Multiplexing OFDM Research Articles

Improved Receivers for Optical Wireless OFDM: An Information Theoretic Perspective

We consider performance enhancement of asymmetrically-clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and related optical OFDM schemes, which are variations of OFDM in intensity-modulated optical wireless communications. Unlike most existing studies on specific designs of improved receivers, this paper investigates information theoretic limits of all possible receivers. For independent and identically distributed (IID) complex Gaussian inputs, we obtain an exact characterization of information rate of ACO-OFDM with improved receivers for all SNRs. It is proved that the high-SNR gain of improved receivers asymptotically achieve 1/4 bits per channel use, which is equivalent to 3 dB in electrical SNR or 1.5 dB in optical SNR; as the SNR decreases, the maximum achievable SNR gain of improved receivers decreases monotonically to a non-zero low-SNR limit, corresponding to an information rate gain of 36.3%. For practically used constellations, we derive an upper bound on the gain of improved receivers. Numerical results demonstrate that the upper bound can be approached to within 1 dB in optical SNR by combining existing improved receivers and coded modulation. We also show that our information theoretic analyses can be extended to Flip-OFDM and PAM-DMT. Our results imply that, for the considered schemes, improved receivers may reduce the gap to channel capacity significantly at low-to-moderate SNR.

Indoor Localization System Based on Mobile Access Point Model MAPM Using RSS With UWB-OFDM

Indoor tracking is one of the most attractive topics in communication and information technology. Indoor localization mechanisms can help people for navigating in complex environments. Those with complex structures such as airports, shopping malls, hospitals, and others have a massive population (Crowdsourcing) that blocks the visibility (NLOS) between the access points and the users. Accordingly, we present the mobile access point model MAPM as a new algorithm for positioning users indoors based on the mathematical model of received signal strength RSS using UWB-OFDM. MAPM participates in crowdsourcing indoors by using users as mobile access points (MAP). That may decrease the use of several static access points (SAP) indoors and increase the localization precision. First, we use ultra-wideband UWB with orthogonal frequency division multiplexing OFDM as a communication gadget between the users and the system. Those have good quality in terms of accuracy, time response, energy consumption, and efficiency against interference. Second, we measure the received signal strength then, we estimate the distance between users and the access points using the mathematical model of RSS. These can be more adapted to changing environments and device heterogeneity than RSSI fingerprints. Third, we calculate the position information by using the Euclidean distance formula. In this way, we can reduce the effect of most of the problems on the indoor positioning system. We simulate the proposed algorithm in a platform based on three tools, MATLAB for system information processing, MYSQL as a system database, and a control interface coded in Java. In the given simulation results, we find that the average MAPM error in the case of 30 users is 10.19 cm, and the detection rate has a value of 86.66%.

Design of high-order QAM modem algorithm

More and more attention has been paid on the issue of bandwidth utilization. Nowadays, with limited frequency spectrum resources, the capacity of traditional communication system has not been able to meet the demands of users. Quadrature Amplitude Modulation (QAM) has become a critical technical solution for broadband wireless access and wireless video communication due to its advantages of high frequency spectrum utilization and high-power spectrum density. In order to further improve the control information transmission performance of high-order QAM, we propose a high-order QAM modulation and demodulation algorithm, which is designed from the aspects of interleave between channels, leading sequence, constellation modulation, frequency domain sampling and (Orthogonal Frequency Division Multiplexing) OFDM generation, etc. The simulation results demonstrate that the algorithm can ensure the reliable reception of control information.

Resource Allocation Algorithm for Physical Layer of Broadband Power Line Carrier Communication Applied to Electric Internet of Things

Broadband power line carrier communication adopts adaptive orthogonal frequency division multiplexing OFDM technology to effectively increase the communication rate, and provides ample communication resource guarantee for the realization of power multiservice applications. Aiming at the problem of broadband power line carrier communication resource allocation, this paper proposes a low-complexity physical layer resource allocation algorithm. First, based on the equal power allocation method, the set of subcarriers required by each user to meet their minimum rate requirements is determined, and the multi-user resource allocation problem is reduced to a single-user optimal power allocation problem, and then the Lagrange multiplier method is used to optimize the power of the sub-carrier set used by each user to further improve the system throughput. Experiments show that the algorithm in this paper has higher throughput and can meet the minimum rate requirements of more users.

A robust filter bank multicarrier system as a candidate for 5G

Frequency spreading filter bank multicarrier (FS-FBMC) is widely considered as a potential candidate for the air interface of the next-generation mobile communication, 5G. The prototype filter plays a pivot role in the frequency–time confinements to obtain a better performance, as a result of mitigating the inter-carrier interference and the inter-symbol interference.In this work, the architecture of single radio access for both FS-FBMC and orthogonal frequency division multiplexing OFDM is presented to demonstrate the idea of combining both multicarrier in a single hardware and reusing OFDM resources for FS-FBMC. The FS-FBMC transceiver is analyzed, and two recently designed Nyquist filters are adopted as prototype filters. The frequency-domain coefficients are calculated for the new Nyquist filters to be suitable for FS-FBMC prototype filters, and the interference coefficients on the adjacent time–frequency grids of the new filters and PHYDYAS are calculated using different overlapping factor. Also, a novel single symbol preamble channel estimation is proposed and a single tap equalizer in the frequency domain is used to track the channel state and recover the distorted data similar to the conventional OFDM. The error performance over noisy and mobile fading channels, and as a function of non-linear distortion demonstrates the strength of FS-FBMC based on the new well-localized prototype filters in the time–frequency domains, which addresses the main shortages of the OFDM that arise from poor spectral stopband characteristics and the amplitude fluctuation over the transmit symbols. Moreover, it is found that the new prototype filters outperform the most commonly used filter, PHYDYAS. Also, it is showed that the proposed channel estimation and new prototype filters support single radio access based OFDM and FS-FBMC that motivate industry to consider FS-FBMC as a promising air interface for 5G.

20Gbit/s-40 GHz OFDM based LEO-GEO Radio over Inter-satellite optical wireless communication (Ro-IsOWC) system using 4-QAM modulation

This work discusses the modeling and the numerical investigation of Ro-IsOWC link between a low earth orbit LEO and geosynchronous earth orbit GEO satellite. 4-level quadrature amplitude modulation 4-QAM signal with orthogonal frequency division multiplexing OFDM technique has been used to transmit high-speed data between two satellites separated at 35,000 km link distance in outer space. The proposed link performance has been numerically evaluated under the impact of operating wavelength, transmission distance, input power, pointing errors, additional losses, and receiver aperture diameter. Signal-to-noise ratio SNR and received electrical power of the information signal are considered as the performance metrics to evaluate the link performance. Through numerical simulations, we report a successful transportation of 20Gbit/s-40GHz information between two satellites over a transmission distance of 35,000 km using the proposed Ro-IsOWC system. Also, an improved link performance has been investigated in this work by using a Square root module SRm technique at the receiver terminal for non-linearity compensation.

Artificial Neural-Network-Based Pre-Distortion for High Loss-Budget 60-km Long-Reach Passive Optical Network

High launch optical power can compensate for severe fading and power loss in long-reach passive optical networks (LR-PONs); however, it also aggravates nonlinear degradation, which necessitates the use of complex DSP-based nonlinear compensation techniques at optical network users (ONUs). DSP-related techniques also necessitate the use of additional hardware/software components by the receiver, which can greatly increase implementation costs and energy consumption, particularly when dealing with large-scale ONU deployment. This is the first study to propose artificial neural network (ANN)-based pre-distortion to eliminate the need for complex DSP at ONUs in a high-launch-power LR-PON, thereby permitting the use of a simplified architecture at the user end. In the first phase of the study, the proposed ANN-based pre-distortion scheme was implemented in a single-channel IMDD OFDM LR-PON, which achieved a data rate of >55 Gbps over 60-km transmission with a loss budget of 30 dB without the need for optical inline- or pre-amplification. In the second phase of experiments, the same scheme was applied to a 4-channel wavelength division multiplexing (WDM) OFDM LR-PON. Here, the proposed scheme achieved data rates of >200 Gbps using launch power of 18 dBm per lane, resulting in a loss budget of roughly 29 dB over 60-km single mode fiber transmission.

Design and Analysis of a Wavelet Packet Modulation Based Differential Chaos Shift Keying Communication System

In this paper, a new multicarrier based DCSK system that is combined a wavelet packet modulation (WPM) with differential chaos shift keying (DCSK) and named WPM–DCSK is proposed. WPM–DCSK system is an extension of orthogonal frequency division multiplexing OFDM–DCSK system that aims to replace the fast Fourier transform in OFDM system with wavelet packet transform and improves the spectral efficiency by removing the cyclic prefix and reduced the complexity by using real operation instead of complex operation. WPM–DCSK system has all the benefit of OFDM–DCSK and furthermore improves the limitations and drawbacks of it. The data rate improvement, the energy saving improvement and data-energy- to-bit-energy-ratio factors are derived and compared with DCSK and OFDM–DCSK systems. The validity of the derived analytic expression of the bit error rate of the proposed system is confirmed by the simulation under an additive white Gaussian noise channel.

Design of encrypted transceiver Non-coherent OFDM with ability to correct coding bits of information

<p>A differential encrypted transceiver was designed in the signal-to-noise ratio systems. A time"-"spread" frequency-"encoded (TSFE) algorithm was proposed using the orthogonal frequency multiplexing multiplier OFDM. The proposed design was verified under the Doppler frequency effect and there was an improvement in the performance of the signal-to-noise ratio system. As a result, the reliability of decoded data was increased and achieves the ability to correct coding bits of information.</p>

Modified Huber ICA-based frequency domain channel equalizer for polarization division multiplexing coherent optical OFDM systems

Polarization division multiplexing coherent optical OFDM (PDM-CO-OFDM) is an approach which ensures reaching high data rates by enabling the utilization of the amplitude, phase and polarization of light at the same time in long-haul transmissions. The channel equalizer is used for the compensation of the linear and nonlinear effects of fiber in the optical receiver, and channel estimation is realized with periodic training symbols. In this study, a channel equalizer based on modified Huber independent component analysis (MHICA) without training symbols (TS) was proposed for the PDM-CO-OFDM systems. Thus, the mathematical model of the PDM-CO-OFDM system and MHICA were analyzed. It is shown in the simulations that the proposed channel equalizer in the receiver can compensate for the linear and nonlinear effects in the optical channel and successfully recover the OFDM signals. In addition, compared to other ICA-based channel equalizers, the proposed channel equalizer is the fastest, and provides slightly improved or similar performance for QPSK and 16-QAM modulated signals respectively. Under the same conditions, the proposed channel equalizer achieves better performance than conventional TS-based frequency domain channel equalizers, both with and without intersymbol frequency-domain averaging (ISFA).

Constant-Envelope Multicarrier Waveforms for Millimeter Wave 5G Applications

A key point of Fifth Generation (5G) wireless networking will be the exploitation of higher frequency bands in the millimeter wave (mm-Wave) spectrum to provide unprecedented data rates to mobile users. In such a perspective, the PHYsical (PHY) layer design priorities should be reconsidered. In this paper, we investigate Constant-Envelope Multicarrier (CE-MC) waveforms for future adoption in mm-Wave 5G transmissions, namely: Constant-Envelope Orthogonal Frequency Division Multiplexing (CE-OFDM) and Constant-Envelope Single-Carrier OFDM (CE-SC-OFDM). These waveforms are obtained by imposing a nonlinear phase modulation to a real-valued OFDM and SC-OFDM signal, respectively. Thanks to their 0dB Peak-to-Average-Power Ratio, such unconventional signaling formats are insensitive to nonlinear distortions and allow to exploit the flexibility of conventional multicarrier systems together with augmented resilience against multipath fading and phase noise. CE-OFDM and CE-SC-OFDM have been assessed by means of computer simulations in a short-range mm-Wave 5G scenario, i.e., downlink transmission in outdoor picocells. Simulation results demonstrate that CE multicarrier waveforms enhance robustness and increase coverage and capacity in the proposed scenario, as compared to conventional OFDM and SC-OFDM counterparts.

Pilot multiplexing OFDM system frequency offset estimation method

The algorithm proposed in this Article is intended for estimated accuracy and network throughput, two indexes of LTE channel, to design an approach for improvement of algorithm, and linear least square algorithm by using of weighted multilayer time-frequency domain LTE-OFDM resource model, for estimation of weighting parameters and the 2D spread spectrum power normalization algorithm. The results of simulation comparison on standard model database show that, while improving estimated accuracy, algorithm proposed in this Article can also remain network throughput at a high level, which verifies efficiency of the algorithm. Practicability of the algorithm is verified in laboratory and the results of comparison on simulation example shows a better effect of channel estimation with the proposed algorithm than standard 2D spread spectrum algorithm and the linear least square algorithm.

Multi-segmental OFDM signals equalization with piecewise linear channel model over rapidly time-varying channels

For rapidly time-varying channels, the performance of (orthogonal frequency division multiplexing) OFDM systems with the conventional one tap equalizer will be significantly degraded. Because the orthogonality between subcarriers is destroyed, the conventional way to combat the inter-carrier interference (ICI) is employing the banded minimum mean square error (MMSE) equalizer, which can save computational efforts introduced by a large number of subcarriers. However, the width of the banded channel matrix is mainly determined by the normalized Doppler frequency in the sense that with the high Doppler frequency the complexity of equalization for one OFDM block will significantly increase with the band width D. In order to reduce the equalization complexity, the authors proposed multi-segmental OFDM signal equalization method with piecewise linear model (PLM) to approximate the time variations and mitigate the corresponding ICI. Its complexity is significantly reduced with the small segments. Furthermore, an alternative MMSE method with the iterative rank-1 matrix updates is proposed to further reduce the complexity. We also derive the theoretical pre-equalized and equalized signal to interference ratio (SIR) for different normalized Doppler frequencies and segment numbers, which implies that the larger segment number can achieve the better performance. Simulation results demonstrate that the proposed method outperforms the conventional banded MMSE equalizer and the partial fast Fourier transform (FFT) method in terms of bit error rate (BER) with almost the same complexity.

A resource allocation evolutionary algorithm for OFDM system

Resource allocation for orthogonal frequency division multiplexing OFDM system, as a core technology for the 4th generation mobile communication system, has shown significant importance in the improvement of system transmission rate. At present, the two-step algorithm is described as a main method to deal with resource allocation for OFDM system. As carrier allocation and power allocation are not independent of each other, the two-step algorithm may result in lower complexity but poor convergence. This paper proposes a mixed evolutionary algorithm to allocate sub-carrier and power at the same time. It combines the simulated annealing algorithm and evolutionary algorithm. This paper also improves the definition of fairness in OFDM system. It can achieves perfect fairness among users while maintaining the efficient capacity performance. Simulation results demonstrate that the proposed resource allocation algorithm can achieve perfect performance, and increase the convergence rate greatly meanwhile efficiently improving the system capacity.

Dynamic resource allocation for multimedia services delivery in cellular/infostation integrated HSR networks

With the rapid development of high-speed railway HSR system, the resource allocation problem in HSR wireless network becomes one of the key issues to improve the efficiency of resource utilisation. In this paper, we investigate the downlink resource allocation problem for multimedia services delivery in HSR multiple-input multiple-output MIMO-orthogonal frequency division multiplexing OFDM system with a cellular/infostation integrated network architecture. Taking the train trajectory and network stability into account, we formulate the problem as a stochastic network optimisation programming, which aims at maximising the overall system utility while keeping the system stable under the total transmission power constraint. To address the NP-hard mixed integer programming, the original problem is firstly transformed into a queue stability problem, and then decomposed into two separate subproblems by the drift-plus-penalty DPP approach. Finally, based on the stochastic optimisation technique, a dynamic resource allocation algorithm is proposed and its efficiency is illustrated by theoretical analysis and numerical simulations.

Low‐complexity peak‐to‐average power ratio reduction method for orthogonal frequency‐division multiplexing communications

The high peak-to-average power ratio (PAPR) of the transmitted signal is a major drawback of multicarrier transmission such as orthogonal frequency-division multiplexing OFDM. A plethora of PAPR reduction techniques has been reported in the literature. Some of the techniques modify the phase and/or amplitude of symbols in the original symbol alphabet (SA) such as selected mapping and partial transmit sequences techniques. However, such methods have shortcomings of a heavy computational burden caused by required multiple inverse fast-Fourier transform (IFFT) operations and bit error rate performance degradation due to side information (SI). In this study, a low-complexity PAPR reduction framework is proposed to jointly modify phase and amplitude values of the original symbols in the alphabet. This framework utilises only one IFFT/FFT operator pair for transmultiplexing of symbols without any SI. The merit of the proposed method to design a SA modifier matrix (SAM) for PAPR reduction is shown through performance comparisons for the application scenarios presented in this study.

Performance of Turbo Coded OFDM Under the Presence of Various Noise Types

A telecommunication system uses carriers in order to transmit information through a cable or wirelessly. If each time only one carrier is transmitted, then the system s signal will not be immune to frequency selective fading. If frequency selective fading includes the working frequency of the system, then the wireless link will not be established. Orthogonal frequency division multiplexing OFDM is the primary solution for coping with inter signal interference and frequency selective fading. Many carriers can be produced by splitting a fast information stream to slower data series. Different orthogonal frequencies carry slower data series. System s performance can be further enhanced with the utilization of turbo codes. Turbo codes make the system more immune to noise effects with excellent BER results. This paper presents the thorough analysis of a turbo coded OFDM scheme using a PCCC technique in the presence of a channel which includes AWGN, phase noise, Rayleigh fading, Rician fading and Doppler shift.

Sparsity-Aware Adaptive Channel Estimation Based on SNR Detection

Time domain synchronous orthogonal frequency division multiplexing OFDM (TDS-OFDM) has a higher spectral efficiency and faster synchronization than standard cyclic prefix OFDM, but suffers from the performance loss over multipath fading channels due to severe interblock-interference. Recently, compressive sensing (CS) is explored to solve those problems, but it heavily relies on the sparsity level of the channel, which is unknown in practice. In this paper, a signal-to-noise ratio-based sparsity estimation method is proposed to detect the sparsity level of the channel. Then we propose the priori aided subspace pursuit algorithm if the channel sparsity meets the theoretical CS model, otherwise we use an improved iterative channel estimation method with the help of the channel sparsity. Simulation results demonstrate that the proposed scheme could improve the robustness and performance of TDS-OFDM systems compared with the conventional iterative methods or recently proposed CS based methods.

TSK type self-organising online fuzzy equalisation to mitigate nonlinear power amplifier distortions in OFDM systems

This paper presents a first order Takagi-Sugeno-Kang TSK type self-constructing, adaptive, online, transversal, fuzzy equaliser to mitigate nonlinear power amplifier distortion effects from received signal in orthogonal frequency division multiplexing OFDM systems. Here, the proposed SOTSKFS equaliser, that attempts to compensate the nonlinear distortions in single-antenna and/or multi-antenna OFDM systems, produces most compact fuzzy rule base with less number of rules in comparison to other online fuzzy equalisers, viz. FSCFNN and SCRFNN. Computer simulations show improved bit-error-rate BER and mean-square-error MSE performances of this proposed evolving fuzzy equalisation technique, when compared to that of the latest power amplifier nonlinearity cancellation techniques in OFDM receiver.

基于SOA的平行双抽运结构偏振复用OFDM信号的全光波长变换

基于SOA的平行双抽运结构偏振复用OFDM信号的全光波长变换