Iterative MMSE Research Articles

Efficient and Low-Complex Signal Detection with Iterative Feedback in Wireless MIMO-OFDM Systems.

To solve error propagation and exorbitant computational complexity of signal detection in wireless multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM) systems, a low-complex and efficient signal detection with iterative feedback is proposed via a constellation point feedback optimization of minimum mean square error-ordered successive interference cancellation (MMSE-OSIC) to approach the optimal detection. The candidate vectors are formed by selecting the candidate constellation points. Additionally, the vector most approaching received signals is chosen by the maximum likelihood (ML) criterion in formed candidate vectors to reduce the error propagation by previous erroneous decision, thus improving the detection performance. Under a large number of matrix inversion operations in the above iterative MMSE process, effective and fast signal detection is hard to be achieved. Then, a symmetric successive relaxation iterative algorithm is proposed to avoid the complex matrix inversion calculation process. The relaxation factor and initial iteration value are reasonably configured with low computational complexity to achieve good detection close to that of the MMSE with fewer iterations. Simultaneously, the error diffusion and complexity accumulation caused by the successive detection of the subsequent OSIC scheme are also improved. In addition, a method via a parallel coarse and fine detection deals with several layers to both reduce iterations and improve performance. Therefore, the proposed scheme significantly promotes the MIMO-OFDM performance and thus plays an irreplaceable role in the future sixth generation (6G) mobile communications and wireless sensor networks, and so on.

Iterative Robust MMSE Receiver for STBC under Channel Information Errors

Iterative Robust MMSE Receiver for STBC under Channel Information Errors

A Semianalytical Performance Prediction Method for an Iterative MIMO MMSE Receiver With Forward and Backward Error Control

This paper proposes a semianalytical performance prediction method for an iterative receiver that processes signals arriving through a frequency-selective multiple-input multiple-output radio channel. Earlier results provide a distribution of the signal-to-interference-plus-noise ratio at the output of a frequency domain soft interference cancellation minimum mean square error equalizer, which is used to approximate the distribution of the log-likelihood ratios (LLRs) of the demapped bits. Mutual information transfer charts establish a bijective relationship between the variance of the LLRs and the mutual information. We assume a 3rd Generation Partnership Project compliant turbo code, whose transfer charts are simulated in advance. By approximating the LLR variance distribution of the demapped equalizer output, we can evaluate the probability of an intersection between an equalizer chart associated with a random channel realization and a fixed decoder chart. This probability provides the frame error rate. Our proposed prediction method allows horizontally and vertically encoded spatial multiplexing schemes. The vertically encoded scheme is complemented by the inclusion of the Chase combining hybrid automatic repeat request protocol. The proposed method allows reasonable receive antenna correlation.

Hybrid Carrier Modulation with Time-Domain Windows and Iterative Equalization over Underwater Acoustic Channels

In this letter, we consider an hybrid carrier modulation (HCM) scheme based on weighted-type fractional Fourier transform (WFRFT) for communications over underwater acoustic channels (UAC). Time domain windowing and a frequency domain iterative MMSE equalization (FD-IMSE) are employed in the HCM-underwater-acoustic system. Numerical results manifest that the HCM outperforms both the multi-carrier modulation and the single carrier modulation in terms of bit-error-ratio over UAC, though with an acceptable increase in computation burden.

Iterative MMSE Detection with Interference Cancellation for Up-Link HARQ Using Frequency-Domain Filtered SC-FDMA MIMO Multiplexing

SUMMARY In this paper, we propose an iterative minimum mean square error detection with interference cancellation (MMSED-IC) for frequency-domain filtered single carrier (SC)-frequency-division multipleaccess (FDMA) uplink transmission. The use of a square-root Nyquist transmit filter reduces the peak-to-average power ratio (PAPR) while increases the frequency-diversity gain. However, if carrier-frequency separation among multiple-access users is kept the same as the one used for the case of roll-off factor α=0 (i.e., brick-wall filter), then the adjacent users’ spectra will overlap and multi-user interference (MUI) occurs. The proposed MMSED-IC can sufficiently suppress the MUI from adjacent users while achieving the maximum frequency-diversity gain. We apply the proposed MMSED-IC to a packet access using filtered SC-FDMA, multi-input multi-output (MIMO) multiplexing, and hybrid automatic repeat request (HARQ). It is shown by computer simulation that filtered SC-FDMA with α = 1 can achieve higher throughput than orthogonal frequency division multiple access (OFDMA).

Semi-Analytical Performance Prediction Methods for Iterative MMSE-IC Multiuser MIMO Joint Decoding

In this paper, two semi-analytical performance prediction methods are proposed and compared for multiuser MIMO transmission over block-fading multipath channels and iterative MMSE successive interference cancellation based joint decoding. In the first method, we develop a completely analytical parameterisation of the whole turbo receiver up to the users' channel decoders. The method which follows the classical framework of extrinsic information transfer charts tracks the evolution of the average mutual information defined at coded bit level and circulating between the multiuser detector and the bank of channel decoders. The modelling of the demapping output in the multiuser detector is based on an explicit calculation of the (conditional) mutual information for each symbol digit in a symbol label under arbitrary (possibly non-uniform) a priori probability distributions on others. Then, shifting in viewpoint and considering user demapping and decoding as a joint process, we present an alternative method which tracks the evolution of the average mutual information defined at symbol level and circulating between the MMSE successive interference based interface and the bank of joint demappers and channel decoders. This allows to avoid the critical issue of parameterising the demapping. Numerical results demonstrate the superiority of the second method for high-order non-linear mapping.

Superposition coded modulation and iterative linear MMSE detection

We study superposition coded modulation (SCM) with iterative linear minimum-mean-square-error (LMMSE) detection. We show that SCM offers an attractive solution for highly complicated transmission environments with severe interference. We analyze the impact of signaling schemes on the performance of iterative LMMSE detection. We prove that among all possible signaling methods, SCM maximizes the output signal-to-noise/ interference ratio (SNIR) in the LMMSE estimates during iterative detection. Numerical examples are used to demonstrate that SCM outperforms other signaling methods when iterative LMMSE detection is applied to multi-user/multi-antenna/multipath channels.

Noncooperative iterative MMSE beamforming algorithms for ad hoc networks

An asynchronous unicast ad hoc network is considered, where each node i is equipped with a receive/transmit beam-former pair (W/sub i/, g/sub i/) designed under a quality-of-service (QoS) SNR constraint. It is first shown that the minimum sum-power beamformers for the network satisfy a weak duality condition, in which the pairs ((g/sub i//sup opt/)*, (W/sub i//sup opt/)*) achieve the same sum power as the primal network. However, the optimum receive beamformer w/sub i//sup opt/ is not in general equal to (g/sub i//sup opt/)*, in contrast to the case of cellular and time-division duplexing networks. Iterative minimum mean-square error (IMMSE) beamforming algorithms are then proposed in which w/sub i/ = g/sub i/* is enforced. These algorithms are shown to be instances of the Power Algorithm in which gi is the maximizing eigenvector of an SNR-related objective matrix. The IMMSE algorithm can also be viewed as a noncooperative beamforming game, in which the payoff includes normalized SNR, and the tax is related to interference caused at other nodes. The existence of fixed points (Nash equilibria) is proved for IMMSE. Furthermore, fixed points of IMMSE are shown to satisfy the first-order necessary conditions for optimization using a network Lagrangian. The IMMSE game is modified to yield a sequential distortionless-response beamforming algorithm, which is shown to be convergent using a Total Interference Function. Extensive simulation results illustrate that IMMSE yields better power efficiency than a greedy noncooperative SNR-maximizing game.

Performance Enhancement of SC/S-MMSE Turbo Receiver for MIMO-SDM/OFDM Transmission

This paper aims to improve the performance of the soft canceller followed by simplified minimum mean-square error (SC/S-MMSE) turbo receiver [11] for multiple-input and multiple-output space-division multiplexing/orthogonal frequency division multiplexing (MIMO-SDM/OFDM) transmission; it performs iterative parallel soft interference cancellation and MMSE filtering, and stream-wise soft-input and soft-output decoding. For this aim, we newly introduce two detection techniques: 1) serial interference cancellation, and 2) cyclic redundancy check (CRC)-assisted interference cancellation and MMSE filter tap computation. Various computer simulations are conducted to evaluate the performance enhancement obtained via the use of the two detection techniques. The computer simulation results show that this paper's proposed serial SC/S-MMSE turbo receiver with CRC achieves frame error rate (FER) performance gain over existing MIMO receivers (MMSE receiver, V-BLAST receiver, parallel SC/MMSE-matched filter (MF) turbo receiver, and parallel SC/S-MMSE turbo receiver) for QPSK, 16QAM and 64QAM modulation while keeping the comparable complexity order.

Iterative mmse Receivers for Space–Time Trellis-Coded CDMA Systems in Multipath Fading Channels

We explore code-division multiple-access (CDMA) systems with multiple transmit and receive antennas combined with space-time trellis codes over a frequency-selective channel. The conventional noniterative multiuser minimum mean square error (NIMU-mmse) detector is generalized to accommodate multiple antennas and multiple paths and then extended to include the turbo principle in an iterative fashion, allowing interference regeneration and cancellation at the receiver. Iterative multiuser mmse (IMU-mmse) receivers employing chip- and symbol-level detectors are derived and their equivalence is demonstrated. Computer simulations show that the proposed iterative mmse equalizers completely remove the interference of the other users in a multiantenna environment; they provide a significant improvement over the NIMU-mmse detector and they effectively achieve the single-user performance, even in a fully loaded system. Two suboptimal iterative mmse detectors, which allow a computational complexity reduction of up to three orders of magnitude compared to the IMU-mmse and still outperform the NIMU-mmse detector, are introduced. The proposed iterative mmse equalizers are analyzed and supported by extensive computer simulations.

Simplified Iterative MMSE Multiuser Detector Using Polynomial-Expansion Approximation

We propose to simplify the inverse matrix computation of the iterative MMSE multiuser detector by using a low-complexity polynomial-expansion matrix approximation. This approximation is an application of the polynomial-expansion multiuser detector. The number of stages is set to the number of users to obtain a linear complexity. Simulations under AWGN and asynchronous multipath channels show that the approximation performs as well as the exact inverse implementation for iterative MMSE multiuser detector.

Space-time iterative receivers for narrowband multichannel networks

The iterative MMSE multiuser detection paradigm is applied to the suppression of cochannel interference in the coded narrowband (multicell) uplink. The equivalent of multiple chips per bit (necessary for MMSE multiuser demodulation) is generated via multisensor reception, the array responses serving as user signatures. This receiver's robustness to overloading allows its sensor count to be much lower than the typical number of other-cell cochannel interferers. A permutation transmit diversity technique that exploits channel time-selectivity is proposed in order to enhance the interuser separation afforded by multisensor reception.