A Survey on OFDM-Based Elastic Core Optical Networking <s> A. OFDM Principle <s> The first book on optical OFDM by the leading pioneers in the field. The only book to cover error correction codes for optical OFDM. It gives applications of OFDM to free-space communications, optical access networks, and metro and log haul transports show optical OFDM can be implemented. It contains introductions to signal processing for optical engineers and optical communication fundamentals for wireless engineers. This book gives a coherent and comprehensive introduction to the fundamentals of OFDM signal processing, with a distinctive focus on its broad range of applications. It evaluates the architecture, design and performance of a number of OFDM variations, discusses coded OFDM, and gives a detailed study of error correction codes for access networks, 100 Gb/s Ethernet and future optical networks. The emerging applications of optical OFDM, including single-mode fiber transmission, multimode fiber transmission, free space optical systems, and optical access networks are examined, with particular attention paid to passive optical networks, radio-over-fiber, WiMAX and UWB communications. Written by two of the leading contributors to the field, this book will be a unique reference for optical communications engineers and scientists. Students, technical managers and telecom executives seeking to understand this new technology for future-generation optical networks will find the book invaluable. William Shieh is an associate professor and reader in the electrical and electronic engineering department, The University of Melbourne, Australia. He received his M.S. degree in electrical engineering and Ph.D. degree in physics both from University of Southern California. Ivan Djordjevic is an Assistant Professor of Electrical and Computer Engineering at the University of Arizona, Tucson, where he directs the Optical Communications Systems Laboratory (OCSL). His current research interests include optical networks, error control coding, constrained coding, coded modulation, turbo equalization, OFDM applications, and quantum error correction. 'This wonderful book is the first one to address the rapidly emerging optical OFDM field. Written by two leading researchers in the field, the book is structured to comprehensively cover any optical OFDM aspect one could possibly think of, from the most fundamental to the most specialized. The book adopts a coherent line of presentation, while striking a thoughtful balance between the various topics, gradually developing the optical-physics and communication-theoretic concepts required for deep comprehension of the topic, eventually treating the multiple optical OFDM methods, variations and applications. In my view, this book will remain relevant for many years to come, and will be increasingly accessed by graduate students, accomplished researchers as well as telecommunication engineers and managers keen to attain a perspective on the emerging role of OFDM in the evolution of photonic networks' - Prof. Moshe Nazarathy, EE Dept., Technion, Israel Institute of Technology. <s> BIB001 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> A. OFDM Principle <s> The Fourier transform data communication system is a realization of frequency-division multiplexing (FDM) in which discrete Fourier transforms are computed as part of the modulation and demodulation processes. In addition to eliminating the banks of subcarrier oscillators and coherent demodulators usually required in FDM systems, a completely digital implementation can be built around a special-purpose computer performing the fast Fourier transform. In this paper, the system is described and the effects of linear channel distortion are investigated. Signal design criteria and equalization algorithms are derived and explained. A differential phase modulation scheme is presented that obviates any equalization. <s> BIB002
OFDM is a special class of the multi-carrier modulation (MCM) scheme that transmits a high-speed data stream by dividing it into a number of orthogonal channels, referred to as subcarriers, each carrying a relatively-low data rate BIB001 . Compared to WDM systems, where a fixed channel spacing between the wavelengths is usually needed to eliminate crosstalk, OFDM allows the spectrum of individual subcarriers to overlap because of its orthogonality, as depicted in Fig. 1 . Furthermore, the inter-symbol interference (ISI) of the OFDM signal can be mitigated as the per-subcarrier symbol duration is significantly longer than that of a single-carrier system of the same total data rate. From the spectrum perspective, the orthogonal condition between multiple subcarriers is satisfied when their central frequencies are spaced n/T s apart, where n is an integer and T s is the symbol duration. It can be seen in Fig. 2(a) that the peak point of a subcarrier's spectrum corresponds to the zero point of other subcarriers' spectra. Therefore, when a subcarrier is sampled at its peak, all other subcarriers have zero-crossings at that point and thus do not interfere with the subcarrier being sampled. This orthogonality leads to a more efficient usage of spectral resources, which is limited for most communication media. In the time domain, the OFDM signal is a synthesis of multiple subcarriers' waveforms, and consists of a continuous stream of OFDM symbols that have a regular symbol period, as shown in Fig. 2(b) . As mentioned above, OFDM is a special form of multicarrier modulation with orthogonality between each subcarrier. A general multi-carrier modulation signal s(t) is represented as BIB001 : s k (t) = Π(t)e where c ki is the ith information symbol at the kth subcarrier, s k is the waveform for the kth subcarrier, N sc is the number of subcarriers, f k is the frequency of the subcarrier, T s is the symbol period, and (t) is the pulse-shaping function. The detector for each subcarrier uses a filter that matches the subcarrier waveform. Therefore, the detected information symbol c ki is given by: between any two subcarriers, given by: If the condition: is satisfied, then the two subcarriers are orthogonal to each other. It can be seen that these orthogonal subcarrier sets, with their frequencies spaced at multiples of the inverse of the symbol periods, can be recovered with the matched filters in Eqn. (4) without inter-carrier interference, despite strong spectral overlapping. It has been shown that OFDM modulation and demodulation can be implemented using inverse discrete Fourier transform (IDFT) and discrete Fourier transform (DFT), respectively BIB002 . The discrete value of the transmitted OFDM signal s(t) is a N-point IDFT of the information symbol c k , and the received information symbol c k is a N-point DFT of the received sampled signal r(t). To reduce the computational complexity of DFT/IDFT, efficient fast Fourier transform and inverse fast Fourier transform (FFT/IFFT) functions are normally used in OFDM systems to implement OFDM modulation and demodulation.