Output-orthogonal Frequency Division Multiplexing Systems Research Articles

Performance Analysis of Low Power Channel Estimator for Multi User MIMO-OFDM System

Channel Estimator plays an important role in reducing the error rate in wireless communication system. Conventional channel Estimators consumed high power consumption due to their complex design architectures. In this paper, a simple low power and high efficient channel Estimator for multi input multi output-orthogonal frequency division multiplexing system has been designed in order to reduce the error rate in the receiver side of the communication system. The performance of the proposed channel Estimator is analyzed interms of signal to noise ratio, bit error rate, power and current consumptions. The proposed low power channel Estimator architecture had been tested with different very large scale integration processors to validate their performance.

Hardware Implementation of the Compressed Beamforming Weights Calculation for the Practical Wireless MIMO-OFDM Communication System

The compressed beamforming weights (CBWs) feedback is used in the IEEE 802.11n/ac WLAN, an example of the practical beamforming multiple input multiple output-orthogonal frequency division multiplexing system, to reduce the amount of feedback information so that the beamformee can respond rapidly to the beamformer. The CBW associated with each sub-carrier includes the quantized angles obtained from QR-decomposition (QRD) of the right singular vectors of each corresponding channel matrix. Efficient matrix QRD and singular value decomposition (SVD) together are therefore desirable for computing the CBWs associated with all sub-carriers. Considering the exemplary antenna configuration of 4 beamformer and 2 beamformee antennas, we propose to apply the same matrix triangulation to compute the SVD of a 2-by-4 matrix and to compute the QRD of a 4-by-2 matrix. We can achieve gate count reduction by exploiting only one matrix triangulation module in our architecture. The VLSI implementation results under the TSMC 90-ns CMOS technology reveal that our architecture requires 194.25K gates while operating at frequency 200.75 MHz. Additionally, with better normalized matrix throughput and gate efficiency, our architecture outperforms one earlier architectural design to compute the CBWs.

Resource allocation for multiple input multiple output‐orthogonal frequency division multiplexing ‐based space division multiple access systems

The problem of the system throughput maximisation and the fairness issue among users is considered for the downlink multiuser multiple input multiple output-orthogonal frequency division multiplexing system with MMSE precoding. Since finding the optimal solution by using the exhaustive search has very high computational burden, the authors propose a low-complexity user selection strategy plus the optimal power allocation in this study. With resorting to the mathematical simplification process, the proposed user selection scheme is designed to compare the related value of SINR. The power allocation is performed after the user selection. However, the power allocation is not in interference-free environment but in the presence of crosstalk, which is a nonlinear non-convex optimisation problem. In this study, the authors use an optimisation technique to obtain the optimal solution of the constrained non-convex nonlinear problem by replacing the objective function with a difference of two convex functions. A bisection-based strategy to solve this problem with interference-awareness to find local optimal solutions is presented in this study. Simulation results show that the performance of the proposed algorithm is close to that of the optimal solution. The trade-off between the system throughput and the fairness among users is also considered.

Analogue joint source‐channel coding for multiple input multiple output–orthogonal frequency division multiplexing systems

AbstractAnalogue joint source‐channel coding (JSCC) has been shown to approach the optimal distortion‐cost trade‐off when transmitting over additive white Gaussian noise channels. In this work, we consider analogue JSCC over frequency‐selective channels using orthogonal frequency division multiplexing (OFDM) modulation and multiple antennas at transmission and/or reception, that is, using a multiple input multiple output(MIMO)‐OFDM system. Because of its high complexity, optimal Minimum Mean Square Error (MMSE) analogue JSCC decoding is infeasible in MIMO‐OFDM systems and a practical two‐stage decoding approach made up of an MMSE estimator followed by a maximum likelihood decoder is proposed instead. Three different alternatives for system optimisation are considered: non‐adaptive coding, adaptive coding and adaptive coding with precoding. We show that the three considered strategies approach the optimal distortion‐cost trade‐off, but the best performance is obtained with the adaptive coding scheme when precoding is utilised. Copyright © 2014 John Wiley & Sons, Ltd.

Inter carrier interference removal in MIMO-OFDM system

This review paper is about the schemes of removing the inter carrier interference in the multiple input multiple output-orthogonal frequency division multiplexing system. The inter carrier interference occurs by the frequency offsets. In the cellular communication system the inter carrier interference arises due to the fully loaded traffic conditions at the cell edge .which is removed by the combining the multiple cell coordinated or frequency reuse .The inter carrier interference occurs when the cyclic prefix length lesser than the channel impulse response .To mitigate this interference use the spatial diversity techniques are used. In this method by using the spatial techniques the length of the cyclic prefix becomes more than the channel impulse response. The inter carrier interference can also be removed by the single input multiple output but this is not the better method to remove the inter carrier interference as it does not remove the inter carrier interference properly. Inter carrier interference arises when the wireless channel estimation is done with the help of Doppler spread information and the data symbols detector. In the wireless channel estimation the inter carrier interference is removed by the parallel interference cancellation and the decision statistically combining method .The parallel interference cancellation and decision statistically combining methods are used at the receiver end.

Maximum likelihood algorithms for joint estimation of synchronisation impairments and channel in multiple input multiple output–orthogonal frequency division multiplexing system

Maximum likelihood (ML) algorithms, for the joint estimation of synchronisation impairments and channel in multiple input multiple output–orthogonal frequency division multiplexing (MIMO–OFDM) system, are investigated in this work. A system model that takes into account the effects of carrier frequency offset, sampling frequency offset, symbol timing error and channel impulse response is formulated. Cramer–Rao lower bounds for the estimation of continuous parameters are derived, which show the coupling effect among different impairments and the significance of the joint estimation. The authors propose an ML algorithm for the estimation of synchronisation impairments and channel together, using the grid search method. To reduce the complexity of the joint grid search in the ML algorithm, a modified ML (MML) algorithm with multiple one-dimensional searches is also proposed. Further, a stage-wise ML (SML) algorithm using existing algorithms, which estimate less number of parameters, is also proposed. Performance of the estimation algorithms is studied through numerical simulations and it is found that the proposed ML and MML algorithms exhibit better performance than SML algorithm.

Capacity of multiuser multiple input multiple output-orthogonal frequency division multiplexing systems with doubly correlated channels for various fading distributions

In this article, the capacity of multiuser multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) system is analysed under Rayleigh, Rician, Lognormal and Weibull fading channels, and compared with each other under both semi- and doubly correlated channels. The distribution of the complex Wishart matrix is utilised to derive closed-form expressions of ergodic capacity of MIMO-OFDM systems under doubly correlated channels when the transmitter has no channel state information (CSI) and the receiver has perfect CSI. The capacity of MIMO-OFDM systems is plotted for various fading channels under different system specifications, such as number of transmit and receive antennas, number of subcarriers and different power levels. The obtained results are used to study the impact of channel correlation on capacity.

Overhead Reduction in Coordinated Beamforming for Multiuser MIMO-OFDM Systems with Limited Feedforward

This letter proposes a method for choosing the best quantized beamforming vector that represents a subcarrier group, for coordinated beamforming in the downlink of multiuser multiple input multiple output-orthogonal frequency division multiplexing systems. The correlation between subcarriers is exploited for reducing the feedforward overhead, while maximizing the sum rate.

PAPR reduction by a single adaptive all-pass filter for OFDM systems

This letter proposes an adaptive all-pass filter (A2PF) based peak-to-average power ratio (PAPR) reduction scheme for signle input single output orthogonal frequency division multiplexing (OFDM) systems. A properly phase rotated OFDM symbol of reduced PAPR is generated by an A2PF with its filter coefficient found by the Newton-Raphson method. For the A2PF scheme, costly side information(SI) transmission is not needed unlike the selected mapping (SLM) scheme. The A2PF scheme achieves PAPR reduction performance comparable to the SLM scheme. Simulation results demonstrate that the A2PF scheme without SI leads to BER performance close to the SLM scheme with SI.