Filter bank-based multicarrier communications (FBMC) have recently attracted increased interest in both wired (e.g., xDSL, PLC) and wireless (e.g., cognitive radio) applications, due to their enhanced flexibility, higher spectral efficiency, and better spectral containment compared to conventional OFDM. A particular type of FBMC, the so-called FBMC/OQAM or OFDM/OQAM system, consisting of pulse shaped OFDM carrying offset QAM (OQAM) symbols, has received increasing attention due to, among other features, its higher spectral efficiency and implementation simplicity. It suffers, however, from an imaginary inter-carrier/inter-symbol interference that complicates signal processing tasks such as channel estimation. This paper focuses on channel estimation for OFDM/OQAM systems based on a known preamble. A review of the existing preamble structures and associated channel estimation methods is given, for both single- (SISO) and multiple-antenna (MIMO) systems. The various preambles are compared via simulations in both mildly and highly frequency selective channels.

Preamble-based Channel Estimation in OFDM/OQAM Systems: A Review

Review: Preamble-based channel estimation in OFDM/OQAM systems: A review

In this paper, we experimentally demonstrate the first 110-Gb/s multi-band superchannel coherent optical orthogonal frequency-division multiplexing based on offset quadrature amplitude modulation (OFDM/OQAM) system. Unlike the conventional orthogonal band-multiplexed OFDM system, no timing or frequency synchronization is required for the OFDM/OQAM system. We further investigate the influence of guard band, and find that very trivial guard band spacing (<20MHz) is required without any sensitivity performance or spectral efficiency degradation. Thus, the newly designed scheme would significantly reduce the implementation constrains for the band-multiplexed superchannel coherent optical OFDM system.

Experimental demonstration of 110-Gb/s unsynchronized band-multiplexed superchannel coherent optical OFDM/OQAM system

We experimentally demonstrate and numerically investigate a discrete-Fourier-transform (DFT) based offset quadrature-amplitude-modulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) system. We investigate the scheme using a set of square-root-raised-cosine functions and a set of super-Gaussian functions as signal spectra. It is shown that offset-QAM OFDM exhibits negligible penalty for all investigated spectra, in contrast to rectangular-function based Nyquist FDM (N-FDM) and sinc-function based conventional OFDM (C-OFDM). The required guard interval (GI) length for dispersion compensation in offset-QAM OFDM is analyzed and shown to scale with twice the subcarrier spacing rather than the full OFDM bandwidth. Experimental results show that 38-Gb/s offset-16QAM OFDM supports 600-km fiber transmission with negligible penalty in the absence of GI while a GI length of eight is required in C-OFDM. Further numerical simulations show that by avoiding the GI, 112-Gb/s polarization multiplexed offset-4QAM OFDM can achieve 23% increase in net data rate over C-OFDM under the same transmission reach. We also discuss the design of the pulse-shaping filter in the DFT-based implementation and show that when compared to N-FDM, the required memory length of the filter for pulse shaping can be reduced from 60 to 2 in offset-QAM OFDM regardless of the fiber length.

DFT-based offset-QAM OFDM for optical communications

Orthogonal frequency-division multiplexing (OFDM) is susceptible to multiple access interference and synchronization errors due to sidelobes, which hinder the integration of various applications and multiple access in OFDM-based optical transmission. In this letter, an adaptively modulated optical filter bank multicarrier with offset quadrature amplitude modulation-based sidelobe suppression is proposed in a wired/wireless converged optical network. We experimentally verified both the improvements in signal performance and spectral efficiency compared with OFDM in a multisender-supported optical network after a 50-km transmission.

AMO-FBMC for Asynchronous Heterogeneous Signal Integrated Optical Transmission

The challenges associated with the OFDM system are addressed. OFDM transmits redundancy in terms of Cyclic Prefix (CP), which decreases the spectral efficiency of the system. A pulse shaping filter for the OFDM systems is proposed to remove the constraint of CP. Also, transmit and receive filters in OFDM system suffer from poor frequency response because of the use of rectangular window function. The non-rectangular window based prototype filters are proposed for the transmitter and receiver end. The comparison of performance of OFDM system and the suggested filter bank based multicarrier systems is provided in terms of BER and the stop band attenuation of the constituent filters.

K. Arya

Papers

Elimination of cyclic prefix of OFDM systems using filter bank based multicarrier systems