3.1 Introduction

The blind multiuser detection techniques discussed in Chapter 2 are especially useful for interference suppression in CDMA downlinks, where a mobile receiver knows only its own spreading sequence. In CDMA uplinks, however, typically the base station receiver has knowledge of the spreading sequences of a group of users (e.g., the users within its own cell ) but not those of the users from other cells . It is natural to expect that some performance gains can be achieved over the blind methods (which exploit only the spreading sequence of a single user) in detecting each user 's data if information about the spreading sequences of the other known users are also exploited [190, 191, 198, 545]. In this chapter we discuss group-blind multiuser detection techniques that suppress intracell interference using knowledge of the spreading sequences and the estimated multipath channels of a group of known users while suppressing intercell interference blindly. Several forms of linear and nonlinear group-blind detectors are developed based on different criteria. These group-blind techniques offer significant performance improvement over the blind methods in a CDMA uplink environment.

The rest of this chapter is organized as follows . In Section 3.2 we introduce various linear group-blind multiuser detectors for synchronous CDMA systems. In Section 3.3 we present analytical performance assessment for linear group-blind multiuser detectors. In Section 3.4 we discuss nonlinear group-blind multiuser detection based on local likelihood search. In Section 3.5 we treat group-blind multiuser detection in general asynchronous CDMA systems with multipath channels. Finally, Section 3.6 contains the mathematical derivations and proofs for some results in this chapter.

The following is a list of the algorithms appearing in this chapter.

• Algorithm 3.1 : Group-blind linear hybrid detector (form I) ”synchronous CDMA

• Algorithm 3.2 : Group-blind linear hybrid detector (form II) ”synchronous CDMA

• Algorithm 3.3 : Slowest-descent-search multiuser detector

• Algorithm 3.4 : Nonlinear group-blind multiuser detector ”synchronous CDMA

• Algorithm 3.5 : Group-blind linear hybrid detector (form I) ”multipath CDMA

• Algorithm 3.6 : Group-blind linear hybrid detector (form II) ”multipath CDMA

• Algorithm 3.7 : Adaptive group-blind linear hybrid multiuser detector ”multipath CDMA

• Algorithm 3.8 : Group-blind linear hybrid detector ”multipath CDMA and correlated noise

• Algorithm 3.9 : Nonlinear group-blind detector ”multipath CDMA