OFDM Scheme Research Articles

Retraction Note: A novel PTS: grey wolf optimizer-based PAPR reduction technique in OFDM scheme for high-speed wireless applications

Retraction Note: A novel PTS: grey wolf optimizer-based PAPR reduction technique in OFDM scheme for high-speed wireless applications

Distributed Symmetric Turbo Coded OFDM Scheme Incorporated with STBC-MIMO Antennas for Coded-Cooperative Wireless Communication under Wideband Noise Jamming Environment

Distributed Symmetric Turbo Coded OFDM Scheme Incorporated with STBC-MIMO Antennas for Coded-Cooperative Wireless Communication under Wideband Noise Jamming Environment

Generalized index and mode modulated OFDM with improved spectral and energy efficiency

AbstractRecently developed trends in wireless communication encounter extremely high surge in data traffic, which makes it inevitable to employ energy efficient techniques to reduce detrimental consequence of carbon emission over society. This concern has motivated us to upgrade our previous work on index and mode modulated orthogonal frequency division multiplexing (IMM‐OFDM) for achieving dual benefits in terms of spectral and energy efficiency. In this paper, we have proposed a generalized index and mode modulated OFDM scheme with variable number of subcarrier activation. Novelty of this generalized scheme is its capability to act as a unified model for classic OFDM and three other benchmark index modulated OFDM schemes along with our previously proposed IMM‐OFDM scheme. This new scheme outperforms those five descendent schemes in terms of energy efficiency and error performance as indicated by simulation results. Spectral efficiency improvement in this scheme is achieved through optimum sets of active subcarrier number, which are determined to gain most optimized trade‐off between spectral and energy efficiency with least detector complexity. This generalized parent scheme can replace individual models of its five descendent schemes and consequently can be considered to be one of the most promising candidates for next generation mobile communication system.

Ultrasound Communication Using the Nonlinearity Effect of Microphone Circuits in Smart Devices

Acoustic communication has become a research focus without requiring extra hardware and facilitates numerous near-field applications such as mobile payment. To communicate, existing researchers use either an audible frequency band or an inaudible one. The former gains a high throughput but endures being audible, which can be annoying to users. The latter, although inaudible, falls short in throughput due to the available (near) ultrasonic bandwidth. In this article, we achieve both high speed and inaudibility for acoustic communication by utilizing the nonlinearity effect on microphones. We theoretically prove the maximum throughput of inaudible acoustic communication by modulating an audible signal onto an ultrasonic band. Then, we design and implement UltraComm , which utilizes a specially designed OFDM scheme. The scheme takes into account the characteristics of the nonlinear speaker-to-microphone channel, aiming to mitigate the effects of signal distortion. We evaluate UltraComm on different mobile devices and achieve throughput as high as 16.24 kbps.

Receiver Design for OFDM Schemes With Low-Resolution ADCs

Receiver Design for OFDM Schemes With Low-Resolution ADCs

Adaptive Coded Modulation for OFDM System

This paper studies the adaptive coded modulation for coded OFDM system using punctured convolutional code, channel estimation, equalization and SNR estimation. The channel estimation based on block type pilot arrangement is performed by sending pilots at every sub carrier and using this estimation for a specific number of following symbols. Signal to noise ratio is estimated at receiver and then transmitted to the transmitter through feedback channel ,the transmitter according to the estimated SNR select appropriate modulation scheme and coding rate which maintain constant bit error ratelower than the requested BER. Simulation results show that better performance is confirmed for target bit error rate (BER) of (10-3) as compared to conventional modulation schemes, the convolutional coded modulation offers a SNR gains of 5 dB compared to uncoded state at BER of 10-3. The proposed adaptive OFDM scheme maintains fixed BER under changing channel conditions.

Complex Complementary Sequence Real Orthogonal Spreading OFDM Scheme for HF Communication Link

Complex Complementary Sequence Real Orthogonal Spreading OFDM Scheme for HF Communication Link

Index and mode modulated orthogonal frequency division multiplexing with enhanced spectral efficiency

AbstractIndex modulation aided orthogonal frequency division multiplexing (OFDM‐IM) is a potential multicarrier transmission technique for wireless data transmission systems due to its attractive error performance and energy efficiency. However, it fails to cope with increasing demand of high data rate in upcoming mobile data services, mainly, due to the lower spectral efficiency. In this communication, an efficient transmission technique, called index and mode modulation OFDM, is proposed that delivers additional information through permutations of multiple modes and indexed bits patterns resulting in higher spectral efficiency. For the proposed technique, a low complexity log‐likelihood ratio detector with suitable algorithm is designed and its computational complexity has been analysed. The simulation results indicate improved performance of this newly proposed scheme in terms of spectral efficiency, bit error rate, as well as energy efficiency over other existing index modulated and multiple mode based OFDM schemes, while maintaining considerably low computational complexity in detection. That proclaims the scheme as a potential transmission technique to meet the data transmission challenges in 5G and beyond.

Performance analysis of FBMC/OQAM systems in frequency-selective channels

Filter bank multicarrier (FBMC) systems based on offset QAM modulation (FBMC/OQAM) represent an interesting alternative to the widely used OFDM scheme for machine type communications or cognitive radio. In this paper the performance of FBMC/OQAM systems exploiting a single-tap receiver in frequency-selective Rayleigh fading channels, is analyzed. In particular, the SER and the asymptotic SER (i.e., for a large number of subcarriers) for any prototype filter, is derived. Moreover, a simple closed-form approximate expression of the asymptotic SER is obtained by taking into account, for each active subcarrier, only intersymbol interference terms due to the considered subcarrier and the adjacent subacarriers, and intercarrier interference terms due to the adjacent subcarriers. The numerical results show that the obtained SER expression can predict the actual performance of the system while the asymptotic SER expression provides a useful upper-bound. Moreover, the curves obtained by exploiting the derived simple closed-form approximate expression can be used to predict the asymptotic upper-bound when the considered prototype filter is adopted.

PERFORMANCE OF MU-MC-DS-CDMA SYSTEM IN RAYLEIGH FADING CHANNEL

The Multi user Multi Carrier Direct sequencing Code Division Multiple Access (MU-MC-DS-CDMA) strategy was developed in response to rising demand for system capacity, higher data rates, and multimedia services. It's essentially a combination of CDMA and OFDM schemes. As a result, MC-CDMA takes the advantages of both CDMA and OFDM technologies. CDMA improves bandwidth consumption performance, whereas OFDM helps to minimize Inter Symbol Interference (ISI) and multipath fading. This dissertation suggests a method for evaluating the performance of multi user MC-DS-CDMA system. BER and PAPR are used to evaluate the results. The Bit Error Rate (BER) output of the proposed method is then examined using MATLAB for various modulation techniques. By using Walsh-Hadamard (W-H) code is used because it eliminates Multiple Access Interference (MAI). In terms of BER, it can be shown that BPSK performs better than QPSK. Key Words: AWGN, BER, ISI, MC-CDMA, Rayleigh Fading Channel, SNR, QPSK, MAI

Hybrid multi-user access scheme for a visible light communication system.

A hybrid multi-user access scheme based on orthogonal frequency-division multiple access and non-orthogonal multiple access (OFDMA-NOMA) is proposed for visible light communication (VLC) systems with a bandwidth-constrained channel. In the scheme, a novel user resource allocation method is used, to the best of our knowledge, to reduce the unfairness among different users caused by the high-frequency fading characteristic of VLC systems. Furthermore, the particle swarm optimization (PSO) is introduced to satisfy the transmitting power requirements of each user and to improve system performance. Simulation results show that, under the same VLC system conditions, the OFDMA-NOMA scheme with PSO has significant improvements in terms of user capacity and transmission rates compared to the purely NOMA scheme and the OFDMA scheme.

Rolling Shutter OFDM Scheme for Optical Camera Communication Considering Mobility Environment Based on Deep Learning

This paper presents a rolling shutter orthogonal frequency-division multiplexing (RS-OFDM) optical camera communication higher rate longer range proposed in IEEE 802.15.7a Task Group (TG7a) using an image sensor as a receiver. OFDM is a digital multi-carrier modulation scheme deployed for broadband wireless communication to resolve the inter-symbol interference (ISI) effect caused by the multipath channel. In optical wireless communication systems, OFDM was applied widely for indoor applications: internet of things, e-health, vehicular, and localization systems. The mobility scenario is a big problem for OWC systems, which reduces the system performance due to the optical channel variation in the processing time. In addition to that, signal detection should be considered in the mobility environment to improve the signal-to-noise ratio of OWC systems. In this paper, we proposed the convolution neural network (CNN) for LED detection in the RS-OFDM system, considering the mobility effect. In addition to that, the deep neural network was applied to detect the start of OFDM frame instead of conventional technology (Van De Beek algorithm). By applying our approach, the RS-OFDM system can achieve long communication (18 m distance) with a low error rate in the 2 m/s velocity environment.

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.

GFDM frame design for low-latency industrial networks

This paper proposes a short packet GFDM-based physical (PHY) layer for industrial wireless networks to reduce latency. In our proposed PHY layer, the conventional OFDM scheme used in the data field of IEEE 802.11 WLAN standards is replaced by GFDM. The preamble size is also reduced from 10 symbols to 1 symbol. Furthermore, the fields of the overall packet structure are optimized in terms of total number of subcarriers and cyclic prefix length. Additionally, a noise-free GFDM scheme is subjected to concatenated channel coding to minimize error rate. Through simulation, packet transmission time is reduced by about 40 ∼ 72% compared to the OFDM-based PHY layer while achieving a PER of order 10^−3. The obtained results show that the GFDM-based PHY layer outperforms its counterpart by exhibiting a lower latency and high reliability. This performance renders the GFDM-based (proposed) PHY layer suitable for adoption in the development of wireless networks for latency and reliability constrained industrial applications. It should be noted that the simulations presented in this paper express our first step in the direction of using GFDM for industrial wireless networks to achieve low latency and high reliability. We therefore consider building a fully functional GFDM based-testbed as part of our future work.

Outage Probability for OTFS Based Downlink LEO Satellite Communication

As an important technique of enabling global access for 6G, low earth orbit satellite (LEO-Sat) communication is still facing the challenges of large path-loss, and severe Doppler effect. This paper studies the reliability performance of a downlink LEO-Sat communication system, where the orthogonal time frequency space (OTFS) scheme is employed to combat severe Doppler effect. Further, the unmanned aerial vehicle (UAV) based cooperative transmission is developed, in order to compensate for the large margin of path-loss caused by the long transmission distance. In particular, the closed-form expression for the outage probability of the OTFS based LEO-Sat transmission is derived, where the novel moment matching approach is used to closely approximate the PDF of a sum of shadowing Rician (SR) variables. Further, the condition of using UAV cooperation is obtained so that the positive reliability gain is guaranteed. Finally, both the theoretical analysis and simulation results show that, the OTFS scheme can significantly outperform the traditional OFDM scheme, while demanding to carefully address the trade-off between reliability improvement and implementation complexity determined by modulation size.

Secure SDM–OFDM signal transmission based on memristive neural network

This paper proposes a physical layer security strategy of space division multiplex orthogonal frequency division multiplexing system based on memristive neural network (MNN). Among them, the two-level chaotic control, the application of the memristive chaotic model with conditional symmetry and the encryption of the MNN are all proposed for the first time in the access network. The memristive chaotic model with conditional symmetry generates 8 multiple masking factors and achieves high-security encryption. In the encryption process, the key space is selected by Logistic mapping, and the MNN encryption mechanism disturbances and compresses bits. The proposed encryption strategy has been proved on the experimental platform. The generated OFDM signals are modulated, which transmit data rate of 124.4 Gb/s over the 2 km multi-core fiber (MCF). Bit error rate (BER) and different anti-interference are analyzed in experiments. The key space of this proposed scheme is 2×10399, which is large enough number to effectively resist any brute force or illegal optical network units (ONUs) intrusion in passive optical network (PON). The results show that the proposed SDM–OFDM​ scheme has high sensitivity and security. This scheme has very reliable safety performance and benefit improvement, and is very promising in the future SDM–OFDM system.

Estimation of Compressible Channel Impulse Response for OFDM Modulated Transmissions

Channel estimation scheme for OFDM modulated transmissions usually combines an initial block-pilot-assisted stage with a tracking one based on comb or scattered pilots distributed among user data in the signal frame. The channel reconstruction accuracy in the former stage has a significant impact on tracking efficiency of the channel variations and the overall transmission quality. The paper presents a new block-pilot-assisted channel reconstruction procedure based on the DFT-based approach and the Least Square impulse response estimation. The proposed method takes into account a compressibility feature of the channel impulse response and restores its coefficients in groups of automatically controlled size. The proposition is analytically explained and tested in a OFDM simulation environment. The popular DFT-based methods including compressed sensing oriented one were used as references for comparison purposes. The obtained results show a quality improvement in terms of Bit Error Rate and Mean Square Error measures in low and mid ranges of signal-to-noise ratio without significant computational complexity growth in comparison to the classical DFT-based solutions. Moreover, additional multiplication operations can be eliminated, compared to the competitive, in terms of estimation quality, compressed sensing reconstruction method based on greedy approach.

CPM-OFDM Performance over Underwater Acoustic Channels

We propose and evaluate the performance of a continuous phase modulation based orthogonal frequency division multiplexing (CPM-OFDM) transceiver for underwater acoustic communication (UAC). In the proposed technique, the mapper in traditional OFDM is replaced by CPM while a realistic model of underwater channel is employed. Bit error rate (BER) as well as peak to average power ratio (PAPR) performance of the proposed scheme is evaluated using Monte-Carlo simulations. The error performance observed clearly establishes the superiority of CPM-OFDM over traditional OFDM schemes. Specifically, a value of 7/16 or 9/16 for the modulation index gives the best error performance. Furthermore, the error performance of the proposed scheme is within acceptable values up to a transmitter–receiver distance of 1.5 km. Additionally, the PAPR performance of the proposed scheme suggests that like other OFDM schemes, a PAPR reduction scheme is mandatory for acceptable PAPR performance of CPM-OFDM.

Subblock design aided orthogonal frequency division multiplexing with all index modulation using search algorithm

AbstractOrthogonal frequency division multiplexing with index modulation (OFDM‐IM) harvests significantly better error performance compared with OFDM due to its design of the index bits. However, the structure of conventional OFDM‐IM scheme does not fully focus on the enhancement of the bit error rate (BER) performance. In the proposed subblock design aided OFDM with all index modulation (SD‐OFDM‐AIM), unconditional pairwise error probability (UPEP) is taken as the objective function to select the subblock realizations with low error rates, leading to the BER performance enhancement. Noticing that UPEP uses the channel state information (CSI), we fully discuss the calculation of CSI and analyze the effect on subblock design under imperfect channel evaluation. Moreover, inspired by sphere decoding method, we propose the low complexity decoder to remove the high burden of computational complexity in former OFDM with all index modulation (OFDM‐AIM) after the reconstruction of the look‐up table. The simulation results demonstrate its superiority at BER performance compared with the index modulated OFDM schemes and OFDM‐AIM.

Peak-to-Average Power Ratio reduction in Wavelet based OFDM using Modified Selective Mapping for Cognitive Radio Applications

The prospect of guaranteed quality of service for primary and secondary users in the expression of regulated Peak-to-Average Power Ratio (PAPR) and Bit Error Rate (BER) can be increased in Cognitive Radios using Wavelet based OFDM systems which localize spectrum in realms of time and frequency. However, cutting the Gordian knot of high PAPR associated with the Multi-Carrier Modulation schemes to operate in the linear part of the power amplifier nourishing the balance between PAPR and BER is difficult. In this paper, the phase of the subcarriers is altered by a value of finite, equally spaced phase shifts. The frame of Wavelet-based OFDM (WOFDM) with minimum PAPR guarantees the minimum quality of service (QoS) in terms of Throughput. BER is then identified and transmitted. This modification is applied to various Wavelets and compared amongst WOFDM and FFT-based OFDM schemes. The novelty of this paper lies in using Hadamard and/or Toeplitz matrix to generate phase sequences in a modified SLM technique of Wavelet-based OFDM systems while maintaining the minimum required QoS in Cognitive Radios. The result shows that the proposed technique reduces the PAPR compared to unmodified SLM techniques. HIGHLIGHTS Wavelet based OFDM systems localize spectrum in realms of time and frequency The sinusoid bases function in OFDM has been replaced by Wavelet bases Selective Mapping (SLM) is a popular technique towards PAPR reduction The primary function of the Cognitive Radio system is to identify the spectrum holes GRAPHICAL ABSTRACT