  In heterogeneous cellular scenarios with macrocells, femtocells or picocells
users may suffer from significant co-channel cross-tier interference. To manage
this interference 3GPP introduced almost blank subframe (ABSF), a subframe in
which the interferer tier is not allowed to transmit data. Vulnerable users
thus get a chance to be scheduled in ABSFs with reduced cross-tier
interference. We analyze downlink scenarios using stochastic geometry and
formulate a condition for the required number of ABSFs based on base station
placement statistics and user throughput requirement. The result is a
semi-analytical formula that serves as a good initial estimate and offers an
easy way to analyze impact of network parameters. We show that while in
macro/femto scenario the residue ABSF interference can be well managed, in
macro/pico scenario it affects the number of required ABSFs strongly. The
effect of ABSFs is subsequently demonstrated via user throughput simulations.
Especially in the macro/pico scenario, we find that using ABSFs is advantageous
for the system since victim users no longer suffer from poor performance for
the price of relatively small drop in higher throughput percentiles.
