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Method for adjusting a measurement cycle in a satellite positioning system signal receiverMethod for adjusting a measurement cycle in a satellite positioning system signal receiver description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070285311, Method for adjusting a measurement cycle in a satellite positioning system signal receiver. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of co-pending U.S. patent application Ser. No. 10/912,516, filed Aug. 5, 2004, which is incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] Embodiments of the present invention generally relate to position location systems. More particularly, the invention relates to a method for adjusting a measurement cycle in a satellite positioning system signal receiver. [0004] 2. Description of the Related Art [0005] Global Positioning System (GPS) receivers use measurements from several satellites to compute position. GPS receivers normally determine their position by computing time delays between transmission and reception of signals transmitted from satellites and received by the receiver on or near the surface of the earth. The time delays multiplied by the speed of light provide the distance from the receiver to each of the satellites that are in view of the receiver. [0006] More specifically, each GPS signal available for commercial use utilizes a direct sequence spreading signal defined by a unique pseudo-random noise (PN) code (referred to as the coarse acquisition (C/A) code) having a 1.023 MHz spread rate. Each PN code bi-phase modulates a 1575.42 MHz carrier signal (referred to as the L1 carrier) and uniquely identifies a particular satellite. The PN code sequence length is 1023 chips, corresponding to a one millisecond time period. One cycle of 1023 chips is called a PN frame or epoch. [0007] GPS receivers determine the time delays between transmission and reception of the signals by comparing time shifts between the received PN code signal sequence and internally generated PN signal sequences. These measured time delays are referred to as "sub-millisecond pseudoranges", since they are known modulo the 1 millisecond PN frame boundaries. By resolving the integer number of milliseconds associated with each delay to each satellite, then one has true, unambiguous, pseudoranges. A set of four pseudoranges together with a knowledge of absolute times of transmission of the GPS signals and satellite positions in relation to these absolute times is sufficient to solve for the position of the GPS receiver. The absolute times of transmission (or reception) are needed in order to determine the positions of the GPS satellites at the times of transmission and hence to compute the position of the GPS receiver. [0008] Positioning systems, such as GPS, have fostered numerous applications that involve tracking people and assets. Various systems provide periodic location of a fixed asset, notification of proximity to pre-requested services, on-demand location identification, or continuous tracking of the location of a person or asset. Presently, such systems engage in satellite measurements at a device being tracked on a schedule unrelated to the relevance of the tracking information. This results in tracking the device continuously or tracking the device too infrequently to be effective. Continuous tracking directly results in increased power consumption in the device. Conversely, accessing the device too infrequently results in decreased accuracy and tracking performance. [0009] Therefore, there exists a need in the art for a method that provides for the automatic adjustment of a measurement cycle in a satellite positioning system signal receiver. SUMMARY OF THE INVENTION [0010] A method for adjusting a measurement cycle in a satellite signal receiver is described. In one embodiment, a notification is received at the satellite signal receiver in response to at least one of a route-critical event and a motion-change event. A frequency of the measurement cycle is then adjusted in response to the notification. In one embodiment, the route-critical event comprises the satellite signal receiver being within a threshold distance of a route-critical location along a route. A motion-change event comprises a change in motion of the satellite signal receiver with respect to a threshold value. [0011] In another embodiment, a mobile receiver includes a satellite signal receiver and a processor. The satellite signal receiver is configured to measure pseudoranges from the mobile receiver to a plurality of satellites as part of a measurement cycle. The satellite signal receiver is further configured to periodically execute the measurement cycle. The processor is configured to adjust the frequency of the measurement cycle in response to a notification indicative of at least one of a route-critical event and a motion-change event. In one embodiment, the mobile receiver further includes a sequential estimation filter, such as a Kalman filter, and the satellite signal receiver is further configured to apply pseudoranges to the sequential estimation filter as part of the measurement cycle. BRIEF DESCRIPTION OF THE DRAWINGS [0012] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. [0013] FIG. 1 is a block diagram depicting an exemplary embodiment of a position location system in which the present invention may be utilized; [0014] FIG. 2 is a flow diagram depicting an exemplary embodiment of a method for adjusting a measurement cycle in a satellite signal receiver in accordance with the invention; and [0015] FIG. 3 is a flow diagram depicting another exemplary embodiment of a method for adjusting a measurement cycle in a satellite signal receiver in accordance with the invention. [0016] To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. DETAILED DESCRIPTION [0017] A method and apparatus for adjusting a measurement cycle in a satellite positioning system signal receiver is described. Those skilled in the art will appreciate that the invention may be used with various types of mobile or wireless devices that are "location-enabled," such as cellular telephones, pagers, laptop computers, personal digital assistants (PDAs), and like type mobile devices known in the art. Generally, a location-enabled mobile device is facilitated by including in the device the capability of processing satellite positioning system (SPS) satellite signals, such as Global Positioning System (GPS) signals. [0018] FIG. 1 is a block diagram depicting an exemplary embodiment of a position location system 100 in which the present invention may be utilized. The system 100 comprises a mobile receiver 102 in communication with a server 108 via a wireless communication network 110 (e.g., a cellular communication network). For example, the server 108 may be disposed in a serving mobile location center (SMLC) of the wireless communication network 110. The mobile receiver 102 obtains satellite measurement data (e.g., pseudoranges, Doppler measurements) with respect to a plurality of satellites 112. The server 108 obtains satellite navigation data (e.g., orbit trajectory information, such as ephemeris) for at least the satellites 112 in view. Position information for the mobile receiver 102 is computed using the satellite measurement data and the satellite navigation data. [0019] Satellite navigation data, such as ephemeris for at least the satellites 112, may be collected by a network of tracking stations ("reference network 114"). The reference network 114 may include several tracking stations that collect satellite navigation data from all the satellites in the constellation, or a few tracking stations, or a single tracking station that only collects satellite navigation data for a particular region of the world. An exemplary system for collecting and distributing ephemeris is described in commonly-assigned U.S. Pat. No. 6,411,892, issued Jun. 25, 2002, which is incorporated by reference herein in its entirety. The reference network 114 may provide the collected satellite navigation data to the server 108. Continue reading about Method for adjusting a measurement cycle in a satellite positioning system signal receiver... 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