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165
Variablerate variablepower MQAM for fading channels
 IEEE Transactions on Communications
, 1997
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Capacity bounds and power allocation for wireless relay channels
 IEEE TRANS. INF. THEORY
, 2005
"... We consider threenode wireless relay channels in a Rayleighfading environment. Assuming transmitter channel state information (CSI), we study upper bounds and lower bounds on the outage capacity and the ergodic capacity. Our studies take into account practical constraints on the transmission/rece ..."
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Cited by 317 (6 self)
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We consider threenode wireless relay channels in a Rayleighfading environment. Assuming transmitter channel state information (CSI), we study upper bounds and lower bounds on the outage capacity and the ergodic capacity. Our studies take into account practical constraints on the transmission/reception duplexing at the relay node and on the synchronization between the source node and the relay node. We also explore power allocation. Compared to the direct transmission and traditional multihop protocols, our results reveal that optimum relay channel signaling can significantly outperform multihop protocols, and that power allocation has a significant impact on the performance.
Adaptive Modulation over Nakagami Fading Channels
, 1998
"... We first study the capacity of Nakagami multipath fading (NMF) channels with an average power constraint for three power and rate adaptation policies. We obtain closedform solutions for NMF channel capacity for each power and rate adaptation strategy. Results show that rate adaptation is the key to ..."
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Cited by 145 (17 self)
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We first study the capacity of Nakagami multipath fading (NMF) channels with an average power constraint for three power and rate adaptation policies. We obtain closedform solutions for NMF channel capacity for each power and rate adaptation strategy. Results show that rate adaptation is the key to increasing link spectral efficiency. We analyze therefore the performance of constantpower variablerate MQAM schemes over NMF channels. We obtain closedform expressions for the outage probability, spectral efficiency and average biterrorrate (BER) assuming perfect channel estimation and negligible time delay. We also analyze the impact of time delay on the BER of adaptive MQAM. Keywords Link Spectral Efficiency, Adaptive Modulation Techniques, and Nakagami Fading. I. Introduction The radio spectrum available for wireless services is extremely scarce, while demand for these services is growing at a rapid pace [1]. Hence spectral efficiency is of primary concern in the design of fut...
Multiuser MIMO Achievable Rates with Downlink Training and Channel State Feedback
"... We consider a MIMO fading broadcast channel and compute achievable ergodic rates when channel state information is acquired at the receivers via downlink training and it is provided to the transmitter by channel state feedback. Unquantized (analog) and quantized (digital) channel state feedback sche ..."
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Cited by 111 (7 self)
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We consider a MIMO fading broadcast channel and compute achievable ergodic rates when channel state information is acquired at the receivers via downlink training and it is provided to the transmitter by channel state feedback. Unquantized (analog) and quantized (digital) channel state feedback schemes are analyzed and compared under various assumptions. Digital feedback is shown to be potentially superior when the feedback channel uses per channel state coefficient is larger than 1. Also, we show that by proper design of the digital feedback link, errors in the feedback have a minor effect even if simple uncoded modulation is used on the feedback channel. We discuss first the case of an unfaded AWGN feedback channel with orthogonal access and then the case of fading MIMO multiaccess (MIMOMAC). We show that by exploiting the MIMOMAC nature of the uplink channel, a much better scaling of the feedback channel resource with the number of base station antennas can be achieved. Finally, for the case of delayed feedback, we show that in the realistic case where the fading process has (normalized) maximum Doppler frequency shift 0 ≤ F < 1/2, a fraction 1 − 2F of the optimal multiplexing gain is achievable. The general conclusion of this work is that very significant downlink throughput is achievable with simple and efficient channel state feedback, provided that the feedback link is properly designed.
Diagonal Algebraic SpaceTime Block Codes
 IEEE Trans. Inform. Theory
"... We construct a new family of linear spacetime block codes by the combination of rotated constellations and the Hadamard transform, and we prove them to achieve the full transmit diversity over a quasistatic or fast fading channels. The proposed codes transmit at a normalized rate of 1 symbol/sec. ..."
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Cited by 103 (7 self)
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We construct a new family of linear spacetime block codes by the combination of rotated constellations and the Hadamard transform, and we prove them to achieve the full transmit diversity over a quasistatic 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 spacetime 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 multiantenna system yields good performances with high spectral efficiency and moderate decoding complexity.
Optimum power allocation for parallel Gaussian channels with arbitrary input distributions
 IEEE TRANS. INF. THEORY
, 2006
"... The mutual information of independent parallel Gaussiannoise channels is maximized, under an average power constraint, by independent Gaussian inputs whose power is allocated according to the waterfilling policy. In practice, discrete signaling constellations with limited peaktoaverage ratios (m ..."
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Cited by 94 (10 self)
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The mutual information of independent parallel Gaussiannoise channels is maximized, under an average power constraint, by independent Gaussian inputs whose power is allocated according to the waterfilling policy. In practice, discrete signaling constellations with limited peaktoaverage ratios (mPSK, mQAM, etc.) are used in lieu of the ideal Gaussian signals. This paper gives the power allocation policy that maximizes the mutual information over parallel channels with arbitrary input distributions. Such policy admits a graphical interpretation, referred to as mercury/waterfilling, which generalizes the waterfilling solution and allows retaining some of its intuition. The relationship between mutual information of Gaussian channels and nonlinear minimum meansquare error (MMSE) proves key to solving the power allocation problem.
Long Range Prediction of Fading Signals: Enabling Adaptive Transmission for Mobile Radio Channels
 IEEE SIGNAL PROCESSING MAGAZINE
, 2000
"... Recently it was proposed to adapt several transmission methods, including modulation, power control, channel coding and antenna diversity to rapidly time variant fading channel conditions. Prediction of the channel coefficients several tenstohundreds of symbols ahead is essential to realize these ..."
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Cited by 38 (3 self)
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Recently it was proposed to adapt several transmission methods, including modulation, power control, channel coding and antenna diversity to rapidly time variant fading channel conditions. Prediction of the channel coefficients several tenstohundreds of symbols ahead is essential to realize these methods in practice. We describe a novel adaptive long range fading channel prediction algorithm (LRP) and its utilization with adaptive transmission methods. This channel prediction algorithm computes the linear Minimum Mean Squared Error (MMSE) estimates of future fading coefficients based on past observations. This algorithm can forecast fading signals far into the future due to its significant memory span, achieved by using a sufficiently low sampling rate for a given fixed filter size. The LRP is validated for standard stationary fading models, and tested with measured data and with data produced by our novel realistic physical channel model. This model accounts for the variation of the amplitude, frequency and phase of each reflected component of the fading signal. Both numerical and simulation results show that long range prediction makes adaptive transmission techniques feasible for mobile radio channels.
Performance of HybridARQ in BlockFading Channels: A Fixed Outage Probability Analysis
"... This paper studies the performance of hybridARQ (automatic repeat request) in Rayleigh blockfading channels in a setting where rate is increased with the average SNR such that a constant outage probability is maintained. HARQ allows for early termination of transmission once the receiver is able t ..."
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Cited by 30 (2 self)
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This paper studies the performance of hybridARQ (automatic repeat request) in Rayleigh blockfading channels in a setting where rate is increased with the average SNR such that a constant outage probability is maintained. HARQ allows for early termination of transmission once the receiver is able to successfully decode, and thus provides an advantage over systems without HARQ. It is shown that HARQ allows the average transmission rate to very quickly approach the ergodic capacity of the fading channel as the maximum number of fading blocks per codeword (which is proportional to the speed of temporal fading) increases, whereas this convergence is much slower without HARQ. Furthermore, although HARQ does not provide an advantage in terms of wellknown highSNR metrics (multiplexing gain and highSNR offset), it is seen to provide a significant advantage throughout the range of practically relevant SNR’s. In addition, incremental redundancy is shown to outperform lowercomplexity Chase combining, particularly at moderate and high SNR’s. I.
Coding versus ARQ in fading channels: how reliable should the PHY be?,” GLOBECOM’09
, 2009
"... Abstract—This paper studies the tradeoff between channel coding and ARQ (automatic repeat request) in Rayleigh blockfading channels. A heavily coded system corresponds to a low transmission rate with few ARQ retransmissions, whereas lighter coding corresponds to a higher transmitted rate but more re ..."
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Cited by 29 (6 self)
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Abstract—This paper studies the tradeoff between channel coding and ARQ (automatic repeat request) in Rayleigh blockfading channels. A heavily coded system corresponds to a low transmission rate with few ARQ retransmissions, whereas lighter coding corresponds to a higher transmitted rate but more retransmissions. The optimum error probability, where optimum refers to the operating point that maximizes the average successful throughput, is derived and is shown to be a decreasing function of the average signaltonoise ratio and of the channel diversity order. A general conclusion of the work is that the optimum error probability is quite large (e.g., 10 % or larger) for reasonable channel parameters, and that operating at a very small error probability can lead to a significantly reduced throughput. I.
Multimode transmission for the MIMO broadcast channel with imperfect channel state information
 IEEE Transactions on Communications
"... This paper proposes a multimode transmission strategy to improve the spectral efficiency achieved by the multipleinput multipleoutput (MIMO) broadcast channel with delayed and quantized channel state information. It adaptively adjusts the number of active users, denoted as the transmission mode, ..."
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Cited by 26 (11 self)
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This paper proposes a multimode transmission strategy to improve the spectral efficiency achieved by the multipleinput multipleoutput (MIMO) broadcast channel with delayed and quantized channel state information. It adaptively adjusts the number of active users, denoted as the transmission mode, to balance transmit array gain, spatial division multiplexing gain, and residual interuser interference. Accurate closedform approximations are derived for the achievable rates for different modes, which are used to select the active mode that maximizes the ergodic throughput. User scheduling algorithms based on multimode transmission are then proposed for the network with a large number of users, to reduce the overall amount of feedback. It is shown that the proposed algorithms provide throughput gains at moderate yet practically relevant signaltonoise ratio. Index Terms MIMO systems, space division multiplexing, broadcast channels, scheduling, feedback, delay effects, adaptive systems. I.