具有占空比和功率约束的高斯信道容量
Capacity of Gaussian Channels with Duty Cycle and Power Constraints
摘要：
在许多无线通信系统中，无线电设备受到占空比约束，也就是说，无线电设备仅在一小部分时间内主动发送信号。例如，在一些低功率系统中，期望具有小的占空比;如果半双工无线电希望接收有用的信号，则半双工无线电不能保持发送;并且认知无线电需要频繁地监听和检测主用户。本文研究了标量离散高斯信道在平均发射功率和占空比约束下的容量问题。首先研究了一个理想化的占空比约束，它可以被看作是对每个码字中的非传输或零符号的最小分数的要求。一个独特的离散输入分布，以实现信道容量。在许多情况下，在确定性传输调度上，数值优化的开-关信令可以实现比高斯信令高得多的速率。这部分是因为码字中的非传输位置可以传达信息。此外，一个更现实的占空比的约束进行了研究，其中的额外成本之间的过渡传输和nontransmissions由于脉冲整形占。实现能力的输入不再是独立的，随着时间的推移，很难计算。作为输入分布的函数的可达到的速率的下限示出为最大化的一阶马尔可夫输入过程，其分布也是离散的，可以有效地计算。本文中的结果表明，在各种占空比的约束下，从通常的模式间歇性的数据包传输可能会产生很大的增益。
英文摘要：
In many wireless communication systems, radios are subject to a duty cycle constraint, that is, a radio only actively transmits signals over a fraction of the time. For example, it is desirable to have a small duty cycle in some low power systems; a half-duplex radio cannot keep transmitting if it wishes to receive useful signals; and a cognitive radio needs to listen and detect primary users frequently. This work studies the capacity of scalar discrete-time Gaussian channels subject to duty cycle constraint as well as average transmit power constraint. An idealized duty cycle constraint is first studied, which can be regarded as a requirement on the minimum fraction of nontransmissions or zero symbols in each codeword. A unique discrete input distribution is shown to achieve the channel capacity. In many situations, numerically optimized on-off signaling can achieve much higher rate than Gaussian signaling over a deterministic transmission schedule. This is in part because the positions of nontransmissions in a codeword can convey information. Furthermore, a more realistic duty cycle constraint is studied, where the extra cost of transitions between transmissions and nontransmissions due to pulse shaping is accounted for. The capacity-achieving input is no longer independent over time and is hard to compute. A lower bound of the achievable rate as a function of the input distribution is shown to be maximized by a first-order Markov input process, the distribution of which is also discrete and can be computed efficiently. The results in this paper suggest that, under various duty cycle constraints, departing from the usual paradigm of intermittent packet transmissions may yield substantial gain.
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