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Most contributions on nonlinear Tomlinson-Harashima precoding (THP) assume complete channel state information (CSI) at the transmitter. However, complete CSI is not available in many wireless systems, and the conventional THP is sensitive to channel mismatch. This article investigates the THP design with imperfect CSI at base station (BS) in spatially correlated multiuser multiple-input multiple-output...
This paper aims to illustrate the performances of different spreading sequences in mean-square-error linear multiuser systems. The analyzed spreading sequences are Walsh codes (length 8 and 32), PN (pseudo-random) sequences and Gold sequences. Influence of correlation between sequences will be studied and the results are shown as BER (Bit Error Rate) depending on SNR (Signal-to-Noise Ratio). The conclusion...
This paper proposes an MMSE detector applying the reciprocal lattice reduction (LR) in MIMO systems. The proposed detector achieves as good as or better BER performances than the LR aided detector using the conventional LLL algorithm and using the Seysen's algorithm in the 4×4 and the 8×8 MIMO systems. It also achieves BER curves to be as steep as or steeper than those using the maximum likelihood...
In this paper, we modify background noise of multi-user detection, by selecting non-Gaussian noise of more harshly conditions such as Laplace noise and Alpha-Stable noise. Under the traditional MMSE algorithm, Comparing the BER of the two noises with Gaussian noise, which can get close to real complex environment and be beneficial to further research.
We utilize a pair of decision feedback equalizers (DFEs) operating in opposite directions in turbo equalization setting to remove the effect of intersymbol interference (ISI) at the receiver. With a specific residual interference processing strategy proposed, the bi-directional DFE (BiDFE) are free from any significant error propagation. A diversity combining scheme is also proposed that effectively...
A novel variable step size least mean squares (VSS-LMS) algorithm based on channel output autocorrelation has been proposed to improve the weakness of previous VSS-LMS for application to unknown channel estimation or system identification in low-SNR in this paper. Computer simulations have been performed to show the performance of the proposed method in frequency selective Rayleigh fading channels...
This paper investigates the performance of multiple input multiple output orthogonal frequency and code division multiplexing (MIMO-OFCDM), where practical channel estimation is carried out with time-multiplexed pilot signals. Conditioned on each channel realization and estimation, the BER of MIMO-OFCDM is analytically evaluated, assuming zero-forcing successive interference cancellation (ZF-SIC)...
In this paper, we present low complexity down-sampled MMSE channel estimation. We reduced MMSE channel estimation complexity by downsampling the MMSE weight matrix. The simulation results show that the bit error rate (BER) performance significantly improved over the least square channel estimation and has comparable BER performance with MMSE channel estimation at low SNR with significant decrease...
In this paper, an adaptive MMSE channel estimation method is proposed for UWB-OFDM system. As we known, the MMSE algorithm is dependent on the auto-correlation of the known signals and the cross-correlation between the known signals and the signals to be estimated. These parameters are difficult to obtain in practice, because it needs a long-term statistic at the cost of huge complexity and time delay...
In this paper, an interference suppression scheme by MMSE combining in OFDM-antenna array with time shifted sampling (TSS) is proposed. An array antenna at a base station has been thoroughly investigated to increase the uplink capacity. The performance of the uplink is not only limited by the correlation between the antenna elements, which strongly depends on the spatial aspects of the channel, as...
The performance of linear filters degrade drastically when applied to mitigate intersymbol interference caused by channels with frequent nulls in their spectral characteristics like, e.g., time-dispersive radio channels. In such cases, the well-known decision feedback equalizer (DFE) is one possible nonlinear approach to improve the quality of the receiver. However, adapting the DFE filter coefficients...
In reality, this is no such thing as perfect channel estimation. But unfortunately, channel estimation errors have never been taken into account by existing soft-output minimum mean square error (MMSE) multiple-input multiple-output (MIMO) detector when calculating the log-likelihood ratio (LLR) for coded bits, i.e., the soft information. As a result, its performance can be substantially degraded...
Lattice reduction aided (LRA) detection with the LLL algorithm has been investigated to achieve the MIMO channel capacity with low computational complexity. This paper proposes an improved LRA-MMSE detection using the forward and the backward reduction LLL algorithms for the 8times8 MIMO to obtain more reliable estimates of the transmitted signals. The proposed method achieved much better BERs than...
This paper investigates the performance of orthogonal frequency and code division multiplexing (OFCDM) systems with multiple input multiple output (MIMO) multiplexing (MIMO-OFCDM), where multi-code transmission is employed to increase the data rate. An analytical approach is presented to evaluate the performance of the system using joint space-frequency detection with zero-forcing successive interference...
This paper studies the fluctuations of the post-processing SNR at the output of the linear MMSE receiver in (receive) correlated multiple input multiple output (MIMO) systems. Although it is known that asymptotically, the SNR behaves like a Gaussian random variable, this approximation may yield to inaccurate estimates for small dimension. In order to circumvent this, we use gamma and generalized gamma...
The estimation of receiving impulse template can be simplified by the transmitted reference (TR) signaling scheme in ultra-wideband communication. However, in multiuser environment, the TR scheme would be severely interfered for its non-coherence. By modulating the transmitted-reference with a pseudo-random code, we propose an analog LMS detection based on minimum mean-square error criterion to suppress...
In this paper, we propose a code-diversity system using adaptive weight control (AWC) to suppress multiple access interference in DS/CDMA system. This proposed system is modified from a conventional code-diversity system using a constant amplitude composite sequence. In a conventional system, interference suppression performance is much degraded against the increment of multiple access users. The...
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