A novel coding strategy is proposed for a broadcast setting with two transmitter (TX) antennas and two single-antenna receivers (RX). The strategy consists of using space-time block coding to send a common message (to be decoded by both RXs) across the two TX antennas, while each TX antenna also sends a private message to one of the RXs. The relative weight of the private and common messages from each TX antenna is tuned to maximize the instantaneous achievable sum-rate of the channel. Closed-form expressions for the optimal weight factors are derived. In terms of the generalized degrees of freedom (GDoF) metric, the new scheme is able to achieve the sum-GDoF with finite precision channel state information at the transmitter (CSIT) of the two user broadcast channel. Moreover, as opposed to the existing rate-splitting schemes, the proposed scheme yields instantaneous achievable rates that are independent of the channel phases. This property is instrumental for link adaptation when only magnitude CSIT is available. Our numerical results indeed demonstrate the superiority of the scheme for the 2-user setting in case of magnitude CSIT. Extension to a more general $K$ -user scenario is briefly discussed.

中文翻译：

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具有幅度 CSIT 的 MISO BC 的时空速率分裂

针对具有两个发射机 (TX) 天线和两个单天线接收机 (RX) 的广播设置提出了一种新颖的编码策略。该策略包括使用空时分组编码在两个 TX 天线上发送公共消息（由两个 RX 解码），同时每个 TX 天线也向其中一个 RX 发送私人消息。来自每个 TX 天线的私有和公共消息的相对权重被调整以最大化信道的瞬时可实现总速率。推导出最优权重因子的封闭式表达式。在广义自由度（GDoF）度量方面，新方案能够在两个用户广播信道的发射机（CSIT）处实现具有有限精度信道状态信息的 sum-GDoF。此外，与现有的速率分割方案相反，提议的方案产生独立于信道相位的瞬时可达到的速率。当只有幅度 CSIT 可用时，此属性有助于链路自适应。我们的数值结果确实证明了在 CSIT 量级的情况下，该方案对于 2 用户设置的优越性。扩展到更一般的 $K$ - 简要讨论了用户场景。