Minimum Output Energy Detector Research Articles

Fuzzy MIMO detector for MC-CDMA systems with carrier frequency offset over multipath fading channels

A multistage fuzzy minimum output energy (MOE) detector is proposed for multiple input multiple output (MIMO) multi-carrier code-division-multiple access (MC-CDMA) uplink systems with carrier frequency offset (CFO) over multipath fading channels. The first stage of the receiver uses a novel MIMO receiver model with offset symbols to achieve a fuzzy CFO-constrained MOE detector that suppresses multiple access interference (MAI) and minimizes cancellation of the desired signal. To suppress noise and to enhance signal reception after the fuzzy MOE detector, a signal subspace projection and minimum mean square error weight combiner is proposed to enhance signal-to-interference-plus-noise ratio and bit error rate performances. Simulation results show that the proposed MIMO detector outperforms conventional MOE detectors and achieves the ideal receiver performance against MAI and CFO effects.

Improved two-stage CMA-based blind receivers for joint equalisation and multiuser detection

In direct sequence-code division multiple access (DS-CDMA) systems over frequency-selective channels, blind joint equalisation and multiuser detection has been the focus subject of research by many researchers. In this scheme, only the desired user's spreading code and timing information are available to the receiver. The two-stage constant modulus algorithm (CMA)-based receiver proposed, implements an adaptive blind joint equalisation and multiuser detection without explicit channel estimation. The first stage of the algorithm can be seen as a linear combination of blind adaptive minimum output energy (MOE) detectors based on total data correlation matrix. In this study, the authors adopt a MOE detector based on interference correlation matrix instead of total data correlation matrix to improve the performance of the first-stage detector, thus achieving an improved two-stage CMA-based blind joint equalisation and multiuser detection algorithm. In addition, the convergence of the proposed adaptive algorithm is analysed. Both the analysis and computer simulation verify the performance improvement of our proposed algorithm.

A novel CFO estimator with joint bisection-searching and complexity-reduction technique for uplink MC-CDMA systems

This paper presents a simple scheme, which speeds the estimation of carrier frequency offset (CFO) as well as reducing the estimation complexity for multicarrier code-division multiple-access (MC-CDMA) uplink. Based on the concept of bisection method, the CFO is efficiently estimated by way of locating the peak value in the output power spectrum of the minimum output energy (MOE) detector. Complexity reduction results from the proposed data vector partition associated with an innovative data processing technique for the MOE detector. Simulation results show that the expected advantage of the proposed scheme can be achieved at the expense of a reasonable performance loss even in the presence of a large CFO.

A Fuzzy MOE Receiver for Uplink MC-CDMA Systems with Carrier Frequency Offset over Multipath Fading Channels

A novel fuzzy minimum output energy (MOE) detector is proposed for uplink multicarrier CDMA (MC-CDMA) systems with carrier frequency offset (CFO) over multipath fading channels. The proposed receiver involves the following stages. First, the fuzzy CFO constrained MOE detector after coarse CFO estimation is proposed to suppress multiple access interference and combat the degradation problem of the conventional MOE detector caused by the CFO effect. Next, using the signal subspace projection technique, the proposed detector can further reduce the enhanced noise due to the fuzzy CFO constrained detector. Finally, the output data obtained from these detectors are coherently combined to offer multipath diversity gain in accordance with the maximum ratio combining criterion. Furthermore, the proposed single input single output (SISO) robust detector can be easily extended for a multiple input multiple output (MIMO) MC-CDMA system with a high rate of performance. Simulation results show that the proposed SISO detector, which offers a similar performance as the optimal detector, can provide robustness against CFO and outperform the conventional detectors. The proposed MIMO detector with spatial multiplexing gain also exhibits excellent performance.

Performance Analysis of Blind Adaptive MOE Multiuser Receivers Using Inverse QRD-RLS Algorithm

The inverse QR (IQRD) recursive least-squares (RLS) algorithm (IQRD-RLS) is very popular because it has good numerical stability and can be mapped onto COordinate Rotation DIgital Computer (CORDIC) processor-based systolic arrays, which are suitable for very large-scale integrated circuits (VLSI) architecture and real-time applications. In this paper, the blind optimal minimum output energy (MOE) detector which is developed for multiuser detection (MUD) in direct-sequence code-division multiple-access (DS-CDMA) systems is implemented using the linearly constrained IQRD-RLS algorithm. Specifically, the max/min approach is combined with subspace tracking for producing the optimal MOE multiuser detector. A new fast subspace tracking algorithm based on Lagrange multiplier methodology and the IQRD-RLS algorithm is developed. A comparative analysis among the recently emerged channel-estimation techniques is conducted using the IQRD-RLS algorithm. The corresponding robust MOE receivers at low SNR are implemented using the IQRD method, and their performances are assessed in terms of SINR, BER, and computational complexity. A robust multiuser receiver is developed by adding a quadratic inequality constraint to the optimal max/min MOE detector. The feasibility of systolic array implementation of the IQRD-based optimal MOE detector is explored. Several simulation experiments are conducted in a severe near-far environment to analyze the IQRD-based receivers and the subspace tracking algorithms.

Robust MOE detector for MC-CDMA downlink systems under carrier frequency offset

In this paper, a performance analysis of carrier frequency offset (CFO) on the minimum output energy (MOE)-based detectors in multi-carrier code-division multiple-access (MC-CDMA) downlink systems is first presented. Furthermore, a blind decision-directed (DD) MOE detector for enhancing robustness against CFO and the finite sample effect is proposed. Numerical study confirms the effectiveness of the proposed method and the performance improvement over conventional detectors.

Low‐complexity robust adaptive generalized sidelobe canceller detector for DS/CDMA systems

AbstractA novel low computational complexity robust adaptive blind multiuser detector, based on the minimum output energy (MOE) detector with multiple constraints and a quadratic inequality (QI) constraint is developed in this paper. Quadratic constraint has been a widespread approach to improve robustness against mismatch errors, uncertainties in estimating the data covariance matrix, and random perturbations in detector parameters. A diagonal loading technique is compulsory to achieve the quadratic constraint where the diagonal loading level is adjusted to satisfy the constrained value. Integrating the quadratic constraint into recursive algorithms seems to be a moot point since there is no closed‐form solution for the diagonal loading term. In this paper, the MOE detector of DS/CDMA system is implemented using a fast recursive steepest descent adaptive algorithm anchored in the generalized sidelobe canceller (GSC) structure with multiple constraints and a QI constraint on the adaptive portion of the GSC structure. The Lagrange multiplier method is exploited to solve the QI constraint. An optimal variable loading technique, which is capable of providing robustness against uncertainties and mismatch errors with low computational complexity is adopted. Simulations for several mismatch and random perturbations scenarios are conducted in a rich multipath environment with near–far effect to explore the robustness of the proposed detector. Copyright © 2008 John Wiley & Sons, Ltd.

Performance Analysis of Blind Adaptive MOE Multiuser Receivers Using Inverse QRD-RLS Algorithm

The inverse QR (IQRD) recursive least-squares (RLS) algorithm (IQRD-RLS) is very popular because it has good numerical stability and can be mapped onto COordinate Rotation DIgital Computer (CORDIC) processor-based systolic arrays, which are suitable for very large-scale integrated circuits (VLSI) architecture and real-time applications. In this paper, the blind optimal minimum output energy (MOE) detector which is developed for multiuser detection (MUD) in direct-sequence code-division multiple-access (DS-CDMA) systems is implemented using the linearly constrained IQRD-RLS algorithm. Specifically, the max/min approach is combined with subspace tracking for producing the optimal MOE multiuser detector. A new fast subspace tracking algorithm based on Lagrange multiplier methodology and the IQRD-RLS algorithm is developed. A comparative analysis among the recently emerged channel-estimation techniques is conducted using the IQRD-RLS algorithm. The corresponding robust MOE receivers at low SNR are implemented using the IQRD method, and their performances are assessed in terms of SINR, BER, and computational complexity. A robust multiuser receiver is developed by adding a quadratic inequality constraint to the optimal max/min MOE detector. The feasibility of systolic array implementation of the IQRD-based optimal MOE detector is explored. Several simulation experiments are conducted in a severe near-far environment to analyze the IQRD-based receivers and the subspace tracking algorithms.

Linearly constrained minimum variance filters for blind multiuser detection

We propose a new blind multiuser detector for frequency-selective multipath channels. Our new linearly constrained minimum variance (LCMV) RAKE receiver is an enhancement to the previously published decorrelating RAKE (D-RAKE) receiver. Compared with the D-RAKE receiver, our LCMV-RAKE receiver processes full information of the desired user and is shown by simulations to provide lower bit-error rates. In some scenarios, our LCMV-RAKE receiver outperforms the minimum output energy detector by M.K. Tsatsanis and Z. Xu (see IEEE Trans. Sig. Processing, vol.46, p.3014-22, 1998). Adaptive implementation of our LCMV-RAKE receiver is demonstrated to be feasible.

RAKE receiver using blind adaptive minimum output energy detection for DS/CDMA over multipath fading channels

To achieve better tracking of time-varying channel parameters, a structure using blind adaptive minimum output energy (MOE) detection in conjunction with RAKE combining diversity for direct-sequence code-division multiple-access communications over frequency selective multipath fading channels is introduced. In this MOE-RAKE structure, the signal replicas received from multiple fading paths are first independently produced by a bank of adaptive MOE detectors and then combined by a RAKE receiver for final symbol decision. A normalised, complex-valued stochastic gradient descent algorithm is developed for the blind adaptation used in the MOE-RAKE. Simulation results show that, in the time-invariant channel, the MOE-RAKE has a performance comparable to the previously proposed MOE and outperforms the conventional RAKE. In the time-varying channel, the MOE-RAKE performs better than the other blind multiuser detection techniques. In practice, to further improve the detector performance, a hybrid scheme started with blind adaptation for the initial updates and then switched to the decision-directed algorithm is desired.

Modified constant modulus algorithm for blind DS/CDMA detection

A new blind adaptive multiuser detector for synchronous DS/CDMA systems based on a modified constant modulus algorithm is proposed. This detector is shown to outperform the minimum output energy detector in a downlink channel occupied by a large number of users. This blind detector is a good candidate for downlink receivers.