WO2005008273A1

WO2005008273A1 - Gps receiver and server for assisted gps

Info

Publication number: WO2005008273A1
Application number: PCT/IB2004/002277
Authority: WO
Inventors: Saul R. Dooley; Andrew T. Yule
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-07-17
Filing date: 2004-07-12
Publication date: 2005-01-27
Also published as: GB0316691D0

Abstract

A server is disclosed which is configured to transmit to a remote GPS receiver upon determining the availability of updated assistance data for assisting the GPS receiver to acquire GPS signals either a signal notifying the GPS receiver of such availability or a signal containing the updated assistance data. Such a server may be configured to both transmit a signal notifying the GPS receiver of such availability and, upon receiving a request from the remote GPS receiver for the updated assistance data, to transmit the updated assistance data to the GPS receiver. Also disclosed is a GPS receiver configured to request from a remote server updated assistance data for assisting the GPS receiver to acquire GPS signals upon determining that such assistance data currently stored by the GPS receiver is invalid.

Description

DESCRIPTION

GPS RECEIVER AND SERVER FOR ASSISTED GPS This invention relates to a server configured to transmit to a remote

GPS receiver assistance data for assisting the GPS receiver to acquire GPS signals and to a GPS receiver configured to request from a remote server such assistance data. PCT patent application, publication number WO02/099454A2 concerns a method and apparatus for generating and distributing satellite tracking information. In particular, the section entitled "Description of the Related Art" of that patent acknowledges the difficulty that a NAVSTAR GPS receiver experiences in downloading ephemeris (satellite orbit and clock data) from a GPS satellite in low signal strength conditions; and also the AGPS solution to this problem in which ephemeris data in GPS signals is received by a GPS receiver at a reference station and transmitted onwards to a remote GPS receiver which uses this ephemeris instead of that transmitted directly from GPS satellites to obtain a position fix. WO02/099454A2 indicates that since the source of AGPS ephemeris is ultimately the GPS satellites, the ephemeris remains valid for only a few hours (because of the simplified satellite orbit model described by standard NAVSTAR GPS ephemeris). As such, AGPS necessitates the remote GPS receiver connecting to a source of ephemeris information either periodically or each time a position fix is desired to ensure it is in possession of up to date ephemeris. Without up to date ephemeris, a remote GPS receiver will not be able to accurately determine its position. In addition, a GPS receiver may use such ephemeris to acquire GPS signals more quickly whereas otherwise, it would have to wait at least 30 seconds to receive and demodulate the entire ephemeris data message on a GPS signal.

In accordance with the present invention, there is provided a server configured to transmit to a remote GPS receiver upon determining the availability of updated assistance data for assisting the GPS receiver to acquire GPS signals either a signal notifying the GPS receiver of such availability or a signal containing the updated assistance data. Such a server may be configured to both transmit a signal notifying the GPS receiver of such availability and, upon receiving a request from the remote GPS receiver for the updated assistance data, to transmit the updated assistance data to the GPS receiver. Further provided in accordance with the present invention is a GPS receiver configured to request from a remote server updated assistance data for assisting the GPS receiver to acquire GPS signals upon determining that such assistance data currently stored by the GPS receiver is invalid. The inventors have realised that whilst conventional AGPS systems require the GPS receiver to obtain assistance data either each time prior to determination of a position fix or periodically, this need not be the case. Rather, ephemeris data which is generally valid for between 2 and 4 hours may be used to determine a position fix repeatedly and only need be updated when it has become invalid. Hence, an improved AGPS system can be provided based on this realisation by providing either a base station / server which upon determining the availability of updated assistance data will provide or offer, e.g. for remuneration, the updated assistance data to a GPS receiver; or a GPS receiver which will active request such assistance data upon determining that such assistance data currently stored by that GPS receiver is invalid. The present invention will now be described, by way of example only, of an embodiment of a mobile cellular telephone comprising a GPS receiver for use in a cellular telephone network with reference to the accompanying schematic drawings in which: Figure 1 shows the geographic layout of a cellular telephone network; Figure 2 shows the mobile cellular telephone MS1 of figure 1 in greater detail; and Figure 3 shows the base station BS1 of figure 1 in greater detail. The geographical layout of a conventional cellular telephone network 1 is shown schematically in figure 1. The network comprises a plurality of base stations BS of which seven, BS1 to BS7, are shown, situated at respective, mutually spaced geographic locations. Each of these base stations comprises the entirety of a radio transmitter and receiver operated by a trunking system controller at any one site or service area. The respective service areas SA1 to SA7 of these base stations overlap, as shown by the cross hatching, to collectively cover the whole region shown. The system may furthermore comprise a system controller SC provided with a two-way communication link, CL1 to CL7 respectively, to each base station BS1 to BS7. Each of these communication links may be, for example, a dedicated land-line. The system controller SC may, furthermore, be connected to a the public switched telephone network (PSTN) to enable communication to take place between a mobile cellular telephone MS1 and a subscriber to that network. A plurality of mobile cellular telephones MS are provided of which three, MS1 , MS2 and MS3 are shown, each being able to roam freely throughout the whole region, and indeed outside it. Referring to figure 2, mobile cellular telephone MS1 is shown in greater detail comprising a communications transmitter (Comm Tx) and receiver (Comm Rx) 21 connected to a communications antenna 20 and controlled by a communications microprocessor (Comm μc) 22 for communication with the base station BS1 with which it is registered. The design and manufacturing of such telephones for two-way communication within a cellular telephone network are well known, those parts which do not form part of the present invention will not be elaborated upon here further. In addition to the conventional components of a mobile telephone, telephone MS1 further comprises a GPS receiver (GPS Rx) 24 connected to a GPS antenna 23 and controlled by a GPS microprocessor (GPS μc) 25 receiving GPS spread spectrum signals transmitted from orbiting GPS satellites. When operative, the GPS receiver 24 may receive NAVSTAR SPS GPS signal through an antenna 23 and pre-process them, typically by passive bandpass filtering in order to minimise out-of-band RF interference, preamplification, down conversion to an intermediate frequency (IF) and analog to digital conversion. The resultant, digitised IF signal remains modulated, still containing all the information from the available satellites, and is fed into a memory of the GPS microprocessor 25. The GPS signals may then be are acquired and tracked in any of several digital receiver channels, typically up to 12, for the purpose of deriving pseudorange information from which the position of the mobile telephone can be determined using conventional navigation algorithms. Such methods for GPS signal acquisition and tracking are well known, for example, see chapter 4 (GPS satellite signal characteristics) & chapter 5 (GPS satellite signal acquisition and tracking) of GPS Principles and Applications (Editor, Kaplan) ISBN 0-89006-793-7 Artech House. The GPS microprocessor 25 may be implemented in the form a general purpose microprocessor, optionally common with the communications microprocessor 22, or a microprocessor embedded in a GPS application specific integrated circuit (ASIC). Cellular telephone network base station BS1 is shown schematically in figure 3. In additional to the conventional components of a base station, it further comprises a GPS antenna 34, receiver 35 and microprocessor 36 which are in substantially continual operation whereby the base station is in constant possession of up to date GPS satellite information. This information includes which of the orbiting satellites are presently in view (such satellites are likely to be common to both telephone and associated base station for even macrocells, obscuration aside); the GPS data message containing an up to date almanac and ephemeris data and satellite clock correction data, and the Doppler shift and current code phase of the GPS satellites signals as observed by the base station. In accordance with the present invention, the GPS processor 25 of mobile telephone MS1 may acquire incoming GPS signals as illustrated in the following example scenarios: Example 1 The GPS receiver of the base station, which as mentioned is in constant possession of up to date GPS satellite information, detects updated ephemeris by a detecting the change in the "Issue of Data" (IOD) field of the GPS satellite data message. In response to this and under the control of the system controller SC via a two-way communication link CL1 , the base station BS1 sends a signal to the mobile telephone MS1 instructing it to ask the user of telephone MS1 whether the user wishes to download to the mobile telephone up to date ephemeris for a specified fee. If the user instructs the mobile telephone to answer "yes", a signal sent by the mobile telephone which causes the base station to transmit the ephemeris and a corresponding fee to be applied to the user's monthly telephone bill. Note, the mode of communication in which the offer of up to date ephemeris and the transfer of up to date ephemeris may be either the same or different, for example, when the offer is made by paging or SMS and the transfer of up to date ephemeris done by GSM transfer. The GPS receiver of mobile telephone MS1 may then use the ephemeris to quickly acquire GPS signals from the time when the ephemeris data is received to the point where it becomes invalid. Example 2 Assuming the GPS receiver of mobile telephone MS1 is in possession of an up to date ephemeris data message, the GPS receiver periodically monitors the Issue of the IOD field of the GPS satellite data message. With an approximate estimate of GPS time, such monitoring would require only occasional and partial demodulation of the GPS data message and hence would not have a significant effect on power consumption. When a change in the IOD occurs, the GPS receiver then requests from the base station BS1 updated ephemeris data to assist the GPS receiver to quickly acquire GPS signals.

Ephemeris is intended to include any GPS parameters satellite orbit and clock correction data that have limited time validity. These parameters may accord with those transmitted by the GPS satellites themselves or, for example, long term ephemeris parameters derived at a base station from those transmitted by the GPS satellites themselves as disclosed in WO02/099454A2. In the above two examples, the IOD field is used in the detection of updated ephemeris although of course changes in other GPS satellite data message parameters might also indicate an update. Furthermore, in the above two examples, the assistance data provided was ephemeris data, however, this could also include ephemeris derivatives such as Doppler estimates and almanac data. The invention has largely been described in the context of NAVSTAR GPS, the all weather, spaced based navigation system developed and currently operated by the US Department of Defense. However, it will be appreciated that the general underlying principles of GPS are universal and not merely limited to NAVSTAR. Accordingly, GPS is intended to refer to any positioning system comprising a plurality of spread spectrum radio transmitters at different locations and a receiver which determines its location based on the time of arrival of the transmissions of the radio transmitters. From a reading of the present disclosure, other modifications will be apparent to the skilled person and may involve other features which are already known in the design, manufacture and use of GPS receivers and component parts thereof and which may be used instead of or in addition to features already described herein.

Claims

1. A server configured to transmit to a remote GPS receiver upon determining the availability of updated assistance data for assisting the GPS receiver to acquire GPS signals either a signal notifying the GPS receiver of such availability or a signal containing the updated assistance data.

2. A server according to claim 1 configured to both transmit a signal notifying the GPS receiver of such availability and, upon receiving a request from the remote GPS receiver for the updated assistance data, to transmit the updated assistance data to the GPS receiver.

3. A GPS receiver configured to request from a remote server updated assistance data for assisting the GPS receiver to acquire GPS signals upon determining that such assistance data currently stored by the GPS receiver is invalid.