XZero：实用的跨技术干扰消除LTE-U/WiFi共存
XZero: On Practical Cross-Technology Interference-Nulling for LTE-U/WiFi Coexistence
摘要：
通过从LTE-U BS向WiFi节点的跨技术干扰置零（CTIN）在空间中放置所谓的共存间隙，可以显著改善LTE-U/WiFi共存。为了交换控制消息，这种协调共存方案需要最近提出的LTE-U和WiFi网络之间的跨技术控制信道（CTC）。然而，不清楚实际的CTIN如何在没有CTIN所需但不能从CTC获得的信道状态信息的情况下操作。我们提出了XZero，第一个实用的CTIN系统，能够快速找到合适的预编码配置用于干扰置零，而不必搜索整个空间的角度方向。XZero执行基于树的搜索，以通过利用从WiFi AP接收的关于测试的零陷方向的反馈来找到零陷波束的方向。我们已经实现了一个原型的XZero使用SDR平台的LTE-U和商品硬件的WiFi和评估其性能在一个大型室内测试平台。评估结果显示，当使用具有四个天线的天线时，在空WiFi节点处的干扰噪声比平均降低15.7 dB。此外，XZero具有亚秒级的重新配置延迟，与朴素的穷举线性搜索相比，其最多小10倍。
英文摘要：
LTE-U/WiFi coexistence can be significantly improved by placing so-called coexistence gaps in space through cross-technology interference-nulling (CTIN) from LTE-U BS towards WiFi nodes. Such coordinated co-existence scheme requires, for the exchange of control messages, a cross-technology control channel (CTC) between LTE-U and WiFi networks which was presented recently. However, it is unclear how a practical CTIN operates in the absence of channel state information which is needed for CTIN but cannot be obtained from the CTC. We present XZero, the first practical CTIN system that is able to quickly find the suitable precoding configuration used for interference nulling without having to search the whole space of angular orientations. XZero performs a tree-based search to find the direction for the null beam(s) by exploiting the feedback received from the WiFi AP on the tested null directions. We have implemented a prototype of XZero using SDR platform for LTE-U and commodity hardware for WiFi and evaluated its performance in a large indoor testbed. Evaluation results reveal on average a reduction by 15.7 dB in interference-to-noise ratio at the nulled WiFi nodes when using a ULA with four antennas. Moreover, XZero has a sub-second reconfiguration delay which is up to 10x smaller as compared to naive exhaustive linear search.
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