One open issue is to determine the duration of the shutdown periods
of these candidates. Unlike simply setting fixed shutdown and
power-on time points for candidate cells (e.g. based on average
daily traffic patterns), a more dynamic shutdown scheme should
be established, that considers the actual cell loads. This way
the risk of negative impact on the cellular network performance
in shutdown scenarios can be minimized. A possible solution is
to calculate maximum uplink and downlink load factor values
[16] for every candidate cell and its priority cells, These values
then can be used as upper bounds for the traffic situation in a
shutdown scenario and a candidate cell can be detached, if the
individual load factor values of all participating cells fall below
the calculated values. Otherwise, the cell breathing effect of
cells in an energy saving scenario may lead to failed connection
setups or dropped connections [17],[6]. In our future work we
will address these issues in more detail.