  In CDMA systems, the received user powers vary due to moving distance of
users. Thus, the CDMA receivers consist of two stages. The first stage is the
power estimator and the second one is a Multi-User Detector (MUD). Conventional
methods for estimating the user powers are suitable for underor fully-loaded
cases (when the number of users is less than or equal to the spreading gain).
These methods fail to work for overloaded CDMA systems because of high
interference among the users. Since the bandwidth is becoming more and more
valuable, it is worth considering overloaded CDMA systems. In this paper, an
optimum user power estimation for over-loaded CDMA systems with Gaussian inputs
is proposed. We also introduce a suboptimum method with lower complexity whose
performance is very close to the optimum one. We shall show that the proposed
methods work for highly over-loaded systems (up to m(m + 1) =2 users for a
system with only m chips). The performance of the proposed methods is
demonstrated by simulations. In addition, a class of signature sets is proposed
that seems to be optimum from a power estimation point of view. Additionally,
an iterative estimation for binary input CDMA systems is proposed which works
more accurately than the optimal Gaussian input method.
