The physical layer of an orthogonal frequency division multiplexing (OFDM) wireless communication system, operating in full-duplex (FD) mode is implemented in this paper, using GNU Radio software and universal software radio peripheral (USRP) hardware technology. The self-interference cancellation (SIC) is achieved on the FD node by applying four different techniques, two in the radio frequency (RF) domain and two in the digital domain. In the RF domain, a passive suppression is obtained by placing the transmit (Tx) and the receive (Rx) antennas such that they generate orthogonal electromagnetic fields. Also, an active signal suppression is achieved by changing the phase and attenuating the self-interference (SI) Tx signal, to generate a local SIC signal. The SIC signal and the Rx signal are then combined before going to the low noise amplifier at the FD node. In the digital domain, two techniques are applied to improve the interference cancellation and the quality of the link: firstly, virtual differentiation of the Tx and Rx signals is achieved by using OFDM symbols with different sizes; secondly, a spreading and precoding technique utilizing the discrete Fourier transform (DFT) is considered. In order to test the practical operation of the FD node, two simultaneous links between the three nodes are established. The results of the implemented system show that the SI can be reduced up to 58 dB which, along with the two digital techniques, allows to have two simultaneous links with a bit error rate similar to the one achieved with just one link without interference, increasing the spectral efficiency.

中文翻译：

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使用 GNU Radio 和 USRP 的全双工 DFTs-OFDM 系统上的自干扰消除


本文采用 GNU Radio 软件和通用软件无线电外围设备 (USRP) 硬件技术，实现了以全双工 (FD) 模式运行的正交频分复用 (OFDM) 无线通信系统的物理层。自干扰消除 (SIC) 是通过应用四种不同的技术在 FD 节点上实现的，其中两种技术在射频 (RF) 域，两种在数字域。在 RF 域中，通过放置发射 (Tx) 和接收 (Rx) 天线以生成正交电磁场来获得无源抑制。此外，通过改变相位并衰减自干扰（SI）Tx信号来实现主动信号抑制，以生成本地SIC信号。然后，SIC 信号和 Rx 信号在进入 FD 节点处的低噪声放大器之前进行组合。在数字域中，采用两种技术来提高干扰消除和链路质量：首先，利用不同大小的OFDM符号实现Tx和Rx信号的虚拟区分；其次，考虑利用离散傅立叶变换(DFT)的扩展和预编码技术。为了测试FD节点的实际运行情况，在三个节点之间建立了两条同时链路。所实施系统的结果表明，SI 最多可降低 58 dB，这与两种数字技术一起，允许同时拥有两条链路，其误码率与仅使用一条链路实现的误码率类似，没有干扰，从而增加了误码率。频谱效率。