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Markus Bullmann
2020-01-28 12:47:52 +01:00
parent c1911fc563
commit e638cecced
5 changed files with 109 additions and 27 deletions
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tex/chapters/3_ftm.tex
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@@ -157,6 +157,7 @@ Assuming that the signal propagates constantly at the speed of light the distanc
%TODO ToF -> distance ToF/2 * c
%TODO IEEE 802.11-2016 6.3.58.1
The accuracy of distance estimate depends on the ability of the hardware to detect the line-of-sight signal, or direct path.
In an indoor environment it is very common that a signal will reach the receiver from different paths with different lengths.
The prime example is a signal which reaches the receiver via a direct line-of-sight propagation plus two reflected paths of the same length.
@@ -170,7 +171,7 @@ Hence, the time resolution is proportional to the inverse of the bandwidth.
In \ieeWifiN the channel bandwidth is \SI{20}{Mhz} in the \SI{2.4}{GHz} range which results in a sampling rate of one sample every \SI{50}{ns}, or one sample every \SI{12.5}{ns} for \SI{80}{Mhz} channels in the \ieeWifiAC \SI{5}{GHz} range.
Assuming that the receiver recognizes the signal at the first sample of the preamble the smallest possible resolution of the range estimate is \SI{15}{m} for \SI{20}{Mhz} bandwidth, and \SI{3.74}{m} for \SI{80}{Mhz}.
To allow much finer resolution the receiver uses super resolution methods to allow sub-sample resolution \cite{TODO}.
%TODO genaue implementierung unbekannt und daher black box
%Therefore, time-based distance estimates can greatly differ from the ideal euclidean distance.
In addition to distance measurements the \ieeWifiFTM standard defines a format to transfer location information about the responder.