Wimax deployment considerations

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  • 1. WiMAX DeploymentConsiderations for Fixed Wireless Access in the 2.5 GHz and 3.5 GHz Licensed Bands June, 2005 Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™.
  • 2. ________________________________________________________________________WiMAX Deployment Considerations for Fixed Wireless Access in the 2.5 GHz and 3.5 GHz Licensed BandsIntroductionThis paper addresses some of the deployment considerations for a wireless metropolitanarea network based on the IEEE 802.16-2004 Air Interface Standard, commonly referredto as WiMAX. This paper will focus on deployments using licensed spectrum in the 2.5GHz and 3.5 GHz frequency bands. With support for COFDM1, deployments in thesebands are especially interesting in today’s wireless access market since they offer thepotential for achieving ubiquitous coverage for high speed access over an entiremetropolitan area with adequate range and capacity for a cost-effective access network.In addition to presenting a detailed view of base station channel capacity versus range,specific deployment examples will be analyzed to the relationship between base stationinfrastructure costs and available spectrum in both frequency bands. The impact onchannel capacity and range when deploying with indoor self-installable customerterminals will also be discussed.Licensed Spectrum for Wireless MANsAlthough both the 3.5 GHz Band and the 2.5 GHz Band are not universally availableworldwide for fixed wireless access, at least one the two bands is available in most everymajor country.3.5 GHz Band: The “3.5 GHz” band is available as a licensed band in many countriesoutside the United States for fixed broadband wireless access. Although the regulationsfor deployment and specific allocations vary considerably country by country, this bandis undoubtedly the most used spectrum for wireless metropolitan area networks (MANs)today.Typical characteristics for the 3.5 GHz band based on a limited country by countrysurvey are: • Total available spectrum - Varies country by country but generally about 200 MHz between 3.4 GHz and 3.8 GHz • Services allowed - Fixed access is usually specified1 COFDM: Coded Orthogonal Frequency Division Multiplex, a modulation scheme that divides a singledigital signal across multiple signal carriers simultaneously. Initial WiMAX products will use 256 carriers. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 2 of 21
  • 3. ________________________________________________________________________ • FDD or TDD - This is mixed, some countries specify FDD only while others allow either FDD or TDD • Spectrum per license - Varies from 2 x 5 MHz to 2 x 56 MHz • License aggregation - Some countries allow license aggregation operators to gain access to more spectrum, others do not allow aggregation2.5 GHz Band: This band is allocated for fixed microwave services in many countriesincluding the United States. Although many of these countries have rules which do notsupport two-way services it is expected that this will change as WiMAX equipmentbecomes more readily available worldwide and operators lobby for more licensedspectrum for both fixed and mobile broadband services. In the United States the FCCmodified the rules for this band in 1998 to allow two-way services and in mid-2004,announced a realignment of the channel plan. With these rule modifications, this band isnow well suited to a WiMAX-based deployment and makes up for the fact that the 3.5GHz band is not available for wireless access in the United States. The following detailsfor the 2.5 GHz band is based on the most recent FCC rules. • Total available spectrum - Total of 195 MHz, including guard-bands and MDS channels, between 2.495 GHz and 2.690 GHz • Services allowed - Fixed two-way or broadcast • FDD or TDD - Both TDD and FDD are allowed • Spectrum per license - 22.5 MHz per license, a 16.5 MHz block paired with a 6 MHz block, a total of 8 licenses • License aggregation - Operators can acquire multiple licenses in one geographical area to increase spectrum holdingsRadio CharacteristicsTwo WiMAX equipment solutions have been selected for analysis. In the 2.5 GHz band,a time division duplex (TDD) solution with a 5 MHz channel bandwidth will be used andin the 3.5 GHz band a frequency division duplex (FDD) solution with dual 3.5MHzbandwidth channels will be used. These are not the only WiMAX equipment solutionsthat are expected to be available in these two bands but they are representative and servethe purposes intended for this paper. Other expected solutions include a TDD solution forthe 3.5 GHZ band with a 7 MHz channel bandwidth and over a period of time, differentchannel bandwidths will be made available in both bands to provide operators with moredeployment options. WiMAX-compliant equipment will also be available in otherfrequency bands. 5.8 GHz products for example, are anticipated at about the same time as3.5 GHz and 2.5 GHz products. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 3 of 21
  • 4. ________________________________________________________________________Table 1 provides a summary of the key downlink radio characteristics that are used forthe range and capacity estimates that follow in later sections of this paper. The systemgain in table 1 is typical of med-performance WiMAX-compliant equipment solutionsthat are expected to be offered by vendors in the coming months. For the 2.5 GHz TDDsolution, a downlink/uplink traffic split of 60/40 is assumed to reflect what is expected tobe a typical traffic pattern for data-centric services. This makes the effective downlink(DL) channel bandwidth 3 MHz and the effective uplink (UL) channel bandwidth 3 MHzand the effective uplink (UL) channel bandwidth 2 MHz. With the same asymmetrictraffic split in the FDD case, the 3.5 MHz uplink channel would not be fully utilized.The DL system gain for indoor self-installable CPE units is approximately 6 dB lowerthan the system gain for outdoor CPEs, primarily due to the difference in antenna gain.There is also additional path loss with indoor CPEs due to wall penetrations and non-optimal installation locations that will typically be off bore-sight to the base stationantenna. This excess path loss is estimated to be about 15 dB.The propagation model that is used to predict the range is based on contributions to theIEEE 802.16 Broadband Wireless Access Working Group by Erceg, et al2 . The proposedpropagation models cover three terrain categories; “A”, “B”, and “C”. “Category A”,being the highest path loss category, is used in this paper to predict propagationcharacteristics in urban environments and “Category C”, the lowest path loss terraincategory, is used propagation predictions in rural environments. The intermediate pathloss condition, “Category B”, is assumed for suburban environment range predictions.Treating these terrain categories as urban, suburban, and rural respectively is a suitableassumption for the purposes of this paper, but in practice each environment must beassessed on its’ specific characteristics. It would not be unusual for example, to encountera rural area with a hilly terrain, extensive trees, and varied building heights making it acandidate for a high-loss propagation condition; “Category A”, rather than “Category C”.Additionally, some urban areas in smaller cities with low and similar building heightsmay qualify for an intermediate loss condition, “Category B”. Attribute 2.5 GHz Band 3.5 GHz BandDuplexing TDD FDDChannel Bandwidth 5 MHz 2 x 3.5 MHzAdaptive Modulation BPSK, QPSK, 16QAM, 64QAM (COFDM-256)Nominal System Gain for 163 dB at BPSK 164 dB at BPSKOutdoor CPEs2 Erceg, et al, “Channel Models for Fixed Wireless Applications”, IEEE 802.16 Broadband WirelessAccess Working Group, February 23, 2001. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 4 of 21
  • 5. ________________________________________________________________________ Attribute 2.5 GHz Band 3.5 GHz BandNominal System Gain forIndoor Self-Installable 157 dB at BPSK 158 dB at BPSKCPEsExcess Path Loss for Indoor 15 dBCPEsTDD DL/UL Traffic Split 60/40 n/a Urban, Suburban, and RuralPropagation Conditions 100% of end-user terminals are non lone-of-sight (NLOS) Table 1: Relevant Radio ParametersThe use of adaptive modulation and adaptive coding enables each end-user link todynamically adapt to the propagation path conditions for that particular link. Whenreceived signal levels are low, as would be the case for users more distant from the basestation, the link automatically throttles down to a more robust, but less efficient,modulation scheme. Since each modulation scheme has a different modulation efficiencythe effective channel capacity can only be determined by knowing what modulation andcoding scheme is being used for each end-user link sharing that particular channel. Thisis readily done if it is assumed that the active subscribers on any given channel areuniformly distributed over the coverage area for that channel and additionally that eachend-user is under the same conditions, i.e. all outdoor CPEs and all non-LOS. In a latersection in this paper we will also look at the impact of a mixed deployment comprised ofboth indoor and outdoor CPEs.Deployments can be range-limited or capacity-limited. In a range-limited case, if auniform distribution of active subscribers with outdoor CPEs is assumed, more than 60%of active users will be operating at either QPSK or BPSK with only 15% operating at64QAM. This is illustrated in the 90-degree sector shown in figure 1. The range estimatesshown in figure 1 apply to a 3.5 GHz deployment in a rural environment with all outdoor,non-LOS CPEs. With the distribution of users as shown, the effective downlink channelcapacity (net user data rate) for a range-limited deployment is 3.8 Mbps as compared to9.7 Mbps for a capacity-limited case with all end-users operating at 64QAM. Assumingthat all end-users are non-LOS is, in many respects, a worse case situation. From apractical standpoint, it is reasonable to expect that some outdoor installations will bewithin line-of-sight or near-LOS to the base station antenna. Since the 64QAM range forLOS or near-LOS exceeds that of BPSK for non-LOS, in practice, some distant end-userswill actually be operating at 64QAM instead of BPSK and thus raise the effectivedownlink channel capacity from the 3.8 Mbps shown. Another factor not taken intoaccount in figure 1 is an allowance for co-channel interference (CCI) from adjacent cells Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 5 of 21
  • 6. ________________________________________________________________________which, in a multi-cellular network, is an added consideration. Excessive interference willalso cause the affected link to move to a more robust but less efficient modulation thusreducing the effective channel capacity. Predictions for LOS, near-LOS, and CCI canoften be accomplished through the use of available RF planning tools along with highresolution 3-D terrain models. However since these two effects tend to offset one another,the approach used in figure 1 for estimating channel capacity represents a very adequatefirst order estimate for effective downlink channel capacity.For fixed services, due to license assignments with limited spectrum, most deploymentswill be capacity-limited rather than range-limited. Exceptions would be very low densityrural areas, particularly those that could be classified as terrains with high propagationloss. BPSK Effective channel capacity at maximum range QPSK = 3.8 Mbps 16QAM 64QAM ~15% ~18% ~39% ~28% 2.0 km 3.0 km 4.4 km 5.2 km Non-LOS Range for Rural Deployment – 3.5 GHz FDD Figure 1: Typical Subscriber Density for a 3.5 GHz Rural DeploymentThe graphs in figures 2 and 3 provide a more quantitative view of the average downlinkchannel capacity and the downlink base station capacity for 3.5 GHz and 2.5 GHz Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 6 of 21
  • 7. ________________________________________________________________________WiMAX base stations respectively. The base stations are configured with six channelsand, as in figure 1, a uniform distribution of active non-LOS subscribers is assumed. Avg DL Channel Capacity 3.5 GHz Band Avg DL Capacity for 6 Channel BS 11 60 9 50 Urban Urban Mbps Mbps 7 Suburban 40 Suburban Rural Rural 5 30 3 20 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Path Length in km Path Length in kmFigure 2: Single Channel and 6-Channel Base Station Downlink Capacity in the 3.5 GHz band Avg DL Channel Capacity 2.5 GHz Band Avg DL Capacity for 6-Channel BS 8 50 7 40 Urban Urban 6 Mbps Mbps Suburban 30 Suburban 5 Rural Rural 4 20 3 10 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Path Length in km BS Spacing in km Figure 3: Single Channel and 6-Channel Base Station Downlink Capacity in the 2.5 GHz BandSince WiMAX-compliant products will be available in a range of configurations frommultiple vendors, varied performance parameters can be expected. Variations in systemgain will affect the range and ultimately, the channel capacity in a typical deployment.Figure 4 shows the sensitivity of the range and effective channel capacity to a +/- 6 dBvariation in system gain in the 3.5 GHz band. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 7 of 21
  • 8. ________________________________________________________________________ 8.0 10.0 Avg DL Channel Capacity Maximum Range in km 7.0 Urban at 1.5 km 9.0 6.0 5.0 Rural Suburban at 2 km 8.0 Mbps 4.0 Suburban 7.0 Rural at 3 km 3.0 Urban 2.0 6.0 Max Channel 1.0 Capacity 0.0 5.0 -8 -6 -4 -2 0 2 4 6 8 -8 -6 -4 -2 0 2 4 6 8 Relative System Gain in dB Relative System Gain in dB Figure 4: Range and Capacity Variation with System Gain in the 3.5 GHz BandMatching Data Density Requirements to Base Station CapacityFor capacity-limited deployment scenarios it is necessary to deploy base stations with abase station to base station spacing sufficient to match the expected density of end-customers. Data density is an excellent metric for matching base station capacity tomarket requirements. Demographic information, including population, households, andbusinesses per sq-km or per sq-mile, is readily available from a variety of sources formost metropolitan areas. With this information and the expected services to be offeredalong with the expected market penetration, data density requirements are easilycalculated. This 6-step process is summarized in figure 5. 1. 2. 3. 4. 5. 6. Target Area Services Expected Expected Required Market Demo- to be Market Number Data Segment graphics Offered Take Rate of Density Customers Mbps per sq-km Figure 5: Determining Market Driven Capacity RequirementsWith a fixed wireless network it is also important to project market requirements severalyears into the future and deploy base stations in accordance to what those projectionsdictate. Unlike mobile networks in which end-users are equipped with handsets havingomni-directional antennas, fixed networks are deployed with a combination of indoor,self-installable CPEs and professionally mounted outdoor units with fixed narrow beamantennas at the subscriber sites carefully aligned for maximum signal strength. The needto insert additional base stations within the coverage area to increase network capacitywill, in most cases, necessitate costly truck-rolls to re-align outdoor-mounted subscriberantennas. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 8 of 21
  • 9. ________________________________________________________________________The assumed market segments and services to be offered for the following examples aresummarized in table 2 and these values are used to generate the graphs shown in figure 6. Overbooking Customer Type Service Description FactorResidential 384 kbps Average 20:1Residential VOIP (20% of users) 128 kbps Average 4:1SME Premium (25%) 1.0 Mbps CIR, 5 Mbps PIR 1:1 (CIR)SME Regular (75%) 0.5 Mbps CIR, 1 Mbps PIR 1:1 (CIR) Table 2: Metrics Used to Calculate Market Data Rate Requirements 30 3 Urban Suburban Required Data Density Required Data Density 25 Suburban Penetration Rural 20 Rural 2 10% 10% 15 5% 5% 2% 2% 10 1 5 0 0 0 2,000 4,000 6,000 8,000 10,000 0 200 400 600 800 1,000 HH per sq-km HH per sq-km 20 4 Urban Suburban 18 Required Data Density Required Data Density Suburban Rural 15 Penetration 3 Rural 13 5% 5% 10 2% 2 2% 8 1% 1% 5 1 3 0 0 0 100 200 300 400 500 600 0 25 50 75 100 SME per sq-km SME per sq-kmFigure 6: Data Density Requirements Based on Demographics Expected Residential and/or SME Market PenetrationIf other services or market segments are to be included such as video on demand, hot spotbackhaul, nomadic services, etc, these would have to be included in the subscriber mix.Adding a hot spot backhaul link for example, is roughly comparable to an additionalbusiness customer. For nomadic applications an estimate can be made as to the number ofusers that are likely to be in the same geographical area during peak busy hour periodsand the required data density increased accordingly. A more thorough analysis when Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 9 of 21
  • 10. ________________________________________________________________________these additional services are added might also include an estimate of traffic patterns. Forexample, the peak period for nomadic customers might be during daytime business hoursand the peak period for residential users early morning and evening hours. In some areastherefore, it may be quite possible to satisfy multiple market segments and applicationswithout significantly increasing base station capacity.Table 3 represents a typical range of data density requirements for an urban, suburban,and rural environment for an average metropolitan area based on the service definitionsin table 2. Urban Suburban RuralResidential Density 4,000 to 8,000 800 to 1,500 200 to 600Penetration 5 to 10% 5 to 10% 5 to 10%SME Density 400 to 600 50 to 100 10 to 30Penetration 2 to 5% 2 to 5% 2 to 5%Data Density Range 10 to 40 Mbps/km2 2 to 7 Mbps/km2 0.5 to 2 Mbps/km2 Table 3: Typical Data Rate Requirements for an Average Metropolitan AreaThe resulting data density for various base station configurations in the 2.5 and 3.5 GHzbands as a function of base station spacing is shown in the following two figures. Figure7 is for an urban area deployment and includes both a 4-channel and an 8-channel basestation configuration. Figure 8 shows the data density for a suburban and rural area with a4-channel and 3-channel base station configuration respectively.The 2.5 GHz TDD plot in the following figures assumes a 60/40 downlink to uplinktraffic split. In practice, with time division duplexing, this split will often be adjusted tomatch average traffic conditions, which will generally favor the downlink direction.The vertical dotted lines in the graphs in figures 7 and 8 represents the base stationspacing requirements necessary to match the maximum of the data density requirementsshown in table 3. The value in having more spectrum is evident in figure 7 showing thatwith 8 channels the base station spacing is approximately 40% greater than a deploymentwith 4 channels to achieve the same 40 Mbps per sq-km data density.The spectrum requirements that are shown in the tables included in figures 7 and 8assume a cell frequency re-use factor of 1. If propagation and deployment conditionswere such that a high potential for co-channel interference, a more conservative cell re-use factor of 2 could be used. This would double the spectrum requirements from those Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 10 of 21
  • 11. ________________________________________________________________________values shown in the tables. This could be a likely scenario when, in a capacity-limitedcase, the base station capacity is such that all subscribers are operating at 64QAM or16QAM. BS DL Data Density BS DL Data Density 50 50 40 3.5 GHz FDD 40 3.5 GHz FDD Mbps/sq-km Mbps/sq-km 30 2.5 GHz TDD 30 2.5 GHz TDD 20 20 10 10 0 0 0.5 1.0 1.5 2.0 1.0 1.5 2.0 2.5 BS Spacing in km BS Spacing in km Band Duplex Channels Spectrum Required Terrain Condition Band Duplex Channels Spectrum Required Terrain Condition2.5 GHz TDD 4 20 MHz Urban NLOS 2.5 GHz TDD 8 40 MHz Urban NLOS3.5 GHz FDD 4 28 MHz Urban NLOS 3.5 GHz FDD 8 56 MHz Urban NLOS Figure 7: Average Base Station DL Data Density for 4 and 8 Channel Base Station Configurations in an Urban Environment BS DL Data Density BS DL Data Density 10 3.0 8 2.5 2.5 GHz TDD 2.5 GHz TDD Mbps/sq-km Mbps/sq-km 3.5 GHz FDD 2.0 3.5 GHz FDD 6 1.5 4 1.0 2 0.5 0 0.0 2.0 3.0 4.0 5.0 3.5 4.5 5.5 6.5 7.5 8.5 9.5 BS Spacing in km BS Spacing in km Band Duplex Channels Spectrum Required Terrain Condition Band Duplex Channels Spectrum Required Terrain Condition2.5 GHz TDD 4 20 MHz Suburban NLOS 2.5 GHz TDD 3 15 MHz Rural NLOS3.5 GHz FDD 4 28 MHz Suburban NLOS 3.5 GHz FDD 3 21 MHz Rural NLOS Figure 8: Average Base Station DL Data Density in a Suburban and Rural Environment Assuming 4 and 3 Channel Base Station Configurations RespectivelyDeployment Examples with Outdoor CPEsIn this section we will look at some hypothetical WiMAX base station deploymentexamples in both bands assuming all outdoor CPEs in each of the three demographicareas; urban, suburban, and rural. The demographics and anticipated number ofresidential and SME customers for these examples are summarized in table 4 along withthe data density that will be required to serve the anticipated number of end-customers or Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 11 of 21
  • 12. ________________________________________________________________________subscribers. A cell frequency re-use factor of 1 is assumed for all of the followingexamples to determine the amount of spectrum required. Urban Suburban RuralGeographical Area to be Covered 60 sq-km 120 sq-km 200 sq-kmExpected Number of Residential 30,000 20,000 5,000CustomersExpected Number of SME 1,500 500 150CustomersRequired Data Density 29 Mbps/km2 5.9 Mbps/km2 1.0 Mbps/km2 Table 4: Demographics for Deployment ExamplesThe base station infrastructure cost per customer is a good metric for providing aquantitative comparison between the various deployment options used to achieve therequired data density. The base station capital expense (CAPEX) has two majorcomponents, a “fixed” component and a “variable” component. The fixed portionincludes all the elements required to acquire and prepare the base station prior to theinstallation of any WiMAX equipment. This includes site acquisition, civil works,backhaul interface equipment, antenna masts, etc. There can be a great deal of variabilityin the fixed costs depending on the region and on the installation. The costs can be quitelow when WiMAX equipment is installed on existing towers located at or near anexisting fiber node for a backhaul connection and quite high in other cases. For theseexamples, the fixed base station CAPEX component is assumed to range between $15Kand $75K per base station. The variable CAPEX component is the WiMAX point-to-multipoint equipment which is closely related to the base station capacity. The WiMAXequipment cost will vary from vendor to vendor and will vary in accordance with specificequipment features. This cost is also expected to decrease over time as the technologymatures and volumes grow. In the following examples the variable base station cost isassumed to range between $5K and $10K per channel to cover equipment and installationcost.Urban Environment Example: Figure 9 summarizes the results for an urban areadeployment showing the number of WiMAX base stations and channels per base stationrequired to meet the data density requirements in each of the two frequency bands. Asone would expect, there is value in having more spectrum available since, in general, dueto the relatively high base station fixed costs it is more economical to deploy fewer highcapacity base stations as opposed to a larger number of low capacity base stations. If theadded spectrum has to be acquired through an auction process however, some of this Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 12 of 21
  • 13. ________________________________________________________________________infrastructure cost benefit will be offset by higher spectrum license fees and should betaken into account for a more accurate cost comparison. 2.5 GHz Urban Deployment 3.5 GHz Urban Deployment Base Station CAPEX/Subscriber Base Station CAPEX/Subscriber $300 $200 $180 $250 $160 $200 $140 High Fxd, Low Var $120 High Fxd, Low Var $150 Avg Fxd, Avg Var $100 Avg Fxd, Avg Var Low Fxd, High Var $80 Low Fxd, High Var $100 $60 $50 $40 $20 $- $- 40 30 20 15 Required Spectrum MHz 56 42 28 21 Required Spectrum MHz 8 6 4 3 Channels/BS 8 6 4 3 Channels/BS 31 42 65 93 # of Base Stations 26 31 48 63 # of Base StationsWiMAX Base Station Equipment $ 5.0 to $ 10.0 per Channel WiMAX Base Station Equipment $ 5.0 to $ 10.0 per ChannelBase Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base Station Base Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base StationCoverage Area = 60 sq-km Data Density = 29 Mbps/sq-km Coverage Area = 60 sq-km Data Density = 29 Mbps/sq-km Figure 9: Urban Deployment ExamplesSuburban Environment Examples: The suburban area examples are summarized infigure 10 and show the same general trends as in the urban examples. The CAPEX persubscriber is lower than the urban case due to the relative mix of residential and businesscustomers. In both the urban and suburban examples, when the base station fixed costsare low, there is little or no cost penalty for deploying a greater number of base stations. 2.5 GHz Suburban Deployment 3.5 GHz Suburban Deployment Base Station CAPEX/Subscriber Base Station CAPEX/Subscriber $160 $160 $140 $140 $120 $120 $100 $100 High Fxd, Low Var High Fxd, Low Var $80 Avg Fxd, Avg Var $80 Avg Fxd, Avg Var Low Fxd, High Var Low Fxd, High Var $60 $60 $40 $40 $20 $20 $- $- 45 30 20 15 Required Spectrum MHz 56 42 28 21 Required Spectrum MHz 9 6 4 3 Channels/BS 8 6 4 3 Channels/BS 14 17 26 33 # of Base Stations 11 14 20 25 # of Base StationsWiMAX Base Station Equipment $ 5.0 to $ 10.0 per Channel WiMAX Base Station Equipment $ 5.0 to $ 10.0 per ChannelBase Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base Station Base Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base StationCoverage Area = 120 sq-km Data Density = 5.9 Mbps/sq-km Coverage Area = 120 sq-km Data Density = 5.9 Mbps/sq-km Figure 10: Suburban Deployment ExamplesRural Environment Examples: Figure 11 includes a summary of the deploymentalternatives analyzed for a typical rural area deployment. As expected, with fewer Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 13 of 21
  • 14. ________________________________________________________________________customers per base station, the CAPEX per subscriber is considerable higher than eitherthe suburban or urban area examples. 2.5 GHz Rural Deployment 3.5 GHz Rural Deployment Base Station CAPEX/Subscriber $200 Base Station CAPEX/Subscriber $180 $180 $160 $160 $140 $140 $120 $120 High Fxd, Low Var $100 High Fxd, Low Var $100 Avg Fxd, Avg Var Avg Fxd, Avg Var Low Fxd, High Var $80 Low Fxd, High Var $80 $60 $60 $40 $40 $20 $20 $- $- 30 20 15 Required Spectrum MHz 42 28 21 Required Spectrum MHz 6 4 3 Channels/BS 6 4 3 Channels/BS 7 9 11 # of Base Stations 6 8 9 # of Base StationsWiMAX Base Station Equipment $ 5.0 to $ 10.0 per Channel WiMAX Base Station Equipment $ 5.0 to $ 10.0 per ChannelBase Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base Station Base Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base StationCoverage Area = 200 sq-km Data Density = 1.0 Mbps/sq-km Coverage Area = 200 sq-km Data Density = 1.0 Mbps/sq-km Figure 11: Rural Deployment ExampleDeployment Examples with Self-Installable Indoor CPEsThe long term goal of most operators for fixed wireless access is to deploy with allindoor, self-installable CPEs. The ability to self-install eliminates the need for a truck-rolland the fully integrated indoor units will be less expensive than the hardened outdoorCPE units. The lower CPE cost also increases the likelihood that customers will purchasetheir own CPE. This not only further reduces CAPEX for the operator but has a tendencyto reduce churn as well. To gain a more quantitative understanding of the benefitshowever, the capacity and range impact of indoor CPEs on the base station infrastructurecost must also be taken into account.In a 3.5 GHz range-limited case approximately 7% of users can be supported with indoorCPEs in a rural environment as shown in figure 12. This percentage is approximately10% and 12% in suburban and urban propagation environments respectively. Sinceapproximately 60% of the indoor CPEs will be operating at a lower modulationefficiency than 64QAM, the effective channel capacity at maximum range is reducedfrom 3.8 Mbps to 3.4 Mbps. These comparisons are summarized for all three propagationenvironments in table 5. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 14 of 21
  • 15. ________________________________________________________________________ BPSK Effective channel capacity at maximum range QPSK = 3.4 Mbps 16QAM 64QAM ~8% Indoor ~18% ~38% ~29% CPEs ~7% 2.0 km 3.0 km 4.4 km 5.2 km NLOS Range for Rural Deployment, outdoor CPEs, 3.5 GHz FDD 1.4 km, Max range for indoor CPEs in rural environment Figure 12: Distribution with Indoor CPEs for a 3.5 GHz Rural Area Deployment Urban Suburban RuralFrequency Band 3.5 GHzMaximum non-LOS Range 2.5 km 3.5 km 5.2 km% Indoor Self-Installable CPEs ~12% ~10% ~7%Channel Capacity at Maximum Range 3.6 Mbps 3.4 Mbps 3.4 MbpsChannel Capacity at Maximum Range 4.3 Mbps 4.0 Mbps 3.8 Mbpswith 100% Outdoor CPEsChannel Capacity Reduction 16% 14% 11% Table 5: Impact of Indoor CPEs on Channel CapacityThe left-hand graph in figure 13 provides a more detailed view of the downlink channelcapacity as a function of range for all three environments. The right-hand graph shows anurban area comparison for a single base station channel comprised of both indoor andoutdoor CPEs compared with a channel comprised entirely of outdoor CPEs. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 15 of 21
  • 16. ________________________________________________________________________ Avg DL Channel Capacity Avg DL Channel Capacity-Urban 10 10 9 9 8 Urban 8 Mbps Mbps 7 7 All Outdoor CPEs Suburban 6 6 With Indoor CPEs 5 Rural 5 4 4 3 3 0.0 1.0 2.0 3.0 4.0 5.0 0.2 0.6 1.0 1.4 1.8 2.2 2.6 Path Length in km Path Length in km Figure 13: Downlink Base Station Channel Capacity with Indoor CPEs in the 3.5 GHz BandTable 6 provides a summary of the demographics that will be used in the followingexamples to better quantify the trade-offs and the impact of deploying with indoor CPEsin the 3.5 GHz band. The coverage areas and anticipated residential customers areidentical to those used in the previous examples. The SME customers, who will generallybe deployed with outdoor CPEs, are ignored for this case to simplify the analysis. Urban Suburban RuralFrequency Band 3.5 GHzGeographical Area to be Covered 60 sq-km 120 sq-km 200 sq-kmExpected Number of Residential 30,000 20,000 5,000CustomersRequired Data Density 10 Mbps/km2 3.2 Mbps/km2 0.5 Mbps/km2 Table 6: Demographics for Deployment with Indoor CPEsFigure 14 shows the data density plots for deployments with all outdoor CPEs ascompared to a mixed deployment with both indoor and outdoor CPEs. The verticaldashed lines show the base station spacing comparisons between the two approaches tomatch the data density requirements indicated in table 6. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 16 of 21
  • 17. ________________________________________________________________________ 6-Channel BS Data Density-Urban 4-Channel BS Data Density-Suburban 40 10 30 8 Mbps/sq-km Mbps/sq-km All Outdoor CPEs 6 All Outdoor CPEs 20 With Indoor CPEs 4 With Indoor CPEs 10 2 0 0 1.0 1.5 2.0 2.5 3.0 1.5 2.0 2.5 3.0 3.5 BS Spacing in km BS Spacing in km 3-Channel BS Data Density-Rural 1.5 Mbps/sq-km 1.0 All Outdoor CPEs With Indoor CPEs 0.5 0.0 5.0 5.5 6.0 6.5 7.0 BS Spacing in km Figure 14: Downlink Base Station Data Density with Indoor CPEs in the 3.5 GHz BandThe trade-offs, using the same metric that was used in the previous examples, aresummarized in figure 15 for the three different deployment scenarios. For eachdeployment environment, case 1 assumes all outdoor CPEs. Case 2 is for a mixeddeployment of indoor and outdoor CPEs in which the base station spacing is adjusted toregain the capacity necessary to achieve the desired data density for that particularenvironment and case 4 shows the base station infrastructure required to support 100%indoor CPEs for each environment. Case 3 is for an intermediate level of indoor CPEsupport. In both the urban and suburban examples the added base station infrastructurecost is more than off-set by the expected $200 to $300 per CPE savings that will berealized when taking into account both equipment cost and installation expense foroutdoor CPE terminals. An added benefit in cases 3 and 4 is the resulting data densitywhich is higher than the minimum required for the anticipated market. This excess basestation capacity can be used to offer other enhanced services or to address additionalmarket segments.In the rural area deployment, with a 3-channel base station the fixed base station CAPEXplays a larger role. If the base station fixed cost is at the low end of the range, adeployment to support all indoor CPEs can still be cost-effective, particularly in view ofthe added data density that can potentially be used to generate additional revenue streams.If base station fixed costs are at the higher end of the range however, it may be difficult Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 17 of 21
  • 18. ________________________________________________________________________to economically justify a base station infrastructure to support more than 40-50% indoorself-installable CPEs. Base Station CAPEX/Subscriber Base Station CAPEX/Subscriber 3.5 GHz Urban Deployment 3.5 GHz Suburban Deployment $120 $200 $180 $100 $160 $140 $80 High Fxd, Low Var $120 High Fxd, Low Var $60 Avg Fxd, Avg Var $100 Avg Fxd, Avg Var $80 $40 Low Fxd, High Var Low Fxd, High Var $60 $40 $20 $20 $- $- Case 1 Case 2 Case 3 Case 4 Case 1 Case 2 Case 3 Case 4 0% 55% 75% 100% % Indoor CPEs 0% 42% 70% 100% % Indoor CPEs 6 6 6 6 Channels/BS 4 4 4 4 Channels/BS 12 17 23 30 # of Base Stations 13 16 26 37 # of Base Stations 10.0 10.0 12.5 12.6 Data Density 3.2 3.2 4.9 4.9 Data DensityWiMAX Base Station Equipment $ 5.0 to $ 10.0 per Channel WiMAX Base Station Equipment $ 5.0 to $ 10.0 per ChannelBase Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base Station Base Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base Station 30,000 Residential customers over an Urban coverage area of 60 sq-km 20,000 Residential customers over a Suburban coverage area of 120 sq-km Base Station CAPEX/Subscriber 3.5 GHz Rural Deployment $800 $700 $600 $500 High Fxd, Low Var $400 Avg Fxd, Avg Var $300 Low Fxd, High Var $200 $100 $- Case 1 Case 2 Case 3 Case 4 0% 16% 50% 100% % Indoor CPEs 3 3 3 3 Channels/BS 6 7 21 40 # of Base Stations 0.5 0.5 2.0 2.3 Data Density WiMAX Base Station Equipment $ 5.0 to $ 10.0 per Channel Base Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base Station 5,000 Residential customers over a Rural coverage area of 200 sq-km Figure 15: 3.5 GHz Deployment Scenarios with Indoor CPEsDeployment for CoverageAll of the deployment examples to this point have been capacity-limited with the desiredbase station capacity determined by projected market requirements based on servicesoffered, demographics and projected market penetration. Another deployment scenario isto deploy the minimum number of base stations necessary to get ubiquitous coverageover a particular area at the outset and only add additional capacity as the need arises toserve a growing number of customers. The added capacity can be achieved by addingbase station channels, to the already deployed base stations assuming sufficient spectrumis available, or by inserting additional base stations if the spectrum is not available. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 18 of 21
  • 19. ________________________________________________________________________Deploying for coverage without regard for projected capacity requirements is a viabledeployment strategy where the market requirements are uncertain and hence difficult toaccurately quantify. For example, this would certainly be a reasonable deploymentapproach for an operator wanting to provide ubiquitous outdoor internet access fornomadic customers over a wide geographical area. When the initial network isoperational the operator will be in a better position to assess and predict traffic patterns,customer acceptance, and market penetration expectations.For this deployment example an urban environment of 60 sq-km is assumed with the goalof providing a minimum of 128 kbps to each nomadic customer that is connected to thenetwork at any given time. It is also assumed that the connected customers are uniformlydistributed over the coverage area. The 60 sq-km urban area can be covered by threebase stations in the 2.5 GHz band. In figure 16, the metric used for comparisons in thisdeployment example is the base station CAPEX per Mbps per sq-km. Cases 1, 2, and 3in figure 16 show the result of adding channels to the three base stations whereas, case 4assumes that additional base stations are inserted to ultimately double the capacity thusgrowing the number of simultaneously supportable nomadic customers from 360 to 720.As expected, with a non-zero fixed cost per base station the more economical approach isto add channels rather than base stations. That is, of course, if the additional spectrumrequired can be acquired at a reasonable cost. Base Station CAPEX/Mbps/sq-km 2.5 GHz Urban Deployment $120 $100 $80 High Fxd, Low Var $60 Avg Fxd, Avg Var $40 Low Fxd, High Var $20 $- Case 1 Case 2 Case 3 Case 4 15 20 30 15 Required Spectrum MHz 3 4 6 3 Channels/BS 3 3 3 6 # of Base Stations 0.7 1.0 1.5 1.5 Data Density Mbps/sqkm 360 480 720 720 Nomadic Customers WiMAX Base Station Equipment $ 5.0 to $ 10.0 per Channel Base Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base Station Provides ubiquitous coverage for nomadic customers over an area of 60 sq-km Figure 16: Range Limited Urban Deployment Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 19 of 21
  • 20. ________________________________________________________________________When additional channels are deployed to increase base station capacity they do not haveto be simultaneously added throughout the entire coverage area, but can be added overtime to specific base stations as needed to cover high growth portions of the coveragearea. This concept is depicted in figure 17 which shows a deployment migration fromthree 3-channel base stations (9 channels total) to three 6-channel base stations (18channels total) over N years with an interim deployment of 13 total channels. 1st Year Interim Nth Year Deployment Deployment Deployment 9 Channels Add 4 Channels Add 5 Channels 2 1 2 1 4 2 1 2 3 4 26 3 5 1 4 2 6 3 5 1 4.9 km 1 4 2 6 5 3 2 3 3 1 4 2 1 1 3 6 5 3 3• 3 x 1200 sectors with 15 MHz of • With 15 MHz of additional spectrum a spectrum in 2.5 GHz band second channel can be added to• 3 Base stations cover 60 sq-km in each sector (total spectrum = 30 range-limited urban deployment MHz)• DL Data density 0.74 Mbps per sq-km • Increases data density to 1.5 Mbps• Supports up to 360 simultaneous non- per sq-km LOS nomadic customers over a 60 sq- • Supports up to 720 simultaneous km coverage area nomadic customers Figure 17: Growing Capacity by Adding Channels or Splitting SectorsConclusionWiMAX-compliant equipment based on the IEEE 802.16-2004 Air Interface Standardwill provide operators the technology necessary to deploy cost-effective wireless metroarea networks with ubiquitous coverage offering broadband services to multiple types ofcustomers. The examples described in this paper point out some of the considerations thatshould be taken into account when planning a WiMAX-based network in the 2.5 GHz or3.5 GHz frequency band. For wireless access networks, accurately projecting present andfuture capacity requirements is important to ensure deployment of the most cost-effective Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 20 of 21
  • 21. ________________________________________________________________________base station infrastructure, particularly in areas where fixed base station costs areexpected to be high. The minimum amount of spectrum for a cost-effective deploymentvaries with the demographics, the targeted market segment, the services being offered,and the cell frequency re-use factor. It is clear, from the examples analyzed in this paper,that from an economic point of view, having more spectrum is generally better thanhaving less spectrum. Copyright 2005 WiMAX Forum “WiMAX Forum™” and "WiMAX Forum CERTIFIED™“ are registered trademarks of the WiMAX Forum™. Page 21 of 21