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15
Achieving a vanishing SNRgap to exact lattice decoding at a subexponential complexity
, 2012
"... Abstract—The work identifies the first lattice decoding solution that achieves, in the general outagelimited MIMO setting and in the highrate and highSNR limit, both a vanishing gap to the errorperformance of the (DMT optimal) exact solution of preprocessed lattice decoding, as well as a computa ..."
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Abstract—The work identifies the first lattice decoding solution that achieves, in the general outagelimited MIMO setting and in the highrate and highSNR limit, both a vanishing gap to the errorperformance of the (DMT optimal) exact solution of preprocessed lattice decoding, as well as a computational complexity that is subexponential in the number of codeword bits. The proposed solution employs lattice reduction (LR)aided regularized (lattice) sphere decoding and proper timeout policies. These performance and complexity guarantees hold for most MIMO scenarios, all reasonable fading statistics, all channel dimensions and all fullrate lattice codes. In sharp contrast to the above very manageable complexity, the complexity of other standard preprocessed lattice decoding solutions is revealed here to be extremely high. Specifically the work is first to quantify the complexity of these lattice (sphere) decoding solutions and to prove the surprising result that the complexity required to achieve a certain ratereliability performance, is exponential in the lattice dimensionality and in the number of codeword bits, and it in fact matches, in common scenarios, the complexity of MLbased solutions. Through this sharp contrast, the work was able to, for the first time, rigorously demonstrate and quantify the pivotal role of lattice reduction as a special complexity reducing ingredient. Finally the work analytically refines transceiver DMT analysis which generally fails to address potentially massive gaps between theory and practice. Instead the adopted vanishing gap condition guarantees that the decoder’s error curve is arbitrarily close, given a sufficiently high SNR, to the optimal error curve of exact solutions, which is a much stronger condition than DMT optimality which only guarantees an error gap that is subpolynomial in SNR, and can thus be unbounded and generally unacceptable for practical implementations. I.
Optimum Power and Rate Allocation for Coded VBLAST
, 902
"... Abstract—An analytical framework for minimizing the outage probability of a coded spatial multiplexing system while keeping the rate close to the capacity is developed. Based on this framework, specific strategies of optimum power and rate allocation for the coded VBLAST architecture are obtained a ..."
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Abstract—An analytical framework for minimizing the outage probability of a coded spatial multiplexing system while keeping the rate close to the capacity is developed. Based on this framework, specific strategies of optimum power and rate allocation for the coded VBLAST architecture are obtained and its performance is analyzed. A fractional waterfilling algorithm, which is shown to optimize both the capacity and the outage probability of the coded VBLAST, is proposed. Compact, closedform expressions for the optimum allocation of the average power are given. The uniform allocation of average power is shown to be near optimum at moderate to high SNR for the coded VBLAST with the average rate allocation (when perstream rates are set to match the perstream capacity). The results reported also apply to multiuser detection and channel equalization relying on successive interference cancelation. Index Terms—Multiantenna (MIMO) system, spatial multiplexing, coded VBLAST, power/rate allocation, waterfilling, performance analysis I.
From MultiKeyholes to Measure of Correlation and Power Imbalance in MIMO Channels: Outage Capacity Analysis
, 2008
"... An informationtheoretic analysis of a multikeyhole channel, which includes a number of statistically independent keyholes with possibly different correlation matrices, is given. When the number of keyholes or/and the number of Tx/Rx antennas is large, there is an equivalent Rayleighfading channe ..."
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Cited by 3 (0 self)
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An informationtheoretic analysis of a multikeyhole channel, which includes a number of statistically independent keyholes with possibly different correlation matrices, is given. When the number of keyholes or/and the number of Tx/Rx antennas is large, there is an equivalent Rayleighfading channel such that the outage capacities of both channels are asymptotically equal. In the case of a large number of antennas and for a broad class of fading distributions, the instantaneous capacity is shown to be asymptotically Gaussian in distribution, and compact, closedform expressions for the mean and variance are given. Motivated by the asymptotic analysis, a simple, fullordering scalar measure of spatial correlation and power imbalance in MIMO channels is introduced, which quantifies the negative impact of these two factors on the outage capacity in a simple and welltractable way. It does not require the eigenvalue decomposition, and has the fullordering property. The sizeasymptotic results are used to prove Telatar’s conjecture for semicorrelated multikeyhole and Rayleigh channels. Since the keyhole channel model approximates well the relay channel in the amplifyandforward mode, these results also apply to the latter.
On Outage Probability and DiversityMultiplexing Tradeoff in MIMO Relay Channels
"... Abstract—Fading MIMO relay channels are studied analytically, when the source and destination are equipped with multiple antennas and the relays have a single one. Compact closedform expressions are obtained for the outage probability under i.i.d. and correlated Rayleighfading links. Lowoutage ap ..."
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Abstract—Fading MIMO relay channels are studied analytically, when the source and destination are equipped with multiple antennas and the relays have a single one. Compact closedform expressions are obtained for the outage probability under i.i.d. and correlated Rayleighfading links. Lowoutage approximations are derived, which reveal a number of insights, including the impact of correlation, of the number of antennas, of relay noise and of relaying protocol. The effect of correlation is shown to be negligible, unless the channel becomes almost fully correlated. The SNR loss of relay fading channels compared to the AWGN channel is quantified. The SNRasymptotic diversitymultiplexing tradeoff (DMT) is obtained for a broad class of fading distributions, including, as special cases, Rayleigh, Rice, Nakagami, Weibull, which may be nonidentical, spatially correlated and/or nonzero mean. The DMT is shown to depend not on a particular fading distribution, but rather on its polynomial behavior near zero, and is the same for the simple “amplifyandforward" protocol and more complicated “decodeandforward ” one with capacity achieving codes, i.e. the full processing capability at the relay does not help to improve the DMT. There is however a significant difference between the SNRasymptotic DMT and the finiteSNR outage performance: while the former is not improved by using an extra antenna on either side, the latter can be significantly improved and, in particular, an extra antenna can be tradedoff for a full processing capability at the relay. The results are extended to the multirelay channels with selection relaying and typical outage events are identified. Index Terms—MIMO, relay channel, outage probability, channel capacity, diversitymultiplexing tradeoff. I.
DiversityMultiplexing Tradeoff in the LowSNR Regime
"... Abstract—An extension of the popular diversitymultiplexing tradeoff framework to the lowSNR (or wideband) regime is proposed. The concept of diversity gain is shown to be redundant in this regime since the outage probability is SNRindependent and depends on the multiplexing gain and the channel p ..."
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Abstract—An extension of the popular diversitymultiplexing tradeoff framework to the lowSNR (or wideband) regime is proposed. The concept of diversity gain is shown to be redundant in this regime since the outage probability is SNRindependent and depends on the multiplexing gain and the channel power gain statistics only. The outage probability under the DMT framework is obtained in an explicit, closed form for a broad class of channels. The low and highSNR regime boundaries are explicitly determined for the scalar Rayleighfading channel, indicating asignificant limitation of the SNRasymptotic DMT when the multiplexing gain is small. Index Terms—Multiantenna (MIMO) system, diversity multiplexing tradeoff. I.
1Backing off from Infinity: Performance Bounds via Concentration of Spectral Measure for Random MIMO Channels
"... Abstract—The performance analysis of random vector channels, particularly multipleinputmultipleoutput (MIMO) channels, has largely been established in the asymptotic regime of large channel dimensions, due to the analytical intractability of characterizing the exact distribution of the objectiv ..."
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Abstract—The performance analysis of random vector channels, particularly multipleinputmultipleoutput (MIMO) channels, has largely been established in the asymptotic regime of large channel dimensions, due to the analytical intractability of characterizing the exact distribution of the objective performance metrics. This paper exposes a new nonasymptotic framework that allows the characterization of many canonical MIMO system performance metrics to within a narrow interval under moderatetolarge channel dimensionality, provided that these metrics can be expressed as a separable function of the singular values of the matrix. The effectiveness of our framework is illustrated through two canonical examples. Specifically, we characterize the mutual information and power offset of random MIMO channels, as well as the minimum mean squared estimation error of MIMO channel inputs from the channel outputs. Our results lead to simple, informative, and reasonably accurate control of various performance metrics in the finitedimensional regime, as corroborated by the numerical simulations. Our analysis framework is established via the concentration of spectral measure phenomenon for random matrices uncovered by Guionnet and Zeitouni, which arises in a variety of random matrix ensembles irrespective of the precise distributions of the matrix entries. Index Terms—MIMO, massive MIMO, confidence interval, concentration of spectral measure, random matrix theory, nonasymptotic analysis, mutual information, MMSE I.
Chalmers Publication Library Shortpacket communications with multiple antennas ShortPacket Communications over MultipleAntenna RayleighFading Channels
"... AbstractMotivated by the current interest in ultrareliable, lowlatency, machinetype communication systems, we investigate the tradeoff between reliability, throughput, and latency in the transmission of information over multipleantenna Rayleigh blockfading channels. Specifically, we obtain fin ..."
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AbstractMotivated by the current interest in ultrareliable, lowlatency, machinetype communication systems, we investigate the tradeoff between reliability, throughput, and latency in the transmission of information over multipleantenna Rayleigh blockfading channels. Specifically, we obtain finiteblocklength, finiteSNR upper and lower bounds on the maximum coding rate achievable over such channels for a given constraint on the packet error probability. Numerical evidence suggests that our bounds delimit tightly the maximum coding rate already for short blocklengths (packets of about 100 symbols). Furthermore, our bounds reveal the existence of a tradeoff between the rate gain obtainable by spreading each codeword over all available timefrequencyspatial degrees of freedom, and the rate loss caused by the need of estimating the fading coefficients over these degrees of freedom. In particular, our bounds allow us to determine the optimal number of transmit antennas and the optimal number of timefrequency diversity branches that maximize the rate. Finally, we show that infiniteblocklength performance metrics such as the ergodic capacity and the outage capacity yield inaccurate throughput estimates.
AmplifyandForward Versus DecodeandForward Relaying: Which is Better?
"... Abstract—Performance of multihop MIMO relay channels under the amplifyandforward and decodeandforward protocols are compared via the capacity and SNR gains. In an Nhop channel of linear topology with multiantenna source and destination and singleantenna relay nodes, the capacity gain of the ..."
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Abstract—Performance of multihop MIMO relay channels under the amplifyandforward and decodeandforward protocols are compared via the capacity and SNR gains. In an Nhop channel of linear topology with multiantenna source and destination and singleantenna relay nodes, the capacity gain of the DF relaying over the AF one does not exceed log 2 N bit/s/Hz and its SNR gain does not exceed N, for any channel realization. This conclusion also applies to selection relaying, to the outage probability/capacity and the ergodic capacity in an arbitrary blockfading channel, and can be further extended to hybrid relaying. The conditions under which the DF and AF relaying have nearly identical performance are identified. I.
1 Optimum Power and Rate Allocation for Coded VBLAST: Average Optimization
, 1010
"... Abstract—An analytical framework for performance analysis and optimization of coded VBLAST is developed. Average power and/or rate allocations to minimize the outage probability as well as their robustness and dual problems are investigated. Compact, closedform expressions for the optimum allocati ..."
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Abstract—An analytical framework for performance analysis and optimization of coded VBLAST is developed. Average power and/or rate allocations to minimize the outage probability as well as their robustness and dual problems are investigated. Compact, closedform expressions for the optimum allocations and corresponding system performance are given. The uniform power allocation is shown to be near optimum in the low outage regime in combination with the optimum rate allocation. The average rate allocation provides the largest performance improvement (extra diversity gain), and the average power allocation offers a modest SNR gain limited by the number of transmit antennas but does not increase the diversity gain. The dual problems are shown to have the same solutions as the primal ones. All these allocation strategies are shown to be robust. The reported results also apply to coded multiuser detection and channel equalization systems relying on successive interference cancelation. Index Terms—Multiantenna (MIMO) system, spatial multiplexing, coded VBLAST, power/rate allocation, performance analysis I.
Backing Off From Infinity: Performance Bounds via Concentration of Spectral Measure for Random MIMO Channels
"... The performance analysis of random vector channels, particularly multipleinputmultipleoutput (MIMO) channels, has largely been established in the asymptotic regime of large channel dimensions, due to the analytical intractability of characterizing the exact distribution of the objective performa ..."
Abstract
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The performance analysis of random vector channels, particularly multipleinputmultipleoutput (MIMO) channels, has largely been established in the asymptotic regime of large channel dimensions, due to the analytical intractability of characterizing the exact distribution of the objective performance metrics. This paper exposes a new nonasymptotic framework that allows the characterization of many canonical MIMO system performance metrics to within a narrow interval under finite channel dimensionality, provided that these metrics can be expressed as a separable function of the singular values of the matrix. The effectiveness of our framework is illustrated through two canonical examples. In particular, we characterize the mutual information and power offset of random MIMO channels, as well as the minimum mean squared estimation error of MIMO channel inputs from the channel outputs. Our results lead to simple, informative, and reasonably accurate control of various performance metrics in the finitedimensional regime, as corroborated by the numerical simulations. Our analysis framework is established via the concentration of spectral measure phenomenon for random matrices uncovered by Guionnet and Zeitouni, which arises in a variety of random matrix ensembles irrespective of the precise distributions of the matrix entries.