Currently communication traffic is explosively increasing with the full-scale operation of the fifth-generation mobile communication system (5G). While some frequency bands have already been allocated to the 5G, the allocated bandwidth is still insufficient. Thus, it is necessary to secure more frequency resources; however, it is difficult to squeeze out new frequency bands, especially in sub-6 GHz bands. To cope with the frequency resource shortage problem, dynamic spectrum sharing technology has attracted attentions since this technology allows dynamic operation of the 5G in the dedicated bands to other systems without interfering with primary users. In this paper, for spectrum sharing in the 2.3 GHz band of Japan, we propose sensing methods efficiently and reliably detecting the field pickup unit (FPU) signal based on ARIB STD-B57. The proposed methods can detect sufficiently low FPU signals with SNR = -10 dB in a multi-path fading environment.