Efficient Orthogonal Frequency Division Multiplexing Research Articles

An Improved QPSK based on a Hybrid Genetic Algorithm for Efficient OFDM Transmission

Lowering the bit error rate (BER) and signal-to-noise ratio (SNR) in orthogonal frequency division multiplexing (OFDM) channels is computationally challenging due to internal weaknesses within modulation schemes. In this paper, the amplitudes of various data sets in the four quadrants of a quadrature phase shift keying (QPSK) signal are varied. Furthermore, a hybrid genetic algorithm (GA) is used for phase allocations during OFDM transmission. These enhancements are done so that the received data can be recovered by considering two different aspects, i.e., phase and its corresponding amplitude. The hybrid GA is created with two main enhancements. Firstly, the wind-driven optimization is used as its selection function, and secondly, a custom three-point crossover is used as its genetic recombination operator. When compared to the conventional QPSK and 64QAM, the enhanced modulation technique has less than 24%-BER in a Rayleigh channel whereas the conventional QPSK and 64QAM show results that spanned up to 40% and 29% BER respectively. The modified QPSK has an improved OFDM channel BER-SNR performance because there is great coherence between its transmitter and receiver.

Efficient Index Modulation-Based MIMO OFDM Data Transmission and Detection for V2V Highly Dispersive Channels

Vehicle-to-vehicle (V2V) communication networks are based on vehicles that wirelessly exchange data, traffic congestion, and safety warnings between them. The design of new V2V systems requires increasingly energetically and spectrally efficient systems. Conventional multiple-input–multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems have been used successfully for the last decade. However, MIMO-OFDM systems need to be improved to face future communication networks in high-mobility environments. This article proposes an efficient index modulation (IM)-based MIMO-OFDM system for V2V channels. The proposed transmission system is evaluated in high Doppler-spread channels. The results demonstrate that the proposed scheme reduces the required computational complexity in data detection and exhibits gains of up to 3 dB in bit error rate (BER) performance when compared to the conventional MIMO-OFDM system under the same conditions and parameters, along with achieving superior spectral efficiency. The results show the viability of implementing the proposed system in practical applications for high-transmission-rate V2V channels.

Demonstration of Non-Hermitian Symmetry (NHS) IFFT/FFT Size Efficient OFDM Non-Orthogonal Multiple Access (NOMA) for Visible Light Communication

We propose and experimentally demonstrate a non-orthogonal multiple access (NOMA) visible light communication (VLC) system using non-Hermitian symmetry (NHS) inverse-fast-Fourier-transform (IFFT)/FFT size efficient (SE) orthogonal frequency division multiplexing (OFDM). Fix power allocation and successive interference cancellation (SIC) algorithms are realized. The power ratio between different users, transmission distance, network cell coverage are investigated. The proposed scheme is also compared with the HS based direct-current optical (DCO)-OFDM NOMA-VLC system.

Analysis of Non-Hermitian symmetry (NHS) IFFT/FFT size efficient OFDM for multiple-client non-orthogonal multiple access (NOMA) visible light communication (VLC) system

Orthogonal-frequency-division-multiplexing (OFDM) format is widely deployed in visible-light-communication (VLC) systems due to its high spectral efficiency. To produce real-valued OFDM signal for VLC, Hermitian-symmetry (HS) is needed during the inverse-fast-Fourier-transform (IFFT) encoding process. However the HS requirement doubles the IFFT/FFT size and increase the encoding complexity. Non-Hermitian symmetry (NHS)-OFDM schemes are proposed, but they have different limitations. In this work, we propose and investigate a non-orthogonal multiple access (NOMA) VLC network serving 2, 3 or 4 clients simultaneously using NHS-OFDM IFFT/FFT size efficient (SE) OFDM format. Numerical analysis of signal amplitude effect to the bit-error-ratio (BER) performance for different users are performed, showing that the BER < 7% forward-error-correction (FEC) limit can be achieved as long as the required signal amplitude ratio of each user is fulfilled. We also compare the proposed system with a typical example of HS-OFDM modulation, i.e. direct-current optical (DCO)-OFDM NOMA-VLC system.

Self-improved grey wolf optimization for estimating carrier frequency offset in SCM-OFDM systems

PurposeThe purpose of this paper is to demonstrate a proficiency for accomplishing optimal CFO and keep down the error among the received and transmitted signal. Orthogonal frequency-division multiplexing (OFDM) is considered as an attractive modulation scheme that could be adopted in wireless communication systems owing to its reliability in opposition to multipath interruptions under different subchannels. Carrier frequency offset (CFO) establishes inter-carrier interference that devastates the orthogonality between the subcarriers and fluctuates the preferred signal and minimizes the effectual signal-to-noise ratio (SNR). This results in corrupted system performance. For sustaining the subcarriers’ orthogonality, timing errors and CFOs have to be approximated and sufficiently compensated for. Single carrier modulation (SCM) is a major feature for efficient OFDM system.Design/methodology/approachThis paper introduces a novel superposition coded modulation-orthogonal frequency-division multiplexing (SCM-OFDM) system with optimal CFO estimation using advanced optimization algorithm. The effectiveness of SCM-OFDM is validated by correlating the transmitted and received signal. Hence, the primary objective of the current research work is to reduce the error among the transmitted and received signal. The received signal involves CFO, which has to be tuned properly to get the signal as closest as possible with transmitted signal. The optimization or tuning of CFO is done by improved grey wolf optimization (GWO) called GWO with self-adaptiveness (GWO-SA). Further, it carries the performance comparison of proposed model with state-of-the-art models with the analysis on bit error rate (BER) and mean square error (MSE), thus validating the system’s performance.FindingsFrom the analysis, BER of the proposed and conventional schemes for CFO at 0.25 was determined, where the adopted scheme at 10th SNR was 99.6 per cent better than maximum likelihood, 99.6 per cent better than least mean square (LMS), 99.3 per cent better than particle swarm optimization (PSO), 75 per cent better than genetic algorithm (GA) and 25 per cent better than GWO algorithms. Moreover, MSE at 1st SNR, the proposed GWO-SA scheme, is 4.62 per cent better than LMS, 60.1 per cent better than PSO, 37.82 better than GA and 67.85 per cent better than GWO algorithms. Hence, it is confirmed that the performance of SCM-OFDM system with GWO-SA-based CFO estimation outperformed the state-of-the-art techniques.Originality/valueThis paper presents a technique for attaining optimal CFO and to minimize the error among the received and transmitted signal. This is the first work that uses GWO-SA for attaining optimal CFO.

Time-Modulated OFDM Directional Modulation Transmitters

In this paper, directional modulation (DM) transmitters, designed for orthogonal frequency-division multiplexing (OFDM) wireless data transfer are proposed using time-modulated arrays. It is shown that by properly designing the switch controlling time sequences the proposed time-modulated OFDM DM systems exhibit promising features, such as 1) requires only one radio frequency chain, 2) the conventional efficient OFDM signal construction approach, i.e., by using inverse fast Fourier transform modules, can be adopted, 3) it is “DM synthesis-free,” meaning that there is no need to resynthesize the array excitation vectors for different secure communication directions, different modulation schemes, and different DM power efficiencies, and 4) the tradeoff between secrecy performance and power efficiency can be flexibly adjusted.

Achievable Rates of Multi-Carrier Modulation Schemes for Bandlimited IM/DD Systems

In this paper, we comprehensively investigate the achievable rates of selected band-limited intensity modulation schemes, which are important for optical wireless communication applications, while accounting for the specific nature of their signal construction (non-negative, real, and baseband), and imposing identical bandwidth and average optical power constraints. Furthermore, we identify/devise methods to effectively trade between these parameters. Three variants of orthogonal frequency division multiplexing (OFDM), namely, asymmetrically clipped optical OFDM (ACO-OFDM), spectrally and energy efficient OFDM (SEE-OFDM), and dc-biased optical OFDM (DCO-OFDM), and single-carrier pulse amplitude modulation are studied. The clipping noise in ACO-OFDM and SEE-OFDM is found to consume a large excess bandwidth. The detrimental effects of this excess bandwidth on the achievable rate are evaluated. For SEE-OFDM, the problem of optimal power allocation among its components is formulated and solved using the Karush–Kuhn–Tucker method. For DCO-OFDM, the clipping noise is modeled and incorporated in the analysis. Among the existing schemes, DCO-OFDM yields the best overall performance, due to its compact spectrum. In order to improve the achievable rate, we propose and analyze two improved distortionless variants, filtered ACO-OFDM and filtered SEE-OFDM (FSEE-OFDM), which yield better spectral efficiency than ACO-OFDM and SEE-OFDM, respectively. FSEE-OFDM, being the most spectrally efficient, outperforms all schemes.

Outage of SEE-OFDM VLC-NOMA Networks

In this letter, an indoor spectrally and energy efficient orthogonal frequency division multiplexing (SEE-OFDM)-based visible light communication (VLC) network with non-orthogonal multiple access (NOMA) is studied. An exact expression of the outage probability for $K$ NOMA users is derived. We also provide an upper bound of the data rate of the SEE-OFDM VLC-NOMA network. Finally, the proposed system model shows its superiority compared with the orthogonal multiple access.

Spectrum Efficient DSI-Based OFDM PAPR Reduction by Subcarrier Group Modulation

High peak-to-average power ratio (PAPR) is a long-standing problem of orthogonal frequency division multiplexing (OFDM) system. Although there have been a plethora of proposals presented to date, most of the proposals sacrifice spectral efficiency to attain low PAPR. In this paper, a concept of subcarrier group modulation (SGM) is proposed to transform those spectrum inefficient schemes into spectrum efficient ones. The SGM scheme groups available subcarriers, and assigns one extra bit to each group depending on one of two different sets of constellation, thereby freeing some subcarriers for PAPR reduction. At the receiver, the constellation set used in a particular group is determined by the maximum-likelihood detection. The SGM scheme can be integrated to different PAPR reduction schemes. In this paper, it is integrated with the dummy sequence insertion (DSI) scheme. The DSI with SGM can attain the same spectral efficiency as the conventional OFDM does. Through simulations, it is found that it can achieve PAPR almost similar to that the conventional DSI scheme does without degrading BER performance significantly over both additive white Gaussian noise and Rayleigh fading channels. In addition to the PAPR reduction application, the proposed scheme can be used to improve throughput of any conventional OFDM systems.

A Hardware-Efficient Synchronization in L-DACS1 for Aeronautical Communications

L-band digital aeronautical communication system type-1 (L-DACS1) is an emerging standard that aims at enhancing air traffic management by transitioning the traditional analog aeronautical communication systems to the superior and highly efficient digital domain. L-DACS1 employs modern and efficient orthogonal frequency-division multiplexing (OFDM) modulation technique to achieve more efficient and higher data rate in comparison to the existing aeronautical communication systems. However, the performance of OFDM systems is very sensitive to synchronization errors such as symbol timing offset (STO) and carrier frequency offset (CFO). STO and CFO estimations are extremely important for maintaining orthogonality among the subcarriers for the retrieval of information. This paper proposes a novel efficient hardware synchronizer for L-DACS1 systems that offers robust performance at low power and low hardware resource usage. Monte Carlo simulations show that the proposed synchronization algorithm provides accurate STO estimation as well as fractional CFO estimation. Implementation of the proposed synchronizer on a widely used field-programmable gate array (FPGA) (Xilinx xc7z020clg484-1) results in a very low hardware usage which consumed 6.5%, 3.7%, and 6.4% of the total number of lookup tables, flip-flops, and digital signal processing blocks, respectively. The dynamic power of the proposed synchronizer is below 1 mW.

Experimental Research on Adaptive 128/64QAM DFT-Spread IFFT/FFT Size Efficient OFDM With a High SE in VLLC System

In this paper, an adaptive inverse fast Fourier transform and fast Fourier transform (IFFT/FFT) size efficient orthogonal frequency division multiplexing (OFDM) modulation scheme with 128/64-quadrature amplitude modulation (QAM) and discrete Fourier transmission-spread (DFT-spread) is proposed and experimentally demonstrated in a visible laser light communication (VLLC) system with a cost-effective 450-nm blue-light laser diode. The experimental results show that the 5.95 Gb/s adaptive IFFT/FFT size-efficient OFDM with the spectral efficiency of 4.76 b/s/Hz transmission over 5-m free-space can be successfully achieved.

An Efficient Orthogonal Frequency Division Multiplexing (OFDM) System and Performance Analysis of Digital Audio Broadcasting (DAB) System

An Efficient Orthogonal Frequency Division Multiplexing (OFDM) System and Performance Analysis of Digital Audio Broadcasting (DAB) System

Spectrally Efficient Multicarrier Transmission With Message-Driven Subcarrier Selection

This paper develops two spectrally efficient orthogonal frequency division multiplexing (OFDM)-based multicarrier transmission schemes: a scheme with message-driven idle subcarriers (MC-MDIS) and another with message-driven strengthened subcarriers (MC-MDSS). The basic idea in MC-MDIS is to carry part of the information, which is named carrier bits, through an idle subcarrier selection while regularly transmitting the ordinary bits on all the other subcarriers. When the number of subcarriers is much larger than the adopted constellation size, higher spectral and power efficiency can be achieved compared with OFDM. The reason is that each idle subcarrier carries more bits than a regular symbol, with no power consumption. Moreover, the existence of idle subcarriers can also decrease possible intercarrier interference between their neighboring subcarriers. In MC-MDSS, the idle subcarriers are replaced by strengthened subcarriers, which, unlike idle subcarriers, can carry both carrier bits and ordinary bits. Therefore, MC-MDSS achieves even higher spectral efficiency than MC-MDIS. Both theoretical analysis and numerical results are provided to demonstrate the performance of the proposed schemes.

LED-ID 시스템을 위한 효율적인 OFDM 프레임 동기화 방식

Abstract In this paper, we propose an efficient OFDM(Orthogonal Frequency Division Multiplexing) frame synchronization scheme for LED- ID(Identification) systems. A frame synchronization is an essential procedure for normal operations of OFDM systems. Bernoulli-Gau-ssian noise is considered in LED-ID systems' environments. In order to enhance the OFDM frame synchronization performance, we add a ROGS(Repeated Orthogonal Gold Sequence) to OFDM signals in the time domain. The power level of a ROGS does not affect a normal operation of the LED-ID systems. Frame synchronization can be achieved successfully over LED-ID channels interfered by impulsive noise owing to good auto and cross-correlation properties of the ROGS.Key words: LED-ID, OFDM, Synchronization, ROGS, m-Sequence \]^MKE/KEIT IT RD Revised January 10, 2014 ; Accepted January 15, 2014. (ID No. 20131210-124)Corresponding Author: Jin-Young Kim (e-mail: jinyoung@kw.ac.kr)

Energy Efficient OFDM Relay Systems

In this paper, we study energy efficient orthogonal frequency division multiplexing (OFDM) relay system, where two source nodes communicate with each other via a half-duplex amplify-and-forward relay node. We aim to maximize the energy efficiency (EE), where both the transmit and circuit power consumptions are taken into consideration. To this end, we optimize the active number of subcarriers and the number of bits to each subcarrier at the two source nodes. The optimal solution turns out to be a bidirectional water-filling bit allocation to minimize the overall transmit power, and a subcarrier reduction algorithm to balance the transmit and circuit power consumptions. When the data amounts at the two source nodes are unequal, the bidirectional water-filling leads to a hybrid one- and two-way relaying strategy, which employs one-way relaying on some subcarriers and two-way relaying on some of the other subcarriers. Simulation results demonstrate that the hybrid one- and two-way relaying with subcarrier reduction, which is optimized towards EE, is more energy efficient than that without subcarrier reduction, which only minimizes the transmit power.

An Efficient OFDM Timing Synchronization for CMMB System

An accurate and rapid synchronization scheme is a prerequisite for achieving high-quality multimedia transmission for wireless handheld terminals, e.g. China multimedia mobile broadcasting (CMMB) system. In this paper, an efficient orthogonal frequency division multiplexing (OFDM) timing synchronization scheme, which is robust to the doubly selective fading channel, is proposed for CMMB system. TS timing is derived by performing an inverse sliding correlation (ISC) between the segmented Sync sequences in the Beacon, which possesses the inverse conjugate symmetry (ICS) characteristic. The ISC can provide sufficient correlative gain even in the ultra low signal noise ratio (SNR) scenarios. Moreover, a fast fine symbol timing method based on the auto-correlation property of Sync sequence is also presented. According to the detection strategy for the significant channel taps, the specific information about channel profile can be obtained. The advantages of the proposed timing scheme over the traditional ones have been demonstrated through both theoretical analysis and numerical simulations.

Digital Compensation of Frequency-Dependent Joint Tx/Rx I/Q Imbalance in OFDM Systems Under High Mobility

Direct conversion orthogonal frequency division multiplexing (OFDM) systems suffer from transmit and receive analog processing impairments such as in-phase/quadrature (I/Q) imbalance causing inter-carrier interference (ICI) among sub-carriers. Another source of performance-limiting ICI in OFDM systems is Doppler spread due to mobility. However, the nature of ICI due to each of them is quite different. Unlike previous work which considered these two impairments separately, we develop a unified mathematical framework to characterize, estimate, and jointly mitigate ICI due to I/Q imbalance and high mobility. Based on our general model, we derive a closed-form expression for the degradation in signal-to-interference-plus-noise ratio (SINR) due to the impairments. Moreover, we exploit the special ICI structure to design efficient OFDM channel estimation and digital baseband compensation schemes for joint transmit/receive frequency-independent (FI) and frequency-dependent (FD) I/Q imbalances under high-mobility conditions.

LDPC-coded OFDM in fiber-optics communication systems [Invited

Low-density parity-check (LDPC) coded orthogonal-frequency-division multiplexing (OFDM) is studied as an efficient coded modulation technique suitable for fiber-optics communication systems. We show that in long-haul fiber optics communications LDPC-coded OFDM increases spectral efficiency and requires simple equalization to deal with chromatic dispersion. LDPC-coded OFDM is also a promising polarization-mode dispersion compensation technique. Several power efficient OFDM schemes and LDPC codes suitable for use in LDPC-coded OFDM optical communication systems are discussed.

LDPC-Coded OFDM Transmission Over Graded-Index Plastic Optical Fiber Links

The possibility of 10-Gb/s transmission over graded-index plastic optical fiber (GI-POF) using the orthogonal frequency-division multiplexing (OFDM) and iteratively decodable codes is demonstrated by simulations. Several classes of low-density parity-check (LDPC) codes suitable for use in LDPC-coded OFDM transmission over GI-POF are presented as well. Several power efficient OFDM schemes are introduced

LDPC-Coded OFDM for Optical Communication Systems with Direct Detection

Low-density parity-check (LDPC) coded orthogonal frequency division multiplexing (OFDM) is proposed as an efficient coded modulation technique suitable for optical communication systems. We show that in long-haul fiber optics communications, LDPC-coded OFDM increases spectral efficiency, and reduces the influence of residual chromatic dispersion and the influence of fiber nonlinearities. LDPC-coded OFDM is as also a promising polarization-mode dispersion (PMD) compensation technique. In free space optical communications, LDPC-coded OFDM improves the immunity to the atmospheric turbulence; while in multimode fiber links, it reduces the influence of intermodal dispersion. In plastic optical fiber links it reduces the influence of dispersion and helps to overcome the bandwidth limitations. Several power efficient OFDM schemes and LDPC codes suitable for use in LDPC-coded OFDM optical communication systems are introduced.