GNSS Position Computation without Ephemeris “Single Shot MS Based”

J. de Salas, F. van Diggelen

Abstract:	In Assisted GPS (GNSS) there is some information in the form of “assistance” data that is sent to the mobile terminal equipped with a GNSS receiver. Assistance data helps the GNSS receiver acquire satellite signals faster and at lower power levels as well as compute its own position. Assistance data is essential in many GNSS use cases but it is especially relevant in emergency calls from mobile terminals (e911, e112) where a fast response and the best sensitivity are required. GNSS assistance data is standardized by 3GPP and 3GPP2 in two different flavours, broadly known as MS Based and MS Assisted in GSM/EDGE; and UE Based and UE Assisted in WCMDA. MS Based methods compute the geographical location inside the mobile terminal whereas MS Assisted methods compute position in the network from satellite measurements (range, Doppler shift) taken by the mobile terminal. MS Based methods enjoy certain performance benefits in position accuracy and response time when compared with MS Assisted methods. However, the amount of assistance data required for MS Based operation is substantially larger than the assistance data required by MS Assisted methods. It is for this latter reason that some network operators choose the MS Assisted methods for their emergency call services. Larger bandwidth requirements are of deep concern if many callers demand the services at the same time because network capacity could be challenged when it is most needed. The subject of this paper is a method that allows the mobile terminal to compute its position inside the terminal and thus enjoys the benefits outlined above but with the same assistance data used in MS Assisted methods, only with increased resolution in some of the fields. We call this method “Single Shot MS Based”. The benefit for network operators is obvious because they can deliver the best performance with the minimum bandwidth requirements. This is especially relevant in emergency call situations as will be discussed further in this paper. Some 3GPP specifications will need to be modified slightly in order to increase the resolution of the relevant assistance data fields. Namely, 3GPP TS 44.031, 3GPP TS 25.331 and 3GPP TS 36.355
Published in:	Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010) September 21 - 24, 2010 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	1094 - 1099
Cite this article:	de Salas, J., van Diggelen, F., "GNSS Position Computation without Ephemeris “Single Shot MS Based”," Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010), Portland, OR, September 2010, pp. 1094-1099.
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