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Next Generation
Signal Enhancement
Date: Prepared by: -------------
8.2. Engineering Consideration
a. Site Selection
Site selection is one of the most critical decisions affecting the overall
performance of the system. A repeater must be located where it can
receive the maximum signal strength from the donor site in order to
maximize the repeater’s output and performance, signal strength greater
than or equal to -75dBm is desired.
Examples of donor antenna locations include (but are not limited to): the
roof of a building adjacent to the affected area, with the antennas mounted
on the highest point in the building; the top of the hill that is obstructing the
donor site’s coverage, with the antennas mounted on poles at ground
level; a water tower with antennas mounted at the top or as the situation
permits.
Distance from both the donor site as well as from the new area to be
covered must be taken into consideration. The repeater unit should be
located close to the donor site so as to receive adequate signal strength
and at the same time it is located in the vicinity of area where coverage is
desired. In addition, the donor antenna associated with the repeater unit
should have line of sight with BTS site to reduce the effects of fading.
Another important aspect when choosing a repeater location is the
availability of AC for operation of the system. Sites where repeater unit is
installed should be easily accessible for the maintenance team.
b. Antenna Selection and Placement
Proper selection of the repeater’s donor and server antennas is crucial in
designing the repeater system. Appropriate antenna characteristics help
to provide proper isolation between the server (coverage) and donor
antennas, which helps to prevent feedback. An isolation of at least 15 dB
more than the gain setting of the repeater is maintained to avoid the
possibility of oscillations.
Specific ways to achieve proper isolation include: using high gain
directional antennas with good Front to Back ratios (25dB or better);
physical separation of the repeater’s donor and server antennas; and
external shielding between antennas. A high gain antenna will help
minimize overall path loss to achieve the desired output power. Donor
antenna gains are typically 10 to 12 dB, while server antennas with gains
as per requirement are deployed.
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The antennas should have proper frequency band of operation.
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Adequate separation is to be ensured from the power lines to
avoid damage to the equipment and humans.
