Selective Encoding Policies for Maximizing Information Freshness
Selective Encoding Policies for Maximizing Information Freshness
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DOI：
10.1109/tcomm.2021.3059871
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发表时间：
2021-09-01
影响因子：
8.3
通讯作者：
Ulukus, Sennur
中科院分区：
文献类型：
--
作者：
Bastopcu, Melih;Buyukates, Baturalp;Ulukus, Sennur
信息源根据观察到的随机现象生成独立且相同分布的状态更新消息，该随机现象基于给定的概率质量函数（PMF）取n个不同的值。这些更新分组在发送器节点处被编码以被发送到接收器节点，该接收器节点想要以尽可能小的年龄跟踪所观察到的随机变量。发射机节点实现选择性k编码策略，使得发射机节点不是编码所有可能的n个实现，而是编码最可能的k个实现。我们考虑了三种不同的关于剩余的n-k个不太可能的实现的策略：最高k个选择性编码，其不管何时从剩余的n-k个值中出现实现;随机选择性编码，其以一定的概率编码并发送剩余的n-k个实现，以进一步通知接收机节点，代价是所选择的k个实现的较长码字;以及利用空符号的最高k选择性编码，当剩余的N-K实现之一时，该最高k选择性编码发送指定的空符号。对于所有这三种编码方案，我们找到平均年龄，并确定年龄最佳的真实的码字长度，包括空符号的码字长度，在后一种方案的情况下，使得在接收机节点的平均年龄最小化。通过对任意PMF的数值计算，我们发现这些选择性编码策略的平均年龄比编码每个实现都要低，并找到了相应的年龄最优k值。由于我们专注于实值码字长度在本文中，在这里研究的每种情况下得到的年龄值作为一个下界，可以通过整数值的码字长度在这种情况下达到。
An information source generates independent and identically distributed status update messages from an observed random phenomenon which takes n distinct values based on a given probability mass function (PMF). These update packets are encoded at the transmitter node to be sent to a receiver node which wants to track the observed random variable with as little age as possible. The transmitter node implements a selective k encoding policy such that rather than encoding all possible n realizations, the transmitter node encodes the most probable k realizations. We consider three different policies regarding the remaining n - k less probable realizations: highest k selective encoding which disregards whenever a realization from the remaining n- k values occurs; randomized selective encoding which encodes and sends the remaining n - k realizations with a certain probability to further inform the receiver node at the expense of longer codewords for the selected k realizations; and highest k selective encoding with an empty symbol which sends a designated empty symbol when one of the remaining n - k realizations occurs. For all of these three encoding schemes, we find the average age and determine the age-optimal real codeword lengths, including the codeword length for the empty symbol in the case of the latter scheme, such that the average age at the receiver node is minimized. Through numerical evaluations for arbitrary PMFs, we show that these selective encoding policies result in a lower average age than encoding every realization, and find the corresponding age-optimal k values. Since we focus on real-valued codeword lengths in this paper, the resulting age value obtained in each case studied here serves as a lower bound to what can be attained by integer-valued codeword lengths in that case.