Timing advance (TA) value
corresponds to the length of time a signal takes to reach the base station from a mobile phone. The TA value is normally
between 0 and 63, with each step representing an advance of one bit period
(approximately 3.69 microseconds). With radio waves travelling at about
300,000,000 metres per second (that is 300 metres per microsecond), one TA step
then represents a change in round-trip distance (twice the propagation range)
of about 1,100 metres. This means that the TA value changes for each 550-metre
change in the range between a mobile and the base station. This limit of
63 × 550 metres is the maximum 35 kilometres that a device can
be from a base station and is the upper bound on cell placement distance.
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