6,116 research outputs found
Capacity of wireless erasure networks
In this paper, a special class of wireless networks, called wireless erasure networks, is considered. In these networks, each node is connected to a set of nodes by possibly correlated erasure channels. The network model incorporates the broadcast nature of the wireless environment by requiring each node to send the same signal on all outgoing channels. However, we assume there is no interference in reception. Such models are therefore appropriate for wireless networks where all information transmission is packetized and where some mechanism for interference avoidance is already built in. This paper looks at multicast problems over these networks. The capacity under the assumption that erasure locations on all the links of the network are provided to the destinations is obtained. It turns out that the capacity region has a nice max-flow min-cut interpretation. The definition of cut-capacity in these networks incorporates the broadcast property of the wireless medium. It is further shown that linear coding at nodes in the network suffices to achieve the capacity region. Finally, the performance of different coding schemes in these networks when no side information is available to the destinations is analyzed
Quantum broadcast channels
We consider quantum channels with one sender and two receivers, used in
several different ways for the simultaneous transmission of independent
messages. We begin by extending the technique of superposition coding to
quantum channels with a classical input to give a general achievable region. We
also give outer bounds to the capacity regions for various special cases from
the classical literature and prove that superposition coding is optimal for a
class of channels. We then consider extensions of superposition coding for
channels with a quantum input, where some of the messages transmitted are
quantum instead of classical, in the sense that the parties establish bipartite
or tripartite GHZ entanglement. We conclude by using state merging to give
achievable rates for establishing bipartite entanglement between different
pairs of parties with the assistance of free classical communication.Comment: 15 pages; IEEE Trans. Inform. Theory, vol. 57, no. 10, October 201
Entanglement-Assisted Capacity of Quantum Multiple-Access Channels
We find a regularized formula for the entanglement-assisted (EA) capacity
region for quantum multiple access channels (QMAC). We illustrate the capacity
region calculation with the example of the collective phase-flip channel which
admits a single-letter characterization. On the way, we provide a
first-principles proof of the EA coding theorem based on a packing argument. We
observe that the Holevo-Schumacher-Westmoreland theorem may be obtained from a
modification of our EA protocol. We remark on the existence of a family
hierarchy of protocols for multiparty scenarios with a single receiver, in
analogy to the two-party case. In this way, we relate several previous results
regarding QMACs.Comment: Published version. 13 pages, 3 figure
Error Performance of Channel Coding in Random Access Communication
A new channel coding approach was proposed in [1] for random multiple access
communication over the discrete-time memoryless channel. The coding approach
allows users to choose their communication rates independently without sharing
the rate information among each other or with the receiver. The receiver will
either decode the message or report a collision depending on whether reliable
message recovery is possible. It was shown that, asymptotically as the codeword
length goes to infinity, the set of communication rates supporting reliable
message recovery can be characterized by an achievable region which equals
Shannon's information rate region possibly without a convex hull operation. In
this paper, we derive achievable bounds on error probabilities, including the
decoding error probability and the collision miss detection probability, of
random multiple access systems with a finite codeword length. Achievable error
exponents are obtained by taking the codeword length to infinity.Comment: submitted to IEEE Transactions on Information Theor
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