Group gain design for overloaded CDMA

What is it about?

In overloaded CDMA decision-feedback receivers may have a bit error probability of at least one user that "floors", i.e. cannot be reduced to zero when the signal-to-noise ratio increases. This problem is a consequence of the overloaded nature of the CDMA system, characterized by a very high correlation among users' signatures and corresponding high multiuser interference that the receiver is not able to cancel. In this paper we show that "floors" can be avoided by properly controlling each users' gain and propose an algorithm that, grouping users, sets gains in such a way that all users have a BER that vanishes. Simulations show that group decision-feedback receivers with simple conventional receivers as constituent blocks, have performances very close to those of the optimal ML receiver.

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