4,301 research outputs found
Distributed MAC Protocol Supporting Physical-Layer Network Coding
Physical-layer network coding (PNC) is a promising approach for wireless
networks. It allows nodes to transmit simultaneously. Due to the difficulties
of scheduling simultaneous transmissions, existing works on PNC are based on
simplified medium access control (MAC) protocols, which are not applicable to
general multi-hop wireless networks, to the best of our knowledge. In this
paper, we propose a distributed MAC protocol that supports PNC in multi-hop
wireless networks. The proposed MAC protocol is based on the carrier sense
multiple access (CSMA) strategy and can be regarded as an extension to the IEEE
802.11 MAC protocol. In the proposed protocol, each node collects information
on the queue status of its neighboring nodes. When a node finds that there is
an opportunity for some of its neighbors to perform PNC, it notifies its
corresponding neighboring nodes and initiates the process of packet exchange
using PNC, with the node itself as a relay. During the packet exchange process,
the relay also works as a coordinator which coordinates the transmission of
source nodes. Meanwhile, the proposed protocol is compatible with conventional
network coding and conventional transmission schemes. Simulation results show
that the proposed protocol is advantageous in various scenarios of wireless
applications.Comment: Final versio
Informed Network Coding for Minimum Decoding Delay
Network coding is a highly efficient data dissemination mechanism for
wireless networks. Since network coded information can only be recovered after
delivering a sufficient number of coded packets, the resulting decoding delay
can become problematic for delay-sensitive applications such as real-time media
streaming. Motivated by this observation, we consider several algorithms that
minimize the decoding delay and analyze their performance by means of
simulation. The algorithms differ both in the required information about the
state of the neighbors' buffers and in the way this knowledge is used to decide
which packets to combine through coding operations. Our results show that a
greedy algorithm, whose encodings maximize the number of nodes at which a coded
packet is immediately decodable significantly outperforms existing network
coding protocols.Comment: Proc. of the IEEE International Conference on Mobile Ad-hoc and
Sensor Systems (IEEE MASS 2008), Atlanta, USA, September 200
Expander Chunked Codes
Chunked codes are efficient random linear network coding (RLNC) schemes with
low computational cost, where the input packets are encoded into small chunks
(i.e., subsets of the coded packets). During the network transmission, RLNC is
performed within each chunk. In this paper, we first introduce a simple
transfer matrix model to characterize the transmission of chunks, and derive
some basic properties of the model to facilitate the performance analysis. We
then focus on the design of overlapped chunked codes, a class of chunked codes
whose chunks are non-disjoint subsets of input packets, which are of special
interest since they can be encoded with negligible computational cost and in a
causal fashion. We propose expander chunked (EC) codes, the first class of
overlapped chunked codes that have an analyzable performance,where the
construction of the chunks makes use of regular graphs. Numerical and
simulation results show that in some practical settings, EC codes can achieve
rates within 91 to 97 percent of the optimum and outperform the
state-of-the-art overlapped chunked codes significantly.Comment: 26 pages, 3 figures, submitted for journal publicatio
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