FR3-DUALIS: from signal processing to spectrum allocation for real-time wideband full-duplex ISAC—a prototype validation at FR3

Abstract Integrated sensing and communication (ISAC) has emerged as a key enabling technology for future 6G networks. Existing implementations encounter fundamental trade-offs: single-band full-duplex systems require complex self-interference cancellation (SIC), time-division approaches compromise continuous sensing, and multi-waveform systems lack hardware reuse, limiting integration efficiency. Time-domain-sampled wideband and multiband prototypes, which could simultaneously improve communication throughput and real-time velocity estimation, remain largely unexplored, despite their potential for practical ISAC deployment.This work presents a wideband dual-band full-duplex ISAC prototype operating in the upper FR3 band with 360 MHz bandwidth per channel. The system operates at 24.25 GHz for bistatic communication and 25.175 GHz for monostatic sensing. Each function uses a dedicated transmit and a receive channel, and the 925 MHz frequency separation provides spectrum-domain isolation between the communication and sensing functions. Experimental validation shows that frequency-separated operation achieves BER = 0 over the tested QPSK-OFDM communication frames, matching the communication-only baseline, while same-frequency dual-function operation results in clear degradation (BER of approximately 0.05). These results confirm that spectrum-domain resource partitioning can suppress cross-function interference without requiring complex digital cancellation. A unified OFDM baseband architecture enables hardware sharing while allowing independent waveform optimization: Zadoff-Chu sequences for sensing improve the peak-to-sidelobe ratio (PSLR) and integrated-sidelobe-level ratio (ISLR) by 2.49 dB and 4.43 dB, respectively, compared with QPSK-based sensing.Beyond system demonstration, we provide a hardware-grounded analysis of wideband ISAC feasibility. Experimental characterization shows that at least 8192 subcarriers are required for stable ranging due to common phase error scaling, and identifies 360 MHz as the maximum sustainable bandwidth under real-time processing constraints. Real-time implementation achieves continuous velocity tracking at 10 Hz with 0.21 m/s resolution using 1000 OFDM symbols per frame.\\bixing{These results reveal a fundamental processing–spectrum trade-off in full-duplex ISAC design: self-interference mitigation can be shifted from an active computational task with \\((\\mathcal{O}(LN))\\) complexity -- where \\((N)\\) is the number of OFDM subcarriers and \\((L)\\) is the number of taps in the self-interference channel model -- to a passive spectrum-allocation decision, at the expense of increased spectrum occupancy and duplicated RF chains. The proposed architecture thus defines a practical operating point for spectrum-abundant deployments and a framework for hardware-constrained wideband ISAC system design.}