Multi-input Multi-output Orthogonal Frequency Division Multiplexing Research Articles

MIMO–OFDM System Analysis and Achievement

Multi-Input–Multi-Output (MIMO) technology has already become crucial in modern communication study, but the needs of anti-interference capability and spectral efficiency are always growing, which poses a significant challenge in future development. In the paper, by analyzing and summarizing the respective characteristics and problems of MIMO system and Orthogonal Frequency Division Multiplexing (OFDM), we investigate the knowledge of MIMO–OFDM system. The theoretical analysis proves that this system can effectively solve the shortcomings of MIMO system and improve the performance of communication system. In addition, in the experimental simulation part, we also evaluate the system performance mainly by analyzing the Bit Error Rate (BER) metrics, while other methods such as channel estimation algorithms and synchronization techniques are also considered.

Highly Accurate Technique for CO-OFDM Channel Estimation Technique Using Extreme Learning Machine (ELM)

In wireless systems, channel estimation is considered a problematic technology, due to the fact of the difference in time between wireless channels and the noise effect. Orthogonal frequency-division multiplexing (OFDM) is a promising candidate for future optical communications and has received wide concern. The article proposed a Coherent Optical (CO) orthogonal frequency division multiplexing (OFDM) scheme, which gives a scalable and flexible solution for increasing the transmission rate, being extremely robust to chromatic dispersion as well as polarization mode dispersion. Nevertheless, both coherent detection and OFDM are prone to phase noise due to the phase mismatch between the laser oscillators at the transmitter and receiver sides and the relatively long OFDM symbol duration compared to that of single carrier communications. An Extreme Learning Machine (ELM) with Pilot Assisted Equalization (PEM) is proposed for compensation of impairments caused by fibre nonlinearity in coherent optical communication systems. Channel estimation using ELM and the value of distortion is sent to the OSTBC receiving end based on the distortion information the data is decoded and pilot data is removed. FFT is applied to the data and QPSK demodulation is done in the data to get its original form. In addition, the article utilized a free-space optical communication system of multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) with a modified receiver structure. Simulation reveals that the proposed model exhibits significant BER (0.0112) performance and provides better spectral efficiency as compared with conventional systems and less computational complexity. This suggested that the proposed method shows better performance by using the CO-OFDM-FSO-MIMO-ELM-based channel estimation technique for high-speed data communication networks in real-time scenarios respectively.

Performance Evaluation of MIMO-OFDM-FSO with Modified Receiver

The performance of free space optical communication system using multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) with a modified receiver structure is evaluated in this paper referred to as MIMO-OFDM-FSO with the modified receiver (MIMO-OFDM-FSO-MR). Utilizing equal gain combining the analysis is done by taking closed-form expression of average bit error rate and throughput. The simulation is performed to estimate various performance parameters such as throughput and bit error rate (BER) for the proposed MIMO-OFDM-FSO-MR model under different turbulence and weather conditions. Simulation reveals that the proposed model exhibits significant BER performance and provides better throughput and spectral efficiency as compared with conventional FSO systems, OFDM-FSO systems, MIMO-FSO systems and Low-density Parity Check (LDPC) coded MIMO-OFDM-FSO systems.

Hierarchical BEM Based Channel Estimation With Very Low Pilot Overhead for High Mobility MIMO-OFDM Systems

Channel estimation for multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems is a challenging issue in high mobility scenarios due to prohibitive pilot overhead and complexity. In this paper, a hierarchical basis expansion model (BEM) based channel estimation scheme is proposed for doubly selective channels, which requires a low pilot overhead and computational complexity. A mixed-BEM is proposed for time-varying channels alongside a complex exponential-BEM (CE-BEM), resulting in very few unknown parameters required for channel estimation. Based on the hierarchical BEM structure, an analytical channel estimation model is derived. By employing the block-structured sparsity and a small number of mixed-BEM coefficients in the antenna-time-BEM domain, a low-complexity estimator is proposed to recover the mixed-BEM coefficients accurately. The lower bound on the mean square error (MSE) of channel estimation is derived to verify the effectiveness of the proposed scheme. Simulation results show that the proposed channel estimation scheme significantly outperforms the existing methods in terms of MSE of channel estimation and bit error rate, with much lower pilot overhead and computational complexity.

Mine Intelligent Receiver: MIMO-OFDM Intelligent Receiver for Mine Information Recovery

With the advancement of an intellectual and numerical society, the coal mining industry has also begun to change to intelligence. As an important aspect of intelligent coal mine construction, coal mine communication has put forward more stringent standards for communication quality. For the complex communication environment in mines, the transmission of communication signals is always damaged by various noises and interferences, resulting in serious distortion of the communication signals received at the receiving end. Therefore, the use of traditional receivers for information recovery has the problem of high bit error rate (BER), which cannot meet the standard of intelligent coal mine construction. Based on this, the aim of this research is to combine convolutional neural networks (CNN) and multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) communication systems to design an intelligent receiver model for complex mine communication systems. At the receiver side, CNNs are used to take the place of all the information processing processes. First, features are extracted from the received IQ signal by the convolutional neural network, and then the original information bit is recovered using a multi-label classifier to finally realize end-to-end information restoration. The experimental results show that the intelligent receiver model designed in this research has more accurate information recovery capability in the complex mine channel environment compared with the traditional receiver. In addition, they also verify that the intelligent receiver can still recover information effectively when the traditional receiver cannot recover information properly in the case of partial loss of received data.

DFT-Based Channel Estimation with Channel Response Mirroring for MIMO OFDM Systems

In this paper, DFT-Based channel estimation with channel response mirroring is proposed and analyzed. In General, pilot symbols for channel estimation in MIMO(Multi-Input Multi-Output) OFDM(Orthogonal Frequency-Division Multiplexing) Systems have a diamond shape in the time-frequency plane. An interpolation technique to estimate the channel response of sub-carriers between reference symbols is needed. Various interpolation techniques such as linear interpolation, low-pass filtering interpolation, cubic interpolation and DFT interpolation are employed to estimate the non-pilot sub-carriers. In this paper, we investigate the conventional DFT-based channel estimation for noise reduction and channel response interpolation. The conventional method has performance degradation by distortion called “edge effect” or “border effect”. In order to mitigate the distortion, we propose an improved DFT-based channel estimation with channel response mirroring. This technique can efficiently mitigate the distortion caused by the DFT of channel response discontinuity. Simulation results show that the proposed method has better performance than the conventional DFT-based channel estimation in terms of MSE.

Simultaneous distribution of wired and two 2 × 2 MIMO wireless OFDM signals over an integrated RoF-PON system

Abstract In this paper, the integration of the radio over fiber technology into a passive optical network (RoF-PON) is proposed to simultaneously distribute wired and two wireless standards each one transports 2 × 2 multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) signals. This simultaneous transmission is operated based on a single centralized optical wavelength and enabled by a polarization division multiplexing technique. The proposed RoF-PON system offers high spectral efficiency and is designed for unlicensed industrial, scientific, and medical bands at 2.4 and 5.8 GHz. The system performance is assessed by measuring the bit error rates (BERs) according to different access distances up to 30 km. After determining the optimum extinction ratio (ER) to modulate the baseband wired signal that allows jointly optical modulation of wireless signals using the same optical wavelength; all the 2 × 2 quadrature amplitude modulation (QAM) MIMO-OFDM wireless signals with a wired signal are successfully delivered without using forward error correction limit. Additionally, the system reliability has been confirmed by adopting other modulations schemes such as 8 and 16 phase-shift keying (PSK) that maintained good constellation diagrams performances. Whereas, the wired signal is analyzed according to its BER and quality Q-factor including high-quality eye diagram patterns. Also, the results revealed that the MIMO-OFDM signals mapped by 16 QAM scheme are given a better performance than PSK schemes when they are accompanied with high data rate baseband wired signal via a PON distance of 30 km.

Phase Rotations of SVD-Based Precoders in MIMO-OFDM for Improved Channel Estimation

In a multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system, the conventional singular value decomposition (SVD) based precoders may destroy the smoothness of the effective channel, - i.e., the concatenation of the precoders and the channel - in the frequency domain, causing difficulties to the channel estimation. This letter proposes a phase-rotated SVD (PR-SVD) via exploiting the phase non-uniqueness of SVD to make the effective channel as smooth as possible in the frequency domain to facilitate the channel estimation. The simulation results verify that the proposed PR-SVD based precoding method can improve the channel estimation and consequently can significantly outperform the state-of-the-art method in bit error rate (BER).

HYBRIDIZATION OF SUBCARRIER INDEX MODULATION AND OFDM WITH MIMO SYSTEM APPLIED TO FSO

Presently free space optical communication (FSO) is a promising technique on which various researches are carried on. The integration of orthogonal frequency division multiplexing (OFDM) and Subcarrier index modulation, conventional OFDM, Multi input multi output OFDM (MIMO-OFDM) concepts are analyzed in this paper. In free space optical communication these techniques are utilized as well as the performance analysis is simulated using MATLAB. This work investigates the significant of SIM modulated MIMO-OFDM in FSO. Also it analyses the superiority of SIM modulated MIMO-OFDM than SIM modulated classical OFDM and simple Subcarrier index modulation over free space optical communication. Here different turbulence conditions are taken to analyze the concept of SIM along with MIMO-OFDM, classical OFDM in free space. Ultimately SIM modulated MIMO-OFDM exhibits better BER performance in the order of 10-6 in comparison to simple SIM and SIM associated OFDM in free space.

Posture-Specific Breathing Detection.

Human respiratory activity parameters are important indicators of vital signs. Most respiratory activity detection methods are naïve abd simple and use invasive detection technology. Non-invasive breathing detection methods are the solution to these limitations. In this research, we propose a non-invasive breathing activity detection method based on C-band sensing. Traditional non-invasive detection methods require special hardware facilities that cannot be used in ordinary environments. Based on this, a multi-input, multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system based on 802.11n protocol is proposed in this paper. Our system improves the traditional data processing method and has stronger robustness and lower bit relative error. The system detects the respiratory activity of different body postures, captures and analyses the information, and determines the influence of different body postures on human respiratory activity.

Performance of Pilot-Aided 3D- OFDM Channel Estimation using Different Antenna Configurations

<p>This paper aims, a 3D-Pilot Aided Multi-Input Multi-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) Channel Estimation (CE) for Digital Video Broadcasting -T2 (DVB-T2)for the 5 different proposed block and comb pilot patterns model and performed on different antenna configuration. The effects of multi-transceiver antenna on channel estimation are addressed with different pilot position in frequency, time and the vertical direction of spatial domain framing. This paper first focus on designing of 5- different proposed spatial correlated pilot pattern model with optimization of pilot overhead. Then it demonstrates the performance comparison of Least Square (LS) &Linear Minimum Mean Square Error (LMMSE), two linear channel estimators for 3D-Pilot Aided patterns on different antenna configurations in terms of Bit Error Rate. The simulation results are shown for Rayleigh fading noise channel environments. Also, 3x4 MIMO configuration is recommended as the most suitable configuration in this noise channel environments.</p>

CFO robust blind receivers for MIMO-OFDM systems based on PARALIND factorizations

Carrier frequency offsets (CFO) is a well known impairment that destroys the orthogonality amongst subcarriers in multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, and the resulting inter-carrier interference significantly degrades the performance of such systems. This paper proposes the CFO robust blind receivers for MIMO-OFDM systems based on parallel profiles with linear dependencies (PARALIND) factorizations. First, we model MIMO-OFDM signal in the presence of CFO to satisfy the PARALIND model, where the symbols, the CFO, and the MIMO channel matrices can be viewed as three independent factor matrices. Such a hybrid tensorial modeling enables a blind and joint estimation of symbols and CFO. Then, in order to improve the fitting precision of the PARALIND model, we introduce two algorithms for fitting the PARALIND model. The first one, called delta alternating least squares (DALS) algorithm, where we predict coarsely by exploiting the increment values between two iterations of the factor matrices, refine these predictions by using the enhanced line search and use these refined values to initialize factor matrices, this procedure helps us avoid the random initialization found in the traditional ALS algorithm. The second one, called orthogonal DALS (ODALS) algorithm that uses the solution of orthogonal constraint for the DALS algorithm to provide the initialization for one more factor matrix. The performance of proposed receivers is illustrated by means of simulation results, and a comparison is made with other approaches that allow to estimate symbols and CFO in two separated steps. Beside a robust to CFO characteristics, our approach gives a better BER performance than other compared blind approaches.

Development of MIMO–OFDM system and forward error correction techniques since 2000s

The multi-input multi-output–orthogonal frequency division multiplexing (MIMO–OFDM) system serves as one of the most promising techniques that support high data rate and high performance in diverse fading channel conditions. The paper presents an overview of MIMO–OFDM wireless technology, covering advances in physical-layer design, various space–time codes, space–frequency codes and efficient concatenated forward error correction techniques, along with interleaving to yield reduced bit error rate performance (BER). Further, the paper presents the evolution of various performance metrics that are reported since the 2000s in the literature. The evolution outcome is examined using a quadratic nonlinear fitting function to assess the interesting performance metrics. Since BER versus SNR analysis is found as the interesting performance study of the MIMO–OFDM system, the current status of the achieved BER under varying SNR is reviewed and presented.

Power Optimization in MIMO-OFDM Systems with Mixed Orthogonal Frequency Division and Space Division Multiple Access Scheme

In recent years, energy efficiency has become a critical metric for green system design and drawn universal attention. In this paper, we propose a new radio resource allocation algorithm to minimize the power consumption of the base station for the multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with different quality of service constraints of users. The discontinuous transmission (DTX) technique is applied in the systems with mixed orthogonal frequency division access and space division multiple access. Radio resources in time, frequency and space domain are optimally allocated to users in two steps: In the first step, the active time in the DTX mode is estimated under the assumption that every user experiences slow time-varying fading in an OFDM frame. In the second step, subcarriers, bits and power are allocated in the active time slots. Although the proposed algorithm is suboptimal due to high computation complexity, simulation results show that the proposed algorithm can reduce the power consumption of the base station and improve resource utilization.

WPAN 간섭원에 의한 MIMO-OFDM WLAN의 성능 열화 분석을 위한 실시간 주파수 간섭 분석 시스템

Abstract In this paper, we have proposed the frequency interference analysis system using both LabVIEW and Universal Software Radio Peripheral(USRP) for performance degradation analysis of Multi Input Multi Output-Orthogonal Frequency Division Multiplexing(MI-MO-OFDM) Wireless Local Area Network(WLAN) due to Wireless Local Area Network(WPAN) interferer. The proposed system consists of three part, i.e., victim, channel, and interferer. Both victim and interferer are implemented by LaBVIEW and a USRP board. Then interfering signal and additive white Gaussian noise are combined with the wanted signals of a victim. Measured Bit Error Rate(BER) at the victim receiver is compared with theoretical BER according to various signal to interference plus noise power ratio (SINR) values. Measured and theoretical BER curves show good agreement. Key words: Frequency Sharing, Frequency Interference, MIMO-OFDM, LabVIEW, USRP WXY9 Z[\]Y^((Department of Computer and Electronic Engineering, Myongji College) *_`9ZaY^GZ((Department of Electrical Engineering, Kookmin University)Manuscript received October 2, 2015 ; Revised November 26, 2015 ; Accepted November 26, 2015. (ID No. 20151002-19S)Corresponding Author: Byung-Jun Jang (e-mail: bjjang@kookmin.ac.kr)

Design of pipeline R2MDC FFT for implementation of MIMO OFDM transceivers using FPGA

In this paper, an area-efficient low power Fast Fourier Transform (FFT) processor is proposed for Multi Input Multi Output--Orthogonal Frequency Division Multiplexing (MIMO-OFDM) that consists of a modified architecture of radix-2 algorithm which is described as Radix-2 multipath delay commutation (R2MDC). Orthogonal frequency-division multiplexing is a popular method for high-data-rate wireless transmission. OFDM may be combined with multiple antennas at both the access point and mobile terminal to increase diversity gain and/or Enhance system capacity on a time-varying multi path fading channel, resulting in a multiple-input multiple-output OFDM system. This paper describes the design of R2MDC FFT for implementation of MIMO OFDM transceiver using FPGA targeted to future wireless LAN systems. The proposed system is pipeline Radix 2multipath delay commutation FFT has been designed for MIMO OFDM. The MIMO OFDM transceivers have been designed according to the proposed OFDM parameters. A low-power efficient and full-pipeline architecture enables the real-time operations of MIMO OFDM transceivers. The FPGA board has been developed to verify their circuit behavior and implementation of MIMO OFDM Transceivers.

Design of MOD-R2MDC FFT for MIMO OFDM in wireless telecommunication system

In this paper, an area-efficient low power Fast Fourier Transform (FFT) processor is proposed for multi input multi output-orthogonal frequency division multiplexing (MIMO-OFDM) in wireless telecommunication system that consists of a modified architecture of radix-2 algorithm which is described as modified radix-2 multipath delay commutation (MOD-R2MDC). Orthogonal frequency-division multiplexing is a popular method for high-data-rate wireless transmission. OFDM may be combined with multiple antennas at both the access point and mobile terminal to increase diversity gain and/or enhance system capacity on a time-varying multi path fading channel, resulting in a multiple-input multiple-output OFDM system. This paper describes the VLSI design of an area efficient MOD-R2MDC FFT for MIMO OFDM system targeted to future wireless telecommunication LAN systems. The proposed system is pipeline modified radix 2 multipath delay commutation FFT has been designed for MIMO OFDM. A low-power efficient and full-pipeline architecture enables the real-time application of MIMO OFDM system.

Pilot Design for Sparse Channel Estimation in Large-Scale MIMO-OFDM System

The pilot design problem in large-scale multi-input-multioutput orthogonal frequency division multiplexing (MIMO-OFDM) system is investigated from the perspective of compressed sensing (CS). According to the CS theory, the success probability of estimation is dependent on the mutual coherence of the reconstruction matrix. Specifically, the smaller the mutual coherence is, the higher the success probability is. Based on this conclusion, this paper proposes a pilot design algorithm based on alternating projection and obtains a nonorthogonal pilot pattern. Simulation results show that applying the proposed pattern gives the better performance compared to applying conventional orthogonal one in terms of normalized mean square error (NMSE) of the channel estimate. Moreover, the bit error rate (BER) performance of the large-scale MIMO-OFDM system is improved.

Energy-Efficient Resource Allocation for MIMO-OFDM Systems Serving Random Sources With Statistical QoS Requirement

This paper optimizes resource allocation that maximizes the energy efficiency (EE) of wireless systems with statistical quality of service (QoS) requirement, where a delay bound and its violation probability need to be guaranteed. To avoid wasting energy when serving random sources over wireless channels, we convert the QoS exponent, a key parameter to characterize statistical QoS guarantee under the framework of effective bandwidth and effective capacity, into multi-state QoS exponents dependent on the queue length. To illustrate how to optimize resource allocation, we consider multi-input-multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. A general method to optimize the queue length based bandwidth and power allocation (QRA) policy is proposed, which maximizes the EE under the statistical QoS constraint. A closed-form optimal QRA policy is derived for massive MIMO-OFDM system with infinite antennas serving the first order autoregressive source. The EE limit obtained from infinite delay bound and the achieved EEs of different policies under finite delay bounds are analyzed. Simulation and numerical results show that the EE achieved by the QRA policy approaches the EE limit when the delay bound is large, and is much higher than those achieved by existing policies considering statistical QoS provision when the delay bound is stringent.

Blind Channel Estimation for MIMO-OFDM Systems With Low Order Signal Constellation

In this paper, we design a new blind channel estimation method for multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems to cope with possible rank deficient signal covariance matrices when symbols are drawn from low order constellations, e.g., BPSK, QPSK, etc. By collecting the signal covariance matrices from a group of carefully selected subcarriers, the proposed method could identify the channel information from a small amount of received blocks. Moreover, the proposed method also outperforms the existing competitor in terms of both estimation performance and computational complexity. The numeral results are provided to corroborate the proposed studies.