Compensation for Frequency Adjustment in Mobile Communication-Positioning Device With Shared Oscillator

Abstract

In a mobile communication device, a method for compensating for a frequency adjustment in an oscillator shared between a communication circuit and a positioning signal receiver is provided. In one embodiment, the method begins to receive and store a positioning signal at a first time point. When, at a second time point, the operating frequency of the shared oscillator is adjusted, the frequency adjustment is recorded. After the positioning signal is completely received and stored, the processing of the positioning signal takes into consideration the frequency adjustment. In that embodiment, the processing hypothesizes a frequency shift in the received positioning signal. According to another aspect of the present invention, a method for determining the operating frequency of an oscillator detects a beginning time point of a reference signal received by the mobile communication device and enables a counter to count in step with a clock signal derived from the oscillator. When an ending time point of the reference signal is received by the mobile communication device, the count is stopped, and the frequency of the oscillator is determined based on the count in the counter and an expected time that elapsed between the beginning time point and the ending time point.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a mobile communication device with a positioning capability. In particular, the present invention relates to a mobile communication device (e.g., a cellular telephone) that is also capable of receiving a global positioning system (GPS) signal, and which shares an oscillator between the communication and positioning functions.[0003]2. Description of the Related Art[0004]The utility of a mobile communication device (e.g., a cellular telephone) is enhanced if it is provided the additional capability of receiving and processing global positioning system (GPS) signals that can be used to determine the position of the mobile communication device.[0005]To provide for both positioning and communication functions, it is possible to share a local oscillator between the receiver and transmitter of the communication circuit and the GPS signal receiver. While sharing a local oscillator can reduce the...

AI Technical Summary

Benefits of technology

"The present invention provides a method for compensating for a frequency adjustment in a mobile communication device. This method allows for accurate processing of positioning data without preventing the communication circuit from accessing the shared oscillator while positioning data is being acquired. The method includes recording the frequency adjustment and processing the positioning signal taking into consideration the frequency adjustment. The invention also includes using reference signals with a known duration or recurring events to determine the frequency of the oscillator. By removing the uncertainty in oscillator frequency, the invention improves the accuracy of positioning data and reduces the Doppler range over which the positioning signal receiver software searches."

Problems solved by technology

While sharing a local oscillator can reduce the cost and bulkiness of such a mobile communication device, there are some practical problems to be overcome to achieve high performance.

However, if such an adjustment is made during the acquisition of a GPS signal, both the mixing frequency and the sampling frequency of the GPS receiver—used in down-converting and digitizing the GPS signal, respectively—are affected.

The received signal may yield an erroneous result, or even a failure to detect the GPS signal.

However, such an approach is undesirable because it prevents the mobile communication device from establishing contact with one or more base stations while a GPS signal is being acquired, which may lead to temporary loss of communication service.

Also, such an approach complicates the control software in the mobile communication device, thereby deterring manufacturers from incorporating positioning capability in their mobile communication devices.

Because of their cost, high power requirements, and bulkiness, however, such oscillators are unsuited for use in a mobile communication device.

In a GPS signal receiver, by removing the uncertainty in oscillator frequency, the Doppler range over which the positioning signal receiver software searches can be further limited.

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