A mobile device, base stations, a backhaul network device for a wireless network system, and a method and a computer program storage product for the mobile device are provided. Each of the base stations is connected to the backhaul network device via a wired connection. The mobile device selects a primary base station and a backup base station from the base stations according to base station information of each base station. The mobile device performs a data transmission procedure with the primary base station during an available interval of a low-duty mode to communicate with the backhaul network device via the primary base station, and performs a connection keeping procedure with the backup base station during an unavailable interval of the low-duty mode. While the data transmission procedure fails, the mobile device performs a data transmission recovery procedure with the backup base station immediately so as to continuously communicate with the backhaul network device via the backup base station.