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Performance of Fountain Codes in Collaborative Relay Networks
 IEEE Trans. Wireless Comm
, 2007
"... Cooperative communications, where parallel relays forward information to a destination node, can greatly improve the energy efficiency and latency in adhoc networks. However, current networks do not fully exploit its potential, as they only use traditional energyaccumulation, which is often used i ..."
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Cited by 33 (9 self)
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Cooperative communications, where parallel relays forward information to a destination node, can greatly improve the energy efficiency and latency in adhoc networks. However, current networks do not fully exploit its potential, as they only use traditional energyaccumulation, which is often used in conjunction with repetition coding or cooperative spacetime codes. In this paper, we show that the concept of mutualinformationaccumulation can be realized with the help of fountain codes, and leads to a lower energy expenditure and a lower transmission time than energy accumulation. We then provide an analysis of the performance of mutual information accumulation in relay networks with N relay nodes. We first analyze the quasisynchronuous scenario where the source stops transmitting and the relay nodes start transmitting after L relay nodes have successfully decoded the source data. We show that an optimum L exists and is typically on the order of 3 or 4. We also give closedform equations for the energy savings that can be achieved by the use of mutualinformationaccumulation at the receiver. We then analyze and provide bounds for an alternate scenario where each relay node starts its transmission to the destination as soon as it has decoded the source data, independent of the state of the other relay nodes. This approach further reduces the transmission time, because the transmission by the relay nodes helps the other relay nodes that are still receiving.
Relay Subset Selection in Wireless Networks Using Partial DecodeandForward Transmission
"... Abstract — This paper considers the problem of selecting a set of relay nodes to assist a transmitting node in a twohop wireless network. Throughputmaximizing relay subset selection is a difficult problem that depends on variables such as node locations and power constraints. It is proposed that a ..."
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Cited by 16 (4 self)
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Abstract — This paper considers the problem of selecting a set of relay nodes to assist a transmitting node in a twohop wireless network. Throughputmaximizing relay subset selection is a difficult problem that depends on variables such as node locations and power constraints. It is proposed that all relays employ partial decodeandforward operations to improve the tractability of the relay selection problem. This allows relay selection to be transformed into a simpler relay placement problem which motivates two proximitybased relay selection algorithms. These algorithms are compared with a greedy algorithm based on relay channel gains to the destination and an algorithm that randomly selects relays. The diversity gain achieved by employing multiple relay nodes is derived. The proposed proximitybased algorithms offer good performance in terms of the expected achieved rate. I.
LowDensity ParityCheck Codes and their Rateless Relatives
"... This survey guides the reader through the extensive open literature that is covering the family of lowdensity paritycheck (LDPC) codes and their rateless relatives. In doing so, we will identify the most important milestones that have occurred since their conception until the current era and eluci ..."
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Cited by 7 (1 self)
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This survey guides the reader through the extensive open literature that is covering the family of lowdensity paritycheck (LDPC) codes and their rateless relatives. In doing so, we will identify the most important milestones that have occurred since their conception until the current era and elucidate the related design problems and their respective solutions.
Routing in cooperative wireless networks with mutualinformation accumulation
 in Proc. IEEE ICC 2008
, 2008
"... Cooperation between the nodes of wireless multihop networks can increase communication reliability, reduce energy consumption, and decrease latency. The possible improvements are even greater when nodes perform mutualinformation accumulation, e.g., by using rateless codes. In this paper, we investi ..."
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Cited by 7 (2 self)
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Cooperation between the nodes of wireless multihop networks can increase communication reliability, reduce energy consumption, and decrease latency. The possible improvements are even greater when nodes perform mutualinformation accumulation, e.g., by using rateless codes. In this paper, we investigate routing problems in such networks. Given a network, a source and a destination, our objective is to minimize endtoend transmission delay under a sum energy constraint. We provide an algorithm that determines which nodes should participate in forwarding the message and what resources (time, energy, bandwidth) should be allocated to each. Our approach factors into two subproblems, each of which can be solved efficiently. For any node decoding order we show that solving for the optimum resource allocation can be formulated as a linear problem. We then show that the decoding order can be improved systematically by swapping nodes based on the solution of the linear program. Solving a sequence of linear program leads to a locally optimum solution in a very efficient manner. In comparison to the cooperative routing, it is observed that conventional shortestpath multihop routings incur additional delays and energy expenditures on the order of 70%. Since this initial solution is centralized, requiring full channel stat information, we exploit the insights to design two distributed routing algorithms that require only local channel state information. We provide simulations showing that in the same networks the distributed algorithms find routes that are only about 25 % less efficient than the centralized solution.
Molisch, “Channel measurements of an indoor office scenario for wireless sensor applications
 in Proc. IEEE Globecom 2007
, 2007
"... Adhoc networks and sensor networks, where nodes communicate with each other without fixed infrastructure, are of great importance for many industrial, environmental, and safetyrelated applications. The fading statistics of the propagation channels between sensor nodes are essential to determine th ..."
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Cited by 3 (0 self)
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Adhoc networks and sensor networks, where nodes communicate with each other without fixed infrastructure, are of great importance for many industrial, environmental, and safetyrelated applications. The fading statistics of the propagation channels between sensor nodes are essential to determine the possible data rate, outage, and latency of sensor networks. In this paper, we present results from a recent measurement campaign that for the first time provides an indepth analysis of the propagation channels between typical sensor node locations in office environments. We analyze the Rice factor as a function of distance and find that it is not a monotonically decreasing function. Even in pure LOS situations, Rice factors are on the order of 10 or less. This has important consequences for analysis of bit error rates, diversity order, and diversity/multiplexing tradeoff in clustered sensor networks.
1 Routing with probabilistic delay guarantees in wireless adhoc networks
"... Fellow, IEEE Abstract—In many wireless adhoc networks it is important to find a route that delivers a message to the destination within a certain deadline (delay constraint). We propose to identify such routes based on average channel state information (CSI) only, since this information can be dist ..."
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Cited by 2 (0 self)
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Fellow, IEEE Abstract—In many wireless adhoc networks it is important to find a route that delivers a message to the destination within a certain deadline (delay constraint). We propose to identify such routes based on average channel state information (CSI) only, since this information can be distributed more easily over the network. Such cases allow probabilistic QoS guarantees i.e., we maximize and report the probability of ontime delivery. We develop a convolutionfree lower bound on probability of ontime arrival, and a scheme to rapidly identify a path that maximizes this bound. This analysis is motivated by a class of infinite variance subexponential distributions whose properties preclude the use of deviation bounds and convolutional schemes. The bound then forms the basis of an algorithm that finds routes that give probabilistic delay guarantees. Simulations demonstrate that the algorithm performs better than shortestpath algorithm based on average CSI. I.
Approximating a Sum of
, 2007
"... A simple, novel, and general method is presented in this paper for approximating the sum of independent or arbitrarily correlated lognormal random variables (RV) by a single lognormal RV. The method is also shown to be applicable for approximating the sum of lognormalRice and Suzuki RVs by a single ..."
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A simple, novel, and general method is presented in this paper for approximating the sum of independent or arbitrarily correlated lognormal random variables (RV) by a single lognormal RV. The method is also shown to be applicable for approximating the sum of lognormalRice and Suzuki RVs by a single lognormal RV. A sum consisting of a mixture of the above distributions can also be easily handled. The method uses the moment generating function (MGF) as a tool in the approximation and does so without the extremely precise numerical computations at a large number of points that were required by the previously proposed methods in the literature. Unlike popular approximation methods such as the FentonWilkinson method and the SchwartzYeh method, which have their own respective shortcomings, the proposed method provides the parametric flexibility to accurately approximate different portions of the lognormal sum distribution. The accuracy of the method is measured both visually, as has been done in the literature, as well as quantitatively, using curvefitting metrics. An upper bound on the sensitivity of the method is also provided.
Scalable Video Streaming Techniques over Cooperative Relay Networks
"... This paper investigates a communication method using unequal loss protected layered video and explores use of this over a cooperative relay network. The method is adapted to prioritized video transmission to explore two prioritized layering (scalable) video techniques. Cooperative communication netw ..."
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This paper investigates a communication method using unequal loss protected layered video and explores use of this over a cooperative relay network. The method is adapted to prioritized video transmission to explore two prioritized layering (scalable) video techniques. Cooperative communication networks can reduce power consumption and benefit wireless networks, where intermediate nodes act as relays of transmitted data, increasing the coverage and network throughput. The methods are therefore evaluated in the context of a number of different relay collaboration strategies using a finite state Markov chain (FSMC) loss model for the wireless channel. Random linear codes are ideally suited to multiple path transmission because the aggregated received symbols over multiple paths assist decoding at the receiver. The results illustrate the advantages for these application scenarios using each considered strategy and analyze the impact in a relaybased network.