为什么存在反馈时块长度和延迟的行为不同
Why block length and delay behave differently if feedback is present
摘要：
对于输出对称的DMC，即使在中等高的速率，固定块长度的通信系统没有显示出改善其错误指数与反馈。在本文中，我们研究了具有固定端到端延迟的系统，并表明反馈通常会在误差指数上提供显着的增益。本文给出了带反馈的固定时延通信系统中符号错误概率的一个新的上界（不确定聚焦界）。这个界限原来有一个类似的形式维特比的界限用于块错误概率的卷积码作为一个函数的固定约束长度。的不确定性聚焦界被证明是渐近实现的无噪声反馈的擦除通道，以及任何输出对称的DMC，具有严格的正零误差容量。此外，即使反馈本身延迟很小，也可以以延迟通用（随时）方式实现。最后，它表明，对于端到端的延迟，它通常是可能的，在高速率击败一般DMC的球包装界-从而提供了一个反例的猜想Pinsker。
英文摘要：
For output-symmetric DMCs at even moderately high rates, fixed-block-length communication systems show no improvements in their error exponents with feedback. In this paper, we study systems with fixed end-to-end delay and show that feedback generally provides dramatic gains in the error exponents. A new upper bound (the uncertainty-focusing bound) is given on the probability of symbol error in a fixed-delay communication system with feedback. This bound turns out to have a similar form to Viterbi's bound used for the block error probability of convolutional codes as a function of the fixed constraint length. The uncertainty-focusing bound is shown to be asymptotically achievable with noiseless feedback for erasure channels as well as any output-symmetric DMC that has strictly positive zero-error capacity. Furthermore, it can be achieved in a delay-universal (anytime) fashion even if the feedback itself is delayed by a small amount. Finally, it is shown that for end-to-end delay, it is generally possible at high rates to beat the sphere-packing bound for general DMCs -- thereby providing a counterexample to a conjecture of Pinsker.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
