In this work, we thoroughly analyze the rate-region provided by the asynchronous transmission in multiple access channels (MACs). We derive the corresponding capacity-regions, applicable to a wide range of pulse shaping methods. We analytically prove that asynchronous transmission enlarges the capacity-region of MACs. Although successive interference cancellation (SIC) can achieve the optimal sum-rate for the conventional uplink non-orthogonal multiple access (NOMA) methods, it is unable to achieve the boundary of the capacity-region for the asynchronous transmission. We demonstrate that for the asynchronous transmission, the optimal SIC decoding order to achieve the maximum sum-rate is based on the users' channel strengths. This optimal ordering is in contrast to the conventional uplink NOMA, where various decoding orders can result in the maximum sum-rate. Furthermore, we provide practical transceiver designs to approach the capacity-region. The memory induced by asynchronous transmission enables the use of the trellis-based detection methods which improves the performance. In addition, we propose a transceiver design, based on channel diagonalization to exploit the frequency-selectivity introduced by timing offsets. The proposed transceiver design, joint with the turbo principle, enables us to achieve a rate pair that is not achievable by the synchronous transmission.

中文翻译：

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多接入信道的异步传输：上行链路 NOMA 的速率域分析和系统设计


在这项工作中，我们彻底分析了多路访问信道（MAC）中异步传输提供的速率区域。我们推导出相应的容量区域，适用于各种脉冲整形方法。我们分析证明异步传输扩大了 MAC 的容量范围。虽然连续干扰消除(SIC)可以实现传统上行链路非正交多址(NOMA)方法的最佳和速率，但是它无法达到异步传输的容量区域的边界。我们证明，对于异步传输，实现最大总速率的最佳 SIC 解码顺序是基于用户的信道强度的。这种最佳排序与传统的上行链路 NOMA 形成对比，在传统的上行链路 NOMA 中，不同的解码顺序可以产生最大总速率。此外，我们还提供实用的收发器设计来接近容量范围。异步传输引起的内存使得能够使用基于网格的检测方法，从而提高了性能。此外，我们提出了一种基于通道对角化的收发器设计，以利用时序偏移引入的频率选择性。所提出的收发器设计与turbo原理相结合，使我们能够实现同步传输无法实现的速率对。