Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
1998-09-09
2001-08-28
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S190000, C375S326000
Reexamination Certificate
active
06282500
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to measuring characteristics of communications signals, and more specifically to obtaining an accumulated phase measurement of a communications signal.
II. Related Art
In general, wireless communications systems can be terrestrial or satellite-based. An example terrestrial wireless communications system includes at least one terrestrial base station and at least one user terminal (for example, a mobile telephone). The base station provides links from a user terminal to other user terminals or communications systems, such as a terrestrial telephone system. An example satellite-based wireless communications system includes at least one terrestrial base station (hereinafter referred to as a gateway), at least one user terminal (for example, a mobile telephone), and at least one satellite for relaying communications signals between the gateway and the user terminal. The gateway provides links from a user terminal to other user terminals or communications systems, such as a terrestrial telephone system.
In such wireless communications systems, the need often arises for a receiver to obtain a measurement of the frequency of a received communications signal. For some applications, a high degree of accuracy is required. One such application is the determination of the location of a user terminal based on the characteristics of communications signals received by the user terminal.
Such frequency measurements are usually taken using an automatic frequency control (AFC) loop in a receiver. However, these measurements are generally of low accuracy. Current AFC techniques measure only “current” phase error, and so achieve phase error accuracy on the order of hundreds of degrees. In wireless communications system employing low signal to noise ratios, such as spread spectrum systems, this accuracy is insufficient. While low accuracy frequency measurements are adequate for acquisition and tracking, higher accuracy is required for applications such as position determination. What is needed is a way to measure phase error with an accuracy on the order of tens of degrees.
One approach to reducing this error is to increase the loop iteration period of the AFC loop (for example, by increasing the period of its integrate-and-dump accumulators). However, this adversely affects acquisition and tracking. For example, if the loop iteration period is increased so as to achieve a standard deviation on the order of 1 Hz, the acquisition time (that is, the time the user terminal requires to acquire the signal) grows to an order of several minutes. Mobile phone users will not tolerate such a delay.
What is needed, therefore, is a system and method for making accurate measurements of the frequency of a received signal in a wireless communications system without adversely affecting other aspects of user terminal performance.
SUMMARY OF THE INVENTION
The present invention is a novel and improved apparatus and method for accurately measuring the accumulated phase of an input signal over a given time interval.
The apparatus includes an automatic frequency control loop for generating a frequency estimate of the frequency of the input signal; a phase error estimator for generating a phase error based on the frequency estimate; and a phase detector for generating an accumulated phase measurement based on the frequency estimate and the phase error.
One advantage of the present invention is that it permits high-accuracy frequency measurements of a signal in a communications system.
Another advantage of the present invention is that its robust open-loop architecture is well-suited for use with communications signals subject to fading.
A further advantage of the present invention is that it employs a cascaded architecture that permits the use of an off-the-shelf automatic frequency control loop in the present invention without significant modification.
REFERENCES:
patent: 5473637 (1995-12-01), Gardner
patent: 5572551 (1996-11-01), Kearney et al.
patent: 5732111 (1998-03-01), Walley
patent: 5914985 (1999-06-01), Ishizu
patent: 0373517 (1990-06-01), None
patent: 0763919 (1997-03-01), None
Agrawal Avneesh
Levanon Nadav
Vijayan Rajiv
Ogrod Gregory D.
Qualcomm Inc.
Shah Kamini
Wadsworth Philip R.
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