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128
Cooperative diversity in wireless networks: efficient protocols and outage behavior
 IEEE Trans. Inform. Theory
, 2004
"... Abstract—We develop and analyze lowcomplexity cooperative diversity protocols that combat fading induced by multipath propagation in wireless networks. The underlying techniques exploit space diversity available through cooperating terminals’ relaying signals for one another. We outline several str ..."
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Cited by 1013 (25 self)
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Abstract—We develop and analyze lowcomplexity cooperative diversity protocols that combat fading induced by multipath propagation in wireless networks. The underlying techniques exploit space diversity available through cooperating terminals’ relaying signals for one another. We outline several strategies employed by the cooperating radios, including fixed relaying schemes such as amplifyandforward and decodeandforward, selection relaying schemes that adapt based upon channel measurements between the cooperating terminals, and incremental relaying schemes that adapt based upon limited feedback from the destination terminal. We develop performance characterizations in terms of outage events and associated outage probabilities, which measure robustness of the transmissions to fading, focusing on the high signaltonoise ratio (SNR) regime. Except for fixed decodeandforward, all of our cooperative diversity protocols are efficient in the sense that they achieve full diversity (i.e., secondorder diversity in the case of two terminals), and, moreover, are close to optimum (within 1.5 dB) in certain regimes. Thus, using distributed antennas, we can provide the powerful benefits of space diversity without need for physical arrays, though at a loss of spectral efficiency due to halfduplex operation and possibly at the cost of additional receive hardware. Applicable to any wireless setting, including cellular or ad hoc networks—wherever space constraints preclude the use of physical arrays—the performance characterizations reveal that large power or energy savings result from the use of these protocols. Index Terms—Diversity techniques, fading channels, outage probability, relay channel, user cooperation, wireless networks. I.
A Network Information Theory for Wireless Communication: Scaling Laws and Optimal Operation
 IEEE Transactions on Information Theory
, 2002
"... How much information can be carried over a wireless network with a multiplicity of nodes? What are the optimal strategies for information transmission and cooperation among the nodes? We obtain sharp information theoretic scaling laws under some conditions. ..."
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Cited by 272 (16 self)
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How much information can be carried over a wireless network with a multiplicity of nodes? What are the optimal strategies for information transmission and cooperation among the nodes? We obtain sharp information theoretic scaling laws under some conditions.
Distributed SpaceTime Coded Protocols for Exploiting Cooperative Diversity in Wireless Networks
 IEEE Trans. Inform. Theory
, 2003
"... Abstract — We develop and analyze spacetime coded cooperative diversity protocols for combating multipath fading across multiple protocol layers in a wireless network. The protocols exploit spatial diversity available among a collection of distributed terminals that relay messages for one another i ..."
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Cited by 225 (10 self)
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Abstract — We develop and analyze spacetime coded cooperative diversity protocols for combating multipath fading across multiple protocol layers in a wireless network. The protocols exploit spatial diversity available among a collection of distributed terminals that relay messages for one another in such a manner that the destination terminal can average the fading, even though it is unknown a priori which terminals will be involved. In particular, a source initiates transmission to its destination, and many relays potentially receive the transmission. Those terminals that can fully decode the transmission utilize a spacetime code to cooperatively relay to the destination. We demonstrate that these protocols achieve full spatial diversity in the number of cooperating terminals, not just the number of decoding relays, and can be used effectively for higher spectral efficiencies than repetitionbased schemes. We discuss issues related to spacetime code design for these protocols, emphasizing codes that readily allow for appealing distributed versions. I.
On The Capacity Of Wireless Networks: The Relay Case
 in Proc. IEEE INFOCOM
, 2002
"... In [1], Gupta and Kumar determined the capacity of wireless networks under certain assumptions, among them pointtopoint coding, which excludes for example multiaccess and broadcast codes. In this paper, we consider essentially the same physical model of a wireless network under a different traffi ..."
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Cited by 179 (9 self)
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In [1], Gupta and Kumar determined the capacity of wireless networks under certain assumptions, among them pointtopoint coding, which excludes for example multiaccess and broadcast codes. In this paper, we consider essentially the same physical model of a wireless network under a different traffic pattern, namely the relay traffic pattern, but we allow for arbitrarily complex network coding. In our model, there is only one active source/destination pair, while all other nodes assist this transmission. We show code constructions leading to achievable rates and derive upper bounds from the maxflow mincut theorem. It is shown that lower and upper bounds meet asymptotically as the number of nodes in the network goes to infinity, thus proving that the capacity of the wireless network with n nodes under the relay traffic pattern behaves like log n bits per second. This demonstrates also that network coding is essential: under the pointtopoint coding assumption considered in [1], the achievable rate is constant, independent of the number of nodes.
On the capacity of large Gaussian relay networks
 IEEE Trans. Inf. Theory
, 2005
"... Abstract—The capacity of a particular large Gaussian relay network is determined in the limit as the number of relays tends to infinity. Upper bounds are derived from cutset arguments, and lower bounds follow from an argument involving uncoded transmission. It is shown that in cases of interest, up ..."
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Cited by 108 (6 self)
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Abstract—The capacity of a particular large Gaussian relay network is determined in the limit as the number of relays tends to infinity. Upper bounds are derived from cutset arguments, and lower bounds follow from an argument involving uncoded transmission. It is shown that in cases of interest, upper and lower bounds coincide in the limit as the number of relays tends to infinity. Hence, this paper provides a new example where a simple cutset upper bound is achievable, and one more example where uncoded transmission achieves optimal performance. The findings are illustrated by geometric interpretations. The techniques developed in this paper are then applied to a sensor network situation. This is a network joint source–channel coding problem, and it is well known that the source–channel separation theorem does not extend to this case. The present paper extends this insight by providing an example where separating source from channel coding does not only lead to suboptimal performance—it leads to an exponential penalty in performance scaling behavior (as a function of the number of nodes). Finally, the techniques developed in this paper are extended to include certain models of ad hoc wireless networks, where a capacity scaling law can be established: When all nodes act purely as relays for a single source–destination pair, capacity grows with the logarithm of the number of nodes. Index Terms—Capacity, CEO problem, joint source–channel coding, network, relay, sensor network, separation theorem, uncoded transmission. I.
Practical Relay Networks: A Generalization of HybridARQ
 IEEE J. SEL. AREAS COMM
, 2005
"... Wireless networks contain an inherent distributed spatial diversity that can be exploited by the use of relaying. Relay networks take advantage of the broadcastoriented nature of radio and require nodebased, rather than linkbased protocols. Prior work on relay networks has studied performance li ..."
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Cited by 93 (2 self)
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Wireless networks contain an inherent distributed spatial diversity that can be exploited by the use of relaying. Relay networks take advantage of the broadcastoriented nature of radio and require nodebased, rather than linkbased protocols. Prior work on relay networks has studied performance limits either with unrealistic assumptions, complicated protocols, or only a single relay. In this paper, a practical approach to networks comprising multiple relays operating over orthogonal time slots is proposed based on a generalization of hybridautomatic repeat request (ARQ). In contrast with conventional hybridARQ, retransmitted packets do not need to come from the original source radio but could instead be sent by relays that overhear the transmission. An information theoretic framework is exposed that establishes the performance limits of such systems in a block fading environment, and numerical results are presented for some representative topologies and protocols. The results indicate a significant improvement in the energylatency tradeoff when compared with conventional multihop protocols implemented as a cascade of pointtopoint links.
Delay and Capacity Tradeoffs in Mobile Ad Hoc Networks: A Global Perspective
"... Since the original work of Grossglauser and Tse, which showed that the mobility can increase the capacity of an ad hoc network, there has been a lot of interest in characterizing the delaycapacity relationship in ad hoc networks. Various mobility models have been studied in the literature, and the ..."
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Cited by 78 (1 self)
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Since the original work of Grossglauser and Tse, which showed that the mobility can increase the capacity of an ad hoc network, there has been a lot of interest in characterizing the delaycapacity relationship in ad hoc networks. Various mobility models have been studied in the literature, and the delaycapacity relationships under those models have been characterized. The results indicate that there are tradeoffs between the delay and the capacity, and that the nature of these tradeoffs is strongly influenced by the choice of the mobility model. Some questions that arise are: (i) How representative are these mobility models studied in the lieterature? (ii) Can the delaycapacity relationship be significantly different under some other “reasonable ” mobility model? (iii) What would the delaycapacity tradeoff in a real network be like? In this paper, we address these questions. In particular, we analyze, among others, some of the mobility models that have been used in the recent related works, under a unified framework. We relate the nature of the delaycapacity tradeoff to the nature of the node motion, thereby providing a better understanding of the delaycapacity relationship in ad hoc networks than earlier works.
Broadcast capacity in multihop wireless networks
 In MobiCom
, 2006
"... Abstract — In this paper we study the broadcast capacity of multihop wireless networks which we define as the maximum rate at which broadcast packets can be generated in the network such that all nodes receive the packets successfully within a given time. To asses the impact of topology and interfer ..."
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Cited by 74 (5 self)
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Abstract — In this paper we study the broadcast capacity of multihop wireless networks which we define as the maximum rate at which broadcast packets can be generated in the network such that all nodes receive the packets successfully within a given time. To asses the impact of topology and interference on the broadcast capacity we employ the Physical Model and Generalized Physical Model for the channel. Prior work was limited either by density constraints or by using the less realistic but manageable Protocol model [1], [2]. Under the Physical Model, we find that the broadcast capacity is within a constant factor of the channel capacity for a wide class of network topologies. Under the Generalized Physical Model, on the other hand, the network configuration is divided into three regimes depending on how the power is tuned in relation to network density and size and in which the broadcast capacity is asymptotically either zero, constant or unbounded. As we show, the broadcast capacity is limited by distant nodes in the first regime and by interference in the second regime. In the second regime, which covers a wide class of networks, the broadcast capacity is within a constant factor of the bandwidth. I.
Transmission capacity of wireless ad hoc networks with successive . . .
 IEEE TRANS. ON INFO. THEORY
, 2005
"... The transmission capacity of a wireless ad hoc network can be defined as the maximum allowable area spectral efficiency such that the outage probability does not exceed some specified threshold. This work studies the improvement in transmission capacity obtainable with successive interference cance ..."
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Cited by 65 (22 self)
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The transmission capacity of a wireless ad hoc network can be defined as the maximum allowable area spectral efficiency such that the outage probability does not exceed some specified threshold. This work studies the improvement in transmission capacity obtainable with successive interference cancellation (SIC), an important receiver technique that has been shown to achieve the capacity of several classes of multiuser channels, but has not been carefully evaluated in the context of an ad hoc wireless network. This paper develops closedform bounds for the transmission capacity of CDMA ad hoc networks with SIC receivers, for both perfect and imperfect interference cancellation. In addition to providing the first closedform capacity results for SIC in ad hoc networks (or, to our knowledge, any type of multiuser detection), designrelevant insights are made possible. In particular, although the capacity gain from perfect SIC is very large, any imperfections in the interference cancellation rapidly degrade its usefulness. More encouragingly from a receiver complexity standpoint, due to the geographic properties of ad hoc networks, only a few – often just one – interfering nodes need to be cancelled in order to get the vast majority of the available performance gain.