Iterative SSBI mitigation-enabled global linearization of seamlessly converged fiber-mmWave transmission systems

Utilizing free-running laser and passive envelope detector (ED)-based mmWave generation and detection,seamlessly converged fiber-mmWave transmission systems can be implemented to enable continuous flows of6G-originated heterogeneous signals across different network segments (fiber and free space). However, due tothe absence of intermediate signal distortion compensation and inherent nonlinear operations of the EDs, suchtransmission systems suffer from ED-induced signal-to-signal beating interference (SSBI) and accumulated signal distortions along the entire transmission link. To effectively address these challenges, this paper theoreticallyinvestigates and experimentally demonstrates the global linearization of a fiber-mmWave converged transmissionsystem by employing an iterative SSBI mitigation technique of low complexity. The optimal number of iterations required for effective SSBI suppression is analytically derived, based on which comprehensive performanceevaluations are undertaken experimentally of a >3.556 Gb/s transmission system comprising a 25 km fiber linkand a 5 m, 36GHzwireless link. Experimental results show that the optimal iteration number can be accuratelyestimated using key transmission system design parameters, including the carrier-to-signal power ratio, modulation index, and scaling factor employed in the iterative SSBI mitigation process. Furthermore, compared withKramers–Kronig receivers, the iterative SSBI mitigation technique reduces the required multiplier and addercounts by >44.4%and>53.7%,respectively, and eliminates the need for additional lookup-table memory, whilestill maintaining similar transmission performance and excellent mmWave frequency tunability, flexible bitratevariation, and adaptive mmWave radio coverage.