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32
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.
SpaceTime Wireless Systems: From Array Processing to MIMO Communications,
, 2006
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Joint noncoherent demodulation and decoding for the block fading channel: a practical framework for approaching Shannon capacity
 IEEE Transactions on Communications
, 2003
"... Abstract—This paper contains a systematic investigation of practical coding strategies for noncoherent communication over fading channels, guided by explicit comparisons with informationtheoretic benchmarks. Noncoherent reception is interpreted as joint data and channel estimation, assuming that th ..."
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Cited by 30 (10 self)
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Abstract—This paper contains a systematic investigation of practical coding strategies for noncoherent communication over fading channels, guided by explicit comparisons with informationtheoretic benchmarks. Noncoherent reception is interpreted as joint data and channel estimation, assuming that the channel is time varying and a priori unknown. We consider iterative decoding for a serial concatenation of a standard binary outer channel code with an inner modulation code amenable to noncoherent detection. For an information rate of about 1/2 bit per channel use, the proposed scheme, using a quaternary phaseshift keying (QPSK) alphabet, provides performance within 1.6–1.7 dB of Shannon capacity for the block fading channel, and is about 2.5–3 dB superior to standard differential demodulation in conjunction with an outer channel code. We also provide capacity computations for noncoherent communication using standard phaseshift keying (PSK) and quadrature amplitude modulation (QAM) alphabets, comparing these with the capacity with unconstrained input provides guidance as to the choice of constellation as a function of the signaltonoise ratio. These results imply that QPSK suffices to approach the unconstrained capacity for the relatively low information and fading rates considered in our performance evaluations, but that QAM is superior to PSK for higher information or fading rates, motivating further research into efficient noncoherent coded modulation with QAM alphabets. Index Terms—Capacity, coding, fading channels, noncoherent detection, wireless communications. I.
Signal Design and Convolutional Coding for Noncoherent SpaceTime Communication on the BlockRayleighFading Channel
 IEEE TRANS. INFORM. THEORY
, 2002
"... We consider the problem of designing signal constellations for the multiple transmitmultiple receive antenna Rayleighfading communication channel, when neither the transmitter nor the receiver know the fading. In particular, by employing the asymptotic union bound (AUB) on the probability of error ..."
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Cited by 22 (4 self)
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We consider the problem of designing signal constellations for the multiple transmitmultiple receive antenna Rayleighfading communication channel, when neither the transmitter nor the receiver know the fading. In particular, by employing the asymptotic union bound (AUB) on the probability of error, we give a new formulation of the problem of signal design for the noncoherent fading channel. Since unitary signals are optimal for this channel (in the limit of large signaltonoise ratios SNRs), the problem can be posed in terms of packings on the Grassmanian manifold. A key difference in our approach from that of other authors is that we use a notion of distance on this manifold that is suggested by the union bound. As a consequence of our use of this distance measure, we obtain signal designs that are guaranteed to achieve the full diversity order of the channel, a result that does not hold when the chordal distance is used. We introduce a new method of recursively designing signals, termed successive updates, to approximately optimize this performance measure. We then examine the use of our signals with several convolutional codes over the fading channel. An upper bound on the bit error probability of the maximumlikelihood decoder is presented together with an asymptotic analysis of that bound.
Joint data detection and channel estimation for OFDM systems
 IEEE Trans. Commun
, 2006
"... Abstract—We develop new blind and semiblind data detectors and channel estimators for orthogonal frequencydivision multiplexing (OFDM) systems. Our data detectors require minimizing a complex, integer quadratic form in the data vector. The semiblind detector uses both channel correlation and no ..."
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Cited by 12 (2 self)
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Abstract—We develop new blind and semiblind data detectors and channel estimators for orthogonal frequencydivision multiplexing (OFDM) systems. Our data detectors require minimizing a complex, integer quadratic form in the data vector. The semiblind detector uses both channel correlation and noise variance. The quadratic for the blind detector suffers from rank deficiency; for this, we give a lowcomplexity solution. Avoiding a computationally prohibitive exhaustive search, we solve our data detectors using sphere decoding (SD) and VBLAST and provide simple adaptations of the SD algorithm. We consider how the blind detector performs under mismatch, generalize the basic data detectors to nonunitary constellations, and extend them to systems with pilots and virtual carriers. Simulations show that our data detectors perform well. Index Terms—Channel estimation, orthogonal frequencydivision multiplexing (OFDM), sphere decoding (SD). I.
MultiGigabit Communication: the ADC Bottleneck 1
"... Abstract—The economies of scale in modern communication systems are enabled by architectures that take advantage of Moore’s law to implement most transceiver functionalities in digital signal processing (DSP). The bottleneck in scaling such “mostly digital ” architectures to multiGigabit rates beco ..."
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Cited by 11 (3 self)
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Abstract—The economies of scale in modern communication systems are enabled by architectures that take advantage of Moore’s law to implement most transceiver functionalities in digital signal processing (DSP). The bottleneck in scaling such “mostly digital ” architectures to multiGigabit rates becomes the analogtodigital converter (ADC): highspeed, highprecision ADCs are either not available, or are too costly and powerhungry. In this paper, we report on recent results on two approaches towards addressing this bottleneck. The first is to simply use drastically lowprecision (14 bit) ADCs than current practice. This could be suitable for applications that require limited dynamic range (e.g., lineofsight communication using small constellations), but there are fundamental and algorithmic questions as to whether all the functions of a communication receiver can be realized with such a significant nonlinearity early in the processing. The second is to use a timeinterleaved ADC, where a large number of lowspeed, highprecision ADCs are employed in parallel to realize a highspeed, highprecision ADC. This is more generally applicable to applications requiring large dynamic range (e.g., large constellations and/or dispersive channels), but the important question is how to effectively address the mismatch between the component ADCs, which leads to a performance floor if left uncompensated. I.
Capacity and Coding for the BlockIndependent Noncoherent AWGN Channel
 IEEE TRANSACTIONS ON INFORMATION THEORY
, 2005
"... Communication over the noncoherent additive white Gaussian noise channel is considered, where the transmitted signal undergoes a phase rotation, unknown to the transmitter and the receiver. The effects of phase dynamics are explicitly taken into account by considering a blockindependent model fo ..."
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Cited by 10 (0 self)
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Communication over the noncoherent additive white Gaussian noise channel is considered, where the transmitted signal undergoes a phase rotation, unknown to the transmitter and the receiver. The effects of phase dynamics are explicitly taken into account by considering a blockindependent model for the phase process: the unknown phase is constant for a block of N complex symbols and independent from block to block. In the first
Joint frequency offset and channel estimation for OFDM systems using pilot symbols and virtual carriers
 IEEE Transactions on Wireless Communications
, 2007
"... Abstract — We consider the joint carrier frequency offset (CFO) and channel estimation for OFDM systems. A novel frequency offset estimator is derived based on maximum likelihood principles by using the pilot symbols embedded in each OFDM symbol. An iterative joint CFO and channel estimator is propo ..."
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Cited by 9 (1 self)
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Abstract — We consider the joint carrier frequency offset (CFO) and channel estimation for OFDM systems. A novel frequency offset estimator is derived based on maximum likelihood principles by using the pilot symbols embedded in each OFDM symbol. An iterative joint CFO and channel estimator is proposed to further reduce the estimation error and improve the system performance. The joint estimator is initialized with the first CFO estimate and linearly interpolated channel estimates. The CFO and channel response estimates are updated by maximum likelihood (ML) and least squares (LS) algorithms. Simulation results show that the proposed joint estimator is effective and can achieve excellent bit error rates in just one iteration.
QAM and PSK codebooks for limited feedback MIMO beamforming
 IEEE Trans. on Commun
, 2009
"... This paper considers the problem of beamforming in multipleinput multipleoutput (MIMO) wireless systems. Assuming perfect channel state information at the receiver, the choice of the beamforming vector is made possible through a noiseless limitedrate feedback to the transmitter. This paper propos ..."
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Cited by 8 (1 self)
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This paper considers the problem of beamforming in multipleinput multipleoutput (MIMO) wireless systems. Assuming perfect channel state information at the receiver, the choice of the beamforming vector is made possible through a noiseless limitedrate feedback to the transmitter. This paper proposes the use of beamforming codebooks based on quadrature amplitude modulation (QAM) and phaseshift keying (PSK) constellations, which essentially eliminates the need for storage of the codebook. We show that such codebooks perform arbitrarily close to the perfect feedback case as the constellation size increases, and that full diversity order is achieved. We demonstrate an equivalence between the beamforming codebook search problem with that of noncoherent sequence detection. Based on this we propose fast beamforming vector search algorithms. MonteCarlo simulations are presented to show that the performance is comparable to the best known codebooks, and that the search complexity can be reduced by several orders of magnitude.
On Block Noncoherent Communication with LowPrecision Phase Quantization at the Receiver
, 905
"... Abstract—We consider communication over the block noncoherent AWGN channel with lowprecision AnalogtoDigital Converters (ADCs) at the receiver. For standard uniform Phase Shift Keying (PSK) modulation, we investigate the performance of a receiver architecture that quantizes only the phase of the ..."
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Cited by 6 (6 self)
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Abstract—We consider communication over the block noncoherent AWGN channel with lowprecision AnalogtoDigital Converters (ADCs) at the receiver. For standard uniform Phase Shift Keying (PSK) modulation, we investigate the performance of a receiver architecture that quantizes only the phase of the received signal; this has the advantage of being implementable without automatic gain control, using multiple 1bit ADCs preceded by analog multipliers. We study the structure of the transition density of the resulting channel model. Several results, based on the symmetry inherent in the channel, are provided to characterize this transition density. A low complexity procedure for computing the channel capacity is obtained using these results. Numerical capacity computations for QPSK show that 8bin phase quantization of the received signal recovers more than 8085 % of the capacity attained with unquantized observations, while 12bin phase quantization recovers above 9095 % of the unquantized capacity. Dithering the constellation is shown to improve the performance in the face of drastic quantization. I.