2 research outputs found
New Power Estimation Methods for Highly Overloaded Synchronous CDMA Systems
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
Blind Adaptive Algorithms for Decision Feedback DS-CDMA Receivers in Multipath Channels
In this work we examine blind adaptive and iterative decision feedback (DF)
receivers for direct sequence code division multiple access (DS-CDMA) systems
in frequency selective channels. Code-constrained minimum variance (CMV) and
constant modulus (CCM) design criteria for DF receivers based on constrained
optimization techniques are investigated for scenarios subject to multipath.
Computationally efficient blind adaptive stochastic gradient (SG) and recursive
least squares (RLS) algorithms are developed for estimating the parameters of
DF detectors along with successive, parallel and iterative DF structures. A
novel successive parallel arbitrated DF scheme is presented and combined with
iterative techniques for use with cascaded DF stages in order to mitigate the
deleterious effects of error propagation. Simulation results for an uplink
scenario assess the algorithms, the blind adaptive DF detectors against linear
receivers and evaluate the effects of error propagation of the new
cancellations techniques against previously reported approaches.Comment: 10 figures; IEEE Transactions on Vehicular Technology, 2006. arXiv
admin note: substantial text overlap with arXiv:1205.438