The NI USRP-2921 (National Instruments Universal Software Radio Peripheral 2921) is a software-defined radio (SDR) hardware platform capable of transmitting and receiving radio frequency signals across a wide frequency range, commonly used in WiFi/CSI sensing research as a flexible, programmable RF front-end. In passive WiFi radar and CSI-based sensing systems, it serves as a critical receiver platform, enabling researchers to capture raw 802.11 WiFi signals emitted by commodity access points and process them for human activity recognition, through-the-wall sensing, and other passive sensing applications without modifying the illuminating transmitter. Its significance lies in its programmability and compatibility with software frameworks such as NI LabVIEW and GNU Radio, which allow fine-grained control over signal acquisition parameters, making it a preferred alternative to commodity network interface cards when experimental flexibility, wide bandwidth capture, or direct access to raw RF waveforms is required.
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