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112
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 305 (5 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.
An overview of limited feedback in wireless communication systems
 IEEE J. SEL. AREAS COMMUN
, 2008
"... It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channe ..."
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Cited by 176 (37 self)
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It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finiterate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, singleuser, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.
MIMO antenna subset selection with spacetime coding
 IEEE Trans. Signal Processing
, 2002
"... Abstract—This paper treats multipleinput multipleoutput (MIMO) antenna subset selection employing spacetime 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 ..."
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Cited by 109 (0 self)
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Abstract—This paper treats multipleinput multipleoutput (MIMO) antenna subset selection employing spacetime 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 spacetime 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 spacetime 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 ECKbased selection, we provide analytical expressions for average SNR and outage probability improvement. For the case when SCKbased selection is used, we derive expressions for coding gain. We also present extensive simulation studies, validating our results. Index Terms—Antenna subset selection, MIMO, spacetime coding.
Transceiver optimization for multiuser MIMO systems
 IEEE Tran. on Signal Processing, 52(1):214 – 226
, 2004
"... Abstract—We consider the uplink of a multiuser system where the transmitters as well as the receiver are equipped with multiple antennas. Each user multiplexes its symbols by a linear precoder through its transmit antennas. We work with the systemwide mean squared error as the performance measure a ..."
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Cited by 66 (10 self)
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Abstract—We consider the uplink of a multiuser system where the transmitters as well as the receiver are equipped with multiple antennas. Each user multiplexes its symbols by a linear precoder through its transmit antennas. We work with the systemwide mean squared error as the performance measure and propose algorithms to find the jointly optimum linear precoders at each transmitter and linear decoders at the receiver. We first work with the case where the number of symbols to be transmitted by each user is given. We then investigate how the symbol rate should be chosen for each user with optimum transmitters and receivers. The convergence analysis of the algorithms is given, and numerical evidence that supports the analysis is presented. Index Terms—MMSE receivers, multiuser MIMO system, receiver beamforming, transmitter beamforming.
Multimode precoding for MIMO wireless systems
 IEEE TRANS. SIGNAL PROCESSING
, 2005
"... Multipleinput multipleoutput (MIMO) wireless systems obtain large diversity and capacity gains by employing multielement antenna arrays at both the transmitter and receiver. The theoretical performance benefits of MIMO systems, however, are irrelevant unless low error rate, spectrally efficient si ..."
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Cited by 33 (4 self)
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Multipleinput multipleoutput (MIMO) wireless systems obtain large diversity and capacity gains by employing multielement antenna arrays at both the transmitter and receiver. The theoretical performance benefits of MIMO systems, however, are irrelevant unless low error rate, spectrally efficient signaling techniques are found. This paper proposes a new method for designing high datarate spatial signals with low error rates. The basic idea is to use transmitter channel information to adaptively vary the transmission scheme for a fixed data rate. This adaptation is done by varying the number of substreams and the rate of each substream in a precoded spatial multiplexing system. We show that these substreams can be designed to obtain full diversity and full rate gain using feedback from the receiver to transmitter. We model the feedback using a limited feedback scenario where only finite sets, or codebooks, of possible precoding configurations are known to both the transmitter and receiver. Monte Carlo simulations show substantial performance gains over beamforming and spatial multiplexing.
Antenna selection for spatial multiplexing with linear receivers
 IEEE Trans. Signal Processing
, 2001
"... Spatial multiplexing is a simple transmission technique for multipleinput multipleoutput (MIMO) wireless communication links in which data is multiplexed across multiple transmit antennas. Spatial multiplexing with low complexity linear receivers, however, suffers due to a lack of diversity advanta ..."
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Cited by 32 (3 self)
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Spatial multiplexing is a simple transmission technique for multipleinput multipleoutput (MIMO) wireless communication links in which data is multiplexed across multiple transmit antennas. Spatial multiplexing with low complexity linear receivers, however, suffers due to a lack of diversity advantage in Rayleigh fading channels. This paper proposes multimode antenna selection which uses a lowrate feedback channel to improve the error rate performance of spatial multiplexing systems with linear receivers. In the proposed technique, for a fixed total data rate, both the number of substreams and the antenna subset used for transmission are dynamically adjusted to the channel using a limited number of feedback bits sent from the receiver. Using multimode selection effectively allowing any number of substreams to be dynamically selected provides additional array gain over standard transmit diversity. Various criteria for selecting the number of substreams and the optimal antenna subset of transmit antennas are derived. Relationships are made between the selection criteria and the eigenmodes of the channel. Monte Carlo simulations demonstrate significant performance improvements in i.i.d., flatfading Rayleigh matrix channels with minimal feedback. 1
Reducedcomplexity transmit/receivediversity systems
 in Proc. IEEE Vehicular Technology Conf. Spring 2001
"... We consider wireless systems with transmit and receive diversity. For reduction of complexity, we propose to use hybrid selection/maximal ratio transmission at one link end, choosing L out of N antennas. We snslyze the performance of such systems, giving analytical bounds and comparing them to compu ..."
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Cited by 29 (15 self)
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We consider wireless systems with transmit and receive diversity. For reduction of complexity, we propose to use hybrid selection/maximal ratio transmission at one link end, choosing L out of N antennas. We snslyze the performance of such systems, giving analytical bounds and comparing them to computer simulations. Outage probability, symbol error probability, and capacity are shown. We domonstrate that in typical cases, a small number of used antennas L is sufficient to achieve considerable performance gains.
VariablePhaseShiftBased RFBaseband Codesign for MIMO Antenna Selection,” submitted to
 IEEE Trans. Sig. Proc
"... We introduce a novel soft antenna selection approach for multiple antenna systems through a joint design fo both RF (radio frequency) and baseband signal processing. When only a limited number of frequency converters are available, conventional antenna selection schemes show severe performance degra ..."
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Cited by 22 (3 self)
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We introduce a novel soft antenna selection approach for multiple antenna systems through a joint design fo both RF (radio frequency) and baseband signal processing. When only a limited number of frequency converters are available, conventional antenna selection schemes show severe performance degradation in most fading channels. To alleviate those degradations, we propose to adopt a transformation of the signals in the RF domain that requires only simple, variable phase shifters and combiners to reduce the number of RF chains. The constrained optimum design of those shifters, adapting to the channel state, is given in analytical form, which requires no search of iterations. The resulting system shows a significant performance advantage for both correlated and uncorrelated channels. The technique works for both transmitter and receiver design, which leads to the joint transceiver antenna selection. When only a signal information stream is transmitted through the channel, the new design can achieve the same SNR gain as the fullcomplexity system while requiring, at most, two RF chains. With multiple information streams transmitted, it is demonstrated by computer experiments that the capacity performance is close to optimum.
Feedback Assisted Transmission Subspace Tracking for MIMO Systems
 IEEE JSAC
, 2003
"... Abstract—This paper describes a feedback assisted stochastic gradient algorithm for transmission tracking of the dominant channel subspaces for multipleinput–multipleoutput (MIMO) communications systems. Subspace tracking is introduced as a means of tracking multiple transmission weights, being th ..."
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Cited by 19 (1 self)
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Abstract—This paper describes a feedback assisted stochastic gradient algorithm for transmission tracking of the dominant channel subspaces for multipleinput–multipleoutput (MIMO) communications systems. Subspace tracking is introduced as a means of tracking multiple transmission weights, being the MIMO generalization of beam steering in the familiar multipleinput–singleoutput case. The subspace solution approximates that of water filling (WF) in some cases, without the complete rate/power allocation required by WF. The gain of subspace tracking in low rank systems is demonstrated, particularly, in the case where the number of transmit antennas exceeds the number of receive antennas. Simulations of ergodic capacity show the utility of both subspace tracking in general and of the specific adaptation algorithm, and simulations of frameerror rates show the utility in a specific coding example. Index Terms—Adaptive arrays, gradient methods, multipleinput–multipleoutput (MIMO) systems, transmitting antennas. I.
Antenna selection for multipleantenna transmission systems: performance analysis and code construction
 IEEE Trans. Inform. Theory
, 2003
"... Abstract—This correspondence studies antenna selection for wireless communications systems that employ multiple transmit and receive antennas. We assume that 1) the channel is characterized by quasistatic Rayleigh flat fading, and the subchannels fade independently, 2) the channel state information ..."
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Cited by 18 (0 self)
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Abstract—This correspondence studies antenna selection for wireless communications systems that employ multiple transmit and receive antennas. We assume that 1) the channel is characterized by quasistatic Rayleigh flat fading, and the subchannels fade independently, 2) the channel state information (CSI) is exactly known at the receiver, 3) the selection is available only at the receiver, and it is based on the instantaneous signaltonoise ratio (SNR) at each receive antenna, and 4) space–time codes are used at the transmitter. We analyze the performance of such systems by deriving explicit upper bounds on the pairwise error probability (PEP). This performance analysis shows that 1) by selecting the set of antennas that observe the largest instantaneous SNR, one can achieve the same diversity gain as the one obtained by using all the receive antennas, provided that the underlying space–time code has full spatial diversity, and 2) in the case of rankdeficient space–time codes, the diversity gain may be dramatically reduced when antenna selection is used. However, we emphasize that in both cases the coding gain is reduced with antenna selection compared to the full complexity system. Based on the upper bounds derived, we describe code design principles suitable for antenna selection. Specifically, for systems with two transmit antennas, we design space–time codes that perform better than the known ones when antenna selection is employed. Finally, we present numerical examples and simulation results that validate our analysis and code design principles. Index Terms—Antenna selection, diversity, multipleinput multipleoutput (MIMO) systems, multipleantenna communications, pairwise error probability (PEP), space–time coding, wireless communications. I.