同频带全双工中集成自干扰射频抵消技术研究

Nowadays, in traditional duplex modes, Frequency-Division Duplexing（FDD) or Time-Division Duplexing (TDD) is usually employed in wireless commucation. However, More precious spectrum resource is consumed in FDD mode, while the data rate is degraded in TDD mode. The realization of single-channel simultaneous bidirectional communication will double the spectrum efficiency and data rate. The biggest barrier is the self-interference when the strong transmitting signal is coupled onto the weak receiving signal internally. In order to avoid the strong self-interference signal deteriorating the reveiver front-end, RF self-interference cancelling will be the indispensable technique to realize the single-channel full-duplex communication. Aiming at the problems in the existing techniques, this proposal is to explore the self-adapting self-interference RF cancelling technique which can be integrated in CMOS process. First, the technique aims at single antenna system, which is distinguished from antenna cancelling scheme that adopting multiple antennas. Second, in this RF cancelling technique, the cancelling signal that has the same magnitude and phase compared with the self-interference signal is produced based on the principle of quadrature vector synthesis. As a result, the cancelling bandwidth limitation is completely broken, and a self-interference rejection up to 40dB or more could be achieved over wider bandwidth. The magnitude-weight control signal of the quadrature vectors is generated in digital domain through detecting the remaining self-interference signal after cancelling. Thus, automatic control is realized. Finally, the technique proposed in this project is easy to integrate using standard CMOS process. It prevents the disadvantages of the existing prototype systems implemented by off-the-shelf components and has the advantages of lower cost, higher integration density and broader applicability to mobile terminal. The proposed self-interference RF cancelling technique will speed up the realization of single-channle simultaneous bidirectional communication.

目前无线通信通常采用频分复用(FDD)或时分复用(TDD)的双工方式，前者占用了更多的频谱资源，后者则降低了数据传输率。同频带全双工的实现可使频谱效率加倍，但最大障碍源于收发机内部发射对接收的自干扰。为了防止过大自干扰信号对接收机的损害，射频抵消技术是实现同频全双工必不可少的技术。针对目前该技术存在的关键问题，本项目旨在探索一种CMOS工艺集成的自干扰射频抵消方案。首先，其不同于多天线方案，而是只采用单天线；其次，该射频抵消技术基于正交矢量合成原理产生幅值和相位与自干扰相同的抵消信号，完全打破了抵消带宽的限制，可以在更宽带宽上实现40dB以上的自干扰抑制；矢量幅度控制信号则通过检测抵消后的残余信号在数字域中生成，可实现自动控制；最后，该方案易于CMOS集成实现，摒弃当前分立元件原型系统的不足，成本更低、集成度更高，而且可应用于移动终端。本项目的自干扰射频抵消方案将加速同频全双工通信的实现。

全双工通信可以在同一频带上实现同时发射和接收，使频谱效率加倍。尤其在占用最密集的频段（100MHz至5GHz），全双工可有效提高稀缺频谱的利用率。因而，同时同频全双工技术（Co-time Co-frequency Full Duplex, CCFD）也受到高速个人无线通信的青睐，被认为是5G潜在关键技术。然而，显著的挑战仍然存在，即源于收发机内部发射对接收的自干扰。因此，探索一种低成本、高集成度、共享天线、宽抵消带宽的射频自干扰抵消技术具有重要的意义。. 本项目针对单频带全双工射频自干扰抵消系统中存在的难题：适用单天线系统、打破抵消带宽限制、CMOS单片集成、自干扰抵消的自适应控制等问题，开展了大量的研究和工程实践工作，具体包括：1）提出了三种有源环形器结构，采用0.18um CMOS工艺，进行了三次流片验证，实现了发射到接收端之间25dB的隔离度； 2）提出了基于正交矢量合成的系统架构，打破了抵消带宽的限制；3）设计了电流域抵消方法，结合正交矢量合成的抵消通路结构，为该方案的CMOS单片集成提供了切实可行的实现方案；4）提出了结合二分搜索法和梯度递减算法的自适应控制方法。本项目研究并设计了所有的电路模块，完成了0.18m CMOS工艺下整个射频自干扰抵消系统芯片的版图设计和流片，实现了在100MHz带宽上70dB的自干扰抵消比，达到国际先进水平。. 本项目共发表论文8篇，其中SCI期刊论文3篇，国际会议论文2篇，申请发明专利8项，另有3篇SCI期刊论文在投。培养博士生1人，硕士生4人。