceived signal code power (RSCP).

To improve both the location accuracy and thesignal strength accuracy of the measured data,the measurements were averaged over a distanceof approximately 14 m.

Figure 2. CBD Radio Design

Figure 3. 2G Drive Test Measurements

Bechtel Telecommunications Technical Journal 60

UMTS CPICH Coverage Plot Generation The first step in generating CPICH coverage plots was to convert the GSM RSCP measurementsinto the equivalent UMTS CPICH power levels.The BCCH transmit power was 43 dBm, 10 dBabove the UMTS CPICH power level of 33 dBm.Also, free-space attenuation of an 1800 MHz RFsignal was 1.2 dB below attenuation at 2100 MHz. Finally, TEMS™ DriveTesterindicated a net loss of 1.8 dB (6 dB feeder lossand 4.2 dBi antenna gain). Table 1summarizes the difference between the measuredGSM RSCP and the UMTS CPICH.

Based on Table 1, the measured GSM RSCP was9.4 dB above the level that would have beenmeasured by the mobile terminal if the UMTS

2100 MHz signal had been transmitted from theexisting 2G sites. So with a target CPICH powerlevel of –81 dBm, the equivalent GSM 1800 MHz signal strength is –81 dBm + 9.4 dB = –71.6 dBm ≈ –72 dBm.

Therefore, a measured GSM 1800 MHz signalhigher than –72 dBm yields a UMTS CPICHsignal higher than the target –81 dBm, makingthe coverage provided by the existing 2G sitesadequate. By the same token, a measured GSM1800 MHz RSCP lower than –72 dBm indicates acoverage hole to be addressed by a new site(s).

Figure 4 shows the plot of the case study’s GSMRSCP drive test data for existing CBD 2G sites.The green points represent locations where theestimated UMTS CPICH coverage from existing2G sites would be acceptable, i.e., better than –81 dBm, which corresponds to a measured GSMRSCP of –72 dBm or better. The yellow pointsrepresent estimated coverage holes.

UMTS 2100 MHz Ec/Io Plot GenerationA CPICH power plot provides basic informationabout coverage, but in UMTS, Ec/Io level bestrepresents the quality of the received signal [2].Basic radio resource management decisions, suchas soft handover, soft handoff, and cell selection,are based on the received Ec/Io level. Therefore,it is essential to obtain good insight regardingEc/Io coverage during the design stage.

TEMS Antenna Gain 4.2 dBi

TEMS Cable Loss –6 dB

TEMS Net Loss –1.8 dB

Attenuation Difference Between 1.8 GHz and 2.1 MHz

1.2 dB

GSM BCCH (43 dBm) –UMTS CPICH (33 dBm) Transmit Power

10 dB

Total Difference BetweenGSM RSCP and UMTS CPICH

10–1.8+1.2 = 9.4 dB

Table 1. Difference Between Measured GSM RSCP and UMTS CPICH

Basic radioresource

managementdecisions, such as

soft handover,soft handoff, and

cell selection, are based on the receivedEc /Io level.

M0246

33144M0001

33146

M0545

M0044 M0462

33255

M095433145

M0956

33175

Figure 4. Measured 2G Signal Strength

August 2005 • Volume 3, Number 1 61

Ec/Io represents the ratio of the best-receivedCPICH power to the total received power in thebandwidth, which includes the thermal noise. So:

(1)

To use GSM measurements in the case study, thebest BCCH was used as the best pilot. The powersof all received BCCHs were summed to computethe total received BCCH power. To simulate theUMTS environment as closely as possible,thermal noise power was also added to the totalreceived BCCH power, i.e.:

(2)

Noise power in the 200 kHz band is:

N = kT · W = –121 dBm (3)

where kT is the noise spectral density of –174 dBm, with W = 200 kHz.

The multiplication by a factor of two in thedenominator of Eq. 2 represents the effect of theinterference power of the common controlchannels, which are transmitted by the UMTSbase station along with the CPICH. The aggregatepower of these common control channels varies,

but is very similar to the CPICH power, hence thereason for using a factor of two.

The Figure 3 spreadsheet was also used to derivethe estimate for the UMTS Ec/Io values. The bestBCCH power in each row (i.e., location) is themaximum of the values under the columnheadings and appears in the third column fromthe right. The total received power, whichappears in the second column from the right, isthe sum of all columns, multiplied by two, plusthe thermal noise power. The Ec/Io value foreach row is the ratio of the two values, whichappears in the last column.

The fact that the noise power is negligiblecompared to the received BCCH powerseliminates the need to scale the BCCH powers tothe equivalent CPICH power levels, as was donein the previous section, since both the numeratorand the denominator would have to be scaled,thereby cancelling each other.

Figure 5 shows the Ec/Io value as computedfrom the measurements of the GSM signal fromthe existing 2G sites. It is clear from the figure thatthe values obtained are within the range oftypical UMTS Ec/Io values, which reaffirms thecorrectness of the approach taken for this study.The red points represent locations where theestimated UMTS Ec/Io coverage from theexisting 2G sites is not adequate.

33160

33037

M0465

M0333

M0546

33175

M095433145

M0956

3302

M0462

M0545

33255

33144

M0246

M0044

M0001

33146

NodeB285_N

NodeB300_N

NodeB283_N

NodeB284_NNodeB360_N

NodeB290_N

NodeB287_T

NodeB343_T

NodeB286_H

NodeB289_N

NodeB288_

Figure 5. Ec/Io Plot Based on the 2G Drive Test

=(Sum of all BCCH powers) ×

2 + noise power

Best BCCH powerEcI0

⎞⎟⎠⎞⎟⎠ measured

= Total received powersBest pilot powerEc

I0

Bechtel Telecommunications Technical Journal 62

ANALYSIS

CPICH PlotFigure 6 shows the study areas with CPICHcoverage problems based on the analysisperformed for the study. Based on this plot, proposed new Nodes B283, B284, B286, B288,and B360 are justified from the standpoint ofsecuring adequate CPICH coverage in theseproblematic areas. No further argument wasnecessary to justify the existence of these sites.

Ec/Io PlotFigure 7 shows the study areas withunsatisfactory Ec/Io levels, based on the analysisperformed for the study. The Ec/Io values shownare taken from the last column in the Figure 3spreadsheet. From the plot, it is evident that (a) the proposed new sites that were justifiedfrom the CPICH coverage perspective are alsojustified from the Ec/Io coverage perspective,and (b) proposed new Nodes B289, B290, and B300 are required to fill in the obvious Ec/Iocoverage holes in their proximity.

Neither coverage perspective—CPICH orEc/Io—justifies adding proposed new NodesB285, B287, and B343. Note that the Ec/Iocoverage hole east of Node B343 will be filled by

Node B288 once it is in place. Therefore, based onthe analysis, these three sites cannot be justified.All other new sites are justified. A summary ofthe analysis is provided in Table 2.

Cost SavingsThe average cost of building a new rooftop site in the case study CBD ranges between US$227,000 and US$265,000. This makes the costsavings generated by eliminating the threeunjustified sites nearly US$757,000 for only thissmall portion of the network. A similar analysisfor the entire network should achieveproportionally higher savings.

CONCLUSIONS

This paper presents a method for using datafrom existing 2G sites to estimate the

achievable UMTS CPICH and Ec/Io coverage by measuring 2G GSM BCCH levels andextrapolating the measurements to equivalentestimated UMTS coverage. This method can andshould be used whenever the UMTS design reliesheavily on existing 2G sites, which is nearlyalways the case. It is particularly useful andnecessary in dense urban areas, where accurateradio propagation models are not available.

Creating CPICHand Ec /Io

coverage plotsbased on 2G drive

tests beforecommencing 3Gradio planning

provides a crucialstarting point forquality optimalradio design.

NodeB284

NodeB283

NodeB300

NodeB285

NodeB360

NodeB290

NodeB286

NodeB343

NodeB287

NodeB288

NodeB289

Figure 6. 3G CPICH Coverage Problem Areas Based on the 2G Drive Test

In its use to design the 3G UMTS network for thecase study CBD, this method achieved two goals:first, credible radio analysis of proposed new siteswas provided in the absence of a reliable radioplanning tool; second, 3 out of 11 proposed new sites were eliminated without sacrificing

coverage quality, thus saving approximatelyUS$757,000 in capital spending. The radioplanning team accepted the analysis as a credibleway to justify the necessity for new sites in thecase study CBD and also to show that some siteswere not necessary. The analysis was the singlemost important element in the approval of theradio design and the accompanying site list.

Based on the results of this case study, it is highly recommended that this method beconsidered a standard general procedure forUMTS and CDMA radio planning. CreatingCPICH and Ec/Io coverage plots based on 2Gdrive tests before commencing 3G radio planningprovides a crucial starting point for qualityoptimal radio design. �

TRADEMARKS

TEMS is a trademark of Telefonaktiebolaget LMEricsson, Sweden.

REFERENCES

[1] J. Laiho, A. Wacker, and T. Novosad, RadioNetwork Planning and Optimisation for UMTS, John Wiley & Sons Ltd., 2002.

[2] H. Holma and A. Toskala, WCDMA for UMTS:Radio Access for Third Generation MobileCommunications, Second Edition, John Wiley &Sons Ltd., 2002.

August 2005 • Volume 3, Number 1 63

Table 2. Summary of Site-by-Site Analysis

SITEJUSTIFIEDBY CPICH

PLOT

JUSTIFIEDBY EC / IO

PLOT

NOTJUSTIFIEDPER THEANALYSIS

Node B283 �� ��

Node B284 �� ��

Node B285 ��

Node B286 �� ��

Node B287 ��

Node B288 �� ��

Node B289 ��

Node B290 ��

Node B300 ��

Node B343 ��

Node B360 �� ��

33160

M0333

33037

33255

33145

33175

M0044

M0001

33144

M0954

M0546

M0956

M0462

33146

3302

M0545

M0465M0465

NodeB283_N

NodeB300_N

NodeB285_N

NodeB286_H

NodeB287_T

NodeB343_T

NodeB288_N

NodeB289_NNodeB360_N

NodeB284_N

NodeB290_N

Figure 7. Ec/Io Problem Areas Based on the 2G Drive Test

Bechtel Telecommunications Technical Journal 64

BIOGRAPHIES

Suvath Lee joined BechtelTelecommunications in 2004and is currently working as asenior UMTS RF engineer inBechtel’s Asia-Pacific Region.

Suvath has 11 years ofexperience in the telecommuni-cations industry, includingmore than 7 years in RFplanning, design, and

optimization of cellular networks. His experienceincludes working for mobile network operators,vendors, consulting firms, and the telecommunicationsregulatory authority. Before joining Bechtel, Suvath wasinvolved in RF planning and optimizing GSM900/1800 MHz, broadband wireless access, and UMTSnetworks. He also worked for Ericsson and Motorola inthe RF design and optimization of Hutchison’s UMTSnetwork in Sydney, Australia, and for Vodafone andLucent Technologies on GSM networks.

Suvath received his BSc in Engineering, with a major intelecommunications, from the University of New SouthWales, Australia.

Amer Catovic joined BechtelTelecommunications in 2003.He is currently a senior UMTSRF engineer on assignment toBechtel’s Asia-Pacific Region.Before this, as a wireless systemengineer with the New JerseyCenter for Wireless Tele-communications, he worked onseveral projects related to the

different aspects of technology and services for next-generation wireless networks, funded by world leadersin the field. Earlier, as a data network engineer withLucent Technologies’ NetCare division, he designed,implemented, tested, and provisioned the infrastructureand services in large-scale core broadband networks.He began his career in 1997 as an RF engineer withMotorola, Turkey.

A member of the Institute of Electrical and ElectronicsEngineers, Dr. Catovic has published numerous papersin international journals and conferences. His areas ofresearch include capacity and coverage optimizationtechniques for UMTS, location estimation techniquesfor wireless networks, resource and mobilitymanagement for wireless networks, and 4G networks.Dr. Catovic is the co-winner of Bechtel Telecom-munications’ Network Planning Alternative DesignAward for 2003. He is a Six Sigma Yellow Belt.

Dr. Catovic received his PhD in WirelessTelecommunications, with emphasis on 3G and 4Gnetworks, from the New Jersey Institute of Technologyin Newark, New Jersey. He received his MS in ElectricalEngineering from Bosphorus University, Istanbul,Turkey, and a joint BS in Electronics Engineering fromUniversité des Sciences et de la Technologie d’Oran,Algeria, and University of Sarajevo, Bosnia.