Elimination of cyclic prefix of OFDM systems using filter bank based multicarrier systems
01 Nov 2008-pp 1-5
TL;DR: A pulse shaping filter for the OFDM systems is proposed to remove the constraint of CP and the non-rectangular window based prototype filters are proposed for the transmitter and receiver end.
Abstract: 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.
Citations
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Posted Content•
TL;DR: In this article, a review of the existing preamble structures and associated channel estimation methods is given, for both single- (SISO) and multiple-antenna (MIMO) systems.
Abstract: 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.
178 citations
TL;DR: A review of the existing preamble structures and associated channel estimation methods is given, for both single- (SISO) and multiple-antenna (MIMO) systems.
157 citations
Cites background from "Elimination of cyclic prefix of OFD..."
...Moreover, because of the good time localization, a CP does not have to be included in the OFDM/OQAM transmission,(1) which leads to still higher transmission rates [80, 5, 74]....
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TL;DR: This paper experimentally demonstrates the first 110-Gb/s multi-band superchannel coherent optical orthogonal frequency-division multiplexing based on offset quadrature amplitude modulation (OFDM/OQAM) system and investigates the influence of guard band, finding that very trivial guard band spacing is required without any sensitivity performance or spectral efficiency degradation.
Abstract: 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.
74 citations
TL;DR: 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), and by avoiding the GI, 112-Gb/s polarization multiplexed offset-4QAM OfDM can achieve 23% increase in net data rate over C-OF DM under the same transmission reach.
Abstract: 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.
37 citations
TL;DR: In this article, an adaptively modulated optical filter bank multicarrier with offset quadrature amplitude modulation-based sidelobe suppression is proposed in a wired/wireless converged optical network.
Abstract: 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.
36 citations
Cites methods from "Elimination of cyclic prefix of OFD..."
...Time synchronization was processed by cross-correlation between the Nyquist critical sampled received signal and preamble....
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...However, by comparing filter characteristics in multicarrier systems [19], performance improvement is possible with different prototype filters such as the Mirabbasi-Martin filter [19] which has better spectrum confinement while satisfying orthogonality among subcarriers compared to filters in previous works [10], [11], [14]–[18]....
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...The used prototype filters are based on raised cosine in [10] or root-raised cosine in [11], [14], and [15] or root Nyquist [18] in [16] and [17]....
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References
More filters
TL;DR: The general technique of parallel transmission on many carriers, called multicarrier modulation (MCM), is explained, and the performance that can be achieved on an undistorted channel and algorithms for achieving that performance are discussed.
Abstract: The general technique of parallel transmission on many carriers, called multicarrier modulation (MCM), is explained. The performance that can be achieved on an undistorted channel and algorithms for achieving that performance are discussed. Ways of dealing with channel impairments and of improving the performance through coding are described, and implementation methods are considered. Duplex operation of MCM and the possible use of this on the general switched telephone network are examined. >
3,995 citations
TL;DR: A discrete-time analysis of the orthogonal frequency division multiplex/offset QAM (OFDM/OQAM) multicarrier modulation technique, leading to a modulated transmultiplexer, is presented.
Abstract: A discrete-time analysis of the orthogonal frequency division multiplex/offset QAM (OFDM/OQAM) multicarrier modulation technique, leading to a modulated transmultiplexer, is presented. The conditions of discrete orthogonality are established with respect to the polyphase components of the OFDM/OQAM prototype filter, which is assumed to be symmetrical and with arbitrary length. Fast implementation schemes of the OFDM/OQAM modulator and demodulator are provided, which are based on the inverse fast Fourier transform. Non-orthogonal prototypes create intersymbol and interchannel interferences (ISI and ICI) that, in the case of a distortion-free transmission, are expressed by a closed-form expression. A large set of design examples is presented for OFDM/OQAM systems with the number of subcarriers going from four up to 2048, which also allows a comparison between different approaches to get well-localized prototypes.
1,020 citations
TL;DR: Various methods of determining the coefficients for this time-domain finite impulse response (FIR) filter are explored and an optimal shortening and a least-squares approach are developed for shortening the channel's impulse response.
Abstract: In discrete multitone (DMT) transceivers an intelligent guard time sequence, called a cyclic prefix (CP), is inserted between symbols to ensure that samples from one symbol do not interfere with the samples of another symbol. The length of the CP is determined by the length of the impulse response of the effective physical channel. Using a long CP reduces the throughput of the transceiver, To avoid using a long CP, a short time-domain finite impulse response (FIR) filter is used to shorten the effective channels impulse response. This paper explores various methods of determining the coefficients for this time-domain filter. An optimal shortening and a least-squares (LS) approach are developed for shortening the channel's impulse response. To provide a computationally efficient algorithm a variation of the LS approach is explored. In full-duplex transceivers the length of the effective echo path impacts the computational requirements of the transceiver. A new paradigm of joint shortening is introduced and three methods are developed to jointly shorten the channel and the echo impulse responses in order to reduce the length of the CP and reduce computational requirements for the echo canceller.
556 citations
"Elimination of cyclic prefix of OFD..." refers background in this paper
...Moreover, the application of simple time domain equalizers [4], [5] shortens the length of equivalent discrete time channel impulse response and, therefore, the necessary length of CP [6]....
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28 Nov 1994
TL;DR: Pulses of finite duration for use in orthogonal frequency division multiplexing (OFDM) using offset QAM modulation is presented and an optimization procedure which minimizes the out-of-band energy under the constraints of zero intersymbol and interchannel interference is presented.
Abstract: This paper presents pulses of finite duration for use in orthogonal frequency division multiplexing (OFDM) using offset QAM modulation. In such a system the pulses will overlap in both frequency and time without intersymbol or interchannel interference. The pulses are generated by an optimization procedure which minimizes the out-of-band energy under the constraints of zero intersymbol and interchannel interference. Low out-of-band energy is important to achieve high bandwidth efficiency, especially when the number of channels is small. The optimization procedure leads to an integral equation which is solved by expanding the pulse in truncated prolate spheroidal wave functions. Examples of optimized pulses and their spectrum are presented for lengths of 2 and 4 symbol intervals.
209 citations
"Elimination of cyclic prefix of OFD..." refers background in this paper
...The required ideal bandwidth efficiency can be achieved by using non-rectangular windows for pulse shaping in such a manner that the cascade of transmit and receive filters meets the Nyquist criterion [7]– [10]....
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...In [10], Vahlin and Holte have proposed the idea of optimal finite duration pulses for OFDM....
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...This algorithm attains the same range of stopband attenuation as that in [10]....
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TL;DR: Channel equalization in filter bank based multicarrier (FBMC) modulation is addressed and a novel structure, consisting of a linear-phase FIR amplitude equalizer and an allpass filter as phase equalizer is found to provide enhanced robustness to timing estimation errors.
Abstract: Channel equalization in filter bank based multicarrier (FBMC) modulation is addressed. We utilize an efficient oversampled filter bank concept with 2x-oversampled subcarrier signals that can be equalized independently of each other. Due to Nyquist pulse shaping, consecutive symbol waveforms overlap in time, which calls for special means for equalization. Two alternative linear low-complexity subcarrier equalizer structures are developed together with straightforward channel estimation-based methods to calculate the equalizer coefficients using pointwise equalization within each subband (in a frequency-sampled manner). A novel structure, consisting of a linear-phase FIR amplitude equalizer and an allpass filter as phase equalizer, is found to provide enhanced robustness to timing estimation errors. This allows the receiver to be operated without time synchronization before the filter bank. The coded error-rate performance of FBMC with the studied equalization scheme is compared to a cyclic prefix OFDM reference in wireless mobile channel conditions, taking into account issues like spectral regrowth with practical nonlinear transmitters and sensitivity to frequency offsets. It is further emphasized that FBMC provides flexible means for high-quality frequency selective filtering in the receiver to suppress strong interfering spectral components within or close to the used frequency band.
201 citations