Blind multiuser deconvolution in fading and dispersive channels

An adaptive near-far resistant technique for the blind joint multiuser identification and detection in asynchronous CDMA systems is analyzed in fading and dispersive GSM channels.Peer ReviewedPostprint (published version

A group-blind multiuser receiver for MC-CDMA systems

In this paper, a group-blind multiuser receiver is investigated for multicarrier code division multiple access (MC-CDMA) systems. In uplink transmissions, the receiver has the knowledge of the spreading sequences of the users within the cell, while the spreading sequences of the users from other cells are unknown. By imposing linear vector constraints on the multiuser detector, group-blind detection can efficiently suppress the known interferers, while mitigating the unknown interferers based on the minimum mean square error (MMSE) principle. A subspace-based channel estimation algorithm is proposed to blindly estimate the channel information. An adaptive implementation of the group-blind multiuser detection is also developed by using signal and noise subspace tracking algorithms. Numerical results show that the performance of the group-blind detector is much better than the subspace-based blind linear MMSE detector.published_or_final_versio

Enhanced Receivers for Interference Cancellation in 3G Systems

Interference cancellation and multiuser detection in CDMA systems are still actual research topics. These techniques enable us to deal with interference and to increase system capacity. In this paper, a so-called Generalized RAKE receiver, an Uplink generalized multiuser detection and a Blind adaptive multiuser detection are described. These algorithms are compared with conventional receivers and their properties are verified via simulations. The results imply that some of these algorithms are able to overcome the performance of the conventional receivers

Adaptive DSP Algorithms for UMTS: Blind Adaptive MMSE and PIC Multiuser Detection

A study of the application of blind adaptive Minimum Mean Square Error (MMSE) and Parallel Interference Cancellation (PIC) multiuser detection techniques to Wideband Code Division Multiple Access (WCDMA), the physical layer of Universal Mobile Telecommunication System (UMTS), has been performed as part of the Freeband Adaptive Wireless Networking project. This study was started with an analysis of Code Division Multiple Access (CDMA) and conventional CDMA detection. After that blind adaptive MMSE and PIC detection have been analyzed for general CDMA systems. Then the differences between WCDMA and general CDMA were analyzed and the results have been used to determine how blind adaptive MMSE and PIC can be implemented in WCDMA systems. Blind adaptive MMSE has been implemented inWCDMASim, aWCDMA simulator and some preliminary simulation results obtained with this simulator are presented. These simulation results do not yet show the performance that was expected of blind adaptive MMSE detection based on simulation results obtained in previous research. The cause for these unexpected results is not yet known and will be the subject of further research.\ud Implementation of PIC detection in WCDMASim was found to require changes to the architecture of the WCDMASim simulator. Implementation of these changes and solving the problems with blind adaptive MMSE detection are considered for future work

SGD Frequency-Domain Space-Frequency Semiblind Multiuser Receiver with an Adaptive Optimal Mixing Parameter

A novel stochastic gradient descent frequency-domain (FD) space-frequency (SF) semiblind multiuser receiver with an adaptive optimal mixing parameter is proposed to improve performance of FD semiblind multiuser receivers with a fixed mixing parameters and reduces computational complexity of suboptimal FD semiblind multiuser receivers in SFBC downlink MIMO MC-CDMA systems where various numbers of users exist. The receiver exploits an adaptive mixing parameter to mix information ratio between the training-based mode and the blind-based mode. Analytical results prove that the optimal mixing parameter value relies on power and number of active loaded users existing in the system. Computer simulation results show that when the mixing parameter is adapted closely to the optimal mixing parameter value, the performance of the receiver outperforms existing FD SF adaptive step-size (AS) LMS semiblind based with a fixed mixing parameter and conventional FD SF AS-LMS training-based multiuser receivers in the MSE, SER and signal to interference plus noise ratio in both static and dynamic environments

DSP Prototyping of Blind Adaptive MMSE Multiuser Detection for Cellular Wireless CDMA Systems

Blind adaptive Minimum Mean Square Error (MMSE) detection is theoretically one of the most promising multiuser detection techniques for cellular wireless Code-Division Multiple Access (CDMA) systems, but its implementation has not yet been studied extensively. Therefore the goal of the research described in this paper is to study the implementation of blind adaptive MMSE detection on the current generation of DSPs and to determine the detectedbits-per-second performance that can be achieved by such an implementation. The blind adaptive MMSE detection algorithm is first analyzed in order to determine how it can be implemented. The algorithm is then implemented in a simulator and the simulator is used to study the adaptive behavior of the algorithm. The simulator is also used to verify the correctness of the implementation of the algorithm by comparing the simulation results obtained with the simulator to simulation results published in literature. When the algorithm is shown to be correct it is implemented on and optimized for a floating-point DSP. This DSP implementation is used to determine the detected-bits-per-second performance that can be achieved by blind adaptive MMSE detection on modern DSPs

Blind multiuser detection using hidden markov models theory

We present an adaptive algorithm based on the theory of hidden Markov models (HMM) which is capable of jointly detecting the users in a DS-CDMA system. The proposed technique is near-far resistant and completely blind in the sense that no knowledge of the signature sequences, channel state information or training sequences is required for any user. In addition to this, an estimate of the signature of each user convolved with its physical channel impulse response (CIR), and an estimate of the background noise variance are provided once convergence is achieved (as well as estimated data sequences). At this moment, and using that CIR estimate, we can switch to any decision-directed (DD) adaptation scheme.Peer ReviewedPostprint (published version