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452
Mobility increases the capacity of adhoc wireless networks
 IEEE/ACM TRANSACTIONS ON NETWORKING
, 2002
"... The capacity of adhoc wireless networks is constrained by the mutual interference of concurrent transmissions between nodes. We study a model of an adhoc network where n nodes communicate in random sourcedestination pairs. These nodes are assumed to be mobile. We examine the persession throughpu ..."
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Cited by 1218 (6 self)
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The capacity of adhoc wireless networks is constrained by the mutual interference of concurrent transmissions between nodes. We study a model of an adhoc network where n nodes communicate in random sourcedestination pairs. These nodes are assumed to be mobile. We examine the persession throughput for applications with loose delay constraints, such that the topology changes over the timescale of packet delivery. Under this assumption, the peruser throughput can increase dramatically when nodes are mobile rather than fixed. This improvement can be achieved by exploiting node mobility as a type of multiuser diversity.
User Cooperation Diversity  Part I: System Description
 IEEE Trans. Commun
"... Mobile users' data rate and quality of service are limited by the fact that, within the duration of any given call, they experience severe variations in signal attenuation, thereby necessitating the use of some type of diversity. In this twopart paper, we propose a new form of spatial diver ..."
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Cited by 639 (23 self)
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Mobile users' data rate and quality of service are limited by the fact that, within the duration of any given call, they experience severe variations in signal attenuation, thereby necessitating the use of some type of diversity. In this twopart paper, we propose a new form of spatial diversity, in which diversity gains are achieved via the cooperation of mobile users. Part I describes the user cooperation strategy while Part II focuses on implementation issues and performance analysis. Results show that, even though the interuser channel is noisy, cooperation leads not only to an increase in capacity for both users but also to a more robust system, where users' achievable rates are less susceptible to channel variations.
Fading Channels: InformationTheoretic And Communications Aspects
 IEEE TRANSACTIONS ON INFORMATION THEORY
, 1998
"... In this paper we review the most peculiar and interesting informationtheoretic and communications features of fading channels. We first describe the statistical models of fading channels which are frequently used in the analysis and design of communication systems. Next, we focus on the information ..."
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Cited by 416 (3 self)
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In this paper we review the most peculiar and interesting informationtheoretic and communications features of fading channels. We first describe the statistical models of fading channels which are frequently used in the analysis and design of communication systems. Next, we focus on the information theory of fading channels, by emphasizing capacity as the most important performance measure. Both singleuser and multiuser transmission are examined. Further, we describe how the structure of fading channels impacts code design, and finally overview equalization of fading multipath channels.
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.
On the optimality of multiantenna broadcast scheduling using zeroforcing beamforming
 IEEE J. SELECT. AREAS COMMUN
, 2006
"... Although the capacity of multipleinput/multipleoutput (MIMO) broadcast channels (BCs) can be achieved by dirty paper coding (DPC), it is difficult to implement in practical systems. This paper investigates if, for a large number of users, simpler schemes can achieve the same performance. Specifica ..."
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Cited by 302 (4 self)
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Although the capacity of multipleinput/multipleoutput (MIMO) broadcast channels (BCs) can be achieved by dirty paper coding (DPC), it is difficult to implement in practical systems. This paper investigates if, for a large number of users, simpler schemes can achieve the same performance. Specifically, we show that a zeroforcing beamforming (ZFBF) strategy, while generally suboptimal, can achieve the same asymptotic sum capacity as that of DPC, as the number of users goes to infinity. In proving this asymptotic result, we provide an algorithm for determining which users should be active under ZFBF. These users are semiorthogonal to one another and can be grouped for simultaneous transmission to enhance the throughput of scheduling algorithms. Based on the user grouping, we propose and compare two fair scheduling schemes in roundrobin ZFBF and proportionalfair ZFBF. We provide numerical results to confirm the optimality of ZFBF and to compare the performance of ZFBF and proposed fair scheduling schemes with that of various MIMO BC strategies.
CrossLayer Design for Wireless Networks
 IEEE Communications Magazine
, 2003
"... As the cellular and PCS world collides with Wireless LANs and Internetbased packet data, new networking approaches will support the integration of voice and data on the composite infrastructure of cellular base stations and Ethernetbased wireless access points. This paper highlights some of the pa ..."
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Cited by 249 (3 self)
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As the cellular and PCS world collides with Wireless LANs and Internetbased packet data, new networking approaches will support the integration of voice and data on the composite infrastructure of cellular base stations and Ethernetbased wireless access points. This paper highlights some of the past accomplishments and promising research avenues for an important topic in the creation of future wireless networks. In this paper, we address the issue of crosslayer networking, where the physical and MAC layer knowledge of the wireless medium is shared with higher layers, in order to provide efficient methods of allocating network resources and applications over the Internet. In essence, future networks will need to provide ”impedance matching ” of the instantaneous radio channel conditions and capacity needs with the traffic and congestion conditions found over the packetbased world of the Internet. Further, such matching will need to be coordinated with a wide range of particular applications and user expectations, making the topic of crosslayer networking an increasingly important one for the evolving wireless buildout. 1
A tutorial on crosslayer optimization in wireless networks
 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS
, 2006
"... This tutorial paper overviews recent developments in optimization based approaches for resource allocation problems in wireless systems. We begin by overviewing important results in the area of opportunistic (channelaware) scheduling for cellular (singlehop) networks, where easily implementable my ..."
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Cited by 248 (30 self)
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This tutorial paper overviews recent developments in optimization based approaches for resource allocation problems in wireless systems. We begin by overviewing important results in the area of opportunistic (channelaware) scheduling for cellular (singlehop) networks, where easily implementable myopic policies are shown to optimize system performance. We then describe key lessons learned and the main obstacles in extending the work to general resource allocation problems for multihop wireless networks. Towards this end, we show that a cleanslate optimization based approach to the multihop resource allocation problem naturally results in a “loosely coupled” crosslayer solution. That is, the algorithms obtained map to different layers (transport, network, and MAC/PHY) of the protocol stack are coupled through a limited amount of information being passed back and forth. It turns out that the optimal scheduling component at the MAC layer is very complex and thus needs simpler (potentially imperfect) distributed solutions. We demonstrate how to use imperfect scheduling in the crosslayer framework and describe recently developed distributed algorithms along these lines. We conclude by describing a set of open research problems.
Multiaccess Fading Channels  Part I: Polymatroid Structure, Optimal Resource Allocation and Throughput Capacities
 IEEE Trans. Inform. Theory
"... In multiaccess wireless systems, dynamic allocation of resources such as transmit power, bandwidths, and rates is an important means to deal with the timevarying nature of the environment. In this twopart paper, we consider the problem of optimal resource allocation from an informationtheoretic p ..."
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Cited by 225 (10 self)
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In multiaccess wireless systems, dynamic allocation of resources such as transmit power, bandwidths, and rates is an important means to deal with the timevarying nature of the environment. In this twopart paper, we consider the problem of optimal resource allocation from an informationtheoretic point of view. We focus on the multiaccess fading channel with Gaussian noise, and define two notions of capacity depending on whether the traffic is delaysensitive or not. In part I, we characterize the throughput capacity region which contains the longterm achievable rates through the timevarying channel. We show that each point on the boundary of the region can be achieved by successive decoding. Moreover, the optimal rate and power allocations in each fading state can be explicitly obtained in a greedy manner. The solution can be viewed as the generalization of the waterfilling construction for singleuser channels to multiaccess channels with arbitrary number of users, and exploits the underlying polymatroid structure of the capacity region. In part II, we characterize a delaylimited capacity region and obtain analogous results.
An overview of limited feedback in wireless communication systems
 IEEE J. SEL. AREAS COMMUN
, 2008
"... It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channe ..."
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Cited by 199 (41 self)
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It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finiterate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, singleuser, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.
Optimal Power Allocation over Parallel Gaussian Broadcast Channels
, 1997
"... We consider the problem of optimal power allocation over a family of parallel Gaussian broadcast channels, each with a di#erent set of noise powers for the users, and obtain a characterization of the optimal solution as well as the resulting capacity region. The solution has a simple greedy struc ..."
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Cited by 198 (4 self)
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We consider the problem of optimal power allocation over a family of parallel Gaussian broadcast channels, each with a di#erent set of noise powers for the users, and obtain a characterization of the optimal solution as well as the resulting capacity region. The solution has a simple greedy structure, just like the corresponding solution to the parallel Gaussian multiaccess channel. It is a generalization of the classic waterfilling solution for parallel singleuser channels. Application of the results to the problem of power control for the downlink wireless fading channel is discussed.