The Experts below are selected from a list of 123 Experts worldwide ranked by ideXlab platform
Vahid Tarokh - One of the best experts on this subject based on the ideXlab platform.
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rate of channel hardening of Antenna selection diversity schemes and its implication on scheduling
arXiv: Information Theory, 2007Co-Authors: Dongwoon Bai, Patrick Mitran, Saeed S. Ghassemzadeh, Robert R Miller, Vahid TarokhAbstract:For a Multiple Antenna System, we compute the asymptotic distribution of Antenna selection gain when the transmitter selects the transmit Antenna with the strongest channel. We use this to asymptotically estimate the underlying channel capacity distributions, and demonstrate that unlike Multiple-input/Multiple-output (MIMO) Systems, the channel for Antenna selection Systems hardens at a slower rate, and thus a significant multiuser scheduling gain can exist - O(1/ log m) for channel selection as opposed to O(1/ sqrt{m}) for MIMO, where m is the number of transmit Antennas. Additionally, even without this scheduling gain, it is demonstrated that transmit Antenna selection Systems outperform open loop MIMO Systems in low signal-to-interference-plus-noise ratio (SINR) regimes, particularly for a small number of receive Antennas. This may have some implications on wireless System design, because most of the users in modern wireless Systems have low SINRs
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Channel Hardening and the Scheduling Gain of Antenna Selection Diversity Schemes
2007 IEEE International Symposium on Information Theory, 2007Co-Authors: Dongwoon Bai, Patrick Mitran, Saeed S. Ghassemzadeh, Robert R Miller, Vahid TarokhAbstract:For a Multiple Antenna System, we compute the asymptotic distribution of Antenna selection gain when the transmitter selects the transmit Antenna with the strongest channel. We use this to asymptotically estimate the underlying channel capacity distributions, and demonstrate that unlike Multiple- input/Multiple-output (MIMO) Systems,the channel for Antenna selection Systems hardens at a slower rate, and thus a significant multiuser scheduling gain can exist. Additionally, even without this scheduling gain, it is demonstrated that transmit Antenna selection Systems outperform open loop MIMO Systems at low signal-to-interference-plus-noise ratio (SINR) regimes, particularly for small number of receive Antennas. This may have some implications on wireless System design, because most of the users in modern wireless Systems have low SINRs.
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variable rate space time block codes in m ary psk Systems
IEEE Journal on Selected Areas in Communications, 2003Co-Authors: Ilmin Kim, Vahid TarokhAbstract:We consider a Multiple Antenna System when combined array processing with space-time coding is used. We present variable rate space-time block codes for two, three, and four transmit Antennas and optimize the transmit power so that the average bit-error rate (BER) is minimized. Numerical results show that this optimum power allocation scheme provides significant gain over the equal power allocation scheme. We then classify all the variable rate space-time block codes having the same code rates and identify the unique code that achieves the lowest BER. We explicitly compute the performance of the variable rate codes over a Rayleigh-fading channel. The proposed variable rate space-time block codes are useful for unequal error protection in Multiple transmit Antenna Systems.
Sriram Vishwanath - One of the best experts on this subject based on the ideXlab platform.
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pilot contamination and precoding in multi cell tdd Systems
IEEE Transactions on Wireless Communications, 2011Co-Authors: Jubin Jose, Alexei Ashikhmin, Thomas L Marzetta, Sriram VishwanathAbstract:This paper considers a multi-cell Multiple Antenna System with precoding used at the base stations for downlink transmission. Channel state information (CSI) is essential for precoding at the base stations. An effective technique for obtaining this CSI is time-division duplex (TDD) operation where uplink training in conjunction with reciprocity simultaneously provides the base stations with downlink as well as uplink channel estimates. This paper mathematically characterizes the impact that uplink training has on the performance of such multi-cell Multiple Antenna Systems. When non-orthogonal training sequences are used for uplink training, the paper shows that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells in an undesirable manner. This paper analyzes this fundamental problem of pilot contamination in multi-cell Systems. Furthermore, it develops a new multi-cell MMSE-based precoding method that mitigates this problem. In addition to being linear, this precoding method has a simple closed-form expression that results from an intuitive optimization. Numerical results show significant performance gains compared to certain popular single-cell precoding methods.
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pilot contamination problem in multi cell tdd Systems
International Symposium on Information Theory, 2009Co-Authors: Jubin Jose, Alexei Ashikhmin, Thomas L Marzetta, Sriram VishwanathAbstract:This paper considers a multi-cell Multiple Antenna System with precoding at the base stations for downlink transmission. To enable precoding, channel state information (CSI) is obtained via uplink training. This paper mathematically characterizes the impact that uplink training has on the performance of multi-cell Multiple Antenna Systems. When non-orthogonal training sequences are used for uplink training, it is shown that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells. This problem of pilot contamination is analyzed in this paper. A multi-cell MMSE-based precoding is proposed that, when combined with frequency/time/pilot reuse techniques, mitigate this problem.
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pilot contamination and precoding in multi cell tdd Systems
arXiv: Information Theory, 2009Co-Authors: Jubin Jose, Alexei Ashikhmin, Thomas L Marzetta, Sriram VishwanathAbstract:This paper considers a multi-cell Multiple Antenna System with precoding used at the base stations for downlink transmission. For precoding at the base stations, channel state information (CSI) is essential at the base stations. A popular technique for obtaining this CSI in time division duplex (TDD) Systems is uplink training by utilizing the reciprocity of the wireless medium. This paper mathematically characterizes the impact that uplink training has on the performance of such multi-cell Multiple Antenna Systems. When non-orthogonal training sequences are used for uplink training, the paper shows that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells in an undesirable manner. This paper analyzes this fundamental problem of pilot contamination in multi-cell Systems. Furthermore, it develops a new multi-cell MMSE-based precoding method that mitigate this problem. In addition to being a linear precoding method, this precoding method has a simple closed-form expression that results from an intuitive optimization problem formulation. Numerical results show significant performance gains compared to certain popular single-cell precoding methods.
Jian Song - One of the best experts on this subject based on the ideXlab platform.
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mutual information and error probability analysis on generalized spatial modulation System
IEEE Transactions on Communications, 2017Co-Authors: Jun Wang, Jintao Wang, Jian SongAbstract:Generalized spatial modulation (GSM) is an extended architecture to the spatial modulation Multiple Antenna System. The GSM System uses Multiple activated transmit Antennas to further exploit the System transmission capacity. In this paper, we consider the GSM Systems with channel diagonalization (CD-) transmitter pre-coder (TPC), channel inversion TPC, and without TPC. For each TPC scheme, the pairwise activated Antenna detection discriminant and closed-form Antenna detection pairwise error probability (PEP) of the GSM System are derived. We use the Antenna detection PEP to calculate the analytical Antenna detection symbol error rate union bound and the mutual information lower bound. We use asymptotic methods to analyze Antenna detection diversity and coding gains of GSM System with or without TPC when the signal-to-noise ratio is high. Together with complexity analysis on the pre-coders and Antenna detectors, we discover the CD-TPC trades the Antenna detection performance for complexity reduction, while the CD-TPC scheme achieves a balance between the performance and complexity. This paper introduces methods to the performance evaluation of the GSM System, and provides a guideline for the GSM System design such as Antenna configuration and TPC schemes selection.
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Mutual Information Analysis on Spatial Modulation Multiple Antenna System
IEEE Transactions on Communications, 2015Co-Authors: Zhecheng An, Su Huang, Jintao Wang, Jun Wang, Jian SongAbstract:Spatial modulation (SM) is a recently proposed Multiple-input Multiple-output (MIMO) architecture that exploits the space domain for information transmission. In this paper, SM Systems with continuous amplitude-phase modulation (APM) and the corresponding maximum likelihood (ML) active transmit Antenna detector are considered. We introduced a method to compute the theoretical transition probability matrix and the mutual information of the ML Antenna detector. For SM Multiple-input single-output (MISO) System, we derive the error probability and the mutual information of the Antenna detector in closed-form. For Multiple receive Antenna SM System, the union bound of error probability and the lower bound of Antenna detection mutual information are proposed. The analytical results are verified by numerical simulation over Rayleigh fading channels. We investigate Systems with different number of Antennas and APM symbol input distributions to evaluate the performance of SM. The joint APM and Antenna detection mutual information of SM Systems is compared to the capacity of vertical Bell Labs layered space-time (V-BLAST) spatial Multiplexing MIMO scheme. Our research gives achievable transmission rates of SM-MISO/MIMO Systems and can be a guideline for suitable application scenarios.
Jubin Jose - One of the best experts on this subject based on the ideXlab platform.
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pilot contamination and precoding in multi cell tdd Systems
IEEE Transactions on Wireless Communications, 2011Co-Authors: Jubin Jose, Alexei Ashikhmin, Thomas L Marzetta, Sriram VishwanathAbstract:This paper considers a multi-cell Multiple Antenna System with precoding used at the base stations for downlink transmission. Channel state information (CSI) is essential for precoding at the base stations. An effective technique for obtaining this CSI is time-division duplex (TDD) operation where uplink training in conjunction with reciprocity simultaneously provides the base stations with downlink as well as uplink channel estimates. This paper mathematically characterizes the impact that uplink training has on the performance of such multi-cell Multiple Antenna Systems. When non-orthogonal training sequences are used for uplink training, the paper shows that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells in an undesirable manner. This paper analyzes this fundamental problem of pilot contamination in multi-cell Systems. Furthermore, it develops a new multi-cell MMSE-based precoding method that mitigates this problem. In addition to being linear, this precoding method has a simple closed-form expression that results from an intuitive optimization. Numerical results show significant performance gains compared to certain popular single-cell precoding methods.
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pilot contamination problem in multi cell tdd Systems
International Symposium on Information Theory, 2009Co-Authors: Jubin Jose, Alexei Ashikhmin, Thomas L Marzetta, Sriram VishwanathAbstract:This paper considers a multi-cell Multiple Antenna System with precoding at the base stations for downlink transmission. To enable precoding, channel state information (CSI) is obtained via uplink training. This paper mathematically characterizes the impact that uplink training has on the performance of multi-cell Multiple Antenna Systems. When non-orthogonal training sequences are used for uplink training, it is shown that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells. This problem of pilot contamination is analyzed in this paper. A multi-cell MMSE-based precoding is proposed that, when combined with frequency/time/pilot reuse techniques, mitigate this problem.
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pilot contamination and precoding in multi cell tdd Systems
arXiv: Information Theory, 2009Co-Authors: Jubin Jose, Alexei Ashikhmin, Thomas L Marzetta, Sriram VishwanathAbstract:This paper considers a multi-cell Multiple Antenna System with precoding used at the base stations for downlink transmission. For precoding at the base stations, channel state information (CSI) is essential at the base stations. A popular technique for obtaining this CSI in time division duplex (TDD) Systems is uplink training by utilizing the reciprocity of the wireless medium. This paper mathematically characterizes the impact that uplink training has on the performance of such multi-cell Multiple Antenna Systems. When non-orthogonal training sequences are used for uplink training, the paper shows that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells in an undesirable manner. This paper analyzes this fundamental problem of pilot contamination in multi-cell Systems. Furthermore, it develops a new multi-cell MMSE-based precoding method that mitigate this problem. In addition to being a linear precoding method, this precoding method has a simple closed-form expression that results from an intuitive optimization problem formulation. Numerical results show significant performance gains compared to certain popular single-cell precoding methods.
Babak Hassibi - One of the best experts on this subject based on the ideXlab platform.
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distributed space time coding in wireless relay networks
IEEE Transactions on Wireless Communications, 2006Co-Authors: Yindi Jing, Babak HassibiAbstract:We apply the idea of space-time coding devised for Multiple-Antenna Systems to the problem of communications over a wireless relay network with Rayleigh fading channels. We use a two-stage protocol, where in one stage the transmitter sends information and in the other, the relays encode their received signals into a "distributed" linear dispersion (LD) code, and then transmit the coded signals to the receive node. We show that for high SNR, the pairwise error probability (PEP) behaves as (logP/P)min{TH}, with T the coherence interval, that is, the number of symbol periods during which the channels keep constant, R the number of relay nodes, and P the total transmit power. Thus, apart from the log P factor, the System has the same diversity as a Multiple-Antenna System with R transmit Antennas, which is the same as assuming that the R relays can fully cooperate and have full knowledge of the transmitted signal. We further show that for a network with a large number of relays and a fixed total transmit power across the entire network, the optimal power allocation is for the transmitter to expend half the power and for the relays to collectively expend the other half. We also show that at low and high SNR, the coding gain is the same as that of a Multiple-Antenna System with R Antennas. However, at intermediate SNR, it can be quite different, which has implications for the design of distributed space-time codes
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modified fincke pohst algorithm for low complexity iterative decoding over Multiple Antenna channels
International Symposium on Information Theory, 2002Co-Authors: Haris Vikalo, Babak HassibiAbstract:In recent years, soft iterative decoding techniques have been shown to greatly improve the bit error rate performance of various communication Systems. For Multiple Antenna Systems employing spacetime codes, however, it is not clear what is the best way to obtain the soft-information required of the iterative scheme with low complexity. In this paper, we propose a modification of the Fincke-Pohst (sphere decoding) algorithm to estimate the maximum a posteriori (MAP) probability of the received symbol sequence. The new algorithm (FP-MAP) solves a nonlinear integer least-squares problem and, over a wide range of rates and SNRs, has polynomial-time (often cubic) expected complexity. The FP-MAP algorithm provides soft detection information for the soft channel decoder. The soft decoder's output is then fed back to the FP-MAP, and iterated on. The performance of the FP-MAP algorithm on a Multiple Antenna System employing turbo code is demonstrated.