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216
Opportunistic Beamforming Using Dumb Antennas
 IEEE Transactions on Information Theory
, 2002
"... Multiuser diversity is a form of diversity inherent in a wireless network, provided by independent timevarying channels across the different users. The diversity benefit is exploited by tracking the channel fluctuations of the users and scheduling transmissions to users when their instantaneous cha ..."
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Cited by 811 (1 self)
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Multiuser diversity is a form of diversity inherent in a wireless network, provided by independent timevarying channels across the different users. The diversity benefit is exploited by tracking the channel fluctuations of the users and scheduling transmissions to users when their instantaneous channel quality is near the peak. The diversity gain increases with the dynamic range of the fluctuations and is thus limited in environments with little scattering and/or slow fading. In such environments, we propose the use of multiple transmit antennas to induce large and fast channel fluctuations so that multiuser diversity can still be exploited. The scheme can be interpreted as opportunistic beamforming and we show that true beamforming gains can be achieved when there are sufficient users, even though very limited channel feedback is needed. Furthermore, in a cellular system, the scheme plays an additional role of opportunistic nulling of the interference created on users of adjacent cells. We discuss the design implications of implementing this scheme in a complete wireless system.
How Much Training is Needed in MultipleAntenna Wireless Links?
 IEEE Trans. Inform. Theory
, 2000
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HighRate Codes that are Linear in Space and Time
 IEEE Trans. Inform. Theory
, 2000
"... Multipleantenna systems that operate at high rates require simple yet effective spacetime transmission schemes to handle the large traffic volume in real time. At rates of tens of bits/sec/Hz, VBLAST, where every antenna transmits its own independent substream of data, has been shown to have good ..."
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Cited by 422 (13 self)
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Multipleantenna systems that operate at high rates require simple yet effective spacetime transmission schemes to handle the large traffic volume in real time. At rates of tens of bits/sec/Hz, VBLAST, where every antenna transmits its own independent substream of data, has been shown to have good performance and simple encoding and decoding. Yet VBLAST suffers from its inability to work with fewer receive antennas than transmit antennasthis deficiency is especially important for modern cellular systems where a basestation typically has more antennas than the mobile handsets. Furthermore, because VBLAST transmits independent data streams on its antennas there is no builtin spatial coding to guard against deep fades from any given transmit antenna. On the other hand, there are many previouslyproposed spacetime codes that have good fading resistance and simple decoding, but these codes generally have poor performance at high data rates or with many antennas. We propose a highrate coding scheme that can handle any...
From theory to practice: an overview of MIMO spacetime coded wireless systems
 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS
, 2003
"... This paper presents an overview of recent progress in the area of multipleinput–multipleoutput (MIMO) space–time coded wireless systems. After some background on the research leading to the discovery of the enormous potential of MIMO wireless links, we highlight the different classes of technique ..."
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Cited by 371 (6 self)
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This paper presents an overview of recent progress in the area of multipleinput–multipleoutput (MIMO) space–time coded wireless systems. After some background on the research leading to the discovery of the enormous potential of MIMO wireless links, we highlight the different classes of techniques and algorithms proposed which attempt to realize the various benefits of MIMO including spatial multiplexing and space–time coding schemes. These algorithms are often derived and analyzed under ideal independent fading conditions. We present the state of the art in channel modeling and measurements, leading to a better understanding of actual MIMO gains. Finally, the paper addresses current questions regarding the integration of MIMO links in practical wireless systems and standards.
Differential spacetime modulation
 IEEE Trans. Inform. Theory
, 2000
"... Abstract—Space–time coding and modulation exploit the presence of multiple transmit antennas to improve performance on multipath radio channels. Thus far, most work on space–time coding has assumed that perfect channel estimates are available at the receiver. In certain situations, however, it may b ..."
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Cited by 269 (1 self)
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Abstract—Space–time coding and modulation exploit the presence of multiple transmit antennas to improve performance on multipath radio channels. Thus far, most work on space–time coding has assumed that perfect channel estimates are available at the receiver. In certain situations, however, it may be difficult or costly to estimate the channel accurately, in which case it is natural to consider the design of modulation techniques that do not require channel estimates at the transmitter or receiver. We propose a general approach to differential modulation for multiple transmit antennas based on group codes. This approach can be applied to any number of transmit and receive antennas, and any signal constellation. We also derive lowcomplexity differential receivers, error bounds, and modulator design criteria, which we use to construct optimal differential modulation schemes for two transmit antennas. These schemes can be demodulated with or without channel estimates. This permits the receiver to exploit channel estimates when they are available. Performance degrades by approximately 3 dB when estimates are not available. Index Terms—Differential modulation, group codes, multipath channels, noncoherent communication, space–time coding, transmit diversity. I.
Representation Theory for HighRate MultipleAntenna Code Design
 IEEE Trans. Inform. Theory
, 2000
"... this paper, we show how to design signal matrices satisfying these requirements. As shown in [1], the design problem for unitary space time constellations is the following: let ..."
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Cited by 119 (15 self)
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this paper, we show how to design signal matrices satisfying these requirements. As shown in [1], the design problem for unitary space time constellations is the following: let
Cayley differential unitary space–time codes
 IEEE Trans. Inform. Theory
, 2002
"... One method for communicating with multiple antennas is to encode the transmitted data differentially using unitary matrices at the transmitter, and to decode differentially without knowing the channel coefficients at the receiver. Since channel knowledge is not required at the receiver, differential ..."
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Cited by 80 (8 self)
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One method for communicating with multiple antennas is to encode the transmitted data differentially using unitary matrices at the transmitter, and to decode differentially without knowing the channel coefficients at the receiver. Since channel knowledge is not required at the receiver, differential schemes are ideal for use on wireless links where channel tracking is undesirable or infeasible, either because of rapid changes in the channel characteristics or because of limited system resources. Although this basic principle is well understood, it is not known how to generate goodperforming constellations of unitary matrices, for any number of transmit and receive antennas and for any rate. This is especially true at high rates where the constellations must be rapidly encoded and decoded. We propose a class of Cayley codes that works with any number of antennas, and has efficient encoding and decoding at any rate. The codes are named for their use of the Cayley transform, which maps the highly nonlinear Stiefel manifold of unitary matrices to the linear space of skewHermitian matrices. This transformation leads to a simple linear constellation structure in the Cayley transform domain and to an informationtheoretic design criterion based on emulating a Cauchy random matrix. Moreover, the resulting Cayley codes allow polynomialtime nearmaximumlikelihood decoding based on either successive nulling/cancelling or sphere decoding. Simulations show that the Cayley codes allow efficient and effective highrate data transmission in multiantenna communication systems without knowing the channel.
Asymptotic Error Probability Analysis of Quadratic Receivers in RayleighFading Channels With Applications to a Unified Analysis of Coherent and Noncoherent SpaceTime Receivers
, 2001
"... A general, asymptotic (high signaltonoise (SNR)) error analysis is introduced for quadratic receivers in frequency flat and multipath Rayleighfading channels with multiple transmit and receive antennas. Asymptotically tight expressions for the pairwise error probabilities are obtained for cohere ..."
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Cited by 66 (14 self)
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A general, asymptotic (high signaltonoise (SNR)) error analysis is introduced for quadratic receivers in frequency flat and multipath Rayleighfading channels with multiple transmit and receive antennas. Asymptotically tight expressions for the pairwise error probabilities are obtained for coherent, noncoherent, and differentially coherent spacetime receivers. Not only is our unified analysis applicable to more general modulation schemes and/or channel models than previously considered, but it also reveals a hitherto unrecognized eigenvalue structure that is common to all of these problems. In addition to providing an easy recipe for computing the asymptotic pairwise error rates, we make some conclusions regarding criteria for the design of signal constellations and codes such as a) the same design criteria apply for both correlated and independent and identically distributed (i.i.d.) fading processes and b) for noncoherent communications, unitary signals are optimal in the sense that they minimize the asymptotic union bound.
Unitary Signal Constellations for Differential Space–Time Modulation With Two Transmit Antennas: Parametric Codes, Optimal Designs, and Bounds
, 2002
"... Differential space–time modulation has been recently proposed in the literature for multipleantenna systems over Rayleighfading channels, where neither the transmitter nor the receiver knows the fading coefficients. For the practical success of differential space–time modulation, it has been show ..."
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Cited by 55 (3 self)
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Differential space–time modulation has been recently proposed in the literature for multipleantenna systems over Rayleighfading channels, where neither the transmitter nor the receiver knows the fading coefficients. For the practical success of differential space–time modulation, it has been shown critical to design unitary space–time signal constellations with large diversity product which is a primary property for the signal constellations to have good performance in high signaltonoise ratio (SNR) scenarios. In this paper, we focus on the design of unitary signal constellations for differential space–time modulation with double transmit antennas. By using the parametric form of a twobytwo unitary matrix, we present a class of unitary space–time codes called parametric codes and show that this class of unitary space–time codes leads to a fivesignal constellation with the largest possible diversity