Transfer of position information to a mobile terminal

Abstract

The invention provides a method of combining satellite positioning system signals and position information derived from such signals in a mobile terminal, when these are available at a first location, with cellular communication signals and a method, system and apparatus for determining the approximate position information for the said mobile terminal when SPS signals are not available at a second location. The approximate position is determined in the mobile terminal only using a position difference vector derived from the cellular communication signals using time offsets and associated time-tags in a method based on the observed time difference of arrival. The computations of cellular position and position difference information are made within the network infrastructure. The invention provides for the security of the user as only position difference information is communicated over the air interface, or transmission time offset measurements which require non-transmitted information to determine a solution. In a further aspect of the invention, the approximate position information is used to provide position assistance information to an SPS receiver for the purposes of (a) satellite signal acquisition with reduced search time and/or (b) initial position information for the calculation of SPS location which thereby avoids the 'integer ambiguity' problem resulting from the repetitive nature of the SPS ranging signals.