For IoT applications LPWA is a useful communication choice that enables us to connect tiny devices spread over the land to the Internet. Since many low-price IoT devices usually need to work with limited power budget, this kind of low-power long-range communication technique is a strong tool to populate IoT deployment. Since LPWA devices are less functional, localization of devices are addressed as one of the important practical problems. UNB (Ultra Narrow Band)-based LPWA networks such as Sigfox are one of the major LPWA services for IoT applications, which have a long communication range more than 10km. However, due to the long-range communications and the property of UNB-based modulation, it is not possible to use state-of-the-art localization techniques with high-accuracy; UNB-based LPWA should use simple methods based on RSSI (Radio Signal Strength Indicator) that involves large position estimation errors. In this paper, we propose a method to improve accuracy of device localization in UNB-based LPWA networks by utilizing portable Access Points (APs). By introducing a distance-based weighting technique, we improve the localization accuracy in combination with stationary and portable APs. We demonstrated that the portable AP and the new weighting technique effectively works in UNB-based LPWA networks.------------------------------This is a preprint of an article intended for publication Journal ofInformation Processing(JIP). This preprint should not be cited. Thisarticle should be cited as: Journal of Information Processing Vol.29(2021) (online)DOI　http://dx.doi.org/10.2197/ipsjjip.29.149------------------------------

\n------------------------------This is a preprint of an article intended for publication Journal ofInformation Processing(JIP). This preprint should not be cited. Thisarticle should be cited as: Journal of Information Processing Vol.29(2021) (online)DOI　http://dx.doi.org/10.2197/ipsjjip.29.149------------------------------