An improvement of the deletion channel capacity upper bound

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.