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57
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 393 (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.
Iterative Waterfilling for Gaussian Vector Multiple Access Channels
 IEEE TRANSACTIONS ON INFORMATION THEORY
, 2001
"... This paper characterizes the capacity region of a Gaussian multiple access channel with vector inputs and a vector output with or without intersymbol interference. The problem of finding the optimal input distribution is shown to be a convex programming problem, and an efficient numerical algorithm ..."
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Cited by 309 (12 self)
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This paper characterizes the capacity region of a Gaussian multiple access channel with vector inputs and a vector output with or without intersymbol interference. The problem of finding the optimal input distribution is shown to be a convex programming problem, and an efficient numerical algorithm is developed to evaluate the optimal transmit spectrum under the maximum sum data rate criterion. The numerical algorithm has an iterative waterfilling int#j pret#4968 . It converges from any starting point and it reaches with in s per output dimension per transmission from the Kuser multiple access sum capacity af t#j just one it#4 at#49 . These results are also applicable to vector multiple access fading channels.
Capacity Regions for Wireless Ad Hoc Networks
 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS
, 2003
"... We define and study capacity regions for wireless ad hoc networks with an arbitrary number of nodes and topology. These regions describe the set of achievable rate combinations between all sourcedestination pairs in the network under various transmission strategies, such as variablerate transmissi ..."
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Cited by 286 (18 self)
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We define and study capacity regions for wireless ad hoc networks with an arbitrary number of nodes and topology. These regions describe the set of achievable rate combinations between all sourcedestination pairs in the network under various transmission strategies, such as variablerate transmission, singlehop or multihop routing, power control, and successive interference cancellation (SIC). Multihop cellular networks and networks with energy constraints are studied as special cases. With slight modifications, the developed formulation can handle node mobility and timevarying flatfading channels. Numerical results indicate that multihop routing, the ability for concurrent transmissions, and SIC significantly increase the capacity of ad hoc and multihop cellular networks. On the other hand, gains from power control are significant only when variablerate transmission is not used. Also, timevarying flatfading and node mobility actually improve the capacity. Finally, multihop routing greatly improves the performance of energyconstraint networks.
Gamal, “Energyefficient packet transmission over a wireless link
 IEEE/ACM Trans. Networking
, 2002
"... Abstract—The paper considers the problem of minimizing the energy used to transmit packets over a wireless link via lazy schedules that judiciously vary packet transmission times. The problem is motivated by the following observation. With many channel coding schemes, the energy required to transmit ..."
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Cited by 148 (5 self)
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Abstract—The paper considers the problem of minimizing the energy used to transmit packets over a wireless link via lazy schedules that judiciously vary packet transmission times. The problem is motivated by the following observation. With many channel coding schemes, the energy required to transmit a packet can be significantly reduced by lowering transmission power and code rate, and therefore transmitting the packet over a longer period of time. However, information is often timecritical or delaysensitive and transmission times cannot be made arbitrarily long. We therefore consider packet transmission schedules that minimize energy subject to a deadline or a delay constraint. Specifically, we obtain an optimal offline schedule for a node operating under a deadline constraint. An inspection of the form of this schedule naturally leads us to an online schedule which is shown, through simulations, to perform closely to the optimal offline schedule. Taking the deadline to infinity, we provide an exact probabilistic analysis of our offline scheduling algorithm. The results of this analysis enable us to devise a lazy online algorithm that varies transmission times according to backlog. We show that this lazy schedule is significantly more energyefficient compared to a deterministic (fixed transmission time) schedule that guarantees queue stability for the same range of arrival rates. Index Terms—Minimum energy transmission, optimal schedules, power control, wireless LAN. I.
Bandwidth Scaling for Fading Multipath Channels
, 1999
"... We show that very large bandwidths on fading multipath channels cannot be effectively utilized by spread spectrum systems that (in a particular sense) spread the available power uniformly over both time and frequency. The approach is to express the input process as an expansion in an orthonormal set ..."
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Cited by 108 (12 self)
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We show that very large bandwidths on fading multipath channels cannot be effectively utilized by spread spectrum systems that (in a particular sense) spread the available power uniformly over both time and frequency. The approach is to express the input process as an expansion in an orthonormal set of functions each localized in time and frequency. The fourth moment of each coefficient in this expansion is then uniformly constrained. We show that such a constraint forces the mutual information to 0 inversely with increasing bandwidth. Simply constraining the second moment of these coefficients does not achieve this effect. The results suggest strongly that conventional direct sequence CDMA systems do not scale well to extremely large bandwidths. To illustrate how the interplay between channel estimation and symbol detection affects capacity, we present results for a specific channel and CDMA signaling scheme.
Bounds on capacity and minimum energyperbit for AWGN relay channels
 IEEE TRANS. INF. THEORY
, 2006
"... Upper and lower bounds on the capacity and minimum energyperbit for general additive white Gaussian noise (AWGN) and frequencydivision AWGN (FDAWGN) relay channel models are established. First, the maxflow mincut bound and the generalized blockMarkov coding scheme are used to derive upper an ..."
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Cited by 108 (2 self)
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Upper and lower bounds on the capacity and minimum energyperbit for general additive white Gaussian noise (AWGN) and frequencydivision AWGN (FDAWGN) relay channel models are established. First, the maxflow mincut bound and the generalized blockMarkov coding scheme are used to derive upper and lower bounds on capacity. These bounds are never tight for the general AWGN model and are tight only under certain conditions for the FDAWGN model. Two coding schemes that do not require the relay to decode any part of the message are then investigated. First, it is shown that the “sideinformation coding scheme ” can outperform the blockMarkov coding scheme. It is also shown that the achievable rate of the sideinformation coding scheme can be improved via time sharing. In the second scheme, the relaying functions are restricted to be linear. The problem is reduced to a “singleletter ” nonconvex optimization problem for the FDAWGN model. The paper also establishes a relationship between the minimum energyperbit and capacity of the AWGN relay channel. This relationship together with the lower and upper bounds on capacity are used to establish corresponding lower and upper bounds on the minimum energyperbit that do not differ by more than a factor of 1 45 for the FDAWGN relay channel model and 1 7 for the general AWGN model.
Broadband fading channels: signal burstiness and capacity
 IEEE Trans. Inform. Theory
, 2002
"... Abstract—Médard and Gallager recently showed that very large bandwidths on certain fading channels cannot be effectively used by direct sequence or related spreadspectrum systems. This paper complements the work of Médard and Gallager. First, it is shown that a key informationtheoretic inequality ..."
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Cited by 64 (5 self)
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Abstract—Médard and Gallager recently showed that very large bandwidths on certain fading channels cannot be effectively used by direct sequence or related spreadspectrum systems. This paper complements the work of Médard and Gallager. First, it is shown that a key informationtheoretic inequality of Médard and Gallager can be directly derived using the theory of capacity per unit cost, for a certain fourthorder cost function, called fourthegy. This provides insight into the tightness of the bound. Secondly, the bound is explored for a widesensestationary uncorrelated scattering (WSSUS) fading channel, which entails mathematically defining such a channel. In this context, the fourthegy can be expressed using the ambiguity function of the input signal. Finally, numerical data and conclusions are presented for directsequence type input signals. Index Terms—Channel capacity, fading channels, spread spectrum, widesensestationary uncorrelated scattering (WSSUS) fading channels. I.
Fifty Years of Shannon Theory
, 1998
"... A brief chronicle is given of the historical development of the central problems in the theory of fundamental limits of data compression and reliable communication. ..."
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Cited by 49 (1 self)
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A brief chronicle is given of the historical development of the central problems in the theory of fundamental limits of data compression and reliable communication.
Mismatched decoding revisited: general alphabets, channels with memory, and the wideband limit
 IEEE Trans. Inform. Theory
, 2000
"... Abstract—The mismatch capacity of a channel is the highest rate at which reliable communication is possible over the channel with a given (possibly suboptimal) decoding rule. This quantity has been studied extensively for singleletter decoding rules over discrete memoryless channels (DMCs). Here we ..."
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Cited by 48 (0 self)
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Abstract—The mismatch capacity of a channel is the highest rate at which reliable communication is possible over the channel with a given (possibly suboptimal) decoding rule. This quantity has been studied extensively for singleletter decoding rules over discrete memoryless channels (DMCs). Here we extend the study to memoryless channels with general alphabets and to channels with memory with possibly nonsingleletter decoding rules. We also study the wideband limit, and, in particular, the mismatch capacity per unit cost, and the achievable rates on an additivenoise spreadspectrum system with singleletter decoding and binary signaling. Index Terms—Capacity per unit cost, channels with memory, general alphabets, mismatched decoding, nearest neighbor decoding, spread spectrum. I.
Crosslayer optimization for energyefficient wireless communications: a survey,” to be published
"... Abstract—Since battery technology has not progressed as rapidly as semiconductor technology, power efficiency has become increasingly important in wireless networking, in addition to the traditional quality and performance measures, such as bandwidth, throughput, and fairness. Energyefficient desi ..."
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Cited by 45 (7 self)
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Abstract—Since battery technology has not progressed as rapidly as semiconductor technology, power efficiency has become increasingly important in wireless networking, in addition to the traditional quality and performance measures, such as bandwidth, throughput, and fairness. Energyefficient design requires a cross layer approach as power consumption is affected by all aspects of system design, ranging from silicon to applications. This article presents a comprehensive overview of recent advances in crosslayer design for energyefficient wireless communications. We particularly focus on a systembased approaches towards energy optimal transmission and resource management across time, frequency, and spatial domains. Details related to energyefficient hardware implementations are also covered. Index Terms – energy efficiency, crosslayer, wireless communications, energy aware I.