This paper we provide a tractable system for 2-tier users, wearable device terminals (WTDs) are in tier 2 and under the control of tier 1 users. Tier 1 user works as full-duplex relay to charge the WTDs on the downlink (DL) based on wireless power transfer (WPT), then help WTDs to transmit the information on the uplink (UL). Both of the users and picocell base stations (BS) are randomly distributed based on homogeneous poison point process (HPPP). We only considered the user association for the tier 1 users that tier 1 users always connect to the closest BS on UL since WTDs tier 2 users are close enough to tier 1 users. In this paper, we analyzed the processes of wireless power transfer on DL and information transmission on UL. We derived analysis of the average harvested energy on DL for both 2-tier users, the average ergodic rate and outage probability on UL for WTDs tier 2 users. According to the analytical results, it is observed that with the density of the picocell base stations increased, the average harvested energy increased, but the average ergodic rate and UL outage probability degraded significantly because of the UL performance decreased.