Coverage Comparison of UMTS Networks in 900 and 2100 MHzFrequency Bands

Afzal Lodhi, Nishita Hathi, Yiannis Gkekas and Petrit Nahi

AIRCOM InternationalCassini Court, Randalls Research Park, Randalls Way, Leatherhead, Surrey, KT22 7TW, UK

Email:afzal.lodhi @aircominternational.com

Keywords: UMTS900, Network Planning, RSCP, SIR

Abstract

Network Operators' growing interest in deploying UMTS in900 MHz is driven by better coverage compared to UMTS at2 100 MHz, especially in rural and new areas. Lower frequencybands provide a number of benefits, such as better radiowave propagation, improved indoor coverage, cost efficientelectronic devices and above all enormous CAPEX savings.This paper presents a coverage comparison between UMTSnetworks in 900 MHz and 2100 MHz frequency bands. Threekey performance indicators, i.e., Pilot RSCP, E/II0 and SIRare formulated and further employed to compare the expectedcoverage of these networks. The analyses are conducted byusing AIRCOM International's radio network planning tool,ASSET. The results are presented in terms of RSCP and SIRcoverage, highlighting the benefits of UNITS in 900 MHzband.

I Introduction

The provision of UMTS services in a cost effective manner hasposed a major challenge to Operators, especially in sparselypopulated and remote areas. The 900 MHz frequency band canpotentially facilitate the provision of UMTS services to usersin such areas because of the significantly smaller radio wavepropagation path loss and better in-door coverage, as comparedto 2100 MHz band. It has been shown that for the offeringof circuit switched (64 kbps) and packet switched (384 kbps)UMTS services, the required number of sites in 900 MHz bandis reduced by 60% compared to that at 2100 MHz [1, 2].Current network deployments mostly use GSM 900 for blanket(country wide) coverage and UNITS 2100 in urban areas.Comparison of GSM and UMTS link budgets reveals that thecell range for a GSM speech service is similar to the cell rangeof UNITS circuit switched (64 kbps) service; which makesit possible to provide a higher rate service within the samecoverage area by co-locating UNITS and GSM sites in 900MHz band. There are many different deploymentscenarios thatcan be employed. Operators may choose to use the entire900 MHz band for UMITS or they may use part of it forLJMTS. It is envisaged that the initial deployment of UNITS900 network will take place in rural areas. The detaileddeployment guidelines and sharing scenarios for individualUMITS and coexisted UNITS and GSM networks (for bothcoordinated (co-located) and uncoordinated operations) in 900and 1800 MHz bands are provided in [3]. These guidelines

conclude that UNITS networks can be efficiently deployed andco-exist with other UMITS and GSM networks in the samegeographical area by maintaining appropriate carrier spacings.The main benefits of UMTS 900 are due to the lower carrierfrequency which allows the signal to propagate further than itsequivalent at 2100 MHz. This better propagation environmenthelps in manufacturing cost effective electronic devices therebyreducing cost for transmit power, in addition to enormousCAPEX savings by deploying significantly less number ofsites. However, the associated drawback of better propagationis the increased interference in the up-link (UL) and down-link(DL) which adversely affect the network performance.In this paper, we present a coverage comparison of UMTS 900and 2 100 networks by using AIRCOM International's networkplanning tool ASSET. This tool can be used to efficientlydimension/plan co-existed (both coordinated or uncoordinated)UMTS and GSM networks in any frequency band. Consideringthe length of the paper, only the coverage aspect of the UMTSnetworks has been analysed. Three key performance indicators(KPIs) related to coverage have been formulated and furtheremployed to compare the expected coverage of these networks:(i) received signal code power (RSCP), (ii) received chipenergy relative to the total received power spectral densityEI/J, and (iii) signal to interference ratio (SIR).The paper is structured as follows: Section 2 describes thenetwork and propagation models as wewll as the coverage KPIsare also formulated in this section. Section 3 presents thecoverage comparison between UMTS 900 and 2100. Finally,section 4 concludes the paper.

2 Network Model and KPI Formulation

The inter-operability requirements for UTRA-FDD mode in the900 MHz band were finalized by 3GPP in December 2005 andthe results were published in [4]. The 900 MHz band whichfalls in Band Class VIII is defined as the paired bands from 880to 915 MHz in the UL, and from 925 to 960 MHz in the DL.The user equipment (UE) and base station (BS) receiver andtransmitter performances are specified in [5] and [6]. In 3GPP,the UTRA-FDD requirements in different frequency bands areexactly the same except for some differences in RF parameters,hence UMTS 900 supports the same services and data rates asUMTS 2100 but the UE sensitivity requirement is relaxed by3dB from -117 dBm in UNITS 2100 to -114 dBm in UMITS900. The BS sensitivity level remains unchanged.For the comparison of UMTS 900 network coverage withUMTS 2100, the RF planning tool ASSET is used. ASSETallows users to specify detailed UNITS equipment and site

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parameters. These parameters are used in combination withgeographical information systems' (GIS) data, advancedpropagation models and traffic models to perform coverageand capacity analysis. It is well known that the coverage inUMTS networks is heavily dependent on the cell-breathingphenomenon [7]. Hence, the coverage analysis for suchsystems cannot be accurately performed without knowing theextent to which the networks are loaded. ASSET employsa static system level Monte-Carlo simulator to model thiseffect. During the Monte Carlo simulation, a number ofdifferent snapshots of the network are generated whichprovide measures of network load. In general, a snapshotrepresent an average instant in time for a random distributionof UF/terminals. These snapshots are then used in calculationsto obtain statistically valid measurements, giving an estimateof the mean network coverage. In each snapshot, the simulatorsequentially evaluates the terminals (precisely once) to seeif they can make a connection to the network. After eachterminal is evaluated, the interference in the network isupdated before moving on to the next terminal. For eachconnection, the network attempts to connect the terminal usingthe best possible scenario. The connection state of each of theterminals is recorded at the end of each snapshot and used togenerate the final outputs.

where IV." is the time-average total DL Noise power. Forsimplicity, only a single UMTS carrier a has been consideredwhich simplifies R"' a

SJk

(4)

where the thermal noise is given by Ný',"`= KTWrI'-,k with TW andq k7 representing temperature in Kelvin, Chip rate andterminal noise figure, respectively. The time average DL TXpower is given by

I = +pio p~conam

of ~psyjc ±UMTs, (5)

weep~y"w n dn P'Y" are the time-average common andsynchronization channel powers. These are calculated byscaling the control channel powers with their respective activityfactors f3 and expressed as

P commonnj

0ýCCPCH P CCPCH +3S CCPCH S CCPCH

+ ACH pA C'H I~PCH pPJCH()

and

psflc 13,PT SCHpP;-C + 'j S C S 5SCR

Finally, the time-average UMTS TX power P,' 'Ts is defined as

The UMTS coverage is normally determined by the Pchannel RSCP, E/II0 and SIR and the same KPIs have bused in the comparison of 900 and 2100 networks. Next, thentities are formulated in a way they are handled in the McCarlo simulator.

2.1.1 Pilot RSCP

The RSCP for the UMTS cell J, terminal k and UMTS cara can be expressed as [7, 8]

where p.gd7 is the Pilot channel TX power and Lilk is theloss given by

Lik=L os k Jpt~o tennan L L Lmha LsplitterJik JK k U.J

where L and G represent losses and gains, respectively. NVhead amplifier (mha) loss is given by Lmho.

2.1.2 Pilot E,/h,

It is defined as the received chip energy, E, relative to the tireceived power spectral density, I,, and can be expressed as

RSCP

(8)k k

whr ~and 31 are the DL traffic channel activity and and itscontrol overhead factors, respectively. The DL traffic channelTX power (only when active) is given by P1K

2.1.3 Pilot SIR

The only difference between Pilot E,1I, and Pilot SIR is thatthe own cell Pilot TX power is not considered as interferenceand can be expressed as [8]

E IR -plIi

R~J RJL4J - .(pconrnmof + pUMfTS) -paPiI! (9ak Jk a C'J c.J

where Ej is the cell orthogonality factor.From (8) and (9), it can he seen that both, Plot E,1I0 and SIRare affected by interference which ultimately depends on thesystem load.

2.2 Propagation Model

The widely used Okumura Hata empirical propagation model isconsidered for calculating the path loss at each pixel/terminallocation. This model can be used in the frequency ranges of500-2200 MHz [7]. The basic equation describing the Hatamodel is given by

Path Loss(dB) = ki + k2 logd + k3 H,. + k4 logHm,,

(3) ±k5logHef f± k 61logH~fflog(d) + k7(Difr loss) (10)

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2.1 Coverage KPIs

(7)

Parameters UMTS 90 UMTS 200]frequency(MHz) 900 2100

k_______ 150.60 162.50k2______ 44.90 44.900

k;3 -2.55 -2.55k40.0 0.0

k,5 -13.82 -13.82k6 -6.55 -6.55

k70.70 0.80__

suburban and rural environments, an area of 30 Km' is chosenwhich includes a range of clutter types and height profiles.For fair comparison, identical three sector UMTS sites aredeployed in the test area with respective 900 MHz and 2100MHz propagation models. The cell and terminal parametersettings are given in table 2. For simplicity, a uniformlydistributed traffic model is used by spreading 1200 terminalsacross the geographic area under consideration. Each terminalis subscribed to a single 12.2 kbps service for which thecoverage KPIs' requirements are used as per table 3.

Table 1: Propagation models parameter settings.

where d represents the distance (kin) from base station (BS)to mobile station (MS) and Hmsý, Hfjj are the height (in) ofMS above ground, effective MS height and effective BS height(in). ki and k 2 represent the constant offset and multiplyingfactors for the log of distance between BS and MS. k3 is the MSantenna height correction factor. k4 and k5 are the multiplyingfactors for the log of MS height and the log of effective antennaheight, respectively. k6 and k 7 are the multiplying factorsfor logHJf flogd and diffraction loss (Diff Loss), respectively.Finally, the k parameters were tuned for 900 and 2100 MHzfrequency bands with the values given in table 1.

3 Coverage Comparison

The comparison between UMTS 900 and 2100 networks issimulated for the island of Jersey. To model a mixture of urban,

Cell ParametersPilot Power (dBm) P,,,"l 33

Cell Antennas Gain (dBi) Git f~ 7.8Max TX Power (dBm) 43

P-CCPCH Power (dBm) P~ cc( 3-0Activity Cý CPCH 0.9

S-CCPCH Power (dBm) PS-C7 r7?TJ 2-7Activity oSCCPCH

P-SCH Power (dBm) -Tj -30Activity Of si 0.1

S -S CH Pow er (d Bm rn 27Activity OjSJ-SCH 0.1

AICH Power (dBm) P~l 22Activity /,3 AC 0.2

PICH Power (dBm) P1jCH 22Activity 0 jC 0.2

Noise Rise Limit (dB) ______ 3Orthogonality Factor ______0.65

Terminal ParametersTerminal Antenna Gain (dBi) Gk~C~ Iý 0

Body Loss (dB) L-Y 0

RSCP 114 dBmE~/I0 -1l3dBSIR -15dB

Table 3: Coverage KPIs minimum requirements.

3.1 Pilot RSCP Comparison

In Fig. 1, the best RSCP plot is shown for UMTS 2100 networkwhere the sites are placed by ensuring the minimum RSCPrequirement is satisfied in 95% of the analysis area. This plotdepicts a picture of average highest RSCP levels and thereforecalculated with fades of 0 dB (no shadowing). It can be seenthat for the required RSCP levels a minimum of 21 sites arerequired to provide adequate coverage. In comparison, thebest RSCP plot of UMTS 900 network is shown in Fig. 2.Again, by using the required RSCP levels UMTS 900 sitesare placed ensuring 95% coverage in the analysis area. Asexpected, the plot shows that UMTS 900 requires only 12 sitesto provide better coverage than UMTS 2 100, thereby reducing.approximately 60% of the original number of sites.

Figure 1: Best Pilot RSCP plot for UMTS 2 100 network.

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Table 2: Cell and terminal parameter settings.

Figure 2: Best Pilot RSCP plot for UNITS 900 network. Figure 4: Pilot SIR plot for UMITS 900 network.

3.2 Pilot SIR Comparison

In Figs. 3 and 4, the SIR plots are shown for UMTS 2100 and900 networks, respectively. These plots are generated afterrunning 100 snapshots and as they also depict a picture ofaverage highest SIR levels, therefore calculated with fades of 0dB. It can be noticed that the amount of simulated traffic plusthe power and resource activity factors of the 12.2 kbps serviceprovides high enough SIR values for UMITS 900 by even using60% of the total sites than UMTS 2 100. Pilot SIR varies hugelywith outer cell interference, hence the above observation is onlytrue for this scenario and can change depending on the amountof traffic, the service type (packet switched or circuit switched)

Figure 3: Pilot SIR plot for UMTS 2100 network.

and their respective activity factors. The E/II0 plots alsodisplay similar trends to that of SIR plots, hence not includeddue to the restricted length of the paper.

4 Concluding Remarks

A brief coverage comparison between UMTS 900 and 2100is presented highlighting the enormous CAPEX savings thatcan be realized by using UMTS 900. With the ever increasingdemand for higher data rate services, UNITS 900 provides aperfect replacement of GSM in 900 MHz Band.

References

[1] UMITS Forum white paper. "Deployment of UMTS in900 MHz band", 2006.

[2] H. Holma and T. Ahonpiiii and Eetu Prieur, "UNITS 900co-existence with GSM 900," IEEE VTC, April 2007.

[3] ECC Report 82, "Compatibility study for UMITSoperarting within the GSM 900 and GSM 900 MHz and1800 frequency bands", May 2006.

[4] 3GPP. TSG RAN. UNITS 900 MHz work item technicalreport. 3GPP TR 25.816, 7.0.0, Release 7.

[5] 3GPP. TSG RAN. BS radio transmission and reception(FDD). 3GPP TR 25.104, 7.5.0, Release 7.

[6] 3GPP. TSG RAN. UE radio transmission and reception(FDD). 3GPP TR 25.101, 7.6.0, Release 7.

[7] J. Laiho, A. Wacker and T. Novosad, Radio networkplanning and optimization for UMTS, Wiley, 2002.

[8] AIRCOM International, "ASSET User Guide," July2007.

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