  This paper proposes a semi-sequential probabilistic model (SSP) that applies
an additional short term memory to enhance the performance of the probabilistic
indoor localization. The conventional probabilistic methods normally treat the
locations in the database indiscriminately. In contrast, SSP leverages the
information of the previous position to determine the probable location since
the user's speed in an indoor environment is bounded and locations near the
previous one have higher probability than the other locations. Although the SSP
utilizes the previous location information, it does not require the exact
moving speed and direction of the user. On-site experiments using the received
signal strength indicator (RSSI) and channel state information (CSI)
fingerprints for localization demonstrate that SSP reduces the maximum error
and boosts the performance of existing probabilistic approaches by 25% - 30%.
