  A macrocell superposed by indoor deployed femtocells forms a
geography-overlapped and spectrum-shared two tier network, which can
efficiently improve coverage and enhance system capacity. It is important for
reducing inter-tier co-channel interference that any femtocell user (FU) can
select suitable access channel according to the path losses between itself and
the macrocell users (MUs). Path loss should be estimated non-cooperatively
since information exchange is difficult between macrocell and femtocells. In
this paper, a novel method is proposed for FU to estimate the path loss between
itself and any MU independently. According to the adaptive modulation and
coding (AMC) mode information broadcasted by the macrocell base station (BS),
FU first estimates the path loss between BS and a MU by using Maximum a
Posteriori (MAP) method. The probability distribution function (PDF) and
statistics of the transmission power of the MU is then derived. According to
the sequence of received powers from the MU, FU estimates the path loss between
itself and the MU by using minimum mean square error (MMSE) method. Simulation
results show that the proposed method can efficiently estimate the path loss
between any FU and any MU in all kinds of conditions.
