Linear Precoder Design Through Cut-Off Rate Maximization in MIMO-OFDM Coded Systems With Imperfect CSIT

The electrical wireless network build 4G TD-LTE network in 1.8GHz band, orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) are the key technologies. The OFDM system is sensitive to carrier frequency offset (CFO) and hence accurate CFO estimates for the OFDM system are essential. In this paper, we study the problem of carrier frequency offset (CFO) in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems, and then a multi-invariance PM algorithm is proposed to estimate CFO in MIMO-OFDM system. The proposed algorithm employs the property of multi-invariance. Simulations show that the proposed algorithm has a better CFO estimation performance than PM.

Publication in the conference proceedings of EUSIPCO, Glasgow, Scotland, 2009

Multiuser channel estimation and prediction in two dimensions for MIMO–OFDM uplinks

Physical layer security is a crucial issue in wireless networks to prevent legitimate communication from eavesdropping. This paper investigates the physical layer security of a wireless multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) communication system in the presence of a multiple-antenna eavesdropper. We first propose a minimum mean square error (MMSE)-based-filter secure MIMO–OFDM system which can destroy the orthogonality of eavesdropper’s signals. The MMSE-based-filter is used at the receiver to suppress the inter-subcarrier interference and disturb the reception of eavesdropper while maintaining the quality of legitimate transmission. Next, we propose another artificial noise (AN)-assisted secure MIMO–OFDM system to further improve the security of the legitimate transmission. The time-domain AN signal is designed to be canceled out at the legitimate receiver. Therefore, AN will disturb the reception of eavesdropper while the legitimate transmission will not be affected. Finally, power allocation for AN signals and subcarriers will be discussed since AN is generated utilizing the residual power of the MIMO–OFDM system. Simulation results are presented to demonstrate the security performance of the proposed transmit filter design and AN-assisted scheme in the MIMO–OFDM system.

For a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system, time-varying multipath fading of channel destroys the orthogonality among subcarriers and leads to serious intercarrier interference (ICI). The system performance degrades more severely as normalized Doppler frequency increases. In order to mitigate the effect of time-varying fading, a low-complexity iterative receiver with joint ICI cancellation and pilot-assisted channel estimation is proposed. The initial channel state information (CSI) is estimated by performing time-domain interpolation and least-square (LS) method on the received pilot symbols. The soft outputs are obtained from the decoders after low-complexity linear minimum mean-square error (LC-LMMSE) detection. In the following stages, the soft outputs are feedback to update the CSI estimation. Furthermore, a ¿linear statistics combining¿ (LSC) technique is used to improve the performance of the proposed equalizer by combining the outputs of LC-LMMSE and parallel interference canceler (PIC) with weighting coefficients estimated by maximizing the signal to interference-plus-noise ratio (SINR) at the output of LSC. The complexity of system is significantly reduced by restricting the interference to neighboring subcarriers and employing the LC-LMMSE by limiting the frequency-domain CSI into diagonal region. The simulation results show that the proposed iterative receiver with estimated CSI approaches the ICI-free bound even at very high mobility scenarios.

In this paper a deterministic parallel factor (PARAFAC) receiver is proposed, for multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. We show that the received signal forms a 4-way tensor whose dimensions are space, time, and frequency, and can be written as a sum of tensor products (over paths and users) of four tensors representing the channel (for two of them), the symbols, and the modulation. Parameters of this model are identified via an alternating least squares (ALS) algorithm, called DEBRE, whose identifiability conditions are pointed out

This paper presents an automatic VHDL generator for a modified fixed-point interpolation QR decomposition algorithm for Spherical Detector (SD) based Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems. A modified algorithm is proposed that moves the bulk of the complex domain calculations to the real domain, by leveraging Givens rotations requiring only additions, multiplications, and inverse square root operations. An efficient inverse square root algorithm is presented along with fixed-point analysis of a typical MIMO-OFDM system in various noisy wireless channels. Autogeneration of VHDL modules is described with results of 2 × 2 and 4 × 4 QR-based SD MIMO detection in terms of FPGA slice registers and slice LUTs.

This paper presents a candidate codeword selection scheme with bit flipping in two step joint decoding of block coded signals in an overloaded multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system. In previous literature, the two step joint decoding scheme has been proposed for complexity reduction of maximum likelihood decoding of a block code in the overloaded MIMO system. However, the two step decoding scheme has not been combined with an outer code. The selection of the candidate codewords in the inner block code may not always be able to provide the metric of a binary coded symbol for the outer code. Candidate codewords are then created through bit flipping in the proposed scheme. It is shown that the two step decoding scheme reduces the complexity by about 0.026 for 4 signal streams with the cost of bit error rate degradation within 0.5dB.

In this paper, a method for estimating the maximum Doppler shift frequency is presented for Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems. This method uses the Autocorrelation Function (ACF) for estimating frequency shift that induces ICI between adjacent OFDM subcarriers. The simulation results investigate the BER performance of OFDM system that achieves transmit and receive diversity by using Alamouti/MRC, as well as the BER performance of MIMO linear detectors Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) under the effect of a Doppler spread channel.

In this paper, we developed a joint AMC-ARQ design combining adaptive modulation and coding at the physical layer with automatic repeat request protocol at the data link layer in multiple-input multiple-output(MIMO) orthogonal frequency division multiplexing(OFDM) systems which is converted into a series of parallel and independent flat sub-channels based on channel matrix singular value decomposition(SVD) at the physical layer. Theoretical derivation supports that our proposed design maximizes the spectral efficiency under prescribed delay and error performance constrains. Simulation results show that this cross-layer design based on channel matrix singular decomposition for MIMO-OFDM obtains more than 2 dB gain in spectral efficiency comparing the traditional SISO cross-layer design.

In this paper, we consider a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system operating over unknown frequency selective fading channels. We propose a novel scheme to obtain frequency synchronization together with multi-antenna channel estimation. Computer simulation results are provided to demonstrate the performance of the proposed scheme.

This paper investigates low complexity detection for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with co-channel interference (CCI). We firstly derive minimum mean square error (MMSE) detection based on sorted QR decomposition (SQRD) and modified MMSE SQRD detection for MIMO-OFDM systems with CCI. Although better performance can be achieved by the new detectors than liner MMSE (LMMSE) detection, the computational complexity is still high due to the required matrix inversion operation. In order to overcome such an issue and design low complexity detection method for MIMO-OFDM systems with CCI, then, we propose an improved MMSE SQRD detector by utilizing a regularization method. The simplification of the regularization parameter calculation in the proposed method is then discussed. Simulation results show that the error performance of the proposed method approaches modified MMSE SQRD detection in presence of CCI, while keeping a much lower complexity.

A new carrier phase and frequency recovery scheme is proposed for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The algorithm uses an extended Kalman filter (EKF) to estimate the instantaneous phase and frequency offset. A linear minimum mean squared error (LMMSE) data-channel extractor is used to isolate the phase and frequency dependent term from the received signal. The proposed algorithm can provide both phase and carrier frequency recovery and has lower complexity than other approaches in the literature. In addition there is very little latency associated with the proposed approach. Simulation results show that the proposed algorithm can track quickly carrier phase and frequency offset and the performance loss compared to the synchronous case is very small.

In this paper, we consider design optimization of low-density parity-check (LDPC) coded multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems for high data rate wireless transmission. First, starting from the maximum-likelihood (ML) principle, we devise a novel expectation-maximization (EM)-based scheme for joint estimation of carrier frequency-offset (CFO) and channel coefficients in MIMO-OFDM systems. Based on simulation results, the performance of joint estimator is quite satisfying. Then, this CFO estimator is incorporated into the initialization step of the turbo receiver. Experimental results show the effectiveness of our receiver design in combating CFO over unknown frequency selective fading channels.

To achieve high spectrum efficiency and combat the detrimental effects of frequency-selective fading, we consider space-time coded (STC) multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM). Specifically, we propose the use of a simple convolutionally coded scheme in an OFDM system to effectively take advantage of the frequency diversity. This scheme is based on the use of a proper distribution of the channel bits in both the space and frequency domains along with an iterative receiver structure. Theoretical and numerical results based upon the use of Monte Carlo simulation will demonstrate the superiority of the proposed CC coded scheme over the conventional STC coded approach.