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209
Breaking Spectrum Gridlock with Cognitive Radios: An Information Theoretic Perspective
, 2008
"... Cognitive radios hold tremendous promise for increasing spectral efficiency in wireless systems. This paper surveys the fundamental capacity limits and associated transmission techniques for different wireless network design paradigms based on this promising technology. These paradigms are unified b ..."
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Cited by 244 (3 self)
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Cognitive radios hold tremendous promise for increasing spectral efficiency in wireless systems. This paper surveys the fundamental capacity limits and associated transmission techniques for different wireless network design paradigms based on this promising technology. These paradigms are unified by the definition of a cognitive radio as an intelligent wireless communication device that exploits side information about its environment to improve spectrum utilization. This side information typically comprises knowledge about the activity, channels, codebooks and/or messages of other nodes with which the cognitive node shares the spectrum. Based on the nature of the available side information as well as a priori rules about spectrum usage, cognitive radio systems seek to underlay, overlay or interweave the cognitive radios ’ signals with the transmissions of noncognitive nodes. We provide a comprehensive summary of the known capacity characterizations in terms of upper and lower bounds for each of these three approaches. The increase in system degrees of freedom obtained through cognitive radios is also illuminated. This information theoretic survey provides guidelines for the spectral efficiency gains possible through cognitive radios, as well as practical design ideas to mitigate the coexistence challenges in today’s crowded spectrum.
Computeandforward: Harnessing interference through structured codes
 IEEE TRANS. INF. THEORY
, 2009
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MIMO broadcasting for simultaneous wireless information and power transfer
 IEEE Trans. Wirless Commun
, 2013
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Interference alignment and cancellation
 In Proceedings of ACM SIGCOMM
, 2009
"... The throughput of existing MIMO LANs is limited by the number of antennas on the AP. This paper shows how to overcome this limitation. It presents interference alignment and cancellation (IAC), a new approach for decoding concurrent senderreceiver pairs in MIMO networks. IAC synthesizes two signal ..."
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Cited by 101 (7 self)
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The throughput of existing MIMO LANs is limited by the number of antennas on the AP. This paper shows how to overcome this limitation. It presents interference alignment and cancellation (IAC), a new approach for decoding concurrent senderreceiver pairs in MIMO networks. IAC synthesizes two signal processing techniques, interference alignment and interference cancellation, showing that the combination applies to scenarios where neither interference alignment nor cancellation applies alone. We show analytically that IAC almost doubles the throughput of MIMO LANs. We also implement IAC in GNURadio, and experimentally demonstrate that for 2x2 MIMO LANs, IAC increases the average throughput by 1.5x on the downlink and 2x on the uplink.
Ergodic interference alignment
 in Proceedings of the International Symposium on Information Theory (ISIT 2009), (Seoul, South Korea
, 2009
"... Abstract—Consider a Kuser interference channel with timevarying fading. At any particular time, each receiver will see a signal from most transmitters. The standard approach to such a scenario results in each transmitterreceiver pair achieving a rate proportional to 1 the single user rate. However ..."
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Cited by 96 (24 self)
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Abstract—Consider a Kuser interference channel with timevarying fading. At any particular time, each receiver will see a signal from most transmitters. The standard approach to such a scenario results in each transmitterreceiver pair achieving a rate proportional to 1 the single user rate. However, given two K well chosen time indices, the channel coefficients from interfering users can be made to exactly cancel. By adding up these two signals, the receiver can see an interferencefree version of the desired transmission. We show that this technique allows each user to achieve at least half its interferencefree ergodic capacity at any SNR. Prior work was only able to show that half the interferencefree rate was achievable as the SNR tended to infinity. We examine a finite field channel model and a Gaussian channel model. In both cases, the achievable rate region has a simple description and, in the finite field case, we prove it is the ergodic capacity region. I.
Interference alignment for cellular networks
 in Communication, Control, and Computing, 2008 46th Annual Allerton Conference
, 2008
"... Abstract — In this paper, we propose a new way of interference management for cellular networks. We develop the scheme that approaches to interferencefree degreeoffreedom (dof) as the number K of users in each cell increases. Also we find the corresponding bandwidth scaling conditions for typical ..."
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Cited by 79 (5 self)
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Abstract — In this paper, we propose a new way of interference management for cellular networks. We develop the scheme that approaches to interferencefree degreeoffreedom (dof) as the number K of users in each cell increases. Also we find the corresponding bandwidth scaling conditions for typical wireless channels: multipath channels and singlepath channels with propagation delay. The scheme is based on interference alignment. Especially for morethantwocell cases where there are multiple nonintended BSs, we propose a new version of interference alignment, namely subspace interference alignment. The idea is to align interferences into multidimensional subspace (instead of one dimension) for simultaneous alignments at multiple nonintended BSs. The proposed scheme requires finite dimensions growing linearly with K, i.e., ∼ O(K). I.
On the DegreesofFreedom of the KUser Gaussian Interference Channel
 IEEE Transactions on Information Theory
, 2008
"... The degreesoffreedom of a Kuser Gaussian interference channel (GIFC) has been defined to be the multiple of (1/2)log 2 P at which the maximum sum of achievable rates grows with increasing P. In this paper, we establish that the degreesoffreedom of three or more user, real, scalar GIFCs, viewed ..."
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Cited by 76 (0 self)
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The degreesoffreedom of a Kuser Gaussian interference channel (GIFC) has been defined to be the multiple of (1/2)log 2 P at which the maximum sum of achievable rates grows with increasing P. In this paper, we establish that the degreesoffreedom of three or more user, real, scalar GIFCs, viewed as a function of the channel coefficients, is discontinuous at points where all of the coefficients are nonzero rational numbers. More specifically, for all K> 2, we find a class of Kuser GIFCs that is dense in the GIFC parameter space for which K/2 degreesoffreedom are exactly achievable, and we show that the degreesoffreedom for any GIFC with nonzero rational coefficients is strictly smaller than K/2. These results are proved using new connections with number theory and additive combinatorics. 1
Interference alignment on the deterministic channel and application to gaussian networks
"... Abstract—An interference alignment example is constructed for the deterministic channel model of the user interference channel. The deterministic channel example is then translated into the Gaussian setting, creating the first known example of a fully connected Gaussian user interference network w ..."
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Cited by 75 (23 self)
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Abstract—An interference alignment example is constructed for the deterministic channel model of the user interference channel. The deterministic channel example is then translated into the Gaussian setting, creating the first known example of a fully connected Gaussian user interference network with single antenna nodes, real, nonzero and constant channel coefficients, and no propagation delays where the degrees of freedom outerbound is achieved. An analogy is drawn between the propagation delay based interference alignment examples and the deterministic channel model which also allows similar constructions for the user channel as well. I.
Reducing repair traffic for erasure codingbased storage via interference alignment
 In Information Theory Proceedings (ISIT), 2009 IEEE International Symposium on, 2009. [WDR07
, 2007
"... Abstract—We consider the problem of recovering from a single node failure in a storage system based on an (n, k) MDS code. In such a scenario, a straightforward solution is to perform a complete decoding, even though the data to be recovered only amount to 1/kth of the entire data. This paper presen ..."
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Cited by 74 (5 self)
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Abstract—We consider the problem of recovering from a single node failure in a storage system based on an (n, k) MDS code. In such a scenario, a straightforward solution is to perform a complete decoding, even though the data to be recovered only amount to 1/kth of the entire data. This paper presents techniques that can reduce the network traffic incurred. The techniques perform algebraic alignment so that the effective dimension of unwanted information is reduced. A A