Results 11  20
of
221
Gradient of mutual information in linear vector Gaussian channels
 IEEE Trans. Inf. Theory
, 2006
"... Abstract — This paper considers a general linear vector Gaussian channel with arbitrary signaling and pursues two closely related goals: i) closedform expressions for the gradient of the mutual information with respect to arbitrary parameters of the system, and ii) fundamental connections between i ..."
Abstract

Cited by 45 (11 self)
 Add to MetaCart
Abstract — This paper considers a general linear vector Gaussian channel with arbitrary signaling and pursues two closely related goals: i) closedform expressions for the gradient of the mutual information with respect to arbitrary parameters of the system, and ii) fundamental connections between information theory and estimation theory. Generalizing the fundamental relationship recently unveiled by Guo, Shamai, and Verdú [1], we show that the gradient of the mutual information with respect to the channel matrix is equal to the product of the channel matrix and the error covariance matrix of the estimate of the input given the output. I.
Cooperative multihop broadcast for wireless networks
 IEEE J. Sel. Areas Commun
, 2004
"... Abstract—We address the minimumenergy broadcast problem under the assumption that nodes beyond the nominal range of a transmitter can collect the energy of unreliably received overheard signals. As a message is forwarded through the network, a node will have multiple opportunities to reliably recei ..."
Abstract

Cited by 44 (1 self)
 Add to MetaCart
Abstract—We address the minimumenergy broadcast problem under the assumption that nodes beyond the nominal range of a transmitter can collect the energy of unreliably received overheard signals. As a message is forwarded through the network, a node will have multiple opportunities to reliably receive the message by collecting energy during each retransmission. We refer to this cooperative strategy as accumulative broadcast. We seek to employ accumulative broadcast in a large scale loosely synchronized, lowpower network. Therefore, we focus on distributed network layer approaches for accumulative broadcast in which loosely synchronized nodes use only local information. To further simplify the system architecture, we assume that nodes forward only reliably decoded messages. Under these assumptions, we formulate the minimumenergy accumulative broadcast problem. We present a solution employing two subproblems. First, we identify the ordering in which nodes should transmit. Second, we determine the optimum power levels for that ordering. While the second subproblem can be solved by means of linear programming, the ordering subproblem is found to be NPcomplete. We devise a heuristic algorithm to find a good ordering. Simulation results show the performance of the algorithm to be close to optimum and a significant improvement over the well known BIP algorithm for constructing energyefficient broadcast trees. We then formulate a distributed version of the accumulative broadcast algorithm that uses only local information at the nodes and has performance close to its centralized counterpart. Index Terms—Distributed algorithm, minimumenergy broadcast, reliable forwarding, wideband regime.
Multipleantenna capacity in the lowpower regime
 IEEE TRANS. INFORM. THEORY
, 2003
"... This paper provides analytical characterizations of the impact on the multipleantenna capacity of several important features that fall outside the standard multipleantenna model, namely: i) antenna correlation, ii) Ricean factors, iii) polarization diversity, and iv) outofcell interference; all ..."
Abstract

Cited by 43 (9 self)
 Add to MetaCart
This paper provides analytical characterizations of the impact on the multipleantenna capacity of several important features that fall outside the standard multipleantenna model, namely: i) antenna correlation, ii) Ricean factors, iii) polarization diversity, and iv) outofcell interference; all in the regime of low signaltonoise ratio. The interplay of rate, bandwidth, and power is analyzed in the region of energy per bit close to its minimum value. The analysis yields practical design lessons for arbitrary number of antennas in the transmit and receive arrays.
Bandwidth and powerefficient routing in linear wireless networks
 IEEE Trans. Inf. Theory
, 2006
"... Abstract—The goal of this paper is to establish which practical routing schemes for wireless networks are most suitable for powerlimited and bandwidthlimited communication regimes. We regard channel state information (CSI) at the receiver and pointtopoint capacityachieving codes for the additiv ..."
Abstract

Cited by 42 (8 self)
 Add to MetaCart
Abstract—The goal of this paper is to establish which practical routing schemes for wireless networks are most suitable for powerlimited and bandwidthlimited communication regimes. We regard channel state information (CSI) at the receiver and pointtopoint capacityachieving codes for the additive white Gaussian noise (AWGN) channel as practical features, interference cancellation (IC) as possible, but less practical, and synchronous cooperation (CSI at the transmitters) as impractical. We consider a communication network with a single source node, a single destination node, and I intermediate nodes placed equidistantly on a line between them. We analyze the minimum total transmit power needed to achieve a desired endtoend rate for several schemes and demonstrate that multihop communication with spatial reuse performs very well in the powerlimited regime, even without IC. However, within a class of schemes not performing IC, singlehop transmission (directly from source to destination) is more suitable for the bandwidthlimited regime, especially when higher spectral efficiencies are required. At such higher spectral efficiencies, the gap between singlehop and multihop can be closed by employing IC, and we present a scheme based upon backward decoding that can remove all interference from the multihop system with an arbitrarily small rate loss. This new scheme is also used to demonstrate that rates of @�� � A are achievable over linear wireless networks even without synchronous cooperation. Index Terms—Cooperation, network information theory, relay networks, routing, wireless networks. I.
Ultrawideband radio design: The promise of highspeed, shortrange wireless connectivity
 in Proc. of the IEEE. Special Issue on Gigabit Wireless
, 2004
"... This paper provides a tutorial overview of ultrawideband (UWB) radio technology for highspeed wireless connectivity. Subsequent to establishing a historical and technological context, it describes the new impetus for UWB systems development and standardization resulting from the FCC’s recent decisi ..."
Abstract

Cited by 38 (1 self)
 Add to MetaCart
This paper provides a tutorial overview of ultrawideband (UWB) radio technology for highspeed wireless connectivity. Subsequent to establishing a historical and technological context, it describes the new impetus for UWB systems development and standardization resulting from the FCC’s recent decision to permit unlicensed operation in the [3.1,10.6] GHz band subject to modified Part 15 rules and indicates the potential new applications that may result. Thereafter, the paper provides a system architect’s perspectives on the various issues and challenges involved in the design of link layer subsystems. Specifically, we outline current developments in UWB system design concepts that are oriented to highspeed applications and describe some of the design tradeoffs involved. Keywords—Personal area networks, wireless, ultrawide band. I. INTRODUCTION AND BACKGROUND
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 ..."
Abstract

Cited by 34 (9 self)
 Add to MetaCart
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.
Capacity Scaling and Spectral Efficiency in Wideband Correlated MIMO Channels
 IEEE TRANSACTIONS ON INFORMATION THEORY
, 2002
"... The dramatic linear increase in ergodic capacity with the number of antennas promised by MIMO wireless communication systems is based on idealized channel models representing a rich scattering environment. Is such scaling sustainable in realistic scattering scenarios? Existing physical models, altho ..."
Abstract

Cited by 28 (8 self)
 Add to MetaCart
The dramatic linear increase in ergodic capacity with the number of antennas promised by MIMO wireless communication systems is based on idealized channel models representing a rich scattering environment. Is such scaling sustainable in realistic scattering scenarios? Existing physical models, although realistic, are intractable for addressing this problem analytically due to their complicated nonlinear dependence on propagation path parameters, such as the angles of arrival and delays. In this paper, we leverage a recently introduced virtual representation of physical models that is essentially a Fourier series representation of wideband MIMO channels in terms of fixed virtual angles and delays. Motivated by physical considerations, we propose a connected model for correlated channels defined by a virtual spatial channel matrix consisting of nonvanishing diagonals with i.i.d. Gaussian entries. The parameter provides a meaningful and tractable measure of the richness of scattering. We derive general bounds for the coherent ergodic capacity and investigate capacity scaling with the number of antennas and bandwidth. In the large antenna regime, we show that linear capacity scaling is possible if scales linearly with the number of antennas. This, in turn, is possible if the number of resolvable paths grows quadratically with the number of antennas. The capacity saturates for linear growth in the number of paths (fixed ). The ergodic capacity does not depend on frequency selectivity of the channel in the wideband case. Increasing bandwidth tightens the bounds and hastens the convergence of scaling behavior. For large bandwidth, the capacity scales linearly with SNR as well. We also provide an explicit characterization of the wideband slope recently proposed by Verdu. Nume...
Capacity and Optimal Resource Allocation in the Degraded Gaussian Relay Channel with Multiple Relays
 In: 40th Allerton Conference on Communication, Control, and Computing
, 2002
"... We determine the capacity region of a degraded Gaussian relay channel with multiple relay stages. This is done by building an inductive argument based on the singlerelay capacity theorem of Cover and El Gamal. We then give an iterative algorithm for determining the optimal power allocation betwe ..."
Abstract

Cited by 27 (2 self)
 Add to MetaCart
We determine the capacity region of a degraded Gaussian relay channel with multiple relay stages. This is done by building an inductive argument based on the singlerelay capacity theorem of Cover and El Gamal. We then give an iterative algorithm for determining the optimal power allocation between the transmitter and the relays. We show that in the case when all noise sources have equal power this results in a coding strategy that delivers SNR growth that is asymptotically linear with the number of relays.
Forwarding Strategies for Gaussian ParallelRelay Networks
, 2004
"... This paper investigates reliable and unreliable forwarding strategies in a parallelrelay network. We consider the problem that maximizes the achievable rate under the total power constraint that allows for the power allocation among the nodes. We approach this problem by solving its dual with the ..."
Abstract

Cited by 26 (0 self)
 Add to MetaCart
This paper investigates reliable and unreliable forwarding strategies in a parallelrelay network. We consider the problem that maximizes the achievable rate under the total power constraint that allows for the power allocation among the nodes. We approach this problem by solving its dual with the objective to communicate to the destination at rate using minimum transmitted power. Motivated by applications in sensor networks, we assume large bandwidth resources allowing orthogonal transmissions at the nodes. In such a network, the energy cost per information bit [1] during the reliable forwarding is minimized by operating in the wideband regime. For the wideband decodeandforward (DF) strategy, we present the optimum parallelrelay solution by identifying the best choice of relay nodes and the optimum power allocation among them. We demonstrate that the data should be sent over a single relay route through one relay that is in the “best ” position in the network. On the other hand, as observed in [2], the benefit of unreliable amplifyandforward (AF) strategy diminishes in the wideband regime. We characterize the optimum bandwidth for AF that minimizes the total energy cost per information bit for our network model. We show that transmitting in the optimum bandwidth allows the network to operate in the linear regime where the achieved rate increases linearly with transmit power. We then identify the best subset of AF relay nodes and characterize the optimum power allocation per dimension among relays, for a given source power and bandwidth. Based on this analysis, we compare the energyefficiency of DF and AF in a onerelay network and show the regions where each strategy is optimal.
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 ..."
Abstract

Cited by 26 (5 self)
 Add to MetaCart
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.