Intelligent software controlled correction of frequency tracking for a local oscillator of a receiver of a wireless device

Abstract

A method and apparatus to perform a real-time drift correction of a local oscillator in a wireless device such as a cordless telephone, and/or to perform software-based frequency tracking of the local oscillator. With respect to the real-time drift correction, the remote handset periodically wakes from a sleep mode and goes into a normal link verification mode. Once in the link verification mode, the remote handset enters a time division duplexing (TDD) mode and attempts to establish a link with a base unit based on the timing of the TDD data frame. After the remote handset establishes a link with the base unit, the remote handset requests a security word from the base unit. Upon receiving the requested security word, the remote handset determines if the requested security word matches a security word of the remote handset. The remote handset implements a software frequency adjustment of its local oscillator. Once per frame, the remote handset enters a timing recovery state where the current state of the frame is compared with a previous state. When the cumulative timing slip is greater than a designated threshold, a frequency adjustment is made. The remote handset continuously adjusts its local oscillator to achieve frequency alignment within, e.g., 1 part per million (ppm). Alternatively, frequency alignment may be achieved to a specified value. Frequency feedback control may be software based to allow frequency tracking between two remote points in a communication system. In this way, the desirability of any frequency correction at particular times may be based on the accuracy of the recovered timing and data, the sensitivity of the mode of the receiving device, etc. For instance, the frequency can be finely adjusted during system acquisition, can be coarsely adjusted during data transfer, and/or can be programmed to essentially ignore or disregard a frequency offset which would otherwise be determined based on erroneously received data and/or timing (e.g., based on frame error information).