Browsing by Subject "Original channels"

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    An improvement of the deletion channel capacity upper bound
    (IEEE, 2013-10) Rahmati, M.; Duman, Tolga M.
    In this paper, we offer an alternative look at channels with deletion errors by considering equivalent models for deletion channels by 'fragmenting' the input sequence where different subsequences travel through different channels. The resulting output symbols are combined appropriately to come up with an equivalent input-output representation of the original channel which allows for derivation of new upper bounds on the channel capacity. Considering a random fragmentation processes applied to binary deletion channels, we prove an inequality relation among the capacities of the original binary deletion channel and the introduced binary deletion subchannels. This inequality enables us to provide an improved upper bound on the capacity of the i.i.d. deletion channels, i.e., C(d) ≤ 0.4143(1 - d) for d ≥ 0.65. We also consider a deterministic fragmentation process suitable for the study of non-binary deletion channels which results in improved capacity upper bounds. © 2013 IEEE.
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    Upper bounds on the capacity of deletion channels using channel fragmentation
    (Institute of Electrical and Electronics Engineers Inc., 2015) Rahmati, M.; Duman, T. M.
    We study memoryless channels with synchronization errors as defined by a stochastic channel matrix allowing for symbol drop-outs or symbol insertions with particular emphasis on the binary and non-binary deletion channels. We offer a different look at these channels by considering equivalent models by fragmenting the input sequence where different subsequences travel through different channels. The resulting output symbols are combined appropriately to come up with an equivalent input-output representation of the original channel which allows for derivation of new upper bounds on the channel capacity. We consider both random and deterministic types of fragmentation processes applied to binary and nonbinary deletion channels. With two specific applications of this idea, a random fragmentation applied to a binary deletion channel and a deterministic fragmentation process applied to a nonbinary deletion channel, we prove certain inequality relations among the capacities of the original channels and those of the introduced subchannels. The resulting inequalities prove useful in deriving tighter capacity upper bounds for: 1) independent identically distributed (i.i.d.) deletion channels when the deletion probability exceeds 0.65 and 2) nonbinary deletion channels. Some extensions of these results, for instance, to the case of deletion/substitution channels are also explored. © 1963-2012 IEEE.