Orthogonal Frequency Division Multiplexing Data Research Articles

Shallow Water Experiment of OFDM Underwater Acoustic Communications

The large variability of communication properties of underwater acoustic channels, and especially the strongly varying instantaneous conditions in shallow waters, is a challenge for the designers of underwater acoustic communication (UAC) systems. The use of phase modulated signals does not allow reliable data transmission through such a tough communication channel. However, orthogonal frequency-division multiplexing (OFDM), being a multi-carrier amplitude and phase modulation technique applied successfully in the latest standards of wireless communications, gives the chance of reliable communication with an acceptable error rate. This paper describes communication tests conducted with the use of a laboratory model of an OFDM data transmission system in a shallow water environment in Wdzydze Lake.

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.

Wideband and Channel Switchable Mode Division Multiplexing (MDM) Optical Power Divider Supporting 7.682 Tbit/s for On-Chip Optical Interconnects.

Silicon photonics (SiPh) are considered a promising technology for increasing interconnect speed and capacity while decreasing power consumption. Mode division multiplexing (MDM) enables signals to be transmitted in different orthogonal modes in a single waveguide core. Wideband MDM components simultaneously supporting wavelength division multiplexing (WDM) and orthogonal frequency-division multiplexing (OFDM) can significantly increase the transmission capacity for optical interconnects. In this work, we propose, fabricate and demonstrate a wideband and channel switchable MDM optical power divider on an SOI platform, supporting single, dual and triple modes. The switchable MDM power divider consists of two parts. The first part is a cascaded Mach-Zehnder interferometer (MZI) for switching the data from their original TE0, TE1 and TE2 modes to different modes among themselves. After the target modes are identified, mode up-conversion and Y-branch are utilized in the second part for the MDM power division. Here, 48 WDM wavelength channels carrying OFDM data are successfully switched and power divided. An aggregated capacity of 7.682 Tbit/s is achieved, satisfying the pre-forward error correction (pre-FEC) threshold (bit-error-rate, BER = 3.8 × 10-3). Although up to three MDM modes are presented in the proof-of-concept demonstration here, the proposed scheme can be scaled to higher order modes operation.

Use of Chaotic Oscillations for Precoding and Synchronization in OFDM

This paper proposes a novel linear precoding method for Orthogonal Frequency Division Multiplexing (OFDM) based on the employment of the chaotic waveforms generated by the fourth-order chaotic oscillator and orthonormalized by the Gram-Schmidt process. The proposed linear precoding method is aimed to increase resilience to the multipath propagation issues and reduce the Peak-to-Average Power Ratio (PAPR) of the transmitted signal. Moreover, the chaotic waveform enables novel timing synchronization methods to be implemented in the receiver. The modelling of baseband Linear Precoded OFDM (LP-OFDM) data transmission system with Rayleigh channel has been performed in Simulink environment to validate the proposed method and to compare the performance to the classic precoding methods, such as Walsh-Hadamard Transform (WHT). Experiments have shown that in a high Signal-to-Noise Ratio (SNR) scenario, the employment of the novel precoding scheme allows reducing Bit Error Ratio (BER) by several dB compared to non-precoded OFDM. The proposed precoding method leads to the reduction of PAPR; however, it is not as efficient as classical precoding schemes, such as WHT. Experimental evidence of synchronization of the chaotic oscillators within 50 samples long time interval is presented.

Performance Estimation and Selection Guideline of SiPM Chip within SiPM-Based OFDM-OWC System

The orthogonal frequency division multiplexing (OFDM), which has high spectral efficiency, is an attractive solution for silicon photomultiplier (SiPM)-based optical wireless communication (OWC) systems to boost data rates. However, the currently available SiPMs are not optimized for implementing the OFDM receiver. Incorporating different types of SiPM at the OFDM receiver results in different data rates at the same condition. Therefore, the receiver designer requires a method for predicting the performance of SiPMs and then selects the best one to build the optimum receiver. In this paper, we first investigate the origin of SiPM’s power-dependent frequency response. The investigation outcome is then used to create a method for predicting the subcarrier SNR. Combining the estimated subcarrier SNR with the bit-loading scheme, we finally propose a general approach for estimating the fundamental OFDM data rate an SiPM chip can support at a given received power. Results are then presented that can be used by the future receiver designer as a guideline to find the best type of SiPM to build the optimum OFDM receiver.

Preamble-Based Symbol Timing Algorithms in OFDM Systems

In orthogonal frequency division multiplexing (OFDM) systems, a preamble is added at the start of the OFDM data frame in order to find the correct frame starting point. In the receiver, the symbol starting point is estimated by a correlation-based timing metric that uses the periodic properties of the preamble. In this study, a novel preamble structure using the constant amplitude zero autocorrelation (CAZAC) sequence is proposed. The performance of the timing synchronization algorithms has been compared with the proposed method in terms of mean squared error (MSE). The simulations are performed under additive white Gaussian noise (AWGN) and Rayleigh multipath fading channels. The simulation results indicate that our proposed method provides better timing MSE performance for the low signal-to-noise ratio (SNR) values.

100-Km Long-Reach Carrierless 5G MMWoF Link With Destructive-Interference-Beating or Single-Sideband-Filtering OFDM

Based on the use of a dual-wavelength controlled quasi-color-free laser diode (QCFLD) transmitter with either destructively interfered beating or single-sideband filtering after receiving at a remote node, the 100-km long-reach (LR) carrierless millimeter-wave over fiber (MMWoF) link with directly-encoded orthogonal frequency-division multiplexing (OFDM) at 10-15 Gbit/s in optical wired and MMW wireless domains is experimentally demonstrated. The optically heterodyned MMW OFDM data by the destructively interfered beating obtains more gain from the RF amplifier than that without carrierless operation, as the MMW carrier with reduced power no longer dominates the gain competition. The destructively-interfered-beating 16-QAM OFDM data can transmit over 100-km SMF and 10-m free-space. The modulation bandwidth can be enhanced from 2 GHz to 2.5 GHz with a raw data rate of 10 Gbit/s after the OFDM subcarrier sidelobe filtering process. The sidelobe filtering suppresses the impact of the QCFLD chirp on the signal-to-noise of the optically heterodyned beating MMW carrierless OFDM data when reducing the sidelobes of each OFDM subcarrier. Besides, the single-sideband-filtered OFDM data can also obtain a higher gain than the double-sideband one due to the relief of RF amplifier saturation. Even though the noise located at the conjugated data band involves in the frequency-down-converted data after MMW down-mixing, the single-sideband-filtered OFDM data still allows the transmission of 8-QAM single-sideband OFDM data with 2 GHz over 100-km in SMF and 10-m in free-space at a raw data rate of 6 Gbit/s in one single-sideband and 12 Gbit/s at both sidebands. In comparison, the destructively-interfered-beating scheme offers large bandwidth and high spectral usage efficiency of 4 bit/s/Hz, whereas the single-sideband-filtering scheme effectively broadens the available bandwidth by saving another spectral sideband for allocating other carriers and data, which facilitate advantages including doubled band usage and half modulation power consumption. Both schemes offer comparable performance for future long-reach carrierless MMWoF applications.

Bidirectional OFDM Based MMW/THzW Over Fiber System for Next Generation Communication

The modern world and modern technology want 5G communication to satiate their urgent need of multi-gigabits data transmission in small cells. For this aspiration, a bidirectional orthogonal frequency division multiplexing (OFDM) based millimeter wave over and terahertz wave over fiber system is proposed and demonstrated for 5G access fronthaul. A comparative study between millimeter-wave (MMW) and terahertz wave (THzW) regarding 5G communication is also analyzed. With the assistance of L and C band quantum dash laser diode, MMW and THzW are generated. For downstream (DS), 10 Gbps/12.5Gbps (for MMW/THzW) OFDM data in L band is transmitted over 50-km/25-km single mode fiber (SMF) and 100-m free space optics (FSO) distance, on the other side for upstream (US) transmission, 6.5 Gbps/10 Gbps OFDM data in C band is communicated over 50-km/25-km SMF plus 100-m FSO link. The selection of L and C band for DS and US transmission provide the advantages to reduce the Rayleigh back scattering effect in our bidirectional system not only that it also helps to mitigate the intensity-noise as compared to the conventional amplified spontaneous emission source. This research work gives an overview for the reliability of MMW and THzW system regarding 5G communication. The capability of our system becomes build up by obtaining low bit error rate (under FEC limit), proper error vector magnitude (<10.2%), and clear constellation diagram.

Quad-Mode VCSEL Optical Carrier for Long-Reach Ka-Band Millimeter-Wave Over Fiber Link

A quad-mode optical carrier generated by mode-deviated injection-locking a vertical-cavity surface-emitting laser (VCSEL) at a beating frequency of 40 GHz is demonstrated for establishing a long-reach millimeter-wave over fiber (MMWoF) link, in which only one mode of the quad-mode optical carriers is modulated by the 16-quadrature amplitude modulation (16-QAM) orthogonal frequency division multiplexing (OFDM) data stream to achieve an optical single-carrier modulation (OSCM). Such an OSCM operation reduces the long-reach single-mode-fiber (SMF) transmission induced RF power fading effect to significantly suppress the frequency notch in the modulated spectrum of the delivered QAM-OFDM data after remotely heterodyne detection. With destructively interfered beating the quad-mode optical carrier at the remote node, the peak power of the optically heterodyned MMW central carrier can be attenuated by 38.3 dB, which saves the gain of the photodetector and electrical amplifier to efficiently boost the carried QAM-OFDM data. This architecture ensures sufficient power of the 16-QAM OFDM data after optoelectrical conversion and facilitates the quad-mode optical carrier based MMWoF link to achieve 50-km wired SMF and 10-m wireless MMW transmissions with the error vector magnitude of 17.2%, signal-to-noise ratio of 15.28 dB, and bit error rate of 3.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at a data rate of 12 Gbps.

Resistor Inductor Capacitor Impedance Optimization of Violet Laser Diodes for Free-Space Quadrature Amplitude Modulation Orthogonal Frequency Division Multiplexing Data Link

To optimize the high-speed modulation package of the TO-can mounted violet laser diode (VLD) for optical wireless communication, three different impedance matching methods with adding or removing resistor/inductor/capacitor (R/L/C) elements are employed to discuss their effects on the direct encoding bandwidth of the VLD. With reducing the parasitic inductance by shortening the cathode/anode pin length of the TO-can VLD, the 2.5-mm-long pin acts as a series inductance to 1.74 nH to enormously improve the modulation bandwidth of the VLD for encoding the 16 quadrature amplitude modulation orthogonal frequency division multiplexing data as high as 20.4 GB/s. Neither the surface mounted device (SMD) resistor nor the SMD inductor in series connection can further improve the modulation bandwidth of the VLD. In contrast, a parallel connection of the VLD with Teflon ring capacitor can somewhat broaden its encodable bandwidth at low biased conditions, whereas the allowable bandwidth still degrades when increasing the VLD bias to enlarge its modulation throughput. Numerical simulations also verify that the shortening pin length (with reducing the inductance) of TO-can VLD is the best selection for bandwidth enlargement. With optimized impedance matching design, the comparison on data transmission characteristics for several 2.5-mm-pin VLDs with different rated powers is presented.

Bidirectional hybrid OFDM based free-space/wireless-over-fiber transport system

We propose and demonstrate a successful application of orthogonal frequency division multiplexing (OFDM), reflective semiconductor optical amplifier and polarization multiplexing techniques to facilitate bidirectional hybrid OFDM based integrated free-space optics and wireless transport system. The downlink 12 Gbps OFDM data-stream and 79 community antenna television (CATV) channels are transmitted over 50 km single mode fiber (SMF) as well as 12 m and 10 m free-space link, respectively. The uplink 10 Gbps/5 GHz and 5 Gbps/3.5 GHz OFDM data streams are communicated over separate 50 km SMF along with 8 m wireless links. We have used 32-quadrature amplitude modulation (QAM) and 16-QAM modulation formats for downlink and uplink, correspondingly. The performance of the system is observed by evaluating carrier-to-noise ratio (CNR), composite second-order (CSO) and composite-triple-beat (CTB) for the CATV signal, and constellations diagrams, bit error rate (BER), signal-to-noise ratio (SNR), and error vector magnitude (EVM) values for the OFDM signals. After transmission over 50 km SMF as well as 10 m free-space, the resulting CNR, CSO and CTB values are > 51 dB, 23.3 dB, respectively. 4 dBm and 3.2 dBm power penalties at BER of $$10^{ - 8}$$, below 13% EVM and > 21.3 dB/ > 22.2 dB SNR values are observed for the uplink 10 Gbps/5 GHz and the 5 Gbps/3.5 GHz OFDM data signals, respectively, over 50 km SMF as well as 8 m wireless is observed.

Reliable OFDM Data Transmission with Pilot Tones and Error-Correction Coding in Shallow Underwater Acoustic Channel

The performance of Underwater Acoustic Communication (UAC) systems are strongly related to the specific propagation conditions of the underwater channel. Horizontal, shallow-water channels are characterised by extremely disadvantageous transmission properties, due to strong multipath propagation and refraction phenomena. The paper presents the results of communication tests performed during a shallow, inland-water experiment with the use of a laboratory model of a UAC system implementing the Orthogonal Frequency-Division Multiplexing (OFDM) technique. The physical layer of data transmission is partially configurable, enabling adaptation of the modulation and channel coding parameters to the specific propagation conditions. The communication tests were preceded by measurement of the UAC channel transmission properties. Based on the estimated transmission parameters, four configurations of OFDM modulation parameters were selected, and for each of them, communication tests were performed with the use of two Error-Correction Coding (ECC) techniques. In each case, the minimum coding rate was determined for which reliable data transmission with a Bit Error Rate (BER) of less than 10 − 4 is possible.

Adaptive Neuro-Fuzzy Inference System-based Nonlinear Equalizer for CO-OFDM Systems

Abstract The principle of orthogonal frequency-division multiplexing (OFDM) is to transmit the data through a large number of multiple orthogonal subcarriers. The coherent optical OFDM (CO-OFDM) is OFDM data that are being modulated to light frequency and being detected in coherent manner. CO-OFDM brings to optical communications the combination of two powerful techniques, coherent optical detection and OFDM. One of the primary challenges in the CO-OFDM system is to remove optical fiber nonlinear effects. This makes nonlinearity compensation a critical task of the CO-OFDM system. So a nonlinear equalizer (NLE) based on adaptive neuro-fuzzy inference system (ANFIS) is presented for CO-OFDM systems to mitigate nonlinearities on long-haul optical communications with high bit rate and bit error rate (BER)of the system. Various performance metrics were analyzed for the proposed ANFIS–NLE, and it is compared with existing techniques such as support vector machine and artificial neural network. From the experimental results, our proposed approach gives better performance in terms of BER and Q-factor on comparing with existing methods.

Cost-efficient half-duplex 10 Gbit/s all-optical indoor optical wireless communication enabled by a low-cost Fabry-Perot laser/photodetector.

To develop an indoor optical wireless communication (OWC) system, both the system complexity/cost and data rate need to be taken into consideration. In this Letter, a cost-efficient half-duplex OWC system for photonic home area network applications is proposed and experimentally demonstrated. A low-cost Fabry-Perot laser diode is proposed to be employed as both the downlink receiver (Rx) and uplink transmitter at the user side. Enabled by the Fabry-Perot transceiver, the indoor transmission of 10Gbit/s four-level pulse-amplitude-modulation signal for both downlinks and uplinks is experimentally achieved over a 1.7km single-mode fiber and 1.1m free space. Moreover, the proposed scheme also enables us to operate an orthogonal frequency division multiplexing (OFDM) signal. The bit error rate levels of multi-gigabit OFDM data for both downlinks and uplinks over a 10h measurements are all under a 7% forward error correction limit of 3.8×10-3, which indicates that the proposed system is robust and, thus, can provide a promising solution for high-speed low-cost home area OWC networks.

Novel Low-Complexity Low-Latency Orthogonal Frequency Division Multiplexing Transmitter

Traditional orthogonal frequency division multiplexing (OFDM) transmitter is implemented by exploiting inverse fast Fourier transform (IFFT), up-sampling, and low pass shaping filter (LPSF) modules, which occupy a large number of hardware resources and severely lower down the operation speed. To address these limitations, we propose a novel OFDM transmitter architecture, by which the aforementioned modules can be discarded and replaced with some simple switches. In the proposed architecture, direct digital synthesis (DDS) method is employed to generate digital sub-carriers and to transform OFDM data from frequency domain to time domain. Through some sophisticated simplifications, the proposed architecture can avoid using multipliers and remarkably save hardware resources. Finally, comparative experiments are carried out on field programmable gate array (FPGA) platform which demonstrates that our DDS-based architecture saves more than half of the hardware resources and doubles the achievable maximum frequency compared with traditional structure.

Secure Key Distribution Strategy in OFDM-PON by Utilizing the Redundancy of Training Symbol and Digital Chaos Technique

A secure key distribution scheme for orthogonal frequency division multiplexing (OFDM) passive optical network system is proposed and experimentally demonstrated. The training symbol (TS), which is used for time synchronization and channel estimation, is formed by adopting a noise-like chaotic sequence. The redundancy of the TS is utilized to embed secure keys. An experiment is performed, in which 7.64 Gb/s 16-quadrature-amplitude-modulation OFDM data and 28.4 Mb/s keys embedded in are successfully transmitted over 25 km standard single mode fiber. The results indicate a promising key distribution method for physical layer secure optical communication.

Coflow routing and spectrum assignment in optical orthogonal frequency division multiplexing data center networks

The communication between data-intensive applications in data centers often involves a collection of parallel flows, usually referred to as a coflow. A coflow between two groups of machines can capture diverse communication patterns observed in data centers. The static coflow routing and spectrum assignment (CofRSA) problem in optical orthogonal frequency division multiplexed data center networks is investigated, when the coflow traffic demands are given. The static CofRSA problem considers the spectrum constraints of the flows between different coflows and those within the same coflow. We formulate the static CofRSA problem as an integer linear programming (ILP) model. The objective of the ILP model is to minimize the used spectrum slots. However, the ILP model cannot achieve an optimal solution within tolerable time for large networks. To solve the problem, two highly efficient heuristic algorithms, the most cofSize first (MCSF) ordering algorithm and the greedy inserting (GI) algorithm, are proposed to achieve suboptimal solutions. The simulation results indicate that ILP provides an optimal solution for small networks, whereas GI and MCSF yield suboptimal solutions in large networks. The results also show that GI provides more efficient solutions than MCSF.

Chaotic reconfigurable ZCMT precoder for OFDM data encryption and PAPR reduction

A secure orthogonal frequency division multiplexing (OFDM) transmission scheme precoded by chaotic Zadoff–Chu matrix transform (ZCMT) is proposed and demonstrated. It is proved that the reconfigurable ZCMT matrices after row/column permutations can be applied as an alternative precoder for peak-to-average power ratio (PAPR) reduction. The permutations and the reconfigurable parameters in ZCMT matrix are generated by a hyper digital chaos, in which a huge key space of ∼10800 is created for physical-layer OFDM data encryption. An encrypted data transmission of 8.9 Gb/s optical OFDM signals is successfully demonstrated over 20 km standard single-mode fiber (SSMF) for 16-QAM. The BER performance of the encrypted signals is improved by ∼2 dB (BER@10−3), which is mainly attributed to the effective reduction of PAPR via chaotic ZCMT precoding. Moreover, the chaotic ZCMT precoding scheme requires no sideband information, thus the spectrum efficiency is enhanced during transmission.

Performance-Improved Secure OFDM Transmission Using Chaotic Active Constellation Extension

We propose and demonstrate a physical-layer security scheme using chaotic active constellation extension (ACE) in orthogonal frequency division multiplexing (OFDM). A super OFDM frame is generated by chaotic frame interleaving in ACE, where hyper digital chaos is applied to generate the chaotic interleaving vectors. A huge key space of size 2048! is provided via the multi-fold encryption to guarantee the secure OFDM data transmission, while the transmission performance is effectively improved via the chaotic ACE algorithm. Secure transmission of 8.9-Gb/s 16-QAM encrypted OFDM signals is demonstrated over a 20-km standard single-mode fiber, which shows reliable robustness against any exhaustive attacks. Moreover, the proposed chaotic ACE scheme improves the spectral efficiency of OFDM transmission, since it does not require any sideband to transmit the frame-interleaving information.

Snapping shrimp noise mitigation based on statistical detection in underwater acoustic orthogonal frequency division multiplexing systems

We propose a mitigation scheme for snapping shrimp noise when it corrupts an orthogonal frequency division multiplexing (OFDM) signal in underwater acoustic communication systems. The OFDM signal distorted by the snapping shrimp noise is filtered by a band-stop filter. The snapping shrimp noises in the filtered signal are detected by a detector with a constant false alarm rate whose threshold is derived theoretically from the statistics of the background noise. The detected signals are reconstructed by a simple reconstruction method. The proposed scheme has a higher detection capability and a lower mean square error of the channel estimation for simulated data and a lower bit error rate for practical ocean OFDM data collected in northern East China Sea than the conventional noise-mitigating methods.