Orthogonal Frequency Division Multiplexing Scheme Research Articles

Experimental Study of Fast Orthogonal Frequency Division Multiplexing Transmission over a Random Media Channel for Optical Wireless Communications

In this paper, a 4 amplitude shift keying (4-ASK) fast orthogonal frequency division multiplexing (FOFDM) scheme was experimentally investigated over a turbulent air–water channel for optical wireless communications. The experiment results showed that the 4-ASK-FOFDM modulated signals were not sensitive to weak atmospheric turbulence, and the bit-error rate (BER) was lower than the 7% forward error correction (FEC) limit of 3.8 × 10−3. Under the condition of the same spectra efficiency, the 4-ASK-FOFDM scheme just had a tiny performance penalty compared to the 16-QAM-OFDM scheme. Consequently, the 4-ASK-FOFDM scheme is a promising alternative to the conventional 16-QAM-OFDM scheme in optical wireless communications.

Security enhancement through high-quality illumination enabled by wavelength-shuffled optical OFDM.

This study presents a novel physical layer security technique that aims to increase the security level by reducing decryption attempts and improving the resistance to security attacks. To achieve this goal, the proposed approach generates signals that resemble Gaussian noise in both the time and frequency domains. This method utilizes a wavelength-shuffled optical orthogonal frequency division multiplexing (OFDM) scheme, which is combined with the standard blue-excited phosphorus lighting approach. Experimental validation of the proposed system demonstrates a secure data rate of 880 Mb/s in the aggregate, followed by a real-time demonstration showing its practicality. Furthermore, the proposed system generates high-quality white light (with a color rendering index of 83 and correlated color temperature of 5040 K), which makes it suitable for practical illumination applications.

SIMULASI SKEMA UNIVERSAL FILTERED MULTI-CARRIER (UFMC) PADA SISTEM KOMUNIKASI DIGITAL

Universal Filtered Multi-Carrier (UFMC) is a multi-carrier modulation scheme that is an alternative to the Orthogonal Frequency Division Multiplexing (OFDM) scheme currently used in 4G communication systems and wireless local area networks (WLAN). The weakness of OFDM lies in the high peak-to-average power ratio (PAPR) value and out-of-band (OOB) emission which can cause interference between carriers. UFMC is one of the schemes used to overcome the weaknesses of OFDM. This research aims to study the performance of UFMC for data transmission on AWGN channel with 256-QAM, 1024-QAM, and 4096-QAM modulation. In addition, 256-point, 512-point, and 1024-point FFTs were also used to see the effect on the achievable bit error rate (BER) and PAPR value. The simulation results show that for all simulated FFT sizes and QAM values, 256-QAM produces the lowest BER value. Using a 1024-point FFT, a BER of 10-3 can be achieved with an SNR of 20 dB. The lowest PAPR value obtained in the simulation is 7.1891 dB.

Distortion-Elimination Hybrid OFDM With Low Complexity for Optical Wireless Communications

In optical wireless communications (OWC), hybrid optical orthogonal frequency division multiplexing (O-OFDM) schemes, such as hybrid asymmetrically clipped O-OFDM (HACO-OFDM) and layered asymmetrically clipped O-OFDM (LACO-OFDM), enjoy both high power and spectral efficiency. However, due to the non-orthogonal transmission of signal components induced by the clipping distortion, successive interference cancellation (SIC) is required in these hybrid O-OFDM schemes, leading to notably increased complexity. In this paper, we conceive novel hybrid O-OFDM schemes to offer both high spectral and power efficiency, whilst possessing low complexity. By elaborately designing a time-domain (TD) distortion elimination methodology at the transmitter, a novel distortion-elimination hybrid O-OFDM (DEHO-OFDM) is first proposed, which combines asymmetrically clipped O-OFDM (ACO-OFDM) and pulse-amplitude-modulated discrete multitone (PAM-DMT) in an interference-free manner. In order to further improve the spectral efficiency, an enhance DEHO-OFDM (EDEHO-OFDM) is designed by activating the remaining subcarrier resources. Both DEHO-OFDM and EDEHO-OFDM can be realized through a single-IFFT transmitter and standard OFDM receiver, leading to much lower complexity than the existing hybrid O-OFDM schemes. Simulation results have demonstrated the superiorities of the proposed schemes over HACO-OFDM and LACO-OFDM in terms of peak-to-average-power ratio (PAPR) and bit error rate (BER).

Wide-field-of-view optical detectors for deep ultraviolet light communication using all-inorganic CsPbBr3 perovskite nanocrystals.

Optical wireless communication (OWC) links suffer from strict requirements of pointing, acquisition, and tracking (PAT) between the transmitter and receiver. Extending the narrow field-of-view (FoV) of conventional light-focusing elements at the receiver side can relax the PAT requirements. Herein, we use all-inorganic CsPbBr3 nanocrystals (NCs) to extend various optical concentrators' FOV to 60°, regardless of the original FOV values of the concentrators. Given the robustness of UV light against communication channel misalignment, the used CsPbBr3 NCs provide another advantage of converting transmitted UVC light into a green color that matches the peak absorption of the widely available Si-based detectors. We evaluated the feasibility of the reported wide FoV optical detectors by including them in deep UV OWC systems, deploying non-return-to-zero on-off keying (NRZ-OOK) and orthogonal-frequency division multiplexing (OFDM) modulation schemes. The NRZ-OOK and OFDM schemes exhibit stable communication over the 60° FoV, providing data transmission rates of 100 Mb/s and 71.6 Mb/s, respectively, a unique capability to the reported design.

Adaptive bias layered optical OFDM based on precoding for IM/DD systems

An adaptive bias layered optical orthogonal frequency division multiplexing (ABLO-OFDM) scheme based on real-valued precoding is proposed in the intensity modulation and direct detection (IM/DD) system. In ABLO-OFDM scheme, multilayer subcarriers are used to transmit data, which can achieve high spectral efficiency (SE) and reduce the peak average power ratio (PAPR). Compared with layered asymmetrically clipped O-OFDM (LACO-OFDM) scheme, only one inverse Fast Fourier transform (IFFT) block is needed in ABLO-OFDM. At the same time, the signal can be demodulated directly using the standard OFDM receiver. In addition, to resist the selective fading effect of the system, low-complexity real-valued precoding, namely discrete cosine transform (DCT) and discrete Hartley transform (DHT), are used to effectively balance the signal-to-noise ratio (SNR) between subcarriers and further reduce the PAPR. The result shows that the PAPR of the ABLO-OFDM system is reduced by 2.7 dB after adaptive bias layering, and the PAPR is further reduced by 2.4 dB at most after precoding. For the layered ABLO-OFDM system with DCT precoding, as the number of subcarrier layers decreases from L = 8 to L = 1, the required receiver optical power (ROP) is reduced by 6 dB. It proves that the ABLO-OFDM system with DCT precoding can achieve higher SE and effectively improve receiver sensitivity.

High Spectral Efficiency Photonics-Based Polarization Multiplexing OFDM Signal Delivery at W-Band

We have implemented a large-capacity, long-haul, and high spectral efficiency photonics-based polarization multiplexing communication system at W-band. The signal delivery up to 119.1 Gb/s with spectral efficiency of 9.9 bit/s/Hz is achieved over a 10 km optic-fiber link and 4600 m wireless link. In our study, we utilize an orthogonal frequency division multiplexing (OFDM) scheme to compensate for the signal impairments caused by the dispersion effect and the wireless multipath effect. Based on a pair of antennas, the antenna polarization multiplexing technique is used to realize the polarization-multiplexed mm-wave signal delivery. Also, only one communication link is required, instead of the complex 2×2 line-of-sight multiple-input multiple-output (MIMO) link. Instead of Cassegrain antennas, the combination of plano-convex lens and horn antenna greatly extends the wireless distance. For increasing the spectral efficiency and throughput of the communication system, we employ higher-order modulation formats, probabilistic shaping (PS) techniques, and a series of equalization algorithms. Based on photonics technology, we have created a record-setting distance-rate product of 547.9 Gb/s•km (119.1 Gb/s × 4.6 km) for an independent channel at W-band.

Clipping-Free Multilayer Optical OFDM for IM/DD-Based Communication Systems

A low-complexity and high-performance clipping-free multilayer optical orthogonal frequency division multiplexing scheme is proposed for optical wireless communication (OWC). At the transmitter, the symbols of multi-layer quadrature amplitude modulation (QAM) are first arranged according to a specific rule in the frequency domain to generate a bipolar time-domain signal using a single inverse fast Fourier transform (IFFT). Then the bipolar signal is superimposed with an adaptive periodic DC bias to meet the real and positive requirements in intensity modulation / direct detection (IM/DD) systems. At the receiver, a zero-value regression (Re0) -based demodulation is proposed to optimize the bit error rate (BER). As the signal generation and demodulation are realized by single IFFT and fast Fourier transform (FFT) respectively, the proposed scheme has nearly the same system complexity as the single-layer modulations and similar spectral efficiency with those advanced multilayer modulations. In addition, the proposed periodic DC improves the power efficiency and avoids the interlayer interference. Numerical simulation results show that, compared with LACO-OFDM [34] with 3 layers, the proposed scheme can attain a PAPR gain of 2.4 dB and BER gain of 1.4 dB and 3 dB for the linear and nonlinear channel, respectively.

Subcarrier-Interactive Dual-Mode OFDM

In this letter, a novel dual-mode index modulation aided orthogonal frequency division multiplexing (DM-OFDM) scheme called subcarrier-interactive (SI-) DM-OFDM is proposed. In the SIDM-OFDM, each subcarrier pair conveys the same QAM modulated symbols to achieve a diversity gain. At the receiver, a low complexity (LC) signal detection algorithm is proposed, i.e., SIDM-OFDM-LC, where each subcarrier interacts with other subcarriers in the same subblock as complementary and non-complementary states to improve BER performance. Moreover, Euclidean distance (ED) of the received signal and channel-noise matrix (CNM) based signal detection algorithms are employed for demodulation, namely SIDM-OFDM-ED and SIDM-OFDM-CNM, respectively. Simulation results confirm that the SIDM-OFDM with the proposed three signal detection algorithms achieves a significantly better BER performance than the existing DM-OFDM scheme at the same spectral efficiency. Also, it is revealed that the SIDM-OFDM-LC reduces the signal detection cost compared to the other two proposed detectors.

10-Gbps visible light communication in a 10-m free space based on violet series-biased micro-LED array and distance adaptive pre-equalization.

In this paper, we fabricated a 3×3 violet series-biased micro-LED array with high-output optical power and applied it in high-speed and long-distance visible light communication. By employing the orthogonal frequency division multiplexing modulation scheme, distance adaptive pre-equalization, and a bit-loading algorithm, record data rates of 10.23 Gbps, 10.10 Gbps, and 9.51 Gbps were achieved at 0.2 m, 1 m, and 10 m, respectively, below the forward error correction limit of 3.8×10-3. To the best of our knowledge, these are the highest data rates achieved by violet micro-LEDs in free space and the first communication demonstration beyond 9.5 Gbps at 10 m using micro-LEDs.

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.

Study and Comparative Analysis of OFDM and UFMC Modulation Schemes

In various areas, wireless systems are used. In order to allocate the available time and frequency resources, these wireless systems require flexible mechanisms. With 5G, transmission rates will be higher, latency will be lower and quality of service and channel capacity will be higher. The physical layer must be able to generate flexible waveforms to meet the above requirements. Currently, Orthogonal Frequency Division Multiplexing (OFDM) transmission does not support 5G communication. In the case of 4G/OFDM, there are many problems in terms of out of band emission, spectral efficiency, and peak to average power ratio (PAPR). An alternative transmission scheme Universal Filtered Multicarrier (UFMC) is introduced to address this problem. The paper compares OFDM with UFMC. The purpose of this paper is to discuss Spectral Density, Spectral Efficiency, Signal to Noise Ratio (SNR) and Bit Error Rate (BER). In comparison to OFDM, UFMC provides better performance.

BER Reduction and Capacity Enhancement with Novel Guard Sequence Selection for Multi-Carrier Communication

Orthogonal frequency division multiplexing (OFDM) is an efficient multicarrier scheme that uses different types of guard intervals such as cyclic prefix (CP) and known symbol padding (KSP) (zero padding (ZP), unique word (UW), etc.) in block formation. Among these guard intervals, CP varies for each block, while other guard intervals remain fixed from block to block. These guard intervals efficiently perform channel estimation, synchronization and remove inter-block interference (IBI); nevertheless, none of the existing schemes develop any relationship between the guard interval (sequence) and the data symbols on different subcarriers of the OFDM block. We present a new idea of selecting the guard interval based on the data symbols of a subset of subcarriers in the block and exploit the high auto-correlation of the selected guard sequence to improve the bit error rate (BER) performance of the system. The results based on a fair comparison show that our enhanced orthogonal frequency division multiplexing (eOFDM) scheme inherits significant improvements in BER and the capacity of a multicarrier system as compared to the existing techniques.

Hybrid Power Line/Wireless System With Optimal Subcarrier Permutation Under Uniform or Optimal Power Allocation

This article studies optimal subcarrier permutation in hybrid power line/wireless systems to either maximize the achievable data rate or minimize the average bit error probability (BEP). In order to better exploit the frequency selectivity of power line and wireless media, subcarrier permutation is optimized under uniform or optimal power allocation over an orthogonal frequency-division multiplexing scheme using maximal-ratio combining. Different from previous works, we demonstrate that the normalized signal-to-noise (nSNR) must be considered instead of the SNR and prove that it can be extended to cases where the minimization of the average BEP and optimal power allocation are considered. Moreover, we show that subcarrier permutation and power allocation problems can be assumed to be decoupled. Numerical results show that performance gains associated with subcarrier permutation become more relevant as the frequency selectivity of the nSNRs increases. In addition, the optimal subcarrier permutation is more effective for minimizing the average BEP than maximizing the achievable data rate and yields similar improvement under the usage of uniform and optimal power allocations.

Multiuser neural network detectors for large scale MIMO OFDM over Rayleigh Winner‐II channel

Large scale (LS) MIMO orthogonal frequency division multiplexing (OFDM) technique satisfies the demands on performance and the service quality preferred in wireless communication system. Since numerous antenna terminals have been incorporated in the base station, multiuser detection is crucial for retrieving the data appropriately. Thus, the complexities of the detectors increase rapidly in large scale MIMO OFDM schemes. A unique neural network detection approach for multiuser detection in LS MIMO OFDM model is presented. The performance of multilayer perceptron (MLPNN) and radial basis (RBNN) detectors with minimum mean square (MMSE) MUDs are analyzed. The neural network multiuser detecting methodologies are also analyzed by the loss function in LS MIMO OFDM systems. The performance analyses of the detectors are also done by analyzing the radiation patterns of the antennas which is equipped at the both ends of the uplink channels. Radial basis MUDs have 23 dB bit error rate which gains over linear MMSE detector and of 14 dB than multilayer perceptron detectors specifically at 10(−5) bit error rate. According to the bit error rate analysis of estimations at the output of the multiuser detector, the suggested neural network models are more effective in reducing multiuser interference in MU LS MIMO OFDM. Analysis also verifies, radial basis function (RBF) multiuser detector are exhibiting an optimal BER performance than multilayer perceptron detector with sufficient number of hidden neurons. This study thus emphasis a RBF MUD scheme for detecting multiuser signals in LS MIMO OFDM system due to its dynamic performance in low probability of bit error.

A Joint Design of SCMA Codebook and PTS-Based PAPR Reduction for Downlink OFDM Scheme

In this paper, a joint design of sparse code multiple access (SCMA) codebook and peak-to-average power ratio (PAPR) reduction based on the partial transmit sequence (PTS) technique is proposed for the downlink orthogonal frequency division multiplexing (OFDM) scheme. A benchmark scheme is firstly devised based on a direct extension of the conventional PTS-based OFDM scheme. Based on the characteristics of the near-optimal SCMA codebook designs reported in our previous work, a PTS-based SCMA-OFDM design is proposed by carefully determining the rotation angles of the SCMA codebooks, according to the adopted signal sub-constellations. A receiver which does not need the side information is further devised. Considering the phase ambiguity issue of the receiver, the PTS angles have been carefully refined. When compared to both the original scheme that does not consider PAPR reduction techniques and the benchmark scheme, the proposed scheme achieves a significantly enhanced PAPR performance with approximately the same error performance. In addition, a comparable PAPR performance, an improved error performance, and a lower computational complexity can be achieved when compared to the clipping-based SCMA-OFDM scheme reported in the previous literature.

On the Fast DHT Precoding of OFDM Signals over Frequency-Selective Fading Channels for Wireless Applications

Due to high power consumption and other problems, it is unlikely that orthogonal frequency-division multiplexing (OFDM) would be included in the uplink of the future 6G standard. High power consumption in OFDM systems is motivated by the high peak-to-average power ratio (PAPR) introduced by the inverse Fourier transform (IFFT) processing kernel in the time domain. Linear precoding of the symbols in the frequency domain using discrete Hartley transform (DHT) could be used to minimise the PAPR problem, however, at the cost of increased complexity and power consumption. In this study, we minimise the computation complexity of the DHT precoding on OFDM transceiver schemes and the consequent power consumption. We exploit the involutory properties of the processing kernels to process the DHT and IFFT as a single-processing block, thus reducing the system complexity and power consumption. These also enable a novel power-saving receiver design. We compare the results to three other precoding schemes and the standard OFDM scheme as the baseline; while improving the power consumption efficiency of a Class-A power amplifier from 4.16% to 16.56%, the bit error ratio is also enhanced by up to 5 dB when using a 12—rate error-correction coding and 7 dB with interleaving.

Joint radar communication system design based on filter bank multicarrier modulation scheme

Since orthogonal frequency division multiplexing (OFDM) signals are sensitive to Doppler shift, OFDM signals with cyclic prefix (CP) not only reduce the communication rate but also result in symmetric pseudo peaks in the ambiguity function of the radar, which eventually lead to the degradation of the performance of the joint radar communication system (JRCS). In this study, a novel JRCS is proposed based on the filter bank multicarrier (FBMC) waveform for the inverse synthetic aperture radar (ISAR) imaging and communication system. On the one hand, FBMC waveforms are capable of low orthogonality between subcarriers, which can counter Doppler and multipath effects. On the other hand, FBMC waveforms do not require CP, so the false targets can be avoided and spectral efficiency can be improved. The influence of multipath effect and Doppler shift on FBMC waveform in an integrated system is analysed in detail, and a Doppler compensation algorithm suitable for FBMC-integrated waveform is proposed. The phase error caused by target motion can be iteratively compensated to obtain a well-focussed ISAR image. Finally, considering the ISAR image entropy after motion compensation as the evaluation metric, extensive simulation experiments verify the noise robustness and effectiveness of the proposed algorithm. Compared with the conventional OFDM and CP-OFDM schemes, the simulation verifies that the proposed waveform design and processing method has better performance in the ISAR imaging and communication integrated system.

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.

High bandwidth series-biased green micro-LED array toward 6 Gbps visible light communication.

In this Letter, a record modulation bandwidth of 1.31 GHz was achieved by a 10 µm c-plane green micro light emitting diode (micro-LED) at a current density of 41.4 kA/cm2. Furthermore, by designing a series-biased 20 µm micro-LED with higher light output power, combined with an orthogonal frequency division multiplexing modulation scheme, a maximum data rate of 5.789 Gbps was achieved at a free-space transmission distance of 0.5 m. This work demonstrates the prospect of c-plane polar green micro-LED in ultrahigh-speed visible light communication, which is expected to realize a high-performance wireless system in the future.