Samples from one access point We measured the signal strength from a single access point over a five minute period. We took the samples one second apart for a total of 300 samples. the histogram range can be as large as 10 dBm or more.
during the online phase, the system should use
more than one sample in the estimation process to have a
better estimate of the signal strength at a location.
Small-Scale Variations These variations happen when the user moves over a small distance (order of wavelength). This leads to changes in the average received signal strength. For the 802.11b networks working at the 2.4 GHz range, the wavelength is 12.5 cm and we measure a variation in the average signal strength up to 10 dBm in a distance as small as 7.6 cm (3 inches) #HORUS System
Trainnig phase
Clustering module is used to group radio map locations based on
the access points covering them. Clustering is used to reduce the
computational requirements of the system and, hence, conserve power (Section 3.7).
Discrete Space Estimator module returns the radio map location
that has the maximum probability given the received signal strength
vector from different access points (Section 3.3).
Correlation Modelling and Handling modules use an autoregressive model
to capture the correlation between consecutive samples from the same access point.
This model is used to obtain a better discrete location estimate using the average
of n correlated samples (Section 3.4).
Continuous Space Estimator takes as an input the discrete estimated user location, one of the radio map locations, and returns a more accurate estimate of the user location in the continuous space (Section 3.5).
Small-Scale Compensator module handles the small-scale variation characteristics of the wireless channel (Section 3.6).