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Distributed storage systems provide reliable access to data through redundancy spread over individually unreliable nodes. Application scenarios include data centers, peer-to-peer storage systems, and storage in wireless networks. Storing data using an erasure code, in fragments spread across nodes, requires less redundancy than simple replication for the(More)
— The exchange of independent information between two nodes in a wireless network can be viewed as two unicast sessions, corresponding to information transfer along one direction and the opposite direction. In this paper we show such information exchange can be efficiently performed by exploiting network coding and the physical-layer broadcast property(More)
FCC has proposed to allow unlicensed operations in the TV broadcast bands. This portion of the spectrum has several desirable properties for more robust data communication as compared to the ISM bands. However, there are a number of challenges in efficiently using the TV bands. For example, the available spectrum is fragmented, and its availability may vary(More)
Traditionally, the channelization structure in IEEE 802.11-based wireless LANs has been fixed: Each access point (AP) is assigned one channel and all channels are equally wide. In contrast, it has recently been shown that even on commodity hardware, the channel-width can be adapted dynamically purely in software. Leveraging this capability, we study the use(More)
—Distributed storage systems often introduce redundancy to increase reliability. When coding is used, the repair problem arises: if a node storing encoded information fails, in order to maintain the same level of reliability we need to create encoded information at a new node. This amounts to a partial recovery of the code, whereas conventional erasure(More)
Motivated by P2P file transfer applications (e.g., BitTorrent) on the Internet, this paper considers the problem of delivering a file from a server to multiple receivers in a P2P network. Each receiver has an associated delay in receiving the file. We aim at understanding the optimal delay region, i.e., the set of all possible delay vectors that can be(More)
In this paper, the network planning problem in wireless ad hoc networks is formulated as economically allocating information carrier supplies such that certain end-to-end communication demands, as a collection of multicast sessions, are fulfilled. This formulation necessitates a cross-layer coupling. We aim at a computational characterization of the(More)
  • Yunnan Wu
  • 2009
In a distributed storage system based on erasure coding, when a storage node fails, repairing the erasure code incurs some network traffic. Previous work has characterized the fundamental tradeoff between storage efficiency and repair network bandwidth. This was done via a cut-based analysis on a graph that models the evolution of information flow in the(More)
A number of studies have shown the abundance of unused spectrum in the TV bands. This is in stark contrast to the overcrowding of wireless devices in the ISM bands. A recent trend to alleviate this disparity is the design of Cognitive Radios, which constantly sense the spectrum and opportunistically utilize unused frequencies in the TV bands. In this paper,(More)
In today's practical communication networks such as the Internet, information delivery is performed by routing. A promising generalization of routing is network coding. The potential advantages of network coding over routing include resource (e.g., bandwidth and power) efficiency, computational efficiency, and robustness to network dynamics. This tutorial(More)