Results 11 - 20 of 2,128

Universal Space-Time Coding

by Hesham El Gamal, Mohamed Oussama Damen - IEEE Trans. Inform. Theory , 2003
"... A universal framework is developed for constructing full-rate and full-diversity coherent space--time codes for systems with arbitrary numbers of transmit and receive antennas. The proposed framework combines space--time layering concepts with algebraic component codes optimized for single-input--si ..."
Abstract - Cited by 143 (7 self) - Add to MetaCart
A universal framework is developed for constructing full-rate and full-diversity coherent space--time codes for systems with arbitrary numbers of transmit and receive antennas. The proposed framework combines space--time layering concepts with algebraic component codes optimized for single-input--single-output (SISO) channels. Each component code is assigned to a "thread" in the space--time matrix, allowing it thus full access to the channel spatial diversity in the absence of the other threads. Diophantine approximation theory is then used in order to make the different threads "transparent" to each other. Within this framework, a special class of signals which uses algebraic number-theoretic constellations as component codes is thoroughly investigated. The lattice structure of the proposed number-theoretic codes along with their minimal delay allow for polynomial complexity maximum-likelihood (ML) decoding using algorithms from lattice theory. Combining the design framework with the Cayley transform allows to construct full diversity differential and noncoherent space--time codes. The proposed framework subsumes many of the existing codes in the literature, extends naturally to time-selective and frequency -selective channels, and allows for more flexibility in the tradeoff between power efficiency, bandwidth efficiency, and receiver complexity. Simulation results that demonstrate the significant gains offered by the proposed codes are presented in certain representative scenarios.
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Space-Time Diversity Systems Based on Linear Constellation Precoding

by Yan Xin, Zhengdao Wang, Georgios B. Giannakis - IEEE TRANS. WIRELESS COMMUN , 2003
"... We present a unified approach to designing space-time (ST) block codes using linear constellation precoding (LCP). Our designs are based either on parameterizations of unitary matrices, or on algebraic number-theoretic constructions. With an arbitrary number of transmit- and receive-antennas, ST-LCP ..."
Abstract - Cited by 128 (8 self) - Add to MetaCart
We present a unified approach to designing space-time (ST) block codes using linear constellation precoding (LCP). Our designs are based either on parameterizations of unitary matrices, or on algebraic number-theoretic constructions. With an arbitrary number of transmit- and receive-antennas, ST-LCP achieves rate 1 symbol/s/Hz and enjoys diversity gain as high as over (possibly correlated) quasi-static and fast fading channels. As figures of merit, we use diversity and coding gains, as well as mutual information of the underlying multiple-input-multiple-output system. We show that over quadrature-amplitude modulation and pulse-amplitude modulation, our LCP achieves the upper bound on the coding gain of all linear precoders for certain values of and comes close to this upper bound for other values of , in both correlated and independent fading channels. Compared with existing ST block codes adhering to an orthogonal design (ST-OD), ST-LCP offers not only better performance, but also higher mutual information for...

Capacity of MIMO systems with antenna selection

by Andreas F. Molisch, Moe Z. Win, Yang-seok Choi, Jack H. Winters , 2005
"... We consider the capacity of multiple-input multiple-output systems with reduced complexity. One link-end uses all available antennas, while the other chooses the L out of N antennas that maximize capacity. We derive an upper bound on the capacity that can be expressed sa sthe sum of the logarithms o ..."
Abstract - Cited by 126 (14 self) - Add to MetaCart
We consider the capacity of multiple-input multiple-output systems with reduced complexity. One link-end uses all available antennas, while the other chooses the L out of N antennas that maximize capacity. We derive an upper bound on the capacity that can be expressed sa sthe sum of the logarithms of ordered chi-square-distributed variables. This bound is then evaluated analytically and compared to the results obtained by Monte Carlo simulations. Our results show that the achieved capacity is close to the capacity of a full-complexity system provided that L is at least as large as the number of antennas at the other link-end. For example, for L=3, N=8 antennas at the receiver and three antennas at the transmitter, the capacity of the reduced-complexity scheme is 20 bits/s/Hz compared to 23 bits/s/Hz of a full-complexity scheme. We also present a suboptimum antenna subset selection algorithm that has a complexity of N2 compared to eht optimum algorithm with a complexity of (N L).
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MIMO antenna subset selection with space-time coding

by Dhananjay A. Gore, Arogyaswami J. Paulraj - IEEE Trans. Signal Processing , 2002
"... Abstract—This paper treats multiple-input multiple-output (MIMO) antenna subset selection employing space-time coding. We consider two cases differentiated based on the type of channel knowledge used in the selection process. We address both the selection algorithms and the performance analysis. We ..."
Abstract - Cited by 113 (0 self) - Add to MetaCart
Abstract—This paper treats multiple-input multiple-output (MIMO) antenna subset selection employing space-time coding. We consider two cases differentiated based on the type of channel knowledge used in the selection process. We address both the selection algorithms and the performance analysis. We first consider the case when the antenna subsets are selected based on exact channel knowledge (ECK). Our results assume the transmission of orthogonal space-time block codes (with emphasis on the Alamouti code). Next, we treat the case of antenna subset selection when statistical channel knowledge (SCK) is employed by the selection algorithm. This analysis is applicable to general space-time coding schemes. When ECK is available, we show that the selection algorithm chooses the antenna set that maximizes the channel Frobenius norm leading to both coding and diversity gain. When SCK is available, the selection algorithm chooses the antenna set that maximizes the determinant of the covariance of the vectorized channel leading mostly to a coding gain. In case of ECK-based selection, we provide analytical expressions for average SNR and outage probability improvement. For the case when SCK-based selection is used, we derive expressions for coding gain. We also present extensive simulation studies, validating our results. Index Terms—Antenna subset selection, MIMO, space-time coding.
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Diversity through coded cooperation

by Todd E. Hunter, Aria Nosratinia - IEEE TRANS. WIRELESS COMMUN , 2006
"... Cooperation provides transmit diversity in cases where wireless transmitters, due to size, power, or other constraints, cannot support multiple antennas. Cooperation involves two single-antenna sources (which we call users) forming a partnership, in which each achieves space-time diversity by using ..."
Abstract - Cited by 111 (0 self) - Add to MetaCart
Cooperation provides transmit diversity in cases where wireless transmitters, due to size, power, or other constraints, cannot support multiple antennas. Cooperation involves two single-antenna sources (which we call users) forming a partnership, in which each achieves space-time diversity by using their partner’s antenna as a relay. We propose a new methodology, called coded cooperation, where cooperation is achieved through channel coding methods, instead of a direct relay or repetition. Each codeword is partitioned into two subsets that are transmitted from the user’s and partner’s antennas, respectively. Coded cooperation achieves impressive gains compared to a non-cooperative system while maintaining the same information rate, transmit power, and bandwidth. We develop tight upper bounds for bit and block error rates, which we validate through simulations. Bit and block error rate results illustrate the improvement of coded cooperation for various combinations of channel conditions between the partners and to the destination.

Signal constellations for quasi-orthogonal space-time block codes with full diversity

by Weifeng Su, Xiang-gen Xia, Senior Member - IEEE Trans. Inform. Theory , 2004
"... Abstract—Space–time block codes (STBCs) from orthogonal designs proposed by Alamouti, and Tarokh–Jafarkhani–Calderbank have attracted considerable attention lately due to their fast maximum-likelihood (ML) decoding and full diversity. However, the maximum symbol transmission rate of an STBC from com ..."
Abstract - Cited by 109 (10 self) - Add to MetaCart
Abstract—Space–time block codes (STBCs) from orthogonal designs proposed by Alamouti, and Tarokh–Jafarkhani–Calderbank have attracted considerable attention lately due to their fast maximum-likelihood (ML) decoding and full diversity. However, the maximum symbol transmission rate of an STBC from complex orthogonal designs for complex signals is only Q R for three and four transmit antennas, and it is difficult to construct complex orthogonal designs with rate higher than I P for more than four transmit antennas. Recently, Jafarkhani, Tirkkonen–Boariu–Hottinen, and Papadias–Foschini proposed STBCs from quasi-orthogonal designs, where the orthogonality is relaxed to provide higher symbol transmission rates. With the quasi-orthogonal structure, the quasi-orthogonal STBCs still have a fast ML decoding, but do not have the full diversity. The performance of these codes is better than that of the codes from orthogonal designs at low signal-to-noise ratio (SNR), but worse at high SNR. This is due to the fact that the slope of the performance curve depends on the diversity. It is desired to have the quasi-orthogonal STBCs with full diversity to ensure good performance at high SNR. In this paper, we achieve this goal by properly choosing the signal constellations. Specifically, we propose that half of the symbols in a quasi-orthogonal design are chosen from a signal constellation set and the other half of them are chosen from a rotated constellation. The resulting STBCs can guarantee both full diversity and fast ML decoding. Moreover, we obtain the optimum selections of the rotation angles for some commonly used signal constellations. Simulation results show that the proposed codes outperform the codes from orthogonal designs at both low and high SNRs. Index Terms—Diversity, multiple antennas, orthogonal designs, quasi-orthogonal designs, space–time block codes (STBC), wireless communications. I.
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Cooperative diversity in wireless networks: Algorithms and architectures

by J. Nicholas Laneman , 2002
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Abstract - Cited by 109 (7 self) - Add to MetaCart
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Diagonal Algebraic Space-Time Block Codes

by Mohamed Oussama Damen, Karim Abed-meraim, Jean-claude Belfiore - IEEE Trans. Inform. Theory
"... We construct a new family of linear space-time block codes by the combination of rotated constellations and the Hadamard transform, and we prove them to achieve the full transmit diversity over a quasi-static or fast fading channels. The proposed codes transmit at a normalized rate of 1 symbol/sec. ..."
Abstract - Cited by 102 (7 self) - Add to MetaCart
We construct a new family of linear space-time block codes by the combination of rotated constellations and the Hadamard transform, and we prove them to achieve the full transmit diversity over a quasi-static or fast fading channels. The proposed codes transmit at a normalized rate of 1 symbol/sec. When the number of transmit antennae n =1, 2 or n is a multiple of 4 we spread a rotated version of the information symbol vector by the Hadamard transform and send it over n transmit antennae and n time periods; for other values of n, we construct the codes by sending the components of a rotated version of the information symbol vector over the diagonal of an nn space-time code matrix. The codes maintain their rate, diversity and coding gains for all real and complex constellations carved from the complex integers ring Z[i], and they outperform the codes from orthogonal design when using complex constellations for n > 2. The maximum likelihood decoding of the proposed codes can be implemented by the sphere decoder at a moderate complexity. It is shown that using the proposed codes in a multi-antenna system yields good performances with high spectral efficiency and moderate decoding complexity.
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On the feasibility of distributed beamforming in wireless networks

by R. Mudumbai, Student Member, G. Barriac, U. Madhow - IEEE Trans. on Wireless Commun , 2007
"... Abstract — Energy efficient communication is a fundamental problem in wireless ad-hoc and sensor networks. In this paper, we explore the feasibility of a distributed beamforming approach to this problem, with a cluster of distributed transmitters emulating a centralized antenna array so as to transm ..."
Abstract - Cited by 92 (16 self) - Add to MetaCart
Abstract — Energy efficient communication is a fundamental problem in wireless ad-hoc and sensor networks. In this paper, we explore the feasibility of a distributed beamforming approach to this problem, with a cluster of distributed transmitters emulating a centralized antenna array so as to transmit a common message signal coherently to a distant Base Station. The potential SNR gains from beamforming are well-known. However, realizing these gains requires synchronization of the individual carrier signals in phase and frequency. In this paper we show that a large fraction of the beamforming gains can be realised even with imperfect synchronization corresponding to phase errors with moderately large variance. We present a master-slave architecture where a designated master transmitter coordinates the synchronization of other (slave) transmitters for beamforming. We observe that the transmitters can achieve distributed beamforming with minimal coordination with the Base Station using channel reciprocity. Thus, inexpensive local coordination with a master transmitter makes the expensive communication with a distant Base Station receiver more efficient. However, the duplexing constraints of the wireless channel place a fundamental limitation on the achievable accuracy of synchronization. We present a stochastic analysis that demonstrates the robustness of beamforming gains with imperfect synchronization, and demonstrate a tradeoff between synchronization overhead and beamforming gains. We also present simulation results for the phase errors that validate the analysis. Index Terms — Distributed beamforming, synchronization, wireless networks, sensor networks, space-time communication.
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Space-Time-Frequency Coded OFDM Over Frequency-Selective Fading Channels

by Zhiqiang Liu, Yan Xin, Student Member, Georgios B. Giannakis - IEEE Trans. Signal Processing , 2002
"... This paper proposes novel space-time-frequency (STF) coding for multiantenna orthogonal frequency-division multiplexing (OFDM) transmissions over frequency-selective Rayleigh fading channels. Incorporating subchannel grouping and choosing appropriate system parameters, we first convert our system in ..."
Abstract - Cited by 87 (2 self) - Add to MetaCart
This paper proposes novel space-time-frequency (STF) coding for multiantenna orthogonal frequency-division multiplexing (OFDM) transmissions over frequency-selective Rayleigh fading channels. Incorporating subchannel grouping and choosing appropriate system parameters, we first convert our system into a set of group STF (GSTF) systems. This enables simplification of STF coding within each GSTF system. We derive design criteria for STF coding and exploit existing ST coding techniques to construct both STF block and trellis codes. The resulting codes are shown to be capable of achieving maximum diversity and coding gains, while affording low-complexity decoding. The performance merits of our design is confirmed by corroborating simulations and compared with existing alternatives.