Minimum Output Energy Receiver Research Articles

Performance of linear minimum‐output energy receiver for self and alien crosstalk mitigation in upstream vectored very high‐speed digital subscriber line

Linear zero-forcing (ZF) canceller does not perform well in the presence of alien crosstalk (AXT) while the receivers based on minimum-mean-square-error (MMSE) criterion require perfect knowledge of the noise covariance matrices. In this study, the authors consider the use of a constrained linear minimum-output energy (MOE) receiver in the presence of self-crosstalk and AXT in upstream vectored very high-speed digital subscriber line systems, that does not require knowledge of the noise correlation matrices and can be trained using the received signals without the use of training sequences. They derive bounds on the performance of the MOE receiver in the digital subscriber line environment and show that it reaches the MMSE performance for self-crosstalk cancellation. They also show that the performance of the proposed receiver lies in between that of the ZF receiver and the non-linear ZF generalised decision feedback equaliser receiver. An adaptation of the canceller coefficients using MOE algorithm shows comparable performance to that of the least mean squares algorithm. The effect of noise correlation on the capacity has also been highlighted via the Cramer-Rao lower bound. Computer simulations are presented to verify the analytical results and demonstrate the performance of the proposed receiver.

A Blind LCMV-Based CFO Estimation for MC-CDMA Systems Over Multipath Fading Channels

This paper proposes a blind carrier frequency offset (CFO) estimation for multi-carrier code-division multiple access systems over multipath fading channels. The scheme first determines a preliminary CFO estimate by maximizing the total output power of a set of correlators, which is constructed with the linearly constrained minimum variance optimization. A fine CFO estimate is subsequently found by solving the well-developed quadratic cost function. Finally, by using the frequency-compensated data, a subspace minimum output energy (MOE) receiver is formed to provide the maximum output signal-to-interference-plus-noise ratio. Numerical results demonstrate that, with the proposed CFO estimation as a stage proceed, the subspace MOE receiver can achieve nearly the performance of the optimal minimum mean square error receiver.

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.

High SNR Performance Analysis of Blind Minimum Output Energy Receivers for Large DS-CDMA Systems

High signal-to-noise ratio (SNR) properties of the minimum output energy (MOE) receiver and the Capon channel estimation technique are analyzed in the case of large direct-sequence code-division multiple-access (DS-CDMA) systems. It is shown that if the noise power tends to zero and the system load is less than one, then the signal-to-interference-plus-noise ratio (SINR) of the MOE receiver tends to infinity and the Capon channel estimate converges to a scaled version of the channel vector of the user-of-interest. For the case when the system load is larger than one, an asymptotic SINR expression is obtained. Furthermore, expressions for the efficiency and asymptotic efficiency of the MOE receiver are derived. Simple approximations of (and upper/lower bounds on) these expressions are found and the effects of the system physical parameters on the performance of the MOE receiver are discussed.

Asymptotic Performance Analysis of Blind Minimum Output Energy Receivers for Large DS-CDMA Systems

The random matrix theory is used to analyze the asymptotic performance of the blind minimum output energy (MOE) receiver in direct-sequence code division multiple-access (DS-CDMA) systems in the presence of unknown multipath channel under the condition that the spreading factor and the number of users go to infinity with the same rate. As a special case, the asymptotic properties of the blind Capon receiver are also studied and the conditions of convergence of the signal-to-interference-plus-noise ratio (SINR) of this receiver to that of the optimal minimum-mean-square error (MMSE) receiver are discussed. In particular, it is shown that the SINR performances of the Capon and MMSE receivers are nearly identical in the uplink scenario, while the performance of the Capon receiver may be considerably inferior to that of the MMSE receiver in the downlink transmission case. As the performance of the Capon receiver is closely related to the performance of the Capon channel estimator, the asymptotic properties of the latter estimator are also studied and the conditions of convergence of the Capon channel estimate to a scaled version of the channel vector of the user-of-interest are obtained.

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.

Blind signal reception in downlink time‐hopping ultrawideband communication system

AbstractUltra wideband (UWB) impulse radio (IR) system is currently being considered for several applications due to its attractive features that include low‐power carrierless modulation and ample multipath diversity. Among the various modulation and multiple‐access schemes, this paper deals with time‐hopping (TH) antipodal pulse amplitude modulation (PAM), operating in the presence of multipath‐fading downlink channel. We develop two types of low‐complexity mobile station (MS) receivers. One is based on the RAKE reception scheme and the other is designed to meet the minimum‐output‐energy (MOE) criterion. However, since accurate channel information is crucial for reliable operation, thereby we propose a blind (non‐data aided) channel estimator. Simulation results show that the MOE receiver outperforms the RAKE receiver in multiuser environment. Moreover, both the channel estimation algorithm and the MOE reception schemes are shown to be reliable and near‐far resistant. Copyright © 2007 John Wiley & Sons, Ltd.

Blind Signal Reception and Channel Estimation in Downlink MC-CDMA Communication System with Transmit Diversity

In this paper, we exploit transmit diversity in downlink multicarrier CDMA (MC-CDMA) system to provide a solution to a high data rate, high capacity, yet reliable and robust to fading channel network. Our first emphasis is on designing a blind (without knowing the undesired users' signatures and channel parameters) MC-CDMA receiver in the mobile station that can suppress the multiple access interference (MAI) and combine the desired signal stemmed from all the transmitting antennas. Two blind signal reception algorithms are proposed and the performances in terms of signal-to-interference-and-noise-ratio (SINR) are comprehensively analyzed. One is based on the decorrelating RAKE (DRAKE) scheme proposed in [IEEE Trans. Communs. 47(7), 1036---1045, 1999] and the other is designed to meet the minimum output energy (MOE) criterion [IEEE Trans. on Information Theory 41(4), 944---996, 1995]. The MOE receiver, though optimum in ideal situation, is semi-blind that the vector channel impulse responses (VCIR) should be explicitly known. While the proposed modified DRAKE receiver is completely blind that it does not require any information of VCIR. Furthermore, we demonstrate that in practical scenario, the modified DRAKE scheme substantially outperforms the MOE receiver. The second part of this paper is to develop an efficient and blind (without requiring training sequences) algorithm to estimate the VCIR of downlink antenna array MC-CDMA system. Simulation results show that both the channel estimation algorithm and the blind reception schemes are reliable and near-far resistant.

Blind Multiuser Detection: FromMOE to Subspace Methods

The minimum output energy (MOE) multiuser receiver has been shown to approach the minimum mean-square-error (MMSE) receiver at high signal-to-noise ratio (SNR). However, performance degradation is incurred by noise induced channel estimation error. In this paper, we propose a Power of R (POR) technique to significantly improve the performance of the MOE receiver. It is shown that the new receiver asymptotically converges to the MMSE receiver without performance penalty. The convergence is established either under high SNR, with large exponent raised in the power of the covariance matrix, or with sufficiently large number of data samples. Connection between our POR method and a widely studied subspace method is investigated from the respective optimization criteria. Asymptotic equivalence between these two methods is also established. Extensive simulations based on finite data samples show that the proposed method significantly outperforms the subspace method in systems with medium to heavy loading, severe multipath distortion, or smaller processing gain. Moreover, adaptive implementation of the proposed method exhibits very robust performance in a dynamic loading environment.

Further Study on MOE-Based Multiuser Detection in Unknown Multipath

The minimum output energy (MOE) receiver has been developed for multiuser detection when multipath distortion is present. Its performance has been shown to be very close to the minimum mean-square-error (MMSE) receiver at high signal to noise ratio. However, due to the additive noise, the constraint vector required to construct the MOE receiver is a biased estimate of the channel vector. Thus, the MOE receiver exhibits degraded performance. To mitigate the noise effect, the constraint cost function is modified to obtain a modified MOE (MMOE) receiver in this paper, leading to a significantly improved channel estimate and detection performance. It is also revealed that the MMOE method converges to the well-known subspace method under certain conditions. In addition to the additive noise, imperfect estimation of the output data covariance matrix also causes performance loss and is studied in details based on perturbation theory.

A decorrelating RAKE receiver for CDMA communications over frequency-selective fading channels

Previous studies showed that multiuser detection in code-division multiple-access (CDMA) communications can be performed without explicit knowledge of users' channel characteristics in a frequency-selective fading environment. However, the computations of these blind approaches are an order of magnitude higher than existing adaptive minimum output energy (MOE) receivers which require at least knowledge of the desired user's channel response. Although the high-complexity problem can be alleviated by constrained adaptive filtering, the tradeoff is a significant drop in receiver performance, especially when the multipath pattern is time varying. In this paper, we present an adaptive receiver for CDMA communications over frequency-selective, and possibly time-varying, wireless channels. A salient feature of the new receiver is that it has complexity and performance comparable to that of the well-known MOE receivers, and yet requires no knowledge of the desired user's channel characteristics.