Low Complex Decision-Feedback Equalization for Time-Reversal Quasi-Orthogonal Space-Time Block Codes

In broadband wireless communication systems, single-carrier transmission with frequency domain equalization (SC-FDE) is regarded as an alternative modulation technique to the orthogonal frequency division multiplexing (OFDM). Compared with OFDM systems, SC-FDE has similar implementation complexity and performance. However, SC-FDE with linear equalizer will suffer from serious performance deterioration under deep frequency selective fading channels. An effective method to solve this problem is to introduce non-linear decision feedback equalization (DFE) to SC-FDE. In this paper, a low complexity iterative decision feedback equalizer in the frequency domain for single- carrier systems is proposed. Based on the minimum mean square error (MMSE) criterion, a simplified parameter estimation method is introduced to calculate the coefficients of the feed-forward and feedback filters, which reduces the implementation complexity of the equalizer. Simulations show that the performance of the proposed algorithm is similar to the traditional iterative block DFE (IBDFE) under various multipath fading channels but with lower complexity.

Single-Carrier Frequency Division Multiple Access (SC-FDMA) has been selected as the uplink transmission scheme in the 3GPP Long Term Evolution standard. SC-FDMA has reduced sensitivity to phase noise and a lower Peak-to-Average Power Ratio (PAPR) compared to Orthogonal Frequency Division Multiple Access. In this paper we propose joint Tomlinson-Harashima Precoding and transmit power allocation for SC-FDMA. We derive the optimum power allocation for SC-FDMA transmission for both Zero-Forcing (ZF) and Minimum Mean-Square Error (MMSE) LE receivers in order to maximize the achievable data rate subject to constant transmit power. Although this improves the system's performance and offers a 1-2 dB improvement over Frequency-Domain Decision Feedback Equalization (FD-DFE), when the proposed transmit power allocation scheme is combined with decision feedback equalization the system incurs a performance degradation due to error propagation. In this paper we propose a joint implementation of the derived power allocation scheme with THP. Here we show that the system's performance is further improved over both FD-LE and FD-DFE when transmit power allocation is applied.

We consider the design of the precoder for a multi-input multi-output (MIMO) communication system equipped with a decision feedback equalizer (DFE) receiver. For such design problems, perfect knowledge of the channel state information (CSI) at both the transmitter and the receiver is usually required. However, in the wireless communications environment, it is often difficult to provide sufficiently timely and accurate feedback of CSI from the receiver to the transmitter for such designs to be practically viable. In this paper, we consider the optimum design of a precoder for a wireless communication link having M transmitter antennas and N receiver antennas (M ≪ N), in which the channels are assumed to be flat fading and may be correlated. We assume that full knowledge of CSI is available at the receiver. At the transmitter however, only the second order statistics of the channels are available. Our goal here is to come up with an efficient design of the optimal precoder for such a MIMO system by minimizing the average arithmetic mean-squared error (MSE) of zero-forcing (ZF) decision feedback detection subject to a constraint on the total transmitting power. Applying some of the properties of the matrix parameters, this non-convex optimization problem can be transformed into a convex geometrical programming problem which can then be efficiently solved using an interior point method. The superior performance of our MIMO system equipped with the optimum precoder is verified by computer simulations.

In this work, we base on multi-layered perceptron neural networks with backpropagation algorithm (MLP/BP) to construct multi-input multi-output (MIMO) decision feedback equalizers (DFEs). The proposal is used to recover distorted quadrature phase-shift keying (QPSK) signal. From the simulations, we note that the proposed scheme can recover severe distorted signals as well as suppress intersymbol interference (ISI), adjacent channel interference (ACI) and background additive white Gaussian noise (AWGN). The better bit-error-rate (BER) and packet-error-rate (PER) performance as compared to a set of least-mean-square (LMS) DFEs is achieved. The presented MLP/BP-based MIMO DFE under the severe ISI channels with ACI and AWGN can improve over 1.5dB at PER=10-1 and BER=10-3.

In a companion paper, we have studied the zero-forcing (ZF) transceiver with decision feedback equalizer (DFE) over slowly time-varying narrowband multiinput multioutput (MIMO) channels. The space-time generalized triangular decomposition (ST-GTD) was used for the design of ZF-DFE transceivers. The space-time geometric mean decomposition (ST-GMD) ZF transceiver minimizes both the arithmetic mean square error (MSE) at the feedback detector and the average uncoded bit error rate (BER) in moderate high signal-to-noise ratio (SNR). This paper addresses the design problem of DFE transceiver without zero-forcing constraint. In the first part, a channel independent temporal precoder is superimposed on the conventional block-wise GMD-based minimum mean square error (MMSE) DFE transceiver to take advantage of the temporal diversity. In the second part, ST-GTD is applied for the design of MMSE DFE transceivers. With accurate channel prediction and space-time powerloading, the proposed ST-GMD MMSE transceiver minimizes the arithmetic MSE at the feedack detector, and maximizes Gaussian mutual information. For practical applications, the ST-GTD MMSE transceiver which does not require channel prediction but shares the same asymptotic BER performance with the ST-GMD MMSE system is also developed. In the convex region, our analysis shows that the proposed MMSE transceivers has better BER performance than the conventional GMD-based MMSE transceiver; the average BERs of the proposed systems are nonincreasing functions of the ST-block size. The superior performance of ST-GMD MMSE transceiver over the ST-GMD ZF transceiver is also verified analytically.

Frequency-domain decision-feedback equalization (FD-DFE) for single carrier modulation avoids interblock interferences (IBIs) by using guard intervals located in between two data blocks. If the period of a guard interval is shorter than that of the channel impulse response, the IBIs cannot be removed by the FD-DFE, which significantly deteriorates its performance. To handle this IBI problem, this letter introduces the adaptive self-orthogonalizing per-tone FD-DFE without channel estimation, where time dispersiveness, one weakness of the per-tone equalization, is compensated by the self-orthogonalization coming from the lattice structure of the Levinson-Durbin algorithm, which dramatically reduces bit-error rates of the proposed FD-DFE, comparing with the existing FD-DFE.

This paper considers the joint design problem of linear precoder, decision feedback equalizer (DFE) and bit allocation for multi-input multi-output (MIMO) broadcast (BC) channels. The problem is formulated as the power minimization problem when the target bit rate and per stream symbol error rate (SER) are specified. For the two-user case, a particular class of joint triangularization (JT) can be applied to obtain the optimal design for the joint optimization problem with quality of service (QoS) constraints, namely, the Minimum Power JT broadcast DFE transceiver (MPJT). For arbitrary number of users, a suboptimal design, the Power Minimized QR DFE broadcast transceiver (PMQR), is also proposed. Numerical results are presented to demonstrate the performance of MPJT and PMQR transceivers under different QoS constraints. 1

Faster-than-Nyquist (FTN) signaling was originally proposed by Mazo, which provides the opportunity of increasing data transmission rate effectively. However, this induces unavoidable ISI effects at the receiver and leads to higher receiver complexity. So far, a number of time domain equalization receiver algorithms have been proposed, which have higher demodulation complexity in FTN system with infinite ISI. Against this background, people put forward low complexity iterative frequency domain decision feedback equalization and simulate to show that frequency domain equalization can reduce computational complexity of FTN. In order to promote the practical application of FTN, this paper expands low complexity IBDFE to frequency-selective fading channels. At the same time, simulation results verify its feasibility.

This letter proposes a particle swarm optimization (PSO)-based multiuser detection (MUD) for the receive-diversity aided space-time block coding (STBC) systems. Due to the receive-diversity, the signals received at the different antennas are faded independently, resulting in an independent log-likelihood function (LLF) for each antenna. To resolve the multi-objective dilemma when choosing one signal estimation for multiple receive antenna-branches, each particle updates its velocity in a Pareto optimal way. Simulations and comparisons with the genetic algorithm and the maximum likelihood detection (MLD) verified the effectiveness of the proposed scheme.

This paper addresses the joint design problem of bit allocation and decision feedback equalizer (DFE) transceiver for multi-input multi-output (MIMO) broadcast (BC) channels. Channel state information (CSI) is assumed to be available both at the transmitter and receivers. The transceiver is designed by minimizing maximum symbol error rate (MAX-SER) under the total power and bitrate constraints. The bit allocation, precoder, feed-forward matrices and feedback matrices are the optimization variables. For the two-user case, a particular class of joint triangularization (JT) can be applied to obtain the optimal design for the problem, which is the optimal JT minimum Max-SER BC DFE transceiver (JTMMS). For arbitrary number of users, the suboptimal design, the QR BC DFE transceiver with bit allocation, is discussed. In the simulations, the Max-SER and average BER performance of the proposed systems are investigated.

This paper builds up the model of the multicarrier direct sequence-code division multiple access (MC DS-CDMA) system with time reversal space-time block coding (TR-STBC) transmit diversity, based on which steepest decreasing constant modulus algorithm (SDCMA) for blind equalization is studied. Simulations are performed and the conclusions are given. The conclusions show that the blind equalization based upon constant modulus algorithm (CMA) is simple and feasible in the MC DS-CDMA system with TR-STBC, and however CMA blind equalization can't improve system performance well when multiple access interference (MAI) is fairly severe.

The faster-than-Nyquist (FTN) signaling is a bandwidth-efficient technology which has drawn attention in the bandwidth-starved world. Since the symbols appear too early, inter-symbol interference (ISI) cannot be avoided in the receiver. Decision feedback equalization (DFE) cancellation is an efficient interference cancellation and signal detection schemes for FTN based communication system. However, since the noise isn't considered, the DFE scheme performs badly at low E b /N 0 . In order to further improve the detection performance, firstly, the detector based on minimum mean square error (MMS E) is investigated to at low E b /No, and then the precoding scheme is introduced in FTN signaling, including: singular value decomposition (SVD), geometric mean decomposition (GMD). Simulation results show that the GMD precoding can perform better than DFE.

In this paper we present a deterministic worst-case framework for reconstruction of discrete data transmissions through dispersive communication channels. This framework can be explored based on robust control ideas and formulations and serves as a complement to existing approaches that reconstruct data by optimizing probabilistic criteria. The particular problems touched upon are: (i) necessary and sufficient conditions for causal and non-causal perfect reconstruction under deterministic magnitude bounded noise for single-input single-output (SISO) and multi-input multi-output (MIMO) channels, (ii) perfect reconstruction based on decision feedback equalizer (DFE) structures, and (iii) necessary and sufficient conditions for perfect reconstruction with DFEs in the presence of channel fading. The /spl lscr//sup 1/ control theory emerges as the natural key player for analysis and synthesis of perfectly reconstructing receivers in this framework.

This paper studies joint transmitter and receiver design for the space-time block coding and spatial multiplexing hybrid communication system with limited feedback. Existed QR group receiver uses QR decomposition of the channel matrix to separate the filtered versions of the multiplexed space-time coded symbol blocks followed by space-time decoder, and the performance of this scheme is usually limited due to diversity lack of the earliest detected block. To overcome this problem, in this paper each space-time data block adaptively selects the appropriate transmit antenna group according to channel state information. Furthermore, this transmit antenna grouping can be derived with low complexity using successive QR decomposition of channel matrix at the receiver, thus only the index of antenna grouping result in a predetermined codebook is needed to fed back to the transmitter. The performance of the proposed schemes is evaluated in correlated channels through computer simulations.

Multiple-input/multiple-output (MIMO) channel models derived from channel sounding experiments conducted at Cairns Army Airfield, Ft. Rucker, AL are used to assess MIMO equalizers based on time-reversal space-time block codes (TR-STBC). For the channels used in this case study, 2 × 1 MIMO equalizer offers an improvement of 0.75 dB to 1.5 dB relative to the ideal informed transmitter using transmit selection diversity. The data also demonstrate that the “best” transmitter-to-receiver antenna combination changes. Consequently, without channel information, the uninformed transmitter has no choice but to use a TR-STBC.