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Netw."],"published-print":{"date-parts":[[2022,8,31]]},"abstract":"<jats:p>Wireless sensor networks have enabled smart infrastructures and novel applications. With the recent roll-out of Narrowband IoT (NB-IoT) cellular radio technology, wireless sensors can be widely deployed for data collection in cities around the world. However, empirical evidence regarding the coverage and connectivity of NB-IoT in dense urban areas is limited. This article presents an empirical study that focuses on evaluating the coverage and connectivity of NB-IoT in a dense urban environment. We have designed an NB-IoT sensor node and deployed over 100 of them in high-rise apartment buildings in Hong Kong. These sensor nodes utilize a commercial NB-IoT network to collect high-resolution water flow data for machine learning model training and provide timely feedback to users. We collect and analyze the empirical NB-IoT signal measurements from the sensor nodes deployed in various challenging outdoor and indoor environments for over three months. These empirical measurements reveal correlations between NB-IoT connectivity and sensor installation environments. We also observe that inter-cell interference, as a result of coverage by multiple neighboring NB-IoT cells in a dense urban environment, is a source of connectivity degradation. We discuss potential issues that IoT application designers and system integrators might encounter in practical NB-IoT devices deployment, and we propose a transmission decision algorithm based on signal measurements for mitigating energy wasted due to transmission failures. Finally, we demonstrate the results and the benefits of using high-resolution water flow data collected by our purpose-built NB-IoT sensor nodes for studying the patterns of domestic water consumption in Hong Kong.<\/jats:p>\n          <jats:p\/>","DOI":"10.1145\/3536424","type":"journal-article","created":{"date-parts":[[2022,5,17]],"date-time":"2022-05-17T13:32:27Z","timestamp":1652794347000},"page":"1-36","update-policy":"https:\/\/doi.org\/10.1145\/crossmark-policy","source":"Crossref","is-referenced-by-count":11,"title":["NB-IoT Coverage and Sensor Node Connectivity in Dense\u00a0Urban\u00a0Environments: An Empirical Study"],"prefix":"10.1145","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0344-7970","authenticated-orcid":false,"given":"Cheuk-Wang","family":"Yau","sequence":"first","affiliation":[{"name":"The University of Hong Kong, Pokfulam, Hong Kong, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8370-9984","authenticated-orcid":false,"given":"Sukanya","family":"Jewsakul","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Pokfulam, Hong Kong, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9014-3205","authenticated-orcid":false,"given":"Man-Ho","family":"Luk","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Pokfulam, Hong Kong, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7072-8692","authenticated-orcid":false,"given":"Angela P. Y.","family":"Lee","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Pokfulam, Hong Kong, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1400-0605","authenticated-orcid":false,"given":"Yun-Hin","family":"Chan","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Pokfulam, Hong Kong, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3454-8731","authenticated-orcid":false,"given":"Edith C. H.","family":"Ngai","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Pokfulam, Hong Kong, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5554-8386","authenticated-orcid":false,"given":"Philip W. 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