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120
Analysis and design of OFDM/OQAM systems based on filterbank theory
- IEEE Trans. Signal Process
, 2002
"... 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 O ..."
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Cited by 93 (7 self)
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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 arbi-trary 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 a number of subcarriers going from four up to 2048, which also allows a comparison between different approaches to get well-localized prototypes. Index Terms—Filterbanks, multicarrier modulation, polyphase representation, pulse shaping, transmultiplexer. I.
Exploiting Input Cyclostationarity for Blind Channel Identification in OFDM Systems
- IEEE Trans. Signal Processing
, 1999
"... Transmitter-induced cyclostationarity has been explored recently as an alternative to fractional sampling and antenna array methods for blind identification of FIR communication channels. An interesting application of these ideas is in OFDM systems, which induce cyclostationarity due to the cyclic p ..."
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Cited by 50 (1 self)
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Transmitter-induced cyclostationarity has been explored recently as an alternative to fractional sampling and antenna array methods for blind identification of FIR communication channels. An interesting application of these ideas is in OFDM systems, which induce cyclostationarity due to the cyclic prefix. In this correspondence, we develop a novel subspace approach for blind channel identification using cyclic correlations at the OFDM receiver. Even channels with equispaced unit circle zeros are identifiable in the presence of any nonzero length cyclic prefix with adequate block length. Simulations of the proposed channel estimator along with its performance in OFDM systems combined with impulse response shortening and Reed--Solomon coding are presented.
Pseudodifferential operators and Banach algebras in mobile communications
- Applied and Computational Harmonic Analysis
"... We study linear time-varying operators arising in mobile commu-nication using methods from time-frequency analysis. We show that a wireless transmission channel can be modeled as pseudodifferential operator Hσ with symbol σ in FL1w or in the modulation space M∞,1w (also known as weighted Sjöstrand ..."
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Cited by 36 (5 self)
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We study linear time-varying operators arising in mobile commu-nication using methods from time-frequency analysis. We show that a wireless transmission channel can be modeled as pseudodifferential operator Hσ with symbol σ in FL1w or in the modulation space M∞,1w (also known as weighted Sjöstrand class). It is then demonstrated that Gabor Riesz bases {ϕm,n} for subspaces of L2(R) approximately diagonalize such pseudodifferential operators in the sense that the as-sociated matrix [〈Hσϕm′,n ′ , ϕm,n〉]m,n,m′,n ′ belongs to a Wiener-type Banach algebra with exponentially fast off-diagonal decay. We indi-cate how our results can be utilized to construct numerically efficient equalizers for multicarrier communication systems in a mobile envi-ronment. 1
Analysis, optimization, and implementation of low-interference wireless multicarrier systems
- IEEE Trans. Wireless Commun
, 2007
"... Abstract-This paper considers pulse shaping multicarrier (MC) systems that transmit over doubly dispersive fading channels. We provide exact and approximate expressions for the intersymbol and intercarrier interference occuring in such systems. This analysis reveals that the time and frequency conc ..."
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Cited by 28 (6 self)
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Abstract-This paper considers pulse shaping multicarrier (MC) systems that transmit over doubly dispersive fading channels. We provide exact and approximate expressions for the intersymbol and intercarrier interference occuring in such systems. This analysis reveals that the time and frequency concentration of the transmit and receive pulse is of paramount importance for low interference. We prove the (nonobvious) existence of such jointly concentrated pulse pairs by adapting recent mathematical results on Weyl-Heisenberg frames to the MC context. Furthermore, pulse optimization procedures are proposed that aim at low interference and capitalize on the design freedom existing for redundant MC systems. Finally, we present efficient FFT-based modulator and demodulator implementations. Our numerical results demonstrate that for realistic system and channel parameters, optimized pulse-shaping MC systems can outperform conventional cyclic-prefix OFDM systems.
Performance Analysis of Synchronous MC-CDMA in Mobile Rayleigh Channel with . . .
- IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY
, 2001
"... Rapid time variations of the mobile communication channel have a dramatic effect on the performance of multicarrier modulation. This paper models the Doppler spread and computes its effect on the bit error rate (BER) for multicarrier code division multiple access (MC-CDMA) transmission and compares ..."
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Cited by 27 (4 self)
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Rapid time variations of the mobile communication channel have a dramatic effect on the performance of multicarrier modulation. This paper models the Doppler spread and computes its effect on the bit error rate (BER) for multicarrier code division multiple access (MC-CDMA) transmission and compares it to orthogonal frequency division multiplexing (OFDM). Also, we evaluate the transmission capacity per subcarrier to quantify the potential of MC-CDMA and (coded-) OFDM. We focus on linear receivers, in particular those using the minimum mean-square error (MMSE) criterion. Our channel and system models allow the computation of analytical performance results. Simulations verify some commonly used, yet critical assumptions.
Channel Identification and Equalization in OFDM-Based Multi-Antenna Systems
- IEEE Trans. Signal Processing
, 2002
"... Abstract—Wireless systems employing multiple antennas at the transmitter and the receiver have recently been shown to have the potential of achieving extraordinary bit rates. Orthogonal frequency division multiplexing (OFDM) significantly reduces receiver complexity in multiantenna broadband systems ..."
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Cited by 23 (0 self)
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Abstract—Wireless systems employing multiple antennas at the transmitter and the receiver have recently been shown to have the potential of achieving extraordinary bit rates. Orthogonal frequency division multiplexing (OFDM) significantly reduces receiver complexity in multiantenna broadband systems. In this paper, we introduce an algorithm for blind channel identification and equalization in OFDM-based multiantenna systems. Our approach uses second-order cyclostationary statistics, employs antenna precoding, and yields unique channel estimates (up to a phase rotation for each transmit antenna). Furthermore, it requires only an upper bound on the channel order, it does not impose restrictions on channel zeros, and it exhibits low sensitivity to stationary noise. We present simulation results demonstrating the channel estimator and the corresponding multichannel equalizer performance. Index Terms—Blind equalization, cyclostationarity, MIMO, multiantenna systems, OFDM.
Optimal training sequences and pilot tones for OFDM systems
- IEEE Communications Letters
, 2001
"... systems transmit data in blocks. The two simplest ways of iden-tifying the channel in OFDM systems are to insert a training sequence between consecutive blocks or to insert pilot tones inside each block. This letter proves that both methods can achieve the same level of performance under certain con ..."
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Cited by 22 (3 self)
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systems transmit data in blocks. The two simplest ways of iden-tifying the channel in OFDM systems are to insert a training sequence between consecutive blocks or to insert pilot tones inside each block. This letter proves that both methods can achieve the same level of performance under certain conditions on the block length. Index Terms—Channel estimation, orthogonal frequency-divi-sion multiplex, pilot tones, training sequence. I.
Efficient Multicarrier Communication for Highly Spread Underwater Acoustic Channels
"... Abstract—In this paper we propose a novel method for communication over underwater acoustic channels that exhibit simultaneously large delay spread and Doppler spread, such as those found in the surf zone. In particular, we propose a coded pulse-shaped multicarrier scheme that converts the doubly di ..."
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Cited by 21 (3 self)
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Abstract—In this paper we propose a novel method for communication over underwater acoustic channels that exhibit simultaneously large delay spread and Doppler spread, such as those found in the surf zone. In particular, we propose a coded pulse-shaped multicarrier scheme that converts the doubly dispersive channel into an inter-carrier interference (ICI) channel with small ICI spread. The resulting ICI is mitigated using a soft noncoherent equalizer that leverages sparsity in the delay-power profile to generate near-optimal bit estimates with low complexity. The noncoherent equalizer uses a delay-power-profile estimate (rather than a channel estimate) which is obtained from pilots. Numerical simulations with surf-zone-like channels demonstrate performance close to genie-aided bounds. Index Terms—Underwater acoustic modems, underwater acoustic channels, multicarrier modulation, noncoherent decoding, turbo equalization, joint estimation and detection, sparse channels. I.
Max-SINR ISI/ICI-Shaping Multicarrier Communication Over the Doubly Dispersive Channel
, 2007
"... For communication over doubly dispersive channels, we consider the design of multicarrier modulation (MCM) schemes based on time–frequency shifts of prototype pulses. We consider the case where the receiver knows the channel state and the transmitter knows the channel statistics (e.g., delay spread ..."
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Cited by 20 (4 self)
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For communication over doubly dispersive channels, we consider the design of multicarrier modulation (MCM) schemes based on time–frequency shifts of prototype pulses. We consider the case where the receiver knows the channel state and the transmitter knows the channel statistics (e.g., delay spread and Doppler spread) but not the channel state. Previous work has examined MCM pulses designed for suppression of inter-symbol/inter-carrier interference (ISI/ICI) subject to orthogonal or biorthogonal constraints. In doubly dispersive channels, however, complete suppression of ISI/ICI is impossible, and the ISI/ICI pattern generated by these (bi)orthogonal schemes can be difficult to equalize, especially when operating at high bandwidth efficiency. We propose a different approach to MCM pulse design, whereby a limited expanse of ISI/ICI is tolerated in modulation/demodulation and treated near-optimally by a downstream equalizer. Specifically, we propose MCM pulse designs that maximize a signal-to-interference-plus-noise ratio (SINR) which suppresses ISI/ICI outside a target pattern. In addition, we propose two low-complexity turbo equalizers, based on minimum mean-squared error and maximum likelihood criteria, respectively, that leverage the structure of the target ISI/ICI pattern. The resulting system exhibits an excellent combination of low complexity, low bit-error rate, and high spectral efficiency.
The WSSUS Pulse Design Problem in Multicarrier Transmission
, 2007
"... Optimal link adaption to the scattering function of wide sense stationary uncorrelated scattering (WSSUS) mobile communication channels is still an unsolved problem despite its importance for next-generation system design. In multicarrier transmission such link adaption is performed by pulse shaping ..."
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Cited by 18 (5 self)
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Optimal link adaption to the scattering function of wide sense stationary uncorrelated scattering (WSSUS) mobile communication channels is still an unsolved problem despite its importance for next-generation system design. In multicarrier transmission such link adaption is performed by pulse shaping, i.e. by properly adjusting the transmit and receive filters. For example pulse shaped Offset–QAM systems have been recently shown to have superior performance over standard cyclic prefix OFDM (while operating at higher spectral efficiency). In this paper we establish a general mathematical framework for joint transmitter and receiver pulse shape optimization for so-called Weyl–Heisenberg or Gabor signaling with respect to the scattering function of the WSSUS channel. In our framework the pulse shape optimization problem is translated to an optimization problem over trace class operators which in turn is related to fidelity optimization in quantum information processing. By convexity relaxation the problem is shown to be equivalent to a convex constraint quasi-convex maximization problem thereby revealing the non-convex nature of the overall WSSUS pulse design problem. We present several iterative algorithms for optimization providing applicable results even for large–scale problem constellations. We show that with transmitter-side knowledge of the channel statistics a gain of 3 − 6dB in SINR can be expected.
