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21
Power allocation for twoway amplifyforward relaying with receive channel knowledge
 in Proc. IEEE 22nd Int. Symp. Personal Indoor and Mobile Radio Commun. (PIMRC
, 2011
"... AbstractThe power allocation problem corresponding to the communication of two sources via a relay with amplifyforward capability is studied from the outage probability perspective. Analog network coding is considered for halfduplex nodes with perfect channel state information at the receiver si ..."
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AbstractThe power allocation problem corresponding to the communication of two sources via a relay with amplifyforward capability is studied from the outage probability perspective. Analog network coding is considered for halfduplex nodes with perfect channel state information at the receiver side. Under a sumpower constraint on the transmit powers of the nodes, an optimal power allocation strategy that minimizes the high signaltonoise ratio approximation of the outage probability is derived and shown to improve the performance significantly. As a reference for comparison, a cutset type bound is also optimized for the setup.
MAC Design for Analog Network Coding * General Terms
"... ABSTRACT Most medium access control (MAC) mechanisms discard collided packets and consider interference harmful. Recent work on Analog Network Coding (ANC) suggests a different approach, in which multiple interfering transmissions are strategically scheduled. Receiving nodes collect the results of ..."
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ABSTRACT Most medium access control (MAC) mechanisms discard collided packets and consider interference harmful. Recent work on Analog Network Coding (ANC) suggests a different approach, in which multiple interfering transmissions are strategically scheduled. Receiving nodes collect the results of collisions and then use a decoding process, such as ZigZag decoding, to extract the packets involved in the collisions. In this paper, we present an algebraic representation of collisions and describe a general approach to recovering collisions using ANC. To study the effects of using ANC on the performance of MAC layers, we develop an ANCbased MAC algorithm, CMAC , and analyze its performance in terms of probabilistic latency guarantees for local packet delivery. Specifically, we prove that CMAC implements an abstract MAC layer service, as defined in We illustrate how this improvement in the MAC layer can translate into faster higherlevel algorithms, by analyzing the time complexity of a multimessage networkwide broadcast algorithm that uses CMAC .
Iterative Deterministic Equivalents for the Performance Analysis of Communication Systems
, 2011
"... In this article, we introduce iterative deterministic equivalents as a novel technique for the performance analysis of communication systems whose channels are modeled by complex combinations of independent random matrices. This technique extends the deterministic equivalent approach for the study ..."
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In this article, we introduce iterative deterministic equivalents as a novel technique for the performance analysis of communication systems whose channels are modeled by complex combinations of independent random matrices. This technique extends the deterministic equivalent approach for the study of functionals of large random matrices to a broader class of random matrix models which naturally arise as channel models in wireless communications. We present two specific applications: First, we consider a multihop amplifyandforward (AF) MIMO relay channel with noise at each stage and derive deterministic approximations of the mutual information after the Kth hop. Second, we study a MIMO multiple access channel (MAC) where the channel between each transmitter and the receiver is represented by the doublescattering channel model. We provide deterministic approximations of the mutual information, the signaltointerferenceplusnoise ratio (SINR) and sumrate with minimummeansquareerror (MMSE) detection and derive the asymptotically optimal precoding matrices. In both scenarios, the approximations can be computed by simple and provably converging fixedpoint algorithms and are shown to be almost surely tight in the limit when the number of antennas at each node grows infinitely large. Simulations suggest that the approximations are accurate for realistic system dimensions. The technique of iterative deterministic equivalents can be easily extended to other channel models of interest and is, therefore, also a new contribution to the field of random matrix theory.
Tensor product based subspace interference alignment for network coding applications
 In Signals, Systems and Computers (ASILOMAR), 2011 Conference Record of the Forty Fifth Asilomar Conference on
, 2011
"... Abstract — In this paper, we develop an interference alignment framework for multisource (nonmulticast) network coding applications. The framework developed here is based on using a tensor product structure for the network coding matrices at nodes in a network. The framework is presented in this ..."
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Abstract — In this paper, we develop an interference alignment framework for multisource (nonmulticast) network coding applications. The framework developed here is based on using a tensor product structure for the network coding matrices at nodes in a network. The framework is presented in this paper in the specific context of exact repair for distributed storage, which is a multisource network coding application. Using this framework, we generalize previously known MDS codes with optimal exact repair in distributed storage. I.
1Asymptotic Capacity and Optimal Precoding in MIMO MultiHop Relay Networks
"... Abstract—A multihop relaying system is analyzed where data sent by a multiantenna source is relayed by successive multiantenna relays until it reaches a multiantenna destination. Assuming correlated fading at each hop, each relay receives a faded version of the signal from the previous level, pe ..."
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Abstract—A multihop relaying system is analyzed where data sent by a multiantenna source is relayed by successive multiantenna relays until it reaches a multiantenna destination. Assuming correlated fading at each hop, each relay receives a faded version of the signal from the previous level, performs linear precoding and retransmits it to the next level. Using free probability theory and assuming that the noise power at relays— but not at destination — is negligible, the closedform expression of the asymptotic instantaneous endtoend mutual information is derived as the number of antennas at all levels grows large. The soobtained deterministic expression is independent from the channel realizations while depending only on channel statistics. This expression is also shown to be equal to the asymptotic average endtoend mutual information. The singular vectors of the optimal precoding matrices, maximizing the average mutual information with finite number of antennas at all levels, are also obtained. It turns out that these vectors are aligned to the eigenvectors of the channel correlation matrices. Thus they can be determined using only the channel statistics. As the structure of the singular vectors of the optimal precoders is independent from the system size, it is also optimal in the asymptotic regime. Index Terms—asymptotic capacity, correlated channel, free probability theory, multihop relay network, precoding. I.
1AmplifyandForward in Wireless Relay Networks
"... A general class of wireless relay networks with a single sourcedestination pair is considered. Intermediate nodes in the network employ an amplifyandforward scheme to relay their input signals. In this case the overall inputoutput channel from the source via the relays to the destination effecti ..."
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A general class of wireless relay networks with a single sourcedestination pair is considered. Intermediate nodes in the network employ an amplifyandforward scheme to relay their input signals. In this case the overall inputoutput channel from the source via the relays to the destination effectively behaves as an intersymbol interference channel with colored noise. Unlike previous work we formulate the problem of the maximum achievable rate in this setting as an optimization problem with no assumption on the network size, topology, and received signaltonoise ratio. Previous work considered only scenarios wherein relays use all their power to amplify their received signals. We demonstrate that this may not always maximize the maximal achievable rate in amplifyandforward relay networks. The proposed formulation allows us to not only recover known results on the performance of the amplifyandforward schemes for some simple relay networks but also characterize the performance of more complex amplifyandforward relay networks which cannot be addressed in a straightforward manner using existing approaches. Using cutset arguments, we derive simple upper bounds on the capacity of general wireless relay networks. Through various examples, we show that a large class of amplifyandforward relay networks can achieve rates within a constant factor of these upper bounds asymptotically in network parameters. I.
Analog Network Coding in Nonlinear Chains
"... The problem of characterizing the optimal rate achievable with analog network coding (ANC) for a unicast communication over general wireless relay networks is computationally hard. A relay node performing ANC scales and forwards its input signals. The sourcedestination channel in such communication ..."
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The problem of characterizing the optimal rate achievable with analog network coding (ANC) for a unicast communication over general wireless relay networks is computationally hard. A relay node performing ANC scales and forwards its input signals. The sourcedestination channel in such communication scenarios is, in general, an intersymbol interference (ISI) channel which leads to the singleletter characterization of the optimal rate in terms of an optimization problem with nonconvex, non closedform objective function and nonconvex constraints. For a special class of such networks, called layered networks, a few key results and insights are however available. To gain insights into the nature of the optimal solution and to construct lowcomplexity schemes to characterize the optimal rate for general wireless relay networks, we need (1) network topologies that are regular enough to be amenable for analysis, yet general enough to capture essential characteristics of general wireless relay networks, and (2) schemes to approximate the objective function in closedform without significantly compromising the performance. Towards these two goals, this work proposes (1) nonlinear chain networks, and (2) two approximation schemes. We show that their combination allows us to tightly characterize the optimal ANC rate with low computational complexity for a much larger class of general wireless relay networks than possible with existing schemes. I.