In order to improve the transmission reliability in current wireless communication systems, the Hybrid Automatic ReQuest (HARQ) protocol is employed to manage the unknown time-varying channel. The acknowledgments are fed back with delay on the return link. To fill up the idle time between a transmission and its acknowledgment, parallel HARQ streams associated with different messages are carried out. In this paper we improve on parallel HARQ by proposing a multi-layer HARQ protocol (also called superposition coding or multi-packet HARQ), where a single transmission may carry information on multiple messages. The multi-layer HARQ protocol works in presence of delay on the return link as parallel HARQ does, and does not require additional feedback such as the channel state information. It aims at improving the accuracy as well as the user’s delay distribution, thus achieving throughput increase. Assuming capacity-achieving codes, we show that the proposed protocol outperforms parallel HARQ in throughput, message error rate, and delay distribution. Using practical codes and decoding algorithms the gains are as well significant, at the expense of the receiver’s complexity.

中文翻译：

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具有延迟反馈的多层 HARQ

为了提高当前无线通信系统的传输可靠性，采用混合自动请求(HARQ)协议来管理未知时变信道。确认在返回链路上延迟反馈。为了填补传输与其确认之间的空闲时间，执行与不同消息相关联的并行 HARQ 流。在本文中，我们通过提出多层 HARQ 协议（也称为叠加编码或多包 HARQ）来改进并行 HARQ，其中单次传输可能携带多条消息的信息。多层 HARQ 协议与并行 HARQ 一样在返回链路上存在延迟的情况下工作，并且不需要额外的反馈，例如信道状态信息。它旨在提高准确性以及用户的延迟分布，从而实现吞吐量的增加。假设容量实现代码，我们表明所提出的协议在吞吐量、消息错误率和延迟分布方面优于并行 HARQ。使用实用的代码和解码算法，增益同样显着，但代价是接收器的复杂性。