Wimax deployment considerations

WiMAX Deployment
Considerations 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™.

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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:

• 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 specified
1
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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• 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 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
• 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 holdings

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 non-
optimal 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 2.5 GHz Band 3.5 GHz Band
Duplexing TDD FDD
Channel Bandwidth 5 MHz 2 x 3.5 MHz
Adaptive Modulation BPSK, QPSK, 16QAM, 64QAM (COFDM-256)
Nominal System Gain for
163 dB at BPSK 164 dB at BPSK
Outdoor CPEs

2
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 157 dB at BPSK 158 dB at BPSK
CPEs
Excess Path Loss for Indoor
15 dB
CPEs
TDD DL/UL Traffic Split 60/40 n/a
Urban, Suburban, and Rural
Propagation Conditions
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
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 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 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 km

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 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 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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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 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 end-
customers. 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. 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 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.

Overbooking
Customer Type Service Description
Factor
Residential 384 kbps Average 20:1

Residential VOIP (20% of users) 128 kbps Average 4:1

SME 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


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

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-km

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 Suburban Rural

Residential Density 4,000 to 8,000 800 to 1,500 200 to 600
Penetration 5 to 10% 5 to 10% 5 to 10%
SME Density 400 to 600 50 to 100 10 to 30
Penetration 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 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 re-
use 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 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 Condition

2.5 GHz TDD 4 20 MHz Urban NLOS 2.5 GHz TDD 8 40 MHz Urban NLOS
3.5 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

Band Duplex Channels Spectrum Required Terrain Condition Band Duplex Channels Spectrum Required Terrain Condition

2.5 GHz TDD 4 20 MHz Suburban NLOS 2.5 GHz TDD 3 15 MHz Rural NLOS
3.5 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 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.

Geographical Area to be Covered 60 sq-km 120 sq-km 200 sq-km
Expected Number of Residential
30,000 20,000 5,000
Customers
Expected Number of SME
1,500 500 150
Customers
Required Data Density 29 Mbps/km2 5.9 Mbps/km2 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-to-
multipoint 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 3.5 GHz Urban Deployment
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 Stations

WiMAX Base Station Equipment $ 5.0 to $ 10.0 per Channel 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 Base Station Civil Works, Backhaul, etc. $ 15.0 to $ 75.0 per Base Station
Coverage 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 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 3.5 GHz Suburban Deployment


$160 $160

$140 $140

$120 $120

$100 $100
High Fxd, Low Var High Fxd, Low 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

Coverage 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 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

$200

$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 Stations

Coverage 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 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
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

Frequency Band 3.5 GHz
Maximum 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 Mbps
Channel Capacity at Maximum Range
4.3 Mbps 4.0 Mbps 3.8 Mbps
with 100% Outdoor CPEs
Channel Capacity Reduction 16% 14% 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 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 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.

Frequency Band 3.5 GHz
Geographical Area to be Covered 60 sq-km 120 sq-km 200 sq-km
Expected Number of Residential
30,000 20,000 5,000
Customers
Required Data Density 10 Mbps/km2 3.2 Mbps/km2 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 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

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.


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
$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



10.0 10.0 12.5 12.6 Data Density 3.2 3.2 4.9 4.9 Data Density

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

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 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 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

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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 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 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.

Page 21 of 21

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