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291
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 ..."
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Cited by 50 (1 self)
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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.
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 ..."
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Cited by 49 (1 self)
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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
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 ..."
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Cited by 48 (9 self)
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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.
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 ..."
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Cited by 44 (11 self)
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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.
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 ..."
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Cited by 43 (8 self)
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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.
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 39 (9 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.
Capacity scaling and spectral efficiency in wideband correlated MIMO channels
 IEEE Trans. Inform. Theory
, 2003
"... Abstract—The dramatic linear increase in ergodic capacity with the number of antennas promised by multipleinput multipleoutput (MIMO) wireless communication systems is based on idealized channel models representing a rich scattering environment. Is such scaling sustainable in realistic scatterin ..."
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Cited by 34 (9 self)
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Abstract—The dramatic linear increase in ergodic capacity with the number of antennas promised by multipleinput multipleoutput (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 aconnected model for correlated channels defined by a virtual spatial channel matrix consisting of nonvanishing diagonals with independent and identically distributed (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 the signaltonoise ratio (SNR) as well. We also provide an explicit characterization of the wideband slope recently proposed by Verdú. Numerical results are presented to illustrate the key theoretical results. Index Terms—Beamforming, empirical eigenvalue distribution, ergodic capacity, Fourier series, frequency selectivity, ray tracing, scattering, spectral efficiency.
Capacity of multipletransmit multiplereceive antenna architectures
 IEEE Trans. Inf. Theory
, 2002
"... codes for high data rates wireless communications: Performance criteria in the presence of channel estimation errors, mobility and multiple ..."
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Cited by 30 (8 self)
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codes for high data rates wireless communications: Performance criteria in the presence of channel estimation errors, mobility and multiple
Sum Rate Characterization of Joint Multiple CellSite Processing
, 2005
"... The sumrate capacity of a cellular system model is analyzed, considering the uplink and downlink channels, while addressing both nonfading and flatfading channels. The focus is on a simple Wynerlike multicell model, where the system cells are arranged on a circle, assuming the cellsites are lo ..."
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Cited by 29 (10 self)
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The sumrate capacity of a cellular system model is analyzed, considering the uplink and downlink channels, while addressing both nonfading and flatfading channels. The focus is on a simple Wynerlike multicell model, where the system cells are arranged on a circle, assuming the cellsites are located at the boundaries of the cells. For the uplink channel, analytical expressions of the sumrate capacities are derived for intracell TDMA scheduling, and a “WideBand ” (WB) scheme (where all users are active simultaneously utilizing all bandwidth for coding). Assuming individual percell power constraints, and using the Lagrangian uplinkdownlink duality principle, an analytical expression for the sumrate capacity of the downlink channel is derived for nonfading channels, and shown to coincide with the corresponding uplink result. Introducing flatfading, lower and upper bounds on the average percell sumrate capacity are derived. The bounds exhibit an O(loge K) multiuser diversity factor for a number of users percell K ≫ 1, in addition to the array diversity gain. Joint multicell processing is shown to eliminate outofcell interference, which is traditionally considered to be a limiting factor in highrate reliable communications. This paper was presented in part at the 9
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 ..."
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Cited by 29 (2 self)
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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.