Patent Application
20070046532
This invention relates generally to Satellite Positioning System (SPS) devices, and more particularly to a method and system for using a secondary satellite receiver to aid in location determinations.
The Global Positioning System (GPS) has 24 satellites orbiting the earth (21 operational and 3 spares). These satellites are arranged into 6 high orbit planes at a height of 10,898 nautical miles or 20,200 kilometers with each orbit containing three or four satellites. The orbital planes form a 55 degree angle with the equator with orbital periods for each satellite of approximately 12 hours.
With no obstruction, there are typically 8-12 satellites visible at any one time from anywhere on earth. Each satellite contains a highly accurate (Rubidium atomic) clock. Taken together, several GPS satellites can represent an extremely accurate time standard available for synchronization at any point on the earth. It is this accurate timing that leads to an application of the GPS satellites separate from their function for navigation. The world's cellular and fiber communications use the time information derived from the GPS satellites for clock synchronization. Each satellite transmits a spread spectrum signal containing a BPSK (Bi-Phase Switched keyed) signal in which 1's and 0's are represented by reversal of the phase of the carrier. This message is transmitted at the L1 frequency 1575.42 MHz at a “chipping rate” of 50 bits per second. The message repeats every 30 minutes and is called the C/A signal (Coarse Acquisition signal). This message contains two important elements, the almanac and the ephemeris. The Almanac contains information about all the satellites in the constellation. This information is regularly updated from ground stations monitoring the system but almanac data remains useful for around one year. The Ephemeris contains short-lived information about the constellation and the particular satellite sending it. The particular satellite's information is updated from the GPS ground stations every four hours. Its validity in calculating position deteriorates gradually over this period as satellites rise and fall above the horizon. There are also other encrypted signals: the P code and Y code that are used for military applications transmitted at frequencies L1 & L2.
GPS signals are typically weak and require a radio frequency (RF) front end that has a low noise figure and very high gain. To derive a position solution including altitude, the GPS receiver must acquire and receive a full set of ephemeris from 4 or more satellites to compute a solution. The transfer of ephemeris from the GPS satellites is relatively slow (noted above as 50 bps), so alternative transmissions sources (such as a cell phone networks) have been used to send ephemeris and frequency uncertainty information to enable a GPS handset to compute a solution more expeditiously.
GPS is an example of a satellite position system (SPS) that may be utilized by a wireless device in combination with an appropriate GPS receiver to pinpoint the location of the wireless device on earth. The array of GPS satellites transmits highly accurate, time coded information that permits a receiver to calculate its exact location in terms of latitude and longitude on earth as well as the altitude above sea level (when 4 or more GPS satellites are acquired). The GPS system is designed to provide a base navigation system with accuracy to within 100 meters for non-military use and greater precision for the military.
As mentioned above, each of the orbiting satellites contains accurate clocks and more particularly four highly accurate atomic clocks. These provide precision timing pulses used to generate a unique binary code (also known as a pseudo random or pseudo noise “PN” code) that is transmitted to earth. The PN code identifies the specific satellite in the constellation. The satellite also transmits a set of digitally coded ephemeris data that completely defines the precise orbit of the satellite. The ephemeris data indicates where the satellite is at any given time, and its location may be specified in terms of a satellite ground track in precise latitude and longitude measurements. The information in the ephemeris data is coded and transmitted from the satellite providing an accurate indication of the exact position of the satellite above the earth at any given time. A ground control station updates the ephemeris data of the satellite once per day to ensure accuracy.
A GPS receiver configured in a wireless device is designed to pick up signals from three, four, or more satellites simultaneously. The GPS receiver decodes the information and, utilizing the time and ephemeris data, calculates the approximate position of the wireless device. The GPS receiver contains a floating-point processor that performs the necessary calculations and may output a decimal display of latitude and longitude as well as altitude on the handset. Readings from three satellites are necessary for latitude and longitude information. A fourth satellite reading is required in order to compute altitude.
Techniques that use cellular based location aiding information, however, still require a cellular network connection that may not necessarily be available within all of the areas within the footprint of the “viewable” GPS satellites. Thus, time to first fix (TTFF) times are usually relatively long.
Even with some additional information, TTFF times may be over thirty seconds because the ephemeris data must be acquired from the SPS system itself, and the SPS receiver typically needs a strong signal to acquire the ephemeris data reliably. These characteristics of a SPS system typically impact the reliability of position availability and power consumption in wireless devices. Typically, the accuracy of location-based solutions may vary from 150 meters to 300 meters in these types of environments. As a result, locating a wireless device in a 300 meter radius zone is unlikely unless there are other methods to help narrow the search.
Attempts at solving this problem have included utilizing pseudolites (such as base stations in a cellular telephone network) in combination with SPS, such as GPS, to determine the location of the wireless device.
Embodiments in accordance with the present invention can utilize information received from a secondary satellite receiver to aid the GPS receiver in a similar manner as cellular phone networks and phone receivers have done. Any SPS capable device such as a GPS receiver (and not necessarily limited to a GPS enabled cell phone) can use information from a secondary satellite receiver such as a satellite digital audio radio receiver. Any SPS capable device such as a GPS device further equipped with another satellite receiver likely to receive higher power or bandwidth than the SPS devices are ideally suited for the embodiments herein.
In a first embodiment of the present invention, a method of determining an approximate location of a device within the footprint of a SPS satellite and a secondary satellite can include the steps of receiving positional assistance information from the SPS satellite (such as a GPS satellite), receiving positional assistance information (such as ephemeris data, precise timing, and frequency uncertainty data) from the secondary satellite (such as a satellite digital radio satellite), optionally receiving positional assistance information from a ground based communication system, and determining the approximate location based on the positional assistance information from the satellite position system satellite and the secondary satellite (and optionally from the positional assistance information from the ground based communication system). Note, the secondary satellite can be unassociated with the SPS satellite and have a higher transmission power or bandwidth than the SPS satellite. The method can optionally include the step of forwarding ephemeris data from a satellite position system ground station to a secondary satellite ground station and transmitting the ephemeris data to the secondary satellite via an uplink for the secondary satellite.
In a second embodiment of the present invention, a system for determining an approximate location of a device within the footprint of a SPS satellite and a secondary satellite can include a SPS receiver for receiving positional assistance information from a SPS satellite, a secondary satellite receiver for receiving positional assistance information such as ephemeris data, frequency, and time from a secondary satellite, and a processor for determining the approximate location based on the positional assistance information from the satellite position system satellite and the secondary satellite.
In a third embodiment of the present invention, a cellular phone can include a SPS receiver for receiving positional assistance information from a SPS satellite, a satellite digital radio receiver for receiving positional assistance information from a satellite radio satellite, and a processor for determining the approximate location based on the positional assistance information from the SPS satellite and the satellite radio satellite. Of course, the cellular phone can further include a cellular transceiver coupled to the SPS receiver. The SPS receiver can be a Global Positioning receiver and the satellite digital radio receiver can be among a satellite digital audio radio receiver and a satellite digital television receiver as examples.
Other embodiments, when configured in accordance with the inventive arrangements disclosed herein, can include a system for performing and a machine readable storage for causing a machine to perform the various processes and methods disclosed herein.
While the specification concludes with claims defining the features of embodiments of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the figures, in which like reference numerals are carried forward.
The aiding that can be received from a cell phone requires that the user be registered to a network and can load network traffic. If the user is not on a network, the GPS receiver reverts to a very slow autonomous mode. Fortunately, in a system 100 as illustrated in
Note, the secondary satellite receiver 102 and the SPS receiver 104 can be part of a device 101 such as a lap top computer or a cellular phone or any other electronic device. The electronic device can further include a display 106 for conveying images to a user of the device, a memory 108 including one or more storage elements (e.g., Static Random Access Memory, Dynamic RAM, Read Only Memory, etc.), an optional audio system 110 for conveying audible signals (e.g., voice messages, music, etc.) to the user of the device, a conventional power supply 112 for powering the components of the device, and a processor 114 comprising one or more conventional microprocessors and/or digital signal processors (DSPs) for controlling operations of the foregoing components.
Referring to
Operationally, the system 300 can operate in accordance a method 400 illustrated in the flow chart of
In light of the foregoing description, it should be recognized that embodiments in accordance with the present invention can be realized in hardware, software, or a combination of hardware and software. A network or system according to the present invention can be realized in a centralized fashion in one computer system or processor, or in a distributed fashion where different elements are spread across several interconnected computer systems or processors (such as a microprocessor and a DSP). Any kind of computer system, or other apparatus adapted for carrying out the functions described herein, is suited. A typical combination of hardware and software could be a general purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the functions described herein.
In light of the foregoing description, it should also be recognized that embodiments in accordance with the present invention can be realized in numerous configurations contemplated to be within the scope and spirit of the claims. Additionally, the description above is intended by way of example only and is not intended to limit the present invention in any way, except as set forth in the following claims.
