The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform
Aria Nosratinia - One of the best experts on this subject based on the ideXlab platform.
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Diversity order in ISI channels with single-carrier frequency-domain equalizers
IEEE Transactions on Wireless Communications, 2010Co-Authors: Ali Tajer, Aria NosratiniaAbstract:This paper analyzes the diversity gain achieved by single-carrier frequency-domain equalizers (SC-FDE) in frequency selective channels, and uncovers the interplay between diversity gain d, channel Memory Length ?, transmission block Length L, and the spectral efficiency R. We specifically show that for the class of minimum mean-square error (MMSE) SCFDE receivers, for rates R ? log L/? full diversity of d = ?+ 1 is achievable, while for higher rates the diversity is given by d = [2-R L + 1. In other words, the achievable diversity gain depends not only on the channel Memory Length, but also on the desired spectral efficiency and the transmission block Length. A similar analysis reveals that for zero forcing SC-FDE, the diversity order is always one irrespective of channel Memory Length and spectral efficiency. These results are supported by simulations.
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Diversity Order in ISI Channels with Single-Carrier Frequency-Domain Equalizers
arXiv: Information Theory, 2009Co-Authors: Ali Tajer, Aria NosratiniaAbstract:This paper analyzes the diversity gain achieved by single-carrier frequency-domain equalizer (SC-FDE) in frequency selective channels, and uncovers the interplay between diversity gain $d$, channel Memory Length $\nu$, transmission block Length $L$, and the spectral efficiency $R$. We specifically show that for the class of minimum means-square error (MMSE) SC-FDE receivers, for rates $R\leq\log\frac{L}{\nu}$ full diversity of $d=\nu+1$ is achievable, while for higher rates the diversity is given by $d=\lfloor2^{-R}L\rfloor+1$. In other words, the achievable diversity gain depends not only on the channel Memory Length, but also on the desired spectral efficiency and the transmission block Length. A similar analysis reveals that for zero forcing SC-FDE, the diversity order is always one irrespective of channel Memory Length and spectral efficiency. These results are supported by simulations.
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diversity order of mmse single carrier frequency domain linear equalization
Global Communications Conference, 2007Co-Authors: Ali Tajer, Aria NosratiniaAbstract:In this paper we investigate the diversity order of single-carrier frequency domain equalizers (SC-FDE). Specifically, we look at minimum mean square error (MMSE) linear equalizers utilizing block-transmission and cyclic prefix. It is shown that the diversity order in these systems depends on data transmission rate, channel Memory Length, as well as transmission block Length. Analyses reveal that with Memory Length v and transmission block Length L, for the rates Rleslog L/v full diversity of v+1 is achievable. For higher rates the achievable diversity order is degraded and is equal to [2-R L]+1. Therefore MMSE SC-FDE has a diversity that varies between 1 and v+1, and achieves full diversity only for a limited range of data rates.
Pooi Yuen Kam - One of the best experts on this subject based on the ideXlab platform.
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adaptive maximum likelihood sequence detection for qpsk coherent optical communication system
IEEE Photonics Technology Letters, 2014Co-Authors: Pooi Yuen KamAbstract:A novel Viterbi-type adaptive maximum likelihood sequence detection algorithm is developed and investigated in coherent optical communication systems in the presence of both laser phase noise and nonlinear phase noise. Compared with the nonadaptive version, it can self-adjust the effective Memory Length of the phase estimator and automatically deliver the optimum bit-error rate performance without requiring any prior statistical knowledge of the optical channel. The phase error variance of the estimator is also analytically investigated.
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a robust glrt receiver with implicit channel estimation and automatic threshold adjustment for the free space optical channel with im dd
Journal of Lightwave Technology, 2014Co-Authors: Tianyu Song, Pooi Yuen KamAbstract:Atmospheric turbulence and pointing errors cause intensity fluctuation of free space optical communication signals and impair link performance. Several receiver structures which could mitigate the signal fluctuations were proposed in the past, but these existing receivers depend highly on the channel model and the model parameters. The performance deteriorates if the channel model or the model parameters are inaccurate. In this paper, we develop a Viterbi-type trellis-search sequence receiver based on the generalized likelihood ratio test principle that jointly detects the data sequence and estimates the unknown channel gain. This receiver requires very few pilot symbols, and therefore, does not significantly reduce the bandwidth efficiency. It is robust in that it continuously performs maximum likelihood (ML) estimation of the unknown channel gain without the knowledge of the channel model, and adapts the decision metric accordingly. It works well in a slowly time-varying environment and its error performance approaches that of ML detection with perfect knowledge of the channel gain, as the Memory Length used for forming the sequence detection metric increases. A new, decision-feedback, symbol-by-symbol receiver with lower implementation complexity and higher Memory efficiency is obtained as an approximation to the sequence receiver. The performance improvement and implementation simplicity of our receivers compared to existing receivers are pointed out.
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maximum likelihood sequence detection in laser phase noise impaired coherent optical systems
Optics Express, 2011Co-Authors: Xuguang Shao, Pooi Yuen KamAbstract:A maximum likelihood sequence detection (MLSD) receiver is used to detect data sequences in single-carrier coherent optical systems in the presence of laser phase noise. It requires no explicit phase estimation and involves only linear operations. It consistently shows improvement in the OSNR penalty (e.g., 1.1 dB at BER = 10−4 with Memory Length L =3) and the laser linewidth tolerance (e.g., around 4 times that of DAML at 1dB OSNR penalty at BER = 10−4 with Memory Length L =3) over the well-known DAML and Mth power approaches in laser phase noise (LPN)-impaired coherent optical systems.
Tadashi Matsumoto - One of the best experts on this subject based on the ideXlab platform.
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a matched filter approximation for sc mmse iterative equalizers
Vehicular Technology Conference, 2001Co-Authors: H Omori, Takahiro Asai, Tadashi MatsumotoAbstract:This paper proposes a new iterative ISI equalization algorithm that offers low computational complexity: order L/sup 2/ with channel Memory Length L. The proposed algorithm is an extension of D. Reynolds and Xiaodong Wang's SC/MMSE (soft canceller followed by MMSE filter) equalizer (see Signal Processing, vol.81, no.5, p.989-95, 2001): approximations are used properly to reduce the computational complexity. It is shown that the approximations used in the proposed algorithm do not cause any serious performance degradation compared to the conventional trellis-based iterative equalization algorithms.
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a matched filter approximation for sc mmse iterative equalizers
IEEE Communications Letters, 2001Co-Authors: H Omori, Takahiro Asai, Tadashi MatsumotoAbstract:This letter proposes a new iterative ISI equalization algorithm that offers low computational complexity: order L/sup 2/ with channel Memory Length L. The proposed algorithm is an extension of Reynolds and Wang's SC/MMSE (soft canceler followed by MMSE filter) equalizer: approximations are used properly to reduce the computational complexity. It is shown that the approximations used in the proposed algorithm do not cause any serious performance degradations from the trellis-based iterative equalization algorithms.
Arumugam Nallanathan - One of the best experts on this subject based on the ideXlab platform.
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delay tolerant distributed linear convolutional space time code with minimum Memory Length under frequency selective channels
IEEE Transactions on Wireless Communications, 2009Co-Authors: Zhimeng Zhong, Arumugam NallanathanAbstract:In cooperative communication networks, the performance of distributed space-time code will be severely degraded if the timing synchronization among relay nodes is not perfect. In this letter, we propose a systematic construction of the so called distributed linear convolutional space-time code (DLCSTC) for multipath fading channels that does not require the synchronization assumption. We derive sufficient conditions on the code design such that the full cooperative and multipath diversities can be achieved under the minimum Memory Length constraint. Then we design DLCSTCs that both have the traceorthonormality property and achieve the full diversity. We show that the proposed codes can also achieve the full diversity for asynchronous cooperative communications with ZF, MMSE and MMSE-DFE receivers under frequency-selective channels. Finally, various numerical examples are provided to corroborate the analytical studies.
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delay tolerant distributed linear convolutional space time code with minimum Memory Length under frequency selective channels
IEEE Transactions on Wireless Communications, 2009Co-Authors: Zhimeng Zhong, Shihua Zhu, Arumugam NallanathanAbstract:In cooperative communication networks, the performance of distributed space-time code will be severely degraded if the timing synchronization among relay nodes is not perfect. In this letter, we propose a systematic construction of the so called distributed linear convolutional space-time code (DLCSTC) for multipath fading channels that does not require the synchronization assumption. We derive sufficient conditions on the code design such that the full cooperative and multipath diversities can be achieved under the minimum Memory Length constraint. Then we design DLCSTCs that both have the traceorthonormality property and achieve the full diversity. We show that the proposed codes can also achieve the full diversity for asynchronous cooperative communications with ZF, MMSE and MMSE-DFE receivers under frequency-selective channels. Finally, various numerical examples are provided to corroborate the analytical studies.
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delay tolerant distributed linear convolutional space time code under frequency selective channels
International Conference on Communications, 2009Co-Authors: Zhimeng Zhong, Shihua Zhu, Arumugam NallanathanAbstract:In cooperative communication networks, the performance of the distributed space-time code (DSTC) will be severely degraded if the timing synchronization among relay nodes are not perfect. In this paper, we propose a systematic construction of the so called distributed linear convolutional space-time code (DLCSTC) for multipath fading channels that does not require the synchronization assumption. We derive sufficient conditions on the code design such that the full cooperative and multipath diversities can be achieved under the minimum Memory Length constraint. Then we design DLCSTCs that both have the trace-orthonormality property and achieve the full diversity. We also study the diversity property of the DLCSTC with suboptimal receivers. We show that the proposed codes can also achieve the full diversity for asynchronous cooperative communications with ZF, MMSE and MMSE-DFE receivers under frequency-selective channels. Finally, various numerical examples are provided to corroborate the analytical studies.
Naftali Tishby - One of the best experts on this subject based on the ideXlab platform.
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The Power of Amnesia: Learning Probabilistic Automata with Variable Memory Length
Machine Learning, 1996Co-Authors: Yoram Singer, Naftali TishbyAbstract:We propose and analyze a distribution learning algorithm for variable Memory Length Markov processes. These processes can be described by a subclass of probabilistic finite automata which we name Probabilistic Suffix Automata (PSA). Though hardness results are known for learning distributions generated by general probabilistic automata, we prove that the algorithm we present can efficiently learn distributions generated by PSAs. In particular, we show that for any target PSA, the KL-divergence between the distribution generated by the target and the distribution generated by the hypothesis the learning algorithm outputs, can be made small with high confidence in polynomial time and sample complexity. The learning algorithm is motivated by applications in human-machine interaction. Here we present two applications of the algorithm. In the first one we apply the algorithm in order to construct a model of the English language, and use this model to correct corrupted text. In the second application we construct a simple stochastic model for E. coli DNA.
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learning probabilistic automata with variable Memory Length
Conference on Learning Theory, 1994Co-Authors: Dana Ron, Yoram Singer, Naftali TishbyAbstract:We propose and analyze a distribution learning algorithm for variable Memory Length Markov processes. These processes can be described by a subclass of probabilistic finite automata which we name Probabilistic Finite Suffix Automata. The learning algorithm is motivated by real applications in man-machine interaction such as hand-writing and speech recognition. Conventionally used fixed Memory Markov and hidden Markov models have either severe practical or theoretical drawbacks. Though general hardness results are known for learning distributions generated by sources with similar structure, we prove that our algorithm can indeed efficiently learn distributions generated by our more restricted sources. In Particular, we show that the KL-divergence between the distribution generated by the target source and the distribution generated by our hypothesis can be made small with high confidence in polynomial time and sample complexity. We demonstrate the applicability of our algorithm by learning the structure of natural English text and using our hypothesis for the correction of corrupted text.
