These changes account for situations where the CQM threshold
might be approximately the same as the currently received signal,
and thus CQM events are triggered often due to measurement
error/small fluctuations. This results in scanning occurring
too frequently.
Firstly, inhibit the immediate scan when the short-scan count
is at the maximum. This keeps bursts of CQM toggling from
causing a torrent of back-to-back scans. This does not inhibit
immediate scans if the CQM triggers a second time (if the signal
falls lower past the hysteresis). This reduces the scan rate in
the worst case (fast-rate toggling high/low CQM events) to the
short scan interval.
Secondly, change the behavior of the short scan count so it acts like
a "leaky bucket". As we perform short-scans, the bucket fills until
it reaches a maximal short-scan count, at which we back-off and
revert to a long scan interval. The short scan count decreases by
one (emptying the bucket) every time we complete a long scan interval
without a low-RSSI CQM event.
This reduces the impact of medium-rate toggling of high/low CQM
events, reducing the number of short-interval scans that occur before
returning to a long-interval if the system was recently doing
short scans.