Apparatus and method to conserve power in a portable gnss unit

Abstract

A device is disclosed that is capable of determining its location using high-power with high accuracy, and using low-power with lower accuracy. By coordinating usage between the high power method and the low power, overall power consumption of the device can be significantly reduced without a significant reduction in accuracy. Such high accuracy may be achieved through the use of a GNSS unit, such a GPS receiver. In addition, the low-power alternative may be achieved using an accelerometer, together with software, hardware or firmware for extrapolating a speed based on the force measurements by the accelerometer. In this manner, the GPS receiver can be operated for only a fraction of overall use, primarily to provide adjustment data necessary to calibrate usage of the accelerometer.

What is claimed is: 
     
         1 . A device comprising:
 a location calculation module configured to determine a location of the device;   a force measurement module configured to measure an external force exerted on the device;   a calculation module configured to calculate a speed of the device based on one of the location or the external force; and   a power control module configured to operate the location calculation module in a high-power state or a low-power state depending on at least one condition.   
     
     
         2 . The device of  claim 1 , wherein the location calculation module is a GNSS receiver, and
 wherein the force measurement module is an accelerometer.   
     
     
         3 . The device of  claim 1 , wherein the location calculation module, when operating in the high-power state, consumes more power than the force measurement module. 
     
     
         4 . The device of  claim 1 , wherein the power control module controls the location calculation module to operate in the low-power state more often than the high-power state. 
     
     
         5 . The device of  claim 1 , wherein the at least one condition includes at least one of whether the location calculation module has been in a current power state for more than a predetermined time interval and whether a fluctuation in the speed calculated by the calculation module exceeds a predetermined threshold. 
     
     
         6 . The device of  claim 1 , wherein when the location calculation module is operating in the low-power state, the calculation module is configured to determine the speed of the device based on a force frequency of the external force and a stored step length. 
     
     
         7 . The device of  claim 1 , wherein the calculation module is configured to calculate a step length of the user when the location calculation module operates in the high-power state, and
 wherein the calculation module is configured to calculate the step length based on the external force measured by the force measurement module and the location determined by the location calculation module.   
     
     
         8 . The device of  claim 7 , wherein the calculation module is configured to calculate the speed based on a combination of the external force and the calculated step length when the location calculation module operates in the low-power state, and
 wherein the calculation module is configured to calculate the speed based on the location when the location calculation module operates in the high-power state.   
     
     
         9 . The device of  claim 8 , wherein the calculation module is configured to calculate the step length when the calculation module determines that a current speed differs from a previous speed by a predetermined threshold. 
     
     
         10 . A device comprising one or more circuits and/or processors configured to:
 determine a location of the device using either a high-power method or a low-power method;   measure an external force exerted on the device;   calculate a speed of the device based on one of the location or the external force; and   control the determining of the location to use the high-power method or the low-power method depending on at least one condition.   
     
     
         11 . The device of  claim 10 , wherein the one or more circuits and/or processors include a GNSS receiver configured receive GNSS signals for determining the location of the device using the high-power method. 
     
     
         12 . The device of  claim 10 , wherein the one or more circuits and/or processors include an accelerometer circuit configured to detect the external force in the form of acceleration. 
     
     
         13 . The device of  claim 10 , wherein the at least one condition includes at least one of a passage of a first predetermined amount of time since the device was started up, or a passage of a second predetermined amount of time since the device began operating using the high-power method. 
     
     
         14 . The device of  claim 10 , wherein the at least one condition includes a determination that a speed of the device has remained within a predetermined range for a predetermined time period. 
     
     
         15 . A device, comprising:
 a device locator configured to receive location information, and to determine locations of the device at a corresponding points in time;   a force detector configured to detect an external force exerted on the device, the external force being indicative of movement of the device; and   a calculator configured to calculate a speed of the device based on the determined locations of the device using either a high-power calculation method or a low-power calculation method.   
     
     
         16 . The device of  claim 15 , further comprising a power controller configured to control the calculator to calculate the speed using the high-power calculation method or the low-power calculation method based on a satisfaction of a predetermined condition. 
     
     
         17 . The device of  claim 15 , wherein, in the high-power calculation method, the calculator is configured to calculate the speed of the device based on the determined locations and the points in time corresponding to the determined locations. 
     
     
         18 . The device of  claim 15 , further comprising a memory that stores a reference force waveform,
 wherein, in the low-power calculation method, the calculator is configured to calculate the speed of the device based on the external force and the reference force waveform.   
     
     
         19 . The device of  claim 16 , further comprising a memory,
 wherein the calculator is configured to store the calculated speed in the memory, together with previously-calculated speeds.   
     
     
         20 . The device of  claim 19 , wherein the predetermined condition while using the high-power calculation method is a determination, based on the stored speeds, that the device has maintained a relatively uniform speed over a predetermined period of time, and
 wherein the predetermined condition while using the low-power calculation method is a determination, based on the stored speeds, that a speed of the device has changed by greater than a predetermined amount during a predetermined period of time.