Motorola MOTOTRBO SYSTEM PLANNER Specifications download pdf (Page 63)

54 System Feature Overview

November, 2008

designed to meet. Note that the Roaming RSSI Threshold is a negative number therefore a high

value is -80dBm and a low value is -120dBm. The colored area is where the radio would roam.

The default value of the Roaming RSSI Threshold is -108dBm. It can be programmed for anything

between -80dBm and -120 dBm. A value of -108dBm is approximately 80% of the good coverage.

Therefore roaming will occur in the outer 20% of coverage. The default value is acceptable for

most configurations but may not be optimal in a some particular configurations. Before setting the

Roaming RSSI Threshold, one must consider the customer’s site configuration.

Consider the following four basic site configurations:

1. Dense Overlapping Coverage (Urban) – This type of coverage consists of dense sites

with generous overlap. This coverage type is often found in large cities or highly populated

areas. Overlapping sites utilize different frequencies. Non-overlapping sites may share

frequencies, but those that do share frequencies need to have different color codes if they

need to be distinguished while roaming. This type of coverage is highly likely to

encountered shared use on one or all of its sites. A radio user may be within coverage of

three to four sites at a time. The time it takes a radio user to move from the coverage of

one site to another is in the range of 10 minutes.

2. Isolated No Overlapping Coverage (Rural) – This type of coverage consists of isolated

sites with little to no overlap. This coverage type is often used for isolated sites in rural

areas, although could be used to cover a single part of a small city. Non-overlapping sites

may share frequencies, but those that do share frequencies need to have different color

codes if they need to be distinguished while roaming. This type of coverage is less likely to

encountered shared use although possible. A radio user will only be within coverage of

one site at any time. The time it takes a radio user to move from the coverage of one site

to another is in the range of multiple hours.

Figure 2-13 Roaming Triggered by Roaming RSSI Threshold Value

Low Roaming RSSI Threshold

High Roaming RSSI Threshold

Not Roaming

Roaming

Good Coverage

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Motorola MOTOTRBO SYSTEM PLANNER Specifications Page 63