User's Manual

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PRELIMINARY Examples of Design Estimates
8.2.3 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
• 6 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 8.1, “Maximum Output Power per
Carrier at RAU,” on page 8-3 provide maximum power per carrier information.
The 800 MHz TDMA table (on page 8-5) indicates that Unison can support 6 car-
riers with a recommended maximum power per carrier of 10.5 dBm. The input
power should be set to the desired output power minus the system gain.
3. Building information:
• 8 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 98.5 dB (10.5 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,
see Section 8.4 on page 8-32.
5. Path Loss Slope: For a rough estimate, Table 8-17, “Estimated Path Loss Slope for
Different In-Building Environments” on page 8-21, 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 98.5 dB, the distance of coverage from
each RAU will be 60/62 meters (198/203 ft). This corresponds to a coverage
area of 11,465/12,079 sq. meters (123,409/129,952 sq. ft.) per RAU (see
Section 8.2.1 for details on path loss estimation). For this case we assumed a circu-
lar radiation pattern, though the actual area covered will depend upon the pattern of
the antenna and the obstructions in the facility.