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D-620003-0-20 Rev J
CONFIDENTIAL
Estimating RF Coverage
6.2.3
Examples of Design Estimates
Example Design Estimate for an 800 MHz TDMA Application
1.
Design goals
:
• Cellular (859 MHz = average of the lowest uplink and the highest downlink
frequency in 800 MHz Cellular band)
• TDMA provider
• 12 TDMA carriers in the system
• –85 dBm design goal (to 95% of the building) — the minimum received power
at the wireless device
• Base station with simplex RF connections
2.
Power Per Carrier
: The tables in Section 6.1, “Maximum Output Power Per
Carrier at RAU,” on page 6-3 provide maximum power per carrier information.
The 800 MHz TDMA table (on page 6-4) indicates that Unison can support 12
carriers with a recommended maximum power per carrier of 7.5 dBm. The input
power should be set to the desired output power minus the system gain.
3.
Building information
:
• Eight floor building with 9,290 sq. meters (100,000 sq. ft.) per floor; total
74,322 sq. meters (800,000 sq. ft.).
• Walls are sheetrock construction, suspended ceiling tiles.
• Antennas used will be omni-directional, ceiling mounted.
• Standard office environment, 50% hard wall offices and 50% cubicles.
4.
Link Budget
: In this example, a design goal of –85 dBm is used. Suppose 3 dBi
omni-directional antennas are used in the design. Then, the maximum RF propa-
gation loss should be no more than 95.5 dB (7.5 dBm + 3 dBi + 85 dBm) over
95% of the area being covered.
It is important to note that a design goal such as
–85 dBm is usually derived taking into account multipath fading and log-normal
shadowing characteristics. Thus, this design goal will only be met “on average”
over 95% of the area being covered. At any given point, a fade may bring the sig-
nal level underneath the design goal.
Note that this method of calculating a link budget is only for the downlink path.
For information to calculate link budgets for both the downlink and uplink paths,
refer to Section 6.4 on page 6-24.
5.
Path Loss Slope
: For a rough estimate, Table 6-12, “Estimated Path Loss Slope for
Different In-Building Environments” on page 6-14, shows that a building with 50%
hard wall offices and 50% cubicles, at 859 MHz, has an approximate path loss slope
(PLS) of 37.6. Given the RF link budget of 95.5 dB, the distance of coverage from
each RAU will be 52 meters (170.6 ft). This corresponds to a coverage area of
8,494 sq. meters (91,425 sq. ft.) per RAU (refer to Section 6.2.1 for details on path
loss estimation). For this case we assumed a circular radiation pattern, though the
actual area covered depends upon the pattern of the antenna and the obstructions in
the facility.
