WiMAX Deployment Considerations for Fixed Wireless Access in the 2.5 GHz and 3.5 GHz Licensed Bands
June, 2005
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WiMAX Deployment Considerations for Fixed Wireless Access in the 2.5 GHz and 3.5 GHz Licensed Bands Introduction
This paper addresses some of the deployment considerations for a wireless metropolitan area network based on the IEEE 802.16-2004 Air Interface Standard, commonly referred to as WiMAX. This paper will focus on deployments using licensed spectrum in the 2.5 GHz and 3.5 GHz frequency bands. With support for COFDM1, deployments in these bands are especially interesting in today’s wireless access market since they offer the potential for achieving ubiquitous coverage for high speed access over an entire metropolitan 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 station infrastructure costs and available spectrum in both frequency bands. The impact on channel capacity and range when deploying with indoor self-installable customer terminals will also be discussed.
Licensed Spectrum for Wireless MANs
Although both the 3.5 GHz Band and the 2.5 GHz Band are not universally available worldwide for fixed wireless access, at least one the two bands is available in most every major country. 3.5 GHz Band: The “3.5 GHz” band is available as a licensed band in many countries outside the United States for fixed broadband wireless access. Although the regulations for deployment and specific allocations vary considerably country by country, this band is 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 country survey are: • •
1
Total available spectrum Services allowed
- Varies country by country but generally about 200 MHz between 3.4 GHz and 3.8 GHz - Fixed access is usually specified
COFDM: Coded Orthogonal Frequency Division Multiplex, a modulation scheme that divides a single digital signal across multiple signal carriers simultaneously. Initial WiMAX products will use 256 carriers.
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________________________________________________________________________ - This is mixed, some countries specify FDD only • FDD or TDD while others allow either FDD or TDD - Varies from 2 x 5 MHz to 2 x 56 MHz • Spectrum per license - Some countries allow license aggregation operators • License aggregation to gain access to more spectrum, others do not allow aggregation 2.5 GHz Band: This band is allocated for fixed microwave services in many countries including the United States. Although many of these countries have rules which do not support two-way services it is expected that this will change as WiMAX equipment becomes more readily available worldwide and operators lobby for more licensed spectrum for both fixed and mobile broadband services. In the United States the FCC modified 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 is now well suited to a WiMAX-based deployment and makes up for the fact that the 3.5 GHz band is not available for wireless access in the United States. The following details for 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 - Fixed two-way or broadcast - Both TDD and FDD are allowed - 22.5 MHz per license, a 16.5 MHz block paired with a 6 MHz block, a total of 8 licenses - Operators can acquire multiple licenses in one geographical area to increase spectrum holdings
Services allowed FDD or TDD Spectrum per license License aggregation
Radio Characteristics
Two 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 and in the 3.5 GHz band a frequency division duplex (FDD) solution with dual 3.5MHz bandwidth channels will be used. These are not the only WiMAX equipment solutions that are expected to be available in these two bands but they are representative and serve the purposes intended for this paper. Other expected solutions include a TDD solution for the 3.5 GHZ band with a 7 MHz channel bandwidth and over a period of time, different channel bandwidths will be made available in both bands to provide operators with more deployment options. WiMAX-compliant equipment will also be available in other frequency bands. 5.8 GHz products for example, are anticipated at about the same time as 3.5 GHz and 2.5 GHz products.
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________________________________________________________________________ Table 1 provides a summary of the key downlink radio characteristics that are used for the range and capacity estimates that follow in later sections of this paper. The system gain in table 1 is typical of med-performance WiMAX-compliant equipment solutions that are expected to be offered by vendors in the coming months. For the 2.5 GHz TDD solution, a downlink/uplink traffic split of 60/40 is assumed to reflect what is expected to be 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 MHz and the effective uplink (UL) channel bandwidth 2 MHz. With the same asymmetric traffic 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 lower than 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 nonoptimal installation locations that will typically be off bore-sight to the base station antenna. 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 the IEEE 802.16 Broadband Wireless Access Working Group by Erceg, et al2 . The proposed propagation models cover three terrain categories; “A”, “B”, and “C”. “Category A”, being the highest path loss category, is used in this paper to predict propagation characteristics in urban environments and “Category C”, the lowest path loss terrain category, is used propagation predictions in rural environments. The intermediate path loss condition, “Category B”, is assumed for suburban environment range predictions. Treating these terrain categories as urban, suburban, and rural respectively is a suitable assumption for the purposes of this paper, but in practice each environment must be assessed on its’ specific characteristics. It would not be unusual for example, to encounter a rural area with a hilly terrain, extensive trees, and varied building heights making it a candidate for a high-loss propagation condition; “Category A”, rather than “Category C”. Additionally, some urban areas in smaller cities with low and similar building heights may qualify for an intermediate loss condition, “Category B”. Attribute Duplexing Channel Bandwidth Adaptive Modulation Nominal System Gain for Outdoor CPEs
2
2.5 GHz Band
3.5 GHz Band
TDD FDD 5 MHz 2 x 3.5 MHz BPSK, QPSK, 16QAM, 64QAM (COFDM-256) 163 dB at BPSK 164 dB at BPSK
Erceg, et al, “Channel Models for Fixed Wireless Applications”, IEEE 802.16 Broadband Wireless Access Working Group, February 23, 2001.
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________________________________________________________________________ Attribute 2.5 GHz Band 3.5 GHz Band Nominal System Gain for Indoor Self-Installable CPEs Excess Path Loss for Indoor CPEs TDD DL/UL Traffic Split Propagation Conditions 60/40 157 dB at BPSK 158 dB at BPSK
15 dB n/a
Urban, Suburban, and Rural 100% of end-user terminals are non lone-of-sight (NLOS) Table 1: Relevant Radio Parameters
The use of adaptive modulation and adaptive coding enables each end-user link to dynamically adapt to the propagation path conditions for that particular link. When received signal levels are low, as would be the case for users more distant from the base station, the link automatically throttles down to a more robust, but less efficient, modulation scheme. Since each modulation scheme has a different modulation efficiency the effective channel capacity can only be determined by knowing what modulation and coding scheme is being used for each end-user link sharing that particular channel. This is readily done if it is assumed that the active subscribers on any given channel are uniformly distributed over the coverage area for that channel and additionally that each end-user is under the same conditions, i.e. all outdoor CPEs and all non-LOS. In a later section in this paper we will also look at the impact of a mixed deployment comprised of both indoor and outdoor CPEs. Deployments can be range-limited or capacity-limited. In a range-limited case, if a uniform 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 at 64QAM. This is illustrated in the 90-degree sector shown in figure 1. The range estimates shown 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 channel capacity (net user data rate) for a range-limited deployment is 3.8 Mbps as compared to 9.7 Mbps for a capacity-limited case with all end-users operating at 64QAM. Assuming that all end-users are non-LOS is, in many respects, a worse case situation. From a practical standpoint, it is reasonable to expect that some outdoor installations will be within line-of-sight or near-LOS to the base station antenna. Since the 64QAM range for LOS or near-LOS exceeds that of BPSK for non-LOS, in practice, some distant end-users will actually be operating at 64QAM instead of BPSK and thus raise the effective downlink channel capacity from the 3.8 Mbps shown. Another factor not taken into account in figure 1 is an allowance for co-channel interference (CCI) from adjacent cells
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________________________________________________________________________ which, in a multi-cellular network, is an added consideration. Excessive interference will also cause the affected link to move to a more robust but less efficient modulation thus reducing the effective channel capacity. Predictions for LOS, near-LOS, and CCI can often be accomplished through the use of available RF planning tools along with high resolution 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 adequate first order estimate for effective downlink channel capacity. For fixed services, due to license assignments with limited spectrum, most deployments will be capacity-limited rather than range-limited. Exceptions would be very low density rural areas, particularly those that could be classified as terrains with high propagation loss.
BPSK
Effective channel capacity at maximum range = 3.8 Mbps
QPSK
16QAM
64QAM
~15%
~18%
2.0 km
~39%
3.0 km
~28%
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 Deployment The graphs in figures 2 and 3 provide a more quantitative view of the average downlink channel capacity and the downlink base station capacity for 3.5 GHz and 2.5 GHz
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________________________________________________________________________ WiMAX base stations respectively. The base stations are configured with six channels and, as in figure 1, a uniform distribution of active non-LOS subscribers is assumed.
Avg DL Channel Capacity 3.5 GHz Band
11 9 Mbps 7 5 3 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 Urban Suburban Rural 60 50 Mbps 40 30 20 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 Urban Suburban Rural
Avg DL Capacity for 6 Channel BS
Figure 2: Single Channel and 6-Channel Base Station Downlink Capacity in the 3.5 GHz band
Avg DL Channel Capacity 2.5 GHz Band
8 7 Mbps Mbps 6 5 4 3 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 Urban Suburban Rural 50 40 30 20 10
Avg DL Capacity for 6-Channel BS
Urban Suburban Rural
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 BS Spacing in km
Figure 3: Single Channel and 6-Channel Base Station Downlink Capacity in the 2.5 GHz Band Since WiMAX-compliant products will be available in a range of configurations from multiple vendors, varied performance parameters can be expected. Variations in system gain 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 dB variation in system gain in the 3.5 GHz band.
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Avg DL Channel Capacity Mbps 8.0 Maximum Range in km 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 -8 -6 -4 -2 0 2 4 6 8 Relative System Gain in dB Rural Suburban Urban 10.0 Urban at 1.5 km 9.0 8.0 7.0 6.0 5.0 -8 -6 -4 -2 0 2 4 6 8 Relative System Gain in dB Suburban at 2 km Rural at 3 km Max Channel Capacity
Figure 4: Range and Capacity Variation with System Gain in the 3.5 GHz Band
Matching Data Density Requirements to Base Station Capacity
For capacity-limited deployment scenarios it is necessary to deploy base stations with a base station to base station spacing sufficient to match the expected density of endcustomers. Data density is an excellent metric for matching base station capacity to market requirements. Demographic information, including population, households, and businesses per sq-km or per sq-mile, is readily available from a variety of sources for most metropolitan areas. With this information and the expected services to be offered along with the expected market penetration, data density requirements are easily calculated. This 6-step process is summarized in figure 5.
1. Target Market Segment
2. Area Demographics
3. Services to be Offered
4. Expected Market Take Rate
5. Expected Number of Customers
6. Required Data Density Mbps per sq-km
Figure 5: Determining Market Driven Capacity Requirements With a fixed wireless network it is also important to project market requirements several years into the future and deploy base stations in accordance to what those projections dictate. Unlike mobile networks in which end-users are equipped with handsets having omni-directional antennas, fixed networks are deployed with a combination of indoor, self-installable CPEs and professionally mounted outdoor units with fixed narrow beam antennas at the subscriber sites carefully aligned for maximum signal strength. The need to insert additional base stations within the coverage area to increase network capacity will, in most cases, necessitate costly truck-rolls to re-align outdoor-mounted subscriber antennas.
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________________________________________________________________________ The assumed market segments and services to be offered for the following examples are summarized in table 2 and these values are used to generate the graphs shown in figure 6. Customer Type Residential Residential VOIP (20% of users) SME Premium (25%) SME Regular (75%) Service Description 384 kbps Average 128 kbps Average 1.0 Mbps CIR, 5 Mbps PIR 0.5 Mbps CIR, 1 Mbps PIR Overbooking Factor 20:1 4:1 1:1 (CIR) 1:1 (CIR)
Table 2: Metrics Used to Calculate Market Data Rate Requirements
30 Required Data Density 25 20 15 10 5 0 0 2,000 4,000 6,000 8,000 10,000 HH per sq-km Rural Suburban Required Data Density Urban Penetration 10% 5% 2% 3 Suburban Rural 2 10% 5% 1 2%
0 0 200 400 600 800 1,000 HH per sq-km
20 Required Data Density Required Data Density 18 15 13 10 8 5 3 0 0 100 200 300 400 500 600 SME per sq-km Rural Urban Suburban Penetration 5% 2% 1%
4 Suburban 3 2 1 0 0 25 50 SME per sq-km 75 100 Rural 5% 2% 1%
Figure 6: Data Density Requirements Based on Demographics Expected Residential and/or SME Market Penetration If other services or market segments are to be included such as video on demand, hot spot backhaul, 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 additional business customer. For nomadic applications an estimate can be made as to the number of users that are likely to be in the same geographical area during peak busy hour periods and the required data density increased accordingly. A more thorough analysis when
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________________________________________________________________________ these additional services are added might also include an estimate of traffic patterns. For example, the peak period for nomadic customers might be during daytime business hours and the peak period for residential users early morning and evening hours. In some areas therefore, it may be quite possible to satisfy multiple market segments and applications without 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 definitions in table 2. Urban Residential Density Penetration SME Density Penetration Data Density Range 4,000 to 8,000 5 to 10% 400 to 600 2 to 5% 10 to 40 Mbps/km2 Suburban 800 to 1,500 5 to 10% 50 to 100 2 to 5% 2 to 7 Mbps/km2 Rural 200 to 600 5 to 10% 10 to 30 2 to 5% 0.5 to 2 Mbps/km2
Table 3: Typical Data Rate Requirements for an Average Metropolitan Area The resulting data density for various base station configurations in the 2.5 and 3.5 GHz bands as a function of base station spacing is shown in the following two figures. Figure 7 is for an urban area deployment and includes both a 4-channel and an 8-channel base station configuration. Figure 8 shows the data density for a suburban and rural area with a 4-channel and 3-channel base station configuration respectively. The 2.5 GHz TDD plot in the following figures assumes a 60/40 downlink to uplink traffic split. In practice, with time division duplexing, this split will often be adjusted to match 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 station spacing requirements necessary to match the maximum of the data density requirements shown in table 3. The value in having more spectrum is evident in figure 7 showing that with 8 channels the base station spacing is approximately 40% greater than a deployment with 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 8 assume a cell frequency re-use factor of 1. If propagation and deployment conditions were such that a high potential for co-channel interference, a more conservative cell reuse factor of 2 could be used. This would double the spectrum requirements from those
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________________________________________________________________________ values shown in the tables. This could be a likely scenario when, in a capacity-limited case, the base station capacity is such that all subscribers are operating at 64QAM or 16QAM.
BS DL Data Density
50 Mbps/sq-km Mbps/sq-km 40 30 20 10 0 0.5 1.0 1.5 2.0 BS Spacing in km 3.5 GHz FDD 2.5 GHz TDD 50 40 30 20 10 0 1.0 1.5 2.0 2.5 BS Spacing in km 3.5 GHz FDD 2.5 GHz TDD
BS DL Data Density
Band
Duplex
Channels Spectrum Required
Terrain
Condition
Band
Duplex
Channels Spectrum Required
Terrain
Condition NLOS NLOS
2.5 GHz 3.5 GHz
TDD FDD
4 4
20 MHz 28 MHz
Urban Urban
NLOS NLOS
2.5 GHz 3.5 GHz
TDD FDD
8 8
40 56
MHz MHz
Urban Urban
Figure 7: Average Base Station DL Data Density for 4 and 8 Channel Base Station Configurations in an Urban Environment
BS DL Data Density
10 Mbps/sq-km Mbps/sq-km 8 6 4 2 0 2.0 3.0 4.0 5.0 BS Spacing in km 2.5 GHz TDD 3.5 GHz FDD 3.0 2.5 2.0 1.5 1.0 0.5 0.0 3.5 4.5 5.5 6.5 7.5 8.5 9.5 BS Spacing in km 2.5 GHz TDD 3.5 GHz FDD
BS DL Data Density
Band
Duplex
Channels Spectrum Required
Terrain
Condition
Band
Duplex
Channels Spectrum Required
Terrain
Condition
2.5 GHz 3.5 GHz
TDD FDD
4 4
20 MHz 28 MHz
Suburban Suburban
NLOS NLOS
2.5 GHz 3.5 GHz
TDD FDD
3 3
15 MHz 21 MHz
Rural Rural
NLOS NLOS
Figure 8: Average Base Station DL Data Density in a Suburban and Rural Environment Assuming 4 and 3 Channel Base Station Configurations Respectively
Deployment Examples with Outdoor CPEs
In this section we will look at some hypothetical WiMAX base station deployment examples in both bands assuming all outdoor CPEs in each of the three demographic areas; urban, suburban, and rural. The demographics and anticipated number of residential and SME customers for these examples are summarized in table 4 along with the data density that will be required to serve the anticipated number of end-customers or
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________________________________________________________________________ subscribers. A cell frequency re-use factor of 1 is assumed for all of the following examples to determine the amount of spectrum required. Urban Geographical Area to be Covered Expected Number of Residential Customers Expected Number of SME Customers Required Data Density 60 sq-km 30,000 1,500 29 Mbps/km2 Suburban 120 sq-km 20,000 500 5.9 Mbps/km2 Rural 200 sq-km 5,000 150 1.0 Mbps/km2
Table 4: Demographics for Deployment Examples The base station infrastructure cost per customer is a good metric for providing a quantitative comparison between the various deployment options used to achieve the required data density. The base station capital expense (CAPEX) has two major components, a “fixed” component and a “variable” component. The fixed portion includes all the elements required to acquire and prepare the base station prior to the installation of any WiMAX equipment. This includes site acquisition, civil works, backhaul interface equipment, antenna masts, etc. There can be a great deal of variability in the fixed costs depending on the region and on the installation. The costs can be quite low when WiMAX equipment is installed on existing towers located at or near an existing fiber node for a backhaul connection and quite high in other cases. For these examples, the fixed base station CAPEX component is assumed to range between $15K and $75K per base station. The variable CAPEX component is the WiMAX point-tomultipoint equipment which is closely related to the base station capacity. The WiMAX equipment cost will vary from vendor to vendor and will vary in accordance with specific equipment features. This cost is also expected to decrease over time as the technology matures and volumes grow. In the following examples the variable base station cost is assumed to range between $5K and $10K per channel to cover equipment and installation cost. Urban Environment Example: Figure 9 summarizes the results for an urban area deployment showing the number of WiMAX base stations and channels per base station required to meet the data density requirements in each of the two frequency bands. As one would expect, there is value in having more spectrum available since, in general, due to the relatively high base station fixed costs it is more economical to deploy fewer high capacity base stations as opposed to a larger number of low capacity base stations. If the added spectrum has to be acquired through an auction process however, some of this
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________________________________________________________________________ infrastructure cost benefit will be offset by higher spectrum license fees and should be taken into account for a more accurate cost comparison.
2.5 GHz Urban Deployment
$300 $250 $200 $150 $100 $50 $40 8 31 30 6 42 20 4 65
$ $ 5.0 15.0
Base Station CAPEX/Subscriber
Base Station CAPEX/Subscriber
3.5 GHz Urban Deployment
$200 $180 $160 $140 $120 $100 $80 $60 $40 $20 $56 8 26 42 6 31 28 4 48
$ $ 5.0 15.0
High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
15 3 93
to to $ $
Required Spectrum MHz Channels/BS # of Base Stations 10.0 per Channel 75.0 per Base Station 29 Mbps/sq-km
21 3 63
to to $ $
Required Spectrum MHz Channels/BS # of Base Stations 10.0 per Channel 75.0 per Base Station 29 Mbps/sq-km
WiMAX Base Station Equipment Base Station Civil Works, Backhaul, etc. Coverage Area = 60 sq-km
WiMAX Base Station Equipment Base Station Civil Works, Backhaul, etc. Coverage Area = 60 sq-km
Data Density =
Data Density =
Figure 9: Urban Deployment Examples Suburban Environment Examples: The suburban area examples are summarized in figure 10 and show the same general trends as in the urban examples. The CAPEX per subscriber is lower than the urban case due to the relative mix of residential and business customers. In both the urban and suburban examples, when the base station fixed costs are low, there is little or no cost penalty for deploying a greater number of base stations.
2.5 GHz Suburban Deployment
$160 $140 $120 $100 $80 $60 $40 $20 $45 9 14 30 6 17 20 4 26
$ $ 5.0 15.0
3.5 GHz Suburban Deployment
Base Station CAPEX/Subscriber
Base Station CAPEX/Subscriber
$160 $140 $120 $100 $80 $60 $40 $20 $56 8 11 42 6 14 28 4 20
$ $ 5.0 15.0
High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
15 3 33
to to $ $
Required Spectrum MHz Channels/BS # of Base Stations 10.0 per Channel 75.0 per Base Station 5.9 Mbps/sq-km
21 3 25
to to $ $
Required Spectrum MHz Channels/BS # of Base Stations 10.0 per Channel 75.0 per Base Station 5.9 Mbps/sq-km
WiMAX Base Station Equipment Base Station Civil Works, Backhaul, etc. Coverage Area = 120 sq-km
WiMAX Base Station Equipment Base Station Civil Works, Backhaul, etc. Coverage Area = 120 sq-km
Data Density =
Data Density =
Figure 10: Suburban Deployment Examples Rural Environment Examples: Figure 11 includes a summary of the deployment alternatives analyzed for a typical rural area deployment. As expected, with fewer
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________________________________________________________________________ customers per base station, the CAPEX per subscriber is considerable higher than either the suburban or urban area examples.
2.5 GHz Rural Deployment 3.5 GHz Rural Deployment
Base Station CAPEX/Subscriber
Base Station CAPEX/Subscriber
$200 $180 $160 $140 $120 $100 $80 $60 $40 $20 $30 6 7 20 4 9 15 3 11
Required Spectrum MHz Channels/BS # of Base Stations
$180 $160 $140 $120 $100 $80 $60 $40 $20 $42 6 6 28 4 8 21 3 9
Required Spectrum MHz Channels/BS # of Base Stations
High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
WiMAX Base Station Equipment Base Station Civil Works, Backhaul, etc. Coverage Area = 200 sq-km
$ $
5.0 15.0
to to
$ $
10.0 per Channel 75.0 per Base Station 1.0 Mbps/sq-km
WiMAX Base Station Equipment Base Station Civil Works, Backhaul, etc. Coverage Area = 200 sq-km
$ $
5.0 15.0
to to
$ $
10.0 per Channel 75.0 per Base Station 1.0 Mbps/sq-km
Data Density =
Data Density =
Figure 11: Rural Deployment Example
Deployment Examples with Self-Installable Indoor CPEs
The long term goal of most operators for fixed wireless access is to deploy with all indoor, self-installable CPEs. The ability to self-install eliminates the need for a truck-roll and the fully integrated indoor units will be less expensive than the hardened outdoor CPE units. The lower CPE cost also increases the likelihood that customers will purchase their own CPE. This not only further reduces CAPEX for the operator but has a tendency to reduce churn as well. To gain a more quantitative understanding of the benefits however, the capacity and range impact of indoor CPEs on the base station infrastructure cost must also be taken into account. In a 3.5 GHz range-limited case approximately 7% of users can be supported with indoor CPEs in a rural environment as shown in figure 12. This percentage is approximately 10% and 12% in suburban and urban propagation environments respectively. Since approximately 60% of the indoor CPEs will be operating at a lower modulation efficiency than 64QAM, the effective channel capacity at maximum range is reduced from 3.8 Mbps to 3.4 Mbps. These comparisons are summarized for all three propagation environments in table 5.
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________________________________________________________________________
BPSK
Effective channel capacity at maximum range = 3.4 Mbps
QPSK
16QAM
64QAM
~8%
Indoor CPEs
~7%
~18%
2.0 km
~38%
3.0 km
~29%
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 Frequency Band Maximum non-LOS Range % Indoor Self-Installable CPEs Channel Capacity at Maximum Range Channel Capacity at Maximum Range with 100% Outdoor CPEs Channel Capacity Reduction 2.5 km ~12% 3.6 Mbps 4.3 Mbps 16%
Suburban 3.5 GHz 3.5 km ~10% 3.4 Mbps 4.0 Mbps 14%
Rural 5.2 km ~7% 3.4 Mbps 3.8 Mbps 11%
Table 5: Impact of Indoor CPEs on Channel Capacity The left-hand graph in figure 13 provides a more detailed view of the downlink channel capacity as a function of range for all three environments. The right-hand graph shows an urban area comparison for a single base station channel comprised of both indoor and outdoor CPEs compared with a channel comprised entirely of outdoor CPEs.
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________________________________________________________________________
Avg DL Channel Capacity
10 9 8 7 6 5 4 3 0.0 1.0 2.0 3.0 4.0 5.0 Path Length in km
10 9 8 7 6 5 4 3 0.2 0.6 1.0 1.4 1.8 2.2 2.6 Path Length in km
Avg DL Channel Capacity-Urban
Mbps
Mbps
Urban Suburban Rural
All Outdoor CPEs With Indoor CPEs
Figure 13: Downlink Base Station Channel Capacity with Indoor CPEs in the 3.5 GHz Band Table 6 provides a summary of the demographics that will be used in the following examples to better quantify the trade-offs and the impact of deploying with indoor CPEs in the 3.5 GHz band. The coverage areas and anticipated residential customers are identical to those used in the previous examples. The SME customers, who will generally be deployed with outdoor CPEs, are ignored for this case to simplify the analysis.
Urban Frequency Band Geographical Area to be Covered Expected Number of Residential Customers Required Data Density 60 sq-km 30,000 10 Mbps/km2
Suburban 3.5 GHz 120 sq-km 20,000 3.2 Mbps/km2
Rural 200 sq-km 5,000 0.5 Mbps/km2
Table 6: Demographics for Deployment with Indoor CPEs Figure 14 shows the data density plots for deployments with all outdoor CPEs as compared to a mixed deployment with both indoor and outdoor CPEs. The vertical dashed lines show the base station spacing comparisons between the two approaches to match the data density requirements indicated in table 6.
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________________________________________________________________________
6-Channel BS Data Density-Urban
40 Mbps/sq-km Mbps/sq-km 30 20 10 0 1.0 1.5 2.0 2.5 3.0 BS Spacing in km All Outdoor CPEs With Indoor CPEs 10 8 6 4 2 0 1.5 2.0 2.5 3.0 3.5 BS Spacing in km All Outdoor CPEs With Indoor CPEs
4-Channel BS Data Density-Suburban
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 Band The trade-offs, using the same metric that was used in the previous examples, are summarized in figure 15 for the three different deployment scenarios. For each deployment environment, case 1 assumes all outdoor CPEs. Case 2 is for a mixed deployment of indoor and outdoor CPEs in which the base station spacing is adjusted to regain the capacity necessary to achieve the desired data density for that particular environment 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 CPE support. In both the urban and suburban examples the added base station infrastructure cost is more than off-set by the expected $200 to $300 per CPE savings that will be realized when taking into account both equipment cost and installation expense for outdoor CPE terminals. An added benefit in cases 3 and 4 is the resulting data density which is higher than the minimum required for the anticipated market. This excess base station capacity can be used to offer other enhanced services or to address additional market segments. In the rural area deployment, with a 3-channel base station the fixed base station CAPEX plays a larger role. If the base station fixed cost is at the low end of the range, a deployment to support all indoor CPEs can still be cost-effective, particularly in view of the 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
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________________________________________________________________________ to economically justify a base station infrastructure to support more than 40-50% indoor self-installable CPEs.
Base Station CAPEX/Subscriber
Base Station CAPEX/Subscriber
3.5 GHz Urban Deployment
$120 $100 $80 $60 $40 $20 $Case 1 0% 6 12 10.0 Case 2 55% 6 17 10.0 Case 3 75% 6 23 12.5 Case 4 100% 6 30 12.6 % Indoor CPEs Channels/BS # of Base Stations Data Density High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
3.5 GHz Suburban Deployment
$200 $180 $160 $140 $120 $100 $80 $60 $40 $20 $Case 1 0% 4 13 3.2 Case 2 42% 4 16 3.2 Case 3 70% 4 26 4.9
$ $ 5.0 15.0
High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
Case 4 100% 4 37 4.9
to to $ $ % Indoor CPEs Channels/BS # of Base Stations Data Density 10.0 per Channel 75.0 per Base Station 120 sq-km
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 30,000 Residential customers over an Urban coverage area of 60 sq-km
WiMAX Base Station Equipment Base Station Civil Works, Backhaul, etc. 20,000
Residential customers over a Suburban coverage area of
Base Station CAPEX/Subscriber
3.5 GHz Rural Deployment
$800 $700 $600 $500 $400 $300 $200 $100 $Case 1 0% 3 6 0.5 Case 2 16% 3 7 0.5 Case 3 50% 3 21 2.0
$ $ 5.0 15.0
High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
Case 4 100% 3 40 2.3
to to $ $ % Indoor CPEs Channels/BS # of Base Stations Data Density 10.0 per Channel 75.0 per Base Station 200 sq-km
WiMAX Base Station Equipment Base Station Civil Works, Backhaul, etc. 5,000
Residential customers over a Rural coverage area of
Figure 15: 3.5 GHz Deployment Scenarios with Indoor CPEs
Deployment for Coverage
All of the deployment examples to this point have been capacity-limited with the desired base station capacity determined by projected market requirements based on services offered, demographics and projected market penetration. Another deployment scenario is to deploy the minimum number of base stations necessary to get ubiquitous coverage over a particular area at the outset and only add additional capacity as the need arises to serve a growing number of customers. The added capacity can be achieved by adding base station channels, to the already deployed base stations assuming sufficient spectrum is available, or by inserting additional base stations if the spectrum is not available.
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________________________________________________________________________ Deploying for coverage without regard for projected capacity requirements is a viable deployment strategy where the market requirements are uncertain and hence difficult to accurately quantify. For example, this would certainly be a reasonable deployment approach for an operator wanting to provide ubiquitous outdoor internet access for nomadic customers over a wide geographical area. When the initial network is operational 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 goal of providing a minimum of 128 kbps to each nomadic customer that is connected to the network at any given time. It is also assumed that the connected customers are uniformly distributed over the coverage area. The 60 sq-km urban area can be covered by three base stations in the 2.5 GHz band. In figure 16, the metric used for comparisons in this deployment example is the base station CAPEX per Mbps per sq-km. Cases 1, 2, and 3 in figure 16 show the result of adding channels to the three base stations whereas, case 4 assumes that additional base stations are inserted to ultimately double the capacity thus growing 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 is to add channels rather than base stations. That is, of course, if the additional spectrum required can be acquired at a reasonable cost.
Base Station CAPEX/Mbps/sq-km
2.5 GHz Urban Deployment
$120 $100 $80 $60 $40 $20 $Case 1 15 3 3 0.7 360 Case 2 20 4 3 1.0 480 Case 3 30 6 3 1.5 720
$ $ 5.0 15.0
High Fxd, Low Var Avg Fxd, Avg Var Low Fxd, High Var
Case 4 15 3 6 1.5 720
to to $ $ Required Spectrum MHz Channels/BS # of Base Stations Data Density Mbps/sqkm Nomadic Customers 10.0 per Channel 75.0 per Base Station 60 sq-km
WiMAX Base Station Equipment Base Station Civil Works, Backhaul, etc.
Provides ubiquitous coverage for nomadic customers over an area of
Figure 16: Range Limited Urban Deployment
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________________________________________________________________________ When additional channels are deployed to increase base station capacity they do not have to be simultaneously added throughout the entire coverage area, but can be added over time to specific base stations as needed to cover high growth portions of the coverage area. This concept is depicted in figure 17 which shows a deployment migration from three 3-channel base stations (9 channels total) to three 6-channel base stations (18 channels total) over N years with an interim deployment of 13 total channels.
1st Year Deployment 9 Channels
Interim Deployment Add 4 Channels
Nth Year Deployment Add 5 Channels
2 1 1 2 3 1 3
4.9 km
2 3
1 2 4 26 3 5 1 4 2 3 1 3
1 4 2 6 5 1 4 2 3 6 5 3 1 4 2 6 5 3
• • • •
3 x 1200 sectors with 15 MHz of spectrum in 2.5 GHz band 3 Base stations cover 60 sq-km in range-limited urban deployment DL Data density 0.74 Mbps per sq-km Supports up to 360 simultaneous nonLOS nomadic customers over a 60 sqkm coverage area
•
With 15 MHz of additional spectrum a second channel can be added to each sector (total spectrum = 30 MHz) Increases data density to 1.5 Mbps per sq-km Supports up to 720 simultaneous nomadic customers
• •
Figure 17: Growing Capacity by Adding Channels or Splitting Sectors
Conclusion
WiMAX-compliant equipment based on the IEEE 802.16-2004 Air Interface Standard will provide operators the technology necessary to deploy cost-effective wireless metro area networks with ubiquitous coverage offering broadband services to multiple types of customers. The examples described in this paper point out some of the considerations that should be taken into account when planning a WiMAX-based network in the 2.5 GHz or 3.5 GHz frequency band. For wireless access networks, accurately projecting present and future capacity requirements is important to ensure deployment of the most cost-effective
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________________________________________________________________________ base station infrastructure, particularly in areas where fixed base station costs are expected to be high. The minimum amount of spectrum for a cost-effective deployment varies 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 than having less spectrum.
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