Frequency-domain equalization for OFDMA-based multiuser MIMO systems with improper modulation schemes (original) (raw)
Multiuser MIMO channel equalization
2006
In MIMO receivers, the channel state needs to be estimated for equalization, detection, and for feedback to the transmitter in case of adaptive modulation and coding. Most current iterative [1, 2, 3] and noniterative schemes in the singleuser MIMO case are training-based and rely on the transmission of pilot symbols. Alternatives to pilot-based algorithms are semiblind schemes which exploit, for example, the known structure of the space-time code to allow reliable channel estimation during ongoing data transmission . Channel estimation and equalization for multiuser MIMO systems involve both information-theoretic [9, 10] and signal processing aspects.
Proceedings of the 4th WSEAS international …, 2010
Code division multiple access (CDMA) suffers from intersymbol interference (ISI) and multi-user interference (MUI) in a frequency-selective multipath fading channel, but when properly designed, it enjoys multipath diversity. Orthogonal frequency division multiple access (FDMA) is a promising MUI free but it dose not enable the multi-path induced diversity without employing error control coding. Group Orthogonal Multi-carrier CDMA (GO-MC-CDMA) merges the advantages of OFDMA and CDMA systems.
Practical low complexity linear equalization for MIMO-CDMA systems
2003
This article first reviews recently proposed techniques for adaptive and direct linear MIMO equalization in the context of MIMO-CDMA systems and in particular with application to a MIMO-extended UMTS-FDD downlink. The focus is thereby mainly on the complexity of the algorithms. The second part of the paper proposes frequency domain (FD) MIMO equalization using the overlap/add FFT method in conjunction with two different lowcomplexity FD-deconvolution techniques to obtain the equalizer coefficients based on explicit channel impulse response estimates. The effects of imperfect channel estimation are discussed. An architecture for the VLSI implementation of the proposed method is suggested and an estimate of the complexity of the proposed circuit is given in the conclusions.
Regularized MIMO Equalization for SC-FDMA Systems
Circuits, Systems, and Signal Processing, 2012
In this paper, we propose an efficient frequency domain equalization scheme for Multiple Input Multiple Output (MIMO) Single-Carrier Frequency-Division Multiple Access (SC-FDMA) systems. The proposed scheme avoids the complexity problem associated with the conventional MIMO Zero-Forcing (ZF) equalizer as well as the noise enhancement problem. The matrix inversion process associated with the proposed equalization scheme is performed in two steps to reduce complexity. A regularization term is added in the second step of the matrix inversion to avoid the noise enhancement. Simulation experiments on uplink MIMO SC-FDMA systems show that the proposed equalization scheme provides better performance than that of the ZF equalizer and its complexity is far less than that of the ZF equalizer.
2009
Joint transmitter-receiver optimization in generalized multicarrier code-division multiplexing (GMC-CDM) systems is investigated in this paper. The optimization consists of a one-tap post-frequency-domain equalizer (post-FDE) and a onetap pre-FDE. While the one-tap post-FDE is optimized under the criterion of minimum mean square error (MMSE), the one-tap pre-FDE is achieved through three stages of optimization, which are operated at different levels and motivated to achieve, possibly, different objectives, including maximum throughput and maximum reliability. Specifically, in our three-stage pre-FDE, the first-stage pre-FDE is operated at the symbol level, concerning only the symbols within a group. The second-stage pre-FDE is carried out at the group level for harmonization among the groups. Finally, the third-stage pre-FDE handles group partition. In this paper, the error and throughput performance of the GMC-CDM systems is investigated when assuming communications over frequency-selective Rayleigh fading channels. It can be shown that the reliability or throughput of the GMC-CDM systems can be significantly improved by employment of the proposed pre-and post-FDE schemes. Furthermore, the pre-and post-FDE algorithms obtained can be implemented with high flexibility, which facilitates a GMC-CDM system to achieve a good tradeoff between its throughput and reliability.
IET Communications, 2011
Similar to the orthogonal frequency division multiple access (OFDMA) system, the single-carrier frequency division multiple access (SC-FDMA) system also suffers from frequency mismatches between the transmitter and the receiver. As a result, in this system, the carrier frequency offsets (CFOs) disrupt the orthogonality between subcarriers and give rise to inter-carrier interference (ICI) and multiple access interference (MAI) among users. The authors present a new minimum mean square error (MMSE) equaliser, which jointly performs equalisation and carrier frequency offsets (CFOs) compensation. The mathematical expression of this equaliser has been derived taking into account the MAI and the channel noise. A low complexity implementation of the proposed equalisation scheme using a banded matrix approximation is presented here. From the obtained simulation results, the proposed equalisation scheme is able to enhance the performance of the SC-FDMA system, even in the presence of estimation errors.
Journal of …, 2011
Adaptive multiuser receivers scheme for MIMO OFDM over Iterative-Equalization for Single-Carrier Transmission, which we refer to as Iterative AMUD MIMO OFDM. It involves the joint iteration of the adaptive minimum mean square error multiuser detection and decoding algorithm with prior information of the channel and interference cancelation in the spatial domain. A partially filtered gradient LMS (Adaptive) algorithm is also applied to improve the convergence speed and tracking ability of the adaptive detectors with slight increase in complexity. The proposed technique is analyzed in slow and fast Rayleigh fading channels in MIMO OFDM systems. The Adaptive Multiuser Detection for MIMO OFDM system (AMUD MIMO OFDM) performs as well as the iterative equalization for single-carrier for higher modulation scheme. The LMS algorithm and maximum a posterior (MAP) algorithm are utilized in the receiver structures. The results of the higher modulation schemes shows that as the modulation order increases, a higher S R is required to obtain the same BER performance at a lower order. The iterative gain is greater for higher modulation orders as compared with lower modulation __________________________________________________________________________________________
IEEE Transactions on Signal Processing, 2000
Channel estimation and tracking pose real problems in broadband single-carrier wireless communication systems employing multiple transmit and receive antennas. An alternative to estimating the channel is to adaptively equalize the received symbols. Several adaptive equalization solutions have been researched for systems operating in the time domain. However, these solutions tend to be computationally intensive. A low-complexity alternative is to adaptively equalize the received message in the frequency domain. In this paper, we present an adaptive frequency-domain equalization (FDE) algorithm for implementation in single-carrier (SC) multiple-input multiple-output (MIMO) systems. Furthermore, we outline a novel method of reducing the overhead required to train the proposed equalizer. Finally, we address the issues of complexity and training sequence design. Other computationally efficient adaptive FDE algorithms for use in SC systems employing single transmit and receive antennas, receive diversity, or space-time block codes (STBC) can be found in the literature. However, the algorithm detailed in this paper can be implemented in STBC systems as well as in broadband spatial multiplexing systems, making it suitable for use in high data rate MIMO applications.
An investigation of MIMO singlecarrier frequency-domain MMSE equalization
2002
In recent years, the ambition to achieve very high data rates in wireless communication systems has fuelled the study of multiple-input multiple-output (MIMO) architectures and has resulted in the need for more advanced equalization techniques. Currently, the wireless industry is at a point where typical time-domain equalization solutions are becoming too complex to implement in MIMO systems. In this paper, a single-carrier frequency-domain equalization (SC-FDE) solution is presented that utilizes the minimum mean-squared error (MMSE) criterion to perform equalization on the received message. The error-rate performance of a system that employs this MMSE equalizer is analyzed.
Equalization methods in OFDM and FMT systems for broadband wireless communications
IEEE Transactions on Communications, 2002
Multicarrier systems are adopted in several standards for their ability to achieve optimal performance in very dispersive channels. In particular, discrete multitone (DMT) and filtered multitone (FMT) systems are two examples where the modulation filter has an ideal rectangular amplitude characteristic in time and frequency domains, respectively.