  Addressing the communication and sensing demands of sixth-generation (6G)
mobile communication system, integrated sensing and communication (ISAC) has
garnered traction in academia and industry. With the sensing limitation of
single base station (BS), multi-BS cooperative sensing is regarded as a
promising solution. The coexistence and overlapped coverage of macro BS (MBS)
and micro BS (MiBS) are common in the development of 6G, making the cooperative
sensing between MBS and MiBS feasible. Since MBS and MiBS work in low and high
frequency bands, respectively, the challenges of MBS and MiBS cooperative
sensing lie in the fusion method of the sensing information in high and
low-frequency bands. To this end, this paper introduces a symbol-level fusion
method and a grid-based three-dimensional discrete Fourier transform (3D-GDFT)
algorithm to achieve precise localization of multiple targets with limited
resources. Simulation results demonstrate that the proposed MBS and MiBS
cooperative sensing scheme outperforms traditional single BS (MBS/MiBS) sensing
scheme, showcasing superior sensing performance
