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Full-duplex (FD)wireless communication, the simultaneoustransmissionandreceptionofwirelesssignalsonthesamefrequencychannel,has garneredsignificant attentionfromtheresearch community over the past decade. Softwaredefined radio (SDR) has become instrumental inbridgingthegapfromtheorytoimplementation,providingtheflexibilitynecessarytodesign anddeployFDradionodes, links,andnetworks. AspartoftheFull-DuplexWireless:FromIntegratedCircuitstoNetworks(FlexICoN)project, wehavedevelopedthreegenerationsofIC-based FDradiosthatutilizeGNURadioastheprimary controlandsignalprocessingplatform.Thispaperpresentsanoverviewof thedesignconsiderationsandtechniquesforimplementingFDin GNURadio,fromthetransmitandreceivesignal processingchainstobroadertestbedintegration. 

Full-duplex (FD) wireless can significantly enhance spectrum efficiency but requires tremendous amount of selfinterference (SI) cancellation. Recent advances in the RFIC community enabled wideband RF SI cancellation (SIC) in integrated circuits (ICs) via frequency-domain equalization (FDE), where reconfigurable RF filters are used to channelize the SI signal path. In [2], we designed and implemented an FDEbased RF canceller on a printed circuit board (PCB). We also presented an optimized canceller configuration scheme based on the derived canceller model, and extensively evaluated the performance of the FDE-based FD radios in a softwaredefined radio (SDR) testbed in different network settings. 

In order to support experimentation with full-duplex (FD) wireless, we integrated the FlexICoN Gen-2 wideband FD radio with the city-scale PAWR COSMOS testbed [1]. In particular, the implemented FD radio consists of an antenna, a customized Gen-2 RF self-interference (SI) canceller box, a USRP software-defined radio (SDR), and a compute node. The RF canceller box includes an RF SI canceller implemented using discrete components on a printed circuit board (PCB), which emulates its RFIC canceller counterpart. The Gen-2 RF SI canceller achieves 50 dB RF SI cancellation across 20 MHz bandwidth using the technique of frequency-domain equalization (FDE) [2]. In this abstract, we present the design and implementation of the remotely accessible Gen-2 wideband FD radio integrated with the COSMOS sandbox at Columbia University. We also present an example real-time wideband FD wireless link demonstration using the GNU Radio software. 

Full-duplex (FD) wireless can significantly enhance spectrum efficiency but requires tremendous amount of selfinterference (SI) cancellation. Recent advances in the RFIC community enabled wideband RF SI cancellation (SIC) in integrated circuits (ICs) via frequency-domain equalization (FDE), where RF filters channelize the SI signal path. Unlike other FD implementations, that mostly rely on delay lines, FDE-based cancellers can be realized in small-formfactor devices. However, the fundamental limits and higher layer challenges associated with these cancellers were not explored yet. Therefore, and in order to support the integration with a software-defined radio (SDR) and to facilitate experimentation in a testbed with several nodes, we design and implement an FDE-based RF canceller on a printed circuit board (PCB). We derive and experimentally validate the PCB canceller model and present a canceller configuration scheme based on an optimization problem. We then extensively evaluate the performance of the FDE-based FD radio in the SDR testbed. Experiments show that it achieves 95 dB overall SIC (52 dB from RF SIC) across 20 MHz bandwidth, and an average link-level FD gain of 1.87×. We also conduct experiments in: (i) uplink-downlink networks with inter-user interference, and (ii) heterogeneous networks with half-duplex and FD users. The experimental FD gains in the two types of networks confirm previous analytical results. They depend on the users’ SNR values and the number of FD users, and are 1.14×–1.25× and 1.25×–1.73×, respectively. Finally, we numerically evaluate and compare the RFIC and PCB implementations and study various design tradeoffs.