Results 1  10
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56
Spectral Efficiency in the Wideband Regime
, 2002
"... The tradeoff of spectral efficiency (b/s/Hz) versus energy perinformation bit is the key measure of channel capacity in the wideband powerlimited regime. This paper finds the fundamental bandwidthpower tradeoff of a general class of channels in the wideband regime characterized by low, but nonz ..."
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Cited by 283 (29 self)
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The tradeoff of spectral efficiency (b/s/Hz) versus energy perinformation bit is the key measure of channel capacity in the wideband powerlimited regime. This paper finds the fundamental bandwidthpower tradeoff of a general class of channels in the wideband regime characterized by low, but nonzero, spectral efficiency and energy per bit close to the minimum value required for reliable communication. A new criterion for optimality of signaling in the wideband regime is proposed, which, in contrast to the traditional criterion, is meaningful for finitebandwidth communication.
The noncoherent Rician fading channel  Part I : Structure of the capacityachieving input
 IEEE TRANS. WIRELESS COMMUN
, 2005
"... Transmission of information over a discretetime memoryless Rician fading channel is considered, where neither the receiver nor the transmitter knows the fading coefficients. First, the structure of the capacityachieving input signals is investigated when the input is constrained to have limited p ..."
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Cited by 27 (5 self)
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Transmission of information over a discretetime memoryless Rician fading channel is considered, where neither the receiver nor the transmitter knows the fading coefficients. First, the structure of the capacityachieving input signals is investigated when the input is constrained to have limited peakedness by imposing either a fourth moment or a peak constraint. When the input is subject to second and fourth moment limitations, it is shown that the capacityachieving input amplitude distribution is discrete with a finite number of mass points in the lowpower regime. A similar discrete structure for the optimal amplitude is proven over the entire signaltonoise ratio (SNR) range when there is only a peakpower constraint. The Rician fading with the phasenoise channel model, where there is phase uncertainty in the specular component, is analyzed. For this model, it is shown that, with only an average power constraint, the capacityachieving input amplitude is discrete with a finite number of levels. For the classical averagepowerlimited Rician fading channel, it is proven that the optimal input amplitude distribution has bounded support.
Channel coherence in the low SNR regime
 in International Symposium on Information Theory (ISIT). IEEE, JuneJuly 2004
, 2007
"... While capacity in the limit of vanishing SNR per degree of freedom is known to be linear in SNR for fading and nonfading channels, regardless of channel side information at the receiver, such asymptotic results hide the cost of channel variability in terms of performance. In this paper, rather than ..."
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Cited by 25 (5 self)
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While capacity in the limit of vanishing SNR per degree of freedom is known to be linear in SNR for fading and nonfading channels, regardless of channel side information at the receiver, such asymptotic results hide the cost of channel variability in terms of performance. In this paper, rather than maintain a fixed channel model with a given coherence and consider a vanishing SNR, we present a model in which coherence, peak energy and SNR are considered jointly. In particular, we show that channel variability, characterized by coherence, when considered in terms of SNR, determines a sublinear term in SNR which reduces the coherent capacity, itself linear in SNR. We explicitly characterize this sublinear term and show how coherence, when considered jointly with SNR, affects the peakiness required in transmissions. We examine how, by using suboptimal training schemes, we may achieve rates that trail coherent capacity by a sublinear term in SNR. 1
Capacity per Unit Energy of Fading Channels with a Peak Constraint
 IEEE Trans. Inform. Theory
, 2004
"... A discretetime singleuser channel with correlated Rayleigh fading is analyzed. At low SNR, the capacity of such a channel is known to be achieved by input signals with large peak powers. Since such burstiness in the input signal may not be practically feasible, the possibility of such signals i ..."
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Cited by 23 (2 self)
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A discretetime singleuser channel with correlated Rayleigh fading is analyzed. At low SNR, the capacity of such a channel is known to be achieved by input signals with large peak powers. Since such burstiness in the input signal may not be practically feasible, the possibility of such signals is eliminated in the model by imposing a peak power constraint on every input symbol. A simple expression is given for the capacity per unit energy, in the presence of a peak constraint. The proof uses an adaptation of the simple formula of Verdu to a channel with memory. In addition to bounding the capacity of a channel with correlated fading, the result gives some insight into the relationship between the correlation in the fading process and the channel capacity.
The noncoherent Rician fading channel – Part II : Spectral efficiency in the low power regime
 IEEE Trans. Wireless Commun
, 2005
"... Abstract—Transmission of information over a discretetime memoryless Rician fading channel is considered, where neither the receiver nor the transmitter knows the fading coefficients. The spectralefficiency/bitenergy tradeoff in the lowpower regime is examined when the input has limited peakednes ..."
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Cited by 23 (7 self)
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Abstract—Transmission of information over a discretetime memoryless Rician fading channel is considered, where neither the receiver nor the transmitter knows the fading coefficients. The spectralefficiency/bitenergy tradeoff in the lowpower regime is examined when the input has limited peakedness. It is shown that if a fourthmoment input constraint is imposed, or the input peaktoaverage power ratio is limited, then in contrast to the behavior observed in averagepowerlimited channels, the minimum bit energy is not always achieved at zero spectral efficiency. The lowpower performance is also characterized when there is a fixed peak limit that does not vary with the average power. A new signaling scheme that overlays phaseshift keying on ON–OFF keying (OOK) is proposed and shown to be optimally efficient in the lowpower regime. Index Terms—Fading channels, lowpower regime, memoryless fading, peak constraints, Rician fading, spectral efficiency. I.
Channel uncertainty in ultra wideband communication systems
 IEEE Transactions on Information Theory
, 2005
"... Abstract—Channel uncertainty limits the achievable data rates of certain ultrawideband systems due to the need to estimate the channel. The use of bursty dutycycled transmission reduces the channel uncertainty because the receiver has to estimate the channel only when transmission takes place, but ..."
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Cited by 14 (8 self)
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Abstract—Channel uncertainty limits the achievable data rates of certain ultrawideband systems due to the need to estimate the channel. The use of bursty dutycycled transmission reduces the channel uncertainty because the receiver has to estimate the channel only when transmission takes place, but the maximum amount of burstiness and hence the possible reduction of channel uncertainty both depend on the spectral efficiency of the modulation scheme used. This general principle is demonstrated by comparing the channel conditions that allow dutycycled directsequence spread spectrum (DSSS) and pulse position modulation (PPM) to achieve the additive white Gaussian noise (AWGN) channel capacity in the wideband limit. We show that dutycycled DSSS systems achieve the wideband capacity as long as the number of independently faded resolvable paths increases sublinearly with the bandwidth, while dutycycled PPM systems can achieve the wideband capacity only if the number of paths increases sublogarithmically. The difference is due to the fact that DSSS is spectrally more efficient than PPM and hence allows more bursty transmission. Index Terms—Channel uncertainty, direct sequence spread spectrum, flash signaling, pulse position modulation (PPM), spectral efficiency, wideband communications. I.
A LowCost TimeHopping Impulse Radio System for High Data Rate Transmission
 EURASIP Journal on Applied Signal Processing, JASP
, 2003
"... We present an efficient, lowcost implementation of timehopping impulse radio that fulfills the spectral mask mandated by the FCC and is suitable for highdatarate, shortrange communications. Key features are: (i) allbaseband implementation that obviates the need for local oscillators and other ..."
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Cited by 9 (5 self)
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We present an efficient, lowcost implementation of timehopping impulse radio that fulfills the spectral mask mandated by the FCC and is suitable for highdatarate, shortrange communications. Key features are: (i) allbaseband implementation that obviates the need for local oscillators and other passband components, (ii) symbolrate (not chip rate) sampling, A/D conversion, and digital signal processing, (iii) fast acquisition due to novel search algorithms, (iv) spectral shaping that can be adapted to accommodate different spectrum regulations and interference environments. Computer simulations show that this system can provide 110Mbit/s at 710m distance, as well as higher data rates at shorter distances under FCC emissions limits. Due to the spreading concept of timehopping impulse radio, the system can sustain multiple simultaneous users, and can suppress narrowband interference effectively.
Noncoherent Capacity of Underspread Fading Channels
, 2008
"... We derive bounds on the noncoherent capacity of widesense stationary uncorrelated scattering (WSSUS) channels that are selective both in time and frequency, and are underspread, i.e., the product of the channel’s delay spread and Doppler spread is small. For input signals that are peak constrained ..."
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Cited by 8 (2 self)
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We derive bounds on the noncoherent capacity of widesense stationary uncorrelated scattering (WSSUS) channels that are selective both in time and frequency, and are underspread, i.e., the product of the channel’s delay spread and Doppler spread is small. For input signals that are peak constrained in time and frequency, we obtain upper and lower bounds on capacity that are explicit in the channel’s scattering function, are accurate for a large range of bandwidth and allow to coarsely identify the capacityoptimal bandwidth as a function of the peak power and the channel’s scattering function. We also obtain a closedform expression for the firstorder Taylor series expansion of capacity in the limit of large bandwidth, and show that our bounds are tight in the wideband regime. For input signals that are peak constrained in time only (and, hence, allowed to be peaky in frequency), we provide upper and lower bounds on the infinitebandwidth capacity and find cases when the bounds coincide and the infinitebandwidth capacity is characterized exactly. Our lower bound is closely related to a result by Viterbi (1967). The analysis in this paper is based on a discretetime discretefrequency approximation of WSSUS time and frequencyselective channels. This discretization explicitly takes into account the underspread
Low SNR Capacity of Fading Channels with Peak and Average Power Constraints
, 2006
"... Flatfading channels that are correlated in time are considered under peak and average power constraints. For discretetime channels, a new upper bound on the capacity per unit time is derived. A low SNR analysis of a fullscattering vector channel is used to derive a complimentary lower bound. Toge ..."
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Cited by 7 (3 self)
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Flatfading channels that are correlated in time are considered under peak and average power constraints. For discretetime channels, a new upper bound on the capacity per unit time is derived. A low SNR analysis of a fullscattering vector channel is used to derive a complimentary lower bound. Together, these bounds allow us to identify the exact scaling of channel capacity for a fixed peak to average ratio, as the average power converges to zero. The upper bound is also asymptotically tight as the average power converges to zero for a fixed peak power. For a continuous time infinite bandwidth channel, Viterbi identified the capacity for MFSK modulation. Recently, Zhang and Laneman showed that the capacity can be achieved with nonbursty signaling (QPSK). An additional contribution of this paper is to obtain similar results under peak and average power constraints.