business case scenarios in the deployment of a wimax™ network

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Business Case Scenariosin the Deployment of a

WiMAX NetworkMarch 2009


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Business Case Scenarios in the Deployment of a WiMAX Network

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Table of Contents

Business Case Scenarios in the Deployment of a WiMAX Network ................. 7

1.0 Introduction ................................................................................................... 7

2.0 Spectrum Choices......................................................................................... 8

2.1 A Comparison of 700 MHz, 2500 MHz, and 3500 MHz: ............................. 9

2.2 Amount of Usable Spectrum: .................................................................... 10

2.3 Frequency Division or Time Division Duplexing ........................................ 12

3.0 Reuse 1 or Reuse 3 ................................................................................... 15

4.0 Alternative Usage Models .......................................................................... 18

4.1 Mobility with Reliable Indoor Coverage ..................................................... 18

4.2 Mobility with Best Effort Indoor Coverage ............................................... 18

4.3 Fixed Usage Model ................................................................................... 194.4 Usage Models: Summary .......................................................................... 19

5.0 WiMAX Base Station Antenna Configurations ........................................... 20

6.0 Conclusion ................................................................................................. 22

References.......................................................................................................... 23


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Figures

Figure 1: Range and Path Loss Comparison........................................................ 9

Figure 2: Meeting Capacity Requirements.......................................................... 11

Figure 3: Upper 700 MHz Band in the US .......................................................... 13

Figure 4: Relative Number of Base Stations Required for TDD or FDD to Meet aSpecific DL Data Density Requirement ....................................................... 15

Figure 5: Frequency Reuse Factor of 1 .............................................................. 16

Figure 6: Frequency Reuse Factor of 3 .............................................................. 17

Figure 7: Varied Usage Models Result in Wide Variation in Coverage............... 20

Figure 8: Advanced Antenna Systems Lowers the Cost/Mbit............................. 21

TablesTable 1: Summary of Comparative Attributes of TDD and FDD ......................... 14


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Business Case Scenarios in the Deployment of aWiMAX Network

1.0 Introduction

It is very important for the operator or network planner to consider a variety offactors before forging ahead with WiMAX equipment choices and deploymentalternatives. This white paper is intended to provide the reader with a perspectiveon the implications that various deployment choices have on the complexity andcost-effectiveness of the final WiMAX network.

From a business case perspective this paper does not go into a detailed financialanalysis of the various alternatives discussed. A detailed study of this nature isbest done on an operator-by-operator basis since it is not possible to generalize

the wide range of variables required for this kind of analysis. One metric howeverthat does seem to be universal in an attempt to quantify differences betweendeployment choices is base station count. Whether dealing with an overlay or aGreenfield deployment scenario the number of base stations required to achievethe necessary geographic coverage or to meet specific data densityrequirements represents the biggest contributor to the overall end-to-end networkinvestment. Base station count therefore, is a good indicator for assessing theviability of the business case. In this context the base station not only includesthe WiMAX equipment but the site development costs which include siteacquisition, towers, weatherized electronic enclosures, cabling, stand-by power,backhaul, etc. Discussions with various operators and network planners indicate

that the WiMAX equipment costs can range from as little as 15% to no more than30% of the total base station cost for a facilities-based operator. The high basestation infrastructure cost has caused many operators to follow a business modelthat shares the base station infrastructure among multiple operators. The WiMAXequipment cost in this case plays a more dominant relative role. Anotherbusiness model that is prevalent is one in which the base station infrastructure isleased. This model simply translates base station infrastructure CAPEX toOPEX. Whichever model is followed, the costs associated with the base stationaccess network will still have a major impact on the viability of the business case.From an investment perspective therefore, the key metric in evaluating thetradeoffs between the deployment choices discussed in this paper will be base

station count.Many factors influence the number of base stations necessary to achieve either aspecific data density required for dense urban or urban regions or to achieveadequate range and coverage over a less populated suburban or rural region.Factors that affect base station count that are discussed in this paper are:frequency band, amount of available spectrum, duplex choice, frequency reuse,usage model, and base station antenna configurations.


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In Section 2.0 various spectrum band choices are considered ranging from 700MHz to 3500 MHz. Closely aligned with the frequency band alternatives is theamount of usable spectrum associated with the different bands and the relativebenefits of deploying with time division (TDD) or frequency division duplex (FDD).

Frequency reuse factors are discussed in Section 3.0. If sufficient usable

spectrum is available a conservative reuse factor will improve channel spectralefficiency and thus provide increased channel throughput but may not always bethe best and most efficient use of the total spectrum assignment.

Section 4.0 provides a discussion of the tradeoffs associated with the choice ofwhich usage model to address. These choices can range from a mobile usagemodel addressing both in-building and outdoor coverage to a fixed usage modelwith the deployment of roof top subscriber units to maximize coverage area witha minimal deployment of base stations.

Section 5.0 provides a brief discussion regarding the relative merits of thevarious base station advanced antenna systems supported by WiMAX.

References listed at the end of the paper are cited throughout the discussion forthe reader desiring to explore the various topics discussed in this paper ingreater detail.

2.0 Spectrum Choices

In many countries the regulatory regime has already determined or will determinethe frequency band and channelization scheme for the licenses issued forWiMAX deployments. In many countries there may only be one choice availablewhile in other countries there may be two or more frequency bands that

operators can consider for the acquisition of spectrum for their WiMAXdeployment. There may also be cases in which prospective operators will be in aposition to provide inputs and suggestions to regulators as to spectrum andchannelization schemes that are best suited for the delivery of broadbandservices over a WiMAX network. In this section we provide some insights as tothe tradeoffs that must be considered with regard to spectrum choices.Specifically we look at:

Frequency band: 700 MHz vs. higher bands in the 2500 and 3500 MHzrange

Amount of spectrum: 10 MHz vs. 30 MHz

Duplexing: FDD or TDD


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2.1 A Comparison of 700 MHz, 2500 MHz, and 3500 MHz:

For comparative purposes the range of country-by-country spectrum alternativescan be conveniently sorted into three groupings; 700 MHz1, 2500 MHz2, and3500 MHz3. From a propagation range perspective the lower bands have anobvious advantage due to the lower path loss. This is illustrated in Figure 1 which

shows the expected path loss versus cell radius for the three frequency bands[Ref. 1]. For a comparable system gain, a 700 MHz deployment will provide aconsiderable range advantage over a 2500 MHz or 3500 MHz deployment. Thisattribute makes 700 MHz especially attractive to cost-effectively cover sparselypopulated regions [Ref. 2].

Figure 1: Range and Path Loss Comparison

Lower building penetration loss in the 700 MHz band can greatly improve thequality of in-building coverage for mobile services and lower cable loss can alsobe used to advantage. Cable loss will be a consideration when base-mountedtransmit power amplifiers are deployed in lieu of tower-mounted transmitters. Inthese cases the transmit power must be sufficient to overcome the cable loss. Inthe 2500 MHz or 3500 MHz band cable losses can range from approximately 2dB for a high performance cable to almost 6 dB for a lower cost cable for a 32

meter tower height. For the same types of cable in the 700 MHz band theselosses will range from 1 dB to about 3 dB. To achieve the same transmit power at

1Includes bands between 450 MHz to 960 MHz also known as UHF

2Includes bands between 2300-2690 MHz

3Includes bands between 3300-3800 MHz


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The chart in Figure 2 summarizes the impact of limited spectrum in an urbanenvironment covering an area of 100 sq-km requiring a high downlink datadensity4.

Figure 2: Meeting Capacity Requirements

Key lessons from the data presented in Figure 2 are:

a) Having 3 times more usable spectrum, in this case, 30 MHz vs. 10 MHz,provides greater than 3 times benefit5 in base station infrastructure costs incapacity-constrained deployments that require data densities of 20 Mbps/sq-km or more. Data density requirements of this magnitude are projected to betypical in urban and dense urban deployments to meet peak busy hour trafficdemands [Ref. 3].

b) With a limited amount of spectrum, 10 MHz in this case, there is no differencein base station requirements for 700, 2500, or 3500 MHz with data densityrequirements of 20 Mbps/sq-km or more.

c) With a limited spectrum allocation, the range benefit of lower frequencies onlycomes into play in areas with lower population densities, in this example,regions requiring data densities of 5 Mbps/sq-km or less.

With more and more countries moving towards the use of auctions for theallocation of spectrum licenses it is important to also consider the impact oflicense costs for a more complete picture of the business case trade-offs.Although it is not possible to accurately quantify the impact of spectrum costssince they will vary greatly from market to market and the number of competing

4Assumes TDD with a channel BW of 10 MHz and a DL to UL traffic ratio of 3:2

5The closer base station to base station spacing results in added cell to cell interference,

therefore more than 3x base stations are required with one-third the spectrum.


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bidders participating in the auctions, it is possible to come up with somegeneralizations.

In any particular band spectrum license cost will be directly proportional tothe amount of spectrum and the population in the geographic region coveredby the license

Since lower frequencies are viewed as more favorable due to lower pathloss and better building penetration, licenses in lower bands will generallycost more than licenses in the higher bands for the same amount ofspectrum and geographic area.

2.3 Frequency Division or Time Division Duplexing

Another important decision that some operators will face is whether to deployWiMAX with Time Division Duplex (TDD) or with Frequency Division Duplex(FDD). The condition under which this choice has to be made is when:

The spectrum allocation consists of paired channels consistent with an FDD

solution

Regulations do not restrict the use of TDD or FDD

The Upper 700 MHz band allocation in the US is a good example of a spectrumallocation that is made up of licenses with paired channels consistent with anFDD solution. FCC regulations however, allow both FDD and TDD operation inthis band thus giving the operator the flexibility to select the duplexing approachthat best fits his requirements. The structure of this band is shown in Figure 3.The license denoted as C-C is especially interesting in that it will support aWiMAX solution with two TDD 10 MHz channels or an FDD WiMAX solution witha 10 MHz downlink channel paired with a 10 MHz uplink channel.


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Figure 3: Upper 700 MHz Band in the US

When given the choice, generally the attributes of TDD make it the preferredduplexing approach for broadband services. This is especially true when trafficon the network is expected to be asymmetric and spectrum is limited [Ref. 5].With asymmetric traffic, one of the channels will be underutilized with FDDwhereas TDD can adapt DL and UL frames to match actual traffic conditions.Although some of this advantage is diminished due to the requirement for interbase station and inter-operator synchronization for interference control. Therewill, in most cases, still be a net gain since it is reasonable to expect that trafficconditions will be similar over a large group of users in the same geographic

region. TDD also assures reciprocity between the DL and UL channels for easychannel quality estimation. This is an important attribute for the implementation ofsome of the more advanced antenna systems.

With a spectrum assignment consisting of paired channels, which is the case forlicense C-C or D-D in Figure 3, TDD requires an outdoor transceiver unit for eachof the paired channels whereas FDD is implemented with a single transceiverthat covers both the DL and UL channels. Another aspect of FDD that can makeit the favored choice in some deployment scenarios is the ability to deal withinterference from high power transmissions from collocated or closely locatedwireless operations in adjacent bands. In these cases it will often be preferable todedicate one channel exclusively to DL in the collocated equipment rather than

running the risk of adjacent channel interference when the channel was operatingin UL mode as would be the case some of the time with TDD.

Table 1 provides a comparison of the attributes for the two duplexing approacheswhen working with a spectrum allocation comprising paired channels.


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Table 1: Summary of Comparative Attributes of TDD and FDD

TDD FDD

Adaptive DL to UL ratio for betterspectral efficiency with asymmetric

traffic

Channel reciprocity for easysupport of closed loop advancedantenna systems

Greater flexibility with frequencyreuse schemes with twoindependent paired channels

Simple transceiver design

Dedicated DL and dedicated ULchannel

Single transceiver to cover twopaired channels

Avoidance of self-interferencebetween DL and UL

Can mitigate interference from DLtransmissions in adjacent channelswith collocated base stationequipment

Figure 4 provides a relative base station deployment comparison for TDD relativeto FDD for a typical capacity-constrained environment. This analysis illustratesthe TDD advantage for DL to UL traffic asymmetries ranging from 3:2 to 3:1. Fora traffic asymmetry of 3:1, deploying with TDD to meet a specific DL data densitywill require almost 40% fewer base stations as compared to a deployment withFDD. DL to UL traffic ratios in the range of 3:1, and possibly higher, are expectedto be typical as traffic becomes more and more data-centric with applicationssuch as web browsing, streaming video and music, and location based services.

On the other hand there may also be regional-specific deployment scenarios inwhich traffic is projected to be symmetric or nearly so. This would be the casewith traffic dominated by voice services or possibly in a business-orientedenvironment where large file transfers are expected in both the DL and ULdirections with roughly equal probability. Under these traffic conditions thedifference in the required number of base stations with FDD or TDD would beinsignificant resulting in FDD being the more cost-effective approach due to thereduced equipment requirements.

The potential for interference from wireless applications in adjacent bands mustalso be considered. If the probability is high, FDD may prove to be the betterdeployment alternative for interference mitigation.


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Figure 4: Relative Number of Base Stations Required for TDD or FDD toMeet a Specific DL Data Density Requirement

3.0 Reuse 1 or Reuse 3

Traditional reuse patterns for conventional cellular deployments adopted cellfrequency reuse factors as high as seven (7) to mitigate intercellular co-channelinterference (CCI). These deployments assured a minimal spatial separation of5:1 between the interfering signal and the desired signal but required seventimes as much spectrum. With technologies such as CDMA, introduced with 3G,and OFDMA, introduced with WiMAX [Ref. 6], more aggressive reuse schemescan be employed to greatly improve overall spectral efficiency.

Two common frequency reuse configurations for a multi-cellular deployment with3-sector base stations and conventional sector antennas are a sector reuse of 3,i.e. (c, 3, 3)6 and a sector reuse of 1, (c, 1, 3) also referred to as universalfrequency reuse. With a frequency reuse of 1 the same channel is deployed ineach of the three (3) base station sectors7 as shown in Figure 58. This approachhas the advantage of using the least amount of spectrum and in many cases,may represent the only deployment alternative due to limited spectrum

6Nomenclature for describing the frequency reuse pattern in this paper is (c, n, s); where c is the

number of base station sites in a cluster, n is the number of unique frequency channels required,

and s is the number of sectors per base station site.7

Another deployment alternative with a single channel is to share the channel over all 3 sectors.This approach effectively splits the channel into three sub-channels and assigns each sub-channel to a specific sector making it comparable to a reuse of 3 with 1/3 the channel bandwidth.

8Due to multipath, reflections, interference from neighboring operators, etc., interference patterns

will be much more complex than depicted in Figures 5 and 6. These figures are meant only toprovide a generalized picture to the reader as to where self-interference is most likely to occur.


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availability. It also eliminates the need for any frequency planning in the layout ofbase stations. With Reuse 1, a pseudorandom subcarrier permutation schemealong with channel segmentation is employed with OFDMA to mitigate co-channel interference (CCI) at the sector boundaries and at the cell-edge [Ref. 6].As a result some channel capacity is sacrificed since some subcarriers will not be

fully utilized throughout the entire cell coverage area.

Figure 5: Frequency Reuse Factor of 1

With reuse 3 a separate channel is deployed in each of the three sectors asshown in Figure 6. This alternative mitigates the interference at the sector andcell edges resulting in a higher channel throughput. Although a reuse of 3 canincrease the channel spectral efficiency by 30-50% the overall spectral efficiencycompared to reuse 1 will be lower since three times as much spectrum isrequired.


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Figure 6: Frequency Reuse Factor of 3

If sufficient spectrum is available to the operator, a potential deployment strategythat can be undertaken is to deploy initially with a reuse of 3 and as demandgrows in the higher density, capacity-constrained environments, over-layadditional channels on a sector-by-sector basis to meet the growing demand.Long term the deployment in these areas will ultimately migrate to a moreaggressive re-use scheme in which all three available channels are deployed ineach sector. In the lower population density areas where capacity is not an issuehowever, a frequency reuse factor of 3 can be maintained.

The discussion of frequency reuse and interference is not complete withoutmentioning beamforming. WiMAX supports higher order antenna arrays orAdaptive Beamforming. Adaptive beamforming enables beam adaptation basedon both channel and interference conditions. This enables the antenna array tonot only maximize signal strength to the desired user but also provides amechanism to null out interference from unwanted sources. With AdaptiveArrays or Adaptive Beamforming, algorithms can be employed to constructivelyenhance both signal to noise and signal to interference ratios in all propagationenvironments to mitigate the effects of self-interference as well as interferencefrom neighboring operators. Signal to Interference ratio increases up to 10 dB in

an urban mobile environment have been reported using these techniques [Ref.7].


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4.0 Alternative Usage Models

In assessing the business opportunity for a Mobile WiMAX deployment anoperator may also want to consider the relative value of alternative usagemodels. Usage models range from one that provides broadband services with full

mobility and coverage for both indoor and outdoor environments to one whichaddresses only fixed broadband services.

4.1 Mobility with Reliable Indoor Coverage

Due to the requirement for portability and long battery-life mobile handhelddevices have limited transmit power and lower antenna gain. Additionally forindoor coverage one must deal with building penetration losses which can rangefrom 10 to 20 dB depending on the frequency band and building characteristics.Despite these challenges the mobile usage model is most interesting in that hasthe greatest revenue potential. To address this market it is necessary to deploy asufficient number of base stations to meet the capacity and most importantly the

requirements for ubiquitous coverage over the geographic area of interest inindoor environments. With the availability of micro-cells, pico-cells, femto-cells,and repeaters the business case to achieve the desired coverage for this usagemodel is greatly improved. These self-contained, low-cost pole mounted unitscan be installed in selected locations to improve coverage at a fraction of the costof additional large-scale macro base stations. Beamforming which benefits boththe downlink as well as the uplink link budget can also be used to enhance in-building coverage. Generally this usage is the most attractive from a businesscase perspective since it provides for quality broadband connections for themaximum number of potential customers.

4.2 Mobility with Best Effort Indoor CoverageSome operators may elect to follow a deployment approach that phases theinfrastructure investment over a longer period of time. Rather than deploying toensure reliable indoor coverage throughout the coverage area, an operator canelect to initially deploy only the number of base stations required to ensure thatmobile customers have good outdoor performance throughout the coverage areabut only best effort service when located inside of buildings. With this scenario,mobile customers at the cell peripheries that are located in a building will befaced with spotty coverage and may have to move near a window or outside thebuilding to get a quality connection. Mobile customers located closer to the basestation site however, would experience a good connection regardless of their

location. This deployment scenario can considerably reduce the required numberof base stations compared to a deployment that takes into account buildingpenetration loss throughout the entire coverage area thus reducing the initialinfrastructure investment. The tradeoff, of course, is the risk of having someinconvenienced customers and the higher churn that may result from the affectedcustomers switching to other operators. Longer term, additional base stations


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together with pico-cells, and femto-cells can be deployed over a period of time toimprove indoor coverage.

4.3 Fixed Usage Model

Another market model that an operator can consider is one that provides a focus

on fixed services. This usage model can take advantage of outdoor mountedsubscriber stations with high gain directional antennas for increased base stationrange and coverage. This eliminates building penetration loss and improves thesystem gain with increased uplink transmitter power and higher antenna gain.The directional subscriber antenna also reduces interference leading to higherspectral efficiency. When considering this usage model an operator must alsoconsider the added expense of a truck-roll and professional installation for thefixed outdoor subscriber terminals. It should be noted however, that this will onlybe necessary at the periphery of the cell coverage area and the cost is onlyincurred when a customer has signed on for service. Customers closer to thebase station will be able to connect with self-installed indoor terminals and over-

the-air-activation. This deployment option will significantly increase the range andcoverage capability of a base station in any of the frequency bands beingconsidered. In the 2500 MHz band for example, the outdoor fixed antenna optionwill provide 4 to 5 times the range and about 20 times advantage in coveragearea over an indoor mobile device. With this deployment model the reducedinfrastructure investment must be traded-off against the reduced addressablemarket due to the inability to adequately cover mobile users. This deploymentapproach can also prove to be the most cost-effective model for reaching themaximum number of customers with the minimal infrastructure cost in ruralenvironments and can be especially appealing in emerging markets.

4.4 Usage Models: SummaryThe relative coverage area estimates for various usage models assuming a (2x2)MIMO base station sector antenna for each case is summarized in Figure 5. Asdescribed above the indoor mobile handset results in the least area coverage perbase station while the roof-top mounted outdoor subscriber terminal provides thegreatest coverage with other usage models falling in between.


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Figure 7: Varied Usage Models Result in Wide Variation in Coverage

Deploying to ensure reliable coverage for indoor mobile applications requires thehighest front-end capital investment but maximizes the addressable market forthe operator. Any of the alternative usage models will reduce the addressablemarket but can nevertheless offer a viable business case for the operator due tothe benefit of lower initial infrastructure cost to cover the geographical area ofinterest. As a market entry strategy, an operator may choose an alternativeapproach to gain a time-to-market advantage and build a core customer base.The operator can then deploy additional base stations over a period of time toimprove coverage and expand the addressable market to include other usagemodels. This phased deployment approach can enhance the business case byspreading the infrastructure investment over a longer period of time.

5.0 WiMAX Base Station Antenna Configurations

WiMAX base station equipment is available today in a wide range ofconfigurations and as new air interface releases become available the range ofoptions available to the operator will increase. Many of the options have to dowith the base station antenna configuration. Since Mobile WiMAX supportsadvanced antenna systems the operator or network planner will be faced withselecting the best option for any particular area of interest.

Key performance benefits that higher order MIMO systems and beamforming

offer are higher peak data rate performance and higher average channel spectralefficiency [Ref. 4, 8]. Under certain conditions range can also be enhanced withthese systems. The capability for higher peak data rates enhances the customerexperience for the delivery of broadband services and increased channelcapacity or range helps to reduce base station requirements necessary to meetdata density or coverage requirements. These added performance benefitshowever, do not come without some added base station complexity and cost


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from both equipment as well as an installation perspective due to the additionalantenna elements. Although complexity may be higher for base stations withhigher order antenna systems they generally offer added value in that they resultin a net lower cost per megabit (see Figure 8) and, potentially, reduce thenumber of required base stations to meet specific downlink data density

requirements.

Figure 8: Advanced Antenna Systems Lowers the Cost/Mbit

The tradeoff that an operator must consider is whether or not to incur theadditional equipment and installation cost for a more advanced base station

antenna option at the outset or opt, initially, for the lowest cost approach andupgrade in the future as warranted by the need for increased performance and/orcapacity. Obviously in the higher density urban centers which will have thehighest capacity demand during the peak busy hour, choosing the solution withthe highest spectral efficiency and highest channel capacity would be a logicaland sensible approach. This will provide a solution that will result in a lowerdeployment cost per megabit with a high probability that the base station capacitywill be fully utilized in the near term to generate operator revenue. Compared to a(1x2) SIMO base station configuration, deploying with higher order (2x2) MIMOor Beamforming plus MIMO can reduce the number of required base stations tomeet the data density requirements in a capacity-constrained environment by 70-

80% [Ref. 4]. In these cases the savings in base station infrastructure costs willgreatly outweigh the increased WiMAX equipment costs.

In the areas with lower population densities surrounding the city center whichtend to be range-limited, the choice may not be as obvious. One must carefullyassess the potential demand and project the growth over time and deployaccordingly. Investing in excess capacity can result in expenditures that may


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never be recaptured by future revenue and under estimating capacity can resultin costly and time-consuming truck-rolls in the future to install base stationupgrades or alternatively, in dissatisfied customers arising from the servicedegradation caused by an overloaded network.

6.0 Conclusion

This paper has provided insights into the tradeoffs associated with some of themany decisions an operator or network planner must make when assessing therelative attributes of the various WiMAX deployment and spectrum alternativesthat are available for consideration. Base station requirements are used as ameans of comparing the relative merits of the various alternatives. This metric isgenerally agreed to be the major component of the total end-to-end networkinvestment and hence a good indicator for assessing the relative viability of thebusiness case when comparing two or more deployment alternatives.

Some of the conclusions drawn are:

Deployments in the UHF (700 MHz) band are well-suited to lower densityrural areas regardless of how much usable spectrum is available

For capacity-constrained environments requiring data densities in excess of20 Mbps per sq-km it is desirable to have access to at least 30 MHz ofusable spectrum, regardless of frequency band for a cost-effectivedeployment.

When one is faced with the option of FDD or TDD deployment, factors thatmust be considered include: DL to UL traffic asymmetry, need for inter-operator synchronization, and the potential for interference from closely

located operations in adjacent bands. Although a more conservative reuse factor of 3 will result in lower

interference and therefore, higher channel capacity the overall spectralefficiency will be reduced compared to reuse 1.

Base station solutions with adaptive beamforming offer the potential for bothsignal enhancement and interference mitigation to provide higher channelcapacity and improved range.

Alternative usage models can greatly impact the base stations required tomeet coverage requirements but lower initial deployment costs must betraded off against a reduced addressable market and the risk of adversely

affecting performance for some customers. Base stations with advanced antenna systems offer benefits that are highly

likely to pay off in high density urban areas but may not always be the mostcost-effective alternative in lower density environments that do not have highcapacity requirements.


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References

1. A Comparative Analysis of Spectrum Alternatives for WiMAX Networks with DeploymentScenarios Based on the U.S. 700 MHz Band, WiMAX Forum website, June 2008.

2. Forum Position Paper for WiMAX Technology in the 700 MHz Band, WiMAX Forumwebsite, March 2008.

3. A Review of Spectrum Requirements for Mobile WiMAX Equipment to Support WirelessPersonal Broadband Services, WiMAX Forum website, September 2007.

4. Mobile WiMAX - A Comparative Analysis of Mobile WiMAX Deployment Alternatives in theAccess Network, WiMAX Forum website, May 2007.

5. Mobile WiMAX-Part II: A Comparative Analysis, WiMAX Forum website, May 2006

6. Mobile WiMAX-Part I: A Performance and Comparative Summary, WiMAX Forum website,September 2006

7. P.H. Lehne, O. Rostbakken, and M. Petersen, Estimating Smart Antenna Performance from

Directional Radio Channel Measurements, Proceedings 50th IEEE Vehicle Tech. Conf. Sept1999, pp 57-61.

8. Introduction to MIMO Systems, Rohde & Schwarz Application Note 1MA102, June 2006,Available on WiMAX Forum website

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