Although the growth of the femtocell could see a sharp rise in the popularity of cellular phones,
there are still concerns regarding interference between femtocells and the external macrocell as
well as similar such devices. Since the femtocell and the macrocell operate in the same range of
frequencies, there is bound to be interference. The main problem of interference arises from the
fact that femtocells are installed in an ad-hoc manner, or independent of the structure of the
cellular network. One simple solution discussed, was for the femtocell to operate on a different
carrier frequency with respect to the macrocell. However, this solution is not simple to implement
since most mobile operators are allotted a fixed spectrum to provide their services, as mentioned
earlier. Another effective solution that successfully tackles femtocell interference for outdoor
mobile users connected to the macrocell is suggested in [15]. To find an effective and logical
solution to this drawback, the Femto-forum [13] has been involved in conducting research into
mitigating the problem of interference in femtocells.
In the 3G architecture, most operators are allotted 2 frequencies for use. So, interference could
also be reduced by allowing femtocells to transmit on the unused second frequency. However,
this still does not resolve interference that may arise between two femtocells that operate on, say
two floors of a building. This scenario may also affect the quality of service and capacity of each
individual femtocell. Another alternative suggested, was for mobile operators to implement a
two-tier femtocell network [2], by sharing spectrum rather than splitting spectrum between the two
tiers.