Movable-Signals Assisted Refocusing for Near-Field Communications with Movable Antenna

Near-field extremely large-scale arrays enable spherical-wave focusing, yet the focused gain is highly sensitive to range drift and lateral mismatch. When analog focusing weights are designed for a nominal location, even mild range variation induces a quadratic phase error across the aperture and sharply degrades the coherent combining gain. This paper studies how to correct this loss by jointly exploiting two reconfigurable degrees of freedom: element-wise movable antennas (MA) under movement and half-wavelength spacing constraints, and movable signals (MS) that retune one common carrier within a narrow window without redesigning the analog weights. Under a Fresnel approximation, we derive an element-wise phase-matched MA geometry family and show that MA-only refocusing becomes spacing-limited when range drift requires aperture compression, whereas joint MA–MS refocusing removes this compression burden whenever the required carrier lies inside the admissible MS window. We further characterize the beamformed channel under a geometric multipath model and show that MA reshapes the effective delay gap while MS aligns the dominant specular components within a finite frequency window. An outage expression is obtained in Marcum-Q form under a Rician effective channel, and a low-complexity alternating search is developed for the constrained MA–MS design. Numerical results validate the Fresnel-domain refocusing rule on the exact spherical-wave model, compare the proposed scheme with stronger practical references, and quantify sensitivity to the Rician factor, reflection strength, grid resolution, and minimum spacing. © 2012 IEEE.