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arXiv 0807.0042cs.ITmath.IT
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输入受限信道容量的简单逆证及统一公式

A Simple Converse Proof and a Unified Capacity Formula for Channels with Input Constraints

Youjian Liu

摘要:

给出了单字母容量公式和无约束信道的逆证明,我们提供了一种简单的方法来扩展相同信道但有约束的结果。由此产生的容量公式是拉格朗日对偶函数的最小值。它给出了一个统一的公式,在这个意义上,它的工作,无论问题是否是凸的。如果问题是非凸的,我们表明,容量可以大于由天真的方法施加约束的最大化的情况下,没有约束的容量公式得到的公式。逆证明的扩展是简单地通过添加一个涉及拉格朗日乘子和约束的项。其余的证明不需要更改。我们将这种证明方法称为拉格朗日逆证明。相比之下,传统的方法需要构造一个更好的凸问题的输入分布或需要引入一个分时变量的非凸问题。我们说明了三个信道的拉格朗日逆证明,经典的离散时间无记忆信道,在发射机处具有非因果信道状态信息的信道,具有有限信道状态反馈的信道。对率失真理论进行了推广。

英文摘要:

Given the single-letter capacity formula and the converse proof of a channel without constraints, we provide a simple approach to extend the results for the same channel but with constraints. The resulting capacity formula is the minimum of a Lagrange dual function. It gives an unified formula in the sense that it works regardless whether the problem is convex. If the problem is non-convex, we show that the capacity can be larger than the formula obtained by the naive approach of imposing constraints on the maximization in the capacity formula of the case without the constraints. The extension on the converse proof is simply by adding a term involving the Lagrange multiplier and the constraints. The rest of the proof does not need to be changed. We name the proof method the Lagrangian Converse Proof. In contrast, traditional approaches need to construct a better input distribution for convex problems or need to introduce a time sharing variable for non-convex problems. We illustrate the Lagrangian Converse Proof for three channels, the classic discrete time memoryless channel, the channel with non-causal channel-state information at the transmitter, the channel with limited channel-state feedback. The extension to the rate distortion theory is also provided.

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