Performance Analysis of Sub-band Full-duplex Cell-free Massive MIMO ISAC Systems

Paper in proceeding, 2026

This paper presents sub-band full-duplex (SBFD) as an alternative to in-band full-duplex (IBFD) for enabling simultaneous wireless communication and sensing in cell-free massive MIMO (CF-mMIMO) systems. Unlike IBFD integrated sensing and communication (ISAC) systems that require self-interference cancellation and the decoupling of mutual interference between uplink communication and radar signals, SBFD employs non-overlapping frequency resources for uplink and downlink or radar transmissions within a predefined SBFD timeslot. In the proposed SBFD CF-mMIMO ISAC system, we demonstrate a multi-target position tracking scheme, where range and angle-of-arrival (AoA) measurements are fused with an extended Kalman filter. We further characterize the joint impact of residual self-interference (SI), access point (AP)-to-AP cross-link interference (CLI), uplink communication interference, and AP-user equipment association on the Cramér-Rao lower bounds (CRLBs) of range and AoA estimation. Results indicate that, in the high residual SI/CLI power regime, SBFD experiences less degradation in range and AoA CRLBs compared to IBFD due to its inherent frequency isolation. Specifically, increasing residual SI/CLI power from 30 dBm to 50 dBm increases the CRLBs by 3.01 m2 and 0.09 rad2 for SBFD compared to an increase of 12.94 m2 and 0.34 rad2 for IBFD at a residual UL communication interference of -10 dBm. Further, performance analysis reveals a performance dependence on power allocation and the ratio of radar to communication sub-band allocation.