3:30, SPCOM-P9.1
VARIABLE STEP-SIZE LMS BLIND CDMA MULTIUSER DETECTOR
Y. GONG, B. FARHANG-BOROUJENY, T. LIM
Adaptive least mean square (LMS) filters with or without training sequences, which are known as training-based and blind detectors respectively, have been formulated to counter interference in CDMA systems. The convergence characteristics of these two LMS detectors are analyzed and compared in this paper. We show that the blind detector is superior to the training-based detector with respect to convergence rate. On the other hand, the training-based detector performs better in the steady state, giving a lower excess mean-square error (MSE) for a given adaptation step-size. A novel decision-directed LMS detector which achieves the low excess MSE of the training-based detector and the superior convergence performance of the blind detector is proposed.

3:30, SPCOM-P9.2
A MULTISTAGE MULTI-CARRIER CDMA RECEIVER WITH BLIND ADAPTIVE MAI SUPPRESSION
J. DENG, G. LIN, T. LEE
Abstract: A multistage multicarrier CDMA (MSMC-CDMA) receiver with enhanced multiple access interference (MAI) suppression is proposed for a reverse link time-multiplexed pilot symbols assisted system over multipath channels. The design of the receiver involves the following procedure. First, a blind adaptive matched filter is attached to each finger to perform despreading and combat MAI. Second, channel estimation and a RAKE combiner gives the estimate of the signal. Finally, signal reconstruction is accomplished by exploiting the channel estimate, data decisions, signal's signature. The reconstructed signal is then subtracted from the data sent to the next stage. With signal reconstruction and subtraction as stages proceed, the MSMC-CDMA receiver can achieve nearly the performance of the optimal maximum SINR (MSINR) receiver, as confirmed by simulations.

3:30, SPCOM-P9.3
FURTHER RESULTS ON BLIND ASYNCHRONOUS CDMA RECEIVERS USING CODE-CONSTRAINED INVERSE FILTER CRITERION
T. LI, J. TUGNAIT
A code-constrained inverse filter criterion (CC-IFC) based approach was presented recently in Tugnait and Li [7, 2000 ICASSP] for blind detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals in multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. The equalizer was determined by maximizing the magnitude of the normalized fourth cumulant of inverse filtered (equalized) data with respect to the equalizer coefficients subject to the fact that the equalizer lies in a subspace associated with the desired user's code sequence. In this paper we analyze the identifiability properties of the approach of [7]. Global maxima and some of the local maxima of the cost function are investigated. These aspects were not discussed in [7]. More extensive simulation comparisons with existing approaches are also provided.

3:30, SPCOM-P9.4
ROBUST BLIND MULTIUSER DETECTION AGAINST CDMA SIGNATURE MISMATCH
S. CUI, Z. LUO, Z. DING
A common problem with the existing blind multi-user CDMA detectors is that their performance is very sensitive to the Signature Waveform Mismatch (SWM) caused by channel distortion. In this paper we consider the problem of designing a blind multi-user CDMA detector which is robust to the SWM. We present a convex formulation for this problem by using the Second Order Cone (SOC) programming. We also propose the use of recently developed interior point methods to efficiently solve the resulting SOC problem. Computer simulations indicate that the performance of our new robust blind multi-user detector is superior.

3:30, SPCOM-P9.5
AVERAGING BLIND SIGN ALGORITHMS FOR ADAPTIVE MULTIUSER DETECTION
G. YIN, V. KRISHNAMURTHY
This paper illustrates the use of ``averaging'' to improve the convergence rate of adaptive sign regressor and sign error blind multiuser detectors. The ingenious concept of averaging was invented by Polyak in 1990 -- this paper analyses the performance of averaging in the sign error and sign regressor adaptive blind multiuser detection algorithms in DS/CDMA Systems. Numerical examples are given to illustrate the performance of the algorithms

3:30, SPCOM-P9.6
BLIND TURBO MULTIUSER DETECTION FOR LONG-CODE UPLINK CDMA WITH UNKNOWN INTERFERENCES
X. WANG, Z. YANG
We consider the problem of demodulating the multiuser symbols in an uplink long-code CDMA system in the presence of unknown out-cell multiple-access interference and narrowband interference. A novel blind Bayesian multiuser detector is derived based on the Bayesian inference of all unknown quantities. The Gibbs sampler, a Markov chain Monte Carlo (MCMC) procedure, is then used for Bayesian computation. Being soft-input and soft-output, the blind Bayesian multiuser detector is designed to be a part of Turbo multiuser receiver, which refines its processing based on the information from the decoding stage.

3:30, SPCOM-P9.7
PERFORMANCE BOUNDS FOR LINEAR BLIND AND GROUP-BLIND MULTIUSER DETECTORS
A. HOST-MADSEN, X. WANG
In blind multiuser detection for CDMA systems, the receiver knows only the code of the user of interest, while in group-blind multiuser detection the receiver knows a subset of codes, e.g., the in-cell users in a basestation. This paper derives bounds for the performance of linear blind and group-blind multiuser detectors. The bounds are derived under a number of different system assumptions. The bounds show the theoretical gain by using group-blind detectors over blind detectors, and they also show that previously developed blind and group-blind detectors are relatively close to optimum among estimators using only second order moments. However, the bounds also show that a considerable gap exist to optimum detectors that are not restricted to second order moments.

3:30, SPCOM-P9.8
BLIND MULTIUSER DETECTION FOR SPACE-TIME CODED CDMA SYSTEMS
X. LU, H. LI
In this paper, we present a linear blind multiuser detector for space-time coded CDMA (Code Division Multiple Access) systems. The proposed blind multiuser receiver makes use of linearly constrained optimization techniques to minimize the mean output energy (MOE), subject to the constraint that the receiver passes the desired user without distortion, and, if possible, annihilates interfering users. Also investigated in this paper is the linear non-blind minimum mean square error (MMSE) multiuser receiver for space-time coded CDMA systems. We show that in term of the receiver output signal to interference and noise ratio (SINR), the performance of MOE receiver is equal to that of the MMSE receiver.