High-speed OFDM Research Articles

High-speed Optical OFDM transmission by reducing the nonlinearity of LEDs in Visible light Communication Systems

High-speed Optical OFDM transmission by reducing the nonlinearity of LEDs in Visible light Communication Systems

Performance Investigation of High-Speed Train OFDM Systems under the Geometry-Based Channel Model

Performance Investigation of High-Speed Train OFDM Systems under the Geometry-Based Channel Model

Evolution and Impact of Wi-Fi Technology and Applications: A Historical Perspective

The IEEE 802.11 standard for wireless local area networking (WLAN), commercially known as Wi-Fi, has become a necessity in our day-to-day life. Over a billion Wi-Fi access points connect close to hundred billion of IoT devices, smart phones, tablets, laptops, desktops, smart TVs, video cameras, monitors, printers, and other consumer devices to the Internet to enable millions of applications to reach everyone, everywhere. The evolution of Wi-Fi technology also resulted in the first commercial piloting of spread spectrum, high speed optical communications, OFDM, MIMO and mmWave pulse transmission technologies, which then became more broadly adopted by cellular phone and wireless sensor networking industries. The popularity and widespread Wi-Fi deployment in indoor areas further motivated innovation in opportunistic cyberspace applications that exploit the ubiquitous Wi-Fi signals. The RF signal radiated from Wi-Fi access points creates an “RF cloud” accessible to any Wi-Fi equipped device hosting or supporting these opportunistic applications. Wi-Fi positioning and location intelligence were the first popular opportunistic applications of Wi-Fi’s RF cloud. Today, researchers are investigating opportunistic applications of Wi-Fi signals for gesture and motion detection as well as authentication and security. This paper provides a holistic overview of the evolution of Wi-Fi technology and its applications as the authors experienced it in the last few decades.

Online digital offset mismatch compensation for high-speed time-interleaved ADC in real-time optical OFDM receiver.

The time-interleaved analog-to-digital converter (TI-ADC) is a good option to realize high-speed data conversion for both single-carrier and multi-carrier optical communication systems. Offset mismatch is one of its drawbacks, which causes distortion in the sampled data and degrades the bit error rate (BER) performance of communication systems. In this article, a low-complexity online digital offset mismatch compensation (OMC) scheme based on time-domain averaging is proposed and implemented with a commercial off-the-shelf field programmable gate array (FPGA) chip for high-speed optical OFDM communications. The proposed OMC scheme is experimentally demonstrated in real-time direct-detection optical OFDM receiver with a 5 GS/s TI-ADC. The experimental results show that the BER performance can be improved by more than an order of magnitude, by using the proposed OMC scheme, for both 16- and 64-QAM modulation formats. The receiver sensitivity can be improved by more than 5-dB in terms of the received optical power at the BER of 1e-3. What's more, the real-time measured BER performance is similar to that of by using offline DSP approaches and has good stability during the measurement period. Numerical simulations are performed under additive white Gaussian noise (AWGN) channel to fully verify the performance of the OMC scheme. It exhibits that the error floor in BER performance can be eliminated by using the OMC scheme and a negligible signal-to-noise ratio (SNR) penalty can be achieved compared with that of offset mismatch-free case.

A Novel Structure of High Speed OFDM Receiver to Overcome ISI and ICI in Rayleigh Fading Channel

High-Speed Orthogonal-Frequency-Division-Multiplexing (HS-OFDM) is an OFDM system with high OFDM symbol rate. In HS-OFDM system, the symbol period is comparable with the multipath delay-spread of the channel. No cyclic-prefix is used with HS-OFDM to increase the bandwidth efficiency. HS-OFDM suffers from Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) signals. In this paper, a complete mathematical model of the received HS-OFDM signal with both ISI and ICI interfering signals are represented. A novel receiver that tracks the time-varying channel gain and reduces the effects of the interfering signals, is proposed based on the deduced mathematical model. The new receiver depends on a new arrangement of decision-feedback equalizer, which is designed in frequency domain. The paper illustrates how the taps of the equalizer are calculated, and it calculates the remaining amount of interference after the use of the proposed receiver. The used model of the wireless channel in HS-OFDM system is the frequency-selective channel. It models the outdoor channel in HS-OFDM system.

Comparison of single-/few-/multi-mode 850 nm VCSELs for optical OFDM transmission.

For high-speed optical OFDM transmission applications, a comprehensive comparison of the homemade multi-/few-/single-transverse mode (MM/FM/SM) vertical cavity surface emitting laser (VCSEL) chips is performed. With microwave probe, the direct encoding of pre-leveled 16-QAM OFDM data and transmission over 100-m-long OM4 multi-mode-fiber (MMF) are demonstrated for intra-datacenter applications. The MM VCSEL chip with the largest emission aperture of 11 μm reveals the highest differential quantum efficiency which provides the highest optical power of 8.67 mW but exhibits the lowest encodable bandwidth of 21 GHz. In contrast, the SM VCSEL chip fabricated with the smallest emission aperture of only 3 μm provides the highest 3-dB encoding bandwidth up to 23 GHz at a cost of slight heat accumulation. After optimization, with the trade-off set between the receiving signal-to-noise ratio (SNR) and bandwidth, the FM VCSEL chip guarantees the highest optical OFDM transmission bit rate of 96 Gbit/s under back-to-back case with its strongest throughput. Among three VCSEL chips, the SM VCSEL chip with nearly modal-dispersion free feature is treated as the best candidate for carrying the pre-leveled 16-QAM OFDM data over 100-m OM4-MMF with same material structure but exhibits different oxide-layer confined gain cross-sections with one another at 80-Gbit/s with the smallest receiving power penalty of 1.77 dB.

Delay division multiplexing orthogonal frequency-division multiple access passive optical networks using low-sampling-rate analog-to-digital converter

In traditional orthogonal frequency-division multiple access passive optical networks (OFDMA PON) or time-division multiplexing access (TDMA) based OFDM PONs, analog-to-digital converters (ADCs) with a high sampling rate are required to demodulate high-speed aggregated OFDM data in order to receive a small portion of the downstream data at optical network users (ONUs). Meanwhile, OFDM signal has a higher peak-to-average power ratio (PAPR) than the single carrier signal, which can result in the nonlinear effect. The resulting nonlinearity reduces the received signal performance. To enhance practicability of the present PONs, according to the sub-Nyquist sampling theory, we propose and detail a delay-division-multiplexing (DDM) scheme to enable a FDMA PON with low-sampling-rate ADCs. Based on pre-allocated relative time delays among the ONUs and discrete Fourier transform spread (DFT-S) technique, pre-processed signals sent from an optical line terminal (OLT) can be detected as different downstream signals following spectral aliasing caused by ADCs operating at a sub-Nyquist sampling rate. In the proposed scheme, as the signal distortion introduced by the propagation, aliasing and time shifted sampling is pre-compensated, the DFT and inverse discrete Fourier transform (IDFT) are unnecessary for de-mapping and picking out the signal at ONUs. Therefore, the proposed DDM scheme greatly enhances cost efficiency and enables a reduction in computational complexity. Meanwhile, DFT-S FDMA signal has low PAPR, which relieves the nonlinear effect in signal E/O conversion and transmission. As a result, the proposed scheme benefits the power budget of the OLT and power consumption of the ONUs. In experiment, we demonstrate that each ONU with an ADC operating at 1/2-1/32 of the Nyquist sampling rate is able to receive 1/2-1/32 of the downstream data, with an insignificant performance penalty. Furthermore, the details of the matrices that include channel response, aliasing and time delay are first analyzed. In addition, training symbol is very important for estimating the channel response, and how to derive and design training symbols is the first study to outline the details of this issue. The effects of fiber dispersion and the sampling instant of an ADC on signal performance are also studied. The results show that the signal performance has some degree of tolerance to sampling instant deviation and the power penalty is less than 0.5 dB to achieve a forward error correction limit of 10-3 after 25 km fiber transmission. The theoretical analysis and experimental results indicate that the proposed scheme can simplify the ONU and reduce the cost of the PON.

Implementation of High Speed OFDM Transceiver using FPGA

Implementation of High Speed OFDM Transceiver using FPGA

基于DCO OFDM的帧内信号时域调整技术研究

In conventional OFDM system,an OFDM symbol will exceeds its guard interval(GI)and seriously interfere with its neighboring symbols when channel characteristic is unsatisfactory.This will cause inter-symbol interference(ISI)and inter-carrier interference(ICI).In high-speed incoherent optical OFDM communication system,a novel time domain reshuffling method for mitigating ISI and ICI based on DCO-OFDM was proposed.This scheme utilized the properties of Fourier Transform.By simple preprocessing subcarrier channels in frequncy domain,sampling sequence of a DCO-OFDM symbol in time domain was exchanged interactively.Thus signal energy was centralized in the central part of a symbol.Numerical simulation indicates that ISI and ICI is significantly reduced and system BER performance is improved effectively due to signal surpassing the GI.In optical OFDM systems with insufficient GI for the popurse of higher information transmission efficiency,the reshuffling scheme also has a great value.

Nonlinearity mitigation for high-speed optical OFDM transmitters using digital pre-distortion

Optical orthogonal frequency-division multiplexing (OOFDM) signal is sensitive to nonlinear distortions induced by optical modulators. We propose and experimentally demonstrate a digital pre-distortion (DPD) algorithm to linearize the optical modulators including electro-absorption modulated lasers (EML) and Mach-Zehnder modulators (MZM) used in high-speed OOFDM transmitters. By using an adaptive DPD algorithm with a learning structure, the inverse transfer function of a modulator, which is based on a polynomial model, has been obtained. In the experiment, the performance improvements with and without considering the memory effects of the DPD model are illustrated. The two typical kinds of high-speed OOFDM signals with a bit rate up to 30-Gb/s have been implemented experimentally. The results show that the nonlinear distortion induced by optical modulators can be compensated by using the DPD algorithm to substantially improve the optical modulation index.

Study of the all-optical high-speed OFDM transmission system based on MAMSK modulation

In this paper, an all-optical orthogonal frequency division multiplexing (OOFDM) system based on the multi-amplitude minimum shift keying (MAMSK) modulation is proposed. A scheme to realize MAMSK is designed, and the influence of modulation index on the performance of MAMSK is discussed. Numerical simulations and analysis are performed, and the comparison between the MAMSK-OOFDM and the MAMSK-WDM system is made. The lowest value of the BER of MAMSK-OOFDM is 3.98×10−6, while that of MAMSK-WDM is 7.94×10−4 when the input power is 0.8 mw and dispersion is completely compensated. The results show that, for its multi-level amplitude and excellent spectrum efficiency, MAMSK-OOFDM can greatly mitigate the effects caused by dispersive and nonlinear phenomena, and it can also effectively improve the capacity of the system.

Transmission of High-Speed (${>} 100$ Gb/s) Direct-Detection Optical OFDM Superchannel

In this paper, we propose and experimentally demonstrate the direct-detection optical orthogonal-frequency-division-multiplexing superchannel (DDO-OFDM-S) and optical multiband receiving method (OMBR) to support >; 100-Gb/s data rate and a longer distance for direct-detection systems. For the new OMBR, we discuss the optimum carrier-to-sideband power ratio (CSPR) both in the cases of back-to-back and after transmission, and derive the analytical form for CSPR which is verified with numerical results. An overhead-efficient training method for in-phase/quadrature-phase imbalance estimation is also introduced in order to obtain a better performance while maintaining the high throughput of the system. With experimental setups, we evaluate the two systems with 1) 16-QAM, 214-Gb/s (190 Gb/s without overhead) and 2) 4-QAM, 117-Gb/s (100 Gb/s without overhead) systems. The new proposals enable the record data rate per wavelength (214 Gb/s) and record distance of 720-km standard single-mode fiber (SSMF) for the >; 100-Gb/s DDO-OFDM systems, and achieve the record optical signal-to-noise ratio sensitivity of 21.2 dB and record distance of 1200-km SSMF ( ~1 dB penalty) for the 100-Gb/s class DDO-OFDM systems.

A simple and efficient frequency offset estimation algorithm for high-speed coherent optical OFDM systems

In this paper, we propose a simple frequency offset estimation (FOE) algorithm for high-speed coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems, which avoids the exhaustive search computations on the integer part of FOE by using a merit function. In time domain, the FOE algorithm can estimate all the frequency offset in the range of [-5GHz, +5GHz], for satisfying the practical application requirement, based on only one redesigned training symbol. In addition, we provide the theoretical analysis about the quantitative influences of the residual frequency offset (RFO) on CO-OFDM systems. In order to reduce the final estimation error, a new zero-overhead residual frequency offset estimation (RFOE) algorithm is also proposed in this paper. Finally, the feasibility and effectiveness of the proposed FOE and RFOE algorithms are demonstrated in a 464 Gbit/s polarization-division multiplexed (PDM) 16-ary quadrature amplitude modulation (QAM) CO-OFDM system by the simulation, and numerical results validate the proposed algorithms.

Joint Mismatch and Channel Compensation for High-Speed OFDM Receivers with Time-Interleaved ADCs

Analog-to-digital converters (ADCs) with high sampling rates and output resolution are required for the design of mostly digital transceivers in emerging multi-Gigabit communication systems. A promising approach is to use a time-interleaved (TI) architecture with slower sub-ADCs in parallel, but mismatch among the sub-ADCs, if left uncompensated, can cause error floors in receiver performance. Conventional mismatch compensation schemes typically have complexity (in terms of number of multiplications) that increases with the desired resolution at the output of the TI-ADC. In this paper, we investigate an alternative approach, in which mismatch and channel dispersion are compensated jointly, with the performance metric being overall link reliability rather than ADC performance. For an OFDM system, we characterize the structure of mismatch-induced interference, and demonstrate the efficacy of a frequency-domain interference suppression scheme whose complexity is independent of constellation size (which determines the desired resolution). Numerical results from computer simulation and from experiments on a hardware prototype show that the performance with the proposed joint mismatch and channel compensation technique is close to that without mismatch. While the proposed technique works with offline estimates of mismatch parameters, we provide an iterative, online method for joint estimation of mismatch and channel parameters which leverages the training overhead already available in communication signals.

Oversampling to reduce the effect of timing jitter on high speed OFDM systems

The impairments caused by timing jitter are a significant limiting factor in the performance of very high data rate OFDM systems. In this letter we show that oversampling can reduce the noise caused by timing jitter. Both fractional oversampling achieved by leaving some band-edge OFDM subcarriers unused and integral oversampling are considered. The theoretical results are compared with simulation results for the case of white timing jitter showing very close agreement. Oversampling results in a 3 dB reduction in jitter noise power for every doubling of the sampling rate.