The present invention relates generally to mobile terminals equipped with a positioning receiver, such as a GPS receiver, and, more particularly, to a method of optimizing the time needed to compute position estimates based on a specified quality of service.
GPS receivers typically determine their location by computing distances between the GPS receiver and a multiplicity of space-based satellites. The space-based satellites transmit navigation messages containing, inter alia, timing data, satellite ephemeris data, almanac data, and correction data. The GPS receiver searches for and acquires the GPS signals transmitted from the space-based satellites, reads the information contained in the GPS signal, and then uses this information to compute its location. This process can be time consuming, often requiring several minutes. For some applications, this can be a prohibitive amount of time.
The integration of GPS receivers with mobile terminals has enabled the GPS receiver to utilize aiding data provided by a land-based mobile communication network to speed up position estimating. This aiding data can include precise orbits (ephemeris), long-term orbital information (almanac), corrections for clock and ionospheric propagation delays, a list of satellites xe2x80x9cin viewxe2x80x9d, time information, as well as other data.
There are several prior art solutions that address the problem of providing aiding data to a GPS receiver integrated with a mobile terminal. These solutions may be categorized as mobile-based, in which the mobile terminal computes its own position, and network-based, in which the network computes the position of the mobile terminal based on measurements transmitted by the mobile terminal to the network. U.S. Pat. No. 5,365,450 discloses an example of a mobile-based solution. In this patent, the network transmits satellite ephemeris data, timing information, or other aiding data to the mobile terminal, which then utilizes this information to acquire GPS satellite signals and to compute a position estimate. There are also several existing U.S. patents, including U.S. Pat. Nos. 5,884,214; 5,874,914; and 5,663,734, which describe network-based solutions. Generally, network-based solutions are based on transmitting estimates of code phase and Doppler for satellites that are visible to a reference location known to be in the vicinity of the mobile terminal. The mobile terminal uses this aiding data to acquire the satellite signals and return measurements to the network, without utilizing ephemeris or other data that is provided by the GPS satellites.
In some cases, the network may provide a broadcast service whereby a server attached to the network can transmit aiding data to all mobile terminals within the network. Alternately, the network may allow the server to broadcast unique aiding data to different geographical regions in the network. A broadcast service is a very efficient way to deliver data that is required by many different mobile terminals. However, there are some circumstances in which the server may not have access to such a broadcast facility. For example, the network may not provide a broadcast facility or it may be fully utilized by other information services. Furthermore, the mobile terminal may not always be able to receive the broadcast from its serving base station, such as when the mobile terminal is already engaged in an active call. Also, if the aiding data is broadcast on a periodic basis (perhaps multiplexed with other information services on a common broadcast channel), then the mobile terminal would be forced to wait for the next periodic transmission to receive the needed information.
The mobile terminal could acquire data from the network via a point-to-point connection with the server. A point-to-point connection may satisfy a mobile terminal""s immediate need for aiding data, but it also occupies one of a limited number of channels in the communication network. Because available bandwidth is limited, it is desirable to minimize the use of a communication channel for this purpose. From the standpoint of the mobile terminal user, this operation has the advantage of minimizing charges for retrieving aiding data from the network (i.e., per-minute, per-use, or per-bit charges).
The present invention relates to a mobile terminal equipped with a GPS receiver. The mobile terminal uses one or more quality of service (QoS) parameters to determine a desired QoS when the current position of the mobile terminal is requested by an application. The mobile terminal determines whether a position estimate satisfying the desired quality of service can be provided with aiding data currently stored in its memory. If so, the currently-stored aiding data is used by the GPS receiver to determine the current position of the mobile terminal. If the aiding data stored in memory is not sufficient to meet the specified quality of service, the mobile terminal may request aiding data from a remote source, such as a server connected to the public land mobile network. The mobile terminal could also command the GPS receiver to acquire any needed information from GPS satellite signals. By use of the QoS parameter, the present invention avoids unnecessary requests for aiding data, thereby reducing network traffic. Moreover, the present invention reduces charges (i.e. per minute, per use, or per bit charges) incurred by users for retrieving aiding data from the network.