Abstract
奥颈迟丑辞耻迟听 feedback , the backoff from capacity due to听 non - asymptotic 听产濒辞肠办听 length 听can be quite substantial for block lengths and error probabilities of interest in many practical applications. In this paper, novel achievability bounds are used to demonstrate that in the听 non - asymptotic 听 regime , the maximal achievable rate improves dramatically thanks to听 variable - length 听 coding 听with听 feedback . For example, for the binary symmetric channel with capacity 1/2 the blocklength required to achieve 90% of the capacity is smaller than 200, compared to at least 3100 for the best fixed-blocklength,听 non - feedback 听 code . Virtually all the advantages of noiseless听 feedback 听are shown to be achievable with decision- feedback 听only. It is demonstrated that the听 non - asymptotic 听behavior of the fundamental limit depends crucially on the particular model chosen for the 鈥渆nd-of-packet鈥 control signal.