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<h1>Chained Cells in Rapid Field Drop</h1>

<p>Chained Cells in Rapid Field Drop feature is designed to
maintain calls in the rapid field drop environment and is especially useful
in the micro cellular environment.</p>


<p>The chained target cells are used to select the most probable
target cell(s) for a handover. Some of the handover parameters will be adapted
dynamically and automatically in order to provide a fast reaction.</p>


<p>Due to the complex nature of the micro-cellular environment,
Turn-a-corner MSs can cause problems. When an MS is turning a corner, the
signal strength of micro-cell may drop by 30 dB due to the losing of line-of-sight
effect. The existing feature rapid field drop in chained cells direct an MS
from horizontal cell to a vertical one, but it may also cause a ping-pong
effect to the in-house slow-moving traffic if the Rapid field drop threshold
is set too high. That is the reason why the new ultimate solution to the turn-a-corner
handover is designed. The new feature is called Enhanced Rapid Field Drop.</p>


<p>The basic idea of Enhanced Rapid Field Drop (ERFD) improvement
is to detect a Deep Dropping Edge (DDE) for serving a cell signal and handover
the call to the correct adjacent cell. The ERFD improvement is particularly
designed for micro cellular networks where the signal strength of an MS can
vary a lot. The DDE algorithm is based on monitoring that continues deep drop
in the serving cell's signal strength (both uplink and downlink) and a few
new handover control parameters.</p>


<p>The adjacent cell evaluation after ERFD is made according
to the normal target cell evaluation, however shorter averaging windows are
used to speed up the decision process.</p>
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