數位預失真輔助之全雙工無線系統

Abstract

在2013年，史丹佛大學的一個研究團隊成功發展出單輸入單輸出之全雙工無線系統，在2014年，他們進一步完成了多輸入多輸出全雙工無線系統。多輸入多輸出全雙工無線系統中，除了自干擾訊號外，還有交叉干擾訊號需要被消除。由於放大器會造成訊號的非線性失真，因此在數位干擾消除器中也需做非線性干擾消除。在做非線性干擾消除時，濾波器需大量的係數，因此會造成高的運算複雜度，這在天線數目增加時會顯得更嚴重。本篇論文提出使用數位預失真技術來解決此問題，為了進一步降低接收機的複雜度，我們使用了限制頻寬之數位預失真技術，此數位預失真器可以有效的降低類比數位轉換器之取樣率數位，使用我們所提出的方法將無須非線性之干擾消除。模擬結果顯示，配合類比干擾消除，我們所提出的方法可達到系統要求，即單輸入單輸出全雙工無線系統自干擾消除達106分貝以上，而多輸入多輸出全雙工無線系統自干擾消除達103分貝以上。

In 2013, a research team in Stanford University announced that it has successfully developed a full-duplex radio (FDR) system. In 2014 it further declares that a MIMO FDR system had also been developed. In MIMO FDR, both self-interference (SI) and cross-interference (CI) cancellation are needed to cancel. To cope with the nonlinearity caused by the power amplifier, the digital canceller has to conduct nonlinear interference cancellation. Since the cancellation costs many filter taps, the computational complexity can be high, especially when the MIMO size is large. This thesis proposes the use of digital predistortor (DPD) to solve the problem. To reduce the complexity of the receiver, the band-limited DPD is employed. With the DPD, the sampling rate of the ADC can be effectively reduced. With the proposed scheme, no nonlinear cancellation is required in the digital canceller. Simulations show that the proposed algorithms, along with analog cancellation, can effectively cancel SI/CI such that the performance requirement can be met, i.e, 106dB for SISO and 103dB for MIMO FDR.