Orthogonal Frequency Division Multiplexing Transmission Research Articles

Precoded OVSB-OFDM transmission system using DML with Kramers-Kronig receiver

Different from the use of IQ modulator or a dual-drive Mach-Zehnder modulator, we investigate an optical vestigial sideband orthogonal frequency division multiplexing (OVSB-OFDM) transmission system using a low-cost directly modulated laser. Precoding techniques and Kramers-Kronig (KK) algorithm are employed to enhance the bit error rate (BER) performance. The KK receiver is applied to eliminate the signal-signal beat interference caused by the square-law detection of the photodetector. Discrete Fourier transform (DFT) and orthogonal circulant matrix transform (OCT) precoding techniques can effectively average the signal-to-noise ratio over the data-carrying subcarriers and improve the BER performance. Through numerical simulation, we discuss the relationship between the order and center frequency of the optical filter and the carrier signal power ratio (CSPR). Furthermore, we study the influence of the KK algorithm and precoding techniques on receiver sensitivity under different transmission distances. The results show that both KK algorithm and precoding technologies can improve receiver sensitivity and extend the transmission distance. The performance of DFT precoding is better than that of OCT precoding. When there is no KK algorithm, the transmission distance of OCT precoding or no precoding is only 20 km at the BER of 3.8e-3; while DFT precoding can extend the transmission distance up to 60 km. With the help of the KK algorithm, OCT precoding and DFT precoding can further extend the transmission distance by up to 40 and 60 km, respectively, compared to the DFT precoding and without the KK algorithm case. The DFT precoding with the KK algorithm can improve the receiver sensitivity of more than 7 dB in terms of received optical power, compared to the no precoding and without the KK algorithm case.

Low Complexity Transmitter Architecture for Optical OFDM Systems

A novel low-complexity optical orthogonal frequency division multiplexing (LCO-OFDM) transmission architecture is proposed in this letter. The LCO-OFDM transmitter consists of two branches, wherein the first and second branches use odd and even subcarriers, respectively. Specifically, only complex multiplications are required in modulated symbols of each branch without Hermitian symmetry and inverse fast Fourier transform operations. Transmission signals of LCO-OFDM can be obtained by transmitting real and imaginary parts of generated complex signals in each branch over two successive orthogonal frequency division multiplexing frames and adding a direct current bias to avoid zero clipping noise. Simulation results showed the optimum performance of LCO-OFDM in terms of both peak-to-average power ratio and bit error rate.

IM/DD probabilistically shaped 64-QAM OFDM-PON transmission assisted by selective-mapping and flexible systematic polar code

Intensity-modulation direct-detection (IM/DD) orthogonal frequency division multiplexing (OFDM) has advantages of low cost and simple structure, which is a promising candidate for next-generation high-speed passive optical networks. In this work, we propose and experimentally demonstrate a look-up-table-based probabilistic shaping scheme assisted by selective-mapping (SLM) and flexible systematic polar code (SPC) to improve the performance of IM/DD 64-QAM OFDM transmission system. Meanwhile, we experimentally compare the performance between the proposed scheme and the joint constant composition distribution matching (CCDM) and low-density parity-check (LDPC). Here, abundant phase sequences in the SLM are generated by chaotic sequence to suppress peak-to-average power ratio (PAPR). The pre-set bits of SPC are utilized for the additional information of probabilistic shaping to reduce the redundancy and the cyclic redundancy check (CRC) aided successive cancellation list (CA-SCL) decoder is used for decoding. Joint probabilistic shaping and PAPR suppression have contributed 4.6-dB and 3-dB bit error ratio performance improvements for the IM/DD 64-QAM OFDM transmission system in the pre and post forward error correction (FEC), respectively.

Joint Symbol Level Precoding and Combining for MIMO-OFDM Transceiver Architectures Based on One-Bit DACs and ADCs

Herein, a precoding scheme is developed for orthogonal frequency division multiplexing (OFDM) transmission in multiple-input multiple-output (MIMO) systems that use one-bit digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) at the transmitter and receiver, respectively, as a means to reduce the power consumption. Two different one-bit architectures are presented. In the first, a single user MIMO system is considered where the DACs and ADCs of the transmitter and the receiver are assumed to be one-bit and in the second, a network of analog phase shifters is added at the receiver as an additional analog-only processing step with the view to mitigate some of the effects of coarse quantization. The precoding design problem is formulated and then split into two NP-hard optimization problems, which are solved by an algorithmic solution based on the Cyclic Coordinate Descent (CCD) framework. The design of the analog post-coding matrix for the second architecture is decoupled from the precoding design and is solved by an algorithm based on the alternating direction method of multipliers (ADMM). Numerical results show that the proposed precoding scheme successfully mitigates the effects of coarse quantization and the proposed systems achieve a performance close to that of systems equipped with full resolution DACs/ADCs.

Real-time IBFD transmission system based on adaptive optical self-interference cancellation using the hybrid criteria regular triangle algorithm.

In this Letter, we first propose and demonstrate a real-time in-band full duplex (IBFD) transmission system based on adaptive optical self-interference cancellation (OSIC). The field programmable gate array (FPGA) is used for high-speed and real-time orthogonal frequency-division multiplexing (OFDM) transmission. The hybrid criteria regular triangle (RT) algorithm is first proposed to combine signal power and the bit error rate (BER) together as the objective function to realize the adaptive control process. With this algorithm, the real-time adaptive OSIC system is able to converge and fully recover the signal of interest (SOI) within 12 sampling times, which is by far the fastest, to the best of our knowledge, convergence under the real-time transmission scenario. Experiments show that the system can achieve 28 dB cancellation depth across 0-1.45 GHz wideband, and 40 dB cancellation depth at 900 MHz, 2.4 GHz, and 5 GHz, which is the best cancellation performance in current real-time adaptive OSIC schemes and shows the potential of our system in different commercial applications.

Application of OFDM transmission method for railway signalling system via track circuit

At present, railway signalling systems in which control information is transmitted via track circuits (rails) have been deployed in many applications, such as automatic train control (ATC) systems in Japan. In these systems, it is difficult to increase the transmission speed due to the transmission characteristics of rails. To overcome this problem, we have proposed a new transmission method using orthogonal frequency division multiplexing (OFDM) and evaluated a configuration in which data judgment using majority decision was applied for improving the bit error rate (BER) characteristics. In this paper, we describe an FPGA implementation of our proposed method and the performance of the implemented devices.

System and Design for Selective OFDM SWIPT Transmission

Simultaneous wireless information and power transfer (SWIPT) augments a wireless device's capability to transmit data by adding a harvesting component to the standard information processing receiver. With SWIPT, both information processing and energy scavenging are combined to allow a SWIPT device to become its own recurrent power source. This article proposes and analyzes the functionality of a novel selective orthogonal frequency-division multiplexing (OFDM) receiver architecture. The architecture leverages the OFDM signal structure to extract the cyclic prefix (CP) of the signal for energy harvesting and selectively harvest a fraction of the received signal for increase energy storage. This article also evaluates the rate-energy (R-E) tradeoff of the system as a means for analyzing the switching time's impact on rate and energy. Additionally, this article examines the feasibility of harvesting sufficient energy to power the OFDM processing portion of the receiver. To understand the feasibility, an optimization problem is developed to minimize the portion of the information signal used for harvesting while ensuring sufficient energy is harvested to perform the processing. To facilitate the evaluation, Monte Carlo simulations are run presenting system level R-E tradeoff and feasibility performance. Selective OFDM transmission is found to provide improved energy harvesting and sustainability.

Multi-Gigabit CO-OFDM System over SMF and MMF Links for 5G URLLC Backhaul Network

The 5G cellular network aims at providing three major services: Massive machine-type communication (mMTC), ultra-reliable low-latency communications (URLLC), and enhanced-mobile-broadband (eMBB). Among these services, the URLLC and eMBB require strict end-to-end latency of 1 ms while maintaining 99.999% reliability, and availability of extremely high data rates for the users, respectively. One of the critical challenges in meeting these requirements is to upgrade the existing optical fiber backhaul network interconnecting the base stations with a multigigabit capacity, low latency and very high reliability system. To address this issue, we have numerically analyzed 100 Gbit/s coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission performance over 400 km single-mode fiber (SMF) and 100 km of multi-mode fiber (MMF) links. The system is simulated over optically repeated and non-repeated SMF and MMF links. Coherent transmission is used, and the system is analyzed in a linear and non-linear regime. The system performance is quantified by bit error ratio (BER). Spectrally efficient and optimal transmission performance is achieved for 400 km SMF and 100 km MMF link. The results designate that MMF links can be employed beyond short reach applications by using them in the existing SMF infrastructure for long haul transmission. In particular, the proposed CO-OFDM system can be efficiently employed in 5G backhaul network. The multi-gigabit capacity and lower BER of the proposed system makes it a suitable candidate especially for the eMBB and URLLC requirements for 5G backhaul network.

Efficient Implementation Technique for OFDM on FPGA

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier system where data bits are encoded to multiple sub-carriers, while being sent simultaneously. The basic idea of OFDM is to divide the available spectrum in a number of narrowband and low-rate orthogonal subcarriers, to prevent interference between the closely carriers. This makes the OFDM system resistant to multipath effect. Due to wide use of OFDM, it is essential to develop a Digital Signal Processor (DSP) to generate OFDM signals present in the various standards, using a reconfigurable platform like Field Programmable Gate Array (FPGA). The objective of the project is to design and implement OFDM transmitter and receiver on FPGA hardware. This project concentrates on developing custom single purpose processor for OFDM with Fast Fourier Transform i.e., FFT and Inverse Fast Fourier Transform i.e., IFFT in an efficient way. The work also includes design of a mapping module (Modulator)(64-QAM), serial to parallel, parallel to serial converter and Vedic multiplier modules and interconnections between them.Basically we are integrating different proposed ideas into a single paper. The design uses 64-point FFT and IFFT for the processing module, which indicate that the processing block contain 64 inputs data. This design is simulated on Zynq UltraScale+ FPGA Board(Part:xczu7ev-ffvf1517-1LV-i) and tested and verified using Xilinx Vivado 2020 software. Simulations on Python is also done to compare our result with the results obtained from that of use of FPGA.

Reduction of Phase-Modulation to Intensity-Modulation Conversion Noise Effect Using Delayed Self-Homodyne Optical Orthogonal Frequency Division Multiplexing System

Self-homodyne optical orthogonal frequency division multiplexing (OFDM) transmission system is a variant of self-coherent systems with a relaxed laser linewidth requirement as opposed to a full coherent system. The system is designed by transmitting a carrier together with the subcarriers, ensuring a strong phase-correlation between them at a receiver compared to the coherent system where only the subcarriers are transmitted. Despite the strong phase-correlation, the laser phase noise (PN) can still degrade the self-homodyne system performance due to the interaction of the PN with a chromatic dispersion (CD) induces a phase-modulation to intensity-modulation (PM-to-IM) conversion noise which cannot be canceled using a balanced-receiver. This imposes a high noise pedestal underneath each subcarrier, with the highest pedestal's peak imposed beneath the subcarriers that are farthest away from the carrier. This in turn produces a phase-decorrelation between the carrier and subcarriers which degrades the Q-factor between the lowest and highest subcarrier frequencies. In this work, the effect of the PM-to-IM conversion noise is reduced for the transmission of up to 174 Gb/s using a simple delay-line assigned to realign the phase-decorrelation of the subcarriers. With this technique, the subcarriers Q-degradation can be improved and the total transmission length can be tripled with Q-improvements of 5.4, 5.3, and 5-dB for 16-quadrature amplitude modulation (QAM) over 1360 km, 32- QAM over 800 km, and 64-QAM over 480 km, respectively, using 10-MHz LW with a 15-GHz total signal bandwidth. For 29 GHz signal bandwidth, the phase-walk-off of the high frequency subcarrier becomes more severe where the introduced delay can increase the transmission length by 2.5 times than without the delay, which increased the signal tolerance to the conversion noise.

Hardware-Efficient All-Digital Architectures for OFDM Backscatter Modulators

Orthogonal frequency-division multiplexing (OFDM) backscatter communication promises to enable ultralow-power wireless devices that are robust to time-varying multipath channels. Traditional OFDM transmitters require the use of power-hungry digital-to-analog converters (DACs) and vector modulators to realize the OFDM signal, adding to the complexity and power consumption of wireless sensor nodes. In this work, we compare three all-digital architectures for OFDM backscatter communication that use RF switches and discrete loads to implement digitally controlled single-sideband OFDM backscatter modulators. We present design analysis, including simulations and measurements, for a selected implementation using five subcarriers having binary phase shift keying (BPSK) modulation at a symbol rate of 250 kSymbols/s and a throughput of 1.25 Mbit/s with a modulator energy consumption of 160 pJ/bit. We also present a five-subcarrier over-the-air validation with 195-kb/s throughput. We demonstrate how the number of RF switch states and the choice of impedances impact the metrics of subcarrier interference ratio and sideband suppression ratio, and we explore how reduced-numeric-precision inverse fast Fourier transform (IFFT) structures impact the theoretical bit-error rate. The all-digital architecture and analysis presented in this article enable new avenues of low-cost, digital OFDM, and multiple-access backscatter communication systems for use in challenging multipath environments.

New Complementary Sets With Low PAPR Property Under Spectral Null Constraints

Complementary set sequences (CSSs) are useful for dealing with the high peak-to-average power ratio (PAPR) problem in orthogonal frequency division multiplexing (OFDM) systems. In practical OFDM transmission, however, certain sub-carriers maybe reserved and/or prohibited to transmit signals, leading to the so-called spectral null constraint (SNC) design problem. For example, the DC sub-carrier is reserved to avoid the offsets in D/A and A/D converter in the LTE systems. While most of the current research focus on the design of low PAPR CSSs to improve the code-rate, few works address the aforementioned SNC in their designs. This motivates us to investigate CSSs with SNC as well as low PAPR property. In this article, we present systematic constructions of CSSs under SNCs and low PAPR. First, we show that mutually orthogonal complementary sets (MOCSs) can be used as seed sequences to generate new CSSs with SNC and low PAPR, and then provide an iterative technique for the construction of MOCSs which can be further used to generate complementary sets (CSs) with low PAPRs and spectral nulls at varying positions in the designed sequences. Next, inspired by a recent idea of Chen, we propose a novel construction of these seed MOCSs with non-power-of-two lengths from generalized Boolean functions.

Joint Cancellation of Phase Noise and NB-IoT Interference in OFDM System

In the scenario of the coexistence of long term evolution (LTE) system using orthogonal frequency division multiplexing (OFDM) and narrowband Internet-of-Things (NB-IoT), when the in-band model is used, the narrowband interference caused by NB-IoT will seriously degrade the performance of OFDM. Meanwhile, the phase noise (PHN) generated by the local oscillators also reduce the reliability of OFDM transmission. In this letter, an algorithm of jointly eliminating NB-IoT interference and PHN is proposed within the sparse Bayesian learning framework for OFDM system, when the channel noise follows non-Gaussian distribution. An iterative solution is derived after the optimization structure is constructed. Simulation results demonstrate that the gain of proposed method over the conventional methods is approximately 1.5-3.5 dB when the bit error rate is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> .

Digital Mobile Fronthaul Based on Performance Enhanced Multi-Stage Noise-Shaping Delta-Sigma Modulator

A novel topology multi-stage noise-shaping (MASH) delta-sigma modulator is proposed for 20-km digital mobile fronthaul (MFH) in this article. In the proposed MASH structure, a newly designed feedback unit is combined with a traditional fourth-order sturdy MASH structure to enhance the noise-shaping capacity. The detailed comparison between the conventional fourth-order single delta-sigma modulator (SDSM) and the proposed new topology MASH is presented in a 512/1024 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) transmission system with the bandwidth of 1.125 GHz. The OFDM signal is quantized to two bits by SDSM/MASH analog-to-digital conversion (ADC), and this digitized signal is transmitted over 20-km single mode fiber (SMF) in 20-Gbaud 4-level pulse amplitude modulation (PAM4) intensity modulation direct detection (IM/DD) system. The signal to noise ratios (SNRs) of the retrieved OFDM signal utilizing the proposed new topology MASH and the fourth-order SDSM ADCs are 38.7dB and 34.5dB, respectively. In the case of 1024-QAM PAM4 system, the error vector magnitude (EVM) floors of the proposed new topology MASH and the conventional fourth-order SDSM schemes are 1.64% and 1.96% over 20-km SMF transmission at off-line digital signal processing (DSP) reception, and 1.2 dB receiver sensitivity improvement is achieved.

A Simple Blind Sampling Frequency Offset Estimation Scheme for Short-Reach DD-OFDM Systems

In this paper, a simple and overhead-free sampling frequency offset (SFO) blind estimation and compensation scheme is proposed and experimentally demonstrated in a short-reach direct detection orthogonal frequency division multiplexing (DD-OFDM) transmission system. After extracting subcarriers of OFDM symbols from multiple OFDM frames, the phase shift is obtained by the fourth-power algorithm, and the obtained results are averaged to perform phase estimation. It can achieve high-precision SFO estimation while ensuring low computational complexity as well as high spectral efficiency. The experimental results show that the SFO estimation accuracy using the proposed scheme can be significantly reduced to as low as ±3 ppm when SFO ranges from -1000 ppm to +1000 ppm after 20-km standard single-mode fiber (SSMF) transmission. Moreover, for the QPSK/16QAM encoded DD-OFDM systems aided by the proposed scheme, up to ±200 ppm SFO can be compensated with slight error vector magnitude (EVM) penalties after 20-km SSMF transmission. Furthermore, the results demonstrate that despite the existence of severe SFO, our proposed SFO compensation scheme can offer nearly negligible power penalties in the DD-OFDM system with optical back-to-back (OBTB) and 20-km SSMF transmission as compared to the ideal case without SFO.

Nonlinear Equalization Based on Artificial Neural Network in DML-Based OFDM Transmission Systems

This article reports the application of an equalizer based on an artificial neural network (ANN), in the form of nonlinear waveform regression, to mitigate nonlinear impairments in directly modulated laser (DML)-based orthogonal frequency-division multiplexing (OFDM) optical transmission. Experiments involving transmission over 0-200 km demonstrate that using an ANN with one hidden layer can greatly reduce nonlinear distortion. The proposed scheme outperformed a Volterra nonlinear equalizer at transmission distances exceeding 25 km. Using a 10G-class DML, the proposed scheme achieved the following data rates: 39.2 Gbps at 100 km (an improvement of 59%) and 33.5 Gbps at 150 km (an improvement of 57%). We also modified the cost function of the ANN during the training procedure to overcome the poor signal-to-noise ratio of the original ANN at low frequencies. This resulted in >30-Gbps transmission over 0-200 km.

Direct Data Detection of OFDM Signals Over Wireless Channels

This paper presents a novel efficient receiver design for wireless communication systems that incorporate orthogonal frequency division multiplexing (OFDM) transmission. The proposed receiver does not require channel estimation or equalization to perform coherent data detection. Instead, channel estimation, equalization, and data detection are combined into a single operation, and hence, the detector performs a direct data detector (D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ). The D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> is applied to key practical wireless systems such as the Long Term Evolution (LTE) and the New Radio (NR) of the fifthgeneration (5G) system. The performance of the proposed D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> is thoroughly analyzed theoretically in terms of bit error rate (BER), where closed-form accurate approximations are derived for several cases of interest, and validated by Monte Carlo simulations. Moreover, extensive complexity analysis are performed to evaluate the system suitability for implementation. The obtained theoretical and simulation results demonstrate that the BER of the proposed D3 is only 3 dB away from coherent detectors with perfect knowledge of the channel state information (CSI) in flat and frequency-selective fading channels for a wide range of signal-to-noise ratios (SNRs). If CSI is not known perfectly, then D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> outperforms the coherent detector substantially, particularly at high SNRs with linear interpolation. The computational complexity of D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> depends on the length of the sequence to be detected, nevertheless, a significant complexity reduction can be achieved using the Viterbi algorithm.

QAM–OFDM transmission in underwater wireless optical communication system with limited resolution DAC

Underwater wireless optical communication (UWOC) can realize high speed, low delay and flexible information transmission. We experimentally demonstrate a 3-m UWOC system using blue laser diode and avalanche photodiode with quadrature amplitude modulation (QAM) and orthogonal frequency division multiplexing (OFDM) transmission. We achieve net bit rates of 6.23 Gb/s at a bit error rate (BER) of 1.55 × 10−3, by using 128-QAM OFDM signals. High-order QAM signals require higher bit resolution of digital-to-analog converter (DAC). Therefore, the effect of quantization noise on transmission performance is further investigated. In order to meet the requirement that the BER is lower than 3.8 × 10−3, the bit resolution of DAC is required to be at least 5, 6 and 7 bit for 32-QAM, 64-QAM and 128-QAM signals, respectively.

A Novel Transceiver Model for Polar Transform Optical (PTO --) OFDM for V isible L ight C ommunication (VLC) Based on Peak to Average Power Ratio Reduction u sing Precoding

Indoor visible light communication (VLC) has the potential of providing high data rates for short-range wireless communication with a relative spatial elevated security in contrast to a radiofrequency wireless one. To support that high data stream, Orthogonal Frequency Division Multiplexing (OFDM) is used; however, due to the limited operational bandwidth of the commercial white light-emitting diode (LED), signal processing techniques are used to increase the efficiency of the OFDM and to adapt OFDM to VLC systems. As a major concern, the intensity modulation direct detection necessary for VLC requires positive real signal, this is dealt with by imposing Hermitian pre-possessing or Cartesian to polar conversion post-processing to the OFDM. The use of the Cartesian to polar converter allows the transmission of complex OFDM symbols through the intensity modulation channel. A polar transform optical (PTO-) OFDM presented here as an improvement and simplification of previous polar optical OFDM schemes gives an efficient transceiver architecture. Nevertheless, both OFDM transmission techniques for Visible optical links, similar to radiofrequency (RF), suffer greatly from irregular excessive Peak-to-Average power ratio (PAPR). Higher PAPR reduces the power efficiency of the On-Off Keying (OOK) based on pulse amplitude modulation (PAM). Furthermore, it also is recommendable to reduce the PAPR for conformity with eye safety. A precoding technique is proposed to reduce the PAPR of intensity-modulated for direct detectability of the OFDM signal destined for the wireless optical link using Cartesian-to-Polar conversion. Based on the enhanced processing at the front ends and using MATLAB simulation, it is proven that the presented model can improve the link parameters including the bit error rate (BER) and signal to noise ratio (SNR) and bandwidth efficient compared to Hermitian modified ones.

Peak Average Power Reduction in NOMA by using PTSCT Technique

Background: High peak power is one of the several disadvantages which need to be addressed for its effective regularization. It hampers the performance of the system due to the utilization of the orthogonal frequency division multiplexing transmission scheme at the sender of the Non-orthogonal multiple access system. Objective: In this work, a new Partial transmission sequence circular transformation reduction technique is designed for Non-orthogonal multiple access schemes. Methods: Partial transmission sequence is considered to be one of the most efficient techniques to reduce the Peak to average power ratio but it leads to high computational complexity. Additionally, a circular transformation is implemented. In the proposed technique, circular transformation and alternate optimization are used. Results: Simulation results reveal that the Peak to average power ratio performance of the proposed technique is better as compared to the conventional partial transmission sequence. Conclusion: It is observed that the proposed technique achieved 80% Peak to average power ratio reduction and 90 % bit error rate performance as compared to the conventional Partial transmission sequence.