Optical Orthogonal Frequency Division Multiplexing Transceiver Research Articles

Stage‐dependent minimum bit resolution maps of full‐parallel pipelined FFT/IFFT architectures incorporated in real‐time optical orthogonal frequency division multiplexing transceivers

Fast Fourier transform (FFT) and inverse FFT (IFFT) are the fundamental algorithms at the heart of optical orthogonal frequency division multiplexing (OOFDM) transceivers. The high digital signal processing (DSP) complexity has become one of the most significant obstacles to experimentally demonstrating real-time high-capacity OOFDM transceivers. In this study, extensive numerical explorations are undertaken, for the first time, of the impacts of each individual transceiver DSP element on the inverse error vector magnitude (IEVM) performance of the OOFDM transceivers incorporating full-parallel pipelined FFT/IFFT architectures. More importantly, FFT/IFFT stage-dependent minimum bit resolution maps are identified, based on which minimum bit resolutions of individual DSP elements of various FFT/IFFT stages can be easily selected according to chosen analogue-to-digital converter/digital-to-analogue converter resolutions. The validity and high accuracy of the identified maps are experimentally verified in field programmable gate array (FPGA)-based platforms. In addition to great ease of practical OOFDM transceiver designs, the maps also significantly reduce the FPGA logic resource usage without degrading the overall transceiver IEVM performance.

Real-time Digital Signal Processing for Optical OFDM-Based Future Optical Access Networks

In this paper, key aspects associated with realizing real-time digital signal processing (DSP)-based optical transceivers for use in future optical access networks are considered. The fundamental principles of optical orthogonal frequency division multiplexing (OOFDM)-based transceivers and their associated DSP implementation are presented. This is followed by an extensive review of the real-time DSP implemented in the end-to-end OOFDM transceivers experimentally demonstrated over the past several years.

OFDM for Next-Generation Optical Access Networks

In this tutorial overview, the principles, advantages, challenges, and practical requirements of optical orthogonal frequency division multiplexing (OFDM)-based optical access are presented, with an emphasis on orthogonal frequency division multiple access (OFDMA) for application in next-generation passive optical networks (PON). General OFDM principles, including orthogonality, cyclic prefix use, frequency-domain equalization, and multiuser OFDMA are summarized, followed by an overview of various optical OFDM(A) transceiver architectures for next-generation PON. Functional requirements are outlined for high-speed digital signal processors (DSP) and data converters in OFDMA-PON. A techno-economic outlook for such a “software-defined,” DSP-based optical access platform is also provided.

Optimizing FFT Precision in Optical OFDM Transceivers

The effects of different system parameters on the performance of real-time optical orthogonal frequency-division-multiplexing (OFDM) transceivers are investigated. Numerical simulations are carried out to search for the optimum arithmetic precision of the fast Fourier transform and its inverse (FFT/IFFT) which are key components in optical OFDM transceivers.

Experimental Demonstrations and Extensive Comparisons of End-to-End Real-Time Optical OFDM Transceivers With Adaptive Bit and/or Power Loading

Experimental demonstrations are reported for end-to-end real-time optical orthogonal frequency division multiplexing (OOFDM) transceivers incorporating three widely adopted adaptive loading techniques, namely, power loading (PL), bit loading (BL), and bit-and-power loading (BPL). In directly modulated distributed-feedback (DFB) laser-based, intensity-modulation, and direct-detection (IMDD) transmission systems consisting of up to 35-km single-mode fibers (SMFs), extensive experimental comparisons between these adaptive loading techniques are made in terms of maximum achievable signal bit rate, optical power budget, and digital signal processing (DSP) resource usage. It is shown that BPL is capable of supporting end-to-end real-time OOFDM transmission of 11.75 Gb/s over 25-km SMFs in the aforementioned systems at sampling speeds as low as 4 GS/s. In addition, experimental measurements also show that BPL (PL) offers the highest (lowest) signal bit rate, and their optical power budgets are similar. The observed signal bit rate difference between BPL and PL is almost independent of sampling speed and transmission distance. All the aforementioned key features agree very well with numerical simulations. On the other hand, BPL-consumed DSP resources are approximately three times higher than those required by PL. The results indicate that PL is a preferred choice for cost-effective OOFDM transceiver design.

Experimental Demonstration of Real-Time Optical OFDM Transmission at 11.25 Gb/s Over 500-m MMFs Employing Directly Modulated DFB Lasers

The fastest ever 11.25-Gb/s real-time end-to-end optical orthogonal frequency-division-multiplexing (OOFDM) transmission over 500-m multimode fibers (MMFs) with a high electrical spectral efficiency of 5.625 bit/s/Hz is experimentally demonstrated, for the first time, in a simple intensity modulation and direct detection (IMDD) system employing a directly modulated distributed-feedback (DFB) laser. An optical power budget as high as 12 dB is achieved with a minimum received optical power of -6.3 dBm for a total channel bit-error rate of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The field programmable gate array (FPGA)-based OOFDM transceivers also have functionalities including variable power loading, performance monitoring, and on-line parameter adjustment.

Statistical Performance Comparisons of Optical OFDM Adaptive Loading Algorithms in Multimode Fiber-Based Transmission Systems

Detailed statistical investigations of the effectiveness of three widely adopted optical orthogonal frequency division multiplexing (OOFDM) adaptive loading algorithms, including power loading (PL), bit loading, and bit-and-power loading (BPL), are undertaken, for the first time, over 1000 statistically constructed worst-case multimode fiber (MMF) links without incorporating inline optical amplification. It is shown that the BPL (PL) algorithm always offers the best (worst) transmission performance. The absolute transmission capacity differences between these algorithms are independent of signal bit rate and increase with both transmission distance and digital-to-analog converter/analog-to-digital converter (DAC/ADC) sampling rate. More importantly, numerical results also indicate that, for both worst-case and normal-case MMF links of less than 300 m, in comparison with the most sophisticated BPL algorithm, the simplest PL algorithm is sufficiently effective in escalating the OOFDM MMF system performance to its maximum potential. The effectiveness of the PL algorithm can be further improved when a large number of subcarriers are utilized. On the other hand, for relatively long MMF links (> 800 m) with their 3-dB bandwidths being much less than the transmitted OOFDM signal spectrum, the BPL algorithm has to be adopted. The aforementioned results have great potential for practical cost-effective OOFDM transceiver architecture design.