Synchronization and Time Resolution Improvement for 802.11 WLAN OWPT Measurement

This paper proposes novel algorithms for synchronizations and time resolution improvements of One Way Propagation Time (OWPT) measurement in the 802.11 Wireless Local Area Network (WLAN). In OWPT measurement, the Mobile Station (MS) records each 802.11 Beacon frame’s arrival time. The Beacon frame’s arrival time minus its Timestamp, which is recorded when the Beacon frame is transmitted from an Access Point (AP), is the Beacon frame’s Propagation Time. The Propagation Time represents the distance between the MS and the AP. Different from microseconds (μs) time resolution Timestamp, the MS can use its high frequency clock to record the Beacon frame’s arrival time in nanoseconds (ns). The proposed algorithms can utilize the ns resolution arrival Time to improve the OWPT measurement time resolution from μs to ns and to highly synchronize the MS with all APs. These algorithms provide opportunity to apply OWPT in 802.11 WLAN for highly accurate indoor localization. In theory, without considering other indoor localization error sources, these algorithms can improve the localization accuracy to sub-meter.